Composite metal oxide catalyst as well as preparation method and application thereof

Abstract

The invention discloses a composite metal oxide catalyst and a preparation method and application thereof, and the specific synthesis steps are as follows: synthesis of a carbon microsphere precursor, synthesis of a hydrotalcite-like compound, and synthesis of a multi-metal composite oxide: calcining the synthesized hydrotalcite-like compound precursor in a specific atmosphere at a specific temperature at a certain heating rate for 3 h to obtain the composite metal oxide catalyst, the components are respectively recorded as FeNiMgAl (at) C-A / N-T. The invention also provides application of the composite metal oxide catalyst in preparation of dimethyl carbonate by a transesterification method. The multi-metal composite oxide catalyst based on the hydrotalcite-like precursor is synthesized through a coprecipitation method and is used for catalyzing the ester exchange reaction of propylene carbonate and methanol, the catalytic activity of the multi-metal composite oxide catalyst is superior to that of a sodium methoxide catalyst used in the industry, and the catalyst can still keep high catalytic activity after being recycled for three times.

Description

Technical Field

[0001] The present invention belongs to the technical field of dimethyl carbonate preparation, and particularly relates to a composite metal oxide catalyst, a preparation method thereof and an application thereof. Background Art

[0002] Dimethyl carbonate (DMC) is a widely used basic organic synthesis raw material that has received much attention in recent years. Due to its very wide range of uses, it is known as the "new cornerstone" of current organic synthesis. The molecular structural formula of dimethyl carbonate is CH3O-CO-OCH3. It can be seen from its structural formula that it contains a carbonyl group, a methyl group, a methoxy group, and a carbomethoxy group, which makes dimethyl carbonate have good reaction activity and is widely used as an important solvent and chemical raw material. With the development of the lithium battery industry, as a raw material for lithium battery electrolyte solvents and for producing electrolyte solvents such as ethyl methyl carbonate, dimethyl carbonate has great market prospects.

[0003] At present, the main synthesis methods of dimethyl carbonate are as follows: phosgene method, transesterification method, urea alcoholysis method, methanol oxidative carbonylation method, carbon dioxide oxidation method, dimethyl oxalate decarbonylation method and other new processes. According to different raw materials, the transesterification method can be divided into the ethylene oxide (EO) route and the propylene oxide (PO) route. The transesterification technology has been continuously promoted and applied in China, but the main disadvantages are: 1. In the production process of the transesterification method, a methanol sodium-methanol solution with a concentration of about 30% is generally used as a catalyst, and the production cost accounts for a high proportion. 2. In the production process, propylene glycol and the methanol sodium catalyst cannot be effectively separated, which affects the normal refining process of the product. 3. At present, most of the hydrolysis carbonization process is used for the conversion and separation of the catalyst, but the catalyst activity is lost after the conversion. Therefore, there is an urgent need to find a new recyclable heterogeneous catalyst suitable for the production of dimethyl carbonate.

[0004] In recent years, due to their special layered structure and chemical properties, hydrotalcite-like compounds (HTLCs) have shown good catalytic activity, selectivity and stability in transesterification reactions. Hydrotalcite has a controllable chemical composition and layered structure, which enables it to provide rich basic active centers in transesterification reactions, thus promoting the progress of the reaction. For example, Mg-Al carbonate-type hydrotalcite shows high catalytic activity and stability in transesterification reactions, while Zn-Al hydrotalcite has good catalytic activity, but its structural stability is poor. Therefore, how to improve the stability of hydrotalcite-based catalysts is the focus of current research. Summary of the Invention

[0005] Based on this, in order to overcome the above problems of the prior art, the present invention provides a preparation method of a hydrotalcite derivative catalyst for the preparation of dimethyl carbonate by transesterification. The present invention effectively adjusts the hydrotalcite structure and realizes the multiple recycling of the hydrotalcite derivative catalyst. To achieve the above object, the present invention discloses the following solutions.

