Process for the synthesis of cyclopentadiene from cyclopentanone

Abstract

The present application relates to a method for synthesizing cyclopentadiene from a biomass platform compound cyclopentanone, which uses cyclopentanone as a raw material, and is synthesized by hydrogenation-deoxidization and dehydrogenation in series in a fixed-bed continuous reactor under the action of a composite metal oxide catalyst of A x B y O z type. The process route is simple, environmentally friendly, and the catalyst is easy to prepare, thus providing a new and effective approach for synthesizing cyclopentadiene from cyclopentanone.

Description

Technical Field

[0001] This invention relates to a method for synthesizing cyclopentadiene from cyclopentanone. Background Technology

[0002] Cyclopentadiene, a crucial chemical, is a fundamental raw material for the production of key organic products such as ferrocene, norbornene, cyclopentene, adamantane, cyclopentane, halocyclopentane, and glutaraldehyde. It can also be used to prepare petroleum resins, unsaturated resins, and high-density aviation fuel JP-10. However, due to its highly reactive chemical properties, cyclopentadiene is commercially sold, transported, and stored in the form of dicyclopentadiene. Currently, the industrial production of cyclopentadiene primarily uses C5 from ethylene cracking as raw material. Cyclopentadiene is dimerized to dicyclopentadiene at a certain temperature, and then high-purity dicyclopentadiene is separated by vacuum distillation, followed by depolymerization to obtain cyclopentadiene. CN1389444A discloses a method for preparing high-purity cyclopentadiene by pyrolysis of crude dicyclopentadiene. This method utilizes a gas-liquid phase pyrolysis process, adding crude dimerized cyclopentadiene to a thermal decomposer containing a heat-carrying liquid heated to 170-350°C. The decomposition products are collected at a condensation temperature of 42-80°C. While this method is efficient and simple, it relies on fossil fuels with limited reserves that cannot be replenished in the short term. Furthermore, it involves repeated depolymerization and distillation processes, resulting in complex equipment and high energy consumption. Therefore, developing a new green and sustainable route for the synthesis of cyclopentadiene is urgently needed.

[0003] Biomass energy, as the only organic carbon source among renewable energy sources on Earth, is abundant, inexpensive, and readily available. It is also a carbon-neutral natural resource; the carbon dioxide produced during its conversion can continue to participate in plant photosynthesis, achieving a carbon cycle and theoretically resulting in zero carbon dioxide emissions. Therefore, using renewable biomass resources to replace traditional fossil fuels as raw materials for the synthesis of high-value-added chemicals has attracted considerable attention. For example, CN113968776A discloses a method for preparing cyclopentanone from biomass raw materials. This system, under certain reaction conditions, can prepare cyclopentanone in a high yield from hemicellulose, xylan, xylose, and arabinose in a single step. However, to date, no literature has reported the synthesis of cyclopentadiene from biomass cyclopentanone. Summary of the Invention

[0004] The key technical problem to be solved by this invention is to provide a method for synthesizing cyclopentadiene from cyclopentanone, using the biomass platform compound cyclopentanone as raw material, in a fixed-bed continuous reactor, through A x B y O zThe hydrogenation-deoxygenation tandem dehydrogenation reaction on a composite metal oxide catalyst converts cyclopentanone into the target product cyclopentadiene in one step, providing a novel, simple, and efficient synthetic method for preparing high-value-added cyclopentadiene chemicals from cyclopentanone.

[0005] This invention is achieved through the following technical solution:

[0006] A method for synthesizing cyclopentadiene from cyclopentanone involves using cyclopentanone as a raw material in a fixed-bed continuous reactor under the action of an AxByOz type composite metal oxide catalyst, via a hydrodeoxygenation-dehydrogenation reaction. The reaction temperature is 400-600℃ (preferably 420-580℃, more preferably 450-570℃), the hydrogen pressure is 0.0001-1 MPa (preferably 0.0001-0.9 MPa, more preferably 0.0001-0.8 MPa), the molar ratio of hydrogen to cyclopentanone is 20-400:1 (30-350:1, more preferably 50-300:1), and the space velocity of cyclopentanone is 0.01-10 h⁻¹. -1 (Preferred 0.05-9h) -1 More preferably 0.1-8h -1 The target product, cyclopentadiene, is obtained by applying the following steps.

