1 s2.0 S0959652619337084 Main

Journal of Cleaner Production 245 (2020) 118838
Contents lists available at ScienceDirect
Journal of Cleaner Production

journal homepage: www.elsevier.com/locate/jclepro
Review
Low temperature oxidation of carbon monoxide for heat recuperation:

A green approach for energy production and a catalytic review
Deep M. Patel a, Pravin Kodgire b, Ankur H. Dwivedi a, *
a
Chemical Engineering Department, Institute of Technology, Nirma University, Sarkhej-Gandhinagar Highway, Ahmedabad, Gujarat, India, 382481
b
Chemical Engineering Department, School of Technology, Pandit Deendayal Petroleum University, Raisan, Gandhinagar, Gujarat, India, 382007
a r t i c l e i n f o a b s t r a c t
Article history: Low-temperature catalytic oxidation of carbon monoxide to carbon dioxide has been broadly studied in
Received 7 March 2019 literature in the view of air purification, recovery of hydrogen and reduction of industrial stack emissions.
Received in revised form However, neither of the previously studied articles has reported the oxidation of carbon monoxide for
8 October 2019
capturing the heat generated in the exothermic reaction and simultaneously utilizing the carbon dioxide
Accepted 10 October 2019
Available online 24 October 2019
for producing chemical/petrochemical products. Thus, the current article unprecedentedly occupies an
important place in literature that discusses various aspects of low-temperature oxidation of carbon
^ as de
Handling editor: Cecilia Maria Villas Bo monoxide for heat recuperation. The present work has identified carbon monoxide as a potential heat
Almeida generator and thereby also unparallely proposed a novel zero carbon emission or NERS process to use
carbon monoxide as a fuel in various industries for energy generation. In order to select the best suitable
Keywords: catalyst for mitigating the activation energy barrier associated with oxidation of carbon monoxide, a
Carbon monoxide oxidation meticulous selection process is described with chronological and categorical literature review, and
Heat recovery thereby concentrating the scattered literature and simultaneously alleviating the complexities involved
Catalytic review
in the catalyst selection procedure. A techno-economic analysis of the proposed NERS process is also
Techno-economic analysis
provided with additional discussion on the benefits of carbon credits in order to confer the potential to
Zero carbon emission
Cleaner approach scale up the process. Thus, the article describes a novel and a cleaner approach for the production of
energy in order to take an important step towards sustainable development.
© 2019 Elsevier Ltd. All rights reserved.
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Literature review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Noble metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Rhodium/lanthanum and their supported catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2.1. Doped catalysts for higher thermal stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2.2. Undoped rhodium catalyst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. Vanadium pentoxide (V2O5) and its supported catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3.1. Undoped V2O5 catalyst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.4. Tin oxides (SnO2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.4.1. Undoped SnO2 catalyst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.4.2. Doped SnO2 catalyst for high activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.5. Ruthenium (Ru) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.5.1. Doped Ru catalyst for high activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.6. Zinc oxide (ZnO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
* Corresponding author.
E-mail addresses: pateldeep7998@hotmail.com (D.M. Patel), pravin.kodgire@
sot.pdpu.ac.in, pravin.kodgire@gmail.com (P. Kodgire), ankur_dwivedi@nirmauni.
ac.in (A.H. Dwivedi).
https://doi.org/10.1016/j.jclepro.2019.118838
0959-6526/© 2019 Elsevier Ltd. All rights reserved.
2 D.M. Patel et al. / Journal of Cleaner Production 245 (2020) 118838
Abbreviations f Fugacity factor

GHSV Gas hourly space velocity
Gt Gigatonsa
Compounds/Materials/Elements i Initial rate of reaction
CO2 Carbon dioxide xi Mole fraction of any ith component
CO Carbon monoxide ni Moles of any ith component
CoDP Cobalt catalysts prepared by Dispersion induced Pm Partial pressure of any ‘m’ species
precipitation %X Percentage Conversion
CoAP Cobalt catalysts prepared by Alkylation induced %D Percentage Dispersion
precipitation A Pre-exponential factor in Arrhenius equation
Cu-BTC Copper-bezene-1,3,5-tricarboxylic acid k Rate constant
CuMnRC CoppereManganese catalysts prepared via reactive E Reaction efficiency
calcination L Root of a quadratic equation
CuMnCoRC(i) CoppereManganese catalysts, doped with “i”% w/ T Temperature
w Cobalt, prepared via reactive calcination t Time
CuMnFA CoppereManganese catalysts prepared via flowing TOF Turn Over Frequency
air calcination R Universal gas constant
CuMnCoFA(i) CoppereManganese catalysts, doped with “i”% w/
w Cobalt, prepared via flowing air calcination Units
CuMnSA CoppereManganese catalysts prepared via stagnant $ Dollar
air calcination gm Grams
CuMnCoSA(i) CoppereManganese catalysts, doped with “i”% w/ hr Hour
w Cobalt, prepared via stagnant air calcination J Joule
HC Hydrocarbons K Kelvin
Oin Inter-lattice Oxygen atom kJ Kilo joule
MeOH Methanol kg Kilogram
MOF Metal Organic Frameworks kWh Kilowatt hour
MIL Materials Institute Lavoisier MJ Mega joule
MCM Mobil Composition of Matter m meters
NTs Nanotubes mg Milligram
SOx Oxides of Sulfur mol Mole
NOx Oxides of Nitrogen Nm3 Normal metric cube
PM Particulate matters
Common
Technical BET Brunaeur-Emmett-Teller Surface Area (m2/g)
P Absolute Pressure of the system under study DHC District Heating and Cooling
Ea Activation energy EELS Electron Energy Loss Spectroscopy
M Any metal used as a catalyst in a reaction FTIR Fourier-transform Infrared Spectroscopy
DH Change in standard Enthalpy IFFCO Indian Farmer Fertilizer Cooperative Limited
DS Change in standard Entropy INR Indian Rupees
DG Change in standard Gibbs free energy L Lakh
w/w Composition weight by weight LEED Low-energy Electron Diffraction
C Concentration MOCs Material of construction
h Efficiency of a process or system NERS process Novel Zero Carbon Emission process
ESP Electrostatic precipitator RIL Reliance Industries Limited
K Equilibrium constant of a reaction SEM Scanning Electron Microscopy
exp exponential TEM Transmission Electron Microscopy
vk Frequency of a kth reaction
3.6.1. Undoped ZnO catalyst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.6.2. Doped ZnO catalysts for high activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.7. Nickel oxide (NiO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.7.1. Undoped NiO catalyst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.7.2. Doped NiO catalyst for high activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.8. Copper-chromites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.8.1. Doped copper-chromite catalyst for high activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.9. Oxides of CeeSn mixture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.9.1. Doped oxides of CeeSn mixture for high activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.10. Composites of transition metal oxides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.10.1. Doped catalysts of transition metal composites for high activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.11. Cerium oxide (CeO2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.11.1. Undoped CeO2 catalyst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
D.M. Patel et al. / Journal of Cleaner Production 245 (2020) 118838 3
3.11.2. Doped CeO2 catalyst for high thermal stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.12. Copper oxides (CuO) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.12.1. Undoped CuO catalyst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.12.2. Doped CuO catalyst for high activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.13. Supported cobalt oxides (Co3O4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.13.1. Doped Co3O4 catalyst for high thermal stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
4. Techno-economic analysis of NERS process for refineries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.1. Separation of CO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.2. Separation of SO2 and NOx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.3. Conversion of CO to CO2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4.4. Conversion of CO2 to CH3OH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Declaration of competing interest . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Supplementary data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
1. Introduction economically extracting the indirect energy from CO by its oxida-

tion to CO2 and further utilizing CO2 to produce chemical or
Since the last few decades, there has been a constant increment petrochemical products. In this perspective, CO is identified as a
in the air pollution index. Industrialization, transportation, com- potential heat generator and a process is designed for cleaner
mercial and terrorist activities are some of the major contributing production of energy by utilizing it as a fuel. The outline of our
factors for this scenario. The major sources of pollution due to designed approach (refer Fig. 1) for reducing carbon emissions has
carbon oxide, COx include steam power plants utilizing coal-fired been prepared by studying various stack emission data of different
combustion systems, automobiles and various chemical industries industries and ambient air quality data of major metropolitan cities
and refineries. Typical emission data from various fossil-fuel based of India. The process derives its name as a “NERS” process by
power plants are shown in Table 1 (Rao, 2007). The combustion including the first, second, third and fourth letter of corresponding
systems of most of the processes mentioned in Table 1 significantly words from “Novel zero carbon emission” process. The brief outline
increases the carbon footprint of a power plant or an industry and of our proposed approach based on the emission data available
thereby adversely affecting the environment, ecosystem, and from the annual report of RIL, is presented in Fig. 2. However, one
biodiversity by increasing global warming. Additionally, as per might expect the addition or elimination of a few steps in the
recent data, the global CO2 emission of 2018 was reported to be proposed process, depending upon the composition of the system
around 33.1 Gt (IEA, 2019) which is the highest recorded till today. under study. This process is quite flexible as it can be used for the
Almost two-third of this amount was from the power sector alone. removal of CO and CO2 from industrial emissions as well as from
It is also recently reported that carbon dioxide emitted from coal ambient air due to the flexibility of separation stages.
combustion is responsible for around 0.3K of the 1K rise in global The first step of the NERS process includes the separation of CO2
average annual temperature of surface, which makes coal the single (which is generally present in a larger proportion as compared to
largest source of global temperature rise (IEA, 2019). The global other pollutants from the industrial emissions) due to following
average annual carbon dioxide concentration in the atmosphere reasons:
was observed to be 407.4 ppm in 2018, which is 2.4 ppm above that
of 2017. Hence, the majority of industries are aiming at economi- Prior separation of CO2 will reduce further complexities in other
cally extracting the energy stored in a variety of substances; with separation steps.
the least emission of pollutants into the atmosphere. In the view- CO2 possesses the potential to produce valuable chemical and
point of this, as per recent Paris Agreement 2015 (Agreement, petrochemical products like Urea, Methanol, etc.
2015), corroborated by the majority of countries across the globe, Technology for separation of CO2 from industrial emissions/
there was a consensus among all the members to keep the increase ambient air with appreciable humidity is currently made
in average global temperature below 2 K to delay the upcoming risk available by a certain group of researchers (as discussed suffi-
of drastic climate change. Various recent efforts made in this di- ciently in the upcoming section of techno-economic analysis of
rection have been reviewed elsewhere (Zhu, 2019). Apart from the NERS process).
energy utilization, CO can be utilized for production of Boron from
Boron oxide (Go €kdai et al., 2017). The present work aims at Hence, without any further ado on already available and
Table 1
Emission data for various combustion systems (Rao, 2007).
Technology Efficiency (%) NOx (gm/kwh) Emissions of SO2 (gm/kwh) CO2 (gm/kwh)
a
Pulverized coal-fired steam plant (without scrubbers) 36 1.29 17.2 884
a
Pulverized coal-fired steam plant (with scrubbers) 36 1.29 0.86 884
a
Fluidized bed coal combustion 37 0.42 0.84 861
Oil-fired steam plant (uncontrolled) 38 1.4 1.6 794
a
Integrated gasification combined cycle system (coal gasification) (IGCC) 42 0.11 0.3 758
Combined-cycle gas turbine 53 0.2 0 345
a
Coal with 2.2% sulfur content in coal based systems.
Fig. 1. Overview of a new zero carbon practice suggested in this article and classification of industries based on amount of CO and CO2 present in the stack emissions.
Fig. 2. Block diagram of a proposed Novel zero carbon emission process (NERS process).
thoroughly studied separation facilities, it is considered that the gas such as SO2 and NOx. As discussed further in the techno-
incorporation of such technologies for separation of CO2 in the first economic analysis section of the article, after the removal of SO2,
step is satisfactory. The separated CO2 can be directly used for a NOx, and CO2, one might expect an almost pure CO stream
further application like in the production of urea, methanol and (neglecting PM and HC). The removal of PM can be entertained by
other useful chemicals/petrochemical products. The second step using cyclone separators or ESP. Since ESP utilizes the coulombic
includes the separation of remaining gaseous components of flue force to separate particulate matters, it has been proved to be the
most effective means of separation of PM as compared to cyclones and frugal innovations in the field of hydrogen production because
which work on the principle of centrifugal forces (weaker than the hydrogen is one of the front-runners in the high operational cost of
coulombic forces in ESP). The third step of the NERS process con- this process. Since CO2 and CO are the basic components of most of
tributes to the conversion of CO to CO2 and the simultaneous the industrial emission, the proposed NERS process can be scaled
extraction of heat from this step at ambient conditions. Due to the up commercially to significantly shrink the use of fossil fuels or
presence of a significantly high activation energy barrier of 170.5 kJ/ electricity for the generation of heat and thereby encouraging the
mol, a catalyst is required to economically carry out this conversion. cleaner production of energy.
Since this step is highly exothermic, it produces a tremendous It seems an arduous job to select the optimum catalyst from
amount of consumable or useful heat (257.2 kJ/mol) in the form of such diverse diffused literature for the oxidation of CO at ambient
Gibbs free energy at 298K. But it is simultaneously accompanied by conditions. The sequential approach adopted in this article is
a very high value of the equilibrium constant of the order of 1045. mentioned in the succeeding section of methodology, to abate the
The above data is derived by using basic thermodynamic correla- intricacies involved in the catalyst selection procedure. Hence the
tions of enthalpy, entropy, Gibb’s free energy and equilibrium current article provides a thorough review of various heteroge-
constant with the use of data available in the literature (Smith et al., neous catalytic systems available in the literature to select the best
2005). However, one must not get lured by the high equilibrium suitable catalyst. Also, a techno-economic analysis of the proposed
constant value, as the reaction is simultaneously accompanied with NERS process has been presented in a successive section. Thus the
a significant barrier of activation energy and hence a catalyst is interested readers will have a rudimentary essence of the techno-
required to carry out such reaction via a different path with less economic analysis of a novel zero carbon emission process, as
activation energy. The primary reason for the inclusion of this third well as those who are perspicaciously interested in scrutinizing the
step is to reduce the dependency on fossil fuels for the generation numerous options of catalysts available in literature shall be
of heat and electricity, which will ultimately curb the number of benefited with the knowledge of an upcoming process, having the
carbon emissions. Hence this step will significantly reduce the potential to induce path-breaking trends in carbon trading
emissions which are being emitted from the fresh usage of fossil practices.
fuels for the above-mentioned purposes. Since heat is a basic utility
along with steam in industries, it can be used in a variety of ways in
an industrial premise. 2. Methodology
Apart from this, if one wishes to utilize already polluted air
(available in the atmosphere); which is a major area of interest in A surge for selecting the best suitable catalyst can be fulfilled by
cities like Gurugram (Most polluted city of the world (IQAir, 2018) following the below-mentioned steps:
which is located near the suburb of Delhi), Taiyuan and New York,
then this process is also expected to be flexible for such demands 1. Identify the need for a catalyst
due to its flexible separation steps and other sub-processes. Hence 2. Determine the selection criterion for selecting the catalyst from
after separation of SOx, NOx, and CO2 from ambient air, CO obtained literature
can be oxidized to CO2 for the generation of heat. The generated 3. Carry out a literature survey for the selection of catalyst
heat can be utilized within nearby buildings to maintain the
ambient temperature, similar to that practiced in modern DHC Here an important criterion for selection of a catalyst would be
techniques which are widely implemented in a country like Ger- “requirement of high conversion at low/ambient temperature”, i.e.
many. To implement the newly proposed process, we have divided it must be sufficiently active at the ambient condition to yield
the worldwide major industries into two groups, based on their 80e90% conversion of CO to CO2 for a longer period. Hence given
emission data, as shown in Fig. 1. The fourth step of the NERS above constraint, a detail chronological review on the development
process varies from industry to industry. Considering the industries of varieties of catalysts reported in the literature is carried out, with
that are producing CO2 in excess (compared to CO), after the sep- simultaneously classifying them in three different groups, to
aration of CO and CO2 from industrial emissions, it is necessary to effectively scrutinize all the available options of catalysts for
store CO until a certain amount of CO is accumulated; which is oxidation of CO. Most of the reviewed catalysts are broadly classi-
sufficient to generate the heat that can satisfy the industrial de- fied as the following groups:
mand. Hence for industries in group-2, after performing appro-
priate calculations based on their emission data and keeping % i. Undoped catalysts
conversion of CO to CO2 in mind, one can estimate the amount of CO
require to be stored. Simultaneously, such industries might possess
an advantage of a large number of valuable products from CO2, after
its separation from emissions. Whereas for industries in group-1,
since the amount of CO will be more, one can either directly
oxidize CO to extract heat or store it, to use it in a controlled manner
(by oxidizing it to CO2), after successfully separating it from other
constituents of emissions. The CO2 generated at the end can be
further utilized by various commercial industries as per their re-
quirements. For example, sugar-producing industries can use it as
an antimicrobial agent (Mall, 2006); fertilizer industries can utilize
it for preparation of Urea (Mall, 2006); CO2 sequestration for
growing plants (Jones and Donnelly, 2004); CO2 fixation for
microalgae growth in production of biofuels and/or wastewater
treatment (Arbib et al., 2014) etc. Moreover, currently, several
researchersare working to convert CO2 to Methanol (Martin et al.,
2016) or back to CO (Schlager et al., 2017). CO2 to Methanol con-
version path is highly recommended only after certain impactful Fig. 3. Recent trend in the field of catalytic oxidation of carbon monoxide.
ii. Doped catalysts with high stability statistics. According to the thorough analysis done by us, though
iii. Doped catalysts with high activity the majority of catalysts discovered in the last five years possess
better efficiency, more than 40% of catalysts suffer from a high cost
It may be observed that although some of the catalysts were of production. The above fact is apparent as the majority of catalyst
discovered near the beginning of the 20th century, they gained systems were observed to possess noble metals in various pro-
more attention belatedly in the same era or the early 21st century. portions. Therefore, we have tried to analyze the majority of cata-
However certain expensive catalysts such as Au, Pd or Pt aren’t lysts which have been discovered or invented in the last half-
discussed due to its high cost and hence celebrated as less potential decade and thereby emphasizing on current state of art to pacify
for commercial application. Moreover, some of the catalysts which the complexities involved in the selection of catalyst. It may be
are discussed in the article are further dismissed due to their lack of observed from various works done in this field of catalysis that a
potential to fulfill the selection criteria or due to its expensive shifting trend of highly active (but costly) noble metals to moder-
preparation techniques. The majority of catalysts discussed in this ately active (but less costly) rare earth and transition metals was
article are provided with their corresponding mechanism and observed during 1950. However, to achieve high activity along with
thorough discussion for their characteristic conversion profile, and better thermal and mechanical stability, the majority of work un-
thereby providing a systematic analysis of the content. dertaken in recent years (2016e18) for the oxidation of carbon
monoxide involves noble metals in various respective proportions.
It is apparent that in a surge of achieving better CO conversion and
3. Literature review yield at low temperatures, majority of researchers are ignoring an
apparent barrier of the high production cost associated with such
A catalyst is a substance which alters the rate of reaction by catalysts. Thus, it is appropriate to say that though shifting trend
changing the reaction path, without affecting its equilibrium from noble metals to plasma-assisted heterogeneous catalysts was
properties. A detailed discussion of the catalysis concept is pro- observed in the past few decades, noble metals have been always
vided by Bartholomew and Farrauto (1998). Low-temperature observed to be present in minor proportion in the majority of
catalytic oxidation of CO has been broadly studied in literature catalysts that exhibit notable conversion at low temperatures. The
from a viewpoint of air purification, recovery of hydrogen and essence of widely explored catalysts for oxidation of CO to CO2
reduction in industrial stack emissions. Recently catalytic oxidation apart from noble metals is shown in Fig. 4 and is discussed with
of carbon monoxide has gained wide attention due to its wide- sufficient details in this paper (see Fig. 5).
spread applications in automobile exhaust, fuel cells and gas sen-
sors. It provides an important tool for the sustainable development
of various products and cleaner production of energy (as discussed 3.1. Noble metals
in the introductory section). In order to understand the oxidation of
CO at low temperatures, many researchers have made painstaking The oxidation of CO on the noble metal catalysts at low reactant
efforts in this field. A general trend observed in this research field of partial pressures was a major area of interest since the advent of the
catalysis is shown in Fig. 3. However, the major challenges are the 20th century. The reaction of CO with O2 has been analyzed by
development and synthesis of economic (in terms of preparation several researchers (Brokaw, 1967) on an active metal surface like
and regeneration cost) and efficient (in terms of selectivity and Pd, Pt, and Rh. Research conclusions of several researchers point out
activity) catalyst system. In spite of such drawbacks, the current two possible reaction mechanism modes for such systems. It has
review on various developments and works done in this field of been concluded that the reaction takes place quite easily (i) if CO is
catalysis over the past few years provides some disappointing pre-adsorbed and O2 is allowed to bombard on it than that when
Fig. 4. Summary of widely explored catalysts for oxidation of CO.

