Co-based high-entropy oxide and preparation method and application thereof

Abstract

The invention relates to a Co-based high-entropy oxide, and belongs to the technical field of metal oxide catalysts. The general molecular formula of the oxide is Cox (ABCD) 1-xO, x in the molecular formula is the molar ratio of Co metal to all metal, and ABCD in the molecular formula is any four or more metal elements of magnesium, aluminum, zinc, manganese, copper, molybdenum and iron. The preparation method comprises the following steps: dissolving all metal precursors in dilute nitric acid according to a molar ratio to form a solution A, adding citric acid and polyethylene glycol into a water-ethanol solution, completely dissolving with ultrasonic waves to form a solution B, slowly adding the solution B into the solution A, mixing, fully stirring to form a sol with highly dispersed molecular scale, evaporating the formed sol to obtain a dry gel, and drying to obtain the metal-based composite material. And calcining the dried gel in air to obtain the oxide. The oxide is used as a catalyst in a carbon dioxide hydrogenation reaction and is used for preparing methane at high temperature and high pressure. The oxide provides a stable and high-temperature-resistant novel catalyst for preparing methane through hydrogenation reaction of carbon dioxide.

Description

TECHNICAL FIELD

[0001] The present application relates to a Co-based high-entropy oxide and a preparation method thereof, and an application of the oxide in carbon dioxide methanation, and belongs to the technical field of metal oxide catalysts (B01J 21 / 00, B01J 23 / 00). BACKGROUND

[0002] In today's society, the large-scale use of fossil energy by humans has led to the emission of a large amount of carbon dioxide, and the excess CO2 in the atmosphere has caused a series of environmental problems, such as the intensification of the greenhouse effect, the rise in the global average temperature, the melting of glaciers, and the rise in sea level. Therefore, it is necessary to reduce carbon emissions as much as possible. Among the existing technologies for reducing carbon emissions, CO2 capture, utilization and storage technology has great development potential, which includes multiple stages such as capture, transportation, utilization and storage, and aims to handle CO2 in industrial production flue gas. However, CO2 capture and storage technology still faces some challenges, such as low capture efficiency, high separation cost, and long-term stability problems of underground storage. In contrast, the conversion and utilization of CO2 have technical diversity and realize the reuse of carbon resources, which has a more positive significance for promoting green and low-carbon economy.

[0003] The conversion and utilization of CO2 is to convert CO2 into carbon-containing chemicals, which can effectively reduce the content of CO2 in the atmosphere. By using renewable energy and high-efficiency catalysts, CO2 hydrogenation technology not only can slow down carbon emissions, but also can realize the effective utilization of carbon resources. The core of this technology is to develop catalysts that can efficiently convert CO2. In the current research results, noble metal catalysts have good performance in CO2 hydrogenation reaction and can maintain activity for a long time, but due to the high cost of raw materials, their application in industry is limited. In addition, metal oxide catalysts also have very excellent catalytic performance for CO2 hydrogenation reaction, and their low price compared with noble metals makes them have greater advantages in industrial application.

[0004] High-entropy metal oxides are a new type of oxide material composed of five or more metal oxides, and Co-based high-entropy oxides have many advantages in catalyzing CO2 hydrogenation reaction. Currently known Co-based high-entropy oxide catalysts, such as the Chinese patent application with publication number CN115837275A, disclose a perovskite-type high-entropy oxide used as a catalyst for CO and CO2 methanation. There is no research report on Co-based high-entropy oxide catalysts and their application in the field of CO2 hydrogenation. SUMMARY

[0005] The technical problem to be solved by the present application is how to design the formula of Co-based high-entropy oxide catalyst and its preparation and application.

[0006] The application provides a Co-based high-entropy oxide, which is generally represented by a molecular formula Co x (ABCD) 1-x O, wherein x in the molecular formula is a molar ratio of Co metal to all metals, the molar ratio ranges from 30% to 50%, and ABCD in the molecular formula are any four or more than four metal elements selected from magnesium, aluminum, zinc, manganese, copper, molybdenum and iron.

