An encapsulated carbon dioxide reduction catalyst, its preparation method and application

Abstract

The present invention discloses a encapsulated carbon dioxide reduction catalyst, its preparation method and application. The steps of the preparation method are as follows: First, a multi-metal precursor template is formed by coordinating metal cations with organic ligands, then the multi-metal precursor template is surface-modified with a surfactant, and then the growth and encapsulation of mesoporous silica are carried out on its outside. Finally, the internal template is pyrolyzed by high-temperature calcination to generate high-entropy metal oxides. The mesoporous silica-encapsulated high-entropy metal oxide catalyst prepared by the present invention has high reaction activity at a relatively low temperature (not higher than 650 °C), the conversion rate of carbon dioxide exceeds 80%, and the synthesis gas ratio of the reaction product is close to the theoretical value. Moreover, the catalyst preparation route of this application is simple, with low energy consumption, novel and stable structure, and has certain industrial application potential, which can play a certain role in promoting the realization of the goals of "carbon peak and carbon neutrality".

Description

Technical Field

[0001] The present invention relates to the technical field of carbon dioxide resource utilization, and particularly relates to a encapsulated carbon dioxide reduction catalyst, a preparation method thereof and an application thereof. Background Art

[0002] Since the Industrial Revolution, the use of a large amount of fossil energy has led to a sharp increase in the content of carbon dioxide in the atmosphere and oceans, thereby triggering a serious greenhouse effect. In the early 19th century, the content of carbon dioxide in the air was 280 ppm. However, just after one century, so far the content of carbon dioxide in the atmosphere has reached 385 ppm. Continuing in this growth mode, the content of carbon dioxide in the atmosphere will reach 600 ppm in the next century, and the resulting greenhouse effect will bring serious environmental problems (such as glacier melting, desertification and extreme weather, etc.). Therefore, scientific researchers have begun to focus on the resource utilization of carbon dioxide. The resource utilization of carbon dioxide can not only reduce the content of carbon dioxide in the atmosphere, but also use the reduction products of carbon dioxide to further prepare high-value-added chemicals for utilization, and a stable carbon cycle can be maintained throughout the process. This solution is a good way to help achieve the goals of "carbon peak" and "carbon neutrality". However, the difficulty of the current route for preparing high-value-added chemicals by carbon dioxide reduction lies in the fact that the carbon dioxide molecule itself has extremely strong chemical inertness and it is very difficult to effectively activate it at a relatively low temperature. Therefore, the core of realizing this technology is to develop a catalyst that can achieve efficient reduction of carbon dioxide and can maintain stable operation.

[0003] Numerous researchers have conducted in-depth studies on catalysts for carbon dioxide reduction, which are mainly classified according to their different reduction methods: Thermal catalytic carbon dioxide reduction: With the assistance of thermal energy, carbon dioxide is activated through the action of a catalyst and reacts with other reactants (such as hydrogen, lower alkanes, etc.) to produce other high-value products. This is also a reduction method with a certain scale of use in industry at present, such as the hydrogenation of carbon dioxide to methanol, etc.; Photocatalytic carbon dioxide reduction: Using light energy to excite the electrons of the catalyst, which jump to the valence band and generate a hole in the conduction band. This "electron-hole" system can effectively activate carbon dioxide at low temperatures or even room temperature, and further produce other products such as carbon monoxide, hydrocarbons or alcohols; Electrochemical catalytic carbon dioxide reduction: Carbon dioxide first forms a hydrated molecule in the electrolyte, then adsorbs on the electrode surface, and finally obtains electrons to form an adsorbed radical anion and is reduced. It has the advantage of low-temperature reduction like the photocatalytic reduction process. The energy supply forms and reaction processes of the three reduction methods are different. Therefore, the catalyst design for carbon dioxide reduction is also diverse, but the core concept lies in being able to stably achieve the highest energy use efficiency to realize the directional reduction of carbon dioxide. Currently, the design of catalyst active centers mainly focuses on noble metals (such as Pt, Ir, Ru, Rh, Pd, Au, etc.) and transition metals (such as Ni, Co, Cu, Fe, Zn, etc.). The design choices of catalyst supports include molecular sieves, metal oxides, mesoporous materials, graphene, metal-organic frameworks (MOFs), etc. The synergistic effects brought by the combination of these active centers and supports are the key to improving catalytic activity and stability. Loading metals on supports generally uses the impregnation method. However, the traditional impregnation method loading will cause the loss of active metals, resulting in a decrease or inactivation of catalyst activity, and it cannot efficiently complete the carbon dioxide reduction reaction and the preparation of high-value chemicals at low temperatures. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides an encapsulated carbon dioxide reduction catalyst, its preparation method and application. The encapsulated multi-metal high-entropy metal oxide catalyst with high entropy effect and lattice distortion effect can be used in the methane carbon dioxide reforming reaction to realize carbon dioxide reduction and resource utilization.