Fig. 5. Activation energy curve for V2O5 catalyzed reaction (Zhu et al., 2011).
(ii) O2 is pre-adsorbed and CO is bombarded. The main reason literature. Au/POMs have achieved a milestone conversion of 100%
behind this observation is that oxygen adsorbs dissociatively, at 298.15K (Yoshida et al., 2017). Though it seems quite an attractive
whereas carbon monoxide adsorbs in non-dissociative fashion and option for industrial application due to its exceptionally high CO
hence, the stability of charged intermediate complex formed due to conversion, it is noteworthy to mention that various difficulties like
dissociative adsorption of oxygen is quite less as compared to that Cl the poisoning of Au substrate, an agglomeration of Au NPs after
of complex formed during reaction path with non-dissociative calcination, decomposition of POMs under alkaline solution and
adsorption of carbon monoxide. Hence, from the few obsolete high manufacturing cost precludes its application at industrial
literature data on this competitive mechanism for oxidation of CO, scale. Recent studies on Cryptomelanes (K(Mn4þ, Mn2þ)8O16) have
the activation energy of the reaction path has been observed to be attracted the attention of certain researchers (Fu et al., 2017) to
around 10 times more during the dissociative adsorption of oxygen dope them with noble metals, due to its high surface area avail-
as compared to that during adsorption of CO. Further, it can be ability. Palladium supported on Cryptomelane type MnOX octahe-
concluded that two governing factors which tend to obscure the dral molecular sieves (OMS-2) were recently studied for the
elementary kinetics of this explosive reaction are: oxidation of CO, toluene and ethyl acetate. It was observed that high
oxygen mobility and low temperate reductibility were two main
(i) Contact surface area and surface history contributing factors responsible for CO conversion of around 90% at
(ii) Rate of reaction 328.15K. Also supports like MnOX, CeO2, Fe2O3, and CoOX were
observed to possess higher conversions, but Cryptomelanes suc-
The above two factors can be justified by the discussion pro- ceeded all others due to high surface area and enhanced inter-
vided in Appendix A on the reaction mechanism of oxidation of CO particle porosity. No chemical mechanism is accurately proposed
on the surface of noble metals. Recently the majority of studies for such catalysts due to the complexities involved in analyzing
have been carried out to determine the history effect and molecular surfaces with very high porosity (It is difficult to determine the
phenomena occurring at the surface of noble metals via ultra-high local chemical mechanism at each pore and its surfaces). Though it
vacuum (UHV), High-pressure Scanning-Tunneling microscopy possesses significantly higher conversion at around 300.15K, such
(STM), near-ambient pressure XPS (NAP-XPS), Infrared reflection catalysts are not an attractive choice for its industrial application
absorption spectroscopy and High-energy surface X-ray diffraction due to high manufacturing cost and difficulties involved in main-
techniques. Various studies (Schiller et al., 2018) on a curved Pd taining optimum reaction parameters during its manufacturing
crystal via UHV showed that the low activity stage of a catalyst is process. However a recent study (Mengfei et al., 2016) on double
due to the presence of the CO poisoning layer, which is successively metal oxides supported ZrO2 and PtOX, i.e. a support layer of MO-
replaced by an active layer of metal oxide and chemisorbed O in MCr2O3 (M ¼ Cu, Ni or Zn) exhibited comparative statistics of per-
variable proportion. However, no precise argument for observed formance along with ease of manufacturing and flexibility under
mechanisms or conversion is provided. Apart from studying surface various operating environment (especially that of CO2 and H2O,
phenomena of the noble metals, significant progress in the doping which is generally encountered in majority of stacks) at larger scale.
of nanoparticles (Yoshida et al., 2017) to increase CO conversion Thus, such newly emerging materials do occupy an important po-
was observed. It was observed that surprisingly Gold-supported on sition in literature due to its potential for large scale applications,
Keggin-type Polyoxometalates (POM) exhibited U-shaped conver- but with the simultaneous hurdle of high manufacturing cost due
sion profile w.r.t temperature. From an infinite number of catalysts to the presence of noble metals. Recent practices demonstrating the
discovered to date in this field, only three of them (Co3O4eSiO2, Ag/ use of the mixture of transition metals and noble metals were
Mg (OH)2 and Au/POM) exhibits the U-shaped curve. The exact observed, which is discussed in section 3.10.
reason behind changes in the nature of a conversion profile at a
certain temperature is still unknown. The majority of researchers 3.2. Rhodium/lanthanum and their supported catalysts
have related this negative activation energy to the reduction in the
number of effective collisions of the CO molecule with the catalyst 3.2.1. Doped catalysts for higher thermal stability
surface at the higher temperature. However, no experimental or Since the mid-20th century, some of the widely explored cata-
theoretical shreds of evidence for such curves are provided in the lysts for oxidation of CO to CO2 are:
(i) Rh/Al2O3 catalysts. Therefore, it won’t be a misnomer to group such vana-

(ii) LaCoO3/Al2O3 dium oxides under an umbrella of “Stubborn realists”, since they
(iii) RheLaCoO3/Al2O3 occupy the position among those few compounds which have
maintained its actual characteristics even after various rigorous
The thermal and the chemical stability of Al2O3 supported cat- efforts by early researchers.
alysts have been already investigated by many researchers
(Ammendola et al., 2014). The alumina supported catalysts of 3.3.1. Undoped V2O5 catalyst
rhodium have been reported to be highly stable, maintaining the Formation of CO2 from CO on bulk V2O5 is thoroughly discussed
original performance and chemical properties over several pro- by various researchers (Abdul-Kareem et al., 1980; Hughes and Hill,
cesses runs, as the dispersion of rhodium on alumina surface re- 1955). In such systems, the concentration of CO in feed must not
mains preserved even around 1073K. Whereas LaCoO3/Al2O3 gets exceed 10% (v/v) because, at higher concentrations, V2O5 catalysts
deactivated after the first cycle due to irreversible migration of deactivate more rapidly due to the poisoning of active sites via
cobalt into Al2O3 lattice, which is in direct contrast to that in the depletion of inter-lattice oxygen (Reddy et al., 1997). Moreover, it
case of alumina supported Rhodium catalysts. One of the few ex- was observed that due to less affinity of CO2 to adsorb on the sur-
amples of synergistic effect has been observed when the combi- face of such catalysts, the concentration of CO2 in the feed doesn’t
nation of the LaCoO3 layer with Al2O3 prevented the aggregation of affect the reaction parameters (Hughes and Hill, 1955) though
Rhodium on its support (LaCoO3/Al2O3) at temperatures above generally CO2 is observed to physisorbed on the surface of various
1073K, which was the previous limitation of Rh/Al2O3. Hence, given transition metal oxides. To achieve higher conversion with a
that the activation energy of Rhe LaCoO3/Al2O3 is sufficiently low simultaneous increase in thermal stability of catalysts, the inter-
(yet to be discovered) for the oxidation to happen at room tem- action of CO with V2O5 nanotubes was explored with theoretical
perature, it may be preferred for the heat extracting oxidation step and experimental shreds of evidence. It was observed that in-
in the NERS process, where high local surface temperatures may be teractions were quite different from that with its bulk form. CO
encountered. molecule adsorbs on the inner and outer walls of V2O5 by physical
and chemical adsorptions (Zhu et al., 2011). Bidentate carbonate ion
3.2.2. Undoped rhodium catalyst was detected to be formed from CO chemisorption, which further
Steady-state kinetics of CO oxidation on clean polycrystalline Rh decomposes on V2O5. Since lattice oxygen of V2O5 participates in
(III) over a wide range of CO and O2 gas-phase compositions and reactions, decomposition of carbonate on the catalyst’s inner wall
surface temperatures for certain pressure range suggests that requires less activation energy and releases more exothermic heat
below 425.15K temperature the reaction rate increases with tem- as compared to that in a single layer and the outside wall of V2O5
perature with reported activation energy of 83.7 kJ/mol, while nanotubes. The strain energy of V2O5 NTs was found to be much
above 450.15K the rate decreases with temperature with reported smaller than that of other transition metal oxides NTs (Zhu et al.,
activation energy of 29.3 J/mol (Ammendola et al., 2014). It is 2011), which must be an additional factor contributing to the
observed that due to negative activation energy value the rate of high stability of nanotubes of vanadium pentoxide as compared to
reaction decreases above 450.15K and hence such catalysts should other transition metal oxides. The reaction mechanism observed on
not be encouraged for its application in any heat recovery system vanadium pentoxide nanotubes is given in Appendix B (i). It is
because even though the system temperature is maintained at noteworthy to report that oxygen atoms available for the reaction
some fixed value by the continuous extraction of heat of are inter-lattice oxygen along with externally supplied oxygen.
exothermic reaction, the local temperature on the heat exchanging However, the amount of inter-lattice oxygen taking part in the re-
surface might be different and non-uniform. Hence, if the local action is negligible. Also, none of the studies exhibiting conversion
temperature fluctuates above 450.15K, the overall efficiency of such profiles, thermal stability and activity of V2O5 NTs are reported in
a heat extraction process will drastically decrease due to a reduc- the literature due to difficulties involved in its synthesis process.
tion in the rate of reaction. Thus we are still far away from achieving nano-revolution in this
field of catalysis. Although one may be able to economically syn-
thesize V2O5 NTs in near future, it might not be a suitable choice for
3.3. Vanadium pentoxide (V2O5) and its supported catalysts NERS process or any other process at industrial scale because of
phase transition of the V2O5 crystal lattice to V2O3 at 773.15K (Su
Slowly but steadily, the interest in this field of catalysis for high and Schlo €gl, 2002) which significantly reduces its activity and
temperature (above 773K) has been observed to be dying since surface area. Since no such studies on V2O5 NTs are available in the
1985 due to high-temperature susceptible behavior of pure vana- literature, it would be interesting to see if lattice of V2O5 NTs also
dium pentoxide which wasn’t improved even after painstaking exhibits the same phase transition and activity reduction as bulk
efforts of various researchers (Van den Berg et al., 1982; Van den V2O5 or not.
Berg et al., 1983) in early 1980s and henceforth it seems like re- Despite the reduction of pure vanadium oxides above 500 C,
searchers have given up against the stubborn characteristic of V2O5 the thermal stability up to 600 C was achieved for V2O5 by adding
SiO2/TiO2 support or Al2O3 support without any significant change
in its activity (Kareem et al., 1980; Hughes and Hill, 1955). The
Table 2
Comparison of various supported Vanadium pentoxide catalysts. observed increase in thermal stability was due to the formation of
strong (-V-O-O-Al-) or (-V-O-O-Si-) bonds. Comparison of BET
Catalyst BETSA (m2/g)
surface area of Al2O3 supported catalysts and SiO2/TiO2 supported
5% V2O5/Al2O3 224.1a catalyst as demonstrated by certain researchers (Reddy et al., 1997;
10% V2O5/Al2O3 219.7a
Reddy and Varma, 2004); as summarized in Table 2, shows that
15% V2O5/Al2O3 173.2a
20% V2O5/Al2O3 161.5a those supported by Al2O3 have a comparatively larger surface area.
25% V2O5/Al2O3 158.8a But certain criticizing results in the literature (Wierzchowski and
20% V2O5/TiO2eSiO2 125b Zatorski, 2003) clearly indicate that Al2O3 supported catalysts
a
(Reddy and Varma, 2004). required pre-activation condition of 623.15K along with main-
b
(Reddy et al., 1997). taining the same temperature throughout the reaction which
Table 3a
Summary of majority of the reviewed Undoped catalysts.
Undoped catalysts
Catalyst Process Conditions* Comments* & Future scopes**

13
Polycrystalline Rhodium Feed: Mixture of CO, CO, O2 and N2 at 298.15 K Thermally unstable at higher temperature (Ammendola et al., 2014)
(Hans-Gϋnther and (exact composition is not reported) % Conversion at 298.15 K ¼ 0
Tilman, 1985) Geometrical surface area ¼ 10.4 cm2
Particle size ¼ Unknown
Adsorptivity of CO ¼ 5 1014 molecules/cm2
Adsorptivity of O2 ¼ 3-5 x 104 molecules/cm2
Structure ¼ polycrystalline ribbon
▪ High market cost (current price: 3300 USD/OZT), and hence its large scale
applications with reduced cost and better thermal stability should be explored.
Vanadium Pentoxide (Bulk) Feed: 250e500 ml/min gas flow-rate of 0e10% (v/v) Thermally unstable at higher temperature (Su and Schlo €gl, 2002).
(Hughes and Hill, 1955) CO þ 100-90% air at 298.15K (1 g catalyst) Ea ¼ 26 kJ/mol
% Conversion at 298.15 K ¼ 0
BETSA (using water) ¼ 240 m2/g
adsorptivity of CO ¼ Unknown
adsorptivity of O2 ¼ Unknown
Structure ¼ Not reported [The catalyst used here was purchased from Davison
Chemical Company (Code No. 903)]
▪ Scope of enhancing the activity of vanadium pentoxide via changing its
dimension or by doping with oxides of Ce, Co, Ni, Pd, Cr, Cu, Zn, Zeolites,
Aluminum Phosphates (ALPOs), etc.
▪ Thermal stability might be easily enhanced by using supports like Titania or
Silica.
Vanadium Pentoxide (NTs) Simulation study via DFT calculations for molecular The current issue in this field is the synthesis of nanotubes at industrial scale
(Zhu et al., 2011) adsorption of a molecule of CO and O2 . It is due to lack of advanced control on certain reaction parameters.
Thus, industrial applications can be explored by studying various other properties
like thermal stability and conversion.
Ea ¼ 19.3 kJ/mol (at ambient conditions)
% Conversion at 298.15 K ¼ Unknown
Particle size ¼ 1.2 nm
Structure ¼ armchair ((n,n), n ¼ 3e8)
▪ A wide window is open for naive researchers to explore theoretical chemistry via
molecular simulations for identifying the effect of various dopants on CO
conversion at ambient conditions.
Tin Oxide (Fuller and All the gas feeds are completely dried by passing Tin oxides are quite susceptible to the moisture content in feed gas or catalyst same.
Warwick, 1973) via various molecular sieves, KOH, etc. Equilibrium conversion is quite low.
Thermal activation of catalyst (1e2 g) was carried Ea ¼ 83.3 kJ/mol
out in dry air for 1 h. % Conversion at 298.15 K ¼ 0
6e7% (v/v) CO þ rest air at the total volumetric BETSA ¼ 36e190 m2/g
flow-rate of 96 cm3 min1 Particle size ¼ (a) 20e36 and (b) 36e72 B.S.S. mesh catalyst granules
Structure ¼ similar to cassiterite
▪ Tin oxide can be used as a dopant (whenever an increase in any transition metal’s
activity is required) due to the presence of highly favorable synergitic
interactions with majority of transition metal oxides.
Commercial Gold fine Pretreatment: Dry air stream at 473.15K for High material cost and preparation cost.
powder (Haruta et al., 30 min. High thermal and mechanical stability. (Chiang et al., 2005)
1989) Feed: 1.0% (v/v) CO mixed with pure air at 1 atm Industrially not preferred due to its high cost. However, few Pharma industries
inlet pressure and flow-rate of 66 mL/min. prefer such catalysts due to the requirement of high product purity.
BETSA ¼ around 1 m2/g
Particle size (TEM) ¼ 4.1 ± 1.4 nm
Structure ¼ Crystalline (precise structural detail is not reported)
▪ Recent focus in this field of catalysis is on the enhancement of activity by
reducing the size of Au (since the majority of properties of Au are strongly
dependent on its size) and its dispersion on active supports like Ceria, Chromites,
Hopcalites, Cobalt oxides, pervoskites of Lanthanum oxides, etc.
▪ Economic aspect of such noble metals must be explored prior to its industrial
application.
Zinc Oxide (Garner and Veal, Pretreatment: Heating in high vacuum at 733.15K The heat of adsorption of CO drops with time due to poor grain conductivity.
1935) for 3hrs. Reaction path: LH mechanism, where adsorption of CO is reversible.
Feed: Partial pressure of CO at Low equilibrium conversion at room temperate.
298.15K ¼ 0.203 mmHg and rest air. Ea ¼ 85 kJ/mol
Catalyst weight ¼ 5.98 g % Conversion at 298.15 K ¼ 0
▪ Though ZnO possess shorter life time, recently majority of research work have
transgressed this limitation, via doping it with various dopants like Pd, Pt, Co,
Ce, Ni, Cu, Sn oxides. However, none of the ZnO doped catalysts were observed to
possess appreciable conversion at room temperature. Thus, upcoming works
should channel their efforts towards achieving the benchmark CO conversion at
ambient conditions, since Zinc oxides are relatively cheaper than the majority of
oxides which are being used as a catalyst in various processes. So achieving
appreciable conversion along with significant life of catalysts should be the main
focus of upcoming research in this field.
(continued on next page)
Table 3a (continued )
Undoped catalysts
Nickel Oxide Refer corresponding articles pertainingto Two different active sites are available on the surface of NiO:
conversions. a-site, which corresponds to O2 sites
b-site, which corresponds to O sites
Higher selectivity of NiO for oxygen above carbon monoxide.
Highly susceptible to acidic conditions.
% Conversion at 298.15K:
0 (Conner and Bennett, 1976)
18 (El Shobaky et al., 1969) [calcination T ¼ 473.15K]
70 (El Shobaky et al., 1969) [calcination T ¼ 523.15K]
BETSA ¼ (146e152) ± 7 m2/g
Particle size ¼ Unknown adsorptivity of CO ¼ 1.9e2.03 cm3/g (at 2 torr pressure)
adsorptivity of O2 ¼ 5e6.6 cm3/g (at 2 torr pressure)
Structure ¼ Crystalline (exact structural details are not reported)
▪ Accurate reason behind the higher selectivity for oxygen is still unknown,
researchers studying theoretical chemistry may investigate the same via DFT
approach.
▪ Additionally, due to negligible equilibrium conversion at ambient conditions,
recently NiO occupies its place as a support (for providing surface area for
dispersion) in majority of recently explored catalysts like CeO2 (NPs)/NiO, Au/NiO,
Pd/NiO, etc. Thus further work is required to be undertaken for exploring more
combinations which could exhibit appreciable activity at mild conditions.
Ceria (Mesoporous) Feed: 1.6% (v/v) CO, 20.8% O2, 77.6% (v/v) N2 at Complexities involved in bulk production of Ceria NPs of required size.
Tang et al. (2015) 1 atm and flow-rate of 25 ml/min (catalyst High cost of manufacturing due to high energy requirement.
weight ¼ 50 mg) High light-off temperature for oxidation of CO.
Pretreatment: N2 stream at 423.15K for 1 h Ea ¼ 55.2 kJ/mol
BETSA ¼ 81 m2/g
Particle size (XRD) ¼ 8.6 nm
Structure ¼ mesoporous
▪ Recent interest in this field of catalysis is to enhance the activity of ceria by
reducing its size, i.e. in last 2 years, around 20 articles addressing focus on
nano Ceria of different shapes have been published.
▪ Additionally, now-a-days Ceria is looked as an active support/promoter for any
doped catalysts rather than as a main active media. Since 2011, significant
amount of work on Ceria NPs have exhibited appreciable results in the fields of
photocatalysis, CO to methanol conversion, etc. Thus this might prove as a
motivation for researchers aiming to contribute in this field of catalysis.
Copper oxide (Bai et al., Feed: 0.9% (v/v) CO, 20% O2, and N2 balanced at More active than tin oxide.
2017) total flow-rate of 150 ml/min (catalyst Ea ¼ 105 ± 2.7 kJ/mol
weight ¼ 0.05 g) Rate of reaction ¼ 0.22 104 mmol/(g.s)
BETSA ¼ 2 m2/g
Particle size (XRD) ¼ 21.3 nm
Structure ¼ crystalline CuO with cell parameter of 0.4684 nm
▪ Since the advent of CuO, majority of researchers have used CuO as a dopant in
preparing various pervoskites, ferrospinels, Copper chromites, Hopcalites, etc.
and have obtained appreciable conversion at temperatures of around 358.15K.
▪ Thus it would be the task of upcoming researchers to sooth this value down to
298.15K.
Cobalt oxide Refer corresponding articles Rate of reaction and equilibrium conversion of CO is quite susceptible to the size of
Cobalt oxides, along with its chemical composition and method of preparation.
Thermal stability of such catalysts is generally around 60e70 h at 298.15K and other
reaction conditions as mentioned in the respective articles.
Nanorods: 100 (Xie et al., 2009)
Nano-Arrays: 0 (Mo et al., 2019)
Bulk: 25e30 (Lou et al., 2014)
Nanowires: 0 (Cao et al., 2017)
Typical characterization data of each catalyst can be referred from respective articles.
▪ Though the activity of nanorods is quite plausible at ambient conditions, such
catalysts didn’t find any industrial application due to its large-scale synthesis
barrier.
▪ Thus, this drawback opens up a new pathways in nanoscience or nanotechnology
to work upon this barrier because cobalt oxide possesses potential to compete
noble metals in case of its activity for oxidation of CO.
*Unless mentioned, all the experiments are carried out in packed bed reactor.
**All the future scopes mentioned hereby (via square bullets) are about the works which are yet to be explored. Moreover the directions provided for future works to be
undertaken are completely based on the view to achieve appreciable conversion at ambient conditions with significant thermal and chemical stability.
Table 3b
Summary of majority of the reviewed Doped catalysts (for higher thermal stability).
Doped catalysts for higher thermal stability