[0007] Further, the specific molecular formula includes the following: Co 0.3 (MgNiCuAl) 0.7 O, Co 0.3 (ZnMnMoFe) 0.7 O, Co 0.3 (NiMnMoFe) 0.7 O, Co 0.3 (ZnMnMoFeNiCu) 0.7 O, Co 0.3 (ZnMgNiCuMnMoFe) 0.7 O, Co 0.4 (MgNiCuAl) 0.6 O, Co 0.4 (ZnMnMoFe) 0.6 O, Co 0.4 (NiMnMoFe) 0.6 O, Co 0.4 (MgNiAlCuZnMo) 0.6 O, Co 0.4 (MgNiAlCuZnMo) 0.6 O, Co 0.4 (NiMgCuMnZnAlMo) 0.6 O, Co 0.5 (MgNiCuAl) 0.5 O, Co 0.5 (ZnMnMoFe) 0.5 O, Co 0.5 (NiMnMoFe) 0.5 O, Co 0.5 (MgNiAlCuZn) 0.5 O or Co 0.5 (MgNiAlCuZnMo) 0.5 O.

[0008] Further, the diffraction peak in the XRD diagram of the Co-based high-entropy oxide indicates that the Co-based high-entropy oxide is a single-phase solid solution rock salt type cubic structure.

[0009] Further, the H2-TPR graph of the Co-based high-entropy oxide indicates that the Co-based high-entropy oxide is not a physical mixture of multiple single metal oxides.

[0010] Further, the CO2-TPD graph of the Co-based high-entropy oxide indicates that various basic sites exist on the surface of the Co-based high-entropy oxide and the Co-based high-entropy oxide has CO2 adsorption capacity.

[0011] Further, the XPS O 1s graph of the Co-based high-entropy oxide indicates that the surface oxygen vacancy content of the Co-based high-entropy oxide is greater than or equal to 22.3%, and that the Co-based high-entropy oxide produces lattice distortion in the process of forming a rock salt type solid solution structure, which improves the redox capacity of the Co-based high-entropy oxide and forms multiple oxygen vacancies in the interior of the Co-based high-entropy oxide that can enhance the CO2 catalytic conversion activity of the Co-based high-entropy oxide.

[0012] The second technical solution provided by the present application to solve the above technical problems is: the preparation method of the Co-based high-entropy oxide of the first technical solution, comprising the following steps: 1) Under the condition of vigorous stirring, at least five kinds of metal precursors are dissolved in dilute nitric acid to form A liquid, the pH of the solution is adjusted to 2-3, and the four metals other than cobalt among the five metals are any four of magnesium, aluminum, zinc, manganese, copper, molybdenum and iron, and the molar ratio of cobalt and the other four metals in the five metals ranges from 1.7:1 to 6:1; 2) After citric acid and polyethylene glycol are completely dissolved in a water-ethanol solution to form B liquid; 3) Slowly add B liquid to A liquid mixture, stir well, form a highly dispersed sol at the molecular scale, citric acid acts as a chelating agent for metal ions, and polyethylene glycol acts as a crosslinking agent, then evaporate the formed sol to obtain a dry gel; 4) Calcine the dry gel in air, the heating rate of calcination is 1-10℃ / min, the calcination temperature is 850-1200℃, and the calcination time is 1-6h, the five metal oxides have large configurational entropy and form a stable single-phase crystal structure, and finally obtain the Co-based high-entropy oxide.

[0013] Preferably, the metal precursors in step 1) are one or more of oxides, chlorides, acetates, nitrates, carbonates, sulfates, sulfites, oxalate ammonium salts, citrates and gluconates.

[0014] Preferably, the volume ratio of water to ethanol in step 2) is 1:5-1:8.

[0015] Preferably, the mass ratio of citric acid to polyethylene glycol in step 2) is 1:7-1:10.

[0016] Preferably, the volume ratio of A liquid and B liquid in step 3) is 1:2-1:4.

[0017] The third technical solution provided by the present application to solve the above technical problems is: the application of the Co-based high-entropy oxide in the technical solution one, as a catalyst for carbon dioxide hydrogenation reaction, catalyzing carbon dioxide and hydrogen to produce methane under high temperature and high pressure.

