A bifunctional composite catalyst, a preparation method and application thereof

Abstract

The application belongs to the technical field of catalysts, and provides a bifunctional composite catalyst and a preparation method and application thereof. The method comprises the following steps: mixing a zeolite molecular sieve, aluminum oxide, calcium oxide and water, and sequentially performing calcination and carbonation to obtain a calcium-based adsorbent; mixing the calcium-based adsorbent, ethanol, a surfactant, a cerium salt, a barium salt, water and ammonia water, and sequentially performing aging and calcination to obtain an intermediate; mixing the intermediate, the surfactant, a nickel salt, an additive salt and ethanol, and sequentially performing reaction and calcination to obtain the bifunctional composite catalyst. The preparation method is simple, convenient to operate and easy to industrialize. The bifunctional composite catalyst obtained by the application has the functions of adsorption and catalysis. After the bifunctional composite catalyst is applied to a CO2 adsorption enhanced methane steam reforming 45-cycle reaction, the methane conversion rate is as high as 99.67%, and the H2 concentration is as high as 99.73%.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, and in particular to a bifunctional composite catalyst, its preparation method, and its application. Background Technology

[0002] With the rapid development of science and technology, environmental pollution and resource shortages are becoming increasingly serious. Hydrogen, as an environmentally friendly renewable energy source, has gained widespread attention. Currently, the main methods for producing hydrogen include fossil fuel hydrogen production, solar hydrogen production, water electrolysis hydrogen production, biological hydrogen production, and nuclear hydrogen production. Among these, methane steam reforming is currently the most important method. However, the methane steam reforming reaction is a strongly endothermic reaction, and at high temperatures, the catalyst is prone to coking, resulting in a very low single-pass conversion rate. To address these issues, in recent years, researchers have attempted to combine catalysts with CO2 adsorbents to remove CO2 in situ during the reaction, shifting the reaction in a direction favorable to H2 formation. Simultaneously, the adsorption-enhanced reforming hydrogen production technology has significantly reduced the reaction temperature, and improved the methane conversion rate and the purity of the produced hydrogen. The key to adsorption-enhanced reforming for hydrogen production lies in the selection of catalysts and adsorbents. Their activity and selectivity limit the reaction rate and yield, and their lifespan is related to the production cost. Therefore, developing efficient catalyst and adsorbent materials is one of the core issues in CO2 adsorption-enhanced methane steam reforming for hydrogen production. Summary of the Invention

[0003] The purpose of this invention is to overcome the problems existing in the prior art and to provide a bifunctional composite catalyst, its preparation method, and its application.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0005] This invention provides a method for preparing a bifunctional composite catalyst, comprising the following steps:

[0006] (1) Zeolite molecular sieve, alumina, calcium oxide and water are mixed and calcined and carbonized in sequence to obtain calcium-based adsorbent;

[0007] (2) The calcium-based adsorbent, ethanol, surfactant, cerium salt, barium salt, water and ammonia are mixed and aged and calcined in sequence to obtain an intermediate.

[0008] (3) The intermediate, surfactant, nickel salt, auxiliary salt and ethanol are mixed and reacted and calcined in sequence to obtain the bifunctional composite catalyst.

[0009] Preferably, the mass ratio of zeolite molecular sieve, alumina, calcium oxide and water in step (1) is 0.8-1.2:0.8-1.2:2-5:0.2-0.5.

[0010] Preferably, the calcination temperature in step (1) is 500–650°C and the time is 0.5–2.5 h;

[0011] The carbonation temperature is 600–700°C, and the time is 5–12 hours.

[0012] Preferably, the surfactant in step (2) is polyvinylpyrrolidone, hexadecyltrimethylammonium bromide or ammonium chloride;

[0013] The mass ratio of the calcium-based adsorbent, ethanol, surfactant, cerium salt, barium salt, and water is 0.05–0.25: 0.8–1.2: 0.01–0.05: 0.1–0.2: 0.01–0.08: 0.05–0.15.