[0007] The chemical structural formulas of the above-mentioned raw material cyclopentanone and the target product cyclopentadiene are shown in Table 1.

[0008] Table 1 Structural formulas of the compounds

[0009]

[0010] Based on the above scheme, preferably, A x B y O z Type-composite metal oxide catalysts include: Cu x Mo y O z Zn x Mo y O z Ni x Mo y O z Co x Mo y O z Mn x Mo y O z Fe x Mo y O z Cr x Mo y O z Cu x W y Oz Ni x W y O z Co x W y O z Fe x W y O z Zn x W y O z Zn x V y O z One or more of the following: x is 0.5-8, preferably 0.8-7, more preferably 1-6; y is 0.5-8, preferably 0.8-7, more preferably 1-6; z is 1-16, preferably 1-14, more preferably 1-12.

[0011] Based on the above scheme, preferably, A x B y O z The composite metal oxide catalyst is prepared by hydrothermal method, deposition precipitation method or citric acid complexation method, and is reduced in hydrogen before use. The reduction conditions are as follows: hydrogen pressure 0.001-2.0 MPa (preferably 0.005-1.5 MPa, more preferably 0.01-1 MPa), hydrogen flow rate 2-300 mL / min (preferably 5-250 mL / min, more preferably 10-200 mL / min), reduction temperature 400-600℃ (preferably 450-580℃, more preferably 480-570℃), and reduction time 0.5-12 h (preferably 0.7-10 h, more preferably 1-8 h).

[0012] Based on the above scheme, preferably, A x B y O z The composite metal oxide catalyst is prepared by a hydrothermal method. The specific preparation process is as follows: a certain amount of metal salt A and metal salt B are mixed and dissolved in deionized water, and ultrasonicated at room temperature to obtain a suspension; the mixed solution is transferred to a hydrothermal reactor with a polytetrafluoroethylene liner, and reacted at 80-220℃ (preferably 90-200℃, more preferably 100-180℃) for 5-48 h (preferably 6-42 h, more preferably 8-36 h), followed by filtration and washing. The resulting powder is dried at 80℃ for 1-8 h (preferably 2-6 h, more preferably 3-5 h), and then calcined at 300-800℃ (preferably 350-750℃, more preferably 400-700℃) for 0.5-6 h (preferably 1-5 h, more preferably 1-4 h) to obtain catalyst A. x B y O z Type of composite metal oxide catalyst.

[0013] Based on the above scheme, preferably, A x B y O z The composite metal oxide catalyst can also be prepared by a deposition-precipitation method. The specific preparation process is as follows: a certain amount of metal salt B is dissolved in deionized water. An ammonia solution with a concentration of 0.5-14 mol / L (preferably 1-8 mol / L, more preferably 1.5-6 mol / L) is used as a precipitant to adjust the pH of the solution to 8-12. Then, an aqueous solution of metal acid salt A is added dropwise. After stirring for 0.5-4 h (preferably 1-3.5 h, more preferably 1-3 h), the resulting precipitate is filtered out, washed with deionized water and ethanol, dried in an oven at 50-120℃ for 4-48 h, and then calcined at 300-800℃ (preferably 350-750℃, more preferably 400-700℃) for 0.5-10 h (preferably 1-8 h, more preferably 1-6 h) to obtain A. x B y O z Type of composite metal oxide catalyst.

