Nothing Special   »   [go: up one dir, main page]

WO2022008942A1 - Ni-silica-based catalysts with highly dispersed nickel particles - Google Patents

Ni-silica-based catalysts with highly dispersed nickel particles Download PDF

Info

Publication number
WO2022008942A1
WO2022008942A1 PCT/IB2020/000597 IB2020000597W WO2022008942A1 WO 2022008942 A1 WO2022008942 A1 WO 2022008942A1 IB 2020000597 W IB2020000597 W IB 2020000597W WO 2022008942 A1 WO2022008942 A1 WO 2022008942A1
Authority
WO
WIPO (PCT)
Prior art keywords
nickel
silicon
catalyst
nsi0
catalyst according
Prior art date
Application number
PCT/IB2020/000597
Other languages
French (fr)
Inventor
Oscar DAOURA
Maya BOUTROS
Franck Launay
Nissrine EL HASSAN
Pascale Massiani
Original Assignee
Sorbonne Universite
Centre National De La Recherche Scientifique
Université Libanaise
University Of Balamand
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sorbonne Universite, Centre National De La Recherche Scientifique, Université Libanaise, University Of Balamand filed Critical Sorbonne Universite
Priority to PCT/IB2020/000597 priority Critical patent/WO2022008942A1/en
Priority to PCT/EP2021/068776 priority patent/WO2022008573A2/en
Publication of WO2022008942A1 publication Critical patent/WO2022008942A1/en

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
    • B01J21/08—Silica
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/74—Iron group metals
    • B01J23/755—Nickel
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/20—Catalysts, in general, characterised by their form or physical properties characterised by their non-solid state
    • B01J35/23—Catalysts, in general, characterised by their form or physical properties characterised by their non-solid state in a colloidal state
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/391—Physical properties of the active metal ingredient
    • B01J35/393—Metal or metal oxide crystallite size
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/391—Physical properties of the active metal ingredient
    • B01J35/394—Metal dispersion value, e.g. percentage or fraction
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J35/61—Surface area
    • B01J35/615—100-500 m2/g
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J35/61—Surface area
    • B01J35/617—500-1000 m2/g
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J35/64—Pore diameter
    • B01J35/647—2-50 nm
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0201—Impregnation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/16—Reducing
    • B01J37/18—Reducing with gases containing free hydrogen
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B3/00—Hydrogen; Gaseous mixtures containing hydrogen; Separation of hydrogen from mixtures containing it; Purification of hydrogen
    • C01B3/02—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen
    • C01B3/32—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air
    • C01B3/34—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents
    • C01B3/38—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents using catalysts
    • C01B3/40—Production of hydrogen or of gaseous mixtures containing a substantial proportion of hydrogen by reaction of gaseous or liquid organic compounds with gasifying agents, e.g. water, carbon dioxide, air by reaction of hydrocarbons with gasifying agents using catalysts characterised by the catalyst
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/02—Processes for making hydrogen or synthesis gas
    • C01B2203/0205—Processes for making hydrogen or synthesis gas containing a reforming step
    • C01B2203/0227—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step
    • C01B2203/0238—Processes for making hydrogen or synthesis gas containing a reforming step containing a catalytic reforming step the reforming step being a carbon dioxide reforming step
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B2203/00—Integrated processes for the production of hydrogen or synthesis gas
    • C01B2203/10—Catalysts for performing the hydrogen forming reactions
    • C01B2203/1041—Composition of the catalyst
    • C01B2203/1047—Group VIII metal catalysts
    • C01B2203/1052—Nickel or cobalt catalysts
    • C01B2203/1058—Nickel catalysts
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/141—Feedstock
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts

