CN108114724B - Preparation method of low temperature catalyst for carbon monoxide water vapor shift - Google Patents

Abstract

The invention discloses a preparation method of a carbon monoxide water vapor shift low-temperature catalyst, and belongs to the technical field of catalysis. The specific content of the method is as follows: dropping a precipitant into a solution containing zinc salt and carrier γ-Al ₂ O ₃ to prepare a zinc hydroxide suspension. Then the precipitant solution and the copper salt solution are added dropwise to the zinc hydroxide suspension simultaneously, the pH value of the solution is adjusted and continuously stirred, and then through suction filtration, washing, drying and roasting, Cu-Zn/γ-Al ₂ is obtained. O ₃ catalyst; the Cu content is 20-40wt%, and the copper-zinc molar ratio is 1:1. The catalyst prepared by this method performs water-steam shift reaction in typical reformed gas, has high activity and stability, and shows higher reactivity than the catalyst prepared by traditional co-precipitation method.

Description

Preparation method of low temperature catalyst for carbon monoxide water vapor shift

Technical field:

The invention belongs to the technical field of catalysis, and in particular relates to a preparation method of a low temperature catalyst for carbon monoxide water vapor shift.

Background technique:

With the advancement of science and technology and the growth of the world's population, the problem of energy shortage has attracted more and more attention. At present, the demand of fossil energy is increasing and the reserves are decreasing day by day. The development of new sustainable energy sources has become one of the most concerned issues in today's society. As a new type of energy, hydrogen energy has the advantages of clean and non-polluting, high combustion calorific value, good thermal conductivity, and recyclable combustion products. Among them, hydrogen production by reforming compounds such as methanol and natural gas is used as a hydrogen source for fuel cells, which has always attracted the attention of researchers. However, the reformed gas usually contains 5%-20% CO, which will lead to the poisoning of the platinum electrode of the proton exchange membrane fuel cell and then seriously degrade the performance of the cell. Therefore, it is necessary to reduce the CO content in the reformed gas, for example by a water-steam shift reaction (CO+ _H2O = _CO2 + _H2 ). The water vapor shift reaction produces the same volume of hydrogen while eliminating CO. In addition, the water-steam shift reaction has been widely used in the synthesis of ammonia, synthesis of methanol, gasoline and the adjustment of the hydrocarbon ratio in the production of synthetic gasoline and the city gas industry. Commercially used shift catalysts are mainly divided into high temperature shift catalysts, low temperature shift catalysts and wide temperature shift catalysts. Low-temperature shift catalysts are generally copper-zinc catalysts, which have high reactivity, but have disadvantages such as poor thermal stability, poor selectivity, and easy contact with air. At present, catalysts are mainly prepared by co-precipitation method. Many factors in the preparation process will lead to low repeatability of catalysts. For example, common factors include pH value, precipitating agent, precipitation temperature, aging time, etc. In view of the importance of water vapor change reaction in industrial processes and the application prospect of purifying hydrogen gas in fuel cell electric vehicles, countries around the world have mainly carried out extensive research on production processes and catalyst preparation, in order to achieve high synthesis activity and stability. Catalysts with good performance and high reproducibility. In view of the deficiencies of the existing catalysts, a nanocomposite structure Cu/ZnAl ₂ O ₄ low temperature water gas shift catalyst with good low temperature activity, thermal stability and long-term stability was synthesized in Chinese patent (CN201510678685.X). It can be seen that the development of a low-temperature water-vapor shift catalyst with high activity and good stability has become one of the keys for this type of catalyst to be suitable for a wider range of reaction systems.

Invention content:

The purpose of the present invention is to provide a preparation method of nanometer Cu-Zn/γ-Al ₂ O ₃ low temperature water vapor shift catalyst with good low temperature activity and stability.