[0014] Based on the above scheme, preferably, A x B y O z The composite metal oxide catalyst can also be prepared using the citric acid complexation method. The specific preparation process is as follows: Weigh out the metal salts of B and A, and citric acid, where M is the total molar amount of metal B (an anion) and metal A (a cation), in a molar ratio M:citric acid = 1:1-1:3 (preferably 1:1.05-1:2, more preferably 1:1.1-1:1.5). Dissolve each separately in deionized water, then mix the solutions uniformly and heat in an evaporating dish until only a solid is formed. After drying at 120°C for 12 hours, calcine at 300-800°C (preferably 350-750°C, more preferably 400-700°C) for 0.5-10 hours (preferably 1-8 hours, more preferably 1-6 hours) to obtain A. x B y O z Type of composite metal oxide catalyst.

[0015] The method described in this invention enables the direct synthesis of high-value-added cyclopentadiene from the biomass platform compound cyclopentanone, providing a novel and effective route for the synthesis of cyclopentadiene from cyclopentanone.

[0016] The beneficial effects of this invention are:

[0017] The process of this invention is simple, easy to operate, and environmentally friendly. It can convert cyclopentanone into cyclopentadiene in one step through a series of hydrogenation-deoxygenation and dehydrogenation reactions, which is a green and efficient new approach.

[0018] The catalyst of this invention is simple to prepare, can be synthesized in large quantities, has mild reaction conditions, a cyclopentanone conversion rate of over 92%, a cyclopentadiene selectivity of over 80%, good catalytic performance, and good stability and regeneration performance.

[0019] This invention employs a fixed-bed continuous flow reactor, in A x B y O z Under the action of a composite metal oxide catalyst, cyclopentanone can be converted into cyclopentadiene in one step, which has the advantages of high operability, low energy consumption and environmental friendliness, and can be used for actual industrial production.

[0020] This invention is the first to use cyclopentanone as a substrate in a fixed-bed continuous reactor to directly synthesize high-value-added cyclopentadiene in one step via a hydrodeoxygenation-dehydrogenation reaction, exhibiting excellent feed conversion and product selectivity. To date, there have been no reports on the synthesis of cyclopentadiene from cyclopentanone via a one-step hydrodeoxygenation-dehydrogenation reaction. Attached Figure Description

[0021] Figure 1 This is a gas chromatogram of the product of cyclopentadiene synthesis from cyclopentanone in Example 7.

[0022] Figure 2 This is a mass spectrum comparison image of the target product, cyclopentadiene. Detailed Implementation

[0023] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0024] Example 1

[0025] (1)A x B y O z Preparation of the CoMoO4 composite metal oxide catalyst: 2.47 g of ammonium molybdate was weighed and dissolved in 200 mL of deionized water. The pH of the solution was adjusted to 9.5 using a 2 mol / L ammonia solution as a precipitant. Cobalt nitrate (4.07 g dissolved in 100 mL of deionized water) aqueous solution was added dropwise. After stirring for 2 h, the precipitate was filtered out, washed with deionized water and ethanol, dried in an oven at 50 °C for 4 h, and then calcined at 500 °C for 2 h to obtain the CoMoO4 composite metal oxide catalyst.

[0026] (2) 0.4 g of the above CoMoO4 catalyst was uniformly mixed with 2 g of quartz sand (40-70 mesh) and packed into a fixed-bed continuous reactor. Then, reduction was carried out for 2 h at a hydrogen pressure of 0.1 MPa, a hydrogen flow rate of 150 mL / min, and a reduction temperature of 480 °C. The reaction temperature was then controlled at 480 °C, the hydrogen pressure at 0.01 MPa, the molar ratio of hydrogen to cyclopentanone at 50:1, and the hourly space velocity of cyclopentanone at 1.33 h⁻¹. -1 The conversion rate of cyclopentanone was 94%, and the selectivity of cyclopentadiene was 83%.

[0027] Example 2

[0028] (1)A x B y O z Preparation of NiMoO4 composite metal oxide catalyst: 1.24 g of ammonium molybdate, 2.04 g of nickel nitrate, and 3.53 g of citric acid were weighed in a molar ratio M:citric acid = 1:1.2, where M is the total molar amount of metal B in the anion state and metal A in the cation state. After dissolving them separately in deionized water, the solutions were mixed evenly and heated in an evaporating dish until only solid was formed. After drying at 120 °C for 12 h, the catalyst was calcined at 550 °C for 5 h to obtain the NiMoO4 composite metal oxide catalyst.