[0006] As a first aspect of the present invention, it lies in providing a synthesis method of a composite metal oxide catalyst, and the specific synthesis steps are as follows: Step 1, synthesis of carbon microsphere precursors: Prepare a sucrose solution, and through a carbonization reaction, form carbon microspheres; Step 2, synthesis of hydrotalcite: Prepare a hydrotalcite precursor containing Fe, Ni, Mg, and Al by the co-precipitation method; it includes the following steps: Prepare a salt solution containing Fe, Ni, Mg, and Al, wherein the molar amounts of Fe:Ni:Mg:Al are [Fe 3+ + [Mg 2+ + [Ni 2+ + [Al 3+ = 0.1 mol / L; M 2+ :M 3+ = 1:1 - 3:1, preferably 2:1, to obtain solution A; prepare a solution B containing NaOH and Na 2 CO 3 ; Drop solution B and solution A into water dispersed with carbon microspheres simultaneously, stir vigorously, and control the pH of the mixed solution by controlling the dropping rate of solution B; heat the obtained slurry; then separate the obtained precipitate, wash, and dry to obtain the hydrotalcite precursor.

[0007] Step 3, synthesis of multi-metal composite oxide: The synthesized hydrotalcite precursor is obtained by calcination at a certain heating rate at a specific temperature in a specific atmosphere, denoted as FeNiMgAl@C - A / N - T. Further, in step 1, the concentration of the sucrose solution is 10% - 30% to form regular and uniform carbon microspheres.

[0008] Further, in step 1, the reaction temperature of the sucrose solution is 120 - 160 °C to facilitate the complete carbonization of sucrose.

[0009] Further, in step 2, the concentrations of the NaOH and Na 2 CO 3 solution are 1.5 mol / L and 0.64 mol / L to better adjust the pH of the solution.

[0010] Further, in step 2, the pH of the mixed solution is controlled within the range of 9-11 to facilitate the formation of FeNiMgAl-LDH precipitate more easily. The inventors' research found that when the pH is lower than 9, very little precipitate is formed and the synthesis yield of the catalyst is very low. When the pH is higher than 11, the catalytic effect of the formed catalyst is not good.

[0011] Further, in step 2, the reaction temperature of the mixed solution is 60-100 °C to facilitate the reaction to proceed rapidly.

[0012] Further, in step 2, the content of the carbon microspheres in deionized water is 10 g / L.

[0013] Further, in step 3, the calcination atmosphere should be an inert gas nitrogen atmosphere or an air atmosphere.

[0014] Further, in step 3, the calcination heating rate is 2-5 °C / min to facilitate the smooth progress of the calcination reaction.

[0015] Further, in step 3, the calcination temperature should be 500-900 °C.

[0016] Further, in step 3, the calcination time is 2-4 h to facilitate the complete calcination of FeNiMgAl-LDH.

[0017] As the second aspect of the present invention, the present invention also provides the application of the composite metal oxide catalyst in the preparation of dimethyl carbonate by the transesterification method.

[0018] As the third aspect of the present invention, the present invention also provides a method for preparing dimethyl carbonate. The catalyst is the composite metal oxide catalyst of the present invention, and the preparation method is as follows: Add propylene carbonate and methanol into a reaction kettle, and add the composite metal oxide catalyst according to 3% of the total feed mass, and heat and keep warm for reaction.

[0019] Compared with the prior art, the advantages and positive effects of the present invention are: 1. The present invention provides a rapid, simple, green and efficient method for synthesizing multi-metal oxides using a hydrotalcite-like precursor. This method not only has simple operation and reaction conditions, but also has cheap reaction raw materials, is green and pollution-free. In addition, this reaction can proceed rapidly, save energy and time. The obtained product shows good catalytic activity as a catalyst for the transesterification reaction of propylene carbonate and methanol. This catalyst is easy to separate and can be recycled during the catalytic process.

[0020] 2. The present invention synthesizes a multi-metal composite oxide catalyst based on a hydrotalcite-like precursor by the co-precipitation method, and uses it to catalyze the transesterification reaction of propylene carbonate and methanol, showing catalytic activity superior to that of the sodium methoxide catalyst used in industry. Moreover, this catalyst can be recycled multiple times while still maintaining high catalytic activity.