1
Rh/Al2O3 Feed: 3000 ppm O2, <2% (v/v) CO and rest N2. Flowrate: 17e18 Nl.h . Highly stable maintaining original performance and chemical
(Ammendola et al., (Catalyst weight: 500 mg) properties over several process runs.
2014) Quite low equilibrium conversion at ambient conditions.
Rh aggregates on the surface of support after certain period of time.
BETSA ¼ 100e139 m2/g
Structure ¼ Crystalline (exact structural details are not reported)
▪ Recently Rhodium supported phases are enveloped with
Lanthanum, Ceria, etc. to form Ferrospinels, Pervoskites type
catalysts.
▪ However, no successful evidence of oxidation of CO at ambient
conditions has been reported for such catalysts. Thus, it would be
an open challenge for modern researchers to explore and discover a
benchmark combination.
LaCoO3/Al2O3 Feed: 3000 ppm O2, <2% (v/v) CO and rest N2. Flowrate: 17e18 Nl.h1. Gets deactivated after first cycle due to irreversible migration of cobalt
(Catalyst weight: 500 mg) into Al2O3 lattice.
BETSA ¼ 139 m2/g
Structure ¼ Pervoskite
▪ Recently Lanthanum cobalt oxides are actively explored in the form
of pervoskites, for reduction of CO from automotive engines. (Patel
and Patel, 2012)
▪ However, none of the catalysts exhibited appreciable conversion at
room temperate. Thus, exploring pervoskites and other crystal
phases in order to achieve appreciable CO conversion at ambient
conditions will be a subject of exploitation for modern researchers.
RheLaCoO3/Al2O3 Feed: 3000 ppm O2, <2% (v/v) CO and rest N2. Flowrate: 17e18 Nl.h1. Prevents the aggregation of Rhodium on its support (LaCoO3/Al2O3) at
(Catalyst weight: 500 mg temperatures above 1073K, which was the previous limitation of Rh/
Al2O3.
Prevents deactivation of catalyst as that in previous case.
BETSA ¼ 116 m2/g
Structure ¼ Unknown
▪ No recent interest has been observed in exploring this combination
of catalysts.
V2O5/Al2O3 Pretreatment: Heating at 423.15K under He flow for 30 min, followed Highly susceptible to sintering.
(Wierzchowski by oxidative pretreatment in the presence of flowing O2 (10% in He, Activation energy is extremely high (Refer Fig. 9).
and Zatorski, 2003) 100 ml/min) at 623.15K for 2 h. After that, cooling under He flow was Low equilibrium conversion at room temperate.
done upto required temperate. Ea ¼ 82 kJ/mol
BETSA ¼ 87e97 m2/g (Wierzchowski and Zatorski, 2003), 158.8
e224.1 m2/g (Reddy and Varma, 2004)
Particle size (SEM) ¼ 200e800 mm
Structure (XRD) ¼ Amorphous
▪ Since alumina supported catalysts are much susceptible to sintering,
a new field of research for oxidation of CO to CO2 on V2O5/Al2O3
eLa2O3eCeO2 is available in the technical world, since the
combinations of Lanthanum oxide and Cerium oxide have
previously shown some promising results with appreciable thermal
stability.
V2O5/TiO2eSiO2 e Thermally stable up to 873.15K. (Reddy and Varma, 2004)
No conversion data or accurate reaction kinetics study is available.
% Conversion at 298.15 K ¼ Unknown
BETSA ¼ 125 m2/g
Structure ¼ Vanadia in crystalline phase, Titania in Rutile phase, and
Silica in its norma crystalline phase
▪ Though such catalysts are among the ones that are least explored
since its discovery, they do possess potential to exhibit
appreciable conversion and thereby possibility to be used at
industrial scale due to following reasons:
- Potential for high conversion: The active Vanadia sites are present
in dispersed form on the support and hence more inter-lattice
oxygen are available for exchange, similar to that observed in case
of V2O5 NTs (Zhu et al., 2011).
- Possibility for industrial application: The thermal stability is above
873.15K which is far from normal operating conditions in NERS
process.
Table 3b (continued )
Doped catalysts for higher thermal stability
CeO2 (NPs)/Al2O3 Feed: 7739 ppm ± 2% CO, 41500 ppm±O2, and helium balanced at Due to less tendency for desorption of CO2 from the surface of alumina
(Wilklow-Marnell total flow-rate of 44.5 mL/min (Catal. Weight ¼ 2.5 g) supported ceria nanoparticles, no observable amount of CO2 was
and Jones, 2017) Pretreatment: None observed below 423.15 K.
Negligible equilibrium conversion at ambient condition.
BETSA ¼ Unknown
Particle size >3 nm
Structure ¼ Unknown
▪ It won’t be inappropriate to say that we are in an era of significant
boom of exploring Ceria catalysts, due to its oxygen storage
capacity along with appreciable mobility of lattice oxygen for
participation in the surface reaction.
▪ Thus a vast field is available for upcoming projects in this field of
catalysis to explore ceria doped catalysts and come up with the
benchmark results at ambient conditions.
Co3O4/Y-Al2O3 (Yang Feed: 3.3% (v/v) CO, 33.3% O2 and balanced Ar with total flow-rate of More exposed Co3þ active sites.
et al., 2018) 45 ml/min (Catal. Weight ¼ 100 mg) The crystallite size of Co3O4 was also observed to be reduced due to
Pretreatment: H2 flow at 573.15K followed by O2 flow at 523.15K. oxidative-reduction pretreatment.
Finally the catalyst was cooled at room temperate via Ar flow. Reaction mechanism: Mars-van Krevelen mechanism.
Slow surface reaction between adsorbed CO and active sites.
BETSA ¼ Unknown
Particle size ¼ 9.7, 14.7 nm
Structure ¼ Co3O4 nanocrystalline on g-Al2O3support
▪ As discussed in the present article, cobalt is widely explored mainly
due to its ability of exhibit 3 different oxidation states at ambient
conditions.
▪ Various combination of cobalt oxides with other dopants have
exhibited an appreciable activity in various fields of catalysis like
wastewater treatment, photo-catalysis (solar-water splitting), etc.
Thus Cobalt oxide catalysts possess great potential for exhibiting
appreciable conversion at ambient conditions and hence majority of
research (since last two years) in oxidation of CO revolves around
enhancing the activity of cobalt oxide catalysts via exploring various
possible combinations.
▪ Therefore researchers might join these ongoing projects or initiate a
new one, in order to enhance the activity of Cobalt oxides because of
the availability of vast literature with modern (2017e2019) and
accurate data.
**All the future scopes mentioned hereby (via square bullets) are about the works which are yet to be explored. Moreover the directions provided for future work are
completely based on the view to achieve appreciable conversion at ambient conditions.
would be quite incongruous in the proposed case since one of the hence corresponding supported catalysts would also not be useful.
objectives of the NERS process is to produce heat at ambient con- Additionally, it is important to note that V2O5/SiO2eTiO2 catalysts
dition rather than to supply the same. Hence, one needs to do a can be considered as a green catalyst since the deactivated waste
trade-off between active surface area and reaction conditions. The posses potential in synthesis of pervious cement (Toghroli et al.,
normal reaction condition would be a more preferable option since 2017) due to the presence of significant proportion of Silica in it,
one can deal with the less active surface area by using more cata- and the presence of Titania enhances the mechanical strength of
lyst, which seems to be a comparatively cheaper option as the cement. Therefore, further work in this field of catalysis should
compared to investing in controlling the reaction conditions at focus on enhancing the activity of V2O5/SiO2eTiO2 due to its po-
623.15K. Since alumina supported catalysts are much susceptible to tential eco-friendly nature.
sintering, a new field of research for the oxidation of CO to CO2 on
V2O5/Al2O3eLa2O3eCeO2 is available in the technical world. As the 3.4. Tin oxides (SnO2)
combination of lanthanum oxide and cerium oxide (Dey and Dhal,
2019) has previously shown some promising results with high 3.4.1. Undoped SnO2 catalyst
thermal stability. To increase its thermal stability, Al2O3 doped with Extraordinary activity of Tin oxide has attracted attention to
La2O3eCeO2 is currently being explored for the reduction of NOx, many researchers. The reaction mechanism followed by oxidation
CO and other harmful pollutants from stack emissions. Hence, one of CO on SnO2 and SnO2/Al2O3 is shown in Appendix B (iii) and the
might think of using V2O5/Al2O3eLa2O3eCeO2 for the oxidation of comparative study of oxidation of CO over SnO2 is shown in
CO. The comparison of reaction kinetics over alumina supported Table 3(a). As per data available in the literature, the surface of SnO2
V2O5 can be seen from Table 3(b) and the corresponding reaction is quite sensitive to calcination conditions, which is due to rapid
mechanism is provided in Appendix B (ii). Due to a high activation changes in the unit cell of SnO2 (Fuller and Warwick, 1973).
energy, V2O5/Al2O3 cannot be used as a catalyst for oxidation of CO Moreover, SnO2 is quite susceptible to moisture, such catalyst might
in ambient conditions. As per data available in the literature quickly get deactivated due to the presence of moisture in the inlet
(Wierzchowski and Zatorski, 2003), the reported conversion was gases for the proposed NERS process. Although water content
observed to be very low at ambient conditions. Simultaneously, within the catalyst decreases with the increase in calcination
SiO2 lacks mechanical strength and TiO2 lacks thermal stability, temperature; but there is a significant decrease in the
Table 3c
Summary of majority of the reviewed Doped catalysts (for high catalytic activity).
Doped catalysts for high catalytic activity

1
Au/Keggin-type Feed: 1% (v/v) CO and rest air at settling velocity of 20,000 mL h g1
cat. Exhibits U-shaped conversion profile w.r.t temperature.
POM (Yoshida (Catal. Weight ¼ 0.15 g) Cl poisoning of Au substrate, agglomeration of Au NPs after
et al., 2017) Pretreatment: None calcination, decomposition of POMs under alkaline solution and high
manufacturing cost precludes its application at industrial scale.
100 (2%Au/POM)
60 (4.2% Au/POM)
5 (10.7% Au/POM)
BETSA ¼ around 7 m2/g
Particle diameter ¼ 30e50 nm
Structure ¼ Keggin
▪ Till date, only three combinations of catalysts (mentioned in the review
section) were observed to exhibit such U-shaped conversion curves.
Thus it would be interesting to know that whether any other
combinations exhibit such behavior.
▪ The exact relation between nature of solid catalysts and the U-shaped
conversion profile is still unknown.
▪ Upcoming research can be focused on determining the correlation
between the above mentioned two parameters, which will provide a
pathway to synthesize the solid catalysts based on the required
conversion profile.
Pd/OMS-2 (Fu et al., Feed: 1.08% (v/v) CO and balanced air at total flow-rate of 50 mL/min High oxygen mobility and low temperate reductibility are the two main
2017) and SV of 60000 mL/(g.h). (Catal. Weight ¼ 50 mg) contributing factors to observed CO conversion of around 90% at
Pretreatment: None 328.15K.
Significant manufacturing cost for industrial applications due to
complexities involved in synthesis of OMS-2 and manufacturing cost
of Pd.
% Conversion at 298.15K ¼ 44
BETSA ¼ 52.9e62.7 m2/g
Particle size ¼ length: 300e400 nm and diameter: 15e20 nm
Morphology ¼ needle-like
Crystal structure ¼ Cryptomelane type
▪ No accurate chemical mechanism is proposed for such catalysts due
to various complexities involved in analyzing the surfaces with very
high porosity (It is generally difficult to determine the local chemical
mechanism at every pore and its surfaces). Thus, using surface
analysis methods like EELS, He-scattering, SEM, etc., upcoming
research might be focusing on determination of exact mechanism.
Also tri- or tetra-combination of OMS-2 with other dopants like Ceria,
Cobalt, CuO, Tin oxide, etc. can be explored, since OMS-2 possess
exceptionally high porosity and serves as a better support for such
catalysts.
SnO2-0.53CuO gels Feed: 5e6% (v/v) CO and rest air at the total flow-rate of 100±2 mL/min Occupies an important place in literature since all the modern efforts
(Catal. Weight ¼ 6.0 g) made to achieve similar benchmark conversion via altering the Cu:Sn
Pretreatment: Continuous air flow (flow-rate and time interval not atomic ratio have been proved to be futile. (Bai et al., 2017)
clearly specified) at 723.15 K followed by cooling via air flow upto Applied across majority of fields of catalysis. (Refer the review section)
room temperate. The atomic ratio of 0.55:1 (Cu:Sn) exhibited the best conversion profile
because exchange of Cu2þ from CuO phase with SnO2 phase has reached
equilibrium at the mentioned proportion.
CO2 inhibition effect was observed to be a rate-limiting step, though
accurately predicted mechanism for particular 0.55 CuOeSnO2 catalyst
is not available in literature.
Less thermal stability. (around 15 min)
% Conversion at 298.15K ¼ 95-100
BETSA ¼ 19.4 m2/g
Particle size ¼ 9 nm (SnO2), 52.4 nm (CuO)
Cell Parameter ¼ 0.4740 nm (SnO2), 0.4692 nm (CuO)
▪ Since appreciable conversion at ambient conditions have been
achieved along with less manufacturing cost (compared to noble
metal catalysts which generally possess conversion in this range),
upcoming research must focus on enhancing the thermal stability of
this combination by keeping its activity intact.
▪ Exact reaction mechanism on the surface of such catalysts is still
unknown, appreciable scope for DFT and experimental studies can
be explored by upcoming researchers.
Pt/SnO2 (Wang Reactor: U-shaped quartz tube High thermal stability.
et al., 2014) Feed: 1% (v/v) CO, 21% O2 and rest N2 at total flow-rate of 30 mL/min or Negligible equilibrium conversion at room temperature.
SV of 90,000 mL g1catalh
1
. % Conversion at 298.15K ¼ 0
Pretreatment: H2 flow at 20 mL/min for 30 min. ▪ The interest in this field of catalysis has started to emerge since last
two years, there is yet so much to be revealed, e.g. (I) various
combinations of Pt/SnO2 with other dopants, (II) effect of change in
Table 3c (continued )
lattice structure on its activity, and (III) reaction mechanisms for