Definitions

  • Ni-silica-based catalysts with highly dispersed nickel particles Ni-silica-based catalysts with highly dispersed nickel particles
  • the present invention relates to catalysts comprising nickel (Ni) and silica (Si), and demonstrating good abilities in the dry reforming of methane reaction (DRM).
  • the DRM converts two major greenhouse gases, CFU and CO2, into a useful chemical feedstock: a mixture of H2 and CO “syngas” with an H2/CO molar ratio equal to the unity adapted for Fischer-Tropsch procedure, as reported by B. Abdullah et al. in J. of Clean. Prod. 162 (2017) 170-185.
  • Different strategies and siliceous supports have been developed and used in order to improve the nickel dispersion and interaction with the support, those features being particularly important in order to protect the Ni nanoparticles from sintering and to avoid side reactions; such side reactions are exemplified in different publications such as in the article of L. Espinosa- Alonso etal. published in J.Am. Chem. Soc. 131 (2009), 131, 16932-16938.
  • Nickel-based catalysts usually suffer from rapid deactivation, due to partial metal oxidation as described by S. M. Kim et al. in J. Am. Chem. Soc. 139 (2017) 1937-1949 or K. Nagaoka et al. in Appl. Catal. A 268 (2004) 151- 158; particle sintering as described by Z. L. Zhang et al. in J. Catal. 158 (1996) 51-63 or L. Xu et al. in ACS Catal.
  • Ni(N03) 2 .xH 2 0 nickel nitrate
  • Ni(N03) 2 .xH 2 0 nickel nitrate
  • one-pot preparation methods have already been investigated in order to generate highly stable silica-based catalysts as described by O. Daoura et al. in Int. J. Hydrogen. Energ. 43 (2016) 17205-17215.
  • siliceous support prepared in acidic medium such as mesoporous SBA-15, make the one-pot preparation difficult due to the amphoteric properties of silica surface.
  • Si-OH groups transform into Si-OH2 + and the resulting surface charge does not favor interactions with the Ni(ll) aqua complexes.
  • MCF mesocellular silica foam
  • Daoura et al. report the preparation of Ni catalyst containing MCF in J. CO2 Util. 24 (2016) 112-119.
  • the classical preparation of those Ni/MCF catalysts requires long steps - at least two days - of hydrothermal treatment rendering thus the synthesis of DRM catalysts difficult.
  • organic porogen molecules, such as swelling and amphiphilic agents are required; and taking into account those agents have to be removed afterward, usually by calcination, thus such a process from the prior art is not suitable for a high-scale catalyst synthesis under a green pathway.
  • an important parameter for the catalyst efficiency is the amount of metal and in particular the Ni content, and the dispersion (fraction of Ni atoms available for catalysis) has to be kept as high as possible, as mentioned above.
  • Many Ni catalysts have been developed, but it is noteworthy that improving the Ni content usually causes a drastic lowering of the dispersion: L. Qian et al. report the preparation of a Ni catalyst for DRM with a Ni wt% (Mass Fraction) of 0.5 having a dispersion rate of 40 in Microp. Mesop. Mater. 243 (2017) 301-310 ; while C. Wang et al.
  • the main aim of the present invention is to provide a nickel containing DRM catalyst easily obtainable with a high Ni content and good dispersions and demonstrating the same or even better activity toward DRM, compared to the nickel catalysts from the prior art.
  • the present invention concerns a nickel-silicon catalyst, wherein the nickel is present in an elemental weight percent (wt%) of 1 to 7.5% considering the total weight of the catalyst, said nickel-silicon catalyst comprising a silicon oxide support bearing the nickel nanoparticles; and wherein the dispersion rate of the catalyst being more than at least 15%.
  • the dispersion rate is calculated using the Fte chemisorption method.
  • the dispersion refers here to the molar percentage of surface Ni atoms compared to the total number of Ni atoms in the sample: ⁇ _ Qads _
  • Nanoparticles of Ni in the context of the invention are objects with sizes below 100 nm, preferably below 10 nm, ideally in the range of 2 to 5 nm. Bigger particles are detrimental to catalysts activity per gram of metal and can be responsible of side-reactions. The sizes were established by using direct observations by Transmission Electron Microscopy as well indirect evaluations using Fh chemisorption measurements.
  • the dispersion rate of the catalyst being more than at least 18%.
  • the dispersion rate of the catalyst being more than at least [0011]
  • the nickel is present in an elemental weight percent of 1.5 to 6.5%.
  • the nickel is present in an elemental weight percent of 2 to 6% and even 2.5 to 5.5%.
  • the silicon oxide support is non-porous.
  • the inventors have noticed, in a completely unexpected manner, that using a non-porous support gives rise to higher nickel dispersion that leads to active and stable catalysts.
  • the textural properties were determined using N2 adsorption- desorption method. Thus, before porosity measurements the samples were dried under vacuum for 2 hours at 250 °C. Then, specific surface areas were determined using BET equation, and Pore diameters and volumes were determined using BJH model according to the description provided by E. P. Barrett, and al. in the article: "The determination of pore volume and area distributions in porous substances. 1. Computations from nitrogen isotherms" Journal of the American Chemical Society, (1951), vol 73(1), pages 373-380.
  • the silicon oxide support comprises Nickel (Ni) phyllosilicate.
  • Ni phyllosilicates as precursors gives rise to excellent activity and stability.
  • the catalysts developed by the inventors exhibit excellent particles dispersion compared to other materials comprising phyllosilicate described in the litterature; see for example the article published by Z. Li et al. in Catai. Sci. Technoi. 8 (2016) 3363-3371, for which the dispersion rate does not exceed 3%.
  • Phyllosilicates are an important group of minerals constituted of tetrahedral and octahedral sheets.
  • tetrahedral sheet consists of Si 4+ , bonded to 4 oxygen atoms and the octahedron consists of Ni 2+ , coordinated with six anions, which can be O 2 ⁇ or OH-.
  • the formation of phyllosilicates needs the combination of three factors, i.e. a metal precursor, a silica source and a basic environment. Superficial silica is partially dissolved due to the alkaline environment, hence generating soluble silicate anions.
  • silicate anions then react with Ni cations, and hydroxide anions in the solution to form the phyllosilicate structure that is further deposited on the remaining silica support as described in Catal. Today2 > 3Q (2020) 3-23 and J. C0 2 Util. 18 (2017) 345-352, by Z. Bian et al.
  • the nickel-silicon catalyst according to the invention does not comprise any cobalt(Co) atom. Co atoms makes the catalyst vulnerable to oxidation leading to deactivation.
  • the nickel-silicon catalyst according to the invention does not comprise any element selected in the group of lanthanide (for example La, Ce) and actinide, and does not contain indium (In), thallium (Tl), tin (Sn) or lead (Pb).
  • lanthanide for example La, Ce
  • actinide does not contain indium (In), thallium (Tl), tin (Sn) or lead (Pb).
  • a catalyst free of these elements is safer to use considering the toxicity of those elements.
  • the particle size is below 6 nm, preferably below 5 and even below 4 nm.
  • the inventors have demonstrated that using NH3 during preparation of the catalysts led to the improvement of the dispersion. This could be reflected by higher accessible nickel surface area due to smaller particle sizes.
  • the particle sizes were measured using Transmission Electron Microscopy (TEM). TEM analyses were performed on a JEOL® 1011 (LaB) or JEOL® 2010 (LaB) microscope operating at 200 kV. The sample powder was ultrasonicated in ethanol and 2 drops of the resulting suspension were deposited on a copper grid coated with a porous carbon film. Observations were made once ethanol was evaporated at room temperature.
  • TEM Transmission Electron Microscopy
  • the present invention concerns also the process for the preparation of a metal(M)-silicon(Si) catalyst for the DRM comprising the following steps:
  • 1- siliceous support (Si02) n is suspended in water (preferably distillated water) ;
  • 2- M(N03)2 is added into the suspension prepared according to step 1;
  • step 2- the mixture obtained in step 2- is allowed under stirring during at least 2 hours at a temperature maintained between rt. (room temperature is supposed to be 20°C) and 60°C;
  • the material obtained at step 4- is calcinated at least 2 hours at 550°C.
  • the metal used in the process disclosed in the present invention is nickel.
  • step 1- comprises the addition of at least 2 mL of aqueous Nhb catalyst prepared with Nhb proved to be more active and stable.
  • the reaction time does not exceed 6 hours, or even 4 hours, at 1 bar.
  • said siliceous support used is selected between mesoporous silica material and non-porous silica material.
  • a mesoporous material is a material containing pores with diameters between 2 and 50 nm, according to lUPAC nomenclature.
  • lUPAC defines microporous material as a material having pores smaller than 2 nm in diameter and macroporous material as a material having pores larger than 50 nm in diameter.
  • the present invention concerns also any of the catalyst presented previously according to the present invention that are obtainable by the process presented above in the frame of said invention.
  • A- Textural properties were determined from N2 adsorption-desorption isotherms recorded on a Belsorp®-max (from BEL JAPANTM) or ASAPTM 2020 (from Micromeritics®) apparatus. Before measurements, the samples were degassed under vacuum for 2 h at 250°C on Belprepll-vac unit or ASAP 2020 (Micromeritics). Specific surface areas were obtained using the BET equation. Pore diameters and specific pore volumes were determined using the BJH model (E. P. Barrett, and al. Journal of the American Chemical Society, (1951), vol 73(1), pages 373-380.). It must be noted that the textural properties were calculated taking into account the siliceous support weight only (without Nickel).
  • TGA Thermogravimetric analyses
  • E- Temperature-Programmed Reduction carried out on an AutoChemTM 2910 or a Micromeritics® 2920 apparatus equipped with a thermal conductivity detector (TCD), was used in order to study the nickel reducibility of calcined materials.
  • the samples 80 mg were heated on quartz wool in a U-shaped quartz tube from rt. to 900°C at a rate of 10°C min- 1 using a 5 vol% hh/Ar gaseous mixture (25 mL.min- 1 ).
  • An isopropanol- liquid N2 mixture AutoChemTM 2910
  • an ice and salt bath was used before the TCD detector to trap the water molecules formed during NiO reduction.
  • the nickel loading was deduced from the amount of H2 consumed during the TPR experiment after controlling that the Ni loading of a reference material was found to be coherent with that determined by inductively-coupled plasma optical emission spectrometry (ICP-OES (Crealins-Villeurbanne)).
  • ICP-OES inductively-coupled plasma optical emission spectrometry
  • the AutoChem and Micrometric apparatus were also used to perform high-temperature H2 reductions mimicking the in situ reduction (detailed later) carried out as a pretreatment step prior to the catalytic test.
  • TEM F- Transmission Electron Microscopy
  • TEM transmission electron microscopy
  • HRTEM images were taken on a JEOL® JEM-2010 UHR operating at 200 kV, equipped with an energy dispersive X-ray (EDX) detector. Materials were analyzed after ultramicrotomy. A few mg of powder were deposited in the bottom of a Beem capsule. Some embedding resin (AGARTM 100) was added and polymerized for 48 h at 60°C. The polymerized blocks were then cut into ultrathin sections (about 70 nm thick) using a diamond knife of a Leica® microtome (ULTRACUT UCT) and deposited on carbon-coated copper grids.
  • AGARTM 100 embedding resin
  • STEM scanning transmission electron microscope
  • HAADF High-angle annular dark-field imaging
  • EDX/mapping was also performed on a JEOL® 2020 microscope on ultra- thin sections of selected samples.
  • G- H2 Chemisorption experiments were performed on a BELSORB-maxTM equipment from BEL JAPANTM. The samples (about 200 mg) were reduced in situ under a flow of H2 (50 mL min- 1 ) at 650°C for 2 h using a ramp of 10°C min- 1 . The sample was then outgassed at 620°C for 2 h under vacuum (about 5.10 1 Pa). A first, H2 chemisorption measurement was performed at 25°C, the pressure at equilibrium being recorded when the pressure variation was below 0.02% per minute. The sample was then outgassed for 2 h at 25°C before a second H2 chemisorption was performed under the conditions described for the first H2 chemisorption.
  • Nickel particle size estimations are based on truncated octahedron geometry, assuming complete reduction, semi spherical particles and a H/Ni adsorption stoichiometry factor of 1.
  • the experimental data were fitted with a Langmuir adsorption equation (Equation 1) and the amount of surface nickel was calculated from the quantity adsorbed at saturation ( Q max in the model).
  • the dispersion refers here to as the molar percentage of surface Ni atoms compared to the total number of Ni atoms in the sample.
  • the sample compartment of the cell was filled with the powder (approximately 30 mg), which was heated in situ under an Ar flow (20 cm 3 min- 1 ) using the following program:
  • I- 29 Si MAS NMR spectra were recorded at 79.5 MFIz with a Briiker® Avance 500 spectrometer and 7 mm (external diameter) zirconia rotors at 6 kHz spinning speed. Chemical shifts of silicon were measured by reference to tetramethylsilane (TMS). 29 Si MAS NMR spectra were obtained with 3.5 ps excitation pulse duration and 10 s recycle delay.
  • the different catalysts were tested using a PID ENG&TECHTM Microactivity Effi Reactor (from Micromeritics®).
  • the solids were loaded on a plug of quartz wool and treated in-situ ai 650 °C for 2 h (10 °C.min- 1 ) in a 5 vol.% H2/Arflow (30 ml_ min- 1 ) in order to achieve a complete reduction of NiO into metallic nickel.
  • the temperature was decreased to 200°C and the dry reforming of methane reaction was started under atmospheric pressure, using a CH 4 /C0 2 /Ar (5/5/90) reacting mixture and at a total Gas Hour Space Velocity (GHSV) of 144 (50 mg of catalyst and 120 ml_ min- 1 total flow) or 960 L g- 1 lv 1 (10 mg of catalyst diluted with 90 mg of fumed silica (Aldrich 381276) and 160 ml_ min- 1 total flow of reactants mixture).
  • GHSV Gas Hour Space Velocity
  • the activity of the catalyst was measured by increasing the reactor temperature from 200 up to 650°C (using a rate of 5°C min- 1 ). The temperature was then maintained at 650°C for 12 h for stability measurements.
  • the gaseous products were analyzed online by a micro-GC (Agilent 490) equipped with Plot-U and Molecular sieves channels and TCD detector. The conversions of methane and carbon dioxide were calculated according to Equations 2 and 3, respectively, and the F /CO ratios were estimated using Equation 4:
  • the silica supports used were commercially available, such as SBA-15 (Sigma-Aldrich® CAS number: 7631-86-9 with 4 nm as pore size), Aerosil® 380 (nSi0 2 ) from Evonic®, or were synthesized (pSiC ⁇ ) as shown below.
  • the later was prepared by using a mixture of cetyltrimethylammonium bromide (CTABr) and Pluronic (P123) as surfactants.
  • CTABr cetyltrimethylammonium bromide
  • Pluronic Pluronic
  • the mixture of CTABr and P123 with an appropriate ratio leads to a porous material with high specific surface area, 4 nm as pore size and a higher wall thickness than SBA-15 according to Microp. Mesop. Mater.
  • TMOS tetramethylorthosilicate
  • Ni-based catalysts were prepared, a first one by the impregnation of commercially available SBA-15 by two solvents, three by the impregnation of nSiC>2 with or without NH3 and two starting from pSi0 2 .
  • Table 1 summarizes the preparation methods of the solids.
  • Table 1 Description of siliceous supports and the Ni/silica materials
  • Ni/SBA-15-TS sample was prepared by the “Two-Solvents” (TS) method. To do so, 1 g of a commercial SBA-15 was suspended in 35 ml_ of cyclohexane, then a volume of water equal to the silica pore volume (as previously determined by N2 physisorption) and containing the appropriate amount of nickel precursor (0.25 g of Ni(N03) 2 .6H 2 0 for 5 wt.% Ni) was added dropwise. The solid was dried one day at room temperature, then overnight at 60°C, and it was finally calcined at 550°C for 5 h (heating rate 1°C min- 1 ).
  • TS Tewo-Solvents
  • Ni5%/pSi0 2 -NH3-N and Ni5%/pSi0 2 -NH3-C The support PS1O2 prepared according to procedure described in the above 11.1 section, was impregnated by nickel nitrate in presence of NH3 before (leading to Ni5%/pSi0 2 -NH 3 -N) and after (leading to Ni5%/pSi0 2 -NH 3 -C) removal of surfactants from the porosity.
  • Ni5%/nSi0 2 it was prepared using a wet impregnation method. To do so, 1 g of Aerosil® 380 was suspended in 30 ml_ of water with 0.25 g of Ni(N03) 2 .6H 2 0 under vigorous stirring for 2 h. Then, the mixture was dried at 60°C and finally calcined 2 h at 550°C (heating rate 1°C min- 1 ).
  • Figure 1 displays the nitrogen adsorption-desorption isotherms of the solids and, Table 2, their textural parameters.
  • Table 2 Physico-chemical properties of calcined Ni-silica based materials and of their respective parents.
  • Nis % /SBA-15-TS (a), Nis % /pSi0 2 - Nhb-N (b), and Ni5 % /pSi0 2 -NH3-C (c) as well as their corresponding supports pSi0 2 (g) and SBA-15 (h) (Fig. 1 A) are characterized by type IV isotherms in agreement with those of mesoporous materials described in C. R. Chimie, 21 (2016) 514-522, by M. Boutros et al.
  • Ni5 % /pSi0 2 -NH3-C (c) showed a decrease in the pore volume which is not the case for Ni5 % /pSi0 2 -NH3-N (b) due to the presence of the surfactant inside the porosity of PS1O2-N during impregnation.
  • both Ni5 % /pSi0 2 -NH3-C and N exhibited around 20% decrease of the specific surface area.
  • Such modification may be related either to the prolonged contact of the calcined siliceous support with NH3 (which could deteriorate the support) and/or to the double calcination of Nis % /pSi0 2 -NFl3-C (before and after impregnation).
  • the presence of hysteresis loop for such solids can be related to inter-granular porosity, which also explains the high N2 volume adsorbed (BJH) especially in the case of the support nSi02.
  • Nis%/nSi02 (d), Nis%/nSi02-NFl3 (e) and Ni3.5%/nSi02-NFl3 (f) are characterized by a decrease of the adsorbed N2 volume.
  • the specific surface area remained more or less unchanged ( c.a . 300 m 2 g- 1 ) for the whole series. It is noteworthy that all of the non-porous solids showed some microporosity that could be detected from their isotherms at very low P/Po.
  • Figure 2 XRD diffraction patterns of calcined (A) and reduced (B) a: Nis%/SBA-15-TS, b: Ni 5% /pSi0 2 -NH 3 -N, c: Ni 5% /pSi0 2 -NH 3 -C, d: Ni 5% /nSi0 2 , e: Ni 5% /nSi0 2 -NH 3 and f: Ni 3.5% /nSi0 2 -NH 3 .
  • Table 3 NiO and Ni° particles size and dispersion estimated from different techniques.
  • FIG 4 FI 2 -TPR profiles of calcined a: Nis % /SBA-15-TS, b: Nis % /pSi0 2 - NHs-N, C: Ni 5% /pSi0 2 -NH 3 -C, d: Ni 5% /nSi0 2 , e: Ni 5% /nSi0 2 -NFl3 and f: Ni3 .5% /nSi0 2 -NH3 recorded with a H 2 5 Vol.%/Ar flow of 30 ml_ min- 1 and a heating rate of 10°C min- 1 .
  • Ni 2p3 /2 peak assigned to NiO for both Nis % /nSi0 2 (d) and Ni5 % /SBA-15-TS (a) could be deconvoluted into two different peaks. Due to their binding energy, those peaks could be attributed to nickel in strong (856 eV) or weak (854.7 eV) interaction with the support (to our knowledge, binding energy of Ni 2p3 /2 of bulk NiO is 853.6-854.4 eV).
  • XPS also showed one peak at higher binding energy (approximately 857 eV) for Nis % /pSi0 2 - NHs-N (b), Ni 3.5% /nSi0 2 -NH 3 (f) and Ni 5% /nSi0 2 -NFl3 (e).
  • Figure 5 TEM images of calcined microtomed A: Ni5 % /pSi0 2 -NH3-N, B: Nis /o /SBA-15-TS, C: Ni 5% /nSi0 2 and D, D’: Ni 5% /nSi0 2 -NH 3 .
  • Figure 6 TEM images of reduced microtomed; a: Nis % /SBA-15-TS, b: Ni 5% /pSi0 2 -NH 3 -N, c: Ni 5% /pSi0 2 -NH 3 -C, d: Ni 5% /nSi0 2 , e: Ni 5% /nSi0 2 -NH 3 and f: Ni3.5%/nSi0 2 -NH3.
  • Figure 7 A: TEM-MAPPING and B: TEM-EDX results for microtomed Ni 5% /pSi0 2 -NH 3 -N.
  • Ni dispersion and its accessibility were estimated from H2 chemisorption measurements (table 3).
  • the determination of Ni dispersion was estimated on the basis of the first Fb isotherm (including reversibly and irreversibly chemisorbed hydrogen) as recommended by Bartolomew C.H. in Catai Lett. 1 (1990) 27-51.
  • Ni3.5%/nSi02-Nhb sample was characterized by the highest dispersion value ( c.a .42%) which corresponds to the smallest nanoparticles (2.4 nm).
  • Ni5 % /nSi0 2 -NH3 showed also a good nickel dispersion (28%) with nickel particle sizes of 3.6 nm.
  • Ni5 % /SBA-15-TS where the nickel was incorporated into the porosity, Ni5 % /pSi0 2 -Nhb-N (Table 3) exhibited better dispersion (19.6% vs. 16%) and smaller particles (5.1 nm vs. 6.2 nm).
  • FT-IR spectra of the calcined samples collected at 120°C are shown in Fig. 8A. All of them were characterized by an absorption band assigned to isolated silanol groups at 3733 cm- 1 [29] in the O-H stretching region.
  • FIG. 8 A and B: DRIFT and C: 29 Si solid state (HPDEC) NMR spectra of calcined d: Ni 5% /nSi0 2 , e: Ni 5% /nSi02-NH 3 , f: Ni 3.5% /nSi0 2 -NH 3 , and i: nSi0 2 .
  • IR spectra in Fig. 8 B were collected using samples diluted in diamond powder. NMR spectra were normalized on Q4.
  • Nickel-based solids prepared in presence of Nhb showed an additional band at 3621 cm- 1 that would be due to the vibration of the OH group linked with Ni atoms or H2O molecule encapsulated between two layers of a phyllosilicate structure in connection with the work reported in J. Phys. Chem. B 101 (1997) 7060-7074 by Burattin P. et al. Indeed, such band did not appear in the spectrum of pure nSi0 2 treated with NH3 (Fig. 9).
  • HPDEC 29 Si solid-state NMR spectrum
  • Figure 8 C shows the 29 Si solid-state NMR spectra of Nis%/nSi02 (d), Nis%/nSi02-NH3 (e), Nb nSiC ⁇ - NH3 (f), and nSiC>2 (i) samples. From those results, a tiny shift (around 1 ppm) toward lower magnetic field of the Q 4 peak in the case of the solids prepared in presence of NH3 could be revealed. Such shift is in agreement with a certain modification of the chemical environment of the Si atoms when ammonia was used.
  • Ni 5% /pSi0 2 -NH 3 -N (b), Ni 5% /SBA-15-TS (a), Ni 3.5% /nSi0 2 -NH 3 (f) and Ni5 % /nSi0 2 (d)
  • FIG 11 A: TGA profiles and B: XRD patents of spent a: Nis % /SBA-15- TS, b: Ni 5% /pSi0 2 -NH 3 -N, d: Ni 5% /nSi0 2 and f: Ni 3.5% /nSi02-NH 3 .
  • Ni3 .5% /nSi0 2 -NH3 exhibited very good conversions (higher than Ni5 % /nSi0 2 -NH3) under this severe reforming environment despite its lower Ni percentage. Those results can be referred to the better dispersion of Ni particles (42 % vs. 28% for N 15%) obtained in the case of this sample.
  • both solids exhibited a very good stability during 12 h at 650°C (Fig. 12 A’ and B’). It can also be noted that those catalysts let to a very selective DRM reaction since the H 2 /CO ratio remained equal to approximately 1 during 12 h (Fig. 12 C and C’).