[0018] Further, the volume ratio of hydrogen to carbon dioxide is 2-5:1, the reaction temperature is 300-500℃, the reaction pressure is 1-4MPa, and the reaction raw gas space velocity is 2000-10000mL•g -1 •h -1 .

[0019] The beneficial effects of the present application are: since a Co-based high-entropy oxide with a new structure is proposed, a new catalyst for carbon dioxide hydrogenation reaction to produce methane is provided. The highly complex structure and multi-component of the high-entropy oxide of the catalyst provide abundant active sites, which are beneficial for adsorbing and activating CO2 molecules. On the Co site, CO2 can be deeply hydrogenated to produce methane. The high-entropy oxide of the catalyst has excellent stability and high-temperature resistance, and can maintain catalytic activity under high temperature and high pressure conditions, thereby realizing efficient CO2 conversion. In addition, the composition and structure of the high-entropy oxide of the catalyst are flexible and variable, and the catalytic performance can be adjusted by reasonably designing the Co active site, so as to realize precise control of the CO2 conversion process. The high-entropy oxide of the catalyst uses a modified Pechini method, which uses citric acid and ethylene glycol to form a network of high molecules to stabilize metal ions, and then the high molecules are heat-treated to form the desired product; citric acid can form a chelate with metal ions, which plays the role of polyester in the Pechini process, and can polymerize with ethylene glycol to form a solid polymer resin; the reaction makes the metal ions uniformly dispersed in the polymer resin, which can ensure atomic-level mixing and generate uniform, single-phase ultra-fine high-entropy oxide powder at a relatively low temperature.

[0020] Compared with the prior art, the high-entropy oxide of the present application has the following advantages: 1. The preparation raw materials are widely available, the preparation process is simple, the preparation time is relatively short, the preparation conditions are easy to accurately control, and the repeatability of the obtained catalyst is good.

[0021] 2. Under the reaction conditions, the high content of Co metal is the active site for the carbon dioxide methanation reaction; the oxygen vacancies generated by the lattice distortion of the high-entropy oxide can quickly adsorb and activate carbon dioxide molecules; in addition, the five metals form a single phase of high-entropy oxide, and the high-entropy effect caused by the disorder of chemical composition significantly slows down the diffusion rate of its metal elements, further improving the high-temperature stability of the high-entropy oxide as a catalyst.

[0022] 3. This invention can change the type and composition of the precursor metal salt in the preparation of high-entropy oxides, and prepare high-entropy oxides with different active centers as catalysts. This helps to overcome the bottleneck that high-entropy oxides are difficult to form single-phase structures as catalysts. It can be widely used in other reaction catalytic systems and has good versatility. Attached Figure Description

[0023] The following description, in conjunction with the accompanying drawings, further illustrates a Co-based high-entropy oxide of the present invention, its preparation, and its applications.

[0024] Figure 1 The XRD patterns are of the Co-based high-entropy oxides prepared in Examples 1-3 of this invention.

[0025] Figure 2 The image shows the H2-TPR diagrams of the Co-based high-entropy oxides prepared in Examples 1-3 of this invention.

[0026] Figure 3 This is the CO2-TPD diagram of the Co-based high-entropy oxides prepared in Examples 1-3 of this invention.

[0027] Figure 4 The image shows the XPS O 1s diagrams of the Co-based high-entropy oxides prepared in Examples 1-3 of this invention. Detailed Implementation Example 1

[0028] This embodiment describes a Co-based high-entropy oxide with the molecular formula Co. 0.3 (MgNiCuAl) 0.7 O, of which Co metal accounts for 40.5% of the molar ratio of the five metals.