[0005] In the first aspect, the present invention provides a preparation method of an encapsulated carbon dioxide reduction catalyst, which is realized by the following technical solutions.

[0006] A preparation method of an encapsulated carbon dioxide reduction catalyst includes the following steps:

[0007] S1. Prepare a multi-metal precursor template

[0008] Dissolve five or more metal nitrates or metal acetylacetonates in a synthetic solvent at a ratio where any metal component does not exceed 50% to obtain a multi-metal precursor solution with a concentration of 0.01 - 10 mol / mL; dissolve the organic ligand in the synthetic solvent to obtain an organic ligand solution with a concentration of 0.01 - 10 mol / mL; mix the multi-metal precursor solution and the organic ligand solution in a volume ratio of (0.5 - 2):1 to prepare a multi-metal precursor template.

[0009] S2. Surface modification of the multi-metal precursor template

[0010] Disperse the multi-metal precursor template prepared in step S1 in a solvent containing a surfactant, and adjust the pH of the mixed solution to 7 - 14; the dosage of the surfactant is 1 - 10 times that of the multi-metal precursor template; the solvent is a mixture of ethanol and water, and the volume ratio of ethanol to water is (0.1 - 10):1.

[0011] S3. Encapsulation of the multi-metal precursor template with mesoporous silica

[0012] Add tetraethyl orthosilicate to the mixture obtained in step S2, stir and mix evenly, and then perform the encapsulation of mesoporous silica; the dosage of tetraethyl orthosilicate is 0.5 - 2 times that of the multi-metal precursor template.

[0013] S4. High-temperature calcination to remove the template agent to form high-entropy metal oxides

[0014] After completing the encapsulation of mesoporous silica, perform washing and drying, and then perform calcination. Calcination can remove the surfactant to form mesoporous channels, and the multi-metal precursor template in the core can form high-entropy metal oxides after calcination

[0015] Further, in step S1, the metal nitrates include zinc nitrate, nickel nitrate, copper nitrate, cobalt nitrate, iron nitrate, zirconium nitrate; the metal acetylacetonates include palladium acetylacetonate and ruthenium acetylacetonate.

[0016] Further, in step S1, the organic ligand includes 2-methylimidazole and terephthalic acid.

[0017] Further, in step S1, the synthetic solvent is selected from one or a combination of methanol, ethanol, water, and N-N dimethylformamide.

[0018] Further, in step S1, the synthesis method adopts one or more of the hydrothermal method, room temperature magnetic stirring method, ultrasonic method, and room temperature static growth method.

[0019] Preferably, in step S1, when the organic ligand is 2-methylimidazole, the metal nitrate is a combination of zinc nitrate, nickel nitrate, copper nitrate, cobalt nitrate, and iron nitrate, the metal acetylacetonate is a combination of palladium acetylacetonate and ruthenium acetylacetonate, the synthesis solvent is methanol, and the synthesis method is the room-temperature static growth method.

[0020] Preferably, in step S1, when the organic ligand is terephthalic acid, the metal nitrate is a combination of nickel nitrate, copper nitrate, cobalt nitrate, zirconium nitrate, zinc nitrate, and iron nitrate, the synthesis solvent is a mixed solvent of N,N-dimethylformamide and ethanol, and the synthesis method is the hydrothermal method.