Landscapes

  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Inorganic Chemistry (AREA)
  • Catalysts (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Abstract

A nickel-silicon catalyst for dry reforming of methane, wherein the nickel is present in an elemental weight percent of 1 to 7.5% considering the total weight of the catalyst, said nickel-silicon catalyst comprising a silicon oxide support bearing the nickel nanoparticles; and wherein the dispersion rate of the catalyst is at least 15%.

Description

Description
Ni-silica-based catalysts with highly dispersed nickel particles
[0001] The present invention relates to catalysts comprising nickel (Ni) and silica (Si), and demonstrating good abilities in the dry reforming of methane reaction (DRM).
[0002] The DRM converts two major greenhouse gases, CFU and CO2, into a useful chemical feedstock: a mixture of H2 and CO “syngas” with an H2/CO molar ratio equal to the unity adapted for Fischer-Tropsch procedure, as reported by B. Abdullah et al. in J. of Clean. Prod. 162 (2017) 170-185. Different strategies and siliceous supports have been developed and used in order to improve the nickel dispersion and interaction with the support, those features being particularly important in order to protect the Ni nanoparticles from sintering and to avoid side reactions; such side reactions are exemplified in different publications such as in the article of L. Espinosa- Alonso etal. published in J.Am. Chem. Soc. 131 (2009), 131, 16932-16938.
[0003] Until now, supported nickel-based materials have been intensively investigated as catalysts for the DRM - named « DRM catalysts » in the following description - as well as in the methanation of coal synthesis gas. Nickel-based catalysts usually suffer from rapid deactivation, due to partial metal oxidation as described by S. M. Kim et al. in J. Am. Chem. Soc. 139 (2017) 1937-1949 or K. Nagaoka et al. in Appl. Catal. A 268 (2004) 151- 158; particle sintering as described by Z. L. Zhang et al. in J. Catal. 158 (1996) 51-63 or L. Xu et al. in ACS Catal. 2 (2012) 1331-1342; and coke formation as described by J. H. Kim et al. in Appl. Catal. A Gen. 197 (2000) 191-200 or F. Frusteri et al. in Carbon 40 (2002) 1063-1070. Different strategies have been developed in order to protect Ni nanoparticles and to avoid side reactions, see for example the article published by J. R. A. Sietsma et al. in Angew. Chem. !nt. Ed. 46 (2007) 4547-4549. Porous supports and especially mesoporous ones have been extensively studied. Their ordered pore structures, high specific surface areas and the resulting confinement effect inside the pore channels are expected to afford highly dispersed nanoparticles with an increasing number of thermodynamically high-energy active surface atoms (see the article published by L. Tarpani et al. in Catal. Commun. 74 (2016) 28-32) and to lead to a more resistant catalyst toward the sintering and coke deposition owing to physical barrier of the pore walls. Most of those catalysts containing Ni developed for the DRM must be obtained by the impregnation of a porous support: S1O2 proved to be one of the best candidate for this purpose, in particular the so- called « SBA-15 » prepared from silica gel is known to be a good support for the Ni containing material, as described in the above mentioned article published by Sietsma and coworkers.
[0004] In the context of DRM, nickel nitrate (Ni(N03)2.xH20) is the most used Ni precursor for the preparation of Ni/Silica catalysts and one-pot preparation methods have already been investigated in order to generate highly stable silica-based catalysts as described by O. Daoura et al. in Int. J. Hydrogen. Energ. 43 (2018) 17205-17215. Nevertheless, siliceous support prepared in acidic medium such as mesoporous SBA-15, make the one-pot preparation difficult due to the amphoteric properties of silica surface. In acidic conditions, Si-OH groups transform into Si-OH2+ and the resulting surface charge does not favor interactions with the Ni(ll) aqua complexes.
[0005] One siliceous support prepared in acidic medium is mesocellular silica foam (MCF); Daoura et al. report the preparation of Ni catalyst containing MCF in J. CO2 Util. 24 (2018) 112-119. The classical preparation of those Ni/MCF catalysts requires long steps - at least two days - of hydrothermal treatment rendering thus the synthesis of DRM catalysts difficult. Moreover, under those conditions, organic porogen molecules, such as swelling and amphiphilic agents are required; and taking into account those agents have to be removed afterward, usually by calcination, thus such a process from the prior art is not suitable for a high-scale catalyst synthesis under a green pathway.
[0006] Besides, an important parameter for the catalyst efficiency is the amount of metal and in particular the Ni content, and the dispersion (fraction of Ni atoms available for catalysis) has to be kept as high as possible, as mentioned above. Many Ni catalysts have been developed, but it is noteworthy that improving the Ni content usually causes a drastic lowering of the dispersion: L. Qian et al. report the preparation of a Ni catalyst for DRM with a Ni wt% (Mass Fraction) of 0.5 having a dispersion rate of 40 in Microp. Mesop. Mater. 243 (2017) 301-310 ; while C. Wang et al. report the preparation of a Ni catalyst for DRM with a Ni wt% of 5-12 having a dispersion rate of only 11 in Catat. Sci. Techno!. 8 (2018) 4877-4890. To date, the methods developed to produce catalysts are not efficient enough to obtain DRM catalysts containing the ideal average of Ni content together with a dispersion rate sufficiently high to perform the DRM in good conditions and to reach very good yield together with great turnover number.
[0007] The main aim of the present invention is to provide a nickel containing DRM catalyst easily obtainable with a high Ni content and good dispersions and demonstrating the same or even better activity toward DRM, compared to the nickel catalysts from the prior art.
[0008] The present invention concerns a nickel-silicon catalyst, wherein the nickel is present in an elemental weight percent (wt%) of 1 to 7.5% considering the total weight of the catalyst, said nickel-silicon catalyst comprising a silicon oxide support bearing the nickel nanoparticles; and wherein the dispersion rate of the catalyst being more than at least 15%. The dispersion rate is calculated using the Fte chemisorption method. The dispersion refers here to the molar percentage of surface Ni atoms compared to the total number of Ni atoms in the sample: ø_ Qads _
Qmax 1+ l/KR
D: Fractional occupancy of the adsorption sites
QadS: Quantity adsorbed
Qmax: Quantity adsorbed on saturation
K: Equilibrium constant
P: Partial pressure of the adsorbate
In order to visualize the nickel dispersion and location, STEM/HAADF and EDX/mapping were also performed on a JEOL® 2020 microscope on ultra- thin sections of selected samples. The inventors have developed a new preparation method, very simple to carry out in comparison to known technologies in this field, giving rise to nickel-derived catalysts exhibiting tiny nanoparticles, high metal support interaction and excellent particles dispersion compared to other known materials. The nickel-silicon catalysts according to the present invention prove to be more readily obtainable compared to the already known nickel DRM catalysts, and demonstrate better activity toward DRM, with excellent stability.
Nanoparticles of Ni in the context of the invention are objects with sizes below 100 nm, preferably below 10 nm, ideally in the range of 2 to 5 nm. Bigger particles are detrimental to catalysts activity per gram of metal and can be responsible of side-reactions. The sizes were established by using direct observations by Transmission Electron Microscopy as well indirect evaluations using Fh chemisorption measurements.
[0009] Advantageously the dispersion rate of the catalyst being more than at least 18%.
[0010] Advantageously the dispersion rate of the catalyst being more than at least [0011] Advantageously the nickel is present in an elemental weight percent of 1.5 to 6.5%.
[0012] More advantageously the nickel is present in an elemental weight percent of 2 to 6% and even 2.5 to 5.5%.
[0013] Advantageously the silicon oxide support is non-porous. The inventors have noticed, in a completely unexpected manner, that using a non-porous support gives rise to higher nickel dispersion that leads to active and stable catalysts. The textural properties were determined using N2 adsorption- desorption method. Thus, before porosity measurements the samples were dried under vacuum for 2 hours at 250 °C. Then, specific surface areas were determined using BET equation, and Pore diameters and volumes were determined using BJH model according to the description provided by E. P. Barrett, and al. in the article: "The determination of pore volume and area distributions in porous substances. 1. Computations from nitrogen isotherms" Journal of the American Chemical Society, (1951), vol 73(1), pages 373-380.
[0014] Advantageously the silicon oxide support comprises Nickel (Ni) phyllosilicate. Using Ni phyllosilicates as precursors gives rise to excellent activity and stability. Moreover, the catalysts developed by the inventors exhibit excellent particles dispersion compared to other materials comprising phyllosilicate described in the litterature; see for example the article published by Z. Li et al. in Catai. Sci. Technoi. 8 (2018) 3363-3371, for which the dispersion rate does not exceed 3%.
[0015] Phyllosilicates are an important group of minerals constituted of tetrahedral and octahedral sheets. In case of nickel-silica-supported phyllosilicates material developed for DRM, tetrahedral sheet consists of Si4+, bonded to 4 oxygen atoms and the octahedron consists of Ni2+, coordinated with six anions, which can be O2· or OH-. In general, the formation of phyllosilicates needs the combination of three factors, i.e. a metal precursor, a silica source and a basic environment. Superficial silica is partially dissolved due to the alkaline environment, hence generating soluble silicate anions. Those silicate anions then react with Ni cations, and hydroxide anions in the solution to form the phyllosilicate structure that is further deposited on the remaining silica support as described in Catal. Today2>3Q (2020) 3-23 and J. C02 Util. 18 (2017) 345-352, by Z. Bian et al.
[0016] Advantageously the nickel-silicon catalyst according to the invention does not comprise any cobalt(Co) atom. Co atoms makes the catalyst vulnerable to oxidation leading to deactivation.
[0017] Advantageously the nickel-silicon catalyst according to the invention does not comprise any element selected in the group of lanthanide (for example La, Ce) and actinide, and does not contain indium (In), thallium (Tl), tin (Sn) or lead (Pb). A catalyst free of these elements is safer to use considering the toxicity of those elements.
[0018] Advantageously the particle size is below 6 nm, preferably below 5 and even below 4 nm. The inventors have demonstrated that using NH3 during preparation of the catalysts led to the improvement of the dispersion. This could be reflected by higher accessible nickel surface area due to smaller particle sizes. The particle sizes were measured using Transmission Electron Microscopy (TEM). TEM analyses were performed on a JEOL® 1011 (LaB) or JEOL® 2010 (LaB) microscope operating at 200 kV. The sample powder was ultrasonicated in ethanol and 2 drops of the resulting suspension were deposited on a copper grid coated with a porous carbon film. Observations were made once ethanol was evaporated at room temperature.
[0019] The present invention concerns also the process for the preparation of a metal(M)-silicon(Si) catalyst for the DRM comprising the following steps:
1- siliceous support (Si02)n is suspended in water (preferably distillated water) ; 2- M(N03)2 is added into the suspension prepared according to step 1;
3- the mixture obtained in step 2- is allowed under stirring during at least 2 hours at a temperature maintained between rt. (room temperature is supposed to be 20°C) and 60°C;
4- the solvent is evaporated;
5- the material obtained at step 4- is calcinated at least 2 hours at 550°C. Advantageously, the metal used in the process disclosed in the present invention is nickel.