[0029] (2) 0.8 g of the above NiMoO4 catalyst was uniformly mixed with 2 g of quartz sand (40-70 mesh) and packed into a fixed-bed continuous reactor. Then, reduction was carried out for 1 h at a hydrogen pressure of 0.05 MPa, a hydrogen flow rate of 120 mL / min, and a reduction temperature of 480 °C. The reaction temperature was then controlled at 500 °C, a hydrogen pressure of 0.001 MPa, a hydrogen to cyclopentanone molar ratio of 100:1, and a cyclopentanone hourly space velocity of 0.67 h⁻¹. -1 The conversion rate of cyclopentanone was 96%, and the selectivity of cyclopentadiene was 85%.

[0030] Example 3

[0031] (1)A x B y O z Preparation of Cu3Mo2O9 composite metal oxide catalyst: 0.50 g ketone acetate and 0.44 g ammonium molybdate were dissolved in 40 mL deionized water and sonicated at room temperature to obtain a suspension; the mixed solution was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner, reacted at 140 °C for 12 h, filtered and washed, the obtained powder was dried at 80 °C for 3 h and then calcined at 600 °C for 3 h to obtain Cu3Mo2O9 composite metal oxide catalyst.

[0032] (2) 0.2 g of the above Cu3Mo2O9 catalyst was uniformly mixed with 2 g of quartz sand (40-70 mesh) and packed into a fixed-bed continuous reactor. Then, the reaction was reduced for 0.5 h at a hydrogen pressure of 0.01 MPa, a hydrogen flow rate of 90 mL / min, and a reduction temperature of 500 °C. The reaction temperature was then controlled at 520 °C, the hydrogen pressure at 0.01 MPa, the molar ratio of hydrogen to cyclopentanone at 100:1, and the space velocity of cyclopentanone at 2.67 h⁻¹. -1 The conversion rate of cyclopentanone was 92%, and the selectivity of cyclopentadiene was 82%.

[0033] Example 4

[0034] (1)A x B y O z Preparation of Fe2(MoO4)3 composite metal oxide catalyst: 1.24 g of ammonium molybdate, 1.89 g of ferric nitrate nonahydrate, and 2.94 g of citric acid were weighed in a molar ratio M:citric acid = 1:1.2. M is the total molar amount of metal B in the anion state and metal A in the cation state. After dissolving them separately in deionized water, the solutions were mixed evenly and heated in an evaporating dish until only solid was formed. After drying at 120 °C for 12 h, the catalyst was calcined at 600 °C for 3 h to obtain the Fe2(MoO4)3 composite metal oxide catalyst.

[0035] (2) 0.4 g of the above Fe2(MoO4)3 catalyst was uniformly mixed with 2 g of quartz sand (40-70 mesh) and packed into a fixed-bed continuous reactor. Then, reduction was carried out for 1 h at a hydrogen pressure of 0.01 MPa, a hydrogen flow rate of 150 mL / min, and a reduction temperature of 550 °C. The reaction temperature was then controlled at 550 °C, the hydrogen pressure at 0.005 MPa, the molar ratio of hydrogen to cyclopentanone at 50:1, and the hourly space velocity of cyclopentanone at 1.33 h⁻¹. -1 The conversion rate of cyclopentanone was 96%, and the selectivity of cyclopentadiene was 84%.

[0036] Example 5

[0037] (1)A x B y O z Preparation of NiWO4 composite metal oxide catalyst: 0.71 g of nickel acetate and 1.32 g of sodium tungstate dihydrate were dissolved in 80 mL of deionized water and sonicated at room temperature to obtain a suspension; the mixed solution was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner, reacted at 120 °C for 24 h, filtered and washed, the obtained powder was dried at 80 °C for 3 h and then calcined at 650 °C for 2 h to obtain the NiWO4 composite metal oxide catalyst.