[0021] 3. By combining different metal elements, the present invention can play the role of an active center in the reaction, reduce the activation energy of the reaction, and thus accelerate the progress of the reaction. This method is simple, efficient, green and does not produce solid waste during the catalytic process, and has important application value in the field of synthesizing dimethyl carbonate by the transesterification method. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The specification drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation to the present invention.

[0023] Figure 1 It is the SEM picture of the carbon microspheres provided by the present invention.

[0024] Figure 2 It is the SEM picture of FeNiMgAl@C-A-600 provided in Example 5 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0026] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. The present invention will be further described through specific embodiments.

[0027] The raw materials selected in the present invention mainly include: nickel nitrate hexahydrate, magnesium nitrate hexahydrate, iron nitrate nonahydrate, sodium carbonate, sodium hydroxide, pure water, and sucrose. The obtained composite metal oxide catalyst has a good catalytic effect in the process of synthesizing dimethyl carbonate using propylene carbonate and methanol.

[0028] Synthesis of carbon microsphere precursors: A certain amount of sucrose was dissolved in 100 ml of deionized water, and then ultrasonic treatment was carried out for 30 min to completely dissolve it. After that, the sucrose solution was transferred to a sealed reaction kettle and reacted at a certain temperature for 24 h. After the reaction, filtration was carried out and thoroughly washed with deionized water, and dried at 80 °C. Specifically, in the dissolution step, the sucrose concentration was 10% - 30% to form regular and uniform carbon microspheres. The reaction temperature of the sucrose solution was 120 - 160 °C to facilitate the complete carbonization of sucrose. The SEM image of the carbon microspheres is as Figure 1 shown. It can be seen from the image that the carbon microspheres have regular spherical shapes, and this structure can greatly increase the surface area of the material.

[0029] Example 1: (1) According to the molar ratio of [Fe 3+ + [Mg 2+ + [Ni 2+ + [Al 3+ = 0.1 mol / L; M 2+ : M 3+ = 2:1, Ni:Mg = 1:1, Fe:Al = 1:1, dissolve Fe(NO 3 ) 3 ·9H2O, Ni(NO 3 ) 2 ·6H 2 O, Mg(NO 3 ) 2 ·6H 2 O and Al(NO 3 ) 3 ·9H 2 O in 100 mL of deionized water to obtain solution A. Solution B is a mixture of NaOH (1.5 mol / L) and Na 2 CO 3 (0.64 mol / L) in deionized water (100 mL). Drop solution B and solution A simultaneously into 150 ml of deionized water dispersed with carbon microspheres, stir vigorously, and maintain pH = 9.5. Heat the obtained slurry at 60 °C for 12 h. Separate the obtained precipitate, wash it thoroughly with deionized water and ethanol, and dry it at 80 °C for 24 h. Finally, calcine the FeNiMgAl@C - LDH precursor in air at 500 °C for 3 h (heating rate 3 °C / min) to obtain the catalyst sample, denoted as FeNiMgAl@C - A - 500.

[0030] (2)Catalytic effect test of FeNiMgAl@C-500: Propylene carbonate and methanol were added to the reaction kettle according to a molar ratio of 1:30, and the catalyst FeNiMgAl@C-A-500 was added at 3% of the total feed mass. It was heated to 100 °C and kept warm for 4 h. After the reaction, the catalyst was recovered to obtain dimethyl carbonate and 1,2-propanediol. Through gas chromatography analysis, the single-pass yield of dimethyl carbonate was 89.44%.

