RU2446878C1 - Catalyst, method of producing support, method of producing catalyst and method of oxidising carbon monoxide - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to catalysts for low-temperature oxidation of carbon monoxide (CO), a method of producing said catalysts and a method of oxidising CO in order to protect the environment from CO pollution. The catalyst for oxidising carbon monoxide is a Pd/C-K composition, where: C is a mesoporous carbon material obtained via carbonisation of rice husks, K is kaolin which contains aluminium, silicon, titanium, iron and calcium oxides. The catalyst is made by saturating a nanocomposite carbon-containing support with an alcohol solution containing palladium nitrate with palladium content 2-5%,said support having the following texture characteristics: S_BET=450-470 m²/g, V_por=0.5-0.6 cm³/g, d_por=3.3-3.5 nm. The carbon-containing support is made through carbonisation of rice husks in a reactor with a copper-chromium catalyst fluidised-bed at temperature 450-470°C, through activation thereof with KCO₃ at temperature 850-900°C and then mixing with kaolin in weight ratio 2/3-1/1 and with water and then moulding. Carbon monoxide is oxidised in the presence or absence of water in a reaction mixture and the catalyst described above.

EFFECT: complete oxidation of carbon monoxide CO at room temperature and suitable moisture content.

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Description

The invention relates to catalysts for the low temperature oxidation of carbon monoxide (CO), a method for their preparation and a method for oxidizing CO in order to protect the environment from CO pollution.

Carbon monoxide is an extremely toxic gas. The effect of CO is based on the fact that it binds to blood hemoglobin more firmly and 200-300 times faster than oxygen. In this case, carboxyhemoglobin is formed, which blocks the processes of oxygen transportation and cellular respiration. The main sources of CO emissions are automobile transport, industrial enterprises, thermal power plants, etc. In the summer season, at an average outdoor temperature of 20 ° C, about 90% of the outside air admixtures penetrate into the living quarters, and 40% in the transition period at a temperature of 25 ° C.

Another danger to humans is closed industrial and residential premises, for example, production shops, vegetable stores, submarines, space stations, etc. It is known that the average daily release of CO by humans is 780 mg. In this case, the MPC for CO is 5 mg / m ³ . A concentration of CO in the air of more than 0.1% (1250 mg / m ³ ) leads to death within 1 h. For example, with a room volume of 60 m ³ and one person in it, the concentration of CO will exceed the MPC by 2.6 times during the day. Therefore, it is necessary to clean the air of industrial and residential premises from carbon monoxide.

An analysis of the literature indicates that the problem of protecting the atmosphere from carbon monoxide does not lose its relevance so far. The solution to this problem is mainly associated with catalytic methods of neutralization. Analysis of ways to reduce carbon monoxide shows that the most effective is the use of oxidative catalysts for gas purification from CO. A distinctive feature of CO oxidation in these cases is that the concentration of CO is low and varies within the range of 100–1000 ppm, while the oxidation should occur at ambient temperature and humidity. These conditions impose certain requirements on catalytic systems and methods for testing them. In particular, the catalysts must operate stably at low (room) temperature and ambient humidity, which is accompanied by condensation of water in the micro / mesopores of the hydrophilic carrier. Accordingly, catalytic systems, in addition to high activity, must have hydrophobic properties to ensure their stable operation at a certain ambient humidity. Therefore, the search for active and stable catalysts for low temperature CO oxidation continues.

One possible approach is to use a hydrophobic carrier for which there are no such problems. It is known that porous carbon-containing materials, such as activated carbon, sibunite, have hydrophobic properties.

Known catalyst 0.3% Pt / C (C - activated carbon, pre-calcined at 400 or 800 ° C in a stream of nitrogen and washed with hydrofluoric acid to remove surface impurities) [JC-S.Wu, Z.-A.Lin, F.- M. Tsai, J.-W. Pan, Low temperature complete oxidation of BTX on Pt / activated carbon catalysts Catalysis Today 63 (2000) 419-426]. The catalyst was prepared by impregnating the carrier in terms of moisture capacity with a solution of H ₂ PtCl ₆ xH ₂ O followed by reduction of H ₂ at 300 ° C for 2 hours. A Pt / Al ₂ O ₃ catalyst was prepared for comparison. It was shown that the Pt / C catalyst is active in the oxidation of benzene, toluene, and xylene: the temperature at which 50% conversion is achieved varies in the range 130–170 ° C, which is approximately 10–15 ° C lower than in Pt / Al ₂ O ₃ . However, the introduction of 6% water into the reaction mixture leads to a slight decrease in the activity of the Pt / C catalyst.