[0014] The concentration of the ammonia solution is 2–3 mol / L; the pH of the solution after mixing is 9–12.

[0015] Preferably, the aging temperature in step (2) is 30-80°C and the time is 1-2 hours;

[0016] The calcination temperature is 550–650℃, and the time is 5–7 hours.

[0017] Preferably, the surfactant in step (3) is polyvinylpyrrolidone, hexadecyltrimethylammonium bromide or ammonium chloride, and the auxiliary salt is samarium salt or zirconium salt;

[0018] The mass ratio of the surfactant, nickel salt, auxiliary salt, and ethanol is 0.005–0.03: 0.25–0.35: 0.02–0.04: 0.8–1.2.

[0019] The mass ratio of the nickel salt in step (3) to the cerium salt in step (2) is 0.25-0.35: 0.1-0.2.

[0020] Preferably, the reaction in step (3) is carried out at a temperature of 70–90°C for 8–11 hours.

[0021] The calcination temperature is 600–900℃, and the time is 1–5 hours.

[0022] The present invention also provides a bifunctional composite catalyst obtained by the preparation method described above.

[0023] The present invention also provides the application of the aforementioned bifunctional composite catalyst in CO2 adsorption-enhanced methane steam reforming for hydrogen production.

[0024] The beneficial effects of this invention are:

[0025] (1) In this invention, zeolite molecular sieves, alumina, calcium oxide, and water are mixed and sequentially calcined and carbonated to obtain a calcium-based adsorbent. The molecular sieve itself has a certain physical adsorption capacity for CO2 gas, which is more conducive to its chemical adsorption by the calcium-based adsorbent. The addition of alumina effectively increases the distribution points of CO2 gas, providing a favorable adsorption environment for the calcium-based adsorbent and playing a supporting and protective role. The calcium-based adsorbent prepared by the method of this invention has a large specific surface area, excellent adsorption efficiency, and stability.

[0026] (2) In this invention, the catalytic component uses cerium oxide and barium oxide as a support. Cerium oxide itself, due to its certain oxygen vacancies, can effectively inhibit the sintering and coking formation of nickel-based catalysts. Furthermore, by adding barium salt, this application reduces the acidity of the cerium oxide support, further overcoming the problems of coking and high-temperature sintering. In addition, the addition of auxiliary salts in the catalytic component can further improve the efficiency of in-situ activation by steam. The catalytic component in this invention exhibits excellent stability and selectivity.

[0027] (3) The preparation method of the present invention is simple, easy to operate and easy to industrialize. The bifunctional composite catalyst obtained by the present invention has both adsorption and catalytic functions. After applying it to CO2 adsorption-enhanced methane steam reforming 45 cycles, the methane conversion rate is as high as 99.67% and the H2 concentration is as high as 99.73%. Detailed Implementation

[0028] This invention provides a method for preparing a bifunctional composite catalyst, comprising the following steps:

[0029] (1) Zeolite molecular sieve, alumina, calcium oxide and water are mixed and calcined and carbonized in sequence to obtain calcium-based adsorbent;

[0030] (2) The calcium-based adsorbent, ethanol, surfactant, cerium salt, barium salt, water and ammonia are mixed and aged and calcined in sequence to obtain an intermediate.

[0031] (3) The intermediate, surfactant, nickel salt, auxiliary salt and ethanol are mixed and reacted and calcined in sequence to obtain the bifunctional composite catalyst.

[0032] In this invention, the mass ratio of zeolite molecular sieve, alumina, calcium oxide and water in step (1) is preferably 0.8-1.2:0.8-1.2:2-5:0.2-0.5, more preferably 0.9-1.1:0.9-1.1:2.5-4:0.3-0.4, and even more preferably 0.95-1:0.95-1:3-3.5:0.33-0.35.