[0029] The XRD pattern of the Co-based high-entropy oxide in this embodiment is as follows: Figure 1 As shown, by Figure 1 As shown in line (a) in the figure, the diffraction peaks of the Co-based high-entropy oxide in this embodiment correspond to a rock salt cubic structure, forming a single-phase solid solution structure. The absence of other oxide impurity peaks proves the successful synthesis of the Co-based high-entropy oxide; its H2-TPR is as follows: Figure 2As shown in line (a), the characteristic peaks at 627℃ and 870℃ correspond to the reduction of bulk oxygen substances, while the main peak and shoulder peak at around 424℃ correspond to the mixed metal components and Co. 2+ The reduction indicates that it is not the mathematical sum of the reduction peaks of the five single metal oxides, proving that the high-entropy oxide is not a simple physical mixture of the five single metal oxides; its CO2-TPD is as follows: Figure 3 As shown, by Figure 3 As shown in line (a), the CO2 desorption peaks at 143℃, 418℃, and 511℃ correspond to the three carbonates: bicarbonate, bidentate carbonate, and monodentate carbonate, respectively. This indicates that the Co-based high-entropy oxide surface in this embodiment possesses various basic sites and exhibits good CO2 adsorption capacity; its XPS O 1s... Figure 4 As shown in line (a), the three peaks at 529.8, 531.4, and 532.8 eV correspond to lattice oxygen, oxygen vacancies, and surface-adsorbed oxygen, respectively. Calculations show that the surface oxygen vacancy content of the Co-based high-entropy oxide in this embodiment is 22.3%. During the formation of a rock-salt-type solid solution structure, metal species with different atomic sizes undergo lattice distortion. This lattice distortion not only alters the redox ability of the high-entropy oxide but also leads to the formation of numerous oxygen vacancies within the Co-based high-entropy oxide of this embodiment, enhancing its CO2 catalytic conversion activity. Figures 1-4 Line (a) in the figures all indicate that the Co-based high-entropy oxide of this embodiment has a unique structure that differs from existing Co-based high-entropy oxides, and is suitable as a catalyst for the carbon dioxide hydrogenation reaction.

[0030] The preparation method of Co-based high-entropy oxide in this embodiment includes the following steps: 1) Under vigorous stirring conditions, five metal precursors, namely magnesium (Mg), nickel (Ni), copper (Cu), aluminum (Al), and cobalt (Co), are dissolved in dilute HNO3 in a molar ratio to form solution A, and the pH of the solution is adjusted to 2-3. The five metal precursors are magnesium chloride, nickel oxide, copper sulfate, aluminum carbonate, and cobalt acetate, respectively. 2) Add citric acid and polyethylene glycol to a water-ethanol solution and dissolve them completely by ultrasound to form solution B; wherein the volume ratio of water to ethanol is 1:5 and the mass ratio of citric acid to polyethylene glycol is 1:7. 3) Slowly add solution B to solution A and mix. The volume ratio of solution A to solution B is 1:3. Stir thoroughly to form a sol with high molecular dispersion. Citric acid is used as a chelating agent for subsequent metal ions, and polyethylene glycol is used as a crosslinking agent for subsequent reactions. Then, evaporate the formed sol to obtain a dry gel. 4) The dried gel was calcined in air at a heating rate of 7℃ / min, a calcination temperature of 1000℃, and a calcination time of 4h. The configurational entropy of the five or more metal oxides was sufficiently large to form a stable single-phase crystal structure, and finally Co-based high-entropy oxidation was obtained.

[0031] This embodiment describes the application of Co-based high-entropy oxides in the methanation of carbon dioxide, using them as catalysts in the hydrogenation reaction of carbon dioxide to produce methane from carbon dioxide and hydrogen under high temperature and pressure. Specifically, the volume ratio of hydrogen to carbon dioxide is 3:1, the reaction temperature is 400°C, the reaction pressure is 2.5 MPa, and the gas hourly space velocity (GHSV) of the reactants is 6500 mL·g. -1 •h -1 The reaction has a methane selectivity of 99% and a carbon dioxide conversion rate of 60%. Example 2

[0032] This embodiment describes a Co-based high-entropy oxide with the molecular formula Co. 0.3 (ZnMnMoFeNiCu) 0.7 O, of which Co metal accounts for 49.5% of the molar ratio of the seven metals.

