Cerium oxide-containing carbon dioxide hydrogenation catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysts, and relates to a cerium oxide-containing carbon dioxide hydrogenation catalyst and a preparation method and application thereof.The catalyst comprises active metal nickel and cerium oxide serving as a carrier, the cerium oxide with a nano structure is prepared by adopting a hydrothermal method, a supported nickel-based catalyst is prepared by adopting an impregnation method, and the supported nickel-based catalyst is prepared by adopting a hydrothermal method. The prepared catalyst is high in oxygen vacancy content, small in metal Ni particle size and uniform in dispersion, and methane preparation through carbon dioxide hydrogenation efficient conversion can be achieved. According to the Ni / CeO2-H catalyst prepared by the invention, the CO2 conversion rate reaches 79%, the selectivity to CH4 is 98%, and the Ni / CeO2-H catalyst shows excellent CO2 conversion rate and methane selectivity, so that the cerium oxide-containing catalyst provided by the invention has excellent CO2 hydrogenation performance and shows excellent catalytic activity, product selectivity and stability. The preparation method is simple and easy to operate, and the prepared catalyst has the characteristics of high activity and good stability and is expected to be used for large-scale industrial application.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to a carbon dioxide hydrogenation catalyst containing cerium oxide, a preparation method thereof, and an application thereof. Background Art

[0002] The application of fossil fuels such as coal, crude oil, and natural gas has greatly promoted the development of human economy and society. However, the excessive release of carbon dioxide into the atmospheric environment has also caused many environmental problems. Reducing carbon dioxide emissions is an important task in the process of global economic development, and reducing the content of carbon dioxide in the atmosphere is one of the key issues that need to be solved urgently. There are three ways to reduce the content of CO2 in the atmosphere: first, directly reduce the emission of CO2; second, capture and store CO2; and finally, convert and utilize CO2. Capturing and utilizing carbon dioxide, and using the captured carbon dioxide to manufacture new products and convert it into high-value industrial products have become one of the effective ways to achieve this goal. The carbon dioxide hydrogenation methanation reaction has attracted much attention because of its simple reaction conditions and the product methane, which is the main component of natural gas and an important raw material for fuel production. However, due to the stable chemical structure of CO2 molecules, the CO2 hydrogenation reaction is greatly restricted in terms of kinetics. Currently, the main catalysts used for the CO2 hydrogenation reaction are supported metal catalysts. The main active components are Group VIII metals (Co, Ni, Ru, Rh, Pd, Pt, etc.), and the carriers are oxides (such as CeO2, Al2O3, TiO2, SiO2, ZrO2, etc.).

[0003] Noble metal catalysts such as Ru have high reaction activity and stability, but due to their high cost, it is difficult to be applied on a large scale. Nickel, as a non-noble metal active component, has attracted much attention due to its good catalytic activity for carbon dioxide hydrogenation. Cárdenas-Arenas et al. compared the reaction activities of Ni / CeO2 and Ni / Al2O3 and found that Ni / CeO2 had more excellent reaction performance. By exploring its reaction mechanism, it was found that Ni had a proper metal-support strong interaction with the CeO2 carrier, and CeO2 could provide more oxygen vacancies, which was beneficial to the activation of CO2 molecules (Appl. Catal. B, 2020, 265, 118538). The highly adjustable nature of cerium oxide makes cerium oxide-based catalysts a commonly used catalyst for carbon dioxide methanation. Li et al. used the hydrothermal method to prepare nanocube cerium oxides with different particle sizes by changing the concentration of the NaOH solution. By comparison, it was found that CeO2-6M had the smallest particle size, about 32 nm, and the most surface oxygen vacancies, and Ni / CeO2-6M had the highest catalytic activity for the CO2 hydrogenation reaction. The surface oxygen vacancies of cerium oxide are effective active sites for dissociating the C-O bond of oxygen-containing compounds (Fuel, 2023, 333, 126369).

