A Ni@Silicalite-1 catalyst for the dry reforming reaction of CH4

Abstract

The present invention discloses a Ni@Silicalite-1 catalyst for CH4 dry reforming reaction, belonging to the technical field of catalyst preparation. The parent Silicalite-1 molecular sieve used is treated with tetrapropylammonium hydroxide solution before introducing Ni. Treating the parent Silicalite-1 molecular sieve with tetrapropylammonium hydroxide solution is to put the parent Silicalite-1 molecular sieve into the tetrapropylammonium hydroxide solution. The mass percentage concentration of the used tetrapropylammonium hydroxide solution is 5-15%, and the solid / liquid ratio of the Silicalite-1 molecular sieve to the tetrapropylammonium hydroxide solution is 0.05-0.15 g / mL; the treatment temperature is 50-90 °C, and the treatment time is 1-4 hours. This preparation method is particularly beneficial to the highly dispersed embedding of a high content of Ni in the Silicalite-1 molecular sieve crystal, improving the activity and catalytic stability of the catalyst.

Description

Technical Field

[0001] The present invention relates to a highly active and highly stable Ni@Silicalite-1 catalyst for catalytic carbon dioxide reforming of methane and a preparation method thereof, belonging to the technical field of catalyst preparation. Background Art

[0002] By using a suitable catalyst, methane and carbon dioxide can be simultaneously catalytically converted into syngas, that is, syngas (CO + H2) is prepared by the dry reforming reaction of methane with CO2, which can provide the necessary raw materials for Fischer-Tropsch synthesis of gasoline and diesel, and can also reduce the emission of CO2 into the atmosphere. Nickel is inexpensive and has high activity and selectivity for the CO2 reforming reaction of CH4. However, a serious drawback of such catalysts is that supported nano-Ni particle catalysts have poor thermal stability. Under high-temperature catalytic reaction conditions, Ni particles are extremely easy to sinter and grow, and carbon deposition is extremely easy to occur on the Ni particles, covering the active centers. Therefore, restricting the coalescence, growth and sintering of nano-Ni particles on the support and suppressing carbon deposition on the catalyst have become the technical keys for the successful industrial application of supported Ni catalysts in the dry reforming reaction of CH4 with CO2.

[0003] Wang Shengping et al. (CN109647495 A) disclosed a method for embedding nickel metal particles in Silicalite-2. The catalyst preparation method is as follows: first, nickel acetylacetonate is used as the nickel precursor, and a Ni-SiO2 intermediate is obtained by a microemulsion method. Then, the intermediate is added to a tetrabutylammonium hydroxide template agent, and solvent-free treatment crystallization is carried out at 170-200 °C for 24-72 hours to obtain a Ni@S-2 catalyst with a nickel loading of 2.5-7.5 wt.%.

[0004] Wang Fagen et al. (CN109225229 A) disclosed a preparation method of a Ni@SiO2 core-shell structure catalyst with nickel nanoparticles as the core and amorphous silica spheres as the shell layer, and the corresponding catalyst is used for the carbon dioxide reforming reaction of methane. For the Ni@SiO2 core-shell structure catalyst, the nickel loading is 3-6 wt.%, and it is obtained by means of L-lysine through a microemulsion method.

[0005] Dai et al. reported a preparation method of a catalyst with Ni particles encapsulated in single-chamber S-1 zeolite crystals, and the corresponding catalyst is used for the carbon dioxide reforming reaction of methane. The structural feature of the corresponding catalyst is that single-chamber Silicalite-1 zeolite crystals encapsulate metal Ni particles.

[0006] In any previous literature, there has been no research report on treating the Silicalite-1 molecular sieve support with tetrapropylammonium hydroxide solution to generate a large number of mesopores and silanol nests in the Silicalite-1 molecular sieve used as the support, ultimately enabling better dispersion and embedding of Ni into Silicalite-1 to prepare a highly active and highly stable Ni@Silicalite-1 catalyst for the dry reforming reaction of methane with carbon dioxide. Summary of the Invention

[0007] The present invention relates to a preparation method of a highly active and highly stable Ni@Silicalite-1 catalyst for the dry reforming reaction of methane with carbon dioxide. The Silicalite-1 parent molecular sieve used as the catalyst support is obtained by treating with tetrapropylammonium hydroxide solution.

