Method for reducing Co particle size through multi-channel Co / CM catalytic membrane

Abstract

The invention belongs to the technical field of membrane catalysis, and relates to a method for reducing the Co particle size of a multi-channel Co / CM catalytic membrane. And coating the surface of the Co / CM catalytic membrane with a polydopamine coating, and then drying and calcining the Co / CM catalytic membrane. According to the method for reducing the particle size of Co in the Co / CM catalytic membrane, the particle size of Co can be effectively reduced, so that the active component Co in the catalytic membrane is re-dispersed, and the activity of the catalytic membrane in a p-nitrophenol catalytic hydrogenation reaction is obviously improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of membrane catalysis and relates to a method for reducing the Co particle size of a multi-channel Co / CM catalytic membrane. Background Art

[0002] As the core component of a catalytic membrane reactor, the performance of a catalytic membrane directly affects the operation efficiency of the reactor. The particle size of metal particles in a catalytic membrane has a significant impact on catalytic activity: the smaller the particle size, the larger the specific surface area, the more active sites are exposed, and the higher the activity of the catalytic membrane. Patent 202410518738 relates to a preparation method of a Co@CM multi-channel ceramic catalytic membrane for p-nitrophenol hydrogenation, that is, using the forced circulation method to load Co onto a dopamine-modified multi-channel ceramic membrane and pyrolyze it to obtain a Co@CM multi-channel ceramic catalytic membrane. This catalytic membrane has excellent performance in the liquid-phase hydrogenation reaction of p-nitrophenol, but the metal particle size on the catalytic membrane is relatively large (>50 nm). Patent 2023111266224 invented a new preparation method of a multi-channel Co / CM ceramic catalytic membrane: using a multi-channel ceramic membrane as a carrier, in-situ growing ZIF-67 on the ceramic membrane through a flow-induced layer-by-layer assembly method, and then pyrolyzing at high temperature to convert ZIF-67 into Co nanoparticles encapsulated by nitrogen-doped carbon, thereby obtaining a multi-channel ceramic catalytic membrane loaded with uniformly dispersed Co nanoparticles. The particle size of ZIF-67-derived Co nanoparticles is significantly reduced compared to that of Co nanoparticles induced by polydopamine reduction, but there is still a need and possibility for further reduction. Chen et al. found that by introducing Zn into ZIF-67 materials, it can act as a "fence" to expand the distance between adjacent Co atoms in space and obtain Co nanoparticles with a smaller particle size. However, the increase in the additional metal Zn makes the preparation cost of the catalytic membrane higher. Therefore, it is urgent to find a more suitable and low-cost method for introducing small-sized Co into a multi-channel ceramic membrane. Summary of the Invention

[0003] The present invention proposes a new method for reducing the Co particle size of a multi-channel Co / CM catalytic membrane to solve the problem of relatively large Co nanoparticle size in a Co-based catalytic membrane.

[0004] A method for reducing the Co particle size of a multi-channel Co / CM catalytic membrane, after coating the surface of the Co / CM catalytic membrane with a polydopamine coating, drying and calcining. The specific steps are as follows: (1) Slowly drop a dilute hydrochloric acid solution into a tris(hydroxymethyl)aminomethane solution to obtain a Tris-HCl buffer solution, add dopamine hydrochloride and mix evenly to obtain a modified solution.

[0005] (2) Under the water bath condition, force the modified solution to circulate through the pores and walls of the ceramic membrane for in-situ loading of dopamine, and then dry to obtain a dopamine-modified ceramic membrane.

[0006] (3) The methanol dispersion of cobalt nitrate hexahydrate is forced to circulate through the pores and wall surfaces of the dopamine-modified ceramic membrane for in-situ loading of cobalt salt.

[0007] (4) It is dried to obtain a ceramic membrane loaded with cobalt salt, and then calcined once to obtain a Co / CM catalytic membrane.