[0031] Example 2: (1)According to the molar ratio of [Fe 3+ +[Mg 2+ +[Ni 2+ +[Al 3+ = 0.1 mol / L; M 2+ :M 3+ =2:1, Ni:Mg = 1:1, Fe:Al = 1:1, Fe(NO 3 ) 3 ·9H2O, Ni(NO 3 ) 2 ·6H 2 O, Mg(NO 3 ) 2 ·6H 2 O and Al(NO 3 ) 3 ·9H 2 O were dissolved in 100 mL of deionized water to obtain solution A. Solution B was a mixture of NaOH (1.5 mol / L) and Na 2 CO 3 (0.64 mol / L) in deionized water (100 mL). Solution B and solution A were simultaneously added dropwise to 150 ml of deionized water dispersed with carbon microspheres, and stirred vigorously to maintain pH = 9.5. The obtained slurry was heated at 80 °C for 12 h. The separated precipitate was thoroughly washed with deionized water and ethanol, and dried at 80 °C for 24 h. Finally, the FeNiMgAl@C-LDH precursor was calcined in air at 500 °C for 4 h (heating rate 5 °C / min) to obtain a catalyst sample, denoted as FeNiMgAl@C-A-500.

[0032] (2)Catalytic effect test of FeNiMgAl@C-500: Propylene carbonate and methanol were added to the reaction kettle according to a molar ratio of 1:30, and the catalyst FeNiMgAl@C-A-500 was added at 3% of the total feed mass. It was heated to 100 °C and kept warm for 4 h. After the reaction, the catalyst was recovered to obtain dimethyl carbonate and 1,2-propanediol. Through gas chromatography analysis, the single-pass yield of dimethyl carbonate was 88.14%.

[0033] Example 3: (1) According to the molar ratio of [Fe 3+ + [Mg 2+ + [Ni 2+ + [Al 3+ = 0.1 mol / L; M 2+ :M 3+ = 2:1, Ni:Mg = 1:1, Fe:Al = 1:1, dissolve Fe(NO 3 ) 3 ·9H2O, Ni(NO 3 ) 2 ·6H 2 O, Mg(NO 3 ) 2 ·6H 2 O and Al(NO 3 ) 3 ·9H 2 O in 100 mL of deionized water to obtain solution A. Solution B is a mixture of NaOH (1.5 mol / L) and Na 2 CO 3 (0.64 mol / L) in deionized water (100 mL). Drop solution B and solution A simultaneously into 150 ml of deionized water dispersed with carbon microspheres, stir vigorously, and maintain pH = 9.5. Heat the obtained slurry at 60 °C for 12 h. Separate the obtained precipitate, wash it thoroughly with deionized water and ethanol, and dry it at 80 °C for 24 h. Finally, calcine the FeNiMgAl@C-LDH precursor in air at 700 °C for 4 h (heating rate 5 °C / min) to obtain a catalyst sample, denoted as FeNiMgAl@C-A-700.

[0034] (2) Catalytic effect test of FeNiMgAl@C-700: Add propylene carbonate and methanol to the reaction kettle according to a molar ratio of 1:30, add the catalyst FeNiMgAl@C-A-700 according to 3% of the total feed mass, heat to 100 °C and keep it warm for 4 h. After the reaction, recover the catalyst to obtain dimethyl carbonate and 1,2-propanediol. Through gas chromatography analysis, the single-pass yield of dimethyl carbonate is 90.14%.

[0035] Example 4: (1) According to the molar ratio of [Fe 3+ + [Mg 2+ + [Ni 2+ + [Al 3+ = 0.1 mol / L; M 2+ :M 3+= 2:1, the molar ratio of Ni:Mg = 1:1, and Fe:Al = 1:1 to dissolve Fe(NO 3 ) 3 ·9H2O, Ni(NO 3 ) 2 ·6H 2 O, Mg(NO 3 ) 2 ·6H 2 O and Al(NO 3 ) 3 ·9H 2 O in 100 mL of deionized water to obtain solution A. Solution B is a mixture of NaOH (1.5 mol / L) and Na 2 CO 3 (0.64 mol / L) in deionized water (100 mL). Solution B and solution A are simultaneously dropped into 150 ml of deionized water dispersed with carbon microspheres, stirred vigorously, and maintained at pH = 9.5. The obtained slurry is heated at 60 °C for 12 h. The separated precipitate is thoroughly washed with deionized water and ethanol, and dried at 80 °C for 24 h. Finally, the FeNiMgAl@C-LDH precursor is calcined in air at 800 °C for 4 h (heating rate 5 °C / min) to obtain a catalyst sample, denoted as FeNiMgAl@C-A-800.