[0033] In this invention, the particle size of the zeolite molecular sieve in step (1) is preferably 0.5-1.5 mm, more preferably 0.7-1.3 mm, and even more preferably 0.8-1 mm; the zeolite molecular sieve is preferably activated before mixing, and the activation temperature is preferably 200-300°C, more preferably 220-280°C, and even more preferably 250-260°C; the activation time is preferably 25-35 min, more preferably 27-33 min, and even more preferably 28-30 min.

[0034] In this invention, the alumina in step (1) is preferably inert alumina, and the particle size of the inert alumina is preferably 0.5-1.5 mm, more preferably 0.7-1.3 mm, and even more preferably 0.8-1 mm.

[0035] In this invention, the mixing in step (1) is preferably done by first mixing the zeolite molecular sieve, alumina and water, and then slowly adding calcium oxide.

[0036] In this invention, after mixing in step (1), the mixture is dried first, and then calcined and carbonated in sequence. The drying temperature is preferably 100-150°C, more preferably 110-140°C, and even more preferably 120-125°C. The drying time is preferably 0.5-1h, more preferably 0.6-0.9h, and even more preferably 0.7-0.8h.

[0037] In this invention, the calcination temperature in step (1) is preferably 500-650°C, more preferably 550-600°C, and even more preferably 570-580°C; the time is preferably 0.5-2.5h, more preferably 1-2h, and even more preferably 1.5-1.7h.

[0038] In this invention, the carbonation in step (1) is preferably carried out under a carbon dioxide atmosphere, the carbonation temperature is preferably 600-700°C, more preferably 620-680°C, and even more preferably 650-660°C; the time is preferably 5-12 hours, more preferably 6-10 hours, and even more preferably 7-8 hours.

[0039] In this invention, the surfactant in step (2) is preferably polyvinylpyrrolidone, hexadecyltrimethylammonium bromide or ammonium chloride, the cerium salt is preferably cerium nitrate, and the barium salt is preferably barium nitrate.

[0040] In this invention, the mass ratio of the calcium-based adsorbent, ethanol, surfactant, cerium salt, barium salt and water in step (2) is preferably 0.05-0.25: 0.8-1.2: 0.01-0.05: 0.1-0.2: 0.01-0.08: 0.05-0.15, more preferably 0.1-0.2: 0.9-1.1: 0.02-0.04: 0.12-0.18: 0.03-0.06: 0.08-0.12, and even more preferably 0.12-0.15: 0.95-1: 0.025-0.03: 0.13-0.15: 0.04-0.05: 0.1-0.11.

[0041] In this invention, the concentration of ammonia in step (2) is preferably 2-3 mol / L, more preferably 2.2-2.8 mol / L, and even more preferably 2.3-2.5 mol / L; the pH of the solution after mixing is preferably 9-12, more preferably 10-11, and even more preferably 10.2-10.5.

[0042] In this invention, the aging temperature in step (2) is preferably 30-80°C, more preferably 40-70°C, and even more preferably 50-60°C; the time is preferably 1-2 hours, more preferably 1.2-1.8 hours, and even more preferably 1.3-1.5 hours.

[0043] In this invention, after the aging process in step (2) is completed, the resulting system is subjected to static standing, filtration, washing and drying in sequence, and then calcined.

[0044] In this invention, the settling time is preferably ≥20h, more preferably ≥22h, and even more preferably ≥24h; the washing consists of sequential water washing and ethanol washing, the number of water washings is preferably ≥3 times, more preferably ≥4 times, and even more preferably ≥5 times; the number of ethanol washings is preferably ≥2 times, more preferably ≥3 times, and even more preferably ≥4 times; the drying temperature is preferably 80~100℃, more preferably 85~95℃, and even more preferably 87~90℃; the drying time is preferably 10~20h, more preferably 12~18h, and even more preferably 15~16h.

[0045] In this invention, the calcination temperature in step (2) is preferably 550-650°C, more preferably 570-630°C, and even more preferably 580-600°C; the time is preferably 5-7 h, more preferably 5.5-6.5 h, and even more preferably 6-6.2 h.