[0021] Further, in step S2, ammonia water is added dropwise to adjust the pH of the mixed solution to 7-14.

[0022] Further, in step S2, the surfactant is selected from one or a combination of cetyltrimethylammonium bromide, polyvinylpyrrolidone, triethylamine, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer, and poloxamer.

[0023] Further, in step S3, the mesoporous silica encapsulation is carried out by the room-temperature magnetic stirring method or the hydrothermal method. Preferably, the mesoporous silica encapsulation is carried out by the room-temperature magnetic stirring method, and the stirring time is more than 12 hours.

[0024] Further, in step S4, the washing and drying methods are as follows: The residual unreacted substances are removed by cross-washing with deionized water and ethanol, and dried in an air atmosphere for more than 12 hours, and the drying temperature is 80-120 °C.

[0025] Further, in step S4, the calcination atmosphere is selected from one or several of air, nitrogen, argon, or hydrogen; the calcination temperature is 500-900 °C, and the calcination time is 4-8 h. Preferably, the calcination atmosphere is an air atmosphere, and the calcination temperature is 700-900 °C.

[0026] In the second aspect, the present invention provides an encapsulated carbon dioxide reduction catalyst, which is realized by the following technical solutions.

[0027] An encapsulated carbon dioxide reduction catalyst prepared by the above preparation method.

[0028] In the third aspect, the present invention provides a use of an encapsulated carbon dioxide reduction catalyst, which is realized by the following technical solutions.

[0029] An application of the above encapsulated carbon dioxide reduction catalyst in carbon dioxide reduction and carbon dioxide resource utilization.

[0030] Further, the encapsulated carbon dioxide reduction catalyst serves as a catalyst for the methane dry reforming reaction. Specifically, the reforming reaction adopts a fixed-bed process, and the raw materials are methane and carbon dioxide diluted with nitrogen. The volume ratio of methane to carbon dioxide is (0.5 - 2):1, the reaction temperature is 450 - 800 °C, the reaction pressure is 0 - 3 MPa, and the space velocity is 600 - 6000 h -1 .

[0031] The present application has the following beneficial effects.

[0032] The synthesis steps of the present invention are simple, and the raw materials are easily available. The synthesized catalyst has a unique core-shell structure, with an outer mesoporous silica shell layer that can act as an "armor" to protect the highly dispersed high-entropy metal oxide particles inside. Its ordered mesopores can achieve good mass transfer function. The high-entropy metal oxide particles can serve as active centers to effectively catalyze the carbon dioxide reduction reaction. Its unique high-entropy effect and lattice distortion effect can effectively activate stable carbon dioxide molecules, thereby realizing the conversion of carbon dioxide at a lower temperature while maintaining stability itself. The present invention can convert carbon dioxide into high-value products through catalytic conversion, bringing considerable benefits. In addition, the present invention helps to understand the activation and conversion mechanism of carbon dioxide on high-entropy metal oxides, and can help to expand the ways of resource utilization of carbon dioxide. Specific Embodiments

[0033] The following further illustrates the present patent application with reference to examples.

[0034] The experimental methods used in the following preparation examples and examples are all conventional methods unless otherwise specified; the materials, reagents, etc. used in the following preparation examples and examples can all be obtained from commercial channels unless otherwise specified.

[0035] In order to complete the efficient carbon dioxide reduction process with low energy consumption, the catalyst adopted by the present invention uses high-entropy metal oxides as the active center, and at the same time adopts the method of mesoporous silica encapsulation, which is beneficial to solving problems such as the loss of active metal caused by the traditional impregnation loading method leading to catalyst deactivation, and further improving the stability of the catalyst. The catalyst of the present invention has a unique core-shell structure, with ordered mesopores on the outer layer and evenly distributed high-entropy metal oxide particles inside. In addition, the present invention also optimizes the pore size of the shell mesoporous silica and the composition ratio of the high-entropy metal. The appropriate pore structure and metal composition ratio are beneficial to further improving the reduction activity of the catalyst for carbon dioxide.