[0036] (2) Catalytic effect test of FeNiMgAl@C-800: Propylene carbonate and methanol are added to the reaction kettle in a molar ratio of 1:30, and the catalyst FeNiMgAl@C-A-800 is added according to 3% of the total feed mass. It is heated to 100 °C and kept warm for 4 h. After the reaction, the catalyst is recovered to obtain dimethyl carbonate and 1,2-propanediol. Through gas chromatography analysis, the single-pass yield of dimethyl carbonate is 90.81%.

[0037] Example 5: (1) According to [Fe 3+ + [Mg 2+ + [Ni 2+ + [Al 3+ = 0.1 mol / L; M 2+ : M 3+ = 2:1, the molar ratio of Ni:Mg = 1:1, and Fe:Al = 1:1 to dissolve Fe(NO 3 ) 3 ·9H 2 O, Ni(NO 3 ) 2 ·6H 2 O, Mg(NO 3 ) 2 ·6H2 O and Al(NO 3 ) 3 ·9H 2 O was dissolved in 100 mL of deionized water to obtain solution A. Solution B was a mixture of NaOH (1.5 mol / L) and Na 2 CO 3 (0.64 mol / L) in deionized water (100 mL). Solution B and solution A were simultaneously added dropwise to 150 mL of deionized water in which carbon microspheres were dispersed, and stirred vigorously to maintain pH = 9.5. The resulting slurry was heated at 60 °C for 12 h. The separated precipitate was thoroughly washed with deionized water and ethanol, and dried at 80 °C for 24 h. Finally, the FeNiMgAl@C-LDH precursor was calcined in air at 600 °C for 4 h (heating rate 5 °C / min) to obtain a catalyst sample, denoted as FeNiMgAl@C-A-600. The SEM image of FeNiMgAl@C-A-600 is as shown in Figure 2 Figure, and it can be seen that after calcination, the material integrated a certain spherical structure, and irregular protrusions were presented on the surface of the sphere, which greatly increased the surface area of the material and improved the catalytic effect of the catalyst.

[0038] (2) Catalytic effect test of FeNiMgAl@C-600: Propylene carbonate and methanol were added to the reaction kettle in a molar ratio of 1:30, and the catalyst FeNiMgAl@C-A-600 was added in an amount of 3% of the total feed mass. It was heated to 100 °C and kept warm for 4 h. After the reaction, the catalyst was recovered to obtain dimethyl carbonate and 1,2-propanediol. Through gas chromatography analysis, the single-pass yield of dimethyl carbonate was 98.47%.

[0039] Example 6: (1) According to the molar ratio of [Fe 3+ + [Mg 2+ + [Ni 2+ + [Al 3+ = 0.1 mol / L; M 2+ : M 3+ = 2:1, Ni:Mg = 1:1, Fe:Al = 1:1, Fe(NO 3 ) 3 ·9H2O, Ni(NO 3 ) 2 ·6H 2 O, Mg(NO 3 ) 2 ·6H 2 O and Al(NO 3 ) 3 ·9H2 O was dissolved in 100 mL of deionized water to obtain solution A. Solution B is a mixture of NaOH (1.5 mol / L) and Na 2 CO 3 (0.64 mol / L) in deionized water (100 mL). Solution B and solution A were simultaneously added dropwise to 150 mL of deionized water in which carbon microspheres were dispersed, and stirred vigorously to maintain pH = 9.5. The resulting slurry was heated at 60 °C for 12 h. The separated precipitate was thoroughly washed with deionized water and ethanol, and dried at 80 °C for 24 h. Finally, the FeNiMgAl@C-LDH precursor was calcined in air at 900 °C for 4 h (heating rate 5 °C / min) to obtain a catalyst sample, denoted as FeNiMgAl@C-A-900.