[0046] In this invention, the surfactant in step (3) is preferably polyvinylpyrrolidone, hexadecyltrimethylammonium bromide or ammonium chloride, the nickel salt is preferably nickel nitrate, nickel oxalate or nickel acetate, the auxiliary salt is preferably samarium salt or zirconium salt, the samarium salt is preferably samarium nitrate, and the zirconium salt is preferably zirconium nitrate.

[0047] In this invention, the mass ratio of surfactant, nickel salt, auxiliary salt and ethanol in step (3) is preferably 0.005-0.03:0.25-0.35:0.02-0.04:0.8-1.2, more preferably 0.01-0.02:0.27-0.33:0.025-0.035:0.9-1.1, and even more preferably 0.012-0.015:0.28-0.3:0.027-0.03:0.95-1.

[0048] In this invention, the mass ratio of the nickel salt in step (3) to the cerium salt in step (2) is preferably 0.25-0.35:0.1-0.2, more preferably 0.27-0.33:0.12-0.18, and even more preferably 0.28-0.3:0.13-0.15.

[0049] In this invention, the temperature of the reaction in step (3) is preferably 70-90°C, more preferably 75-85°C, and even more preferably 77-80°C; the time is preferably 8-11h, more preferably 9-10h, and even more preferably 9.5-9.8h.

[0050] In this invention, after the reaction in step (3) is completed, the resulting system is sequentially filtered and dried, and then calcined.

[0051] In this invention, the drying temperature is preferably 60-100°C, more preferably 70-90°C, and even more preferably 75-80°C; the drying time is preferably 12-18 hours, more preferably 13-17 hours, and even more preferably 15-16 hours.

[0052] In this invention, the calcination temperature in step (3) is preferably 600-900℃, more preferably 700-800℃, and even more preferably 720-750℃; the time is preferably 1-5h, more preferably 2.5-4h, and even more preferably 3-3.5h.

[0053] The present invention also provides a bifunctional composite catalyst obtained by the preparation method described above.

[0054] The present invention also provides the application of the aforementioned bifunctional composite catalyst in CO2 adsorption-enhanced methane steam reforming for hydrogen production.

[0055] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0056] Example 1

[0057] Zeolite molecular sieves with a particle size of 1 mm were activated at 250 °C for 30 min to obtain activated molecular sieves. 1 g of activated molecular sieves, 1 g of inert alumina with a particle size of 1 mm and 0.35 g of water were initially mixed, and then 3.5 g of calcium oxide was slowly added. The mixture was dried at 125 °C for 0.8 h, and then calcined at 580 °C for 1.5 h. After calcination, the mixture was carbonized at 650 °C for 8 h under a carbon dioxide atmosphere to obtain a calcium-based adsorbent.

[0058] 1.5g of calcium-based adsorbent, 10g of ethanol, 0.25g of polyvinylpyrrolidone, 1.5g of cerium nitrate, 0.5g of barium nitrate, 1g of water, and 2.5mol / L ammonia solution were mixed. After mixing, the pH of the solution was 10.5. The resulting solution was aged at 50℃ for 1.5h, then allowed to stand for 22h. After standing, the solution was filtered, and the resulting filter cake was washed four times with water, then three times with ethanol, dried at 90℃ for 15h, and finally calcined at 600℃ for 6h to obtain an intermediate. The intermediate, 0.15g of polyvinylpyrrolidone, 3g of nickel nitrate, 0.3g of samarium nitrate, and 10g of ethanol were mixed and reacted at 80℃ for 9.5h. After the reaction, the mixture was filtered, and the resulting filter cake was dried at 80℃ for 16h, and finally calcined at 750℃ for 3h to obtain a bifunctional composite catalyst.

