CN109513446A - A kind of preparation method of isobutene or Oxidation of t-Butanol synthesizing methyl methacrylaldehyde catalyst - Google Patents

Abstract

The invention relates to a preparation method and application of a composite metal oxide catalyst that uses a surfactant as a template to regulate and obtain a nanoscale cluster structure. In the preparation process of the catalyst, one or more surfactants are added as templates to react with other components. After drying and calcining, the pore diameter is 2-7 nanometers, the diameter is about 0.3-8 microns, and the specific surface area is 30-8 microns. 300m ² /g composite metal oxide catalyst with nanoscale cluster structure. The catalyst is used in the reaction of synthesizing methacrolein by oxidation of isobutene or tert-butanol, and has high product yield and long service life.

Description

A kind of preparation method of catalyst for synthesizing methacrolein by oxidation of isobutene or tert-butanol

technical field

The invention relates to a preparation method for obtaining a composite metal oxide catalyst with a nanoscale spherical cluster structure through regulation and control using a surfactant as a template, and belongs to the field of catalyst preparation and application.

Background technique

Methyl methacrylate (MMA) is mainly used in the production of plexiglass, PVC additives and the second monomer for the production of acrylic fibers, etc. It can also be used in the production of coatings, adhesives, lubricants and textile dyes. It is a Important organic chemical raw materials and chemical products.

Due to the use of highly toxic and highly corrosive hydrocyanic acid and sulfuric acid, the environmental pollution is great, making the traditional production process of MMA (acetone cyanohydrin method) gradually replaced by the C4 clean process with less environmental pollution, high atomic utilization efficiency, and meeting the requirements of green chemistry. replace.

As a key reaction of the C4 clean production process, the catalyst for synthesizing methacrolein (MAL) from isobutene or tert-butanol has been developed by foreign companies such as Japan and Germany since the 1980s. After decades of hard work, the catalysts used in this type of reaction are mainly positioned as Mo-Bi-Fe-Co-O multi-component composite metal oxide catalysts, and some catalysts have been industrialized, but they are different from mature industrial catalysts in other industries. In comparison, this type of catalyst still has problems such as low selectivity and short life, resulting in low atomic utilization, more three wastes, and high production costs.

Because the reaction of isobutene or tert-butanol oxidation to methacrolein is a strong exothermic reaction, it is easy to generate local heat accumulation in the catalyst bed, resulting in the loss of the main active component Mo of the catalyst, thereby shortening the service life of the catalyst. Patents CN1210511A, CN145946A, and US Pat4250339 suppress the loss of Mo components during the reaction process by loading, diluting the catalyst, and adding specific components, respectively, but these methods have more or less reduced the activity of the catalyst and the product yield; CN103769159A , CN1647853A improve the distribution of catalyst active components by preparing a supported catalyst for the reaction of synthesizing methacrolein by oxidation of isobutene or tert-butanol, but the activity of the catalyst is still low; Adding polymer compounds to improve the pore structure and specific surface area of the catalyst, but the obtained catalyst pore structure is irregular and uncontrollable.

Therefore, it is necessary to develop an efficient composite metal oxide catalyst with high specific surface area and controllable pore structure. By introducing surfactants in the preparation process, using their effects of emulsification, suspension, micelles and solubilization, the regularization and clustering of molecular structures are induced, and the formation of spherical packing structures is promoted to achieve the purpose of increasing the specific surface area. , so as to improve the activity of the catalyst, and at the same time achieve rapid heat removal, reduce the loss rate of active components and prolong the service life.

SUMMARY OF THE INVENTION

The main purpose of the present invention is to obtain highly selective and long-lived efficient composite metal oxide catalysts, and propose a method for regulating and controlling the composite metal oxide catalysts that obtain nanoscale cluster structures with surfactants as templates, the method The prepared catalyst has a large specific surface area and an ordered mesoporous structure. Compared with the traditional catalyst, the catalyst has more active centers that can participate in the reaction, and has good mass transfer effect and high catalytic efficiency. The carbon hydroxyl groups and cations contained in the surfactant can adjust the acidity and alkalinity of the catalyst, so as to adjust the oxidation-reduction property of the catalyst and achieve the purpose of improving the performance of the catalyst. The pore structure formed by the surfactant during the roasting process can effectively increase the heat transfer rate and achieve the effect of alleviating heat collection, thereby improving the life of the catalyst (stable and continuous operation for more than 1000 hours).

One of the purposes of the present invention is to solve the problem of low catalyst activity in the prior art for isobutylene or tert-butanol oxidation to synthesize methacrolein, and to provide a composite metal oxide catalyst for synthesizing methacrolein , the catalyst has high activity.

The second object of the present invention is to solve the problem of short catalyst life in the prior art for isobutene or tert-butanol oxidation to synthesize methacrolein, and to provide a composite metal oxide catalyst for synthesizing methacrolein , the catalyst has a long lifetime.

The third object of the present invention is to provide a method for preparing a composite metal oxide catalyst for solving the above problems. The method adds a surfactant to make the composite metal oxide into a pore size of 2 to 7 nanometers and a diameter of about 0.3 nanometers. Nano-scale particles with a cluster structure of ~8 microns and a specific surface area of 30-300 m ² /g.

