CN110433806A - A kind of cobalt-aluminium composite oxide catalyst and its preparation method and application - Google Patents

Abstract

The invention relates to the technical field of catalyst preparation, and discloses a cobalt-aluminum composite oxide catalyst and its preparation method and application. The metal salt solutions of cobalt and aluminum are respectively used as precursors, and polymer microspheres are used as templates. The template is soaked in the precursor solution, and the cobalt-aluminum composite oxide catalyst is obtained through impregnation and roasting, and a three-dimensional ordered multi-level porous structure with mesopore and macropore structure is created through polymer microspheres, increasing the The specific surface area of the catalyst is increased, so that the prepared catalyst has a larger transmission channel, which is conducive to the reactant molecules entering the channel from all directions, reducing the diffusion resistance, thereby improving the convective mass transfer efficiency between gases, and is beneficial to all Catalytic activity of the cobalt-aluminum composite oxide catalyst. At the same time, the larger transmission channel can effectively prevent molecules from clogging when reacting on the pore wall or channel, which will affect the reaction process, and improve the catalytic conversion efficiency of the catalyst.

Description

A kind of cobalt-aluminum composite oxide catalyst and its preparation method and application

technical field

The invention relates to the technical field of catalyst preparation, in particular to a cobalt-aluminum composite oxide catalyst and a preparation method and application thereof.

Background technique

Volatile organic compounds, also referred to as VOCs (Volatile Organic Compounds), refer to volatile organic compounds with a boiling point below 260°C at normal pressure and a saturated vapor pressure above 70Pa at normal temperature, mainly including aldehydes, aromatic hydrocarbons and halogenated hydrocarbons Large categories, which generally exist in indoor and outdoor air. VOCs are very easy to generate photochemical smog under light conditions, causing greenhouse effect and ozone layer destruction, and their toxicity, carcinogenicity, teratogenicity and mutagenicity will have a significant impact on human health. At present, the treatment methods of VOCs include physical adsorption, chemical absorption, biodegradation, catalytic combustion, photocatalytic reduction, and thermal combustion. Among them, the catalytic combustion method has attracted much attention due to its advantages of low energy consumption, high conversion rate and no secondary pollution.

The catalysts currently used for the catalytic combustion of VOCs mainly include noble metal catalysts and non-noble metal catalysts. Noble metal catalysts, such as commonly used Pt and Pd catalysts, have the advantages of high low-temperature light-off activity, complete catalytic oxidation, and high product selectivity for the catalytic combustion of VOCs, but there are also problems such as: precious metal resources are scarce, expensive, and easy to sinter at high temperatures And loss, purification of VOCs containing S, Cl, N and other heteroatoms are easy to be poisoned. Non-metallic catalysts are mainly perovskite-type and spinel-type catalysts containing transition metals such as Cr, Mn, Fe, Co, and Cu, which are low in price, good in stability, and have high activity for catalytic combustion reactions. The activity of spinel-type cobalt oxide (Co ₃ O ₄ ) on the catalytic combustion of VOCs can even be compared with that of noble metal catalysts, which has attracted widespread attention.

For example, the prior art discloses a method for preparing an active cobalt-based catalyst for the low _- temperature catalytic combustion of propane, in which _Al2O3 powder is added to the Co precursor solution, and the co-precipitation method is used to obtain the cobalt-based catalyst precursor. The cobalt-based catalyst is prepared by calcination, surface reduction and further high-temperature treatment under high temperature conditions. Although the catalyst prepared by this method has good thermal stability and good dispersion of surface active cobalt oxide, the loading of cobalt oxide is low and the number of active bits is low. However, the overall activity of the catalyst is not high; in addition, the catalyst obtained by loading the cobalt precursor on the surface of the alumina support by coprecipitation does not have a uniform and ordered pore structure, which is not conducive to the gas exchange under high space velocity conditions. The convective mass transfer process leads to low catalytic combustion activity of the catalyst for VOCs.

Contents of the invention

Therefore, the technical problem to be solved in the present invention is to overcome the defect that the existing catalysts used to catalyze the combustion of VOCs do not have a uniform and ordered pore structure, which leads to the low catalytic activity of the catalyst, thereby providing a cobalt-aluminum composite oxide catalyst According to the preparation method, the cobalt-aluminum composite oxide catalyst prepared by the method has high catalytic activity, has a mesoporous and macroporous hierarchical pore structure, a large specific surface area, and a small cobalt-aluminum spinel grain size. Meanwhile, the present invention also provides the application of the cobalt-aluminum composite oxide catalyst.