[0033] The XRD pattern of the Co-based high-entropy oxide in this embodiment is as follows: Figure 1 As shown, by Figure 1 As shown in line (b), the diffraction peaks of the Co-based high-entropy oxide in this embodiment correspond to a rock-salt cubic structure, forming a single-phase solid solution structure, proving the successful synthesis of the Co-based high-entropy oxide; its H2-TPR is as follows: Figure 2 As shown in line (b), the characteristic peaks at 621℃ and 845℃ correspond to the reduction of bulk oxygen, while the main peak and shoulder peak at around 324℃ correspond to the mixed metal components and Co. 2+ The reduction; its CO2-TPD is as follows Figure 3 As shown by line b, from Figure 3 As shown in line (b), the CO2 desorption peaks at 263℃, 382℃, and 576℃ correspond to the three carbonates: bicarbonate, bidentate carbonate, and monodentate carbonate, respectively. This indicates that the Co-based high-entropy oxide surface in this embodiment possesses various basic sites and exhibits good CO2 adsorption capacity; its XPS O 1s... Figure 4 As shown in line (b), the oxygen vacancy content on the surface of the Co-based high-entropy oxide in this embodiment is 44.5% after calculation and analysis. Figures 1-4 Line (b) in the figures all indicate that the Co-based high-entropy oxide of this embodiment has a unique structure that differs from existing Co-based high-entropy oxides, and is suitable as a catalyst for the carbon dioxide hydrogenation reaction.

[0034] The preparation method of Co-based high-entropy oxide in this embodiment includes the following steps: 1) Under vigorous stirring conditions, seven metal precursors, namely zinc (Zn), manganese (Mn), molybdenum (Mo), iron (Fe), nickel (Ni), copper (Cu), and cobalt (Co), were dissolved in dilute HNO3 in a molar ratio to form solution A, and the pH of the solution was adjusted to 2-3. The seven metal precursors are zinc oxide, manganese sulfate, molybdenum nitrate, ammonium iron oxalate, nickel oxide, copper sulfate, and cobalt citrate. 2) Add citric acid and polyethylene glycol to the water-ethanol solution and dissolve them completely by ultrasound to form solution B; the volume ratio of water to ethanol is 1:8, and the mass ratio of citric acid to polyethylene glycol is 1. 3) Slowly add solution B to solution A and mix. The volume ratio of solution A to solution B is 1:4. Stir thoroughly to form a highly dispersed sol at the molecular scale. Citric acid is used as a chelating agent for subsequent metal ions, and polyethylene glycol is used as a crosslinking agent for subsequent reactions. Then, evaporate the formed sol to obtain a dry gel. 4) The dried gel was calcined in air at a heating rate of 10℃ / min, a calcination temperature of 1200℃, and a calcination time of 1.5h. The seven metal oxides had sufficiently large configurational entropy to form a stable single-phase crystal structure, and finally, Co-based high-entropy oxide catalyst was obtained.

[0035] In this embodiment, the Co-based high-entropy oxide is used as a catalyst in the hydrogenation reaction of carbon dioxide to produce methane from carbon dioxide and hydrogen under high temperature and pressure. The volume ratio of hydrogen to carbon dioxide is 5:1, the reaction temperature is 490°C, the reaction pressure is 4 MPa, and the gas hourly space velocity (GHSV) of the reactants is 10000 mL·g. -1 •h -1 The reaction exhibits a methane selectivity of 98% and a carbon dioxide conversion rate of 58%. Example 3

[0036] This embodiment presents a Co-based high-entropy oxide, with the molecular formula Co. 0.4 (ZnMnMoFe) 0.6 O, of which Co metal accounts for 30.5% of the molar ratio of the five metals.