each crystals, etc.
Cu/SnO2 (Li et al., Reactor: U-shaped quartz tube reactor. Quite less susceptible to the presence of moisture.
2015) Feed: 1% (v/v) CO, 21% O2 and rest N2 with total flow-rate of 40 mL/min Appreciable thermal stability.
or SV of 24000 mL h1 g1
catal. Negligible equilibrium conversion at ambient conditions.
Pretreatment: H2 flow at 30 mL/min for 30 min at required reaction % Conversion at 298.15 K ¼ 0
temperature. BETSA ¼ 116e196 m2/g
Particle size ¼ 2.1e4.3 nm
Structure ¼ SnO2 in tetragonal rutile phase, and Cu2þ ions incorporated
into the crystal lattice of SnO2
▪ Such catalysts are actively exploited in the other fields of catalysis
like photo-catalysis, electrocatalysis, etc., however, very less data
is available in the literature that exhibits several aspects of this
combination for oxidation of CO.
Ru/Al2O3 Feed: 0.5% (v/v) CO, 0.5% O2 and balanced He. Oxidative activity of CO on Ru/Al2O3 is initiated at temperature of
Ru/SiO2 (Chin et al., Pretreatment: 5% (v/v) O2 and balanced N2 at 573.15 K for 2 h. Also 523.15K and for Ru/SiO2 at 483.15K with appreciable conversion.
2006) cases of with reductive pretreatment, i.e. 5% (v/v) H2 and balanced N2 In-spite of difference in intermediate species, the observed mechanism
were also explored. (Appendix B(iv),(v)) and rate limiting step were found to be same in
both the SiO2 and Al2O3 supported catalysts.
▪ Recently, few researchers have tried to manifest the activity of Ru
catalysts by changing its size and shape in the form of
nanospheres and nanorods for oxidation of CO. However, the results
haven’t shown appreciable conversion at ambient conditions due to
high surface activation energy of Ru supported catalysts, which isn’t
altered appreciably with change in its size.
▪ Researchers working in the physical chemistry area possess a great
scope of altering the crystal structure of such supported catalysts
in order to explore the crystal arrangement having the least surface
activation energy.
RueAl mixed e Poor dispersion of Ru in Al composite.
catalysts (Chen Unfavorable complex formation on the surface of supports.
et al., 2018) % Conversion at 298.15K ¼ Unknown
▪ Researchers undertaking research work in this field channelize their
efforts towards enhancing the dispersion of Ru and controlling the
growth of unwanted complex formation on the surface of supported
catalysts.
ZnO/Li-(Fe3þ)xOy Kindly refer the article (Tatarchuk, 2014) for specific details, since The activity of the catalysts are strongly affected by the structure of the
(Tatarchuk, varying flow conditions were used for each and every sample under ferrite spinel formed as a result of the solid-solid interaction between
2014) study in order to determine particular characteristic of a catalyst. Fe2O3, ZnO and Li2O.
BETSA ¼ Unknown
Particle size ¼ Variable
Structure ¼ Spinel
▪ Till date, only ferro-spinel structures have been explored in this field
of catalysis. Thus, it would be interesting to examine various other
crystal arrangements for achieving appreciable conversion at
ambient conditions.
NieAl2O3 (Deraz, e Activation energy of such catalyst is a strong function of calcination
2003) temoerature of catalysts and ZnO content.
Significantly high activation energy for reaction at room temperate.
% Conversion at 298.15K ¼ Unknown
BETSA ¼ 135 m2/g (Tcalci ¼ 1073 K); 270 m2/g (Tcalci ¼ 673 K)
Particle size ¼ 6 nm (Tcalci ¼ 673 K); 8.5 nm (Tcalci ¼ 873 K)
Structure ¼ Crystalline
▪ Recently pervoskites, ferro-spinels and other forms of crystal
structures doped with oxides of Ni, Al, La, etc. have been actively
explored and studied by various researchers. However, no appre-
ciable results have been achieved at ambient conditions.
▪ Thus, it would be a challenging task for modern researchers to
explore and discover the best possible combination of such metal
oxides and its crystalline structure.
NiO (Li) Feed conditions are variable. Refer the article for exact information. Reaction mechanism is strongly established in the article.
(El Shobaky et al., No study on thermal stability is available.
1969) % Conversion at 298.15K:
NiO (Ga) 60 (NiO (Li))
(El Shobaky et al., 68-70 (NiO (Ga))
1969) ▪ Due to lower manufacturing and handling costs as compared with the
majority of other catalysts, such catalysts possess potential application
at industrial scale. However, no thorough study on its thermal stability
is available in the literature.
▪ Thus, an imminent work to be undertaken must be the study of
thermal properties of such catalysis and thereby filling up the gap of
the information required for industrial utilization of such catalysts.
LaNi0.5Cu0.5O3 (Yi Feed: 5% (v/v) NO, 10% CO and balanced He with SV of 36000 mL h1 Follows Langmuir-Hinshelwood (L-H) mechanisms.
et al., 2019) g1
cat. (Catal. Weight ¼ 50 mg) Negligible equilibrium conversion at ambient conditions.
Pretreatment: Pure N2 flow for 1 h at 383.15K. % Conversion at 298.15K ¼ 0
BETSA ¼ 15 m2/g
Structure ¼ Pervoskite
▪ Due to its ability to remove two toxic pollutants at a time, i.e NO and
CO, such catalysts possess great potential to replace the majority of
existing pollutant treatment catalysts.
▪ However, prior to its industrial application, a thorough study of
thermal properties of such catalysts are required (which isn’t
available in the literature) in order to account for the aging problems
associated with them.
NiO/CeO2 (NPs) Feed: 500 ppm CO, 20% (v/v) O2 and balanced Ar gas at flow-rate of Reported values of negative Activation energy clearly indicates the
(Singhania and 100 mL/min (Catal. Weight: 0.5 g) presence of ineffective collisions between CO and O2 molecules.
Gupta, 2018) Pretreatment: None High thermal stability (more than 100 h).
NiO/Co3O4 (Yi et al., Feed: 1.6% (v/v) CO, 20.8% O2 and balanced N2 with SV of 30,000 mL % Conversion at 298.15K ¼ 0-10
2018) h1g1cat. BETSA ¼ 44e50 m2/g
Pretreatment: Pure N2 flow at 373.15K for 1 h. Particle size (TEM) ¼ 17.4 nm, 25.1 nm
Structure ¼ NieCe solid solution
▪ High thermal stability and appreciable activity at around 423.15K
(70% conversion), makes such catalysts potential candidate to be
used in the removal of pollutants from automobile exhausts and
furnace emissions.
▪ NiO phase is more active than Co3O4 phase of a catalyst, which is
against majority of data supporting the high activity of Co3O4 phase.
% Conversion at 298.15K ¼ 5-10
BETSA ¼ 83e135 m2/g
Particle size ¼ 2.9e10.9 nm
Structure ¼ Variable (refer article)
Cr2O3/CuO (Mobini Feed: 10% (v/v) CO, 20% O2 and balanced Ar gas at GHSV of 60,000 mL/ % Conversion at 298.15K ¼ 5-10
et al., 2017) gcat.h. BETSA ¼ 4.5e46.9 m2/g
Pretreatment: 20% O2 balanced with Ar at 573.15K for 1 h. Particle size ¼ 15.4e23.2 nm
▪ The activity of the catalyst with Cu:Cr ¼ 1:2 (molar ratio) was
reported to be the highest because:
1. The catalyst with Cu:Cr in molar ratio of 1:2 possesses smallest
particles size with highest surface area, as per data available in
literature.
2. Formation of pure CuCr2O4 along with traces of CuO.
3. Acquisition of ion-exchange equilibrium between Cu and Cr ions.
▪ Data available in the literature coherently provides the argument for
conversion profile and thermal stability, a detail kinetic study for the
mentioned catalysts is still unavailable. Thus, upcoming work in this
field should focus on determination of the reaction mechanism and
kinetic.
CeO2eSnO2 Feed: 50 ml pulses of CO or CO þ O2 mixture (2:1 by volume) were The rate of formation of CO2 was not observed to be same as rate of
(Sasikala et al., injected to catalyst samples at different temperatures. disappearance of CO because of back-reaction of CO2 with the catalyst
2001) Pretreatment: Heating in He gas at 573.15K for 2 h. surface and thereby forming carbonate species.
SnO2 being easily reducible, it provides oxygen for formation of CO2.
After the formation of CO2, reduced form of Tin oxide extracts an
oxygen atom from neighboring CeO2 unit.
BETSA ¼ 53e80 m2/g
▪ In-spite of extensive studies available in literature, the rate limiting
step of the mechanism is still not accurately known. Thus, for the
researchers pursuing their interest in Molecular simulations, this
opens up a gateway to carry out DFT studies and MD analysis in
order to provide a transparent picture of this reaction.
Mn2O3eSnO2 Feed: 50e100 mL respective pulses of CO and O2. SnO2 acts as an oxygen carrier in order to rejuvenate Mn2O3 active
(Kulshreshtha Pretreatment: None phase.
et al., 1996) High surface activation energy due to presence of strong FeeOeSn or
MneOeSn bonds seems to be one of the possible reasons behind high
temperature requirement.
Ea ¼ 22.6 kJ/mol
▪ Recently bimetallic alloys have been actively explored in order to
reduce the high surface activation energy. Thus, this opens a path
for studying possible combinations for determining reaction kinetics
and the effect of various physico-chemical parameters on its activity.
Nanoparticles of Feed: 2000 ppm CO, 1.5% (v/v) O2 and balanced N2 at total flow-rate of Order of activity of different shapes of CuO/g-Al2O3 for oxidation of CO:
CuO/Al2O3 1 L/min. (Catal. Weight ¼ 10 g) Needle-like > Sheet-like > Grain-like.
(Antony et al., % Conversion at 298.15K ¼ 0
2018) BETSA ¼ 186e190 m2/g
Particle size ¼ Variable
Structure ¼ Variable
▪ Literature is not yet bestowed with thorough kinetic studies of such
different shapes of CuO catalyst and the reasons (available in
literature) for conversion profiles of such catalysts are still
obfuscating. Thus, it would the interesting to take up upcoming
research to reduce the opacity of these catalytic reactions
CuO/Ce0.75Zr0.25O2- Feed: 1% (v/v) CO, 1% O2 and balanced N2 at total flow-rate of 200 mL/ The caalytic activity for CO oxidation decreases in the order of CuO/
1
d (Kang et al., min or GHSV of 60,000 h . (Catal. Weight ¼ 200 mg) Ce0.75Zr0.25O2-d>Cu0.07Ce0.75Zr0.25O2-d>Ce0.75Zr0.25Od
2018) Pretreatment: None % Conversion tat 298.15K ¼ 0
BETSA ¼ 57.2522 m2/g
Structure ¼ Refer article for detailed discussion
▪ Majority of kinetics studies till date focused on determining a
particular reaction mechanism via experimental results of partial
pressure/concentration of reactants. But none of the study
anticipated for the presence of multiple reaction pathway at a time
on the catalyst surface for oxidation of CO to CO2. Thus, this article
(Kang et al., 2018) occupies an important place in literature of CO
oxidation, since it was the first one in past few decades that has
anticipated and experimentally confirmed the presence of multiple
reaction pathways at a time.
▪ This approach provides an important method of interpreting the
reaction rate data in order to determine the rate law. Thus,
upcoming research work must adhere to the same in order to get
accurate details.
CuO/Ti0.5Sn0.5O0.2 Feed: 1.6% (v/v) CO, 20.8% O2 and balanced N2 at 30,000 mL g1 cath
1
. The reduction of surface CuO takes the leading part for catalytic
(Wu et al., 2018) (Catal. Weight ¼ 50 mg) reaction.
Pretreatment: None Probable mechanism: classical L-H reaction mechanism.
BETSA ¼ 35.8 m2/g
Structure ¼ Crystalline having lattice parameters: a ¼ b ¼ 4.6924 Å,
c ¼ 3.0141 Å
▪ The study exhibiting the effect of physico-chemical parameters,
thermal properties on the conversion is still unavailable in literature.
Thus, upcoming work can focus on exploring various crystal struc-
tures and thermal properties of this combination.
▪ A steady increase in CO oxidation activity is observed in the range of
423.15e473.15 K, such catalysts occupies an important place in the
list of potential catalysts in view of industrial application for
oxidation of the furnace stack emissions and automobile emissions.
**All the future scopes mentioned hereby (via square bullets) are about the works which are yet to be explored. Moreover the directions provided for future works are
completely based on the view to achieve appreciable conversion at ambient conditions.
corresponding surface area of the catalyst due to thermal aging. Cu-modified Tin oxides have attracted many researchers due to its
Therefore, calcination must be carried out at a lower temperature to wide application in fields like gas sensors (Choi S.W. et al., 2014(1)),
yield a catalyst with a high surface area. Further, if calcined at a photocatalysis (Zheng et al., 2010), electrodes (Choi S.H. et al., 2013)
lower temperature, apart from higher moisture content it increases and ceramics (Zhang et al., 2015) with limited reports on its
the corresponding catalyst activation temperature required for at application for pollution elimination. The atomic ratio of 0.55:1
least 50% conversion of CO. The observed trends of lower CO con- (Cu: Sn) exhibited the best conversion profile because the exchange
version in the samples which are calcined at lower temperature of Cu2þ from the CuO phase with the SnO2 phase has reached
must be attributed to rate limiting CO2 desorption step, i.e. due to equilibrium at the mentioned proportion. Moreover, the results
slower rate of desorption of CO2, free surface area is not instanta- presented in the above-mentioned article are quite promising for
neously made available to the upcoming reactant molecules and the oxidation of CO at room temperature because the reported
hence conversion drops due to lack of available sites with the specific surface area of the catalyst is around 140 m2 g-1 for calci-
respect to time. However, being our selection criterion is not ful- nation temperature of 723.15K, with the rate of reaction of around
filled, tin oxide would not be a good choice for the oxidation of CO. 7000 mol CO (g catalyst)-1hr-1. Hence SnO2/0.55 CuO seems to be
one of the possible options for utilizing as a catalyst because even
3.4.2. Doped SnO2 catalyst for high activity around reaction temperature of 353.15K, 96% CO conversion was
In order to embark upon the drawbacks of SnO2 certain re- reported and can be observed in Fig. 8. Such high activity of
searchers (Fuller and Warwick, 1974) have previously designed bespoke catalyst is due to the presence of ≡SneOeCu-groups on
SnO2eCuO gels with different Cu:Sn atomic ratios and thereby the surface which donates the inter-lattice oxygen for oxidation of
optimizing the best suitable catalyst for oxidation of CO. Recently, CO.
Recent efforts (Bai et al., 2017) to study the effect of doping on catalysts by changing its size and shape in the form of nanospheres
SnO2 showed that none of the possible combinations of SnO2eCuO and nanorods for the oxidation of CO which again botched to
exhibits the comparative performance as that of 0.55 CuOeSnO2. provide higher activity at room temperature. Given above
Anomalous to undoped SnO2 catalysts, CO2’s inhibitory effect was mentioned observed trends of various attempts in this field of
observed to be a rate-limiting step, though accurately predicted catalysis, it can be easily concluded that Ru supported catalysts do
mechanism for particular 0.55 CuOe SnO2 catalyst is not available not possess potential active sites (which is present in pure Ru). This
in the literature. However, it is observed that the majority of copper must be either due to poor dispersion of Ru or unfavorable complex
oxide doped SnO2 exhibits Mars-van Krevelen mechanisms. formation on the surface of supports (as recently observed (Chen
Comparative kinetics study results, especially the activation energy et al., 2018) to the surface of RueAl catalysts). The above conclu-
of such catalysts are shown in Table 3(c). The significant reduction sion is drawn from the fact that though pure Ru possesses appre-
in activity was observed within 15 min and hence such catalysts ciable activity, the majority of Al supported Ru doesn’t; hence the
would require a large number of regeneration cycles. Thus, before availability of Ru active sites on the surface must not significant.
opting for such catalysts being, they are sufficiently dynamic, Thus, it is hereby suggested that researchers who are undertaking
regeneration cost must be taken into account. Recently, efforts have their work in this field, must direct their efforts towards enhancing
been made to achieve higher CO conversion by doping Pt (Wang the dispersion of Ru and controlling the growth of unwanted
et al., 2014), Cu (Li et al., 2015) and various other elements (Fe, complex formation on the surface of supported catalysts.
Ta, Cr, etc.) on Tin oxide, and the prepared compounds exhibited
appreciable activities for oxidation of CO, though none of them
were observed to be sufficiently active at room temperature. These 3.6. Zinc oxide (ZnO)
observations are still unanswered and need accurate DFT studies to
observe the dynamics of catalyst molecules to account for the re- 3.6.1. Undoped ZnO catalyst
sults mentioned in the above works. The interactions of carbon monoxide with ZnO have been
studied extensively in the literature (Garner, 1947; Garner and Veal,
3.5. Ruthenium (Ru) 1935; Kelley and Anderson, 1935). The inter-lattice oxygen of ZnO
was found to be an active participant in the oxidation of carbon
Ruthenium is one of the rarest metals that are found on earth. It monoxide, which is shown in the mechanism described in
is generally found uncombined in nature; however, it is also Appendix B (vi). Even in the presence of externally supplied oxygen,
observed to be associated with other platinum metals in the min- the mechanism for the oxidation of CO over ZnO is also accompa-
erals pentlandite ((Fe, Ni)9S8) and pyroxinite. It has recently been nied by an exchange of inter-lattice oxygen and is shown below
extracted from the wastes of nickel refining for commercial appli- (refer R.1 to R.3):
cations like manufacturing chip resistors and electrical contacts,
coating of anodes in electrochemical cells for chlorine production, CO þ 2O2 þ 2Zn2þ 4 CO2
3 þ 2Zn
2þ
þ2e R.1
catalytic production of ammonia and acetic acid. Additionally, it
also possesses potential use in the solar cell due to the favorably CO2
3 þ 2Zn
2þ
þ 0.5O2 þ 2e 4 CO2
3 þ O
2
þ 2Zn2þ R.2
lower band-gap. However, since it is highly susceptible to chemical
attacks, the majority of its commercial application has been CO2
3 / CO2 þ O
2
R.3
observed to be in doped form. The main motivation behind working
in this field of the catalyst lies in a finding from various articles The above mechanism is further corroborated by a recent FTIR
available in literature, i.e. the activity order observed among Rh, Ru analytical study of the interaction of CO with ZnO (Noei et al., 2011).
and Pt are Ru > Rh > Pt. Hence, due to the highest observed activity The reaction does not occur with an appreciable rate at tempera-
among the three rarest metals, researchers are trying since then to tures below 523.15K due to the complexities involved in exchange
overcome the difficulties associated with Ru by using various of CO and CO2 with the surface of the catalyst, as reported in
combinations of catalysts. literature (Winter 1958); hence pure ZnO is also not a good
contributor to the list of best suitable catalyst for CO oxidation at
3.5.1. Doped Ru catalyst for high activity low temperature. The comparative kinetic study of oxidation of CO
Ruthenium supported catalysts like Ru/Al2O3 and Ru/SiO2 have on ZnO along with various other catalysts is shown in Table 3(a).
been thoroughly studied in the literature by various group of re-
searchers. Based on the conclusions drawn from previously
mentioned article on the presence of intermediate species on the 3.6.2. Doped ZnO catalysts for high activity
surface of such catalysts, it is cognizable to say that silica exhibits a Though the exact reason for less activity of ZnO for CO oxidation
significant synergistic effect along with providing appreciable is not accurately justified in literature, many researchers have tried
structural stability (recently explored by a group of researcher to transgress the limitations of pure ZnO, i.e. low activity, via doping
(Nosrati et al., 2018) working on pervious cements) as compared to with Li-(Fe3þ)xOy (Tatarchuk, 2014), Fe2O3eLa2O3-(Co/Ni/Cu/Mn/
that by alumina. It was observed that oxidative activity of CO on Ru/ Mg)eAl2O3 (Yiquan et al., 2012), NieAl2O3 (Deraz, 2003) and
Al2O3 is significantly higher than that of Ru/SiO2 (Chin et al., 2006), thereby modifying the crystal structure of the solid catalyst.
the exact reason of which is still unknown. The above difference in Various efforts have been made to enhance its activity by doping it
activity was because different adsorbed species were present on with noble metals, but due to extremely high manufacturing costs,
both the catalysts. In spite of the difference in intermediate species, it would be immature to compare and discuss them here. However,
the observed mechanism (Appendix B (iv), (v)) and rate-limiting albeit above-mentioned researchers have made painstaking efforts,
step were found to be the same in both the SiO2 and Al2O3 sup- no successful results in this field of catalysis is yet reported for
ported catalysts. However, due to the unfavorable conversion pro- oxidation of CO. Thus, this field adds onto the list of various chal-
file (primarily due to high activation energy), such catalyst doesn’t lenges faced in different respective fields of catalysts for oxidation
fulfill our selection criterion and hence using such adsorbents of CO, and thereby demanding a more rigorous approach to induce
would again contradict the basic purpose of producing heat. Re- activity in such comparatively cheap alternatives for oxidation of
searchers have also recently tried to manifest the activity of Ru CO.
3.7. Nickel oxide (NiO) NiO for oxygen above carbon monoxide. Further, the accurate
conversion profile of oxidation of CO over pure NiO has been still
3.7.1. Undoped NiO catalyst not observed in the literature due to its vulnerable nature in the
The activity of Nickel oxide catalysts has been ardently studied presence of an even slightly acidic environment (SO2, NOx, etc.).
and cogently presented by various researchers in the literature
(Conner and Bennett, 1976; El Shobaky et al., 1969; Gravelle and
3.7.2. Doped NiO catalyst for high activity
Teichner, 1969). Two different active sites are available on the
Various promoters like Li, Ga, etc. were previously used by a
surface of the NiO catalyst:
group of researchers (El Shobaky et al., 1969) to increase the activity
of NiO for the oxidation of CO at room temperature. The trend in the
a-site, which corresponds to O2 sites
activity of various NiO catalysts is as shown below (here the in-
b-site, which corresponds to O sites
tegers in the bracket represent corresponding calcination temper-
ature ( C) and letters represent a corresponding doped chemical
The interaction of CO and O2 with a and b active sites of NiO
element): NiO (200) < NiO (Li) (250) < NiO (Ga) (250) < NiO (250)
catalysts can be shown via the following mechanism (Conner and
The cogent reason behind the observation of such a trend is still not
Bennett, 1976) (refer R.4 to R.9),
available in the literature, with a satisfying argument. Apart from
catalytic properties, doped and undoped nickel oxides have
O2 þ 2a / 2Oa R.4
established their importance as n-type and p-type semiconductors.
The corresponding mechanisms are provided in Appendix B ((vii),
CO þ Oa / CO2a R.5
(viii), and (ix)). Additionally, the steady-state conversion for NiO (Li)
(250), NiO (Ga) (250) and NiO (250) is appreciably above 60%, such
CO2a þ Ob 4 CO2 Ob þ a R.6
catalysts produce a good impression to be in the list of the best
possible options, given that their thermal stability or sintering
CO2 Ob 4 CO2 þ Ob R.7
point is sufficiently high enough. Hence a detailed study of the
stability of such catalysts must be carried out before choosing to
CO2 Ob þ CO 4 CO2O3Ob R.8
fulfill the selection criterion. Apart from the above-mentioned
catalysts, even supports like SiO2, Li, Au, Pt, CoOx and CeO2 were
CO2O3Ob þ Oa / 2CO2 þ Ob þ a R.9
explored in the early 20th century, among which the one with Au
and Pt exhibited appreciable activity at room temperate due to
The literature is still not bestowed with the accurate reason
synergistic effect which is discussed in a further section of transi-
behind the above-observed mechanism, i.e. higher selectivity of
tion metals. Recently shifting trends are observed in this field of
Fig. 6. Oxidation of CO in presence of NO on LaNi0.5Cu0.5O3 pervoskites (Yi et al., 2019).