[0004] Ni / CeO2 has attracted much attention in the catalysts for hydrogenation of carbon dioxide due to its high catalytic activity and low price. Preparing a highly active Ni / CeO2 catalyst for efficient resource utilization of CO2 has important research significance. Cerium oxide is usually prepared by methods such as solid-phase method, gas-phase method, precipitation method, combustion method, and hydrothermal method. The solid-phase method requires a high temperature during the reaction, has strict requirements for reaction equipment, and the prepared nanoparticles have a wide particle size distribution range, low purity, and irregular shapes. The gas-phase method uses expensive equipment and has low production, making it difficult to be popularized industrially. In the precipitation method, the obtained precipitate is difficult to wash and filter, and the product purity is easily affected by the precipitating agent. The combustion method requires a flame temperature as high as 2000 °C, making it difficult to achieve industrial production. The cerium oxide particles prepared by the hydrothermal method have uniform particle size, large specific surface area, and abundant oxygen vacancies. After loading the non-precious metal Ni, high-efficiency conversion of CO2 can be achieved; and Ni is not prone to problems such as sintering and agglomeration and poor stability during the reaction. Summary of the Invention

[0005] One of the technical problems to be solved by the present invention is to solve the problems in the prior art such as low yield and purity of cerium oxide, wide particle size distribution range, poor dispersion and easy agglomeration, and low surface oxygen vacancy content. The present invention provides a CO2 hydrogenation catalyst containing cerium oxide, which has the characteristics of many oxygen vacancies, high activity, and strong stability. The present invention also provides a preparation method of a CO2 hydrogenation catalyst containing cerium oxide, which has the characteristics of easy operation, strong repeatability, and high universality.

[0006] In order to achieve the above object, the technical solutions adopted by the present invention are as follows:

[0007] The present invention provides, in a first aspect, a preparation method of a CO2 hydrogenation catalyst containing cerium oxide, and the preparation method includes the following steps:

[0008] (1) Dissolve a cerium salt precursor in a solvent, then add a precipitating agent and a dispersant, and stir until evenly mixed to obtain a mixed solution;

[0009] (2) Transfer the mixed solution into a hydrothermal autoclave, and carry out hydrothermal reaction at a temperature of 100-200 °C for 4-96 h. After hydrothermal treatment, filter or centrifuge to obtain a precipitate;

[0010] (3) Wash and dry the precipitate to obtain a solid powder;

[0011] (4) Grind the solid powder evenly, and calcine at 300-600 °C for 2-8 h to obtain cerium oxide powder;

[0012] (5) Prepare a nickel catalyst supported on cerium oxide by an impregnation method using the cerium oxide powder and a nickel salt precursor, denoted as Ni / CeO2-H catalyst.

[0013] Further, in step (1), the cerium salt precursor includes one or more of Ce(NO3)3·6H2O, CeCl3·7H2O, and Ce(Ac)3·xH2O; the solvent is one or more of deionized water, ethylene glycol, and benzyl alcohol; the precipitant includes one or more of glacial acetic acid, oxalic acid, and ammonia water; the dispersant includes one or more of polyvinylpyrrolidone, glucose, and acrylamide.

[0014] Further, in step (1), the stirring time is 0.5 - 8 h; in step (2), the hydrothermal reaction conditions are to react at a temperature of 160 - 180 °C for 4 - 72 h.

[0015] Further, in step (3), the drying conditions are to dry at a temperature of 60 - 150 °C for 6 - 48 h; preferably, the drying temperature is 80 - 120 °C and the time is 8 - 12 h.

[0016] Further, in step (4), the roasting operation conditions are to grind the solid powder evenly, transfer it into a muffle furnace, and heat it up to 300 - 600 °C at a heating rate of 1 - 10 °C / min for roasting for 2 - 8 h. -1 and roast for 2 - 8 h.

[0017] Further, in step (5), the nickel salt precursor includes one or more of Ni(NO3)2·6H2O, NiCl2·6H2O, NiSO4·6H2O, and Ni(Ac)2·4H2O.

[0018] Further, in step (5), the impregnation method includes, but is not limited to, equal volume impregnation method, excess impregnation method, and multiple impregnation methods for preparation. After impregnation, roasting is carried out, and the roasting conditions are to heat up to 400 - 500 °C at a heating rate of 1 - 5 °C / min and hold for 2 - 4 h. -1 and hold for 2 - 4 h.

[0019] The second aspect of the present invention also provides a carbon dioxide hydrogenation catalyst containing cerium oxide, which is prepared by the above preparation method. The catalyst includes active metal nickel and cerium oxide as a carrier; wherein, the content of active metal nickel is 1 wt% - 30 wt%, and the content of cerium oxide is 70 wt% - 99 wt%; preferably, the content of active metal nickel is 3 wt% - 20 wt%.

[0020] Among them, the cerium oxide carrier is prepared by a hydrothermal method, has a nanostructure and a high surface oxygen vacancy content.