[0038] (2) 0.4 g of the above NiWO4 catalyst was uniformly mixed with 2 g of quartz sand (40-70 mesh) and packed into a fixed-bed continuous reactor. Then, reduction was carried out for 2 h at a hydrogen pressure of 0.02 MPa, a hydrogen flow rate of 90 mL / min, and a reduction temperature of 550 °C. The reaction temperature was then controlled at 570 °C, a hydrogen pressure of 0.05 MPa, a hydrogen to cyclopentanone molar ratio of 75:1, and a cyclopentanone hourly space velocity of 2.67 h⁻¹. -1 The conversion rate of cyclopentanone was 95%, and the selectivity of cyclopentadiene was 83%.

[0039] Example 6

[0040] (1)A x B y O z Preparation of the Zn3(VO4)2 composite metal oxide catalyst: 1.10 g of zinc acetate and 0.47 g of ammonium metavanadate were dissolved in 60 mL of deionized water and sonicated at room temperature to obtain a suspension; the mixed solution was transferred to a hydrothermal reactor with a polytetrafluoroethylene liner, reacted at 160 °C for 12 h, filtered and washed, and the obtained powder was dried at 80 °C for 3 h and then calcined at 550 °C for 4 h to obtain the Zn3(VO4)2 composite metal oxide catalyst.

[0041] (2) 0.2 g of the Zn3(VO4)2 catalyst and 0.2 g of the NiWO4 catalyst synthesized in Example 5 were mechanically mixed, and then uniformly mixed with 2 g of quartz sand (40-70 mesh). The mixture was then packed into a fixed-bed continuous reactor, and reduced for 0.5 h at a hydrogen pressure of 0.01 MPa, a hydrogen flow rate of 120 mL / min, and a reduction temperature of 500 °C. The reaction temperature was then controlled at 550 °C, the hydrogen pressure at 0.001 MPa, the molar ratio of hydrogen to cyclopentanone at 100:1, and the space velocity of cyclopentanone at 1.33 h⁻¹. -1 The conversion rate of cyclopentanone was 97%, and the selectivity of cyclopentadiene was 87%.

[0042] The experimental results of Examples 1-6 above are shown in Table 2.

[0043] Table 2 shows the synthesis of cyclopentadiene from cyclopentanone via hydrogenation-deoxygenation-dehydrogenation.

[0044] Example catalyst Cyclopentanone conversion rate / % Cyclopentadiene selectivity / % Example 1 <![CDATA[CoMoO4]]> 94 83 Example 2 <![CDATA[NiMoO4]]> 96 85 Example 3 <![CDATA[Cu3Mo2O9]]> 92 82 Example 4 <![CDATA[Fe2(MoO4)3]]> 96 84 Example 5 <![CDATA[NiWO4]]> 95 83 Example 6 <![CDATA[Zn3(VO4)2+NiWO4]]> 97 87

[0045] Example 7

[0046] (1)A x B y O zPreparation of the Zn3Mo2O9 composite metal oxide catalyst: 2.47 g of ammonium molybdate was weighed and dissolved in 200 mL of deionized water. The pH of the solution was adjusted to 9.2 using a 4 mol / L ammonia solution as a precipitant. Then, zinc nitrate (4.16 g dissolved in 100 mL of deionized water) aqueous solution was added dropwise. After stirring for 2 h, the precipitate was filtered out, washed with deionized water and ethanol, dried in an oven at 50 °C for 6 h, and then calcined at 600 °C for 1 h to obtain the Zn3Mo2O9 composite metal oxide catalyst.

[0047] (2) 0.8 g of the above Zn3Mo2O9 catalyst was uniformly mixed with 2 g of quartz sand (40-70 mesh) and packed into a fixed-bed continuous reactor. Then, reduction was carried out for 1 h at a hydrogen pressure of 0.01 MPa, a hydrogen flow rate of 150 mL / min, and a reduction temperature of 550 °C. The reaction temperature was then controlled at 550 °C, the hydrogen pressure at 0.01 MPa, the molar ratio of hydrogen to cyclopentanone at 100:1, and the space velocity of cyclopentanone at 0.67 h⁻¹. -1 The conversion rate of cyclopentanone was 95%, and the selectivity of cyclopentadiene was 86%.