catalysis since the majority of modern research works are slowly enhancement in the uniformity of particle size distribution. With
shifting from exploring NiO doped catalysts for CO þ O2 reaction to such CueCr catalysts, it is observed that copper acts as an active
that for CO þ NO reaction. In the view of the above trends, per- phase, whereas chromium acts as a simulator of reduction of the
voskite of nickel oxides like LaNiO3, LaNi0.5Cu0.5O3 are being copper phase via the formation of CuCr2O4 phase in the spinel
actively explored by various groups of researchers (Yi et al., 2019). structure. The high thermal and chemical stability of such a spinel
The majority of pervoskites including LaNi0.5Cu0.5O3 are observed structure espouses its eminent catalytic properties. Since the
to follow Langmuir-Hinshelwood (L-H) mechanisms. For example, advent of nanoscience, researchers have been actively involved in
in order to understand the reaction occurring on the surface of altering the properties of various substances by changing its di-
LaNi0.5Cu0.5O3, consider Fig. 6 which shows that initially Cu2þ, Ni3þ, mensions. Certain researchers (Mobini et al., 2017) have recently
and Cuþ sites are occupied by NOx molecules. As the temperate is provided the exhaustive study of nanocrystalline CuO doped Cr2O3
increased to around 423.15e473.15 K, some of the adsorbed NOx in different proportions. The activity of the catalyst with Cu:
desorbs in the form of N2O/N2 and the emptied Cu2þ and Cuþ sites Cr ¼ 1:2 (molar ratio) was reported to be the highest. Various
are filled with CO molecules. Additionally, the oxygen vacancies are possible reasons behind this observation are provided below:
also created due to desorption of adsorbed NOx which enhances the
conversion of NO to N2O. Further, as the temperature is increased to The catalyst with Cu: Cr in the molar ratio of 1:2 possesses the
523.15Ke623.15K, the majority of adsorbed CO and NOx desorbs in smallest particle size with high surface area, as per data avail-
the form of N2 and CO2 along with the transition of Cu2þ to Cuþ able in the literature (Mobini et al., 2017).
which enhances the further chemisorption of incoming CO mole- Formation of pure CuCr2O4 along with traces of CuO.
cule. Such catalysts might be useful (given that they possess suffi- Acquisition of ion-exchange equilibrium between Cu and Cr
cient thermal, mechanical and chemical stability) for reducing ions.
industrial stack gases because generally the gases from the furnaces
possess the temperate in the above-mentioned range and thereby Though the data available in literature coherently provide the
reducing emissions of extremely poisonous gases like NO and CO in argument for conversion profile and thermal stability, a thorough
the atmosphere. However, due to a high temperate requirement for kinetic study for the above-mentioned catalysts is still unavailable
initiation of oxidation of CO to CO2 along with the occurrence of the and hence it would not be prudent to provide the possible reasons
majority of side reactions, such catalysts won’t be of practically behind such performance profiles. Since the temperature required
useful in the proposed NERS process. for appreciable conversion is quite high for such catalysts, it would
Recently efforts have been made to increase the activity of NiO an egregious choice for the oxidation of CO at ambient conditions
catalyst by doping it on ceria nanoparticles (NPs) (Singhania and for simultaneous recuperation of heat.
Gupta, 2018) and bulk ceria (Tang et al., 2015) via solution com-
bustion method of preparation. However, the results seem to be 3.9. Oxides of CeeSn mixture
quite futile for its application on an industrial scale due to the
following two reasons: 3.9.1. Doped oxides of CeeSn mixture for high activity
Ceria based catalysts have been exhaustively studied in litera-
Complexities involved in bulk production of Ceria NPs of the ture due to its eminent redox behavior. Generally, they have been
required size. known to regulate the partial pressure of oxygen in the exhausts of
The high cost of manufacturing due to the high energy automobiles due to an equilibrium reduction of Ce4þ to Ce3þ
requirement. (Fornasiero et al., 1996; Hori et al., 1998; Trovarelli, 1996). Tin oxide
High light-off temperature for the oxidation of CO. has been widely used as a catalyst in many processes due to its ease
of establishing equilibrium between Sn4þ and Sn2þ at around
In order to tackle the above-mentioned drawbacks, Nickel oxide 473.15K. The comparative kinetic study of SeO2, CeO2, and corre-
supported with cobalt oxides were recently investigated by a group sponding mixtures are provided in Table 3(c). The apparent
of researchers (Yi et al., 2018; Kim et al., 2018) who provided reduction in activation energy for the oxidation of CO over mixed
conclusive evidences and suggested that NiO phase is more active oxides is due to the ease of availability of lattice oxygen in these
than the Co3O4 phase of a catalyst, which is against the majority of samples. Surprisingly the rate of formation of CO2 was not observed
data supporting the high activity of Co3O4 phase. Even the above- to be the same as the rate of disappearance of CO because of back-
mentioned catalyst failed to achieve higher conversion at reaction of CO2 with the catalyst surface and thereby forming car-
ambient conditions due to the absence of a significant synergistic bonate species (Sasikala et al., 2001). The proposed mechanism as
effect which is a general cause of increasing activities of the ma- per available data on oxidation of CO over CeeSn mixed catalyst in
jority of doped catalysts. the absence of external oxygen is shown below (refer R.10 to R.12):
3.8. Copper-chromites CeO2eSnO2 þ CO 4 CeO2eSnO2(CO) R.10
3.8.1. Doped copper-chromite catalyst for high activity CeO2eSnO2(CO) 4 CeO2eSnO þ CO2 R.11
Due to its low ground state electronic surface energy, chromium
and its oxides have been studied comprehensively by various re- CeO2eSnO 4 CeOeSnO2 R.12
searchers (Acharyya et al., 2015, 2014; Beshkar et al., 2015; Chiu
et al., 2011). Simultaneously copper oxide (CuO) has also been SnO2 being easily reduced, it provides oxygen for the formation
studied for the oxidation of CO which suggested that at ambient of CO2. After the formation of CO2, the reduced form of tin oxide
conditions, copper (II) oxide (CuO) gets deactivated by its conver- extracts an oxygen atom from the neighboring CeO2 unit. In-spite of
sion to copper (I) oxide (Cu2O), due to its interaction with carbon such extensive studies available in the literature, the rate-limiting
monoxide. Due to the co-operative effect of two metals based step of the above mechanism is still not accurately known. The
composite, binary mixtures are being explored since the 1930s. The article presented by (Sasikala et al., 2001) showed that even at
presence of chromium enhances the reduction of copper (II) oxide 373.15K, almost zero or negligible conversion of CO to CO2 was
and reduces the particle size along with simultaneous observed. The prime reason behind such a conversion profile is still
unidentified since accurate knowledge of the rate-determining step

is not available. Thus, due to its inability to filter through a selection
criterion, such a catalyst won’t be a prudent choice for the oxidation
of CO at ambient conditions.
3.10. Composites of transition metal oxides
3.10.1. Doped catalysts of transition metal composites for high

activity
Composites of transition metal oxides have been used exten-
sively for dehydrogenation, oxidation, hydrolysis, etc. due to the
presence of a synergistic effect between its constituents which
enhances its activity. A synergistic effect can be defined as an “ac-
tivity enhancing effect” due to a combination of two or more active
phase. Two important reasons behind the existence of such a
synergetic effect are:
Solid solution/compound formation due to the interaction be-

tween constituent species.
An insular control mechanism involving the constant regener-
ation of consumed sites by other oxides which revitalize itself
from the feed mixture.
Based on various studies available in the literature, the role of

individual metal ion during the exhibition of synergetic effect is
assumed to be dependent on standard Gibbs free energy change
(DG ) involved in the dissociation of a metal-oxygen bond. Ac-
cording to various data on the interaction of transition metal and
inter-lattice oxygen, it can be inferred that higher the value of DG ,
more difficult is the reduction/deactivation process. Immense
studies on iron oxides, tin oxides, manganese oxides, and their
corresponding mixed oxides are also available in the literature Fig. 7. Mars-van Krevlen mechanism for oxidation of CO over bulk Ceria (Color code:
which ultimately concludes that the mixture of transition metals Red e Oxygen, White e Cerium)[1: Adsorption of CO on the surface oxygen, 1a: For-
have higher activity than corresponding individual oxides due to mation of CO2 by removal of surface lattice oxygen, 2: Rejuvenation of surface active
site by donation of an oxygen atom by externally supplied oxygen]. (For interpretation
following reasons: of the references to colour in this figure legend, the reader is referred to the Web
version of this article.)
High mobility of oxygen on the surface of mixed oxides and
hence, depleted oxide layer quickly gets rejuvenated via oxygen
in the reactant mixture. oxide (1e10% w/w of NdxOy/LaxOy/ThxOy/YxOy/GdxOy/TbxOy/
Synergetic effects between constituent oxides. DyxOy) (Zhou et al., 2013) were greatly exploited. Some of these
catalysts containing rare earth exhibited plausible activities
A comparative study (Kulshreshtha et al., 1996) implies that (50e60% conversion) and hence possess great potential for indus-
from various combinations of transition metal oxides of Fe, Sn and trial application additionally due to their long service life, good
Mn, Mn2O3þSnO2 (due to more synergetic effect) possess more water resistivity, low cost, and good thermal stability. The main
activity. The interaction of CO with Mn2O3þSnO2 (in the absence of question about its use is regarding the availability of rare earth and
external oxygen) is shown in Appendix B(x), which depicts that hence, it must be accounted for properly before deciding whether
SnO2 acts as an oxygen carrier to rejuvenate Mn2O3 active phase. or not to use such catalysts. An extensive and detailed catalytic
However, due to the unavailability of sufficient data, the interaction review for the oxidation of CO (specially dedicated to transition
of CO with Mn2O3þSnO2 in the presence of externally supplied metals) is available in the literature (Royer and Duprez, 2011),
oxygen and corresponding rate law is still unknown. The compar- which must be referred for gaining knowledge beyond this article.
ative study of the above-mentioned catalysts based on the activa- A recent ground-breaking discovery of achieving around 100%
tion energy for the oxidation of CO is shown in Table 3(c) which is conversion at the least possible manufacturing cost, by using
clearly as per trends of corresponding catalytic activities. Unfortu- spinel-shaped MnCo2O4.5 as a catalyst (Baida et al., 2019) may also
nately, any of these combinations is not useful because of the high- occupy an important place among the best possible catalyst for
temperature requirement for appreciable conversion. The high oxidation of CO at room temperature. Additionally, a German group
surface activation energy due to the presence of strong FeeOeSn or of researchers (Biemelt et al., 2016) has recently transgressed the
MneOeSn bonds seems to be one of the possible reasons behind previous limitation of catalyst-deactivation under humid condi-
high-temperature requirement along with the higher tendency of tions (generally encountered in various practical applications of
Fe and Sn mixed oxides to deactivate. The high strength of bonds such catalysts) of Hopcalite catalysts, by preparing nanoparticles of
must be attributed to the strong overlapping of external d-orbits of Hopcalite (CuMnOx) catalysts via flame spray pyrolysis. Since such
Fe or Sn and p-orbits of oxygen. catalysts have achieved the conversion of around 60e70% at normal
Recently, in order to reduce high surface activation energy, room temperate, such catalysts (being economically handy due to
bimetallic alloys made up of combinations of Au, Pd, Pt, Ni, Cu moderate preparation cost) are one of the few potential candidates
(Robinson et al., 2018); combinations of Ɣ-alumina carrier (75e98% for its application in NERS process.
w/w), bimetal (1e15% w/w of Ag/Cu/Fe/Co/Ni/Mn) and rare earth
3.11. Cerium oxide (CeO2) from the hereby discussed catalysts, Ceria doped with Thoria,
Copper, Nickel, Manganese and Iron have been also investigated,
3.11.1. Undoped CeO2 catalyst but none of them exhibited even light-off temperate below 473.15K
Ceria possesses its long history of application as a support ma- and thus are of no specific interest to discuss hereby.
terial in various heterogeneous catalysts and also as a catalyst in
automobile converters. Generally, Ceria is incorporated as oxygen 3.12. Copper oxides (CuO)
storage or release material. Ceria is a potential catalyst for oxidation
of CO to CO2 at lower temperature via Mars-van Krevelen type 3.12.1. Undoped CuO catalyst
mechanism as shown in Fig. 7 wherein lattice oxygen is used in step Copper oxides are used in varieties of important applications
1 to form carbon dioxide followed by the rejuvenation of surface by due to its following properties:
the donation of an oxygen atom by an externally supplied oxygen
molecule. Moreover, temperature-programmed desorption/reduc- High thermal stability
tion studies coupled with in-situ IR spectroscopy by certain re- High electrical conductivity
searchers (Wu et al., 2012) gesticulates the presence of Attractive antimicrobial properties
intermediate carbonate species in the above mechanism. Recently
nanoparticles of ceria are widely explored for the oxidation of CO It is a p-type semiconductor and is also used in varieties catalytic
due to following reasons: applications like photo-catalysis of effluent dyes, oxidative dehy-
drogenation of alcohols, thermal degradation of ammonium
Increased lattice defects and coordinated unsaturated sites. perchlorate, and electro-catalysis via reduction of carbon dioxide to
Enhanced lattice oxygen mobility due to more defects in the liquid fuels and the oxidation of carbon monoxide, etc. Abundant
lattice. availability and less cost are some additional advantages associated
Enhanced CO adsorption affinity due to more exposed surface with this catalyst. However, because of its insignificant activity at
area and more defects in the lattice. ambient temperature, significant studies are being carried out to
Ease of conversion between Ce3þ and Ce4þ. overcome this limitation. Major approaches to mitigate this prob-
lem deals with the following:
3.11.2. Doped CeO2 catalyst for high thermal stability Change in physical size
Alumina supported nano ceria particles (Wilklow-Marnell and Change in chemical composition
Jones, 2017) have been recently synthesized for oxidation of CO in
order to curb the conventional practice of pre-treatment and to
achieve high sintering resistance via reduction in chemical poten- 3.12.2. Doped CuO catalyst for high activity
tial (equal to product of the adhesion energy of specific metal/oxide Modern studies (Antony et al., 2018) on nanosheets, needles and
combination and total contact area between nanoparticles and grains-like CuO/Ɣ-Al2O3 for the oxidation of CO utilize the concept
support) of nanoparticles. The comparative kinetic behavior of of size reduction to increase its activity. Alumina has been used as a
alumina supported ceria nanoparticles and other catalysts are support to increase the catalyst dispersion, surface area and to
shown in Table 3(b). However, due to the poor tendency of facilitate maximum interaction. Relative comparison of Nano-
desorption of CO2 from the surface of alumina supported ceria sheets, needles and grains-like supporting catalyst based on its
nanoparticles, no observable amount of CO2 was observed below pore size, pore-volume, BETSA and conversion profile are available
423.15 K. Hence this option is also a reluctant choice to satisfy the in the above-mentioned article. The crux of the comparative study
selection criterion of our process. The recent studies on ceria of the above-mentioned catalysts of different shapes is shown
impregnated Au particles (Zhang et al., 2017) exhibited certain below: Order of activity of different shapes of CuO/Ɣ-Al2O3 for the
outstanding results. It was observed that the temperature required oxidation of CO: Needle-like > Sheet-like > Grain-like Literature is
to achieve a 70% conversion is almost 313.15K due to the presence not yet presented with thorough kinetic studies of such different
of the two most active sites ever known in the history of catalytic shapes of CuO catalyst and hence the reasons for conversion pro-
oxidation of CO. The article also successfully addressed one of the files of such catalysts are still obfuscating. According to the data
most intriguing questions in the nanoscience literature, i.e., which available in the literature (Antony et al., 2018), no appreciable
shape of nano-catalyst to be preferred and why? In conclusion, conversion is observed at 300.15K. Thus, such catalysts are reluc-
nanotubes were found to the most active followed by nanorods. tant to filter through the selection criterion of our process. Recently
Nanocubes were the least active of all three because of the for- conscientious attempts have also been made to alter the activities
mation of Au aggregates on CeO2 surfaces. A recent study (GAO of CuO by altering its chemical composition (Kang et al., 2018; Wu
et al., 2016) on carbon nanotubes doped with FeþCuxO/CeO2 cat- et al., 2018). Researchers have tried to modify the activity of CuO by
alysts concluded that the activity is not significant at room tem- supporting it with Ti0.5Sn0.5O2 and adding iron particles to it and
perature, though selectivity is 100% and hence such catalysts also by preparing CuO/Ce0.75Zr0.25O2-d but unfortunately, none of
cannot be used in NERS process. It was also observed that gold is them were successful to achieve higher activity for oxidation of
more susceptible to particle size changes, crystal structure altering carbon monoxide at low temperature.
and supporting selection than the majority of transition and noble
metals. The exact reason behind the above-mentioned observation 3.13. Supported cobalt oxides (Co3O4)
demands DFT studies of such catalysts (which isn’t available with
accurate details) addressing the exact reason behind the above- 3.13.1. Doped Co3O4 catalyst for high thermal stability
observed facts. Addressing the cost associated with above Cobalt possesses imperious catalytic properties as compared to
mentioned Au/CeO2 catalysts, certain researchers (Lu et al., 2018) the majority of transition metals due to the following reasons:
have replaced the gold by a mixture of copper and manganese
oxides, along with obtaining the comparative results as gold cata- Cobalt can exist in þ1, þ2 and þ 3 oxidation states, which allow
lysts. Thus, such catalysts seem to be a potential candidate in the list the rapid transfer of electrons between these states and thereby
of suitable catalysts for oxidation of CO at room temperature. Apart speeding up the reactions.
Table 4
Catalytic activity data of some recently explored catalysts.
Sr. Catalysts Mechanism for Ea (at 25 C) %X at normal Feasible option for proposed process Reason behind References
No oxidation of CO (kJ/mol) room T (25 C) negation
1 CuCe0.75Zr0.25Od M-K mechanism Unknown <30 No High activation Bin et al. (2019)
temperature
2 LaMnO3 Unknown Unknown 0 No High activation Huang et al.
temperature (2018)
3 LaMn0.8Fe0.2O3 Unknown Unknown 0 No High activation Huang et al.
temperature (2018)
4 CuO.Fe2O3 ER mechanism 41.84 93 Yes e Rezaei et al.
(2018)
5 CuMnOxCoy COþA/CO-A Unknown 0e30 No High activation Dey et al.
CO-AþO24I temperature (2017)
I/CO2þA
(A ¼ active site;
I ¼ unknown
intermediate)
6 Doped/Undoped ER mechanism or 20e30 Unknown No Low sintering Krishnan et al.
Graphenes LH mechanism point (2018)
7 Mn3Co16Ox coated with Mars-van Krevelen Unknown 40 Yes, because at 20 K above room temperature, %X e Zhou et al.
polymer nanofilm mechanism increases upto 85% for about 1 month (2018)
8 Aluminium alloys Unknown Unknown 0 No High activation Lukiyanchuk
(FeCrAlCu) temperature et al. (2017);
9 Bi/Ti-MCM-41 Unknown Unknown 5e10 No High activation Mohamed et al.
temperature (2018);
10 CueOeCe solid solution Unknown Unknown 0 No High activation Hossain et al.
temperature (2018)
11 Cu1.5Mn1.5O4 Unknown Unknown 60e70 Yes e Biemelt et al.
(2016)
12 MnCo2O4.5 Unknown Unknown 100 Yes e Baida et al.
(2019)
Cobalt chemicals can react to produce more than one ion to (-Co3þ-O-).CO(surface) / (-Co3þ-O-)-CO(surface) R.14
exhibit catalysis in its solution form.
Cobalt possesses great ability to accept atoms from other mol- (-Co3þ-O-)-CO(surface) /(-Co2þ)(surface) þ CO2(g) R.15
ecules and thereby forming complex molecules, due to its ability
to exhibit different valences. (-Co2þ)(surface) þ 0.5O2 / (-Co3þ-O-)(surface) R.16
In solid-state Cobalt possesses vacancies within their crystal
lattice which allows for exhibiting far-fetching catalytic However, the results presented in the same article dictate that
properties. even around 373.15K, no appreciable conversion was observed,
which must be due to a slow surface reaction between adsorbed CO
Due to its attractive catalytic properties, cobalt has been studied and active sites. Hence this option is also eliminated from our quest
in various physical forms like nanoarrays (Mo et al., 2019), nano- of the best suitable catalyst. Details regarding various catalysts
particles and supported nanoparticles (Yang et al., 2018). The cat- explored by researchers in the past two years are presented
alytic activity of Co3O4/Ɣ-Al2O3 was found to be the function of the concisely in Table 4 along with corresponding reported data. Hence,
valency of cobalt, the interaction between two phases and the from the above literature survey, it is apparent that there are only a
crystalline size of Co3O4. Such catalyst has been widely investigated few catalysts that can be considered to oxidize CO to CO2 at room
for Fischer-Tropsch synthesis, water splitting, removal of dyes, temperature.
oxidation of CO to CO2, etc. Extensive studies on the oxidation of CO Few suitable options for the NERS process, from the above study,
over alumina supported cobalt oxide is provided in the literature are summarized below:
(Yang et al., 2018) to study the effects of pretreatment conditions.
The XPS studies presented in the same article concluded that more i. SnO2/0.55CuO
enhanced interaction of CO was observed with oxidative-reductive ii. Mn3Co16Ox
pretreated Co3O4/Ɣ-Al2O3 as compared to that with untreated iii. Fe3Co16Ox
Co3O4/Ɣ-Al2O3, due to more exposed Co3þ active sites after such v. Cu1.5Mn1.5O4
treatments and hence oxidative-reductive pretreatments have vi. MnCo2O4.5
been proven to be beneficial to increase the CO conversion. More-
over, the crystallite size of Co3O4 was observed to be reduced due to After discussing the varieties of options of catalysts available in
oxidative-reduction pretreatment and hence is one of the the literature, the remaining part of this paper deals with economic
contributing reasons behind its increased activity. Increasing cobalt analysis of the NERS process. Since economic considerations are as
loading results in a reduction of the ratio of Co3þ to Co2þ (Yang important as technical; economic analysis must be carried out with
et al., 2018) and hence the catalytic activity simultaneously re- significant accuracy and valid assumptions before the imple-
duces. The interaction of CO with Co3O4 follows Mars-van Krevelen mentation of any process. We have tried to utilize the literature up
mechanism (refer R.13 to R.16): to its maximum potential, to carry out an economic analysis of this
process. However, certain gaps in this analysis have been encoun-
CO(g) þ (-Co3þ-O-)(surface) / (-Co3þ-O-).CO(surface) R.13 tered due to the unavailability of certain data, which shall be filled
by us after our further work in the concerned area or field of
Table 5
Stack emission data of RIL based on stack emission monitoring report of 2014.
a
Species Concentration (mg/Nm3) (on dry basis) a
Total composition (kg/hr) (on dry basis)
SO2 2256 11.3