CuO / AC catalysts are known [JWHSmith, P. Westreich, H. Abdellatif, P. Filbee-Dexter, AJSmith, TEWood, LMCroll, JHReynolds, JRDahn. The investigation of copper-based impregnated activated carbons prepared from water-soluble materials for broad spectrum respirator applications. // J. Hazard. Mater. 180 (2010) 419-428], which were obtained by impregnating granules (0.5-1.7 mm) of activated carbon synthesized from coconut husk with an aqueous solution of Cu (NO ₃ ) ₂ or a mixed aqueous solution of Cu (NO ₃ ) ₂ and Na ₂ MoO ₄ designed to absorb gases containing SO ₂ , NH ₃ , HCN.

Catalysts are known [US 4212854, B01D 53/62; B01D 53/86; B01J 23/40], representing the composition Pd / Pt / activated carbon / Na ₂ CO ₃ . It was shown that at an initial CO concentration of 100 ppm, a H ₂ O content of 1.5 or 2.5 vol.% And a mixture volume velocity of 12000 h ^-1 , the CO conversion reaches 80% at 30 and 20 ° C on catalysts containing 0.5% Pd and 0.3% Pd-0.3% Pt, respectively; the catalyst works more efficiently in a humid environment (0.6% H ₂ O). The disadvantage of such catalysts is the incomplete conversion of CO at a temperature of 20 ° C.

Closest to the proposed technical solution, which is taken as a prototype, is a catalyst (0.5 ÷ 2.0)% Pt / C [US 4652537, B01J 23/42; B01D 53/86; B01J 31/06; B01J 037/34] obtained by treating activated carbon pretreated with hydrochloric acid at 90 ° C for 4 hours with an aqueous solution of H ₂ PxCl ₆ x6H ₂ O at 90 ° C for 4 hours followed by cooling to room temperature and adding to the resulting suspension with stirring an aqueous solution of Na ₂ CO ₃ for 30 minutes The resulting suspension was cooled to 0 ° C and at this temperature, platinum was reduced with an aqueous solution of KBH ₄ for 2 hours. Then the suspension was filtered, the precipitate was washed with hot water and the precipitate was dried at 120 ° C, 2 h. The resulting catalyst was treated with 3% H ₂ O ₂ at room temperature for 1 h, then dried at 20 ° C, 2 h

The activity of the catalysts was determined in the oxidation reaction of CO, the concentration of which in the reaction mixture was 1590-2360 ppm, at room temperature and humidity; the volumetric feed rate of the reaction mixture was 5000 and 10000 h ^-1 . It was shown that the conversion of CO using 0.5% Pt / C catalyst is 68% at a space velocity of 5000 h ^-1 . An increase in platinum up to 2%, i.e. the use of a 2% Pt / C catalyst can increase the conversion of CO to 98% at a space velocity of 5000 h ^-1 ; however, an increase in space velocity to 10,000 h ⁻¹ leads to a decrease in CO conversion to 96%.

The disadvantage of this catalyst is that, firstly, when the volumetric feed rate of the reaction mixture is 10,000 h ^-1 , it does not provide 100% CO conversion at room temperature and humidity; secondly, it is obtained by a complex multi-stage procedure for applying the active component using a chlorine-containing precursor and treatment with appropriate solutions.

The objective of the invention is to develop a granular catalyst, which is a palladium deposited on a molded nanocomposite carbon-containing material, providing complete oxidation of CO at room temperature and appropriate humidity.

To solve this problem, a carbon monoxide oxidation catalyst is proposed containing a noble metal of the platinum group deposited on a carbon-containing support, which is a Pd / CK composition, where: C is a mesoporous carbon material obtained by carbonization of rice husk, K is kaolin including aluminum oxides, silicon, titanium, iron and calcium. The palladium content in the catalyst is 2 ÷ 5 wt.%. The ratio C / K is 2/3 ÷ 1/1.

The problem is also solved by the method of preparation of a carbon-containing carrier, which is prepared by carbonization of rice husk in a reactor with a fluidized bed of copper-chromium catalyst at a temperature of 450-470 ° C, its activation with potassium carbonate KCO ₃ at a temperature of 850-900 ° C and subsequent mixing with kaolin in bulk ratio 2/3 ÷ 1/1 and water and molding, the obtained nanocomposite carbon-containing carrier has the following texture characteristics: S _BET = 450-470 m ² / g, V _then = 0.5-0.6 cm ³ / g, d _then = 3.3-3.5 nm.