[0048] In the preparation of the Zn3Mo2O9 catalyst in Example 7, other conditions remained unchanged, and different Zn / Mo ratios of Zn were obtained by varying the mass of ammonium molybdate added. x Mo y O z The composite metal oxide catalyst is shown in Examples 8-12. The obtained Zn... x Mo y O z 0.8 g of catalyst and 2 g of quartz sand (40-70 mesh) were uniformly mixed and packed into a fixed-bed continuous reactor. Reduction was carried out for 1 h at a hydrogen pressure of 0.01 MPa, a hydrogen flow rate of 150 mL / min, and a reduction temperature of 550 °C. Then, the reaction was carried out at 550 °C, a hydrogen pressure of 0.01 MPa, a hydrogen to cyclopentanone molar ratio of 100:1, and a cyclopentanone hourly space velocity of 0.67 h⁻¹. -1 The reaction takes place under specific conditions.

[0049] Table 3. Zn with different Zn / Mo ratios x Mo y O z Catalytic hydrogenation-deoxygenation-dehydrogenation of cyclopentanone to synthesize cyclopentadiene

[0050]

Claims

1. A method for synthesizing cyclopentadiene from cyclopentanone, characterized in that, The method is as follows: using cyclopentanone as a raw material, in a fixed-bed continuous reactor, under A... x B y O z Under the action of a composite metal oxide catalyst, a hydrodeoxygenation-dehydrogenation reaction is carried out at a reaction temperature of 400-600℃, a hydrogen pressure of 0.0001-1 MPa, a hydrogen to cyclopentanone molar ratio of 20-400:1, and a cyclopentanone space velocity of 0.01-10 h⁻¹. -1 The target product cyclopentadiene can then be obtained. The A x B y O z Type-composite metal oxide catalysts include: Cu x Mo y O z Zn x Mo y O z Ni x Mo y O z Co x Mo y O z Fe x Mo y O z Ni x W y O z Co x W y O z Fe x W y O z Zn x V y O z One or more of the following; wherein x is 0.5-8, y is 0.5-8, and z is 1-16.

2. The method according to claim 1, characterized in that: The reaction temperature was 420-580℃, the hydrogen pressure was 0.0001-0.9 MPa, the molar ratio of hydrogen to cyclopentanone was 30-350:1, and the space velocity of cyclopentanone was 0.05-9 h⁻¹. -1 .

3. The method according to claim 2, characterized in that: The reaction temperature was 450-570℃, the hydrogen pressure was 0.0001-0.8 MPa, the molar ratio of hydrogen to cyclopentanone was 50-300:1, and the space velocity of cyclopentanone was 0.1-8 h⁻¹. -1 .

4. The method according to claim 1, characterized in that: x is 0.8-7, y is 0.8-7, and z is 1-14.

5. The method according to claim 4, characterized in that: x is 1-6, y is 1-6, z is 1-12.

6. The method according to claim 1 or 4, characterized in that: The A x B y O z The composite metal oxide catalyst is prepared by hydrothermal method, deposition precipitation method or citric acid complexation method, and is reduced in hydrogen before use; the reduction conditions are: hydrogen pressure 0.001-2.0MPa, hydrogen flow rate 2-300mL / min, temperature 400-600℃, time 0.5-12h.

7. The method according to claim 6, characterized in that, The reduction treatment conditions are: hydrogen pressure 0.005-1.5 MPa, hydrogen flow rate 5-250 mL / min, temperature 450-580℃, and time 0.7-10 h.

8. The method according to claim 7, characterized in that, The conditions for the reduction treatment are: hydrogen pressure 0.01-1 MPa, hydrogen flow rate 10-200 mL / min, temperature 480-570℃, and time 1-8 h.