[0008] (5) Dilute hydrochloric acid solution is slowly added dropwise to the tris(hydroxymethyl)aminomethane solution to obtain a Tris-HCl buffer solution, and dopamine hydrochloride is added and mixed evenly to obtain a coating solution.

[0009] (6) Under the water bath condition, the coating solution is forced to circulate through the pores and wall surfaces of the Co / CM catalytic membrane for in-situ loading of dopamine, and then dried to obtain a Co / CM catalytic membrane coated with polydopamine, and then calcined twice.

[0010] Preferably, in step (1) or (5), the concentration of the tris(hydroxymethyl)aminomethane solution is 0.075 - 0.125 mol / L, and the pH of the Tris-HCl buffer solution is 8 - 9; the concentration of dopamine hydrochloride in the modification solution or the coating solution is 1 - 7 g / L.

[0011] Preferably, in step (1) or (5), the flow rate of the dopamine solution forced to circulate through the ceramic membrane is 2 - 5 L / h, the water bath temperature is 25 - 45 °C, and the forced circulation time is 12 - 20 h.

[0012] Preferably, the temperature of the first calcination in step (4) is 700 °C and the calcination time is 5 h; the temperature of the second calcination in step (6) is 600 - 800 °C and the calcination time is 3 - 7 h, and the calcination atmosphere in both step (4) and step (6) is argon.

[0013] In the above step (4), when the obtained Co / CM catalytic membrane is directly calcined at high temperature without coating a polydopamine layer, serious agglomeration of cobalt will occur and the activity will decrease; however, after coating another layer of polydopamine and then calcining at high temperature, the nitrogen-doped carbon after the pyrolysis of polydopamine will redisperse the cobalt, the particle size of the cobalt particles becomes smaller, and the activity of the catalytic membrane is improved.

[0014] Compared with the prior art, the advantages and positive effects of the present invention are as follows: The method for reducing the Co particle size in the multi-channel Co / CM catalytic membrane proposed by the present invention can effectively reduce the Co particle size, re-disperse the active component Co in the catalytic membrane, and significantly improve the activity of the catalytic membrane in the catalytic hydrogenation reaction of p-nitrophenol. Brief Description of the Drawings

[0015] Figure 1 It is the TEM characterization and particle size distribution diagram of the catalytic membrane. Detailed Embodiments

[0016] In order to more clearly understand the above-mentioned objects, features and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

[0017] In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the present invention is not limited to the limitations of the specific embodiments disclosed in the following specification.

[0018] Example 1 (1) Prepare 250 mL of a 0.1 mol / L aqueous solution of tris(hydroxymethyl)aminomethane, adjust the pH of the solution to 8.5 using 0.01 mol / L dilute hydrochloric acid, and then add dopamine hydrochloride with stirring until the concentration reaches 3.0 g / L. Mix evenly to obtain a modified solution. One end of a multi-channel ceramic membrane tube (commercially available, alumina, 19 channels, pore diameter about 1000 nm, diameter 3 cm, length 8 cm) is sealed, and then the modified solution is forced to circulate from the inside of the membrane tube channel to the outside of the membrane tube at a flow rate of 35 o °C and 3.5 L / h to modify the ceramic membrane (the devices and membrane modules used in the modification process can refer to CN117160510A), and control the modification time to be 16 h. After the modification is completed, take out the membrane tube and place it in an oven at 70 o °C for drying for 10 h, and the obtained membrane tube is denoted as DA / CM-3.0.

[0019] (2) Prepare 250 mL of a 0.1 mol / L cobalt nitrate hexahydrate methanol solution, refill the DA / CM-3.0 multi-channel ceramic membrane into the membrane module, and control the cobalt nitrate hexahydrate methanol solution to flow from the inside of the membrane tube channel to the outside of the membrane tube at a flow rate of 35 o °C and 3.5 L / h to force the cobalt nitrate hexahydrate methanol solution to flow through the membrane pores for cobalt loading, and control the loading time to be 12 h. After the loading is completed, take out the membrane tube and place it in an oven at 70 o °C for drying for 10 h, and the obtained membrane tube is denoted as Co / CM-3.0-0.1.