[0036] Example 1

[0037] The preparation method of the mesoporous silica encapsulated PdNiZnCuCo high-entropy metal oxide catalyst (PdNiZnCuCo@meso SiO2) is as follows:

[0038] (1) Preparation of multi-metal precursor template: Weigh 0.305 g of Pd(acac)2, 0.291 g of Ni(NO3)2·6H2O, 0.297 g of Zn(NO3)2·6H2O, 0.291 g of Co(NO3)2·6H2O, and 0.242 g of Cu(NO3)2·6H2O into beaker A. Then add 25 mL of methanol solvent to the beaker and sonicate for 20 minutes to ensure that the metal salts are completely dissolved and well mixed.

[0039] (2) Weigh 0.82 g of 2-methylimidazole into beaker B, and also add 25 mL of methanol. Sonicate until completely dissolved. Then quickly pour the solution in beaker B into beaker A for mixing, and continue to sonicate for 10 minutes to ensure the solution is well mixed. Beaker A is left standing at room temperature for 24 hours. The obtained product is collected by centrifugation, washed alternately with methanol and deionized water, and finally washed with water once, and then dried in an oven at 60 °C for standby.

[0040] (3) Weigh 0.25 g of cetyltrimethylammonium bromide (CTAB) into beaker C, add a mixed solution of 10 mL of ethanol and 10 mL of deionized water, stir to dissolve, add 0.1 g of the product obtained in beaker A, sonicate to disperse evenly, then add 1 mL of 30% ammonia water, and subsequently add 0.5 mL of tetraethyl orthosilicate (TEOS). Continue to stir for 12 hours. The product is collected by centrifugation, washed alternately with ethanol and deionized water, and then dried at 60 °C for standby.

[0041] (4) The product obtained in step (3) is placed in a crucible and calcined in a muffle furnace at 900 °C for 6 hours. After cooling to room temperature, it is taken out and ground to obtain a mesoporous silica-encapsulated PdNiZnCuCo high-entropy metal oxide catalyst.

[0042] Example 2

[0043] A preparation method of an encapsulated carbon dioxide reduction catalyst, which is different from Example 1 in that:

[0044] (3) Weigh 0.5 g of cetyltrimethylammonium bromide (CTAB) into beaker C, add a mixed solution of 10 mL of ethanol and 10 mL of deionized water, stir to dissolve, add 0.1 g of the product obtained in beaker A, sonicate to disperse evenly, then add 1 mL of 30% ammonia water, and subsequently add 0.5 mL of tetraethyl orthosilicate (TEOS). Continue to stir for 12 hours. The product is collected by centrifugation, washed alternately with ethanol and deionized water, and then dried at 60 °C for standby.

[0045] Example 3

[0046] A preparation method of an encapsulated carbon dioxide reduction catalyst, which is different from Example 1 in that:

[0047] (3) Weigh 0.125 g of cetyltrimethylammonium bromide (CTAB) into beaker C, add a mixed solution of 10 mL of ethanol and 10 mL of deionized water. After stirring and dissolving, add 0.1 g of the product obtained in beaker A. After ultrasonic dispersion until uniform, add 1 mL of 30% ammonia water, and then add 0.5 mL of tetraethyl orthosilicate (TEOS). Continue stirring for 12 hours. The product is collected by centrifugation, washed alternately with ethanol and deionized water, and then dried at 60 °C for standby.

[0048] Example 4

[0049] A preparation method of an encapsulated carbon dioxide reduction catalyst, which is different from Example 1 in that:

[0050] (3) Weigh 0.25 g of polyvinylpyrrolidone (PVP) into beaker C, add a mixed solution of 10 mL of ethanol and 10 mL of deionized water. After stirring and dissolving, add 0.1 g of the product obtained in beaker A. After ultrasonic dispersion until uniform, add 1 mL of 30% ammonia water, and then add 0.5 mL of tetraethyl orthosilicate (TEOS). Continue stirring for 12 hours. The product is collected by centrifugation, washed alternately with ethanol and deionized water, and then dried at 60 °C for standby.