9. The method according to claim 6, characterized in that, The hydrothermal method includes the following steps: dissolving a metal salt of A and a metal salt of B in deionized water, and sonicating at room temperature to obtain a suspension; reacting the suspension at 80-220℃ for 5-48 hours, then filtering, washing, drying at 80℃ for 1-8 hours, and then calcining at 300-800℃ for 0.5-6 hours to obtain A. x B y O z Type of composite metal oxide catalyst; The precipitation method includes the following steps: dissolving the metal salt of B in deionized water, adjusting the pH to 8-12 using a 0.5-14 mol / L ammonia solution as a precipitant, adding an aqueous solution of the metal acid salt of A dropwise, stirring for 0.5-4 hours, filtering out the precipitate, washing with deionized water and ethanol, drying at 50-120℃ for 4-48 hours, and then calcining at 300-800℃ for 0.5-10 hours to obtain A. x B y O z Type of composite metal oxide catalyst; The citric acid complexation method includes the following steps: Weigh out the metal salts of B and A, and citric acid, in a molar ratio M:citric acid = 1:1~1:3, where M is the total molar amount of metal B and metal A; dissolve each separately in deionized water, then mix the solutions evenly and heat in an evaporating dish until only a solid is formed; dry at 120℃ for 12 hours, then calcine at 300-800℃ for 0.5-10 hours to obtain A. x B y O z Type of composite metal oxide catalyst.

10. The method according to claim 9, characterized in that, The hydrothermal method includes the following steps: dissolving a metal salt of A and a metal salt of B in deionized water, and sonicating at room temperature to obtain a suspension; reacting the suspension at 90-200℃ for 6-42 h, then filtering, washing, drying at 80℃ for 2-6 h, and then calcining at 350-750℃ for 1-5 h to obtain A. x B y O z Type of composite metal oxide catalyst; The precipitation method includes the following steps: dissolving the metal salt of B in deionized water, adjusting the pH to 8-12 using a 1-8 mol / L ammonia solution as a precipitant, adding an aqueous solution of the metal acid salt of A dropwise, stirring for 1-3.5 h, filtering out the precipitate, washing with deionized water and ethanol, drying at 50-120℃ for 4-48 h, and then calcining at 350-750℃ for 1-8 h to obtain A. x B y O z Type of composite metal oxide catalyst; The citric acid complexation method includes the following steps: Weigh the metal salts of B and A, and citric acid, in a molar ratio M:citric acid = 1:1.05~1:2, where M is the total molar sum of metal B and metal A; dissolve each separately in deionized water, then mix the solutions uniformly and heat in an evaporating dish until only a solid is formed; after drying at 120℃ for 12 hours, calcine at 350-750℃ for 1-8 hours to obtain A. x B y O z Type of composite metal oxide catalyst.

11. The method according to claim 10, characterized in that, The hydrothermal method includes the following steps: dissolving a metal salt of A and a metal salt of B in deionized water, and sonicating at room temperature to obtain a suspension; reacting the suspension at 100-180℃ for 8-36 h, then filtering, washing, drying at 80℃ for 3-5 h, and then calcining at 400-700℃ for 1-4 h to obtain A. x B y O z Type of composite metal oxide catalyst; The precipitation method includes the following steps: dissolving the metal salt of B in deionized water, adjusting the pH to 8-12 using a 1.5-6 mol / L ammonia solution as a precipitant, adding an aqueous solution of the metal acid salt of A dropwise, stirring for 1-3 hours, filtering out the precipitate, washing with deionized water and ethanol, drying at 50-120℃ for 4-48 hours, and then calcining at 400-700℃ for 1-6 hours to obtain A. x B y O z Type of composite metal oxide catalyst; The citric acid complexation method includes the following steps: Weigh out the metal salts of B and A, and citric acid, in a molar ratio M:citric acid = 1:1.1~1:1.5, where M is the total molar amount of metal B and metal A; dissolve each separately in deionized water, then mix the solutions uniformly and heat in an evaporating dish until only a solid is formed; after drying at 120℃ for 12 hours, calcine at 400-700℃ for 1-6 hours to obtain A. x B y O z Type of composite metal oxide catalyst.

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