In the preparation method of a carbon monoxide water vapor shift low-temperature catalyst provided by the present invention, the active components of the catalyst are Cu and Zn, the carrier is γ-Al ₂ O ₃ , the Cu content is 20-40wt%, and the copper-zinc molar ratio is 1:1 Precipitate is prepared by distributed precipitation method, and then through suction filtration, washing, drying and roasting, the Cu-Zn/γ-Al ₂ O ₃ catalyst is obtained; the specific steps of the preparation method are as follows:

(1) Prepare a precipitant solution of a certain concentration, add dropwise to a solution containing zinc salt and carrier γ-Al ₂ O ₃ and continuously stir until the pH value is 9 to obtain a zinc hydroxide suspension, and continue after the titration is completed. Stir for 40min;

(2) prepare a copper salt solution of a certain concentration, slowly drop the precipitant solution and the copper salt solution in the step (1) into the zinc hydroxide suspension obtained in the step (1), continuously Stir and keep the pH value at 8. When the copper salt is added dropwise, continue to add the precipitant solution to the pH value of 9. The obtained suspension is stirred in a 60°C water bath for 2-4 hours, then suction filtered, and Wash with distilled water to pH 7, and dry the solid in an oven at 80°C for 12-24h to obtain a precipitate precursor;

(3) calcining the precipitation precursor at 400° C. for 2 hours in an oxidizing atmosphere to prepare the carbon monoxide water vapor shift low-temperature catalyst Cu-Zn/γ-Al ₂ O ₃ .

The copper salt is Cu(NO ₃ ) ₂ ·3H ₂ O, CuSO ₄ ·5H ₂ O or CuCl ₂ ·2H ₂ O, and the concentration is 0.06-0.15mol/L; the zinc salt is Zn(NO ₃ ) ₂ 6H ₂ O, ZnSO ₄ , 7H ₂ O or ZnCl ₂ , the concentration is 0.05-0.12 mol/L; the precipitating agent is any one of ammonia water, sodium carbonate, sodium hydroxide, and sodium bicarbonate, and the concentration is 0.4mol/L; the oxidizing atmosphere is any one of air, oxygen or a mixture of oxygen and nitrogen

The specific catalyst evaluation method used in the present invention is as follows: the evaluation device adopts a fixed bed reactor; the raw material gas is 3% CO, 12% H ₂ O, and N ₂ is balanced. The catalyst loading amount is 0.06g; the reaction temperature is 150-300°C, and the space velocity is 30000mL/(g·h). The reaction was carried out under normal pressure conditions, and the gas was detected online by a gas chromatograph after passing through the catalyst.

The present invention has the following technical characteristics:

1. The Cu-Zn/γ-Al ₂ O ₃ catalyst of the present invention has a nanocomposite structure, and the active components are CuO and ZnO.

2. Compared with the catalyst prepared by the traditional co-precipitation method, the Cu-Zn/γ-Al ₂ O ₃ catalyst of the present invention has good low-temperature activity and stability for the water-steam shift reaction, and has a good application prospect.

Description of drawings:

Figure 1 shows the catalytic activity of the Cu-Zn/γ-Al ₂ O ₃ catalyst prepared by the distributed precipitation method and the Cu-Zn/γ-Al ₂ O ₃ catalyst prepared by the co-precipitation method in the water-steam shift reaction.

Figure 2 shows the stability of the Cu-Zn/γ-Al ₂ O ₃ catalyst prepared by the distributed precipitation method and the Cu-Zn/γ-Al ₂ O ₃ catalyst prepared by the co-precipitation method in the water-steam shift reaction.

Detailed ways:

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, but the present invention is not limited to the following embodiments.

Example 1:

(1) Weigh 4.242g Na ₂ CO ₃ into a 100ml volumetric flask, add distilled water and shake to constant volume, as a precipitant for later use. Weigh 1.175g of Zn(NO ₃ ) ₂ ·6H ₂ O into a 100ml beaker, add 50ml of distilled water to dissolve, and then add 0.103g of technical grade γ-Al ₂ O ₃ . The Na ₂ CO ₃ solution was slowly added dropwise to the above-mentioned Zn salt-containing solution at room temperature, and the dropwise addition was stopped when the end point was pH=9, to obtain a zinc hydroxide suspension. After the dropwise addition was completed, stirring was continued for 40 min.