Advantageously, step 1- comprises the addition of at least 2 mL of aqueous Nhb catalyst prepared with Nhb proved to be more active and stable. Advantageously, during step 1- the reaction time does not exceed 6 hours, or even 4 hours, at 1 bar.
Advantageously, said siliceous support used is selected between mesoporous silica material and non-porous silica material. A mesoporous material is a material containing pores with diameters between 2 and 50 nm, according to lUPAC nomenclature. For comparison, lUPAC defines microporous material as a material having pores smaller than 2 nm in diameter and macroporous material as a material having pores larger than 50 nm in diameter.
The present invention concerns also any of the catalyst presented previously according to the present invention that are obtainable by the process presented above in the frame of said invention.
[0020] Other advantages and characteristics of the present invention are described in details in the following experimental part in connection with the figures, which is only made for explanatory purposes and cannot serve to limit the scope of the invention.
[0021] EXPERIMENTAL PART [0022] I. Analysis and characterisation methods
[0023] A- Textural properties were determined from N2 adsorption-desorption isotherms recorded on a Belsorp®-max (from BEL JAPAN™) or ASAP™ 2020 (from Micromeritics®) apparatus. Before measurements, the samples were degassed under vacuum for 2 h at 250°C on Belprepll-vac unit or ASAP 2020 (Micromeritics). Specific surface areas were obtained using the BET equation. Pore diameters and specific pore volumes were determined using the BJH model (E. P. Barrett, and al. Journal of the American Chemical Society, (1951), vol 73(1), pages 373-380.). It must be noted that the textural properties were calculated taking into account the siliceous support weight only (without Nickel).
[0024] B- Wide angles XRD measurements were performed on a Briiker® D8 Advance diffractometer (CuKa = 1.54 A). The data were recorded in the 2 theta range between 5 and 90° using 30 kV and 10 mA conditions, a step size of 0.01° and 1 s per step. The average nickel/nickel oxide particles size was calculated from the Schemer equation: D = Kl/booeq, where K is a constant (K=0.9), l = 1.54 A, b is the full width at half maximum (FWHM) of the diffraction peak and Q is the peak position.
[0025] C- The X-ray photoelectron spectra (XPS) were collected on an Omicron® Argus™ X-Ray photoelectron spectrometer using a monochromatic Al Ka (hv= 1486.6 eV) X-ray source having a 300 W electron beam power. The emission of photoelectrons from the sample was analyzed at a take-off angle of 45° under ultra-high vacuum conditions (1 x 108 Pa). XP spectra were collected at pass energy of 20 eV for C 1s, Si 2p, Ni 2p and O 1s core XPS levels. The charging effects were corrected by adjusting the binding energy of the C 1s peak from carbon contamination to 284.6 eV. The peak areas were determined after subtraction of a Shirley background (Nagash and al. Chem. Mater., (2006), 18, 10, 2480-2488). The atomic ratio calculations were performed after normalization using Scofield factors. Spectrum processing was carried out using the Casa™ XPS software package under the condition described by M. P. Seah in, Surface and Interface Analysis, (1980),vol.2, lss.6, 222-239.
[0026] D- Thermogravimetric analyses (TGA) were performed in order to quantify the amounts of carbon deposited on the spent catalysts using a TA® SDT Q600™ thermal analyzer instrument. Measurements were carried out from rt. to 900°C (heating rate 10°C min-1) in flowing air (100 mL.min-1).
[0027] E- Temperature-Programmed Reduction (TPR), carried out on an AutoChem™ 2910 or a Micromeritics® 2920 apparatus equipped with a thermal conductivity detector (TCD), was used in order to study the nickel reducibility of calcined materials. The samples (80 mg) were heated on quartz wool in a U-shaped quartz tube from rt. to 900°C at a rate of 10°C min-1 using a 5 vol% hh/Ar gaseous mixture (25 mL.min-1). An isopropanol- liquid N2 mixture (AutoChem™ 2910) or an ice and salt bath (Micromeritics® 2920) was used before the TCD detector to trap the water molecules formed during NiO reduction. The nickel loading was deduced from the amount of H2 consumed during the TPR experiment after controlling that the Ni loading of a reference material was found to be coherent with that determined by inductively-coupled plasma optical emission spectrometry (ICP-OES (Crealins-Villeurbanne)). The AutoChem and Micrometric apparatus were also used to perform high-temperature H2 reductions mimicking the in situ reduction (detailed later) carried out as a pretreatment step prior to the catalytic test.
[0028] F- Transmission Electron Microscopy (TEM) analyses were performed on a JEOL®-1011 (LaB) or JEOL®-2010 (LaB) microscope operating at 200 kV. The sample powder was ultrasonicated in ethanol and 2 drops of the resulting suspension were deposited on a copper grid coated with a porous carbon film. Observations were made once ethanol was evaporated at room temperature.
Microtomed Solids: transmission electron microscopy (TEM) images and HRTEM images were taken on a JEOL® JEM-2010 UHR operating at 200 kV, equipped with an energy dispersive X-ray (EDX) detector. Materials were analyzed after ultramicrotomy. A few mg of powder were deposited in the bottom of a Beem capsule. Some embedding resin (AGAR™ 100) was added and polymerized for 48 h at 60°C. The polymerized blocks were then cut into ultrathin sections (about 70 nm thick) using a diamond knife of a Leica® microtome (ULTRACUT UCT) and deposited on carbon-coated copper grids. In order to visualize the nickel dispersion and location, a scanning transmission electron microscope (STEM) technique was used: which is named High-angle annular dark-field imaging (HAADF); and EDX/mapping was also performed on a JEOL® 2020 microscope on ultra- thin sections of selected samples.
[0029] G- H2 Chemisorption experiments: were performed on a BELSORB-max™ equipment from BEL JAPAN™. The samples (about 200 mg) were reduced in situ under a flow of H2 (50 mL min-1) at 650°C for 2 h using a ramp of 10°C min-1. The sample was then outgassed at 620°C for 2 h under vacuum (about 5.101 Pa). A first, H2 chemisorption measurement was performed at 25°C, the pressure at equilibrium being recorded when the pressure variation was below 0.02% per minute. The sample was then outgassed for 2 h at 25°C before a second H2 chemisorption was performed under the conditions described for the first H2 chemisorption. Nickel particle size estimations are based on truncated octahedron geometry, assuming complete reduction, semi spherical particles and a H/Ni adsorption stoichiometry factor of 1. The experimental data were fitted with a Langmuir adsorption equation (Equation 1) and the amount of surface nickel was calculated from the quantity adsorbed at saturation ( Qmax in the model). The dispersion refers here to as the molar percentage of surface Ni atoms compared to the total number of Ni atoms in the sample.
Figure imgf000013_0001
D: Fractional occupancy of the adsorption sites
QadS: Quantity adsorbed
Qmax: Quantity adsorbed on saturation
K: Equilibrium constant
P: Partial pressure of the adsorbate
[0030] H- Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS):
[0031] -> The experiment was performed using a Tensor II Bruker® spectrometer with a DRIFTS cell (Praying Mantis™ Diffuse Reflectance Accessory). Diffuse reflectance infrared spectra were recorded in the 4000-600 cm-1 range (resolution 4 cm-1, 128 scans/spectrum, Mercury cadmium telluride (MCT) detector).
The sample compartment of the cell was filled with the powder (approximately 30 mg), which was heated in situ under an Ar flow (20 cm3 min-1) using the following program:
Figure imgf000013_0002
[0032] All spectra were recorded in situ and were converted into Kubelka-Munk units after subtraction of the spectrum recorded on the dehydrated KBr sample (Fluka®, purity >99.5%), according to Kubelka P., et al. in Zeitschrift fiir technische Physik, (1931), Vol.12, pp. 593-601.
[0033] -> When information dealing with wavenumbers below 600 cm-1 were needed (in the 4000-200 cm-1 range), the diffuse reflectance infrared spectra were recorded using a Bmker® Vertex 70 spectrometer (4 cm-1 resolution, 512 scans/spectrum, DLATGS detector and wide range FIR-MIR beamsplitter). About 40 mg of powder, corresponding to a mechanical mixture of 20 mg of sample in 20 mg of diamond powder, was placed inside a heated crucible located in a Thermo Spectra-Tech high temperature cell equipped with two diamond windows and with appropriate gas inlet and outlet connections as to pass the gas flow through the sample bed. The reference spectrum was recorded with the diamond powder itself (size 6 pm).
[0034] I- 29Si MAS NMR: spectra were recorded at 79.5 MFIz with a Briiker® Avance 500 spectrometer and 7 mm (external diameter) zirconia rotors at 6 kHz spinning speed. Chemical shifts of silicon were measured by reference to tetramethylsilane (TMS). 29Si MAS NMR spectra were obtained with 3.5 ps excitation pulse duration and 10 s recycle delay.
[0035] J- Catalytic measurements
The different catalysts were tested using a PID ENG&TECH™ Microactivity Effi Reactor (from Micromeritics®). The solids were loaded on a plug of quartz wool and treated in-situ ai 650 °C for 2 h (10 °C.min-1) in a 5 vol.% H2/Arflow (30 ml_ min-1) in order to achieve a complete reduction of NiO into metallic nickel. After this pretreatment step, the temperature was decreased to 200°C and the dry reforming of methane reaction was started under atmospheric pressure, using a CH4/C02/Ar (5/5/90) reacting mixture and at a total Gas Hour Space Velocity (GHSV) of 144 (50 mg of catalyst and 120 ml_ min-1 total flow) or 960 L g-1 lv1 (10 mg of catalyst diluted with 90 mg of fumed silica (Aldrich 381276) and 160 ml_ min-1 total flow of reactants mixture).
[0036] Firstly, the activity of the catalyst was measured by increasing the reactor temperature from 200 up to 650°C (using a rate of 5°C min-1). The temperature was then maintained at 650°C for 12 h for stability measurements. The gaseous products were analyzed online by a micro-GC (Agilent 490) equipped with Plot-U and Molecular sieves channels and TCD detector. The conversions of methane and carbon dioxide were calculated according to Equations 2 and 3, respectively, and the F /CO ratios were estimated using Equation 4:
CH4 conversion, % =
Figure imgf000015_0001
x ioo (Equation 2)
Figure imgf000015_0002
C02 conversion,
Figure imgf000015_0003
x 100 (Equation 3)
^^2(in) (Equation 4)
Figure imgf000015_0004
The catalytic performances were also compared to thermodynamic curves calculated using the HSC Chemistry Software (version 7.1) at 1 atm, from 0 -1000 °C, at inlet feed ratio of CO2/CH4 =1 and assuming no carbon formation occurring during reaction.
[0037] II. Preparation of the materials
[0038] In this part, the preparation of the siliceous supports and the nickel incorporation method will be detailed.
[0039] 11.1 Silica supports
[0040] The silica supports used were commercially available, such as SBA-15 (Sigma-Aldrich® CAS number: 7631-86-9 with 4 nm as pore size), Aerosil® 380 (nSi02) from Evonic®, or were synthesized (pSiC^) as shown below. The later was prepared by using a mixture of cetyltrimethylammonium bromide (CTABr) and Pluronic (P123) as surfactants. The mixture of CTABr and P123 with an appropriate ratio leads to a porous material with high specific surface area, 4 nm as pore size and a higher wall thickness than SBA-15 according to Microp. Mesop. Mater. 89 (2006) 179-185 published by W.-H. Zhang et al. The synthesis of pSiC>2 was performed according to the procedure described by W.-H. Zhang et al. ( Microp . Mesop. Mater. 89 (2006) 179-185) using 4 g of the triblock copolymer (EO20PO70EO20, Pluronic P123) dissolved in a mixture of 37 wt% HCI (20 ml_) and distilled water (130 ml_) at 40°C. Three hours later, 1 g of CTABr was added to the solution and stirred for 30 min. After total dissolution, 6.6 g of tetramethylorthosilicate (TMOS) were added and the resulting suspension was stirred at 40°C for 20 h. After hydrothermal treatment for 24 h at 100°C, the suspension was filtered and the recovered solid (PS1O2-N) was washed, dried and calcined at 550°C for 5 h (heating rate 1 °C min-1) affording pSi02- C.