In order to solve the above-mentioned technical problems, the present invention provides a method for preparing a cobalt-aluminum composite oxide catalyst, using a metal salt solution of cobalt and aluminum as a precursor, using polymer microspheres as a template, and soaking the template in The cobalt-aluminum composite oxide catalyst is obtained by impregnating and calcining the precursor solution.

Further, the preparation method includes the following steps:

Disperse metal salts of cobalt and aluminum in a mixed solution of water and ethanol to form a metal ion solution;

The polymer microspheres are added to the metal ion precursor solution, left to stand, and suction filtered, and the obtained solid is dried and calcined to obtain the cobalt-aluminum composite oxide catalyst.

Further, the cobalt metal salt is at least one of cobalt nitrate or cobalt chloride; the aluminum metal salt is at least one of aluminum nitrate or aluminum chloride.

Further, the molar ratio of the metal salt of cobalt to the metal salt of aluminum is (0.5-3):1;

In the solution, the total concentration of cobalt ions and aluminum ions is 1.0 mol/L, and the volume ratio of water and ethanol is 1:1.

Further, the polymer microspheres are at least one of polystyrene nanospheres, polymethyl methacrylate nanospheres or styrene-methyl methacrylate-acrylic acid copolymer nanospheres.

Furthermore, the polymer microspheres have a particle size of 400-600 nm, are prepared by a soap-free emulsion polymerization method, and are self-assembled by a centrifugation method.

Furthermore, the rotational speed of the centrifuge is 1000r/min.

Further, the drying is at 80° C. for 12 hours.

Further, the calcination is to calcine the dried catalyst precursor in an air atmosphere at 500° C. for 2 hours.

Furthermore, the step of heating the dried catalyst precursor from 25°C to 500°C at a heating rate of 1°C/min is also included before the calcination.

The present invention also provides a cobalt-aluminum composite oxide catalyst prepared according to the above preparation method.

Further, the catalyst has a pore structure of mesopores and macropores, with a specific surface area of 94-140 m ² /g.

Further, the cobalt-aluminum composite oxide is uniformly dispersed in the pore wall skeleton, and the grain size of the cobalt-aluminum spinel is 9-15 nm.

The present invention also provides a cobalt-aluminum composite oxide catalyst prepared according to the above preparation method or an application of the above cobalt-aluminum composite oxide catalyst in catalytic combustion of VOCs.

Further, the VOCs are benzene, the temperature of the catalytic reaction is 100-450°C, the volume fraction of benzene in the raw gas is 0.516‰, the volume fraction of oxygen is 21%, nitrogen is used as the balance gas, and the space velocity is 36000mL/g h.

The technical solution of the present invention has the following advantages:

1. The preparation method of the cobalt-aluminum composite oxide catalyst provided by the present invention uses the metal salt solution of cobalt and aluminum as a precursor respectively, and polymer microspheres as a template, and adds the polymer microspheres to the In the metal ion precursor solution, the cobalt-aluminum composite oxide catalyst can be obtained by impregnating and roasting, and a three-dimensional ordered multi-level porous structure with mesopore and macropore structure is created by polymer microspheres, which increases the catalyst's The specific surface area enables the prepared catalyst to have larger transmission channels, which is conducive to the reactant molecules entering the channels from all directions, reducing the diffusion resistance, thereby improving the convective mass transfer efficiency between gases, and is beneficial to the cobalt- Catalytic activity of aluminum composite oxide catalysts. At the same time, the larger transmission channel can effectively prevent molecules from clogging when reacting on the pore wall or channel, which will affect the reaction process, and improve the catalytic conversion efficiency of the catalyst. In addition, in the cobalt-aluminum composite oxide catalyst obtained by the method, the cobalt and aluminum oxides are evenly dispersed in the pore wall skeleton, which is beneficial to the fixation and dispersion of the catalyst active material and improves the catalytic activity per unit mass of cobalt.

2. The preparation method of the cobalt-aluminum composite oxide catalyst provided by the present invention, by using polymer microspheres as a template to create a catalyst with a pore structure, by adjusting the particle size of the microspheres and other factors to obtain different pore shapes, The pore shape can be adjusted flexibly, which is convenient for further chemical modification of the catalyst.