(2) Weigh 0.947g of Cu(NO ₃ ) ₂ ·3H ₂ O into a 100ml beaker, add 50ml of distilled water to dissolve. The precipitant Na ₂ CO ₃ solution and the above-mentioned Cu salt solution were slowly added dropwise to the zinc hydroxide suspension at the same time, with constant stirring during the simultaneous dropwise addition, and the pH was controlled to be about 8. When the copper salt was added dropwise, the precipitant Na ₂ CO ₃ solution was continued to be added dropwise until the pH was 9. The obtained suspension was further stirred in a 60° C. water bath for 2 h, then suction filtered and washed with distilled water until the pH was 7. The solid was dried in an oven at 80°C for 12-24h to obtain a precipitate precursor. The precipitate precursor was calcined at 400 °C for 2 h in an air atmosphere to obtain a Cu-Zn/γ-Al ₂ O ₃ (SP) catalyst.

Example 2:

(1) Weigh 4.247g Na ₂ CO ₃ into a 100ml volumetric flask, add distilled water and shake to constant volume, as a precipitant for later use. Weigh 1.155g of ZnSO ₄ ·7H ₂ O into a 100ml beaker, add 50ml of distilled water to dissolve, and then add 0.105g of technical grade γ-Al ₂ O ₃ . The Na ₂ CO ₃ solution was slowly added dropwise to the solution containing the Zn salt at room temperature, and the dropwise addition was stopped when the end point was pH=9, to obtain a zinc hydroxide suspension. After the dropwise addition was completed, stirring was continued for 40 min.

(2) Weigh 0.945g of Cu(NO ₃ ) ₂ ·3H ₂ O into a 100ml beaker, add 50ml of distilled water to dissolve. The precipitant Na ₂ CO ₃ solution and the above-mentioned Cu salt solution were slowly added dropwise to the zinc hydroxide suspension at the same time, with constant stirring during the simultaneous dropwise addition, and the pH was controlled to be about 8. When the copper salt was added dropwise, the precipitant Na ₂ CO ₃ solution was continued to be added dropwise until the pH was 9. The obtained suspension was further stirred in a 60° C. water bath for 2 h, then suction filtered and washed with distilled water until the pH was 7. The solid was dried in an oven at 80°C for 12-24h to obtain a precipitate precursor. The precipitate precursor was calcined at 400 °C for 2 h in an air atmosphere to obtain a Cu-Zn/γ-Al ₂ O ₃ (SP) catalyst.

Example 3:

(1) Weigh 4.243g Na ₂ CO ₃ into a 100ml volumetric flask, add distilled water and shake to constant volume, as a precipitant for later use. Weigh 0.688g of ZnCl ₂ ·2H ₂ O into a 100ml beaker, add 50ml of distilled water to dissolve, and then add 0.102g of technical grade γ-Al ₂ O ₃ . The Na ₂ CO ₃ solution was slowly added dropwise to the solution containing the Zn salt at room temperature, and the dropwise addition was stopped when the end point was pH=9, to obtain a zinc hydroxide suspension. After the dropwise addition was completed, stirring was continued for 40 min.

(2) Weigh 0.941 g of Cu(NO ₃ ) ₂ ·3H ₂ O into a 100 ml beaker, and add 50 ml of distilled water to dissolve. The precipitant Na ₂ CO ₃ solution and the above-mentioned Cu salt solution were slowly added dropwise to the zinc hydroxide suspension at the same time, with constant stirring during the simultaneous dropwise addition, and the pH was controlled to be about 8. When the copper salt was added dropwise, the precipitant Na ₂ CO ₃ solution was continued to be added dropwise until the pH was 9. The obtained suspension was further stirred in a 60° C. water bath for 2 h, then suction filtered and washed with distilled water until the pH was 7. The solid was dried in an oven at 80°C for 12-24h to obtain a precipitate precursor. The precipitate precursor was calcined at 400 °C for 2 h in an air atmosphere to obtain a Cu-Zn/γ-Al ₂ O ₃ (SP) catalyst.