[0041] II.2 Insertion of Ni
[0042] Six Ni-based catalysts were prepared, a first one by the impregnation of commercially available SBA-15 by two solvents, three by the impregnation of nSiC>2 with or without NH3 and two starting from pSi02. Table 1 summarizes the preparation methods of the solids.
[0043] Table 1: Description of siliceous supports and the Ni/silica materials
Figure imgf000016_0001
Figure imgf000017_0001
[0044]
[0045] Preparation of Ni5%/SBA-15-TS: The Ni/SBA-15-TS sample was prepared by the “Two-Solvents” (TS) method. To do so, 1 g of a commercial SBA-15 was suspended in 35 ml_ of cyclohexane, then a volume of water equal to the silica pore volume (as previously determined by N2 physisorption) and containing the appropriate amount of nickel precursor (0.25 g of Ni(N03)2.6H20 for 5 wt.% Ni) was added dropwise. The solid was dried one day at room temperature, then overnight at 60°C, and it was finally calcined at 550°C for 5 h (heating rate 1°C min-1).
[0046] Preparation of Ni5%/pSi02-NH3-N and Ni5%/pSi02-NH3-C: The support PS1O2 prepared according to procedure described in the above 11.1 section, was impregnated by nickel nitrate in presence of NH3 before (leading to Ni5%/pSi02-NH3-N) and after (leading to Ni5%/pSi02-NH3-C) removal of surfactants from the porosity.
[0047] The effect of NH3 on the stabilization of Nickel was also studied on non- porous siliceous support. Commercial (Aerosil® 380) non-porous silica (named nSi02) was impregnated with two different amounts of nickel 5 wt.% and 3.5 wt.% (Ni3.5% and Ni5%/nSi02-NH3).
[0048] Preparation of Ni5%/nSi02: it was prepared using a wet impregnation method. To do so, 1 g of Aerosil® 380 was suspended in 30 ml_ of water with 0.25 g of Ni(N03)2.6H20 under vigorous stirring for 2 h. Then, the mixture was dried at 60°C and finally calcined 2 h at 550°C (heating rate 1°C min-1).
[0049] The other solids, synthesized in the presence of NH3 (Ni5%/nSi02-NH3, Ni3.5%/nSi02-NH3, Ni5%/pSi02-NH3-N and Ni5%/pSi02-NH3-C), were prepared using a modified wet impregnation method. Briefly, 1 g of siliceous (nSi02 or pSi02-C or -N) support was suspended in 30 ml_ of distilled water and a volume (around 2-3 ml_) of NFb 30% (pH = 9) at 60°C for 10 min. Then, the adequate quantity of Ni(N03)2.6H20 dissolved in 5 ml_ of distilled water was added dropwise to the S1O2 suspension under vigorous stirring. After 2 h of stirring at 60°C, the suspension was filtered and the solid washed with water, dried at 60°C during 24 h and finally calcined 2 h at 550°C (heating rate = 1°C min-1).
[0050] III. Results
[0051] The impact of the preparation method on the textural properties of the solids as well as on the nickel characteristics will be analyzed in this part.
[0052] 111.1 Physico-chemical properties of calcined and reduced solids
[0053] Figure 1 displays the nitrogen adsorption-desorption isotherms of the solids and, Table 2, their textural parameters.
[0054] Table 2: Physico-chemical properties of calcined Ni-silica based materials and of their respective parents.
Figure imgf000018_0001
Materials Isotherms
(wt.%) (m2 g 1) (cm3 g-1) (nm)
SBA-15 (h) — 567 0.4 4
Ni5%/SBA-15-TS (a) 4.7 355 0.3 4 pSi02 (g) — 832 0.8 4
Nis%/pSi02 -NHs-N (b) 5.1 592 0.8 4
Ni5%/pSi02 -NHs-C (c) 5.1 581 0.7 4 nSiOi (i) 341 2.8 Ni5%/nSi02 (d) 4.8 315 1.4
Ni5%/nSi02-NH3 (e) 5.8 340 1.0
Ni3.5%/nSi02-NH3 (f) 3.5 300 1.0 a Nickel content estimated from H2 consumption during TPR measurements; b Total N2 volume from BJH desorption; c Average pores diameter deduced from BJH desorption pore size distribution.
[0055] According to the lUPAC classification, Nis%/SBA-15-TS (a), Nis%/pSi02- Nhb-N (b), and Ni5%/pSi02-NH3-C (c) as well as their corresponding supports pSi02 (g) and SBA-15 (h) (Fig. 1 A) are characterized by type IV isotherms in agreement with those of mesoporous materials described in C. R. Chimie, 21 (2018) 514-522, by M. Boutros et al.
[0056] In Figure 1: N2 adsorption-desorption isotherms at -196°C of a: Nis%/SBA- 15-TS, b: Ni5%/pSi02-NH3-N, c: Ni5°/o/pSi02-NH3-C, d: Ni5%/nSi02, d’: reduced Nis%/nSi02, e: Ni5%/nSi02-NH3, e’: reduced Ni5%/nSi02-NH3, f: Ni3.5%/nSi02-NH3, f: reduced Ni3.5%/nSi02-NH3, g: PS1O2, h: SBA-15 and i: nSi02.
[0057] Discussion: contrary to what could be expected for SBA-15, the hysteresis observed in the case of the commercial SBA-15 used in this work (Figure 1 (h)) before and after impregnation, was closer to H5 type that can be associated with certain pore structures containing both open and partially blocked mesopores (e.g., plugged hexagonal templated silicas). Compared to its support, Ni/SBA-15-TS displayed a decrease in the pore volume (- 25%) and the specific surface area (-40%). Such modifications in the textural parameters could be related either to the incorporation of Ni in the porosity and/or more preferentially to some pores blocking since the plug observed on the impregnated solid was relatively more important than on the corresponding naked support. On the other hand, as expected, compared to its parent support (pSi02 (g)), Ni5%/pSi02-NH3-C (c) showed a decrease in the pore volume which is not the case for Ni5%/pSi02-NH3-N (b) due to the presence of the surfactant inside the porosity of PS1O2-N during impregnation. Moreover, both Ni5%/pSi02-NH3-C and N exhibited around 20% decrease of the specific surface area. These two solids with their support exhibited (Fig. 1 A) H2(a) hysteresis loops shapes in agreement with more complex pore structures (Fig. 1 A). Such observation is the consequence of using a mixture of two structure-directing agents, i.e. P123 and CTABr. Compared with the literature, pSi02 prepared with P123: CTABr molar ratio of 1 :4 exhibited typically the same isotherms, hysteresis loop, pore size and volume with relatively larger surface area (832 instead 650 m2 g-1). It has also to be mentioned that the hysteresis loop in the case of Ni5%/pSi02-NH3-C seems to be a little bit flattened. Such modification may be related either to the prolonged contact of the calcined siliceous support with NH3 (which could deteriorate the support) and/or to the double calcination of Nis%/pSi02-NFl3-C (before and after impregnation).
[0058] Ni5%/nSi02 (d), Ni5%/nSi02-NFl3 (e) and Ni3.5%/nSi02-NH3 (f) samples as well as the corresponding naked support nSi02 (i) (Fig. 1 B and B’) exhibit type II isotherms (lUPAC classification) whose shapes are characteristic of the aggregation of their non-porous grains [25]. The presence of hysteresis loop for such solids can be related to inter-granular porosity, which also explains the high N2 volume adsorbed (BJH) especially in the case of the support nSi02. Compared to their support, Nis%/nSi02 (d), Nis%/nSi02-NFl3 (e) and Ni3.5%/nSi02-NFl3 (f) are characterized by a decrease of the adsorbed N2 volume. However, the specific surface area remained more or less unchanged ( c.a . 300 m2 g-1) for the whole series. It is noteworthy that all of the non-porous solids showed some microporosity that could be detected from their isotherms at very low P/Po.
[0059] Reduced Nis%/nSi02, Ni3.s% and Ni5%/nSi02-NH3 were also analyzed by N2 sorption (Fig. 1 C) showing very similar isotherms before and after reduction. However, the specific surface areas decreased for the three reduced samples (265, 291 and 260 m2 g-1 for Nis%/nSi02, Ni5%/nSi02-NH3 and Ni3.5%/nSi02-NH3, respectively), which may be caused by the heat treatment during the reduction step. In addition, it could be noticed that the total N2 adsorbed volume was somewhat higher after reduction in the case of solids prepared in presence of NH3 (1.2 vs. 1.0 cm3 g-1 for both Ni3.s% and Ni5%/nSi02-NH3) compared to those prepared without ammonia (1.3 vs. 1.4 cm3 g-1 for Nis%/nSi02).
[0060] III.2 NiO and Ni° characterizations
[0061] XRD patterns for the calcined samples (NiO) (Fig. 2 A) showed a wide peak between 20°= 15-30° due to diffusion effects by the amorphous silica walls. Five intensive diffraction peaks at 20° = 37.3°, 43.1°, 62.8°, 75.4° and 77° corresponding to NiO (JCPDS no. 89-7130) were also detected on the calcined Nis%/SBA-15-TS (a) and Nis%/nSi02 (d). Particles size for these two samples, estimated from Schemer equation, were 5.7 nm and 13.8 nm (Table 3), respectively thus highlighting the advantages of porous materials such as SBA-15. In contrast, no peaks corresponding to crystalline NiO were detected for all the other solids prepared in the presence of NH3. However, three peaks were noticeable at 20° = 34.1°, 36.7° and 60.5° for those solids. After reduction in conditions similar to those used just before the catalytic test (2 h at 650°C) (Fig. 2 B), three peaks corresponding to Ni° at 20° = 44°, 52° and 76° (JCPDS no. 70-1849) were detected for Nis%/SBA- 15-TS (a) and Ni5%/nSi02 (d).
[0062] Figure 2 : XRD diffraction patterns of calcined (A) and reduced (B) a: Nis%/SBA-15-TS, b: Ni5%/pSi02-NH3-N, c: Ni5%/pSi02-NH3-C, d: Ni5%/nSi02, e: Ni5%/nSi02-NH3 and f: Ni3.5%/nSi02-NH3.
[0063] Table 3: NiO and Ni° particles size and dispersion estimated from different techniques.
Before catalytic tests Spent
Ni°
Materials NiO size a Ni° size a Ni° size b D c Ni° size d size a
(nm) (nm) (nm) (%) (nm)
(nm)
Nis%/SBA-15-TS 5.7 6.5 6.1 16.0 6.2 6.7
Ni5%/nSi0 13.8 17.1 19.3 4.8 21.2 16.7
Ni5%/nSi02-NH3 PS e No Peaks 3.3 28.0 3.6 n.d. f
No
Nb.5%/nSi02-NH3 PS e No Peaks n.d. f 41.7 2.4
Peaks
Ni5%/pSi02-NH3-N PS e No Peaks 4.2 19.6 5.1 3.8 a From the Scherrer equation (XRD); b From TEM images by counting more than 400 particles; c Nickel dispersion calculated from H2 chemisorption; d From H2 chemisorption; e PS: Phyllosilicates; f n.d.: Not determined.
[0064] Discussion; no significant changes in the particles size occurred during the reduction of NiO in the case of Ni5%/SBA-15-TS. On the contrary, after reduction, Nis%/nSi02 showed bigger Ni° particles (17.1 nm) than the NiO ones (table 3) which evidences sintering.
[0065] In the same line with the XRD results of the calcined solids, no peaks could be noticed after the reduction of the materials synthesized in the presence of NH3 despite Ni loading values comprised between 3.5 and 5 wt.%. Such observations (no NiO/Ni0 peaks) could be related to the small size of the nanoparticles and their good dispersion on the support when Nhb was used.
[0066] Additional results:
[0067] X-Ray Photoelectron Spectroscopy (Fig. 3) and Temperature-programmed reduction (Fig. 4) analyses were carried out on the calcined solids in order to study, first, the presence of nickel (especially for the solids prepared in presence of NFb), then its oxidative state and to investigate their reduction behaviors.
[0068] XPS measurements performed on Nis%/SBA-15-TS (a), Ni5%/pSi02-NFl3-N (b), Ni5%/nSi02 (d), Ni5%/nSi02-NFl3 (e) and Ni3.5%/nSi02-NH3 (f) exhibited, for all those solids, two main peaks corresponding to Ni 2p3/2 and Ni 2pi/2 with their satellites.
[0069] In figure 3: XPS spectra of calcined a: Nis%/SBA-15-TS, b: Ni5%/pSi02-NFl3- N, d: Ni5%/nSi02, e: Ni5%/nSi02-NFl3 and f: Ni3.5%/nSi02-NH3.
[0070] In figure 4: FI2-TPR profiles of calcined a: Nis%/SBA-15-TS, b: Nis%/pSi02- NHs-N, C: Ni5%/pSi02-NH3-C, d: Ni5%/nSi02, e: Ni5%/nSi02-NFl3 and f: Ni3.5%/nSi02-NH3 recorded with a H2 5 Vol.%/Ar flow of 30 ml_ min-1 and a heating rate of 10°C min-1.
[0071] Discussion: The Ni 2p3/2 peak assigned to NiO for both Nis%/nSi02 (d) and Ni5%/SBA-15-TS (a) could be deconvoluted into two different peaks. Due to their binding energy, those peaks could be attributed to nickel in strong (856 eV) or weak (854.7 eV) interaction with the support (to our knowledge, binding energy of Ni 2p3/2 of bulk NiO is 853.6-854.4 eV). XPS also showed one peak at higher binding energy (approximately 857 eV) for Nis%/pSi02- NHs-N (b), Ni3.5%/nSi02-NH3 (f) and Ni5%/nSi02-NFl3 (e). This higher energy identified only for those solids, could be related to nickel in stronger interaction with the support which is not the case for Nis%/SBA-15-TS (a) and Ni5%/nSi02 (d).