[0021] The size of nickel metal particles is less than 10 nm and they are evenly dispersed on the cerium oxide carrier.

[0022] The application of the cerium oxide-containing carbon dioxide hydrogenation catalyst in the reaction of hydrogenating carbon dioxide to methane includes the following steps:

[0023] (1) Before the reaction, the catalyst is subjected to in-situ reduction pretreatment. The reduction temperature is 300 - 600 °C, and the reduction atmosphere is hydrogen or a mixture of hydrogen and an inert gas;

[0024] (2) In an atmospheric fixed-bed reactor, the reaction temperature is controlled at 200 - 400 °C, the molar ratio of H2 to CO2 in the raw material gas is 0.5 - 6, and the volumetric space velocity is 6000 - 120000 mLh -1 g cat -1 .

[0025] In step (1) of the application of the cerium oxide-containing carbon dioxide hydrogenation catalyst in the reaction of hydrogenating carbon dioxide to methane, the temperature of the in-situ reduction pretreatment is 400 - 500 °C, and the reduction atmosphere is pure hydrogen; in step (2), the molar ratio of H2 to CO2 in the raw material gas is 2 - 4, and the gas volumetric space velocity is 12000 - 90000 mLh -1 g cat -1 .

[0026] Compared with the prior art, the present invention has at least the following beneficial effects:

[0027] 1) The cerium oxide-containing carbon dioxide hydrogenation catalyst of the present invention is composed of a metal nickel active component and a cerium oxide support. A cerium oxide support with a rich oxygen vacancy content is prepared by a hydrothermal method; the Ni nanoparticles are small in size and evenly dispersed, with high metal utilization rate, effectively reducing the preparation cost of the catalyst.

[0028] 2) The CO2 conversion rate of the Ni / CeO2-H catalyst prepared in the present invention reaches 79%, and the selectivity for CH4 is 98%. It shows excellent CO2 conversion rate and methane selectivity, indicating that the cerium oxide-containing catalyst provided by the present invention has excellent CO2 hydrogenation performance, exhibiting excellent catalytic activity, product selectivity, and stability.

[0029] 3) The present invention adds a dispersant to the solvent in the hydrothermal reaction to make the cerium oxide evenly dispersed. The metal nickel is loaded onto the support cerium oxide by an impregnation method. The oxygen vacancy can serve as an adsorption site for CO2, promoting the activation of CO2. The C atom of CO2 can combine with the oxygen vacancy to form a carbonate intermediate, promoting the progress of the CO2 methanation reaction. The oxygen vacancy can promote the cleavage of the C - O bond of CO2 by providing electrons to generate a formic acid intermediate.

[0030] 4) The preparation method of the cerium oxide-containing catalyst provided by the present invention is simple in operation and reliable in method. The adjustable range of cerium oxide prepared by the hydrothermal method is large, which is beneficial to large-scale production and use.

[0031] 5) The cerium oxide-containing catalyst provided by the present invention is used in the carbon dioxide methanation reaction, with high reaction activity, high selectivity for methane products, and excellent stability of the catalyst. Description of the Drawings

[0032] Figure 1 a is the evaluation diagram of the carbon dioxide reaction performance of the catalysts in Examples 1 and 2 and Comparative Example 1 of the present invention; Figure 1 b is the evaluation diagram of the carbon dioxide reaction performance of the catalysts in Example 1 and Comparative Examples 2 and 3 of the present invention (reaction conditions: atmospheric pressure, 200 - 400 °C, GHSV = 60000 mLh -1 g cat -1 );

[0033] Figure 2 a is the X-ray diffraction (XRD) pattern of the catalysts in Examples 1 and 2 and Comparative Example 1 of the present invention; Figure 2 b is the X-ray diffraction (XRD) pattern of the catalysts in Example 1 and Comparative Examples 2 and 3 of the present invention;

[0034] Figure 3 is the high-resolution transmission electron microscope (HRTEM) image of the catalysts in Examples 1 and 2 and Comparative Example 1 of the present invention;

[0035] Figure 4 is the high-resolution transmission electron microscope (HRTEM) image of the catalysts in Example 1 and Comparative Examples 2 and 3 of the present invention. Detailed Embodiments