NOx 151.93 7.6
PM 316.05 15.8
CO 181.1 9.1
HC (Hydrocarbons) 81.4 4.1
b
CO2 4000 ppm 392
a
Based on an assumption that emissions from all the units are released at same ambient conditions.
b
Density of CO2 is taken as 1.96 kg/m3.
application. filter made up of porous granulates which are modified with

amines that bind CO2 in conjunction with moisture in the air. This
4. Techno-economic analysis of NERS process for refineries bond gets dissolved at around 373.15K and hence giving pure CO2,
which can be further collected or utilized further in this designed
The following section provides a techno-economic analysis of approach. The summary of the process which is currently being
the NERS process for industries in group-2 (as mentioned in Fig. 1), commercialized by Climeworks is shown in Appendix D. As per
because the majority of the chemical producing and refining in- current cost estimation data provided by Climeworks, the operating
dustries belong to this group. For industries in group-2, certain cost will be up to $400 per metric ton of captured CO2 at industrial
challenges faced for the utilization of CO2 (Lin and Biddinger, 2017) scale. However, work is still under progress to cut this cost down to
are: $100 per metric ton of captured CO2 (Climeworks, 2018). It is
further claimed by the authorities that their CO2 capture technol-
Separation of CO2 from industrial emissions. ogy is fully automated which can be controlled through touch
Different sources of CO2 from the same industrial premises. screen display and are also suitable for autonomous 24 7 opera-
Storage of highly pressurized CO2 at ambient conditions. tions. The nominal CO2 capacity of the single CO2 collector is
Deactivation of catalysts used in specific applications. approximated to be 135 kg/day (Climeworks, 2018). However, this
value may vary with various factors like temperature, humidity,
Hence, all the above factors are taken into account, while and air composition. Moreover, the utility of this equipment is
designing the steps of the NERS process. Considering the stack simultaneously accompanied by requirements of hot water at
emission monitoring report demonstrating data of April 2014- 373.15K and cold water at a temperature less than 288.15K
September 2014 of Reliance Industries Limited, situated in Jamna- (Climeworks, 2018). As per the information specified by the support
gar district of Gujarat in India, the average composition of the total team of Climeworks, initial purchasing cost depends on the ca-
stack emissions from all the units of the refinery (except sulfur pacity of equipment, which is summarized in Table 6. Total cost
removing units) is calculated and is summarized in Table 5. Due to (including capital and operational cost) for large scale plants like
the unavailability of CO2 data in the stack emission monitoring RIL is approximated to be $600/ton CO2. Since the total CO2 gen-
report of 2014, it is assumed to be around 4000 ppm, which is eration is estimated to around 9408 kg/day, the best possible option
almost below the TLV of CO2. Also, due to the absence of emission for such refineries would be 48 units of CO2 separator with 200 kg/
rate data, it is assumed to be 50,000 m3/hr at ambient conditions day capacity. Hence, an initial investment of $48 M would be
(298.15K, 1atm). Hence, the average compositions of individual required.
species in terms of its mass flow rates are shown in Table 5.
4.2. Separation of SO2 and NOx
4.1. Separation of CO2
After the separation of CO2, we would aim to obtain pure CO
Recently, various techniques have been developed and proposed from the remaining off-gases. Limited literature is available on the
for the separation of CO2 from industrial flue gas, which is thor- separation of CO as a pure component from flue gases. Majority of
oughly reviewed in many articles in the literature. However, the works have been published for separation of CO from mixtures of
majority of the process still face the problem of high initial and CO/N2 (Toshima and Hara, 2000), CO/H2/N2/CH4/CO2 (Xie et al.,
operational cost due to the complex design of the process, but 1997), CO/CO2/O2 (Cacho-Bailo et al., 2017), CO/CO2/SO2 (Matito-
simultaneously many of them are still in practice by various in- Martos et al., 2014), etc. using zeolites or MOF as adsorbents.
dustries. Due to the absence of certain economic data on the pro- However, generally, MOF serves as better adsorbents over zeolites
cesses available in the literature, we would not be able to compare due to its large pore size and surface area available for adsorption.
its practical feasibility. However, due to the availability of enough Since flue gas (after removing CO2) contains gases like SO2 and NO2,
economic and technical data of recently developed membrane which possess dipole moments greater than CO, such gases will
separator by Climeworks Inc., Switzerland; the further calculations polarize the adsorbent material quickly and in greater magnitude
are based on this technology. The separator includes a membrane as compare to CO and hence, ability of CO to adsorb on the majority
of available adsorbent will be less as compared to that of the gases
like SO2 and NO2. Therefore, rather than separating CO from the
Table 6
Purchasing cost of CO2 separator, developed by Climeworks (2018)
mixture, one must target the molecules with greater dipole
moment (SO2 and NOx) for ease of separation via adsorption.
Equipment capacity (kg/day) Purchasing cost of equipment ($)
Considering various factors like selectivity, working capacity and
8 400000 absolute adsorption, a group of researchers (Sun et al., 2014) have
80 600000 suggested that Cu-BTC and MIL-47 are the best suitable options for
200 1000000
separating SO2 from a given mixture of flue gas at 313.15K
Table 7
Results of adsorption of SO2 and NOx based on Monte-Carlo Simulations.
Species Selectivitya Absolute adsorption (mol/kg Cu-BTC) Working capacity (mol/kg Cu-BTC)
SO2 75 0.1 0.1

NOx 2.8 0 0
a
Calculated by equation given in literature (Sun et al., 2014).
temperature and 1 bar pressure. At the same condition, NOx can be quantity of coal is required (based on the heating value provided in
selectively removed from a given mixture of flue gas via Cu-BTC. the literature (The engineering toolbox, 2018)). The cost of such
This work does possess the potential for industrial-scale due to coal would be around $1030/year based on the global average cost
the higher selectivity and working capacity (the difference between of Bituminous coal available in literature (EIA, 2019), which shall be
loading during adsorption and during desorption) of suggested directly cut down (or saved) after the implementation of NERS
adsorbents. Rather than installing two different adsorbers for SO2 process. Moreover, a corresponding transportation cost which is
and NOx using two different adsorbent (MIL-47 and Cu-BTC for SO2 approximated to be around $100/year, which is based on average
and NOx respectively), it is economical to install an equipment with coal transportation cost available in literature (EIA, 2019) shall also
Cu-BTC adsorbent since its possess appreciable selectivity, working be cut down or saved. Therefore, total savings by refineries would
capacity and absolute adsorption for both SO2 and NOx as compared be around $1130/year. However, since the calculated value is based
to other components of flue gas. The literature results of adsorption on an average cost of Bituminous and average global expenditure
of SO2 and NOx on Cu-BTC at 1 bar pressure and 313.15K are sum- on transportation (without considering the distance between coal
marized in Table 7. Hence, assuming that theoretical data for the manufacturing site and delivery site), the actual savings would be
flue gas available in literature (Sun et al., 2014) is applicable for higher than theoretical predicted savings. Additionally, in countries
stack gases of such refineries, since the type of gaseous components like India, carbon taxes are levied on the amount of coal, which is
and its composition are almost same (neglecting the presence of either produced or imported. Currently, a carbon tax is around INR
nitrogen, which is a valid assumption since its presence won’t affect 400/ton of coal in India and hence such refineries in India
the adsorption process to appreciable extent due to its lesser (importing 20.34 tons of coal per year, based on previously shown
amount of selectivity as compared to SO2 and NOx), one can calculations) might save an additional amount of around $117/year.
calculate the theoretical amount of adsorbent (Cu-BTC) required for Therefore, Indian refineries can expect an overall savings of around
separation of SO2 and NOx from stack gases of such refineries, $1247/year from this step of the NERS process. The above calcula-
which comes out to be 201663.82 kg/hr. However, the actual tions are only for a single refinery like RIL. If one calculates the
amount of Cu-BTC required would be always greater than the statistics across all the refineries and allied chemical industries in
above-mentioned value since we haven’t accounted for poisoning, detail, more insight can be obtained on the total saving by all such
sintering (may occur due to certain regenerative cycles since industries per year. More importantly, carbon emissions will be
adsorption and desorption are exothermic and endothermic pro- significantly reduced; which will help the refineries to increase its
cess respectively) and fouling. Accounting for the above-mentioned carbon credit via a simultaneous reduction in greenhouse emis-
factors, we have assumed that almost 1.5 times theoretically sions and thereby abating its harmful effects on the environment.
calculated adsorbent (which is a general assumption in the ma- The waste of the catalyst may be utilized to produce porous con-
jority of chemical engineering applications) and hence one requires cretes (Toghroli et al., 2018) which may find application in con-
3.02 105 kg/hr of Cu-BTC. Poor mass transfer and regeneration struction sector.
problems associated with packed bed adsorber, multi-stage
counter-current fluidized bed adsorber should be preferred.
Further, the lack of experimental data on mass transfer co-efficient,
adiabatic equilibrium curve, and corresponding adsorption equi-
librium expression, makes it difficult to predict the size and hence
the cost of the separation tower at the present situation.
4.3. Conversion of CO to CO2
Upon complete separation of SO2 and NOx, pure CO stream can

be then transferred to a specially designed packed bed reactor,
where oxidation of CO to CO2 will be carried out with simultaneous
heat recovery, in the presence of a best possible combination of
catalyst and support which is discussed in the previous section. At
present, lack of sufficient data prohibits the exact cost estimation of
this process and hence it demands an arduous study in this section.
One can estimate the savings due to the utilization of heat gener-
ated in this step. Assuming almost 90% conversion of CO to CO2, the
amount of heat generated in this step can be calculated based on
the value of Gibbs free energy at 298.15K (i.e. 257.2 kJ/mol) and the
value of CO generated per hour (given in Table 5). Calculations
based on the above statistic justifies that 6.56 105 MJ of energy Fig. 8. Relation between T and %CO oxidation for (A) SnO2/0.55 CuO at initial condition
(30 min after thermal activation with hot air at around 673K), (B) SnO2/0.55 CuO at
can be produced per annum. Assuming Medium-volatile Bitumi- steady state condition (after allowing catalyst to equilibrate for 40hr), (C) SnO2/1.03
nous coal is being used to generate the same amount of heat in CuO at initial condition, (D) SnO2/1.03 CuO at steady state condition (Fuller and
furnaces in the majority of the refineries, around 20335 kg/year Warwick, 1974).
Fig. 9. Flow-diagram for production of CH3OH from CO2 (Perez- Fortes et al., 2016).
Table 8 1. Compression of Feed gases up to reactor feed pressure

Economic analysis of Methanol (MeOH) production step. 2. Heating of pressurized feed and feeding to the reactor
Entities Values Values per year 3. Separation of Methanol from water
a
Capital costs $561.045/ton MeOH/year $1.360 M/year
Variable costs a
$724.74/ton MeOH/year $1.757 M/year Two major reactions occurring in a reactor are (refer R.17 to
Fixed costs a
$28.2/ton MeOH/year $0.068 M/year R.18):
b
Revenue generated $500/ton MeOH/year $1.212 M/year
a rez-Fortes et al., 2016).
Based on values available in literature (Pe CO2 þ 3H2 CH3OH þ H2O R.17
b
Based on recent global price (WV Coal, 2018) ($500/metric ton) of methanol and
total amount of methanol generated from conversion of CO2 which is directly and CO2 þ H2 CO þ H2O R.18
indirectly (in the form of CO) present in industrial emissions.
The second reaction is undesired one and is curbed by using a