[0059] Example 2

[0060] Zeolite molecular sieves with a particle size of 0.5 mm were activated at 220℃ for 33 min to obtain activated molecular sieves. 0.9 g of activated molecular sieves, 0.9 g of inert alumina with a particle size of 0.5 mm and 0.3 g of water were initially mixed, and then 2.5 g of calcium oxide was slowly added. The mixture was dried at 110℃ for 0.9 h, and then calcined at 550℃ for 2 h. After calcination, the mixture was carbonized at 620℃ for 10 h under a carbon dioxide atmosphere to obtain a calcium-based adsorbent.

[0061] 1 g of calcium-based adsorbent, 9 g of ethanol, 0.2 g of hexadecyltrimethylammonium bromide, 1.2 g of cerium nitrate, 0.3 g of barium nitrate, 0.8 g of water, and 2.3 mol / L ammonia solution were mixed. After mixing, the pH of the solution was 10. The resulting solution was aged at 40 °C for 1.8 h, then allowed to stand for 21 h. After standing, the solution was filtered, and the resulting filter cake was washed 5 times with water, then 3 times with ethanol, dried at 85 °C for 18 h, and finally calcined at 550 °C for 7 h to obtain an intermediate. The intermediate, 0.1 g of hexadecyltrimethylammonium bromide, 2.7 g of nickel oxalate, 0.25 g of samarium nitrate, and 9 g of ethanol were mixed and reacted at 70 °C for 11 h. After the reaction, the mixture was filtered, and the resulting filter cake was dried at 70 °C for 17 h, and finally calcined at 700 °C for 4 h to obtain a bifunctional composite catalyst.

[0062] Example 3

[0063] Zeolite molecular sieves with a particle size of 1.3 mm were activated at 280℃ for 27 min to obtain activated molecular sieves. 1.1 g of activated molecular sieves, 1.1 g of inert alumina with a particle size of 1.3 mm and 0.4 g of water were initially mixed, and then 4 g of calcium oxide was slowly added. The mixture was dried at 150℃ for 0.5 h, and then calcined at 600℃ for 1 h. After calcination, the mixture was carbonized at 700℃ for 5 h under a carbon dioxide atmosphere to obtain a calcium-based adsorbent.

[0064] 2.5g of calcium-based adsorbent, 12g of ethanol, 0.5g of ammonium chloride, 2g of cerium nitrate, 0.8g of barium nitrate, 1.5g of water, and 3mol / L ammonia solution were mixed. After mixing, the pH of the solution was 11. The resulting solution was aged at 70℃ for 1.3h, then allowed to stand for 24h. After standing, the solution was filtered, and the resulting filter cake was washed four times with water, then four times with ethanol, dried at 100℃ for 10h, and finally calcined at 650℃ for 5h to obtain an intermediate. The intermediate, 0.3g of ammonium chloride, 3.5g of nickel acetate, 0.4g of samarium nitrate, and 12g of ethanol were mixed and reacted at 90℃ for 8h. After the reaction, the mixture was filtered, and the resulting filter cake was dried at 100℃ for 12h, and finally calcined at 800℃ for 2.5h to obtain a bifunctional composite catalyst.

[0065] The bifunctional composite catalysts obtained in Examples 1-3 were used for CO2 adsorption-enhanced CH4 / H2O reforming hydrogen production reactions. The specific experimental steps were as follows: 4.0 g of the composite catalysts from Examples 1-3 (all with a particle size of 0.35 mm) were loaded into a fixed-bed reactor. The composite catalysts were reduced at 650 °C with H2 at a flow rate of 50 mL / min for 1 h. Then, the temperature was lowered to 600 °C under a N2 atmosphere at a flow rate of 100 mL / min, followed by a reaction under an atmosphere of CH4 (flow rate of 18.7 mL / min) and water vapor (flow rate of 74.8 mL / min) for 1 h. After the reaction, the reactor temperature was raised to 750 °C under a N2 atmosphere for regeneration for 1 h, followed by a temperature reduction to 600 °C and switching of the reaction gas. This cycle was repeated 45 times. The composition of the produced gas was analyzed by gas chromatography, and the performance test results of the bifunctional composite catalysts obtained in Examples 1-3 are shown in Table 1.

