A hierarchical porous carbon-based CuZn catalyst, its preparation method and application

Abstract

The present invention discloses a hierarchical porous carbon-based CuZn catalyst, its preparation method and application, belonging to the technical field of catalyst preparation and application. The hierarchical porous carbon-based CuZn catalyst uses coconut shell residues as raw materials, and a hierarchical porous carbon material with a high specific surface area and a narrow mesopore distribution is prepared by step-by-step activation, and then it is prepared by synchronous equal-volume impregnation of composite metal ions and calcination in an inert gas. The coconut shell-based hierarchical porous carbon material of the present invention is renewable, has a high specific surface area and mesopore volume, and a narrow mesopore distribution. It can replace hydrogen reduction to generate a Cu-ZnO active interface. At the same time, the preparation of the hierarchical porous carbon-based catalyst can improve the space-time yield and catalytic life of the catalytic hydrogenation of CO2 to methanol.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst preparation, and particularly relates to a hierarchical porous carbon-based CuZn catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] In the field of catalytic hydrogenation of CO2 to methanol, supported metal Cu catalysts have been widely studied and applied in its industrial catalytic reactions. The composite carriers commonly used in industry are Al2O3 and ZnO, where Al2O3 is the structural assistant of the catalyst, and the interface between metal Cu and ZnO is the active site for catalytic hydrogenation of CO2. However, during the process of catalytic hydrogenation of CO2 to methanol, a large amount of water by-products will be generated. Under high-temperature conditions, the formed hydrothermal atmosphere will cause changes in the Al2O3 carrier and the migration and aggregation of metal Cu nanoparticles, resulting in inactivation. Therefore, for the reaction of catalytic hydrogenation of CO2 to methanol, it is required that the catalyst has certain water resistance under the reaction conditions to improve the service life of the supported CuZn catalyst. At the same time, for CuZn catalysts prepared with metal oxide carriers such as Al2O3 and SiO2, after loading CuO and ZnO, they need to be reduced by high-temperature hydrogen at 300 °C to generate the Cu-ZnO active interface, which increases the preparation cost of the catalyst.

[0003] The porous carbon materials prepared from forestry residues such as coconut shells have the advantages of being renewable, carbon neutral, good hydrothermal stability, high strength, good reducibility, etc. The carbon-based catalysts prepared therefrom should be able to reduce the catalyst preparation cost and improve the stability of the reaction of catalytic hydrogenation of CO2 to methanol. However, the coconut shell carbon materials prepared by ordinary methods still have the disadvantages of low specific surface area, low mesopore volume, wide mesopore distribution, etc. At the same time, there is still a need to break through the construction of a highly dispersed and strongly interacting Cu-ZnO interface on the surface of the carbon material. Summary of the Invention

[0004] One technical problem solved by the present invention is to provide a hierarchical porous carbon-based CuZn catalyst. Another technical problem to be solved by the present invention is to provide a preparation method of a hierarchical porous carbon-based CuZn catalyst. Another technical problem to be solved by the present invention is to provide an application of a hierarchical porous carbon-based CuZn catalyst in the catalytic hydrogenation of CO2 to methanol. Utilize the reducibility of the carbon material to promote the formation of the Cu-ZnO active interface, utilize the high specific surface area, narrow-distribution mesopores of the hierarchical porous carbon material prepared by stepwise activation and the synchronous impregnation-pyrolysis method to improve the dispersion and interaction of the Cu-ZnO interface, and the carbon-based catalyst prepared from the coconut shell carbon material with high mechanical strength does not require subsequent shaping. Rely on the high hydrothermal stability of the carbon material to improve the service life of the catalyst, and finally improve the activity and stability of the catalytic hydrogenation of CO2 to methanol.

[0005] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0006] A preparation method of a hierarchical pore carbon-based CuZn catalyst, wherein the catalyst uses a hierarchical pore granular carbon material as a carrier and a nano Cu-ZnO interface as an effective active site, and is obtained by a synchronous impregnation-pyrolysis method.

[0007] In the preparation method of the hierarchical pore carbon-based CuZn catalyst, in the synchronous equal-volume impregnation-pyrolysis method, after the hierarchical pore granular carbon material is saturated with an aqueous composite solution of Cu(NO3)2·3H2O and Zn(NO3)2·6H2O, it is calcined in an inert atmosphere to form a hierarchical pore carbon-based CuZn catalyst.

[0008] In the preparation method of the hierarchical pore carbon-based CuZn catalyst, the calcination temperature is 290-310°C, the inert atmosphere is nitrogen or argon, and the calcination time is 3.5-4.5 h; preferably, the calcination temperature is 300°C, the inert atmosphere is nitrogen, and the calcination time is 4.