3. The preparation method of the cobalt-aluminum composite oxide catalyst provided by the present invention further limits factors such as the consumption of active material cobalt oxide and structural aid aluminum oxide, the kind of solvent, total metal ion concentration and roasting temperature and time, so that The prepared cobalt-aluminum composite oxide catalyst has a three-dimensional ordered hierarchical pore structure of mesopores and macropores, a large specific surface area, and a small grain size of cobalt-aluminum spinel, which is beneficial to catalyze the combustion of VOCs.

4. The preparation method of the cobalt-aluminum composite oxide catalyst provided by the present invention uses the mixed solution of water and ethanol as the solvent of the metal salt, which is cheap, easy to get and non-toxic, and the method is simple in process, strong in operability, and environmentally friendly. It is friendly, and helps to reduce the production cost of the catalyst, and is convenient for industrial promotion and application.

5. The cobalt-aluminum composite oxide catalyst provided by the present invention has a three-dimensional ordered macroporous structure with large pore size and good permeability, which is beneficial to the convective mass transfer process between gases, and effectively prevents molecules from being trapped in the pore wall. Or blockage occurs during the reaction on the channel, which affects the reaction process and greatly improves the catalytic conversion activity of the catalyst. Using alumina as a structural aid can not only reduce the grain size of cobalt aluminum spinel, improve the dispersion of cobalt oxide, but also promote the formation of macroporous structure and increase the specific surface area, thereby further improving the activity of the catalyst.

6. The application of the cobalt-aluminum composite oxide catalyst provided by the present invention has good catalytic combustion performance for gaseous benzene, reduces the activation energy of benzene combustion, and makes the conversion rate of gaseous benzene at 337°C as high as 90%.

Description of drawings

In order to more clearly illustrate the specific implementation of the present invention or the technical solutions in the prior art, the following will briefly introduce the accompanying drawings that need to be used in the specific implementation or description of the prior art. Obviously, the accompanying drawings in the following description The drawings show some implementations of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative work.

Fig. 1 is the X-ray powder diffraction spectrogram of cobalt-aluminum composite oxide catalyst in the embodiment 1 of the present invention;

Fig. 2 is the nitrogen absorption and desorption curve and pore size distribution curve of the cobalt-aluminum composite oxide catalyst in Example 1 of the present invention;

Fig. 3 is the scanning electron micrograph of cobalt-aluminum composite oxide catalyst in the embodiment 1 of the present invention;

Fig. 4 is the transmission electron microscope figure of cobalt-aluminum composite oxide catalyst in the embodiment of the present invention 1;

Fig. 5 is the element distribution figure of cobalt-aluminum composite oxide catalyst in the embodiment of the present invention 1;

Fig. 6 is a graph showing the test results of the activity of the cobalt-aluminum composite oxide catalyst for the catalytic combustion of benzene in Example 1 of the present invention.

Detailed ways

The following examples are provided in order to further understand the present invention better, are not limited to the best implementation mode, and do not limit the content and protection scope of the present invention, anyone under the inspiration of the present invention or use the present invention Any product identical or similar to the present invention obtained by combining features of other prior art falls within the protection scope of the present invention.

If no specific experimental steps or conditions are indicated in the examples, it can be carried out according to the operation or conditions of the conventional experimental steps described in the literature in this field. The reagents or instruments used, whose manufacturers are not indicated, are all commercially available conventional reagent products.

In the following examples, the polymer microspheres have a particle size of 400-600 nm, are prepared by a soap-free emulsion polymerization method, and are self-assembled by a centrifugation method at a rotational speed of 1000 r/min. Such as polystyrene microspheres can be prepared by the following method:

Add 750mL of water and 46.7g of styrene monomer to a 1000mL three-necked flask (the styrene monomer is washed 3 times with 10% NaOH solution to remove the polymerization inhibitor), mechanically stir at room temperature, and pass nitrogen gas under the liquid surface for 30 Minutes later, 30 mL of an aqueous solution in which 0.467 g of potassium persulfate was dissolved was added dropwise, the temperature was raised to 75° C., and nitrogen gas was flowed over the liquid surface to initiate polymerization, and reflux was condensed for 10 hours. After the reaction is finished, the polystyrene nanometer mother liquor is obtained. The mother liquor was centrifuged for 24 hours (1000 r/min at a rotational speed), the supernatant was removed, and then dried in an oven at 60° C. for 4 hours to obtain neatly arranged polystyrene nanospheres.

Other polymer microspheres, such as polymethyl methacrylate nanospheres or styrene-methyl methacrylate-acrylic acid copolymer nanospheres, can also be prepared by similar methods or purchased commercially.