[0008] The treatment of the parent Silicalite-1 molecular sieve with tetrapropylammonium hydroxide solution refers to treating the Silicalite-1 molecular sieve support obtained after calcination with a tetrapropylammonium hydroxide solution with a mass percentage concentration of 3-10% at a solid / liquid ratio of 0.03-0.10 g / mL for 1-4 hours at a temperature of 50-90 °C. When treating the Silicalite-1 parent molecular sieve with tetrapropylammonium hydroxide solution, the optimal mass percentage concentration of the tetrapropylammonium hydroxide solution is 6-8%, the optimal treatment solid / liquid ratio is 0.04-0.06 g / mL, the optimal treatment temperature is 70-80 °C, and the optimal treatment time is 2-3 hours. Then it is cooled and centrifuged. The solid product obtained by centrifugation is dried at 100-130 °C.

[0009] The Ni@Silicalite-1 catalyst involved in the present invention is obtained by directly impregnating the Silicalite-1 molecular sieve obtained from the above treatment with a Ni salt and then mixing it with a tetrapropylammonium hydroxide templating agent solution, or directly mixing it with a Ni salt and a tetrapropylammonium hydroxide templating agent solution and then performing hydrothermal crystallization. The hydrothermal crystallization temperature used is 120-190 °C, and the optimal temperature is 160-180 °C. The hydrothermal crystallization time used is 48-120 h, and the optimal time is 48-72 h. The above Ni salts include nickel nitrate, nickel chloride, nickel sulfate, and their ammonia complexes, and the optimal Ni salts are nickel nitrate, nickel chloride, or a mixture thereof.

[0010] Among the above technical solutions, the best solution is to directly impregnate nickel nitrate with the Silicalite-1 molecular sieve obtained by the above treatment. For each gram of the Silicalite-1 molecular sieve obtained by the above treatment, 2 mL of an aqueous solution containing 0.88 Ni (NO 3 ) 2 · 6H 2 O is added for impregnation. The resulting mixture is stirred at 50°C until dry, and then 20 mL of the centrifuge containing Si and tetrapropylammonium hydroxide template obtained after the above treatment of the parent Silicalite-1 and 20 mL of deionized water are added. After thorough mixing, the mixture is hydrothermally crystallized at 170°C for 72 hours. Finally, the solid product is centrifuged, dried, and calcined in air to obtain a catalyst sample.

[0011] Furthermore, in the above technical solution, the drying temperature after hydrothermal treatment is 100-150° C., and the drying time after hydrothermal treatment is 2-12 hours; the calcination temperature after hydrothermal treatment is 500-600° C., and the calcination time after hydrothermal treatment is 2-5 hours.

[0012] Beneficial effects of the present invention:

[0013] The Ni@Silicalite-1 catalysts prepared by treating the Silicalite-1 parent molecular sieve as a catalyst carrier using the method of the present invention (Examples 3 and 4 in Table 1) have the following three beneficial effects compared with the catalyst prepared without such treatment (Comparative Example 1 in Table 1): (1) higher Ni dispersion; (2) higher catalyst activity; and (3) higher catalytic stability.

[0014] Specific embodiment of the preparation of Ni@Silicalite-1 catalyst involved in the present invention

[0015] The parent Silicalite-1 molecular sieve was treated with tetrapropylammonium hydroxide as shown in Examples 1 and 2. The Ni@Silicalite-1 catalyst of the present invention was further prepared from the Silicalite-1 molecular sieve obtained by the treatment as shown in Examples 3 and 4.

[0016] Example 1

[0017] 6 g of a parent Silicalite-1 molecular sieve, obtained by calcining the Silicalite-1 molecular sieve in air at 500°C for 4 hours, was added to a beaker containing 120 mL of a 6 wt.% TPAOH solution. The mixture was stirred at 80°C for 2 hours, then cooled and centrifuged. The solid product obtained by centrifugation was dried at 100°C. This yielded 4.4 g of treated Silicalite-1 molecular sieve and 118 mL of centrifuge liquid. The centrifuge liquid was measured to contain 14 mg / mL of silicon and a small amount of TPAOH, yielding molecular sieve A.

[0018] Example 2

[0019] 1.28 g of the parent Silicalite-1 molecular sieve, which is obtained by calcining the Silicalite-1 molecular sieve in air at 500 °C for 4 h, is added to a beaker containing 15 mL of a TPAOH solution with a mass percentage concentration of 7 wt.%. Stir at 70 °C for 3 hours. Molecular sieve mixture B is obtained.

[0020] Example 3

[0021] Take 1 g of molecular sieve A obtained in Example 1 and impregnate it into 2 mL of an aqueous solution containing 0.88 g of Ni(NO3)2·6H2O. Stir the resulting mixture at 50 °C until dry, then add 20 mL of the centrifugate obtained in Example 1 (containing 14 mg / mL of silicon and a small amount of TPAOH) and 20 mL of deionized water and stir for half an hour. Then transfer the resulting mixture to a 100 mL hydrothermal reaction kettle and hydrothermally crystallize at 170 °C under rotating conditions (20 revolutions per minute) for 72 hours. Centrifuge and separate the solid product, dry it, and then calcine it in air at 500 °C for 4 h to obtain a catalyst sample.