[0051] Example 5

[0052] A preparation method of an encapsulated carbon dioxide reduction catalyst, which is different from Example 1 in that:

[0053] (4) The product obtained in step (3) is placed in a crucible and placed in a muffle furnace. It is calcined at 850 °C for 6 hours, taken out and ground after cooling to room temperature to obtain a mesoporous silica-encapsulated PdNiZnCuCo high-entropy metal oxide catalyst.

[0054] Example 6

[0055] A preparation method of an encapsulated carbon dioxide reduction catalyst, which is different from Example 1 in that:

[0056] (4) The product obtained in step (3) is placed in a crucible and placed in a muffle furnace. It is calcined at 800 °C for 6 hours, taken out and ground after cooling to room temperature to obtain a mesoporous silica-encapsulated PdNiZnCuCo high-entropy metal oxide catalyst.

[0057] Example 7

[0058] A preparation method of an encapsulated carbon dioxide reduction catalyst, which is different from Example 1 in that:

[0059] (1) Preparation of multi-metal precursor template: Weigh 0.393 g of Pt(acac)2, 0.291 g of Ni(NO3)2·6H2O, 0.297 g of Zn(NO3)2·6H2O, 0.291 g of Co(NO3)2·6H2O, and 0.242 g of Cu(NO3)2·6H2O into beaker A respectively. Then add 25 mL of methanol solvent to the beaker and ultrasonicate for 20 minutes to ensure that the metal salts are completely dissolved and well mixed.

[0060] Example 8

[0061] A preparation method of an encapsulated carbon dioxide reduction catalyst, which is different from that of Example 1 in that:

[0062] (1) Weigh 0.23 g of Pd(NO3)2, 0.291 g of Ni(NO3)2·6H2O, 0.297 g of Zn(NO3)2·6H2O, 0.291 g of Co(NO3)2·6H2O, and 0.242 g of Cu(NO3)2·6H2O into beaker A respectively. Then add 25 mL of methanol solvent to the beaker and ultrasonicate for 20 minutes to ensure that the metal salts are completely dissolved and well mixed.

[0063] (2) Weigh 1.66 g of terephthalic acid into beaker B, and also add 25 mL of methanol and ultrasonicate until completely dissolved. Then quickly pour the solution in beaker B into beaker A for mixing, and continue ultrasonication for 10 minutes to ensure the solution is well mixed. Beaker A is left standing at room temperature for 24 hours. The obtained product is collected by centrifugation, washed alternately with methanol and deionized water, and finally washed with water once, and then dried in an oven at 60 °C for standby.

[0064] Comparative Example 1

[0065] A preparation method of a carbon dioxide reduction catalyst is as follows:

[0066] (1) Take 0.23 g of Pd(NO3)2, 0.291 g of Ni(NO3)2·6H2O, 0.297 g of Zn(NO3)2·6H2O, 0.291 g of Co(NO3)2·6H2O, and 0.242 g of Cu(NO3)2·6H2O into beaker A respectively, and add 15 mL of deionized water to dissolve the metal salts.

[0067] (2) Weigh 25 g of commercial MCM-41, directly impregnate it with the solution in step (1), and dry it at 100 °C for standby.

[0068] (3) The calcination process is the same as that in step (4) of Example 1.

[0069] Catalyst performance detection

[0070] It was carried out on a 20 mL adiabatic micro fixed-bed reactor. 1 g of the catalyst prepared in Examples 1-8 and Comparative Example 1 was weighed and mixed with 5 mL of quartz sand, and then loaded into the middle section of the reaction tube. The two ends were filled with quartz sand and quartz wool. During the programmed temperature rise process, nitrogen was continuously introduced for purging. It was stabilized at 300 °C and 450 °C for 20 minutes respectively. After the temperature was raised to the reaction temperature of 650 °C and maintained for 30 minutes for catalyst activation, the reaction gas was introduced. The feed ratio of methane to carbon dioxide in the reaction raw materials was 1:1, nitrogen was used as the carrier gas and continuously introduced, the feed flow rate was 100 mL / min, the reaction pressure was 0.1 MPa, and the reaction space velocity was 1800 h -1 . Analysis started 30 minutes after the reaction began to ensure stable operation at the start of the reaction. After that, gas was introduced into the gas chromatograph for 1 minute every 1 hour for product analysis. The experimental results are shown in Table 1 below.