[0072] The TPR profiles displayed in figure 4 showed that the solids prepared in the presence of Nhb are characterized by higher reduction temperatures with one ill-defined and broad peak located between 450 and 900°C (b, c, e, f). In contrary, the catalysts prepared in the absence of Nhb exhibited two more defined reduction peaks (a, d). The first, at lower temperature, (400°C) can be attributed to the reduction of bulk NiO with low metal-support interaction and/or big aggregates. However, the second (600-650°C) was tentatively assigned to the reduction of the NiO species strongly interacting with Si02. In parallel, the Ni wt.% values estimated from the consumed H2 quantity are summarized in table 3. Further, we checked, by ICP-EOS for Ni5%/nSi02-NH3 (e) that the value obtained by H2-TPR (5.8%) are very similar to that obtained by ICP-EOS (5.9%).
[0073] Monitoring of calcined and reduced solids:
[0074] Figure 5: TEM images of calcined microtomed A: Ni5%/pSi02-NH3-N, B: Nis/o/SBA-15-TS, C: Ni5%/nSi02 and D, D’: Ni5%/nSi02-NH3.
[0075] Figure 6: TEM images of reduced microtomed; a: Nis%/SBA-15-TS, b: Ni5%/pSi02-NH3-N, c: Ni5%/pSi02-NH3-C, d: Ni5%/nSi02, e: Ni5%/nSi02-NH3 and f: Ni3.5%/nSi02-NH3.
[0076] The calcined (Fig. 5) and reduced (Fig. 6) solids were analyzed by transmission electron microscopy in order to evaluate the morphology of the nickel particles, as well as their size (summarized in table 3) and their dispersion on the supports. Calcined Nis%/SBA-15-TS (Fig. 5 B) and Ni5%/nSi02 (Fig. 5 C) materials prepared without using NH3, clearly exhibited NiO particles. In particular, Ni5%/nSi02 showed big nickel aggregates. Those results are in good correlation with XRD analyses. TEM images of Nis%/SBA-15-TS (Fig. 5 B) revealed small particles inside the porosity but big aggregates on the external surface of the grains. In the presence of IMH3, no nickel particles could be observed but some branch like structures were detected on the external surface of the siliceous grains for both porous (Ni5%/pSi02-NH3-N) and non-porous (Ni5%/nSi02-NH3) solids (Fig. 5 A and D, respectively). It has to be noticed also that, after their reduction, TEM of Ni5%/SBA-15-TS (Fig. 6 a) and Ni5%/nSi02 (Fig. 6 d) emphasized no significant modification in their morphologies (dispersion, porosity etc...).
[0077] In contrast, the lamellar structures observed on the calcined solids prepared in presence of IMH3 (Fig. 5 A and B) were not detectable anymore after the reduction step. Instead of them, well-dispersed and tiny nanoparticles of, normally, Ni° (because it appears after reduction) on the grains surface could be detected in the case of the non-porous support (Fig. 6 e and f). In the case of porous solids, (Nis%/pSi02-NFl3-N and Nis%/pSi02-NFl3-C (Fig. 6 b and c, respectively)) most of the observed particles coated the outer grains surface of the porous support and no nickel particles were detected in their porosity.
[0078] EDX/MAPPING and EDX analyses:
[0079] Figure 7: A: TEM-MAPPING and B: TEM-EDX results for microtomed Ni5%/pSi02-NH3-N.
[0080] EDX/MAPPING (Fig. 7 A) and EDX (Fig. 7 B) analyses were carried out on the reduced Ni5%/pSi02-NH3-N in order to confirm the absence of nickel (Ni°) inside the porosity. Indeed, both techniques revealed that Ni mainly occupied the external surface of this material.
[0081] The nickel dispersion and its accessibility were estimated from H2 chemisorption measurements (table 3). The determination of Ni dispersion was estimated on the basis of the first Fb isotherm (including reversibly and irreversibly chemisorbed hydrogen) as recommended by Bartolomew C.H. in Catai Lett. 1 (1990) 27-51.
[0082] Discussion: Clearly, these analyses emphasized that the use of Nhb during the impregnation step, led to the improvement of the dispersion. This could be reflected by higher accessible nickel surface area due to smaller particles sizes. The Ni3.5%/nSi02-Nhb sample was characterized by the highest dispersion value ( c.a .42%) which corresponds to the smallest nanoparticles (2.4 nm). Despite its higher nickel content, Ni5%/nSi02-NH3 showed also a good nickel dispersion (28%) with nickel particle sizes of 3.6 nm.
[0083] The comparison of the particle dimensions in Ni5%/nSi02-NH3 (3.6 nm) with Ni5%/nSi02 (19 nm) clearly indicates that ammonia has an important effect on the dispersion (see Table 3). Surprisingly, for the sample based on porous supports impregnated in presence of Nhb (Ni5%/pSi02-Nhb-N), despite the deposition of nickel mainly on the outer grains surface, this last showed good dispersion and relatively small particles. Compared with Ni5%/SBA-15-TS, where the nickel was incorporated into the porosity, Ni5%/pSi02-Nhb-N (Table 3) exhibited better dispersion (19.6% vs. 16%) and smaller particles (5.1 nm vs. 6.2 nm).
[0084] Infrared - FT-IR
[0085] FT-IR spectra of the calcined samples collected at 120°C (after treatment at 300°C under airflow) are shown in Fig. 8A. All of them were characterized by an absorption band assigned to isolated silanol groups at 3733 cm-1 [29] in the O-H stretching region.
[0086] In figure 8: A and B: DRIFT and C: 29Si solid state (HPDEC) NMR spectra of calcined d: Ni5%/nSi02, e: Ni5%/nSi02-NH3, f: Ni3.5%/nSi02-NH3, and i: nSi02. IR spectra in Fig. 8 B were collected using samples diluted in diamond powder. NMR spectra were normalized on Q4.
[0087] Nickel-based solids prepared in presence of Nhb (Fig. 8 A e and f) showed an additional band at 3621 cm-1 that would be due to the vibration of the OH group linked with Ni atoms or H2O molecule encapsulated between two layers of a phyllosilicate structure in connection with the work reported in J. Phys. Chem. B 101 (1997) 7060-7074 by Burattin P. et al. Indeed, such band did not appear in the spectrum of pure nSi02 treated with NH3 (Fig. 9).
[0088] In figure 9: IR spectrum (DRIFT) of calcined S1O2 after treatment with NH3 without nickel.
[0089] Discussion: The frequency range lower than 1500 cm-1 of the spectra of Ni5%/nSi02, Ni5%/nSi02-NH3, and nSi02(Fig. 8 B d, e and i respectively) was further analyzed after the dilution of those samples with up to 50% of diamond powder. On the contrary to what is observed for nSi02 and Ni5%/nSi02; Nis%/nSi02-NH3 exhibited a different signature between 750 and 625 cm-1 which could be due to the presence of a small band (at around 665 cm-1) in this region (see the zoomed part from Fig. 8 B).
[0090] 29Si solid-state NMR spectrum (HPDEC) is widely used to characterize amorphous silica. This technique enables the silicon atoms of bulk silica (Q4= Si(OSi)4) to be distinguished from silanol groups, also terminal silanol groups (Q3= Si(OSi)3(OH)) from geminal silanol groups (Q2 = Si(OSi)2(OH)2). In addition, this method facilitates the evaluation of the chemical environment of the Si atoms. A modification in this environment will be reflected by certain chemical shift (ppm). Figure 8 C shows the 29Si solid-state NMR spectra of Nis%/nSi02 (d), Nis%/nSi02-NH3 (e), Nb nSiC^- NH3 (f), and nSiC>2 (i) samples. From those results, a tiny shift (around 1 ppm) toward lower magnetic field of the Q4 peak in the case of the solids prepared in presence of NH3 could be revealed. Such shift is in agreement with a certain modification of the chemical environment of the Si atoms when ammonia was used.
[0091] IV. Activity of the catalysts toward DRM
[0092] The catalytic performances of selected solids were analyzed under two different set of conditions: Y: Catalyst weight: 50 mg, ChU and CO2 conversion: 200-650 °C (5 °C min-1), conversions stability at 650 °C during 12 h, GHSV = 144 L g-1 lv1 and Z: Catalyst weight: 10 mg diluted with 90 mg of fumed silica (Aldrich, CAS 381276), ChU and CO2 conversion: 200- 650 °C (5 °C min-1), conversions stability at 650 °C during 12 h, GHSV = 960 L g-1 h-1.
[0093] IV.1 Catalytic test under GHSV = 144 L g-1 h 1
[0094] Ni5%/pSi02-NH3-N (b), Ni5%/SBA-15-TS (a), Ni3.5%/nSi02-NH3 (f) and Ni5%/nSi02 (d) (see in Figure 10: Catalytic performances of a: Nis%/SBA-15- TS, b: Ni5%/pSi02-NH3-N, d: Ni5%/nSi02 and f: Ni35%/nSi02-NH3) were chosen to be tested in the DRM reaction in order to check the influence of the preparation method (two porous solids with and without NH3 and two non-porous ones characterized by the higher (42%) and lower (approximately 5%) nickel dispersion also with and without NH3).
[0095] After in situ reduction under H2 (5 vol.% flow: 30 ml_ min-1) at 650°C during 2 h, their performances were evaluated firstly in terms of CH4 and CO2 conversions versus temperatures until 650°C then at the same temperature during 12 h for the stability test.
[0096] The conversions of CH4 and CO2 rise while increasing the temperature (Fig.
10 A and B). Under these conditions, the solids prepared in presence of NH3 Ni5%/pSi02-NH3-N (b) and Ni3.5%/nSi02-NH3 (f) were very active with CH4 and CO2 conversions (approximately 80% at 650°C) very close to the thermodynamic equilibrium ones and reached an H2/CO ratio close to 1 (good selectivity). Nis%/SBA-15-TS (a) solid exhibited also good performances. On the other hand, Nis%/nSi02 (d) turned out to be less active with CH4 and CO2 conversions of approximately 30%. Those results emphasized that i) adding NH3 during the synthesis seems to be very interesting since both mesoporous and non-porous supports led to very good performances, ii) when NH3 was not used, the mesoporosity played a crucial role towards enhancing the catalytic behavior of the solids.
[0097] From the stability test, the samples prepared in the presence of NH3 turned out to be more stable and selective than the others, with the same reactant’s conversions and H2/CO ratio close to unity during 12 h. On the contrary, Ni5%/nSi02 (d) and Nis%/SBA-15-TS (a) showed a decrease up to 15% of the conversions just after 1 h on steam and a H2/CO molar ratio < 1.
[0098] Characterization of the spent catalysts at GHSV = 144 L g-1 h 1: the coke deposition after catalytic test was evaluated by thermogravimetric analyses. From the results displayed in figure 11 A, it can be noticed that the higher weight loss (amount of deposited carbon) was detected for Nis%/nSi02 (d).
[0099] In figure 11: A: TGA profiles and B: XRD patents of spent a: Nis%/SBA-15- TS, b: Ni5%/pSi02-NH3-N, d: Ni5%/nSi02 and f: Ni3.5%/nSi02-NH3.
[00100] The quantity of coke was reduced when a mesoporous SBA-15 support was used instead of non-porous silica (Nis%/SBA-15-TS (a)), which could be related to the confinement of nickel inside the regular and ordered pores of SBA-15. The solids prepared in the presence of IMH3 (d and f) did not show any coke deposition, which confirms the stabilization of Ni NPs. In addition, the spent solids were analyzed by XRD and the particles sizes of Ni° were estimated using the Debye Schemer equation. From XRD patterns (Fig. 11 B), no significant sintering occurred during the catalytic tests when comparing the Ni° particles sizes before and after the catalytic test (Table 3).
[00101] IV.2 Catalytic test under GHSV = 960 L g-1 h 1
[00102] In order to better evaluate the catalytic properties of Ni/nSi02-NH3 solids prepared without any surfactant, which could be more advantageous for industry, additional catalytic tests were performed.
[00103] To do so, the impact of the dispersion and Ni loading on the reactivity (see N i3.5% - Ni5%/nSi02-NH3 samples) was studied under kinetic regime (GHSV = 960 L g-1 IT1), far from the equilibrium conversion (Fig. 12).
[00104] In Figure 12: Catalytic performances of e: Nis%/nSi02-NH3 and f: Ni3.5%/nSi02-NH3 under GHSV = 960 L g-1 lv1.
[00105] According to U. Oemar U. et al. in Catal. Sci. Techno/. 6 (2016) 1173-1186, most of the studies conducted for Ni/silica are carried out at low gas hourly space velocities (GHSVs). Thus, it is important to know that the GHSV used here (960 L g-1 lv1) is among the highest one found in the literature for the DRM while using Ni-silica based catalysts especially. As discussed before and owing to the endothermic nature of this reaction, the conversions of CH4 and CO2 increase with temperature (Fig. 12 A and B). Ni3.5%/nSi02-NH3 exhibited very good conversions (higher than Ni5%/nSi02-NH3) under this severe reforming environment despite its lower Ni percentage. Those results can be referred to the better dispersion of Ni particles (42 % vs. 28% for N 15%) obtained in the case of this sample. In addition, both solids exhibited a very good stability during 12 h at 650°C (Fig. 12 A’ and B’). It can also be noted that those catalysts let to a very selective DRM reaction since the H2/CO ratio remained equal to approximately 1 during 12 h (Fig. 12 C and C’).