Example 1

A preparation method of cobalt-aluminum composite oxide catalyst, comprising the steps of:

(1) Preparation of metal ion precursor solution: Weigh 10.91g Co(NO ₃ ) ₂ ·6H ₂ O and 4.69g Al(NO ₃ ) ₃ ·9H ₂ O and dissolve in 50mL of water and ethanol mixed solution (volume ratio of 1 : 1), obtaining the mixed solution (Co/Al=3) that total metal ion concentration is 1mol/L;

(2) Catalyst preparation: Slowly add polystyrene nano-microspheres to the above mixed solution, let it stand for 6 hours, then filter the remaining solution with suction, dry the obtained solid in an oven at 80°C for 12 hours, and then place it Put it into a muffle furnace for calcination, the heating rate is 1°C/min, and keep at 500°C for 2 hours to obtain a cobalt-aluminum composite oxide catalyst.

X-ray powder diffractometer is used to carry out crystal phase test to above-mentioned catalyst, and the result is shown in Fig. 1, can know from Fig. 1, the main phase of described catalyst is spinel, and average grain size is 15nm.

The above catalyst was tested by BET method, and the results showed that as shown in Figure 2, the adsorption isotherm type was type II, the pores included mesopores and macropores, and the BET specific surface area was 94m ² /g.

The catalyst was tested with a scanning electron microscope, and the results are shown in Figure 3. From Figure 3, it can be seen that the catalyst has spherical holes with a diameter of 370nm and a window with a diameter of 100nm.

The above-mentioned catalyst is tested with a transmission electron microscope, and the results show as shown in Figure 4 and Figure 5, as can be seen from Figure 4, the catalyst has a three-dimensional network pore structure, as can be seen from Figure 5, cobalt, aluminum in the catalyst And oxygen elements are evenly distributed in the macropore wall skeleton.

Example 2

A preparation method of cobalt-aluminum composite oxide catalyst, comprising the steps of:

(1) Preparation of metal ion precursor solution: Weigh 7.28g Co(NO ₃ ) ₂ 6H ₂ O and 9.38g Al(NO ₃ ) ₃ 9H ₂ O in 50mL of water and ethanol mixed solution (volume ratio of 1 : 1), obtaining the mixed solution (Co/Al=1) that total metal ion concentration is 1mol/L;

(2) Catalyst preparation: Slowly add polystyrene nano-microspheres to the above mixed solution, let it stand for 6 hours, then filter the remaining solution with suction, dry the obtained solid in an oven at 80°C for 12 hours, and then place it Put it into a muffle furnace for calcination, the heating rate is 1°C/min, and keep at 500°C for 2 hours to obtain a cobalt-aluminum composite oxide catalyst.

The crystal phase of the catalyst was tested with an X-ray powder diffractometer, and the results showed that the main phase of the catalyst was spinel, and the average grain size was 12nm.

The above catalyst was tested by BET method, and the results showed that the adsorption isotherm type was type II, the pores included mesopores and macropores, and the BET specific surface area was 116m ² /g.

The above catalyst was tested with a scanning electron microscope, and the results showed that the catalyst had spherical holes with a pore diameter of 350 nm and pore windows with a pore diameter of 125 nm.

The above-mentioned catalyst was tested with a transmission electron microscope, and the results showed that the catalyst had a three-dimensional network pore structure, and cobalt, aluminum and oxygen elements were evenly distributed in the macropore wall skeleton.

Example 3

A preparation method of cobalt-aluminum composite oxide catalyst, comprising the steps of:

(1) Preparation of metal ion precursor solution: Weigh 4.85g Co(NO ₃ ) ₂ 6H ₂ O and 12.50g Al(NO ₃ ) ₃ 9H ₂ O and dissolve in 50mL water and ethanol mixed solution (volume ratio of 1 : 1), obtaining the mixed solution (Co/Al=0.5) that total metal ion concentration is 1mol/L;

(2) Catalyst preparation: Slowly add polystyrene nano-microspheres to the above mixed solution, let it stand for 6 hours, then filter the remaining solution with suction, dry the obtained solid in an oven at 80°C for 12 hours, and then place it Put it into a muffle furnace for calcination, the heating rate is 1°C/min, and keep at 500°C for 2 hours to obtain a cobalt-aluminum composite oxide catalyst.

The crystal phase of the catalyst was tested with an X-ray powder diffractometer, and the results showed that the main phase of the catalyst was spinel, and the average grain size was 9 nm.

The above catalyst was tested by BET method, and the results showed that the adsorption isotherm type was type II, the pores included mesopores and macropores, and the BET specific surface area was 140m ² /g.