[0009] In the preparation method of the hierarchical pore carbon-based CuZn catalyst, the total loading amount of Cu and Zn in the hierarchical pore carbon-based CuZn catalyst is 25%-35%, and the ratio is 0.8-1.2; preferably, the total loading amount of Cu and Zn is 30%, and the ratio is 1.

[0010] In the preparation method of the hierarchical pore carbon-based CuZn catalyst, the preparation of the hierarchical pore granular carbon material: using coconut shell residues with a 20-40 mesh sieve as raw materials, pyrolyzing and carbonizing at 500-600°C for 1 h, and then obtaining the hierarchical pore granular carbon material by a step-by-step activation method; preferably, the pyrolysis and carbonization temperature is 550°C.

[0011] In the preparation method of the hierarchical pore carbon-based CuZn catalyst, the step-by-step activation is to first use a carbon dioxide atmosphere to activate at 870-890°C for 50 min; then use a water vapor atmosphere to activate at 840-860°C for 60 min; preferably, the activation temperature in the nitrogen atmosphere is 880°C, and the activation temperature in the water vapor atmosphere is 850°C.

[0012] The preparation method of the hierarchical pore carbon-based CuZn catalyst includes the following steps:

[0013] (1) Using coconut shell residues as raw materials, after pyrolyzing and carbonizing, first activate in a carbon dioxide atmosphere to obtain a microporous carbon material, and continue to activate in a water vapor atmosphere to obtain a hierarchical pore carbon material;

[0014] (2) Prepare a composite aqueous solution of Cu(NO3)2·3H2O and Zn(NO3)2·6H2O, slowly add the hierarchically porous carbon material into the solution, and after ultrasonic treatment and vacuum stirring impregnation, until the aqueous solution is completely saturated and adsorbed by the hierarchically porous carbon material;

[0015] (3) After vacuum drying at 60 °C for 12 h, calcine in a nitrogen atmosphere to prepare a hierarchically porous carbon-based CuZn catalyst.

[0016] The hierarchically porous carbon-based CuZn catalyst prepared by the above method.

[0017] Application of the above hierarchically porous carbon-based CuZn catalyst in the hydrogenation of CO2 to methanol.

[0018] The application of the hierarchically porous carbon-based CuZn catalyst in the hydrogenation of CO2 to methanol. Add the hierarchically porous carbon-based CuZn catalyst into a micro fixed-bed reactor, and prepare methanol under the conditions of 260 °C, V(H2) / V(CO2) = 3 / 1, GHSV = 14400 ml / g / h, and 3 MPa pressure.

[0019] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0020] The present invention uses renewable coconut shell residues as raw materials and adopts a step-by-step activation method to prepare a hierarchically porous carbon material carrier, which has the advantages of large specific surface area, narrow mesopore distribution (2 - 5 nm), high hydrothermal stability, and high mechanical strength. It can effectively promote the dispersion and formation of the nano Cu-ZnO active interface, improve the thermal stability of the carbon-based CuZn catalyst, and the prepared particulate catalyst can be directly used for heterogeneous continuous catalytic reactions in a fixed-bed reactor.

[0021] Adopt a synchronous impregnation-pyrolysis method to prepare a carbon-based CuZn catalyst, which improves the dispersion and interaction of the Cu-ZnO interface; the created hierarchically porous carbon-based CuZn catalyst is applied to the continuous fixed-bed reaction of CO2 catalytic hydrogenation to methanol, which has the advantages of low cost, high conversion rate, high methanol space-time yield, and good stability, and has good industrialization prospects. Specific embodiments

[0022] The following combines specific embodiments to further clarify the present invention. The embodiments are implemented on the premise of the technical solution of the present invention. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0023] Example 1

[0024] Using coconut shell residues sieved with a 20 - 40 mesh sieve as raw materials, pyrolyzing and carbonizing at 550 °C for 1 h, and activating with carbon dioxide at 880 °C for 50 min to prepare the microporous carbon material AC1, and then continuing to activate with steam at 850 °C for 60 min to prepare the hierarchical porous carbon material AC2.

[0025] The specific surface area of AC1 was measured to be 1435 m 2 / g, the total pore volume was 0.502 cm 3 / g, and the microporosity was 83%. The specific surface area of AC2 was 2210 m 2 / g, the total pore volume was 1.185 cm 3 / g, the mesopore volume was 0.38 cm 3 / g, and the mesopore distribution range was 2 - 5 nm.

[0026] Example 2

[0027] Prepare a composite aqueous solution of Cu(NO3)2·3H2O and Zn(NO3)2·6H2O (Cu:Zn = 1, total amount is 30%). Slowly add AC2 into the solution. After ultrasonic and vacuum stirring impregnation until the aqueous solution is completely saturated adsorbed by AC2; after vacuum drying at 60 °C for 12 h, calcine at 300 °C for 4 h in a nitrogen atmosphere to prepare the CuZn / AC2 catalyst.