[0022] Example 4

[0023] Add the molecular sieve mixture B obtained in Example 2 to 2 mL of an aqueous solution containing 0.88 g of Ni(NO3)2·6H2O, then add 20 mL of a TPAOH solution with a mass percentage concentration of 3% and stir for half an hour. Then transfer the resulting mixture to a 100 mL hydrothermal reaction kettle and hydrothermally crystallize at 160 °C under rotating conditions (20 revolutions per minute) for 96 hours. Centrifuge and separate the solid product, dry it, and then calcine it in air at 500 °C for 4 h to obtain a catalyst sample.

[0024] Comparative Example 1

[0025] Take 1.28 g of the parent Silicalite-1 molecular sieve used in Example 1 but not treated with TPAOH, directly impregnate it into 2 mL of an aqueous solution containing 0.88 g of Ni(NO3)2·6H2O, stir the resulting mixture at 50 °C for half an hour, then add 40 mL of a TPAOH solution with a mass percentage concentration of 3 wt.% and stir for half an hour. Then transfer the mixture to a 100 mL hydrothermal reaction kettle and crystallize at 170 °C for 72 hours. Centrifuge and separate the solid product, dry it, and then calcine it in air at 500 °C for 4 h to obtain a catalyst sample.

[0026] Example 5

[0027] Take 1.28 g of the parent Silicalite-1 molecular sieve, which is obtained by calcining the Silicalite-1 molecular sieve in air at 500 °C for 4 h. Add it to a beaker containing 20 mL of a TPAOH solution with a mass percentage concentration of 6 wt.%. Stir at 80 °C for 2 hours, then cool to 50 °C, and add 22 mL of an aqueous solution containing 0.88 g of Ni(NO3)2·6H2O and stir for half an hour. Finally, transfer the mixture to a 100 mL hydrothermal reactor and crystallize at 170 °C for 72 hours. Centrifuge and separate the solid product, dry it, and then calcine it in air at 500 °C for 4 h to obtain the catalyst sample.

[0028] Example 6

[0029] The difference from Example 5 is that the parent Silicalite-1 molecular sieve is obtained by calcining the Silicalite-1 molecular sieve in air at 550 °C for 3 h, and other conditions are the same as in Example 5 to obtain the catalyst sample.

[0030] Table 1 Comparison of the dry reforming reaction activity of methane with CO2 (reaction conditions: 800 °C, CH4:CO2 = 1:1, total reaction gas space velocity GHSV = 900000 ml·g cat -1 ·h -1 )

[0031]

Claims

1. Application of a Ni@Silicalite-1 catalyst in the dry reforming reaction of CH4 with CO2, characterized in that, The parent Silicalite-1 molecular sieve used in the preparation of the catalyst was treated with tetrapropylammonium hydroxide solution before introducing Ni; The specific preparation method of the catalyst is as follows: treating the parent Silicalite-1 molecular sieve with tetrapropylammonium hydroxide solution, then mixing it with nickel salt, and obtaining the catalyst through hydrothermal crystallization, separating the product, drying, and calcining in the presence of tetrapropylammonium hydroxide template agent; Treating the parent Silicalite-1 molecular sieve with tetrapropylammonium hydroxide solution means putting the parent Silicalite-1 molecular sieve into tetrapropylammonium hydroxide solution. The mass percentage concentration of the used tetrapropylammonium hydroxide solution is 5-15%, and the solid-liquid ratio of Silicalite-1 molecular sieve to tetrapropylammonium hydroxide solution is 0.05-0.15 g / mL; the treatment temperature is 50-90 °C, and the treatment time is 1-4 hours; The parent Silicalite-1 molecular sieve is the Silicalite-1 molecular sieve support obtained after calcination.

2. The application according to claim 1, wherein: The mass percentage content of metallic Ni is between 5 and 15%.

3. The application according to claim 1, wherein: The said nickel salts include nickel nitrate, nickel chloride, nickel sulfate and their ammonia complexes.

4. The application according to claim 1, characterized in that: The used hydrothermal crystallization temperature is 120-190 °C, and the used hydrothermal crystallization time is 48-120 h.

5. The application according to claim 1, characterized in that: The drying temperature after hydrothermal treatment is 100-150 °C, and the drying time after hydrothermal treatment is 2-12 hours; the calcination temperature after hydrothermal treatment is 500-600 °C, and the calcination time after hydrothermal treatment is 2-5 hours.

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