The problem is also solved by the method of preparation of the catalyst, which is prepared by impregnation with an alcohol solution containing palladium nitrate in terms of Pd 2 ÷ 5%, a nanocomposite carbon-containing carrier with texture characteristics: S _BET = 450-470 m ² / g, V _pore = 0.5- 0.6 cm ³ / g, d _pore = 3.3-3.5 nm.

The catalyst is dried and calcined at a temperature of 300-320 ° C in an inert atmosphere.

The problem is also solved by the method of oxidation of carbon monoxide in the presence of water and a catalyst, which is carried out in the presence of the catalyst described above. The concentration of carbon monoxide in the reaction mixture is not higher than 100 ppm.

The oxidation of carbon monoxide is carried out in the presence of water in the reaction mixture corresponding to the vapor pressure at a temperature of 20 ° C.

The oxidation of carbon monoxide can also be carried out in the absence of water in the reaction mixture.

The oxidation of carbon monoxide is carried out by feeding the reaction mixture with a space velocity of 5000 h ^-1 - 24000 h ^-1 .

Distinctive features of the proposed catalyst and method for its preparation are:

1. The active component of the catalyst is Pd, and the carrier is a molded carbon nanocomposite material that combines activated carbon and kaolin, taken in a mass ratio of 2/3 ÷ 1/1.

2. A method of preparing a molded carbon nanocomposite material, including the carbonization of rice husk in a fluidized bed reactor at 450-470 ° C, followed by mixing with powdered potassium carbonate, calcining at 850-900 ° C and washing with distilled water to a neutral medium with an intermediate washing with a 3M HCl solution. The obtained carbon material is dried at 120 ° C to constant weight and mixed with kaolin in a mass ratio of 2/3 ÷ 1/1 in the presence of water to obtain a paste, which is molded as extrudates, dried at 120 ° C and calcined at 900 ° C.

3. The method of applying the active component, including impregnating the carrier with an alcoholic solution of palladium nitrate.

4. The method of oxidation of carbon monoxide, the concentration of which is 100 ppm, while the reaction mixture is supplied with a space velocity equal to 24000 h ^-1 .

Testing of the catalysts in the CO oxidation reaction is carried out in an automated setup with a flow reactor and mass spectrometric analysis of the gas mixture using a quadrupole mass spectrometer (Stanford Research Systems, QMS 200 Gas Analyzer) at room temperature in the absence and presence of water. The initial catalyst fraction 0.25-0.5 mm, cooled to a temperature of 20 ° C, serves the reaction mixture at a speed of 500 cm ³ / min, containing:

1) 100 ppm CO, 1.0 vol.% O ₂ , 0.5 vol.% Ne, balance - helium;

2) 100 ppm CO, 1.0 vol.% O ₂ , 0.5 vol.% Ne, H ₂ O, corresponding to vapor pressure at a temperature of 20 ° C, balance - helium.

The volumetric feed rate of the reaction mixture is 24000 h ^-1 . During the reaction, the concentrations of CO, O ₂ and CO ₂ are monitored. The concentration measurement at each point is carried out with a frequency of 0.34 Hz.

The essence of the invention is illustrated by the following examples, showing the change in activity (temperatures at which the corresponding degrees of conversion of carbon monoxide are reached) depending on the palladium content in the catalyst, the method for their preparation and CO oxidation in the absence and presence of water in the reaction mixture.

The main characteristics of the catalysts and the conversion of CO are shown in Fig.1-7.

Examples 1-6 illustrate the composition and method of producing catalysts, which is a Pd-containing active component deposited on a nanocomposite carbon-containing carrier, characterized by a high specific surface, while the oxidation of carbon monoxide is carried out at room temperature and a volumetric feed rate of the reaction mixture of 24000 ^-1 , in the absence and presence of water, corresponding to vapor pressure at a temperature of 20 ° C.

Example 1

30 g of rice husk (lignin content - 15 wt.%, Cellulose - 31%, ash - 19%) are carbonized in a fluidized bed reactor with a copper-chromium supported catalyst composition: 1.75% (wt.) CuO + 3.5% MgO + 6.5% Cr ₂ O ₃ deposited on γ-Al ₂ O ₃ at a temperature of 465 ° C with a contact time of 2.5 seconds and α = 1.5. Activation is carried out using KCO ₃ at 900 ° C for 1 h. The heating rate to the activation temperature is 5 ° C / min. After activation and washing, the product is mixed with kaolin in a mass ratio to carbon of 1: 1 and water to obtain a moldable paste, which is molded using an extruder with a die with a diameter of 6 mm. After molding, the granules are dried at 120 ° C and calcined at 900 ° C for 1 h. The obtained carbon-containing material - CK has S _BET = 462 m ² / g, V _pore = 0.5 cm ³ / g, d _pore = 3, 3 nm.