[0036] Example 1

[0037] Measure 2 mL of deionized water, 2 mL of glacial acetic acid, and 52 mL of ethylene glycol in sequence, add 2.61 g of Ce(NO3)3·6H2O and 0.04 g of polyvinylpyrrolidone (PVP), and stir for 30 min. Transfer the mixed solution to a 100 mL hydrothermal reactor, place it in an oven, keep it at 180 °C for 6 h, then take it out. Wait for the solution to cool to room temperature, pour off the upper yellowish-brown solution to obtain a purple precipitate. Wash the precipitate with deionized water until neutral, and then place it in an oven at 60 °C for drying. After complete drying, transfer the product to a crucible, place it in a muffle furnace, and keep it at 400 °C for 4 h to obtain pale yellow cerium oxide powder. According to the loading amount and water absorption, weigh 0.25 g of Ni(NO3)2·6H2O and an appropriate amount of deionized water, mix them evenly, add 0.95 g of CeO2 powder, mix them evenly, and then place them in an oven at 60 °C for drying. Grind the obtained solid powder and place it in a muffle furnace, and heat it to 400 °C at a heating rate of 5 °C min -1 and cool to room temperature after calcining for 3 h to obtain 5% Ni / CeO2-H catalyst.

[0038] Example 2

[0039] Weigh 1.80 g of glucose, 1.06 g of acrylamide, and 2.17 g of Ce(NO3)3·6H2O in sequence and dissolve them in 64 mL of deionized water. Stir and drop in 3.2 mL of 25 wt% ammonia water. Stir the mixture at room temperature for 5 h, then transfer it to a hydrothermal reactor, place it in an oven, and keep it at 180 °C for 72 h. Wait for the solution to cool to room temperature and collect the precipitate. Wash the precipitate with deionized water until neutral, and then place it in an oven at 60 °C for drying. After complete drying, transfer the product to a crucible, place it in a muffle furnace, and heat it to 600 °C at a heating rate of 5 °C min -1 and keep it for 2 h to obtain pale yellow cerium oxide powder. According to the loading amount and water absorption, weigh 0.25 g of Ni(NO3)2·6H2O and an appropriate amount of deionized water, mix them evenly, add 0.95 g of CeO2 powder, mix them evenly, and then place them in an oven at 60 °C for drying. Grind the obtained solid powder and place it in a muffle furnace, and heat it to 400 °C at a heating rate of 5 °Cmin -1 and cool to room temperature after calcining for 3 h to obtain 5% Ni / CeO2-H-A catalyst.

[0040] Example 3

[0041] Weigh 1.80 g of glucose, 1.06 g of acrylamide, and 2.17 g of Ce(NO3)3·6H2O in sequence and dissolve them in 64 mL of deionized water. Stir and dropwise add 3.2 mL of 25 wt% ammonia water. Stir the mixture at room temperature for 5 h, then transfer it to a hydrothermal reactor, place it in an oven, and maintain it at 180 °C for 72 h. Wait for the solution to cool to room temperature and collect the precipitate. Wash the precipitate with deionized water until neutral and then place it in an oven at 60 °C for drying. After complete drying, transfer the product to a crucible, place it in a muffle furnace, and heat it to 600 °C at a heating rate of 5 °C min -1 to obtain pale yellow cerium oxide powder after holding for 2 h. Weigh 0.25 g of Ni(NO3)2·6H2O solid and place it in a beaker, add 10 mL of deionized water, dissolve and stir evenly. Then add 0.95 g of CeO2 solid, stir vigorously for 30 min, and then place it in a water bath at 60 °C and stir and evaporate until it becomes viscous. Place the obtained sample in an oven at 60 °C for drying. After complete drying, take it out and grind it, and place it in a muffle furnace and heat it to 400 °C at a heating rate of 5 °C min -1 to obtain 5% Ni / CeO2-H-EI catalyst after calcining for 3 h at the heating rate.

[0042] Example 4

[0043] Measure 2 mL of deionized water, 2 mL of glacial acetic acid, and 52 mL of ethylene glycol in sequence, add 2.61 g of Ce(NO3)3·6H2O and 0.04 g of polyvinylpyrrolidone (PVP), and stir for 30 min. Transfer the mixed solution to a 100 mL hydrothermal reactor, place it in an oven, take it out after maintaining it at 180 °C for 6 h, wait for the solution to cool to room temperature, pour out the upper layer of yellowish-brown solution to obtain a purple precipitate. Wash the precipitate with deionized water until neutral and then place it in an oven at 60 °C for drying. After complete drying, transfer the product to a crucible, place it in a muffle furnace, and obtain pale yellow cerium oxide powder after maintaining at 400 °C for 4 h. Weigh 0.15 g of Ni(NO3)2·6H2O according to the loading amount and water absorption and mix it evenly with an appropriate amount of deionized water, then add 0.97 g of CeO2 powder, mix evenly and place it in an oven at 60 °C for drying. Grind the obtained solid powder and place it in a muffle furnace, and heat it to 400 °C at a heating rate of 5 °C min -1 to obtain 3% Ni / CeO2-H catalyst after calcining for 3 h and cooling to room temperature.