[0028] Add this catalyst into a hydrothermal reaction kettle containing 20 mL of water, keep it at 150 °C for 8 h, wait until it cools to room temperature, filter and dry. The obtained sample is CuZn / AC2 - H.

[0029] Comparative Example 1

[0030] Prepare a composite aqueous solution of Cu(NO3)2·3H2O and Zn(NO3)2·6H2O (Cu:Zn = 1, total amount is 30%). Slowly add AC1 into the solution. After ultrasonic and vacuum stirring impregnation until the aqueous solution is completely saturated adsorbed by AC1; after vacuum drying at 60 °C for 12 h, calcine at 300 °C for 4 h in a nitrogen atmosphere to prepare the CuZn / AC1 catalyst.

[0031] Comparative Example 2

[0032] Prepare a composite aqueous solution of Cu(NO3)2·3H2O and Zn(NO3)2·6H2O (Cu:Zn = 1, total amount is 30%). Slowly add mesoporous SiO2 into the solution. After ultrasonic and vacuum stirring impregnation until the aqueous solution is completely saturated adsorbed by mesoporous SiO2; after vacuum drying at 60 °C for 12 h, calcine at 300 °C for 4 h in a nitrogen atmosphere to prepare the CuZn / SiO2 catalyst.

[0033] Comparative Example 3

[0034] Under the conditions of Cu:Zn = 1 and a total amount of 30%, aqueous solutions of Cu(NO3)2·3H2O and Zn(NO3)2·6H2O were respectively prepared. AC2 was slowly added to the Cu(NO3)2·3H2O solution. After ultrasonic treatment and vacuum stirring impregnation, until the aqueous solution was completely saturated and adsorbed by AC2; after vacuum drying at 60 °C for 12 h, in a nitrogen atmosphere, it was calcined at 300 °C for 2 h. The prepared product was added to the Zn(NO3)2·6H2O aqueous solution, and the above process was repeated to prepare the Cu-Zn / AC2 catalyst.

[0035] Comparative Example 4

[0036] Under the conditions of Cu:Zn = 1 and a total amount of 30%, aqueous solutions of Cu(NO3)2·3H2O and Zn(NO3)2·6H2O were respectively prepared. AC2 was slowly added to the Zn(NO3)2·6H2O solution. After ultrasonic treatment and vacuum stirring impregnation, until the aqueous solution was completely saturated and adsorbed by AC2; after vacuum drying at 60 °C for 12 h, in a nitrogen atmosphere, it was calcined at 300 °C for 2 h. The prepared product was added to the Cu(NO3)2·3H2O aqueous solution, and the above process was repeated to prepare the Zn-Cu / AC2 catalyst.

[0037] Comparative Example 5

[0038] A composite aqueous solution of Cu(NO3)2·3H2O and Zn(NO3)2·6H2O (Cu:Zn = 1, total amount 30%) was prepared. Al2O3 prepared by calcining aluminum nitrate was slowly added to the solution. After ultrasonic treatment and vacuum stirring impregnation, until the aqueous solution was completely saturated and adsorbed by mesoporous SiO2; after vacuum drying at 60 °C for 12 h, in a nitrogen atmosphere, it was calcined at 300 °C for 4 h. The prepared catalyst was added to a hydrothermal reaction kettle containing 20 mL of water and kept at 150 °C for 8 h. After cooling to room temperature, it was filtered and dried, and the obtained sample was CuZn / Al2O3-H.

[0039] Comparative Example 6

[0040] A composite aqueous solution of Cu(NO3)2·3H2O and Zn(NO3)2·6H2O (Cu:Zn = 2, total amount 30%) was prepared. AC2 was slowly added to the solution. After ultrasonic treatment and vacuum stirring impregnation, until the aqueous solution was completely saturated and adsorbed by AC2; after vacuum drying at 60 °C for 12 h, in a nitrogen atmosphere, it was calcined at 300 °C for 4 h to prepare the CuZn / AC2-2 catalyst.

[0041] Comparative Example 7

[0042] Prepare a composite aqueous solution of Cu(NO3)2·3H2O and Zn(NO3)2·6H2O (Cu:Zn = 0.5, total amount is 30%). Slowly add AC2 into the solution. After ultrasonic treatment and vacuum stirring impregnation until the aqueous solution is completely saturated adsorbed by AC2. After drying in vacuum at 60°C for 12 h, calcine at 300°C for 4 h in a nitrogen atmosphere to prepare the CuZn / AC2-0.5 catalyst.

[0043] Comparative Example 8

[0044] Prepare a composite aqueous solution of Cu(NO3)2·3H2O and Zn(NO3)2·6H2O (Cu:Zn = 1, total amount is 20%). Slowly add AC2 into the solution. After ultrasonic treatment and vacuum stirring impregnation until the aqueous solution is completely saturated adsorbed by AC2. After drying in vacuum at 60°C for 12 h, calcine at 300°C for 4 h in a nitrogen atmosphere to prepare the CuZn / AC2-20 catalyst.