A portion of CK equal to 0.3604 g is poured into 2 ml of an alcohol solution containing 0.0244 g of Pd (NO ₃ ) ₂ ; the resulting catalyst is dried at room temperature, and then calcined at 300 ° C in an inert atmosphere for 2 hours. The catalyst has a composition of: 1% Pd / CK.

Example 2

30 g of rice husk (lignin content - 15 wt.%, Cellulose - 31%, ash - 19%) are carbonized in a fluidized bed reactor with a copper-chromium supported catalyst composition: 1.75% (wt.) CuO + 3.5% MgO + 6.5% Cr ₂ O ₃ deposited on γ-Al ₂ O ₃ at a temperature of 450 ° C with a contact time of 2.5 seconds and α = 1.5. Activation is carried out using KCO ₃ at 850 ° C for 1 h. The heating rate to the activation temperature is 5 ° C / min. After activation and washing, the product is mixed with kaolin in a mass ratio to carbon of 2: 3 and water to obtain a moldable paste, which is molded using an extruder with a die with a diameter of 6 mm. After molding, the granules are dried at 120 ° C and calcined at 900 ° C for 1 h. The resulting carbon-containing material - CK has S _BET = 450 m ² / g, V _pore = 0.6 cm ³ / g, d _pore = 3, 5 nm.

A portion of CK equal to 0.4075 g, pour 2.2 ml of an alcohol solution containing 0.0556 g of Pd (NO ₃ ) ₂ ; the resulting catalyst is dried at room temperature and then calcined at 300 ° C in an inert atmosphere for 2 hours. The catalyst has a composition of: 2% Pd / CK.

Example 3

Similar to example 1, the difference is that a CK sample of 0.4439 g is poured into 2.4 ml of an alcohol solution containing 0.124 g of Pd (NO ₃ ) ₂ . The catalyst has a composition of: 4% Pd / CK.

Example 4

Similar to example 1, the difference is that a CK sample of 0.8205 g is poured into 4.1 ml of an alcohol solution containing 0.2895 g of Pd (NO ₃ ) ₂ . The catalyst has a composition of: 5% Pd / CK.

Example 5

Similar to example 4, the difference is that the catalyst is calcined at 150 ° C in an inert atmosphere for 2 hours. The catalyst has a composition of: 5% Pd / C-K.

Example 6

Similar to example 4, the difference is that the catalyst is calcined at 320 ° C in an inert atmosphere for 2 hours. The catalyst has a composition of: 5% Pd / C-K.

Example 7

Similar to example 2, the difference is that the catalyst 2% Pd / CK is tested in the reaction mixture supplied with a space velocity of 5000 h ^-1 .

The oxidation rates of CO in all examples are shown in Fig.1-7.

Figure 1. Time versus CO conversion for a 1% Pd / C-K catalyst calcined at 300 ° C.

Figure 2. Time versus CO conversion for a 2% Pd / C-K catalyst calcined at 300 ° C.

Figure 3. Time versus CO conversion for 4% Pd / C-K catalyst calcined at 300 ° C.

Figure 4. Time versus CO conversion for a 5% Pd / C-K catalyst calcined at 300 ° C.

Figure 5. Time versus CO conversion for a 5% Pd / C-K catalyst calcined at 150 ° C.

6. Time versus CO conversion for a 5% Pd / C-K catalyst calcined at 320 ° C.

7. Time versus CO conversion for a 2% Pd / C-K catalyst calcined at 300 ° C.

As can be seen from the above examples and Fig., The proposed Pd / C-K catalysts can solve the problem of effective oxidation of CO at its concentration in the reaction mixture equal to 100 ppm, if the Pd content is 4-5%; moreover, the catalysts work more efficiently in the presence of water: on a 5% Pd / C-K catalyst, the CO conversion reaches 100%; at the same time, on this catalyst, in the absence of water in the reaction mixture, CO conversion reaches only 90%, and after 40 minutes of catalyst operation, it gradually decreases to 25%.

The decrease in the palladium content in the catalyst is accompanied by a decrease in its activity: the conversion of CO in the presence of water is 90% and remains unchanged during operation of the 4% Pd / C-K catalyst; when using a 2% Pd / C-K catalyst, the CO conversion only at the initial moment reaches 90%, and then after 4 minutes it decreases to 40% and remains unchanged; 1% Pd / C-K catalyst is inactive. The conversion of CO on 4% Pd / C-K and 2% Pd / C-K catalysts in the absence of water is lower and they work less stable. Thus, a 5% Pd / C-K catalyst provides effective CO removal at room temperature and humidity.