[0044] Example 5

[0045] Measure 2 mL of deionized water, 2 mL of glacial acetic acid and 52 mL of ethylene glycol in sequence, add 2.61 g of Ce(NO3)3·6H2O and 0.04 g of polyvinylpyrrolidone (PVP), and stir for 30 min. Transfer the mixed solution to a 100 mL hydrothermal reactor, place it in an oven, keep it at 180 °C for 6 h and then take it out. Wait for the solution to cool to room temperature, pour off the upper layer of yellowish-brown solution to obtain a purple precipitate. Wash the precipitate with deionized water until neutral, and then place it in an oven at 60 °C for drying. After complete drying, transfer the product to a crucible, place it in a muffle furnace, keep it at 400 °C for 4 h to obtain pale yellow cerium oxide powder. According to the loading amount and water absorption, weigh 0.51 g of Ni(NO3)2·6H2O and an appropriate amount of deionized water, mix them evenly, add 0.90 g of CeO2 powder, mix them evenly and then place them in an oven at 60 °C for drying. Grind the obtained solid powder and then place it in a muffle furnace, and heat it to 400 °C at a heating rate of 5 °C min -1 and cool to room temperature after calcining for 3 h to obtain 10% Ni / CeO2-H catalyst.

[0046] Example 6

[0047] Measure 2 mL of deionized water, 2 mL of glacial acetic acid and 52 mL of ethylene glycol in sequence, add 2.61 g of Ce(NO3)3·6H2O and 0.04 g of polyvinylpyrrolidone (PVP), and stir for 30 min. Transfer the mixed solution to a 100 mL hydrothermal reactor, place it in an oven, keep it at 180 °C for 6 h and then take it out. Wait for the solution to cool to room temperature, pour off the upper layer of yellowish-brown solution to obtain a purple precipitate. Wash the precipitate with deionized water until neutral, and then place it in an oven at 60 °C for drying. After complete drying, transfer the product to a crucible, place it in a muffle furnace, keep it at 400 °C for 4 h to obtain pale yellow cerium oxide powder. According to the loading amount and water absorption, weigh 0.76 g of Ni(NO3)2·6H2O and an appropriate amount of deionized water, mix them evenly, add 0.85 g of CeO2 powder, mix them evenly and then place them in an oven at 60 °C for drying. Grind the obtained solid powder and then place it in a muffle furnace, and heat it to 400 °C at a heating rate of 5 °C min -1 and cool to room temperature after calcining for 3 h to obtain 15% Ni / CeO2-H catalyst.

[0048] Example 7

[0049] Measure 2 mL of deionized water, 2 mL of glacial acetic acid and 52 mL of ethylene glycol successively, add 2.61 g of Ce(NO3)3·6H2O and 0.20 g of polyvinylpyrrolidone (PVP), and stir for 30 min. Transfer the mixed solution to a 100 mL hydrothermal reactor, place it in an oven, keep it at 180 °C for 6 h, then take it out. After the solution cools to room temperature, pour off the upper layer of yellowish-brown solution to obtain a purple precipitate. Wash the precipitate with deionized water until it is neutral, and then place it in an oven at 60 °C for drying. After complete drying, transfer the product to a crucible, place it in a muffle furnace, and keep it at 400 °C for 4 h to obtain pale yellow cerium oxide powder. According to the loading amount and water absorption, weigh 0.25 g of Ni(NO3)2·6H2O and mix it evenly with an appropriate amount of deionized water, then add 0.95 g of CeO2 powder. After mixing evenly, place it in an oven at 60 °C for drying. Grind the obtained solid powder and place it in a muffle furnace, and heat it to 400 °C at a heating rate of 5 °C min -1 and cool it to room temperature after calcining for 3 h to obtain 5% Ni / CeO2-H-PVP catalyst.