[0045] Comparative Example 9

[0046] Prepare a composite aqueous solution of Cu(NO3)2·3H2O and Zn(NO3)2·6H2O (Cu:Zn = 1, total amount is 40%). Slowly add AC2 into the solution. After ultrasonic treatment and vacuum stirring impregnation until the aqueous solution is completely saturated adsorbed by AC2. After drying in vacuum at 60°C for 12 h, calcine at 300°C for 4 h in a nitrogen atmosphere to prepare the CuZn / AC2-40 catalyst.

[0047] Example 3

[0048] Load the catalysts prepared in the above Example 2 and Comparative Examples 1-9 into a micro fixed-bed reactor respectively. Under the conditions of 260°C, V(H2) / V(CO2) = 3 / 1, GHSV = 14400 ml / g / h, and 3 MPa pressure, the results of the space-time yield and selectivity of the reaction are shown in Table 1.

[0049] Table 1 Space-time yield and selectivity of catalytic hydrogenation of CO2 to methanol

[0050] Catalyst Selectivity (%) <![CDATA[Space-time yield (g MeOH Kg cat -1 h -1 )]]> CuZn / AC2 41 121 CuZn / AC2-H 44 118 CuZn / AC1 42 52 <![CDATA[CuZn / SiO2]]> 44 49 Cu-Zn / AC2 31 76 Zn-Cu / AC2 31 42 <![CDATA[CuZn / Al2O3-H]]> 43 106 CuZn / AC2-2 18 59 CuZn / AC2-0.5 27 38 CuZn / AC2-20 19 28 CuZn / AC2-40 25 58

[0051] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of a hierarchical pore carbon-based CuZn catalyst, characterized in that, The catalyst is prepared by a synchronous impregnation-pyrolysis method using a hierarchical porous granular carbon material as a carrier and a nano Cu-ZnO interface as an effective active site; Preparation of the hierarchical porous granular carbon material: Using coconut shell residue with a 20-40 mesh sieve as a raw material, pyrolytic carbonization is carried out at 500-600 °C for 1 h, and then a hierarchical porous granular carbon material is obtained by a stepwise activation method; The stepwise activation is to first use a carbon dioxide atmosphere to activate at 870-890 °C for 50 min; then use a water vapor atmosphere to activate at 840-860 °C for 60 min.

2. The preparation method of the hierarchical pore carbon-based CuZn catalyst according to claim 1, wherein, The synchronous impregnation-pyrolysis method is that after the hierarchical porous granular carbon material is saturated with an aqueous solution of Cu(NO3)2·3H2O and Zn(NO3)2·6H2O, it is calcined in an inert atmosphere to form a hierarchical porous carbon-based CuZn catalyst.

3. The preparation method of the hierarchical porous carbon-based CuZn catalyst according to claim 2, characterized in that, The calcination temperature is 290-310 °C, the inert atmosphere is nitrogen or argon, and the calcination time is 3.5-4.5 h.

4. The preparation method of the hierarchical porous carbon-based CuZn catalyst according to claim 2, characterized in that, The total loading of Cu and Zn in the hierarchical porous carbon-based CuZn catalyst is 25%-35%, and the ratio is 0.8-1.

2.

5. The preparation method of the hierarchical pore carbon-based CuZn catalyst according to claim 1, characterized in that, It includes the following steps: (1) Using coconut shell residue as a raw material, after pyrolytic carbonization, first activate in a carbon dioxide atmosphere to obtain a microporous carbon material, and then activate in a water vapor atmosphere to obtain a hierarchical porous carbon material; (2) Prepare an aqueous solution of Cu(NO3)2·3H2O and Zn(NO3)2·6H2O, slowly add the hierarchical porous carbon material into the solution, and after ultrasonic and vacuum stirring impregnation, until the aqueous solution is completely saturated and adsorbed by the hierarchical porous carbon material; (3) After vacuum drying at 60 °C for 12 h, calcine in a nitrogen atmosphere to prepare a hierarchical porous carbon-based CuZn catalyst.

6. The hierarchical porous carbon-based CuZn catalyst prepared by the method according to any one of claims 1-5.

7. The application of the hierarchical porous carbon-based CuZn catalyst according to claim 6 in the hydrogenation of CO2 to methanol.

8. Use of the hierarchical pore carbon-based CuZn catalyst according to claim 7 in the preparation of methanol by hydrogenation of CO2, characterized in that, Add the hierarchical porous carbon-based CuZn catalyst into a micro fixed-bed reactor, and prepare methanol under the conditions of 260 °C, V(H2) / V(CO2) = 3 / 1, GHSV = 14400 mL / g / h, and 3 MPa pressure.