4.4. Conversion of CO2 to CH3OH catalyst with greater selectivity. Prior feed entering in an atmo-
spheric distillation column for separation of methanol and water,
The next step would be the conversion of CO2 to other valuable the process stream coming from the reactor is depressurized and
products like methanol, polyurethanes or methane. Detail studies the mainstream is flashed to separate unreacted CO2 and H2, which
on the production of methanol from CO2 are available in the liter- are sent back to the reactor. The basic layout details of this process
ature (Van-Dal and Bouallou, 2013; Cost Insights, 2018) and reports are shown in Fig. 9.
of successful implementation of efficient technologies in this Cost estimation and all the process utilities required for the
connection are also available (WV Coal, 2019) in various parts of the production of methanol from CO2 are enlisted in the literature
rez-Fortes et al., 2016) by using CHEMCAD software. These data
(Pe
world. Since methanol is an important petrochemical feedstock for
the majority of fuels and potential fuel very soon, one can design a are available for Cu/ZnO/Al2O3 catalyst at reactor feed condition of
final step for the production of methanol. Methanol production 76 bar and 483.15K, with a conversion rate of 22% and a total con-
from CO2 can be divided into three different stages: version of 94% for the entire process. Neglecting the uncertainties
Table 9
Economic analysis of the NERS process.
Sr.No. Sub-steps Initial investment ($) Total cost (Fixed þ Variable) ($/year) Approximate Revenue generated ($/year)
1 Separation of CO2 48 M 2.06 M e

2 Separation of SO2 and NOx Aa Ba e
3 Extraction of heat from CO to CO2 conversion Ca Da 0.032 Mb
4 Conversion of CO2 to Methanol 1.36 M 1.83 M 1.212 M
Total: (49.36 þ AþC) M (3.89 þ BþD) M 1.244 M
a
Any arbitrary value (Yet to be determined by our further experiments).
b
The amount may vary based on local environmental taxes levied on an industry.
in cost variations, approximate cost of methanol production from industries which directly utilize CO2 in their process might avoid an
CO2 as per literature (Pe rez-Fortes et al., 2016) is summarized in excess economic burden from the conversion of CO2 to CH3OH.
Table 8. The calculation of the total amount of methanol generated Further, in upcoming years, since Climeworks has claimed to
from the conversion of CO2 is shown in Appendix C. Since total reduce its operating cost to around $100/ton CO2 separated, one
amount of CO2 available will be 3546.1 tons/year and overall con- may also expect a reduction in separation costs. Simultaneously, a
version of CO2 to Methanol is 94%, total Methanol that can be reduction in variable cost of methanol production from CO2 can be
produced by refineries based on their emission data will be 2424.3 observed if there would be a reduction in the cost of H2 since the
tons/year. Hence, the total revenue from Methanol production will cost of hydrogen accounts for almost 70e80% of the total variable
be $1.2 M/year. Simultaneously, total fixed cost, the variable cost, cost. To observe a significant reduction in the cost of H2, frugal
and capital cost involved will be $0.07 M/year, $1.8 M/year and innovation in the field of electrolysis of water must be expected.
$1.4 M/year respectively. Since, the capital cost is a one-time initial The NERS process is still immature to scale up until researchers
investment, whereas fixed and variable costs are the one which from different fields work together to reduce the cost of CO2 sep-
needs to be paid by a company in order to run a business, the total aration and H2 production. One might expect path-breaking trends
cost for operating such plant would be (summation of fixed cost in the reduction of global warming and air pollution, along with
and variable cost), be around $1.8 M/year. Hence, such refineries simultaneous progress in a country’s economy by trading carbon
may need to compensate for $0.6 M/year in this particular step. The credit in the global market, after successful implementation of this
economic analysis of the entire NERS process is summarized in process.
Table 9. One can easily conclude that the incorporation of methanol
production as a final step significantly increases the economic 5. Conclusions
burden on the process. The main reason behind such results is an
apparent high cost of hydrogen production (Pe rez-Fortes et al., A detailed catalytic review suggested that from widely dispersed
2016). More importantly, refineries like RIL can earn around 3434 literature, only four catalysts can filter through the selection
carbon credits per year (1 ton CO2 captured ¼ 1 carbon credit) due constraint of the proposed NERS process. The major burning issues
to capture and utilization of CO2 which is generally directly emitted of global warming and air toxification will be directly abashed via
into the atmosphere. Since the value of CO2 equivalent of CO is very the implementation of the proposed NERS process, since energy
less; we haven’t taken it into account while calculating carbon and other useful chemicals/petrochemical products are being pro-
credit. Simultaneously, a significant reducing in the use of coal is duced from carbon emissions, which are usually amalgamations of
estimated, plus the corresponding carbon emissions will also be a noxious gas (CO) and one of the major greenhouse gas (CO2). An
reduced. As observed from the data available in the previous sec- indirect effect of reduction in carbon emissions will be the reduc-
tion of CO to CO2 conversion, around 21 tons of coal will be cut tion of CO2 hold-up burden on the atmosphere and thereby
down per year per refinery, due to recovery of heat from the cor- restoring the balance in the biological ecosystem. Given that the
responding step and hence, we are assuming that the company economic barriers of CO2 separation and H2 production are trans-
demands a vehicle having a maximum payload capacity of gressed, the proposed NERS process further ensures a steady
approximately 24 tons (One of the available standard sizes of growth in the global carbon market due to an increase in global
Heavy-Load vehicles) for the same purpose. As per data available in carbon credit trading practices. Thus the article establishes a strong
the literature (Seo et al., 2016), the empty weight of such vehicle premise for an iconoclastic notion of the utilization of carbon
would be around 40 tons and the corresponding CO2 emission from emissions as a fuel, rather than discarding them as unwanted
the vehicle will be around 1600 g/km (for a gross weight of vehicle products.
of 64 tons at its full loading capacity). Further, assuming that the
distance between the coal mine and the procurement site to be Declaration of competing interest
around 100 km (actual data may vary for different refineries), on an
average two carbon credits might be earned by such refinery. None.
Simultaneously, the emission of other gases like SOx, NOx, and CO
from such vehicles will also be reduced. A significant reduction in Acknowledgment
such emissions due to transportation might be observed if this
process will be implemented by the majority of large scale in- We would like to sincerely thank Dr. Ankush V. Biradar (Senior
dustries. Hence, such refineries might earn around a total of 3436 Scientist, Inorganic Materials and Catalysis Division, CSIR-CSMCRI,
carbon credits per year, the monetary value of which may vary from Bhavnagar, Gujarat, INDIA) for his valuable suggestions while
project to project. However, as per the most recent data available amending this article.
from a public platform, the value of a carbon credit purchased
through Gold Standard certified projects for energy efficiency is Appendix A. Supplementary data
around $8.8/ton of CO2 equivalent. Since the total amount of CO2
generated by refineries like RIL is around 3436 tons/year, hence- Supplementary data to this article can be found online at
forth such refineries might earn an additional profit of around https://doi.org/10.1016/j.jclepro.2019.118838.
$30237/year. Simultaneously, such refineries might additionally
expect relief from environmental taxes, due to a significant
References
reduction in flow rates of industrial emissions due to the removal of
CO and CO2. Abdul-Kareem, H.K., Hudgins, R.R., Silveston, P.L., 1980. Forced cycling of the cata-
Moreover if this process is adopted in all the refineries across lytic oxidation of CO over a V2O5 catalystdII Temperature cycling. Chem. Eng.
Sci. 35, 2085e2088.
the country, one might expect the significant contribution of a
Acharyya, S.S., Ghosh, S., Adak, S., Sasaki, T., Bal, R., 2014. Facile synthesis of
country in trading carbon credits in the global market, and thereby CuCr2O4 spinel nanoparticles: a recyclable heterogeneous catalyst for the one
significantly affecting an economy of a country. Additionally, due to pot hydroxylation of benzene. Catal. Sci. Technol. 4, 4232e4241.
its ability to achieve a significant reduction in air pollutants, one Acharyya, S.S., Ghosh, S., Siddiqui, N., Konathala, L.N.S., Bal, R., 2015. Cetyl alcohol
mediated synthesis of CuCr2O4 spinel nanoparticles: a green catalyst for se-
can expect additional monetary support from the national gov- lective oxidation of aromatic CeH bonds with hydrogen peroxide. RSC Adv. 5,
ernment. Industries like IFFCO and other fertilizer producing 4838e4843.
Agreement, P., 2015. United Nations Framework Convention on Climate Change. 90058-X.
Paris, Fr. Fuller, M.J., Warwick, M.E., 1973. The catalytic oxidation of carbon monoxide on tin
Ammendola, P., Lisi, L., Ruoppolo, G., 2014. Partial oxidation of tar into syngas over (IV) oxide. J. Catal. 29, 441e450. https://doi.org/10.1016/0021-9517(73)90251-0.
Rh-based catalysts. Combust. Sci. Technol. 186, 563e573. https://doi.org/ GAO, M., JIANG, N., ZHAO, Y., et al., 2016. Copper-cerium oxides supported on car-
10.1080/00102202.2014.883254. bon nanomaterial for preferential oxidation of carbon monoxide. J. Rare Earths
Antony, A., Sun, M.Y., Jin-Hyo, B., You, H.B., 2018. Nano sheets, needles and grains- 34 (1), 55e60. https://doi.org/10.1016/S1002-0721(14)60577-9.
like CuO/g-Al2O3 catalysts’ performance in carbon monoxide oxidation. J. Solid Garner, W.E., 1947. 234. The reduction of oxides by hydrogen and carbon monoxide.
State Chem. 265, 431e439. https://doi.org/10.1016/j.jssc.2018.06.031. J. Chem. Soc. 1239e1244.