Claims

Claims
Claim 1. A nickel-silicon catalyst, wherein the nickel is present in an elemental weight percent of 1 to 7.5% considering the total weight of the catalyst, said nickel-silicon catalyst comprising a silicon oxide support bearing the nickel nanoparticles; and wherein the dispersion rate of the catalyst is at least 15%.
Claim 2. A nickel-silicon catalyst according to claim 1 , wherein the dispersion rate of the catalyst is at least 18%.
Claim 3. A nickel-silicon catalyst according to any of claim 1 to 2, wherein the dispersion rate of the catalyst is at least 25%.
Claim 4. A nickel-silicon catalyst according to any of claim 1 to 3, wherein the nickel is present in an elemental weight percent of 1.5 to 6.5%.
Claim 5. A nickel-silicon catalyst according to any of claim 1 to 4, wherein the nickel is present in an elemental weight percent of 2 to 6%.
Claim 6. A nickel-silicon catalyst according to any of claim 1 to 5, wherein the silicon oxide support is non-porous.
Claim 7. A nickel-silicon catalyst according to any of claim 1 to 6, wherein the silicon oxide support comprises nickel phyllosilicate.
Claim 8. A nickel-silicon catalyst according to any of claim 1 to 7, wherein the nickel-silicon catalyst according to the invention does not comprise any cobalt atom.
Claim 9. A nickel-silicon catalyst according to any of claim 1 to 8, wherein the nickel-silicon catalyst according to the invention does not comprise any element selected in the group of lanthanide and actinide, and does not contain indium, thallium, tin or lead.
Claim 10. A nickel-silicon catalyst according to any of claim 1 to 9, wherein the particule size is below 6 nm.
Claim 11. Process for the preparation of a metal-silicon catalyst for the dry reforming of methane reaction comprising the following steps:
1- suspending siliceous support in water ;
2- adding a mixture of M(N03)2 in the suspension according to step 1- ; 3- the mixture obtained in step 2- is allowed under stirring during at least 2 hours at a temperature and maintained between 20 and 60°C ;
4- evaporating the solvent ; and
5- the material obtained at step 4- is calcinated at least 2 h at 550°C.
Claim 12. Process according to claim 11, wherein the metal used is nickel.
Claim 13. Process according to any of claim 11 to 12, wherein step 1- comprise the addition of at least 2 ml_ of aqueous Nhb.
Claim 14. Process according to any of claim 11 to 13, wherein during step 1- the reaction time does not exceed 4 hours at 1 bar.
Claim 15. Process according to any of claim 11 to 14, wherein said siliceous support used is selected between mesoporous silica material and non- porous silica material.
Claim 16. A nickel-silicon catalyst according to any of claim 1 to 10, obtainable by the process according to any of claim 11 to 15.
PCT/IB2020/000597 2020-07-07 2020-07-07 Ni-silica-based catalysts with highly dispersed nickel particles WO2022008942A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
PCT/IB2020/000597 WO2022008942A1 (en) 2020-07-07 2020-07-07 Ni-silica-based catalysts with highly dispersed nickel particles
PCT/EP2021/068776 WO2022008573A2 (en) 2020-07-07 2021-07-07 Ni-silica-based catalysts with highly dispersed nickel particles