[0020] (3) Place Co / CM-3.0-0.1 in a tubular furnace, heat it from the initial temperature (room temperature) to 700 o °C for calcination, and keep it at the target temperature of 700 o °C for 5 h, where the heating rate is 5 o °C / min, the calcination atmosphere is argon, and after the calcination is completed, it is naturally cooled to room temperature, and the obtained sample is marked as Co / CM catalytic membrane.

[0021] (4) Coating with polydopamine coating and pyrolysis Re-prepare 250 mL of an aqueous solution of tris(hydroxymethyl)aminomethane with a concentration of 0.1 mol / L, adjust the pH of the solution to 8.5 using dilute hydrochloric acid with a concentration of 0.01 mol / L, and then add dopamine hydrochloride under stirring to prepare a dopamine coating solution with a concentration of 3.0 g / L. Then load the Co / CM catalytic membrane into a forced-flow membrane module, and then control the coating solution to circulate forcibly from the inside of the membrane tube channel to the outside of the membrane tube at a temperature of 35 o °C and a flow rate of 3.5 L / h, and control the coating time to be 16 h. After the coating is completed, take out the membrane and dry it in an oven at 70 o °C for 10 h. The obtained sample is labeled Co / CM-3.0.

[0022] Place Co / CM-3.0 in a tubular furnace, heat it from the initial temperature (room temperature) to 700 o °C for calcination, and hold it at the target temperature of 700 o °C for 5 h, where the heating rate is 5 o °C / min, the calcination atmosphere is argon, and after the calcination is completed, it is naturally cooled to room temperature. The obtained sample is labeled Co / CM-3.0-700.

[0023] Verification of catalytic effect: Dissolve 1.0 g of p-nitrophenol in a mixed solvent of 250 mL of ethanol and deionized water with a volume ratio of 1:11.5. Take 0.4 mL of the reaction solution as the initial sample, add 3.92 g of NaBH4 and stir until the solid is dissolved, and then add the reaction solution to the storage tank of the flow-through membrane reactor. Control the reaction raw materials to pass through the bottom of the open membrane tube at a flow rate of 3.5 L / h through a peristaltic pump, flow out from the inner channel of the catalytic membrane and through the side membrane pores. When the reaction solution flows to the outlet of the membrane module, start timing. After the reaction solution flows out of the membrane module, it is circulated into the storage tank, and 0.4 mL of the reaction solution is taken every 5 min. After the reaction is completed, empty the reaction solution and add a mixed solvent of ethanol and deionized water with a volume ratio of 1:11.5 to the storage tank to rinse the residual liquid on the catalytic membrane for 30 min. After the rinsing is completed, take out the catalytic membrane and dry it in an oven at 70 o °C for 10 h and dry it for storage for the next reaction. Use high-performance liquid chromatography to detect the product composition. After detection, the conversion rate is 89.0% and the selectivity is 100% after 10 min of reaction.

[0024] Example 2 Unless otherwise specified, this embodiment is the same as Embodiment 1. Specifically, the difference between this embodiment and Embodiment 1 lies in the process of step (4). The process of coating with a polydopamine coating and pyrolysis in this embodiment is as follows: Re-prepare 250 mL of a tris(hydroxymethyl)aminomethane aqueous solution with a concentration of 0.075 mol / L, adjust the pH of the solution to 8.5 using dilute hydrochloric acid with a concentration of 0.01 mol / L, and then add dopamine hydrochloride under stirring to prepare a dopamine coating solution with a concentration of 1.0 g / L. Then load the Co / CM catalytic membrane into a forced-flow membrane module, and then control the coating solution to circulate forcibly from the inside of the membrane tube channel to the outside of the membrane tube at a flow rate of 2 L / h at 25 o °C, and control the coating time to be 12 h. After the coating is completed, take out the membrane and place it in an oven at 60 o °C for 8 h. The obtained sample is labeled Co / CM-1.0.