[0040] (2) Catalytic effect test of FeNiMgAl@C-900: Propylene carbonate and methanol were added to the reaction kettle in a molar ratio of 1:30, and the catalyst FeNiMgAl@C-A-900 was added in an amount of 3% of the total feed mass. It was heated to 100 °C and kept warm for 4 h. After the reaction, the catalyst was recovered to obtain dimethyl carbonate and 1,2-propanediol. Through gas chromatography analysis, the single-pass yield of dimethyl carbonate was 89.64%.

[0041] Example 7: (1) According to the molar ratio of [Fe 3+ + [Mg 2+ + [Ni 2+ + [Al 3+ = 0.1 mol / L; M 2+ : M 3+ = 2:1, Ni:Mg = 1:1, Fe:Al = 1:1, Fe(NO 3 ) 3 ·9H2O, Ni(NO 3 ) 2 ·6H 2 O, Mg(NO 3 ) 2 ·6H 2 O and Al(NO 3 ) 3 ·9H 2 O were dissolved in 100 mL of deionized water to obtain solution A. Solution B is NaOH (1.5 mol / L) and Na 2 CO 3A mixture of (0.64 mol / L) in deionized water (100 mL). Solution B and solution A were simultaneously dropped into 150 mL of deionized water dispersed with carbon microspheres, and stirred vigorously to maintain pH = 9.5. The obtained slurry was heated at 60 °C for 12 h. The separated precipitate was thoroughly washed with deionized water and ethanol, and dried at 80 °C for 24 h. Finally, the FeNiMgAl@C-LDH precursor was calcined in air at 600 °C for 2 h (heating rate 5 °C / min) to obtain a catalyst sample, denoted as FeNiMgAl@C-A-600.

[0042] (2)Catalytic effect test of FeNiMgAl@C-600: Propylene carbonate and methanol were added to the reaction kettle in a molar ratio of 1:30, and the catalyst FeNiMgAl@C-A-600 was added in an amount of 3% of the total feed mass. It was heated to 100 °C and kept warm for 4 h. After the reaction, the catalyst was recovered to obtain dimethyl carbonate and 1,2-propanediol. Through gas chromatography analysis, the single-pass yield of dimethyl carbonate was 97.94%.

[0043] Example 8: (1)According to the molar ratio of [Fe 3+ + [Mg 2+ + [Ni 2+ + [Al 3+ = 0.1 mol / L; M 2+ : M 3+ = 2:1, Ni:Mg = 1:1, Fe:Al = 1:1, dissolve Fe(NO 3 ) 3 ·9H2O, Ni(NO 3 ) 2 ·6H 2 O, Mg(NO 3 ) 2 ·6H 2 O and Al(NO 3 ) 3 ·9H 2 O in 100 mL of deionized water to obtain solution A. Solution B is NaOH (1.5 mol / L) and Na 2 CO 3A mixture of (0.64 mol / L) in deionized water (100 mL). Solution B and solution A were simultaneously dropped into 150 mL of deionized water dispersed with carbon microspheres, and stirred vigorously to maintain pH = 12. The obtained slurry was heated at 60 °C for 12 h. The separated precipitate was thoroughly washed with deionized water and ethanol, and dried at 80 °C for 24 h. Finally, the FeNiMgAl@C-LDH precursor was calcined in air at 600 °C for 2 h (heating rate 5 °C / min) to obtain a catalyst sample, denoted as FeNiMgAl@C-A-600.

[0044] (2)Catalytic effect test of FeNiMgAl@C-600: Propylene carbonate and methanol were added to the reaction kettle in a molar ratio of 1:30, and the catalyst FeNiMgAl@C-A-600 was added in an amount of 3% of the total feed mass. It was heated to 100 °C and kept warm for 4 h. After the reaction, the catalyst was recovered to obtain dimethyl carbonate and 1,2-propanediol. Through gas chromatography analysis, the single-pass yield of dimethyl carbonate was 75.34%.