The above catalyst was tested with a scanning electron microscope, and the results showed that the catalyst had spherical holes with a pore diameter of 375nm and pore windows with a pore diameter of 115nm.

The above-mentioned catalyst was tested with a transmission electron microscope, and the results showed that the catalyst had a three-dimensional network pore structure, and cobalt, aluminum and oxygen elements were evenly distributed in the macropore wall skeleton.

Example 4

A preparation method of cobalt-aluminum composite oxide catalyst, comprising the steps of:

(1) Preparation of metal ion precursor solution: Weigh 8.92g CoCl ₂ 6H ₂ O and 1.67g AlCl ₃ and dissolve in 50mL water and ethanol mixed solution (volume ratio is 1:1) to obtain a total metal ion concentration of 1mol /L mixed solution (Co/Al=3);

(2) Catalyst preparation: Slowly add polymethyl methacrylate nano-microspheres to the above mixed solution, let stand for 6 hours, then suction filter the remaining solution, place the obtained solid in an oven at 80°C for 12 hours, and then Put it into a muffle furnace for calcination, the heating rate is 1°C/min, and keep at 500°C for 2 hours to obtain a cobalt-aluminum composite oxide catalyst.

The crystal phase of the above catalyst was tested with an X-ray powder diffractometer, and the results showed that the main phase of the catalyst was spinel, and the average grain size was 15nm.

The above catalyst was tested by BET method, and the results showed that the adsorption isotherm type was type II, the pores included mesopores and macropores, and the BET specific surface area was 96m ² /g.

The above catalyst was tested with a scanning electron microscope, and the results showed that the catalyst had spherical holes with a pore diameter of 373nm and pore windows with a pore diameter of 105nm.

The above-mentioned catalyst was tested with a transmission electron microscope, and the results showed that the catalyst had a three-dimensional network pore structure, and cobalt, aluminum and oxygen elements were evenly distributed in the macropore wall skeleton.

Example 5

A preparation method of cobalt-aluminum composite oxide catalyst, comprising the steps of:

(1) Preparation of metal ion precursor solution: Weigh 8.92g CoCl ₂ 6H ₂ O and 1.67g AlCl ₃ and dissolve in 50mL water and ethanol mixed solution (volume ratio is 1:1) to obtain a total metal ion concentration of 1mol /L mixed solution (Co/Al=3);

(2) Catalyst preparation: Slowly add styrene-methyl methacrylate-acrylic acid copolymer nanospheres to the above mixed solution, let it stand for 6 hours, then suction filter the remaining solution, and place the obtained solid in an oven at 80°C Dry it for 12 hours, put it into a muffle furnace and bake it at a heating rate of 1°C/min, and keep it at 500°C for 2 hours to obtain a cobalt-aluminum composite oxide catalyst.

The crystal phase of the above catalyst was tested with an X-ray powder diffractometer, and the results showed that the main phase of the catalyst was spinel, and the average grain size was 15nm.

The above catalyst was tested by BET method, and the results showed that the adsorption isotherm type was type II, the pores included mesopores and macropores, and the BET specific surface area was 101m ² /g.

The above catalyst was tested with a scanning electron microscope, and the results showed that the catalyst had spherical holes with a pore diameter of 342nm and pore windows with a pore diameter of 95nm.

The above-mentioned catalyst was tested with a transmission electron microscope, and the results showed that the catalyst had a three-dimensional network pore structure, and cobalt, aluminum and oxygen elements were evenly distributed in the macropore wall skeleton.

Comparative example 1

A preparation method of cobalt oxide catalyst, comprising the steps of:

(1) Preparation of metal ion precursor solution: Weigh 14.55g Co(NO ₃ ) ₂ ·6H ₂ O and dissolve in 50mL water and ethanol mixed solution (1:1 volume ratio) to obtain a metal ion concentration of 1mol/L The solution;

(2) Catalyst preparation: Slowly add polystyrene microspheres to the above metal ion precursor solution, let it stand for 6 hours, then filter the remaining solution with suction, dry the obtained solid in an oven at 80°C for 12 hours, and then place the It was put into a muffle furnace for calcination, the heating rate was 1° C./min, and it was kept at 500° C. for 2 hours to obtain a cobalt oxide catalyst.

The crystal phase of the catalyst was tested with an X-ray powder diffractometer, and the results showed that the main phase of the catalyst was spinel, and the average grain size was 24nm.