[0025] Place Co / CM-1.0 in a tube furnace, raise the temperature from the initial temperature (room temperature) to 600 o °C for calcination, and keep it at the target temperature of 600 o °C for 3 h, where the heating rate is 3 o °C / min, the calcination atmosphere is argon, and after the calcination is completed, let it cool naturally to room temperature. The obtained sample is labeled Co / CM-1.0-600.

[0026] Apply the catalytic membrane Co / CM-1.0-600 to the catalytic reaction of hydrogenating p-nitrophenol to p-aminophenol. After 10 min of reaction, the conversion rate is 78.6% and the selectivity is 100%.

[0027] Embodiment 3 Unless otherwise specified, this embodiment is the same as Embodiment 1. Specifically, the difference between this embodiment and Embodiment 1 lies in the process of step (4). The process of coating with a polydopamine coating and pyrolysis in this embodiment is as follows: Re-prepare 250 mL of a tris(hydroxymethyl)aminomethane aqueous solution with a concentration of 0.125 mol / L, adjust the pH of the solution to 9.0 using dilute hydrochloric acid with a concentration of 0.01 mol / L, and then add dopamine hydrochloride under stirring to prepare a dopamine coating solution with a concentration of 7.0 g / L. Then load the Co / CM catalytic membrane into a forced-flow membrane module, and then control the coating solution to circulate forcibly from the inside of the membrane tube channel to the outside of the membrane tube at a flow rate of 6 L / h at 45 o °C, and control the coating time to be 20 h. After the coating is completed, take out the membrane and place it in an oven at 80 o °C for 12 h. The obtained sample is labeled Co / CM-7.0.

[0028] Place Co / CM-7.0 in a tube furnace, raise the temperature from the initial temperature (room temperature) to 800 oC was calcined and kept at the target temperature of 800 o °C for 7 h, where the heating rate was 6 o °C / min, the calcination atmosphere was argon, and after the calcination, it was naturally cooled to room temperature. The obtained sample was labeled as Co / CM-7.0-800.

[0029] The catalytic membrane Co / CM-7.0-800 was applied to the catalytic reaction of hydrogenating p-nitrophenol to p-aminophenol. After 10 min of reaction, the conversion rate was 81.3% and the selectivity was 100%.

[0030] Comparative Example 1 The difference between this comparative example and Example 1 was that the Co / CM catalytic membrane was directly applied to the catalytic reaction of hydrogenating p-nitrophenol to p-aminophenol without subsequent treatment. After 10 min of reaction, the conversion rate was 74.3%.

[0031] Comparative Example 2 The difference between this comparative example and Example 1 was that the prepared Co / CM catalytic membrane was directly placed in a crucible and then placed in a tube furnace for high-temperature calcination. The calcination conditions were in an argon atmosphere, rising from room temperature to the target temperature of 700 o °C at a rate of 5 o °C / min, and maintaining at the target temperature for 5 h. Then, the sample was naturally cooled to room temperature, and the obtained membrane tube was denoted as the Co / CM-0.0-700 catalytic membrane. The Co / CM-0.0-700 catalytic membrane was applied to the catalytic reaction of hydrogenating p-nitrophenol to p-aminophenol. After 10 min of reaction, the conversion rate was 55.5%.