[0045] To verify the cyclic stability of the catalyst, a cyclic stability experiment was carried out with the catalysts obtained in each example. The specific experimental scheme was as follows: After each catalytic effect test, the reaction substrate and reaction products were distilled out by vacuum distillation, and then the catalyst was washed twice with methanol and placed in a vacuum drying oven at 80 °C for 12 h, and then the next catalytic effect test was carried out. According to this test method, 10 cyclic tests were carried out. According to the test results, it can be seen that the cyclic stability of the catalyst prepared by the present invention is good. In particular, the catalyst provided in Example 5 can still maintain a DMC yield of 88.63% after ten cycles. The specific test results are as follows:

[0046] The above content is only an example and explanation of the concept of the present invention. Those skilled in the art of this technology can make various modifications or supplements to the described specific embodiments or use similar methods to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined by this claim book, they should all belong to the protection scope of the present invention.

Claims

1. A method for synthesizing a composite metal oxide catalyst, characterized in that: The specific synthesis steps are as follows: Step 1, synthesis of carbon microsphere precursor: preparing sucrose solution, and forming carbon microspheres through carbonization reaction; Step 2, synthesis of hydrotalcite-like substances: preparing a hydrotalcite-like substance precursor containing Fe, Ni, Mg and Al by a coprecipitation method; comprising the following steps: Prepare a salt solution containing Fe, Ni, Mg, and Al, wherein the molar ratio of Fe:Ni:Mg:Al is [Fe 3+ ] +[Mg 2+ ]+[Ni 2+ ] +[Al 3+ ] = 0.1 mol / L; M 2+ :M 3+ =1:1-3:1, obtain solution A; prepare solution B containing NaOH and Na2CO3; simultaneously drop solution B and solution A into water dispersed with carbon microspheres, stir vigorously, and control the pH of the mixed solution by controlling the dropping speed of solution B; heat the obtained slurry; and then separate the obtained precipitate, wash, and dry to obtain a hydrotalcite precursor; Step 3, synthesis of multi-metal composite oxides: the synthesized hydrotalcite-like precursor is calcined at a specific temperature under a specific atmosphere at a certain heating rate to obtain FeNiMgAl@CA / NT.

2. The method for synthesizing the composite metal oxide catalyst according to claim 1, characterized in that: In step 1, the concentration of the sucrose solution is 10%-30%; the reaction temperature of the sucrose solution is 120-160°C.

3. The method for synthesizing the composite metal oxide catalyst according to claim 1, characterized in that: In step 2, the concentrations of the NaOH and Na2CO3 solutions are 1.5 mol / L and 0.64 mol / L respectively.

4. The method for synthesizing the composite metal oxide catalyst according to claim 1, characterized in that: In step 2, the pH of the mixed solution is controlled within the range of 9-11.

5. The method for synthesizing the composite metal oxide catalyst according to claim 1, characterized in that: In step 2, the reaction temperature of the mixed solution is 60-100°C.

6. The method for synthesizing a composite metal oxide catalyst according to claim 1, characterized in that: In step 2, the content of the carbon microspheres in deionized water is 10 g / L.

7. The method for synthesizing a composite metal oxide catalyst according to claim 1, characterized in that: In step 3, the calcination atmosphere should be an inert gas nitrogen atmosphere or an air atmosphere.

8. The method for synthesizing a composite metal oxide catalyst according to claim 1, characterized in that: In step 3, the calcination heating rate is 2-5°C / min, the calcination temperature should be 500-900°C, and the calcination time is 2-4h.

9. Use of the composite metal oxide catalyst according to any one of claims 1 to 8 in preparing dimethyl carbonate by ester exchange method.

10. A method for preparing dimethyl carbonate, characterized in that: The catalyst is the composite metal oxide catalyst according to any one of claims 1 to 8, and the preparation method is: add propylene carbonate and methanol into a reaction kettle, add the composite metal oxide catalyst according to 3% of the total feed weight, and heat and keep the reaction.

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