On the one hand, 5% Pd is a relatively high noble metal content. However, it should be noted that the bulk density of this catalyst is not comparable with the density, for example, 2% Pd / Al ₂ O ₃ , which according to [SU 1833204, B01J 37/02; B01J 23/44] also has low temperature activity: at room temperature, the catalyst provides 75% CO conversion in the region of CO concentrations close to the MPC. It turned out that the bulk density of 5% Pd / CK and 2% Pd / Al ₂ O ₃ catalysts is 0.204 and 0.601 g / cm ^3, respectively, therefore, when loading 0.5 cm ^{3 of} catalyst into the reactor, the catalyst weights will be 0.102 and 0.297 g; and the palladium content in them will be comparable, namely: 0.0051 and 0.0059 g of Pd. Therefore, the proposed 5% Pd / CK catalyst does not increase the palladium consumption relative to the 2% Pd / Al ₂ O ₃ catalyst and reduces the cost compared to the 2% Pt / C catalyst used as a prototype.

On the other hand, the activity of the proposed catalysts increases with a decrease in the volumetric feed rate of the reaction mixture, since the contact time is increased and, as shown in the prototype, the conversion, ceteris paribus, increases; this is also confirmed in the proposed application: a decrease in the volumetric feed rate of the reaction mixture from 24000 to 5000 h ^-1 allows to increase the conversion of CO from 40 to 90% when using a 2% Pd / CK catalyst.

Claims (9)

1. The catalyst for the oxidation of carbon monoxide containing a noble metal of the platinum group deposited on a carbon-containing carrier, characterized in that it is a Pd / CK composition, where C is a mesoporous carbon material obtained by carbonization of rice husk, K is kaolin, including aluminum oxides, silicon, titanium, iron and calcium, carbon nanocomposite carrier С-K has the following texture characteristics: S _BET = 450-470 m ² / g, V _por = 0.5-0.6 cm ³ / g, d _por = 3, 3-3.5 nm, and the palladium content is 2 ÷ 5 wt.%. 2. The catalyst according to claim 1, characterized in that the C / K ratio is 2/3 ÷ 1/1. 3. A method of preparing a carbon-containing support for a carbon monoxide oxidation catalyst, characterized in that the carbon-containing support is prepared by carbonizing rice husk in a fluidized bed copper-chromium catalyst reactor at a temperature of 450-470 ° C, activating its KCO ₃ at a temperature of 850-900 ° C and subsequent mixing with kaolin in a mass ratio of 2/3 ÷ 1/1 and water and molding, the resulting nanocomposite carbon-containing carrier has the following texture characteristics: S _BET = 450-470 m ² / g, V _then = 0.5-0.6 cm ³ / g, d _pore = 3.3-3.5 nm. 4. The method of preparation of the catalyst for the oxidation of carbon monoxide containing a noble metal of the platinum group deposited on a carbon-containing carrier, with subsequent stages of drying and calcination at a temperature of 300-320 ° C in an inert atmosphere, characterized in that the catalyst is prepared by impregnation with an alcohol solution containing nitrogen acid palladium in terms of Pd 2 ÷ 5%, carbon nanocomposite carrier with texture characteristics: S _BET = 450-470 m ² / g, V _pore = 0.5-0.6 cm ² / g, d _pore = 3.3 -3.5 nm to obtain the composition Pd / CK, where C is mez the porous carbon material produced by carbonizing rice husk, K - kaolin comprising aluminum oxides, silicon, titanium, iron and calcium. 5. The method of oxidation of carbon monoxide in the presence of water and a catalyst, characterized in that it is carried out in the presence of a catalyst according to any one of claims 1 and 2 or prepared according to claim 4. 6. A method according to claim 5, characterized in that the concentration of carbon monoxide in the reaction mixture is not more than 100 million ^-1. 7. The method according to claim 5, characterized in that the oxidation of carbon monoxide is carried out in the presence of water in the reaction mixture corresponding to vapor pressure at a temperature of 20 ° C. 8. The method according to claim 5, characterized in that the oxidation of carbon monoxide can be carried out in the absence of water in the reaction mixture. 9. The method according to claim 5, characterized in that the oxidation of carbon monoxide is carried out by feeding the reaction mixture with a space velocity of 5000 h ^-l - 24000 h ^-l .

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