[0032] Powders were scraped from the surfaces and channels of the Co / CM in Comparative Example 1, the Co / CM-3.0-700 prepared in Example 1, and the Co / CM-0.0-700 catalytic membrane prepared in Comparative Example 2 for transmission electron microscopy characterization, and the particle sizes of the active component Co were statistically analyzed. The results were as Figure 1 shown. Among them Figure 1 a, Figure 1 d were the TEM images and particle size distributions of the Co / CM catalytic membrane, Figure 1 b, Figure 1 e were the TEM images and particle size distributions of the Co / CM-3.0-700 catalytic membrane, Figure 1 c, Figure 1 f were the TEM images and particle size distributions of the Co / CM-0.0-700 catalytic membrane. Through Figure 1It can be seen that the Co nanoparticles in the Co / CM catalytic membrane are sparsely distributed and have a relatively large average particle size of 53.1 nm. In the Co / CM-0.0-700 catalytic membrane after direct high-temperature calcination, the Co nanoparticles undergo significant agglomeration due to the sintering effect, and the average particle size is 80.3 nm. However, in the Co / CM-3.0-700 catalytic membrane obtained by coating the Co / CM catalytic membrane with a polydopamine coating and then performing high-temperature calcination, the average particle size of the Co nanoparticles decreases to 40.2 nm. This is because nitrogen-doped carbon is formed during the pyrolysis of polydopamine, which can interact with large Co nanoparticles through N defects, inhibit their migration, and cut them into smaller particles, offsetting the agglomeration phenomenon caused by high temperature.

[0033] As described above, the above are only the preferred embodiments of the present invention, and the present invention is not limited to other forms. Any person skilled in the art may use the disclosed technical content to make changes or modifications into equivalent embodiments with equivalent changes and apply them to other fields. However, as long as it does not depart from the technical solution content of the present invention, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for reducing Co particle size using a multi-channel Co / CM catalytic membrane, characterized in that: The surface of the Co / CM catalytic membrane is coated with a polydopamine coating and then dried and calcined.

2. The method for reducing Co particle size using a multi-channel Co / CM catalytic membrane according to claim 1, characterized in that: Here are the steps: (1) slowly adding a dilute hydrochloric acid solution to a tris(hydroxymethyl)aminomethane solution to obtain a Tris-HCl buffer solution, adding dopamine hydrochloride and mixing well to obtain a modified solution; (2) Under water bath conditions, the modified liquid is forced to circulate through the pores and walls of the ceramic membrane to load dopamine in situ, and then dried to obtain a dopamine-modified ceramic membrane; (3) forcing a methanol dispersion of cobalt nitrate hexahydrate to circulate through the pores and walls of the dopamine-modified ceramic membrane to load the cobalt salt in situ; (4) drying to obtain a cobalt salt-loaded ceramic membrane, and calcining once to obtain a Co / CM catalytic membrane; (5) slowly dropping a dilute hydrochloric acid solution into a tris(hydroxymethyl)aminomethane solution to obtain a Tris-HCl buffer solution, adding dopamine hydrochloride and mixing evenly to obtain a coating solution; (6) Under water bath conditions, the coating liquid is forced to circulate through the pores and walls of the ceramic membrane to load dopamine in situ, dry, obtain a polydopamine-coated catalytic membrane, and perform secondary calcination.

3. The method for reducing Co particle size using a multi-channel Co / CM catalytic membrane according to claim 2, characterized in that: In step (1) or (5), the concentration of the tris(hydroxymethyl)aminomethane solution is 0.075-0.125 mol / L, the pH value of the Tris-HCl buffer solution is 8-9; and the concentration of dopamine hydrochloride in the modification solution or the coating solution is 1-7 g / L.

4. The method for reducing Co particle size using a multi-channel Co / CM catalytic membrane according to claim 2, characterized in that: In step (1) or (5), the flow rate of the dopamine solution forced to circulate through the ceramic membrane is 2-5 L / h, the water bath temperature is 25-45° C., and the forced circulation flow time is 12-20 h.

5. The method for reducing Co particle size using a multi-channel Co / CM catalytic membrane according to claim 2, characterized in that: The primary calcination temperature of step (4) is 700° C. and the calcination time is 5 h. The secondary calcination temperature of step (6) is 600-800° C. and the calcination time is 3-7 h. The calcination atmosphere of both step (4) and step (6) is argon.

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