Arbib, Z., Ruiz, J., Alvarez-Díaz, P., Garrido-Pe rez, C., Perales, J.A., 2014. Capability of Garner, W.E., Veal, F.J., 1935. 357. The heat of adsorption of gases on ZnO and ZnO-
different microalgae species for phytoremediation processes: wastewater ter- Cr2O3 at low pressures and room temperatures. J. Chem. Soc. 1487e1495.
tiary treatment, CO2 bio-fixation and low cost biofuels production. Water Res. Gravelle, P.C., Teichner, S.J., 1969. Carbon monoxide oxidation and related reactions
49, 465e474. on a highly divided nickel oxide. In: Advances in Catalysis. Elsevier,
Bartholomew, C.H., Farrauto, R.J., 1988. Fundamentals of Industrial Catalytic Pro- pp. 167e266.
cesses, Secon Edition. Wiley Publication. https://doi.org/10.1002/ Go€kdai, D., Gürü, M., Tog rul, T., 2017. A new approach to the manufacturing of
9780471730071. elemental boron from boron oxide by carbon monoxide. Int. J. Hydrogen Energy
Bai, X., Chai, S., Liu, C., Ma, K., Cheng, Q., Tian, Y., Ding, T., Jiang, Z., Zhang, J., 42 (28), 18028e18033.
Zheng, L., Li, X., 2017. Insight on CuO-SnO2 catalysts for catalytic oxidation of Hans-Gϋnther, L., Tilman, W., 1985. The oxidation OF carbon monoxide ON poly-
CO: identification of active copper species and reaction mechanism. Chem- crystalline rhodium under knudsen conditions. Appl. Surf. Sci. 24, 251e258.
CatChem. https://doi.org/10.1002/cctc.201700460. Haruta, M., Yamada, N., Kobayashi, T., Jiji, S., 1989. Gold catalysts prepared by co-
Baida, T., Murayama, T., Nellaiappan, S., et al., 2019. Ultra-low-temperature CO precipitation for low-temperature oxidation of hydrogen and of carbon mon-
oxidation activity of octahedral site cobalt species in Co3O4 based catalysts: oxide. J. Catal. 115 (2), 301e309. https://doi.org/10.1016/0021-9517(89)90034-1.
unravelling the origin of the unique catalytic property. J. Phys. Chem. C 123 (32), Hori, C.E., Permana, H., Ng, K.Y.S., Brenner, A., More, K., Rahmoeller, K.M., Belton, D.,
19557e19571. https://doi.org/10.1021/acs.jpcc.9b04136. 1998. Thermal stability of oxygen storage properties in a mixed CeO2-ZrO2
Beshkar, F., Zinatloo-Ajabshir, S., Salavati-Niasari, M., 2015. Preparation and char- system. Appl. Catal. B Environ. 16, 105e117.
acterization of the CuCr 2 O 4 nanostructures via a new simple route. J. Mater. Hughes, M.F., Hill, G.R., 1955. Rate law and mechanism for the oxidation of carbon
Sci. Mater. Electron. 26, 5043e5051. monoxide over a vanadium oxide catalyst. J. Phys. Chem. 59, 388e391. https://
Biemelt, T., Wegner, K., Teichert, J., et al., 2016. Hopcalite nanoparticle catalysts with doi.org/10.1021/j150527a002.
high water vapour stability for catalytic oxidation of carbon monoxide. Appl. Hossain, S.T., Azeeva, E., Zhang, K., Zell, E.T., Bernard, D.T., Balaz, S., Wang, R., 2018.
Catal. B Environ. 184, 208e215. https://doi.org/10.1016/j.apcatb.2015.11.008. A comparative study of CO oxidation over Cu-O-Ce solid solutions and CuO/
Bin, F., Kang, R., Wei, X., Hao, Q., Dou, B., 2019. Self-sustained combustion of carbon CeO2 nanorods catalysts. Appl. Surf. Sci. 455 (15), 132e143. https://doi.org/
monoxide over CuCe0.75Zr0.25Od. Proc. Combust. Institue 37 (4), 5507e5515. 10.1016/j.apsusc.2018.05.101. In this issue.
https://doi.org/10.1016/j.proci.2018.05.114. Huang, X., Niu, P., Pan, H., Shang, X., 2018. Micromorphological control of porous
Brokaw, R.S., 1967. Ignition kinetics of carbon monoxide-oxygen reaction. In: Symp. LaMnO3 and LaMn0.8Fe0.2O3 and its catalytic oxidation performance for CO.
(Int.) on Comb., 11, pp. 1063e1073, 1. J. Solid State Chem. 265, 218e226. https://doi.org/10.1016/j.jssc.2018.06.002.
Cacho-Bailo, F., Matito-Martos, I., Perez-Carbajo, J., Etxeberría-Benavides, M., IEA, 18 July 2019. “Global Energy & CO2 Status Report: CO2 Emissions.” Emissions.
Karvan, O., Sebastia n, V., Calero, S., Te
llez, C., Coronas, J., 2017. On the molecular IEA. www.iea.org/geco/emissions/.
mechanisms for the H 2/CO 2 separation performance of zeolite imidazolate IQAir, 2018. 2018 World Air Quality Report, vol. 5. Region & City PM2. Ranking.
framework two-layered membranes. Chem. Sci. 8, 325e333. Jones, M.B., Donnelly, A., 2004. Carbon sequestration in temperate grassland eco-
Cao, C., Xing, L., Yang, Y., Tian, Y., Ding, T., Zhang, J., et al., 2017. Diesel soot elimi- systems and the influence of management, climate and elevated CO2. New
nation over potassium-promoted Co3O4 nanowires monolithic catalysts under Phytol. 164, 423e439.
gravitation contact mode. Appl. Catal. B Environ. 218, 32e45. Kang, R., Wei, X., Bin, F., Wang, Z., Hao, Q., Dou, B., 2018. Reaction mechanism and
Chen, Y.-I., Zheng, Z.T., Jhang, J.-W., 2018. Thermal stability of Ru-Al multilayered kinetics of CO oxidation over a CuO/Ce0. 75Zr0. 25O2-d catalyst. Appl. Catal.
thin films on inconel 617. Metals 8, 514. Gen. 565, 46e58. https://doi.org/10.1016/j.apcata.2018.07.026.
Chiang, C., Wang, A., Wan, B., Mou, C., 2005. High catalytic activity for CO oxidation Kareem, A.K., Jain, A., Silveston, P.L., Hudgins, R.R., 1980. Harmonic behaviour of the
of gold nanoparticles confined in acidic support Al-SBA-15 at low temperatures. rate of catalytic oxidation of CO under cycling conditions. Chem. Eng. Sci. 35,
J. Phys. Chem. B 109, 18042e18047. 273e282. https://doi.org/10.1016/0009-2509(80)80097-2.
Chin, S.Y., Williams, C.T., Amiridis, M.D., 2006. FTIR studies of CO adsorption on Kelley, K.K., Anderson, C.T., 1935. Contributions to the Data on Theoretical Metal-
Al2O3-and SiO2-supported Ru catalysts. J. Phys. Chem. B 110, 871e882. https:// lurgy. III. Free Energies.
doi.org/10.1021/jp053908q. Kim, H., Lee, H., Yu, A., Jeong, J.H., Lee, Y., Kim, M.H., Lee, C., Kim, Y.D., 2018. Syn-
Chiu, T.-W., Yu, B.-S., Wang, Y.-R., Chen, K.-T., Lin, Y.-T., 2011. Synthesis of nanosized thesis and catalytic activity of electro spun NiO/Co2O4 nanotubes for CO and
CuCrO2 porous powders via a self-combustion glycine nitrate process. J. Alloy. acetaldehyde oxidation. Nanotechnology 29, 175702. https://doi.org/10.1088/
Comp. 509, 2933e2935. 1361-6528/aaaf12.
Choi, S.W., Katoch, A., Zhang, J., Kim, S.S., 2014. One-pot synthesis of Au-loaded Krishnan, R., Wu, S., Chen, H., 2018. Nitrogen-doped penta-graphene as a superior
SnO2 nanofibers and their gas sensing. Sens. Actuators B 202, 38e45. catalytic activity for CO oxidation. Carbon 132, 257e262. https://doi.org/
Choi, S.H., Kang, Y.C., 2013. One-pot facile synthesis of Janus-structured SnO2-CuO 10.1016/j.carbon.2018.02.064.
composite nanorods and their application as anode in Li-ion batteries. Nano- Kulshreshtha, S.K., Gadgil, M.M., Sasikala, R., 1996. Synergistic effects during CO
scale 5, 4662e4668. oxidation over mixed oxides. Study of (Fe 2 O 3þ SnO 2) and (Mn2O3þ SnO2)
Climeworks, 2018. https://www.climeworks.com/our-products/. (Accessed 18 systems. Catal. Lett. 37, 181e185.
October 2019). Li, Y.R., Peng, H.G., Xu, X.L., Peng, Y., Wang, X., 2015. Facile preparation of meso-
Conner, W.C., Bennett, C.O., 1976. Carbon monoxide oxidation on nickel oxide. porous Cu-Sn solid solution as active catalysts for CO oxidation. RSC Adv. 5,
J. Catal. 41, 30e39. https://doi.org/10.1016/0021-9517(76)90197-4. 25755e25764. https://doi.org/10.1039/C5RA00635J.
Cost Insights, 2018. https://www.costinsights.com/. (Accessed 18 October 2019). Lin, H., Biddinger, E.J., 2017. Challenges and opportunities for carbon dioxide utili-
Deraz, Nasr-Allah M., 2003. Catalytic oxidation of carbon monoxide on non-doped zation. Energy Technol. 5, 771e772.
and zinc oxide-doped nickel-alumina catalysts. Colloids Surf., A 218 (1e3), Lou, Y., Wang, L., Zhao, Z., Zhang, Y., Lu, G., et al., 2014. Low-temperature CO
213e223. https://doi.org/10.1016/S0927-7757(02)00595-2. oxidation over Co3O4-based catalysts: significant promoting effect of Bi2O3 on
Dey, S., Ganesh, C.D., Prasad, R., Mohan, D., 2017. Effect of nitrate metal (Ce, Cu, Mn Co3O4 catalyst. Appl. Catal. B Environ. 146, 43e49.
and Co) precursors for the total oxidation of carbon monoxide. Resour. Efficient Lu, S., Guo, Y., Lin, J., Li, C., 2018. Supported copper-manganese catalyst and its
Technol. 3 (3), 293e302. https://doi.org/10.1016/j.reffit.2016.12.010. preparation method and application of low-temperature catalytic oxidation of
Dey, S., Dhal, G.C., 2019. Cerium catalysts applications in carbon monoxide oxida- carbon monoxide. Fam. Zhu. Shen. CN 107537515, A 20180105.
tions. Mat. Sci. Energy Technol. https://doi.org/10.1016/j.mset.2019.09.003. Lukiyanchuk, I., Rudnev, V.S., Serov, M.M., Krit, B.L., 2017. Effect of copper coating on
El Shobaky, G., Gravelle, P.C., Teichner, S.J., 1969. Influence of the surface structure of fibers made of aluminium alloy, titanium, and FeCrAl alloy surface morphology
a nickel oxide catalyst on the mechanism of the room-temperature oxidation of and activity in CO oxidation. Appl. Surf. Sci. 436 https://doi.org/10.1016/
carbon monoxide. J. Catal. 14, 4e22. https://doi.org/10.1016/0021-9517(69) j.apsusc.2017.11.287.
90350-9. Mall, I.D., 2006. Petrochemical Process Technology. Macmillan.
EIA, 18 July 2019. “Coal Prices and Outlook.” Coal Prices and Outlook - Energy Martin, O., Martín, A.J., Mondelli, C., Mitchell, S., Segawa, T.F., Hauert, R., Drouilly, C.,
Explained, Your Guide to Understanding Energy - Energy Information Admin- Curulla-Ferre , D., Pe
rez-Ramírez, J., 2016. Indium oxide as a superior catalyst for
istration. EIA. www.eia.gov/energyexplained/index.php?page¼coal_prices. methanol synthesis by CO2 hydrogenation. Angew. Chem. Int. Ed. 55,
Fornasiero, P., Balducci, G., Monte, R., Kaspar, J., 1996. V sergo, G. Gubitosa, A. Fer- 6261e6265.
rero, M. Graziani. J. Catal. 164, 173. Matito-Martos, I., Martin-Calvo, A., Gutierrez-Sevillano, J.J., Haranczyk, M.,
Fu, Z., Liu, L., Song, Y., Ye, Q., Cheng, S., Kang, T., Dai, H., 2017. Catalytic oxidation of Doblare, M., Parra, J.B., Ania, C.O., Calero, S., 2014. Zeolite screening for the
carbon monoxide, toluene, and ethyl acetate over the xPd/OMS-2 catalysts: separation of gas mixtures containing SO 2, CO 2 and CO. Phys. Chem. Chem.
effect of Pd loading. Front. Chem. Sci. Eng. 11 (2), 185e196. https://doi.org/ Phys. 16, 19884e19893.
10.1007/s11705-017-1631-5. Mengfei, L., Yun, D., Aiping, J., Jiqing, L., 2016. Catalyst for catalytic oxidation of
Fuller, M.J., Warwick, M.E., 1974. The catalytic oxidation of carbon monoxide on carbon monoxide and preparation method thereof. Fam. Zhua. Shenq. CN
SnO2 CuO gels. J. Catal. 34, 445e453. https://doi.org/10.1016/0021-9517(74) 106040260, A 20161026.
Mo, S., He, H., Ren, Q., Li, S., Zhang, W., Fu, M., Chen, L., Wu, J., Chen, Y., Ye, D., 2019. Toshima, N., Hara, S., 2000. Gas separation by metal complexes: membrane sepa-
Macro porous Ni foam-supported Co3O4 nanobrush and nanomace hybrid ar- rations. Encycl. Sep. Sci.
rays for high-efficiency CO oxidation. J. Environ. Sci. 75, 136e144. Trovarelli, A., 1996. Catalytic properties of ceria and CeO2-containing materials.
Mobini, S., Meshkani, F., Rezaei, M., 2017. Synthesis and characterization of nano- Catal. Rev. 38, 439e520.
crystalline copperechromium catalyst and its application in the oxidation of
Van-Dal, E.S., Bouallou, C., 2013. Design and simulation of a methanol production
carbon monoxide. Process Saf. Environ. Prot. 107, 181e189. https://doi.org/ plant from CO2 hydrogenation. J. Clean. Prod. 57, 38e45.
10.1016/j.psep.2017.02.009. Van den Berg, J., Brans-Brabant, J.H.L.M., Van Dillen, A.J., Gens, J., Lammers, M.J.J.,
Mohamed, S.K., Ibrahim, A.A., Mousa, A.A., Beitha, M.A., El-Sharkway, E.A., 1982. Catalytic oxidation of carbon monoxide over silver-vanadium bronze
Hassan, H.M.A., 2018. Facile fabrication of ordered mesoporous Bi/Ti-MCM-41 (Ag0.35V2O5). Br. Bunsenes Phys. Chem. 86 (1), 43e45.
nanocomposites for visible light-driven photocatalytic degradation of methy- Van den Berg, J., Brans-Brabant, J.H.L.M., Van Dillen, A.J., Gens, J., Lammers, M.J.J.,
lene blue and CO oxidation. Separ. Purif. Technol. 195, 174e183. https://doi.org/ 1983. The effect of oxidation of copper-vanadium bronze (Cu0.35V2O5) on its
10.1016/j.seppur.2017.12.008. activity in catalytic oxidation of carbon monoxide. Br. Bunsenes Phys. Chem.
Noei, H., Wo €ll, C., Muhler, M., Wang, Y., 2011. The interaction of carbon monoxide https://doi.org/10.1002/bbpc.19830871224.
with clean and surface-modified zinc oxide nanoparticles: a UHV-FTIRS study. Wang, X., Tian, J.S., Zheng, Y.H., Xu, X.L., Liu, W.M., Fang, X.Z., 2014. Tuning Al2O3
Appl. Catal. Gen. 391, 31e35. surface with SnO2 to prepare improved supports for Pd for CO oxidation.
Nosrati, A., Zandi, Y., Shariati, M., et al., 2018. Portland cement structure and its ChemCatChem 6 (6), 1604e1611. https://doi.org/10.1002/cctc.201402052.
major oxides and fineness. Smart Struct. Syst. 22 (4), 425e432. Wierzchowski, P.T., Zatorski, L.W., 2003. Kinetics of catalytic oxidation of carbon
Patel, F., Patel, S., 2012. LaCoO3 pervoskite catalysts for the environmental appli- monoxide and methane combustion over alumina supported Ga2O3, SnO2 or
cation of Auto motive CO oxidation. Res. J. Recent Sci. 1, 178e184. V2O5. Appl. Catal. B Environ. 44, 53e65. https://doi.org/10.1016/S0926-
rez-Fortes, M., Scho
Pe € neberger, J.C., Boulamanti, A., Tzimas, E., 2016. Methanol 3373(03)00009-2.
synthesis using captured CO2 as raw material: techno-economic and environ- Wilklow-Marnell, M., Jones, W.D., 2017. Catalytic oxidation of carbon monoxide by
mental assessment. Appl. Energy 161, 718e732. a-alumina supported 3 nm cerium dioxide nanoparticles. Mol. Catal. 439, 9e14.
Rao, C.S., 2007. Environmental Pollution Control Engineering. New Age https://doi.org/10.1016/j.mcat.2017.06.015.
International. Winter, E.R.S., 1958. The reactivity of oxide surfaces. Advances in Catalysis. Elsevier,
Reddy, B.M., Ganesh, I., Reddy, E.P., 1997. Study of dispersion and thermal stability of pp. 196e241.
V2O5/TiO2 SiO2 catalysts by XPS and other techniques. J. Phys. Chem. B 101, Wu, Y., Dong, L., Li, B., 2018. Effect of iron on physicochemical properties: enhanced
1769e1774. https://doi.org/10.1021/jp963091o. catalytic performance for novel Fe2O3 modified CuO/Ti0. 5Sn0. 5O2 in low
Reddy, E.P., Varma, R.S., 2004. Preparation, characterization, and activity of Al2O3- temperature CO oxidation. Mol. Catal. 456, 65e74. https://doi.org/10.1016/
supported V2O5 catalysts. J. Catal. 221, 93e101. j.mcat.2018.07.005.
Rezaei, P., Rezaei, M., Meshkani, F., 2018. Low Temperature CO Oxidation over Wu, Z., Li, M., Overbury, S.H., 2012. On the structure dependence of CO oxidation
Mesoporous Iron and Copper Mixed Oxides Nanopowders Synthesized by a over CeO2 nanocrystals with well-defined surface planes. J. Catal. 285, 61e73.
Simple One-Pot State Method. Process Safety and Environment Protection. WV Coal, 18 July 2019. “West Virginia Coal Association.” West Virginia Coal Associ-
https://doi.org/10.1016/j.psep.2018.08.024. ation, WV Coal. www.wvcoal.com/.
Robinson, R., Caracciolo, D., Shan, S., Wang, S., Luo, J., Zhong, C., 2018. In situ FTIR Xie, Y., Zhang, J., Qiu, J., Tong, X., Fu, J., Yang, G., Yan, H., Tang, Y., 1997. Zeolites
determination of surface adsorption species over bimetallic alloy catalysts in modified by CuCl for separating CO from gas mixtures containing CO 2.
catalytic oxidation of carbon monoxide. In: Abstracts of Papers, 256th ACS Adsorption 3, 27e32.
National Meeting & Exposition, Boston, MA, United States, CATL-339. Xie, X., Li, Y., Liu, Z., Haruta, M., Shen, W., 2009. Low-temperature oxidation of CO
Royer, S., Duprez, D., 2011. Catalytic oxidation of carbon monoxide over transition catalyzed by Co3O4 nanorods. Nature 458, 746e749.
metal oxides. ChemCatChem 3 (1), 24e65. Yang, J., Guo, J., Wang, Y., Wang, T., Gu, J., Peng, L., Xue, N., Zhu, Y., Guo, X., Ding, W.,
Sasikala, R., Gupta, N.M., Kulshreshtha, S.K., 2001. Temperature-programmed 2018. Reduction-oxidation pretreatment enhanced catalytic performance of
reduction and CO oxidation studies over CeeSn mixed oxides. Catal. Lett. 71, Co3O4/Al2O3 over CO oxidation. Appl. Surf. Sci. 453, 330e335. https://doi.org/
69e73. https://doi.org/10.1023/A:1016656408728. 10.1016/j.apsusc.2018.05.103.
Schiller, F., Iiyn, M., Perez-Dieste, Escudero C., Huck-Iriart, C., del Arbol, N.R., Yi, Y., Zhang, P., Qin, Z., Yu, C., Li, W., Qin, Q., Li, B., Fan, M., Liang, X., Dong, L., 2018.
Hagman, B., Merte, L.R., Bertram, F., Shipilin, M., Blomerg, S., Gustafson, J., Low temperature CO oxidation catalysed by flower-like Ni-Co-O: how physi-
Lundgren, E., Ortega, J.E., 2018. Catalytic oxidation of carbon monoxide on a cochemical properties influence catalytic performance. RSC Adv. 8, 7110e7122.
curved Pd crystal: spatial variation of active and poisoning phases in stationary https://doi.org/10.1039/C7RA12635B.
conditions. J. Am. Chem. Soc. 140 (47), 16245e16252. Yi, Y., Liu, H., Chu, B., Qin, Z., Dong, L., He, H., Tang, C., Fan, M., Bin, L., 2019. Catalytic
Schlager, S., Dibenedetto, A., Aresta, M., Apaydin, D.H., Dumitru, L.M., removal NO by CO over LaNi0.5M0.5O3 (M ¼ Co, Mn, Cu) pervoskite oxide cat-
Neugebauer, H., Sariciftci, N.S., 2017. Biocatalytic and bioelectrocatalytic ap- alysts: tune surface chemical composition to improve N2 selectivity. Chem. Eng.
proaches for the reduction of carbon dioxide using enzymes. Energy Technol. 5, J. 369, 511e521. https://doi.org/10.1016/j.cej.2019.03.066.
812e821. Yiquan, Y., Guoxing, C., Hongqiao, L., Jianqiang, F., Qiaoling, Li, 2012. Catalyst for
Seo, J., Park, J., Oh, Y., Park, S., 2016. Estimation of total transport CO2 emissions catalytic oxidation of carbon monoxide in catalytic smoke in cigarette, and
generated by medium-and heavy-duty vehicles (MHDVS) in a sector of Korea. preparation and application thereof. Fam. Zhua. Shenq. CN 102553601, A
Energies 9, 638. 20120711.
Singhania, A., Gupta, S.M., 2018. Nickel nanocatalyst ex-solution from ceria-nickel Yoshida, T., Murayama, T., Sakaguchi, N., Okumara, M., Ishida, T., Haruta, M., 2017.
oxide solid solution for low temperature CO oxidation. J. Nanosci. Nano- Carbon monoxide oxidation by polyoxometalate-supported gold nano-
technol. 18, 4614e4620. https://doi.org/10.1166/jnn.2018.15342. particulate catalysts: activity, stability, and temperature-dependent activation
Smith, J.M., Van Ness, H.C., Abbott, M.M., 2005. Introduction to Chemical Engi- properties. Angew. Chem. Int. 130 https://doi.org/10.1002/anie.201710424.
neering Thermodynamics, seventh ed. McGraw-Hill. Zhang, R., Lu, K., Zong, L., Tong, S., Wang, X., Zhou, J., Lu, Z., Feng, G., 2017. Control
€ gl, R., 2002. Thermal decomposition of divanadium pentoxide V 2 O 5:
Su, D.S., Schlo synthesis of CeO2 nanomaterials supported gold for catalytic oxidation of car-
towards a nanocrystalline V 2 O 3 phase. Catal. Lett. 83, 115e119. bon monoxide. Mol. Cat. 422, 173e180.
Sun, W., Lin, L., Peng, X., Smit, B., 2014. Computational screening of porous metal- Zhang, T.S., Kong, L.B., Song, X.C., Du, Z.H., Xu, W.Q., Li, S., 2015. Densification
organic frameworks and zeolites for the removal of SO2 and NOx from flue behaviour and sintering mechanisms of Cu- or Co-doped SnO2: a comparative
gases. AIChE J. 60, 2314e2323. study. Acta Mater. 62, 81e88.
Tang, C., Li, J., Yao, X., Sun, J., Cao, Y., Zhang, L., Gao, F., Deng, Y., Dong, L., 2015. Zheng, X.J., Wei, Y.J., Wei, L.F., Xie, B., Wei, M.B., 2010. Int. J. Hydrogen Energy 35,
Mesoporous NiO-CeO2 catalysts for CO oxidation: nickel content effect and 11709e11718.
mechanism aspect. Appl. Catal. Gen. 494, 77e86. https://doi.org/10.1016/ Zhou, J., Yao, W., Liu, Y., Zhang, H., Zou, J., He, D., 2013. Rare earth oxide-modified Ɣ-
j.apcata.2015.01.037. alumina supported bimetalluc catalyst for normal -temperature catalytic
Tatarchuk, T., 2014. Catalytic oxidation of carbon monoxide on lithium-zinc ferrites oxidation of carbon monoxide and its preparation method. Fam. Zhua. Shenq.
with a spinel structure. Ekolo gia Tech. 22 (1), 70e75. CN 102989482, A 20130327.
The engineering toolbox, 2018. https://www.engineeringtoolbox.com/fuels-higher- Zhou, Y., Jun, Y., Dongsen, M., Mao, H., 2018. A highly moisture-resistant binary M 3
calorific-values-d_169.html. (Accessed 18 October 2019). Co 16 O x composite oxide catalysts wrapped by polymer nanofilm for effective
Toghroli, A., Shariati, M., Sajedi, F., et al., 2018. A review on pavement porous low temperature CO oxidation. Appl. Catal. Gen. 559 https://doi.org/10.1016/
concrete using recycled waste materials. Smart Struct. Syst. 22 (4), 433e440. j.apcata.2018.04.010.
https://doi.org/10.12989/sss.2018.22.4.433. Zhu, G., Qu, Z., Zhuang, G., Xie, Q., Meng, Q., Wang, J., 2011. CO oxidation by lattice
Toghroli, A., Shariati, M., Rehan, M., Ibrahim, Z., 2017. Investigation on composite oxygen on V2O5 nanotubes. J. Phys. Chem. C 115, 14806e14811. https://doi.org/
polymer and silica fume rubber aggregate pervious concrete. In: Fifth Inter- 10.1021/jp2026175.
national Conference on Advances in Civil, Structural and Mechanical Engi- Zhu, Q., 2019. Developments on CO2-utilization technologies. Clear Energy 3 (2),
neering. https://doi.org/10.15224/978-1-63248-132-0-56. 85e100.

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Journal of Cleaner Production 245 (2020) 118838

Contents lists available at ScienceDirect

Journal of Cleaner Production

Low temperature oxidation of carbon monoxide for heat recuperation:

Abbreviations f Fugacity factor

3.6.1. Undoped ZnO catalyst . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.11.2. Doped CeO2 catalyst for high thermal stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

1. Introduction economically extracting the indirect energy from CO by its oxida-

Fig. 4. Summary of widely explored catalysts for oxidation of CO.

(i) Rh/Al2O3 catalysts. Therefore, it won’t be a misnomer to group such vana-

Catalyst Process Conditions* Comments* & Future scopes**

Catalyst Process Conditions* Comments* & Future scopes**

Doped catalysts for higher thermal stability

Catalyst Process Conditions* Comments* & Future scopes**

Doped catalysts for higher thermal stability

Catalyst Process Conditions* Comments* & Future scopes**

Doped catalysts for high catalytic activity

Catalyst Process Conditions* Comments* & Future scopes**

Doped catalysts for high catalytic activity

Catalyst Process Conditions* Comments* & Future scopes**

lattice structure on its activity, and (III) reaction mechanisms for

Doped catalysts for high catalytic activity

Catalyst Process Conditions* Comments* & Future scopes**

Doped catalysts for high catalytic activity

Catalyst Process Conditions* Comments* & Future scopes**

Fig. 6. Oxidation of CO in presence of NO on LaNi0.5Cu0.5O3 pervoskites (Yi et al., 2019).

3.8. Copper-chromites CeO2eSnO2 þ CO 4 CeO2eSnO2(CO) R.10

unidentiﬁed since accurate knowledge of the rate-determining step

3.10. Composites of transition metal oxides

3.10.1. Doped catalysts of transition metal composites for high

Solid solution/compound formation due to the interaction be-

Based on various studies available in the literature, the role of

SO2 2256 11.3

application. ﬁlter made up of porous granulates which are modiﬁed with

SO2 75 0.1 0.1

4.3. Conversion of CO to CO2

Upon complete separation of SO2 and NOx, pure CO stream can

Table 8 1. Compression of Feed gases up to reactor feed pressure

The second reaction is undesired one and is curbed by using a

1 Separation of CO2 48 M 2.06 M e

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