The above catalyst was tested by BET method, and the results showed that the adsorption isotherm type was type II, the catalyst only had a mesoporous structure, and the BET specific surface area was 28 m ² /g.

Experimental example Catalyst activity test

The test reaction was carried out on a normal pressure fixed bed reaction device, the amount of catalyst used was 100mg, the space velocity was 36000mL/h·g, the flow rate was 60mL/min, the volume fraction of benzene in the raw gas was 0.516‰, and the volume fraction of oxygen was 21%. , Nitrogen is used as the balance gas, and the activity of the catalyst is tested at a reaction temperature of 100-450°C. Among them, the benzene content of the reactor outlet gas was detected by a GC9790 II gas chromatograph (Zhejiang Fuli Analytical Instrument Co., Ltd.).

The activity of the catalyst is expressed by the conversion rate of benzene, and the calculation formula is: C ₆ H ₆ conversion rate (%)=([C ₆ H ₆ ] raw material gas-[C ₆ H ₆ ] after reaction)/[C ₆ H ₆ ] Feed gas * 100%, according to the conversion rate situation of catalytic reaction temperature and benzene, make corresponding graph as this catalyst to the active test result figure of benzene catalytic combustion, as Fig. 6 is the catalyst catalytic benzene combustion of the embodiment of the present invention 1 Graph of test results. Then, according to the graphs of different catalysts, find out the corresponding temperatures when the benzene conversion rate is 50% and 90%, and the results are shown in Table 1 below.

Table 1 Catalytic activity of different catalysts

catalyst Example 1 Example 2 Example 3 Example 4 Example 5 Comparative example 1 T₅₀(℃) 307 352 332 313 310 323 T₉₀(℃) 337 391 364 342 341 368

As can be seen from the data in the above table, the cobalt-aluminum composite oxide catalyst of the present invention can effectively reduce the activation energy of the benzene combustion reaction and has good catalytic activity. It can also be seen that the addition of alumina structural aids can effectively improve catalytic activity of the catalyst.

Apparently, the above-mentioned embodiments are only examples for clear description, rather than limiting the implementation. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. And the obvious changes or changes derived therefrom are still within the scope of protection of the present invention.

Claims (10)

1. A preparation method for a cobalt-aluminum composite oxide catalyst, characterized in that, the metal salt solution of cobalt and aluminum is used as a precursor, and the template is soaked in the precursor solution, which is obtained by impregnating and roasting The cobalt-aluminum composite oxide catalyst. 2. preparation method according to claim 1, is characterized in that, comprises the steps: Disperse metal salts of cobalt and aluminum in a mixed solution of water and ethanol to form a metal ion precursor solution; The polymer microspheres are added to the metal ion precursor solution, left to stand, and suction filtered, and the obtained solid is dried and calcined to obtain the cobalt-aluminum composite oxide catalyst. 3. the preparation method according to claim 1 or 2, is characterized in that, the metal salt of described cobalt is at least one in cobalt nitrate or cobalt chloride; The metal salt of described aluminum is aluminum nitrate or aluminum chloride at least one of the 4. according to the arbitrary described preparation method of claim 1-3, it is characterized in that, the mol ratio of the metal salt of described cobalt and the metal salt of described aluminum is (0.5～3):1; In the solution, the total concentration of cobalt ions and aluminum ions is 1.0 mol/L, and the volume ratio of water and ethanol is 1:1. 5. according to the arbitrary described preparation method of claim 1-4, it is characterized in that, described polymer microsphere is polystyrene nanosphere, polymethyl methacrylate nanosphere or styrene-methacrylic acid At least one of the methyl ester-acrylic acid copolymer nanospheres. 6. The preparation method according to any one of claims 1-5, characterized in that the calcination is calcination of the dried catalyst precursor in an air atmosphere at 500° C. for 2 hours. 7. A cobalt-aluminum composite oxide catalyst prepared according to any one of claims 1-6. 8 . The cobalt-aluminum composite oxide catalyst according to claim 7 , characterized in that the catalyst has a pore structure of mesopores and macropores, and a specific surface area of 94-140 m ² /g. 9. according to the described cobalt-aluminum composite oxide catalyst of claim 7 or 8, it is characterized in that, described cobalt-aluminum composite oxide is evenly dispersed in the pore wall framework, and the grain size of cobalt-aluminum spinel is 9 ~ 15nm. 10. A cobalt-aluminum composite oxide catalyst prepared according to any one of claims 1-6 or a cobalt-aluminum composite oxide catalyst according to any one of claims 7-9 in catalytic VOCs combustion in the application.