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/IB2020/000597 WO2022008942A1 (en) 2020-07-07 2020-07-07 Ni-silica-based catalysts with highly dispersed nickel particles

Publications (1)

Publication Number Publication Date
WO2022008942A1 true WO2022008942A1 (en) 2022-01-13

Family

ID=73059988

Family Applications (2)

Application Number Title Priority Date Filing Date
PCT/IB2020/000597 WO2022008942A1 (en) 2020-07-07 2020-07-07 Ni-silica-based catalysts with highly dispersed nickel particles
PCT/EP2021/068776 WO2022008573A2 (en) 2020-07-07 2021-07-07 Ni-silica-based catalysts with highly dispersed nickel particles

Family Applications After (1)

Application Number Title Priority Date Filing Date
PCT/EP2021/068776 WO2022008573A2 (en) 2020-07-07 2021-07-07 Ni-silica-based catalysts with highly dispersed nickel particles

Country Status (1)

Country Link
WO (2) WO2022008942A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114620686A (en) * 2022-04-02 2022-06-14 湘潭大学 Method for preparing synthesis gas through dry reforming reaction of methane and catalyst thereof

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008043060A2 (en) * 2006-10-05 2008-04-10 Research Triangle Institute Highly dispersed nickel hydrogenation catalysts and methods for making the same
WO2014125309A2 (en) * 2013-02-18 2014-08-21 Teesside University Supported metal catalyst
CN105964261A (en) * 2016-05-24 2016-09-28 昆明理工大学 Preparation method of anti-carbon accumulation and anti-sintering methane dry reforming Ni-based catalyst
WO2018203836A1 (en) * 2017-05-05 2018-11-08 National University Of Singapore Method of preparing a metal-silicon oxide catalyst
CN108855095A (en) * 2018-02-08 2018-11-23 贵州理工学院 Methane reforming multicore shell hollow type catalyst nickel-nisiloy hydrochlorate-SiO2Preparation method

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008043060A2 (en) * 2006-10-05 2008-04-10 Research Triangle Institute Highly dispersed nickel hydrogenation catalysts and methods for making the same
WO2014125309A2 (en) * 2013-02-18 2014-08-21 Teesside University Supported metal catalyst
CN105964261A (en) * 2016-05-24 2016-09-28 昆明理工大学 Preparation method of anti-carbon accumulation and anti-sintering methane dry reforming Ni-based catalyst
WO2018203836A1 (en) * 2017-05-05 2018-11-08 National University Of Singapore Method of preparing a metal-silicon oxide catalyst
CN108855095A (en) * 2018-02-08 2018-11-23 贵州理工学院 Methane reforming multicore shell hollow type catalyst nickel-nisiloy hydrochlorate-SiO2Preparation method

Non-Patent Citations (28)

* Cited by examiner, † Cited by third party
Title
B. ABDULLAH ET AL., J. OF CLEAN. PROD., vol. 162, 2017, pages 170 - 185
BARTOLOMEW C.H., CATAL. LETT., vol. 7, 1990, pages 27 - 51
BURATTIN P., J. PHYS. CHEM. B, vol. 101, 1997, pages 7060 - 7074
C. WANG, CATAL. SCI. TECHNOL., vol. 8, 2018, pages 4877 - 4890
CAS, no. 7631-86-9
CATAL. TODAY, vol. 339, 2020, pages 3 - 23
DAOURA ET AL.: "report the preparation of Ni catalyst containing MCF", J. CO UTIL., vol. 24, 2018, pages 112 - 119
E. P. BARRETT, JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol. 73, no. 1, 1951, pages 373 - 380
E. P. BARRETT: "The determination of pore volume and area distributions in porous substances. 1. Computations from nitrogen isotherms", JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, vol. 73, no. 1, 1951, pages 373 - 380, XP001145601, DOI: 10.1021/ja01145a126
F. FRUSTERI ET AL., CARBON, vol. 40, 2002, pages 1063 - 1070
J. H. KIM ET AL., APPL. CATAL. A GEN., vol. 197, 2000, pages 191 - 200
J. R. A. SIETSMA ET AL., ANGEW. CHEM. INT. ED., vol. 46, 2007, pages 4547 - 4549
K. NAGAOKA ET AL., APPL. CATAL. A, vol. 268, 2004, pages 151 - 158
KUBELKA P. ET AL., ZEITSCHRIFT FUR TECHNISCHE PHYSIK, vol. 12, 1931, pages 593 - 601
L. ESPINOSA-ALONSOETAL, J. AM. CHEM. SOC., vol. 131, no. 131, 2009, pages 16932 - 16938
L. QIAN, MICROP. MESOP. MATER., vol. 243, 2017, pages 301 - 310
L. TARPANI ET AL., CATAL. COMMUN., vol. 74, 2016, pages 28 - 32
L. XU ET AL., ACS CATAL, vol. 2, 2012, pages 1331 - 1342
M. BOUTROS, C. R. CHIMIE, vol. 21, 2018, pages 514 - 522
M. P. SEAH, SURFACE AND INTERFACE ANALYSIS, vol. 2, 1980, pages 222 - 239
NAGASH, CHEM. MATER., vol. 18, no. 10, 2006, pages 2480 - 2488
O. DAOURA ET AL., INT. J. HYDROGEN. ENERG., vol. 43, 2018, pages 17205 - 17215
S. M. KIM ET AL., J. AM. CHEM. SOC., vol. 139, 2017, pages 1937 - 1949
U. OEMAR U. ET AL., CATAL. SCI. TECHNOL., vol. 6, 2016, pages 1173 - 1186
W.-H. ZHANG ET AL., MICROP. MESOP. MATER., vol. 89, 2006, pages 179 - 185
Z. BIAN, J. CO2 UTIL., vol. 18, 2017, pages 345 - 352
Z. L. ZHANG ET AL., J. CATAL., vol. 158, 1996, pages 51 - 63
Z. LI ET AL., CATAL SCI. TECHNOL., vol. 8, 2018, pages 3363 - 3371

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114620686A (en) * 2022-04-02 2022-06-14 湘潭大学 Method for preparing synthesis gas through dry reforming reaction of methane and catalyst thereof

Also Published As

Publication number Publication date
WO2022008573A2 (en) 2022-01-13
WO2022008573A3 (en) 2022-03-03

Similar Documents

Publication Publication Date Title
Daoura et al. One-pot prepared mesoporous silica SBA-15-like monoliths with embedded Ni particles as selective and stable catalysts for methane dry reforming
Li et al. Co-doped MgAl-LDHs nanosheets supported Au nanoparticles for complete catalytic oxidation of HCHO at room temperature
Gálvez et al. Enhanced catalytic stability through non-conventional synthesis of Ni/SBA-15 for methane dry reforming at low temperatures
Zhang et al. Ni/Ln 2 Zr 2 O 7 (Ln= La, Pr, Sm and Y) catalysts for methane steam reforming: the effects of A site replacement
Yang et al. Steam CO2 reforming of methane over La1− xCexNiO3 perovskite catalysts
Siang et al. Methane bi-reforming over boron-doped Ni/SBA-15 catalyst: Longevity evaluation
Wang et al. Synthesis, characterization and catalytic performance of MgO-coated Ni/SBA-15 catalysts for methane dry reforming to syngas and hydrogen
Varisli et al. Hydrogen from ammonia over cobalt incorporated silicate structured catalysts prepared using different cobalt salts
Bian et al. Ni-based catalyst derived from Ni/Al hydrotalcite-like compounds by the urea hydrolysis method for CO methanation
Xiao et al. Dehydrogenation of propane over a hydrothermal-synthesized Ga 2 O 3–Al 2 O 3 catalyst in the presence of carbon dioxide
Sidik et al. CO 2 reforming of CH 4 over Ni/mesostructured silica nanoparticles (Ni/MSN)
Reddy et al. Reforming of methane with carbon dioxide over Pt/ZrO2/SiO2 catalysts—Effect of zirconia to silica ratio
Dai et al. Catalytic activity of mesoporous Ni/CNT, Ni/SBA-15 and (Cu, Ca, Mg, Mn, Co)–Ni/SBA-15 catalysts for CO 2 reforming of CH 4
Coelho et al. Effect of the active metal on the catalytic activity of the titanate nanotubes for dry reforming of methane
EP3638415A1 (en) Lanthanide-supported transition metal catalysts and uses thereof
Ahmad et al. Design of Ni/La2O3 catalysts for dry reforming of methane: Understanding the impact of synthesis methods
Li et al. Dry reforming of methane towards CO-rich hydrogen production over robust supported Ni catalyst on hierarchically structured monoclinic zirconia nanosheets
Sholeha et al. Enhanced CO 2 methanation at mild temperature on Ni/zeolite from kaolin: effect of metal–support interface
Daoura et al. Mesocellular silica foam-based Ni catalysts for dry reforming of CH4 (by CO2)
Ahmad et al. Solution combustion synthesis of Ni/La 2 O 3 for dry reforming of methane: tuning the basicity via alkali and alkaline earth metal oxide promoters
Sebai et al. Preparation and characterization of 5% Ni/γ-Al2O3 catalysts by complexation with NH3 derivatives active in methane steam reforming
Joshy et al. Surface basicity mediated rapid and selective adsorptive removal of Congo red over nanocrystalline mesoporous CeO 2
Wan et al. Facile synthesis of a sintering-resistant zeolite confined Ni catalyst for efficient CO x-free hydrogen generation from ammonia decomposition
Long et al. High active and coke-resistant CeNiO3-based catalyst for methane bi-reforming
Xia et al. NiO supported on Y 2 Ti 2 O 7 pyrochlore for CO 2 reforming of CH 4: insight into the monolayer dispersion threshold effect on coking resistance

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 20800982

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

122 Ep: pct application non-entry in european phase

Ref document number: 20800982

Country of ref document: EP

Kind code of ref document: A1