[0037] The XRD pattern of the Co-based high-entropy oxide in this embodiment is as follows: Figure 1 As shown, by Figure 1 As shown by line (c), the diffraction peaks of the Co-based high-entropy oxide in Example 3 correspond to a rock-salt cubic structure, forming a single-phase solid solution structure, proving the successful synthesis of the Co-based high-entropy oxide in this example; its H2-TPR is as follows: Figure 2 As shown in line (c), the characteristic peaks at 599℃ and 828℃ correspond to the reduction of bulk oxygen, while the main peak and shoulder peak at around 329℃ correspond to the mixed metal components and Co, respectively. 2+ The reduction; its CO2-TPD is as follows Figure 3 As shown, byFigure 3 As shown in line (c), the CO2 desorption peaks at 268℃, 458℃, and 585℃ correspond to the three carbonates: bicarbonate, bidentate carbonate, and monodentate carbonate, respectively. This indicates that the Co-based high-entropy oxide in this embodiment possesses various basic sites and exhibits good CO2 adsorption capacity; its XPS O 1s... Figure 4 As shown by line (c), the surface oxygen vacancy content of the Co-based high-entropy oxide in this embodiment is 49.6% after calculation and analysis. Figures 1-4 Line (c) in the figures all indicate that the Co-based high-entropy oxide of this embodiment has a unique structure that differs from existing Co-based high-entropy oxides, and is suitable as a catalyst for the hydrogenation reaction of carbon dioxide.

[0038] The preparation method of Co-based high-entropy oxide in this embodiment specifically includes the following steps: 1) Under vigorous stirring conditions, five metal precursors, namely zinc (Zn), manganese (Mn), molybdenum (Mo), iron (Fe), and cobalt (Co), were dissolved in dilute HNO3 at a molar ratio to form solution A, and the pH of the solution was adjusted to 2-3. The five metal precursors are zinc gluconate, manganese acetate, molybdenum oxide, ferrous sulfate, and cobalt acetate, respectively. 2) Add citric acid and polyethylene glycol to the water-ethanol solution and dissolve them completely by ultrasound to form solution B. The volume ratio of water to ethanol is 1:5 and the mass ratio of citric acid to polyethylene glycol is 1:7. 3) Slowly add solution B to solution A and mix. The volume ratio of solution A to solution B is 1:2. Stir thoroughly to form a sol with high molecular dispersion. Then evaporate the sol to obtain a dry gel. 4) The dried gel was calcined in air at a heating rate of 1.5℃ / min, a calcination temperature of 860℃, and a calcination time of 6h. The configurational entropy of the five or more metal oxides was sufficiently large to form a stable single-phase crystal structure, and finally a Co-based high-entropy oxide catalyst was obtained.

[0039] The application of the Co-based high-entropy oxide in this embodiment is as a catalyst in the hydrogenation reaction of carbon dioxide, catalyzing the production of methane from carbon dioxide and hydrogen under high temperature and pressure. Specifically, the volume ratio of hydrogen to carbon dioxide is 2:1, the reaction temperature is 300°C, the reaction pressure is 1 MPa, and the gas hourly space velocity (GHSV) of the reactants is 2100 mL·g. -1 •h -1 The methane selectivity of the reaction was 99%, and the carbon dioxide conversion rate was 59%.

[0040] The above description is only a preferred embodiment of the present invention, but the present invention is not limited thereto. All equivalent substitutions or modifications made to the concepts and technical solutions of the present invention should be covered within the protection scope of the present invention.

Claims

1. A Co-based high-entropy oxide, characterized in that: The general molecular formula is represented as Co. x (ABCD) 1-x O, where x in the molecular formula represents the molar ratio of Co metal to all metals, ranging from 30% to 50%, and ABCD in the molecular formula represent any four or more metallic elements selected from magnesium, aluminum, zinc, manganese, copper, molybdenum, and iron.

2. The Co-based high-entropy oxide according to claim 1, characterized in that: The specific Co-based high-entropy oxides include the following: What 0.3 (MgNiCuAl) 0.7 Oh, what 0.3 (ZnMnMoFe) 0.7 Oh, what 0.3 (NiMnMoFe) 0.7 Oh, what 0.3 (ZnMnMoFeNiCu) 0.7 Oh, what 0.3 (ZnMgNiCuMnMoFe) 0.7 Oh, what 0.4 (MgNiCuAl) 0.6 ABOUT, What 0.4 (ZnMnMoFe) 0.6 About / What 0.4 (NiMnMoFe) 0.6 About / What 0.4 (MgNiAlCuZnMo) 0.6 About / What 0.4 (MgNiAlCuZnMo) 0.6 About / What 0.4 (NiMgCuMnZnAlMo) 0.6 About / What 0.5 (MgNiCuAl) 0.5 O, Co 0.5 (ZnMnMoFe) 0.5 O, Co 0.5 (NiMnMoFe) 0.5 O, Co 0.5 (MgNiAlCuZn) 0.5 O or Co 0.5 (MgNiAlCuZnMo) 0.5 O.