[0050] Example 8

[0051] Measure 2 mL of deionized water, 2 mL of glacial acetic acid and 52 mL of ethylene glycol successively, add 2.61 g of Ce(NO3)3·6H2O and 0.04 g of polyvinylpyrrolidone (PVP), and stir for 30 min. Transfer the mixed solution to a 100 mL hydrothermal reactor, place it in an oven, keep it at 180 °C for 24 h, then take it out. After the solution cools to room temperature, pour off the upper layer of yellowish-brown solution to obtain a purple precipitate. Wash the precipitate with deionized water until it is neutral, and then place it in an oven at 60 °C for drying. After complete drying, transfer the product to a crucible, place it in a muffle furnace, and keep it at 400 °C for 4 h to obtain pale yellow cerium oxide powder. According to the loading amount and water absorption, weigh 0.25 g of Ni(NO3)2·6H2O and mix it evenly with an appropriate amount of deionized water, then add 0.95 g of CeO2 powder. After mixing evenly, place it in an oven at 60 °C for drying. Grind the obtained solid powder and place it in a muffle furnace, and heat it to 400 °C at a heating rate of 5 °C min -1 and cool it to room temperature after calcining for 3 h to obtain 5% Ni / CeO2-H-24h catalyst.

[0052] Comparative Example 1

[0053] Weigh 21.71 g of Ce(NO3)3·6H2O and dissolve it in 200 mL of ethylene glycol solution with a volume fraction of 80%, place it in an oil bath at 50 °C, and slowly drop 50 mL of 3 mol L -1The ammonia water solution changes from colorless to a pale yellow suspension. It is maintained in an oil bath at 50 °C for 24 h. The obtained suspension is centrifuged, washed with absolute ethanol until the pH = 7, and then dried in an oven at 60 °C. After complete drying, the product is transferred to a crucible and placed in a muffle furnace, heated to 500 °C at a heating rate of 5 °C min -1 and maintained for 1 h to obtain pale yellow cerium oxide powder. According to the loading amount and water absorption, 0.25 g of Ni(NO3)2·6H2O and an appropriate amount of deionized water are weighed and mixed evenly, then 0.95 g of CeO2 powder is added. After mixing evenly, it is dried in an oven at 60 °C. The obtained solid powder is ground and then placed in a muffle furnace, heated to 400 °C at a heating rate of 5 °C min -1 and calcined for 3 h. After cooling to room temperature, a 5% Ni / CeO2-HP catalyst is obtained.

[0054] Comparative Example 2

[0055] 2 mL of deionized water, 2 mL of glacial acetic acid, and 52 mL of ethylene glycol are measured in sequence, 2.61 g of Ce(NO3)3·6H2O and 0.04 g of polyvinylpyrrolidone (PVP) are added, and the mixture is stirred for 30 min. The mixed solution is transferred to a 100 mL hydrothermal reactor, placed in an oven, kept at 180 °C for 400 min and then taken out. After the solution cools to room temperature, the upper layer of brownish-yellow solution is poured off to obtain a purple precipitate. The precipitate is washed with deionized water until neutral and then dried in an oven at 60 °C. After complete drying, the product is transferred to a crucible and placed in a muffle furnace. After maintaining at 400 °C for 4 h, pale yellow cerium oxide powder is obtained. 3.33 g of nitrosyl ruthenium nitrate solution (1.5 wt% Ru) is weighed and placed in a beaker, 10 mL of deionized water is added, stirred evenly, then 0.95 g of CeO2 powder is added. After stirring vigorously for 30 min, it is placed in a water bath at 60 °C and stirred and evaporated until it becomes viscous. The obtained sample is dried in an oven at 60 °C. After complete drying, it is taken out and ground, and placed in a muffle furnace at a heating rate of 5 °C min -1 and heated to 400 °C for calcination for 3 h to obtain a 5% Ru / CeO2-H catalyst.

[0056] Comparative Example 3

[0057] Measure 2 mL of deionized water, 2 mL of glacial acetic acid, and 52 mL of ethylene glycol in sequence, add 2.61 g of Ce(NO3)3·6H2O and 0.04 g of polyvinylpyrrolidone (PVP), and stir for 30 min. Transfer the mixed solution to a 100 mL hydrothermal reactor, place it in an oven, keep it at 180 °C for 400 min, then take it out. Wait for the solution to cool to room temperature, pour out the upper yellowish-brown solution to obtain a purple precipitate. Wash the precipitate with deionized water until neutral, and then place it in an oven at 60 °C for drying. After complete drying, transfer the product to a crucible, place it in a muffle furnace, and keep it at 400 °C for 4 h to obtain pale yellow cerium oxide powder. Weigh 0.25 g of Co(NO3)2·6H2O solid and place it in a beaker, add 10 mL of deionized water, dissolve and stir evenly, then add 0.95 g of CeO2 solid, stir vigorously for 30 min, then place it in a water bath at 60 °C and stir and evaporate until it becomes viscous. Place the obtained sample in an oven at 60 °C for drying. After complete drying, take it out and grind it, and place it in a muffle furnace and heat it up at a heating rate of 5 °C min -1 to 400 °C and calcine for 3 h to obtain 5% Co / CeO2-H catalyst.