[0071] Table 1: Experimental results of the catalytic performance of each catalyst under the same reaction conditions

[0072]

[0073] Judging from the reaction results, under the same reaction conditions, the catalysts used in Examples 1-8 could achieve CH4 conversion rates and CO2 conversion rates of over 80%, and had good reaction performance. However, the catalyst used in Comparative Example 1 had poor reaction effects, with a CH4 conversion rate of only 23% and a CO2 conversion rate as low as 20%. Therefore, the mesoporous silica encapsulated high-entropy metal oxide catalysts prepared in Examples 1-8 had obvious reaction activity advantages.

[0074] The examples of this specific implementation manner are all preferred examples of the present invention, and do not limit the protection scope of the present invention accordingly. Therefore, all equivalent changes made according to the structure, shape, and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A preparation method of an encapsulated carbon dioxide reduction catalyst, characterized in that: It includes the following steps: S1. Prepare a multi-metal precursor template Dissolve five or more metal nitrates or metal acetylacetonates in a synthesis solvent according to the proportion that any metal component does not exceed 50% to obtain a multi-metal precursor solution with a concentration of 0.01~10 mol / mL; Dissolve the organic ligand in the synthesis solvent to obtain an organic ligand solution with a concentration of 0.01~10 mol / mL; mix the multi-metal precursor solution and the organic ligand solution according to the volume ratio of (0.5~2):1 to prepare a multi-metal precursor template; S2. Perform surface modification on the multi-metal precursor template Disperse the multi-metal precursor template prepared in step S1 in a solvent containing a surfactant, and adjust the pH of the mixed solution to 7~14; the dosage of the surfactant is 1~10 times that of the multi-metal precursor template; the solvent is a mixture of ethanol and water, and the volume ratio of ethanol to water is (0.1~10):1; S3. Encapsulate the multi-metal precursor template with mesoporous silica Add tetraethyl orthosilicate to the mixture obtained in step S2, stir and mix evenly, and then perform the encapsulation of mesoporous silica; the dosage of the tetraethyl orthosilicate is 0.5~2 times that of the multi-metal precursor template; S4. Remove the template agent by high-temperature calcination to form a high-entropy metal oxide After the encapsulation of mesoporous silica is completed, wash and dry, and then perform calcination; In step S1, the metal nitrates include zinc nitrate, nickel nitrate, copper nitrate, cobalt nitrate, iron nitrate, and zirconium nitrate; the metal acetylacetonates include palladium acetylacetonate and ruthenium acetylacetonate; In step S1, the organic ligand includes 2-methylimidazole and terephthalic acid; In step S3, the encapsulation of mesoporous silica adopts the room-temperature magnetic stirring method or the hydrothermal method.

2. The preparation method of a packaged carbon dioxide reduction catalyst according to claim 1, characterized in that: In step S1, the synthesis solvent is selected from one or a combination of methanol, ethanol, water, and N-N dimethylformamide.

3. The preparation method of an encapsulated carbon dioxide reduction catalyst according to claim 1, characterized in that: In step S2, the surfactant is selected from one or a combination of cetyltrimethylammonium bromide, polyvinylpyrrolidone, triethylamine, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer, and poloxamer.

4. The preparation method of an encapsulated carbon dioxide reduction catalyst according to claim 1, wherein: In step S4, the calcination atmosphere is selected from one or several of air, nitrogen, argon, or hydrogen; the calcination temperature is 500~900 °C, and the calcination time is 4~8 h.

5. An encapsulated carbon dioxide reduction catalyst prepared by the preparation method according to any one of claims 1-4.

6. An application of the encapsulated carbon dioxide reduction catalyst according to claim 5 in carbon dioxide reduction and carbon dioxide resource utilization.

7. The application according to claim 6, characterized in that: The encapsulated carbon dioxide reduction catalyst is used as a catalyst for the methane carbon dioxide reforming reaction.

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