Example 4:

(1) Weigh 4.242g Na ₂ CO ₃ into a 100ml volumetric flask, add distilled water and shake to constant volume, as a precipitant for later use. Weigh 1.178g of Zn(NO ₃ ) ₂ ·6H ₂ O into a 100ml beaker, add 50ml of distilled water to dissolve, and then add 0.103g of technical grade γ-Al ₂ O ₃ . The Na ₂ CO ₃ solution was slowly added dropwise to the solution containing the Zn salt at room temperature, and the dropwise addition was stopped when the end point was pH=9, to obtain a zinc hydroxide suspension. After the dropwise addition was completed, stirring was continued for 40 min.

(2) Weigh 1.003g of CuSO ₄ ·3H ₂ O into a 100ml beaker, add 50ml of distilled water to dissolve. The precipitant Na ₂ CO ₃ solution and the above-mentioned Cu salt solution were slowly added dropwise to the zinc hydroxide suspension at the same time, with constant stirring during the simultaneous dropwise addition, and the pH was controlled to be about 8. When the copper salt was added dropwise, the precipitant Na ₂ CO ₃ solution was continued to be added dropwise until the pH was 9. The obtained suspension was further stirred in a 60° C. water bath for 2 h, then suction filtered and washed with distilled water until the pH was 7. The solid was dried in an oven at 80°C for 12-24h to obtain a precipitate precursor. The precipitate precursor was calcined at 400 °C for 2 h in an air atmosphere to obtain a Cu-Zn/γ-Al ₂ O ₃ (SP) catalyst.

Example 5:

(1) Weigh 4.240g Na ₂ CO ₃ into a 100ml volumetric flask, add distilled water and shake to constant volume, as a precipitant for later use. Weigh 1.172g of Zn(NO ₃ ) ₂ ·6H ₂ O into a 100ml beaker, add 50ml of distilled water to dissolve, and then add 0.103g of technical grade γ-Al ₂ O ₃ . The Na ₂ CO ₃ solution was slowly added dropwise to the solution containing the Zn salt at room temperature, and the dropwise addition was stopped when the end point was pH=9, to obtain a zinc hydroxide suspension. After the dropwise addition was completed, stirring was continued for 40 min.

(2) Weigh 0.535g of CuCl ₂ ·3H ₂ O into a 100ml beaker, add 50ml of distilled water to dissolve. The precipitant Na ₂ CO ₃ solution and the above-mentioned Cu salt solution were slowly added dropwise to the zinc hydroxide suspension at the same time, with constant stirring during the simultaneous dropwise addition, and the pH was controlled to be about 8. When the copper salt was added dropwise, the precipitant Na ₂ CO ₃ solution was continued to be added dropwise until the pH was 9. The obtained suspension was further stirred in a 60° C. water bath for 2 h, then suction filtered and washed with distilled water until the pH was 7. The solid was dried in an oven at 80°C for 12-24h to obtain a precipitate precursor. The precipitate precursor was calcined at 400 °C for 2 h in an air atmosphere to obtain a Cu-Zn/γ-Al ₂ O ₃ (SP) catalyst.

Example 6:

Weigh 4.244g Na ₂ CO ₃ into a 100ml volumetric flask, add distilled water and shake to constant volume, as a precipitant for later use. Weigh 1.168g Zn(NO ₃ ) ₂ ·6H ₂ O and 0.946g Cu(NO ₃ ) ₂ ·3H ₂ O respectively into a 100ml beaker, add 50ml distilled water to dissolve, and then add 0.106g technical grade γ-Al ₂ O ₃ . After ultrasonically dispersed uniformly, Na ₂ CO ₃ solution was slowly added dropwise to the above solution containing Cu salt and Zn salt at room temperature, and the dropwise addition was stopped when the end point was pH=9 with constant stirring. After the titration, the mixture was heated and stirred in a water bath at 60°C for 4 hours, then filtered with suction and washed with distilled water until the pH was 7. The solid was dried in an oven at 80°C for 12-24h, and then calcined at 400°C for 2h in an air atmosphere to obtain a Cu-Zn/γ-Al ₂ O ₃ (CP) catalyst.