[0058] I. Performance evaluation of carbon dioxide hydrogenation reaction

[0059] Evaluate the carbon dioxide hydrogenation reaction performance of the catalysts prepared in Examples 1 to 3 and Comparative Examples 1 to 3 respectively. Weigh 0.1 g of the catalyst and load it into the quartz reaction tube of a fixed-bed reactor. First, perform H2 reduction treatment on the above catalyst, in-situ reduction at 500 °C for 2 h. After the reduction is completed, cool it below the reaction temperature and introduce the raw material gas for reaction. Carbon dioxide hydrogenation reaction conditions: atmospheric pressure, reaction temperature 200 - 400 °C, molar ratio of H2 to CO2 in the raw material gas is 4, and the volumetric space velocity of the raw material gas is 60000 mLh -1 g cat -1 . The raw material gas and reaction products are analyzed online by an Agilent 8860 gas chromatograph equipped with a TDX-01 packed column and a TCD detector.

[0060] As can be seen from Figure 1 a, within the range of 200 - 400 °C, the CO2 conversion rates of the two catalysts 5% Ni / CeO2-H and 5% Ni / CeO2-H-A prepared by hydrothermal method for cerium oxide supported Ni are higher than that of the 5% Ni / CeO2-HP catalyst. At a reaction temperature of 360 °C, the CO2 conversion rates of the two catalysts 5% Ni / CeO2-H and 5% Ni / CeO2-H-A reach 79%, and the selectivity of CH4 is 98%; while the CO2 conversion rate of the 5% Ni / CeO2-HP catalyst is only 47%, and the selectivity of CH4 is 93%. As can be seen from Figure 1It can be seen that 5% Ni / CeO2-H exhibits higher CO2 conversion and methane selectivity than 5% Ru / CeO2-H (noble metal catalyst) and 5% Co / CeO2-H, indicating that the cerium-containing catalyst provided by the present invention has excellent CO2 hydrogenation performance.

[0061] From Figure 2 the XRD results, it can be seen that in Examples 1 and 2 and Comparative Example 1 ( Figure 2 a), and in Examples 3 and Comparative Examples 2 and 3 ( Figure 2 b), no obvious characteristic diffraction peaks of metallic nickel appear in the XRD patterns, indicating that the Ni metal particle size is small and the metal is highly dispersed.

[0062] From Figure 3 the HRTEM results, the lattice fringes of the cerium oxide support and metallic nickel can be seen, indicating that the metal is successfully loaded onto the cerium oxide support, and no obvious aggregation of metallic nickel can be observed in HRTEM, indicating that metallic nickel is highly dispersed on the cerium oxide support.

[0063] From Figure 4 the HRTEM results, the lattice fringes of the cerium oxide-based corresponding metal can be seen, indicating that the metal is successfully loaded onto the cerium oxide support, and no obvious metal aggregation can be observed in HRTEM, indicating that the metal is highly dispersed on the cerium oxide support.

[0064] In summary, the present invention uses a hydrothermal method to prepare a cerium oxide support and prepares a supported Ni catalyst containing cerium oxide by an impregnation method. The preparation method of the catalyst in the present invention is simple in operation, good in repeatability, and conducive to large-scale industrial use. The supported catalyst using cerium oxide prepared by the hydrothermal method in the present invention has a high oxygen vacancy content, small and uniformly dispersed active metal Ni particles. The cerium-containing catalyst provided by the present invention is used for the CO2 methanation reaction, has high reaction activity, high product selectivity, and the catalyst has good stability. The present invention provides an effective implementation scheme for the resource utilization of CO2.