[0066] Table 1. Performance test results of the bifunctional composite catalysts obtained in Examples 1-3

[0067]

[0068]

[0069] As can be seen from the above embodiments, the present invention provides a method for preparing a bifunctional composite catalyst, comprising the following steps: mixing zeolite molecular sieve, alumina, calcium oxide, and water, and sequentially calcining and carbonating to obtain a calcium-based adsorbent; mixing the calcium-based adsorbent, ethanol, surfactant, cerium salt, barium salt, water, and ammonia, and sequentially aging and calcining to obtain an intermediate; mixing the intermediate, surfactant, nickel salt, auxiliary salt, and ethanol, and sequentially reacting and calcining to obtain the bifunctional composite catalyst. The preparation method of the present invention is simple, convenient to operate, and easy to industrialize. The bifunctional composite catalyst obtained by the present invention has both adsorption and catalytic functions. When applied to a CO2 adsorption-enhanced methane steam reforming reaction for 45 cycles, the methane conversion rate reached as high as 99.67%, and the H2 concentration reached as high as 99.73%.

[0070] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a bifunctional composite catalyst, characterized in that, Includes the following steps: (1) Zeolite molecular sieve, alumina, calcium oxide and water are mixed and calcined and carbonized in sequence to obtain calcium-based adsorbent; (2) The calcium-based adsorbent, ethanol, surfactant, cerium salt, barium salt, water and ammonia are mixed and aged and calcined in sequence to obtain an intermediate. (3) The intermediate, surfactant, nickel salt, auxiliary salt and ethanol are mixed and reacted and calcined in sequence to obtain the bifunctional composite catalyst. The surfactant in step (3) is polyvinylpyrrolidone, hexadecyltrimethylammonium bromide or ammonium chloride, and the auxiliary salt is samarium salt or zirconium salt; The mass ratio of the surfactant, nickel salt, auxiliary salt, and ethanol is 0.005–0.03: 0.25–0.35: 0.02–0.04: 0.8–1.

2. The mass ratio of the nickel salt in step (3) to the cerium salt in step (2) is 0.25-0.35: 0.1-0.

2.

2. The preparation method according to claim 1, characterized in that, The mass ratio of zeolite molecular sieve, alumina, calcium oxide and water in step (1) is 0.8-1.2:0.8-1.2:2-5:0.2-0.

5.

3. The preparation method according to claim 1 or 2, characterized in that, The calcination temperature in step (1) is 500–650℃, and the time is 0.5–2.5 h; The carbonation temperature is 600–700°C, and the time is 5–12 hours.

4. The preparation method according to claim 3, characterized in that, The surfactant mentioned in step (2) is polyvinylpyrrolidone, hexadecyltrimethylammonium bromide, or ammonium chloride; The mass ratio of the calcium-based adsorbent, ethanol, surfactant, cerium salt, barium salt, and water is 0.05–0.25: 0.8–1.2: 0.01–0.05: 0.1–0.2: 0.01–0.08: 0.05–0.

15. The concentration of the ammonia solution is 2–3 mol / L; the pH of the solution after mixing is 9–12.

5. The preparation method according to claim 4, characterized in that, The aging temperature in step (2) is 30–80°C, and the time is 1–2 hours; The calcination temperature is 550–650℃, and the time is 5–7 hours.

6. The preparation method according to claim 1, characterized in that, The reaction in step (3) is carried out at a temperature of 70–90°C for 8–11 hours. The calcination temperature is 600–900℃, and the time is 1–5 hours.

7. The bifunctional composite catalyst obtained by the preparation method according to any one of claims 1 to 6.

8. The application of the bifunctional composite catalyst of claim 7 in CO2 adsorption-enhanced methane steam reforming for hydrogen production.

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