3. The Co-based high-entropy oxide according to claim 1, characterized in that: The diffraction peaks in the XRD pattern of the Co-based high-entropy oxide indicate that the Co-based high-entropy oxide has a single-phase solid solution rock salt cubic structure.

4. The Co-based high-entropy oxide according to claim 1, characterized in that: The H2-TPR diagram of the Co-based high-entropy oxide indicates that the Co-based high-entropy oxide is not a physical mixture of multiple single metal oxides.

5. The Co-based high-entropy oxide according to claim 1, characterized in that: The CO2-TPD diagram of the Co-based high-entropy oxide shows that various alkaline sites exist on the surface of the Co-based high-entropy oxide and it has CO2 adsorption capacity.

6. The Co-based high-entropy oxide according to claim 1, characterized in that: The XPSO 1s plot of the Co-based high-entropy oxide shows that the oxygen vacancy content on the surface of the Co-based high-entropy oxide is greater than or equal to 22.3%, and that the Co-based high-entropy oxide will produce lattice distortion during the formation of the rock salt type solid solution structure. The lattice distortion improves the redox ability of the Co-based high-entropy oxide and forms multiple oxygen vacancies inside the Co-based high-entropy oxide that can enhance the CO2 catalytic conversion activity of the Co-based high-entropy oxide.

7. A method for preparing the Co-based high-entropy oxide according to claim 1, characterized in that: Includes the following steps: 1) Under vigorous stirring conditions, at least five metal precursors are dissolved in dilute nitric acid in a molar ratio to form solution A. The pH of the solution is adjusted to 2-3. The four metals other than cobalt are any four of magnesium, aluminum, zinc, manganese, copper, molybdenum and iron. The molar ratio of cobalt to the other four metals is in the range of 1.7:1-6:

1. 2) Add citric acid and polyethylene glycol to the water-ethanol solution and dissolve them completely using ultrasound to form solution B; 3) Slowly add solution B to solution A and mix thoroughly to form a highly dispersed sol at the molecular scale. Citric acid is used as a chelating agent for metal ions, and polyethylene glycol is used as a cross-linking agent. Then, evaporate the formed sol to obtain a dry gel. 4) The dried gel was calcined in air at a heating rate of 1-10℃ / min, a calcination temperature of 850-1200℃, and a calcination time of 1-6h. The five metal oxides had large configurational entropy and formed a stable single-phase crystal structure, finally yielding Co-based high-entropy oxides.

8. The method for preparing the Co-based high-entropy oxide according to claim 7, characterized in that: The metal precursor in step 1) is one or more of oxides, chlorides, acetates, nitrates, carbonates, sulfates, nitrites, ammonium oxalate, citrates, and gluconates; the volume ratio of water to ethanol in step 2) is 1:5-1:8; the mass ratio of citric acid to polyethylene glycol in step 2) is 1:7-1:10; and the volume ratio of solution A to solution B in step 3) is 1:2-1:

4.

9. An application of the Co-based high-entropy oxide according to claim 1, characterized in that: It is used as a catalyst in the hydrogenation reaction of carbon dioxide to produce methane from carbon dioxide and hydrogen under high temperature and pressure.

10. The application of the Co-based high-entropy oxide according to claim 9, characterized in that: The volume ratio of hydrogen to carbon dioxide is 2–5:1, the reaction temperature is 300–500℃, the reaction pressure is 1–4 MPa, and the gas hourly space velocity (GHSV) of the reactants is 2000–10000 mL·g. -1 •h -1 .

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