[0065] The above embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims

1. A preparation method of a cerium oxide-containing catalyst for hydrogenation of carbon dioxide, characterized in that, The preparation method comprises the following steps: (1) Dissolve a cerium salt precursor in a solvent, then add a precipitant and a dispersant, and stir until evenly mixed to obtain a mixed solution; (2) Transfer the mixed solution into a hydrothermal autoclave, carry out hydrothermal reaction at a temperature of 100 - 200 °C for 4 - 96 h, and after hydrothermal treatment, filter or centrifuge to obtain a precipitate; (3) Wash and dry the precipitate to obtain a solid powder; (4) Grind the solid powder evenly, and calcine it at 300 - 600 °C for 2 - 8 h to obtain cerium oxide powder; (5) Prepare a nickel catalyst supported on cerium oxide by an impregnation method using the cerium oxide powder and a nickel salt precursor, denoted as Ni / CeO2-H catalyst.

2. The preparation method of the carbon dioxide hydrogenation catalyst containing cerium oxide according to claim 1, characterized in that, In step (1), the cerium salt precursor includes one or more of Ce(NO3)3·6H2O, CeCl3·7H2O, Ce(Ac)3·xH2O; the solvent is one or more of deionized water, ethylene glycol, benzyl alcohol; the precipitant includes one or more of glacial acetic acid, oxalic acid, ammonia water; the dispersant includes one or more of polyvinylpyrrolidone, glucose, acrylamide.

3. The preparation method of the carbon dioxide hydrogenation catalyst containing cerium oxide according to claim 1, characterized in that, In step (1), the stirring time is 0.5 - 8 h; in step (2), the hydrothermal reaction conditions are to react at a temperature of 160 - 180 °C for 4 - 72 h.

4. The preparation method of the carbon dioxide hydrogenation catalyst containing cerium oxide according to claim 1, wherein In step (3), the drying conditions are to dry at a temperature of 60 - 150 °C for 6 - 48 h; preferably, the drying temperature is 80 - 120 °C and the time is 8 - 12 h.

5. The preparation method of the carbon dioxide hydrogenation catalyst containing cerium oxide according to claim 1, characterized in that, In step (4), the operating conditions for roasting are to grind the solid powder evenly, transfer it into a muffle furnace, and heat it to 300 - 600 °C at a heating rate of 1 - 10 °C min -1 and roast for 2 - 8 h.

6. The preparation method of the carbon dioxide hydrogenation catalyst containing cerium oxide according to claim 1, characterized in that, In step (5), the nickel salt precursor includes one or more of Ni(NO3)2·6H2O, NiCl2·6H2O, NiSO4·6H2O, Ni(Ac)2·4H2O.

7. The preparation method of the carbon dioxide hydrogenation catalyst containing cerium oxide according to claim 1, characterized in that, In step (5), the impregnation method includes, but is not limited to, preparation by the equal-volume impregnation method, the excess impregnation method, or the multiple impregnation method. After impregnation, calcination is carried out. The conditions for calcination are heating to 400 - 500 °C at a heating rate of 1 - 5 °C / min -1 and maintaining at this temperature for 2 - 4 h.

8. A carbon dioxide hydrogenation catalyst containing cerium oxide, characterized in that, Prepared by the preparation method according to any one of claims 1 to 7, the catalyst includes active metal nickel and cerium oxide as a carrier; wherein, the content of the active metal nickel is 1 wt% - 30 wt%, and the content of cerium oxide is 70 wt% - 99 wt%; preferably, the content of the active metal nickel is 3 wt% - 20 wt%.

9. Use of the cerium oxide-containing carbon dioxide hydrogenation catalyst according to claim 8 in the reaction of carbon dioxide hydrogenation to methane, characterized in that, Comprises the following steps: (1) Carry out in-situ reduction pretreatment on the catalyst before the reaction, the reduction temperature is 300 - 600 °C, and the reduction atmosphere is hydrogen or a mixture of hydrogen and an inert gas; (2) In an atmospheric pressure fixed-bed reactor, the reaction temperature is controlled at 200 - 400 °C, the molar ratio of H2 to CO2 in the feed gas is 0.5 - 6, and the gas hourly space velocity is 6000 - 120000 mLh -1 g cat -1 ; Preferably, the carbon dioxide conversion rate of the catalyst ≥ 79%.

10. The application according to claim 9, wherein In step (1), the temperature of the in-situ reduction pretreatment is 400 - 500 °C, and the reduction atmosphere is pure hydrogen; in step (2), the molar ratio of H2 to CO2 in the feed gas is 2 - 4, and the gas hourly space velocity is 12000 - 90000 mL h -1 g cat -1 .

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