Example 7:

The catalyst prepared above was sieved, and 0.06 g of the catalyst with a particle size of 20-40 mesh was weighed, and the performance test of the water vapor shift reaction was carried out on a fixed-bed quartz tube reactor. The inner diameter of the quartz tube was 8 mm, and the air velocity of the reaction gas was 30000 mL/(g·h). The composition of the reaction gas by volume is: 3% CO, 12% H ₂ O, 85% N ₂ . The samples were raised from room temperature to 400°C in an air atmosphere of 30ml/min and kept for 2h before the reaction performance test. Then, the sample was cooled by switching to the Ar atmosphere. After cooling to below 150°C, the reaction gas was switched to react. During the reaction, the temperature was programmed to increase from 150°C to 300°C at a rate of 1°C/min. During this period, a Fury 9790 gas chromatograph, a TDX-01 column, and a TCD detector were used for online detection. The catalyst performance test results are shown in Figure 1. The water vapor shift reaction activity of Cu-Zn/γ-Al ₂ O ₃ catalyst prepared by distributed precipitation method at low temperature is obviously better than that of catalyst prepared by traditional co-precipitation method. The reaction temperature was fixed at 220° C. to carry out the stability test of the catalyst, as shown in FIG. 2 . The Cu-Zn/γ-Al ₂ O ₃ catalyst prepared by the distributed precipitation method always maintained a CO conversion rate of 90% in the 50h stability test. The CO conversion of the catalyst prepared by the traditional co-precipitation method was about 46% at the beginning of the reaction, and then increased to about 60%, and the stability was also maintained for nearly 50 hours.

Claims (2)

1. A process for preparing the low-temp catalyst for steam transform of CO features that the active components of said catalyst are Cu and Zn, and the carrier is gamma-Al₂O₃The Cu content is 20-40 wt%, and the molar ratio of copper to zinc is 1: 1; preparing the precipitate by a fractional precipitation method, and preparing Cu-Zn/gamma-Al by suction filtration, washing, drying and roasting₂O₃A catalyst; the preparation method comprises the following specific steps:

(1) preparing a precipitator solution with a certain concentration, and dropwise adding the precipitator solution into a solution containing zinc salt and a carrier gamma-Al₂O₃Continuously stirring the solution until the pH value is 9 to obtain a zinc hydroxide suspension, and continuously stirring for 40min after titration is finished;

(2) preparing a copper salt solution with a certain concentration, slowly dripping the precipitator solution and the copper salt solution obtained in the step (1) into the zinc hydroxide suspension obtained in the step (1) at the same time, continuously stirring and keeping the pH value at 8, continuously dripping the precipitator solution after the dripping of the copper salt is finished until the pH value is 9, continuously stirring the obtained suspension in a water bath at 60 ℃ for 2-4h, then carrying out suction filtration, washing with distilled water until the pH value is 7, and drying the solid in an oven at 80 ℃ for 12-24h to obtain a precipitate precursor;

(3) calcining the precipitate precursor for 2h at 400 ℃ in an oxidizing atmosphere to prepare the carbon monoxide water-vapor transformation low-temperature catalyst Cu-Zn/gamma-Al₂O₃。

2. The method according to claim 1, wherein the copper salt is Cu (NO)₃)₂·3H₂O、CuSO₄·5H₂O or CuCl₂·2H₂O, the concentration is 0.06-0.15 mol/L; the zinc salt is Zn (NO)₃)₂·6H₂O、ZnSO₄·7H₂O or ZnCl₂The concentration is 0.05-0.12 mol/L; the precipitator is any one of ammonia water, sodium carbonate, sodium hydroxide and sodium bicarbonate, and the concentration is 0.4 mol/L; the oxidizing atmosphere is any one of air, oxygen or a mixed gas of oxygen and nitrogen.

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