One aspect of the present invention relates to a kind of above-mentioned composite metal oxidation catalyst prepared by the inventive method, its general formula is:

MO ₁₂ BI _A Fe _B Cu _C X _d y _e z _f o _m -n _n

in,

X is at least one selected from Co, Mg, Ni, V, Ti, Cr, W, Zn;

Y is at least one selected from alkaline earth metals or alkali metals;

Z is at least one selected from La, Ce, Nd, Zr, Nb, Yb, Er, Sb, Sr, Ag;

N is at least one selected from surfactants with 5 to 25 carbon atoms;

a, b, c, d, e, f, g, m, n represent the atomic ratio of each element in a catalyst cluster, wherein,

The range of a is selected from 0.5 to 5;

The range of b is selected from 0.4～4;

The range of c is selected from 0.05～2;

The range of d is selected from 0.1 to 8;

The range of e is selected from 0.1～6;

The range of f is selected from 0.1～4;

The range of n is selected from 0.02～5;

m is the number of oxygen atoms satisfying the oxidation states of the above elements.

Another aspect of the present invention relates to a kind of preparation method of above-mentioned composite metal oxide, and its preparation procedure is as follows:

a) Under certain conditions, take a certain amount of surfactant and dissolve it in water, mix it with a certain proportion of mixed metal salt solution, stir and age and reflow at a certain temperature to form the required suspension slurry.

b) drying the suspension slurry formed after the aging reflux under certain conditions to obtain a catalyst precursor.

c) Calcining the precursor prepared in the above steps under certain conditions to obtain a composite metal oxide catalyst.

Wherein, the surfactant used in the step (a) is selected from at least one of ionic liquid surfactant and nonionic liquid surfactant, wherein the preferred imidazole ionic liquid surfactant of ionic liquid surfactant, Quaternary ammonium salt ionic liquid surfactants, pyridine ionic liquid surfactants, tetrafluoroboric acid ionic liquid surfactants, hexafluorophosphate ionic liquid surfactants and dication ionic liquid surfactants. Among them, the ionic liquid surfactants contain 5 to 25 carbon atoms, such as 1-hexyl-3-methylimidazolium ion, 1-hexanoic acid-3-methylimidazolium ion, octylpyridinium ion, undecyltrimethyl Acetate, chloride, nitrate, carbonate of ammonium ion, 1-octyl-3-methylimidazolium pyridinium ion; non-ionic liquid surfactant is preferably, but not limited to, containing 8 to 35 carbon atoms Compounds such as sodium stearate, sodium stearyl sulfate, polyethylene glycol, sodium dodecylbenzenesulfonate, polysorbate-80, sodium laurate, sodium lauroyl glutamate.

During the dissolving process of the surfactant in step (a), the ratio of surfactant to water is 1:1 to 100, and the dissolution temperature is not particularly limited; the mass ratio of surfactant to mixed metal salt is 1:2 to 200 , the mixing temperature is 30-90°C, the aging temperature is 30-100°C, and the aging time is 0.5-24h.

The compounds of metal elements used in step (a) need to be soluble in water, and the others are not particularly limited, and their nitrates, chlorides, acetates, etc. can be used.

The mixing mode of the surfactant and the mixed metal salt solution in the process (a) can be selected to be added dropwise, the surfactant solution is added dropwise to the mixed metal salt solution, the mixed metal salt solution is added dropwise to the surfactant solution or directly mixed at least one.

The drying method in step (b) can be at least one of atmospheric pressure stirring evaporation drying, centrifugal spray drying, rotary evaporation drying, vacuum drying, suction filtration drying and microwave drying, and the drying temperature is 50-200°C.

The roasting device in the process (c) can be a tube furnace, a box furnace, a mesh belt kiln, a roller kiln, etc., the roasting temperature is 280-550 ° C, the roasting time is 2-16 hours, and the roasting atmosphere is oxygen-containing An oxidizing atmosphere with a volume ratio of 20-50%, such as air, pure oxygen, a mixture of oxygen and inert gases, etc.

The third aspect of the present invention relates to the application of the above-mentioned composite metal oxide catalyst in the reaction of synthesizing methacrolein by oxidation of isobutene or tert-butanol. The raw material isobutene, water and air or a gas mixture containing a certain amount of oxygen are preheated and passed into a fixed-bed reactor equipped with a catalyst for reaction to synthesize methacrolein. The used gas mixture containing a certain amount of oxygen has an oxygen content of 10% to 50%, and the remaining components can be a mixture of one or more inert gases such as nitrogen, helium, and argon.

The reaction products were analyzed online by gas chromatography.

The conversion rate calculation method of isobutene is as follows:

X (isobutene)%=[1-(amount of unreacted isobutene/amount of supplied isobutene)]×100%

The selectivity calculation method for methacrolein is as follows:

S (methacrolein) % = [amount of produced methacrolein / (amount of isobutylene supplied - amount of unreacted isobutylene)] x 100%

The reaction conditions for the composite metal oxide catalyst of the present invention to be used in the oxidation of isobutylene to synthesize methacrolein are shown in the examples.

Detailed ways

The present invention is illustrated below with examples, but the scope of the present invention is not limited by the examples.

Example 1

Weigh 5g of undecyltrimethylammonium acetate, stir and dissolve it in 200ml of deionized water at 30°C to obtain material A. Measure 50ml of deionized water, add 45g of ammonium molybdate, and dissolve to obtain material B; measure 30ml of deionized water, add 8g of bismuth nitrate, 3g of copper nitrate, 12g of iron nitrate, 27g of cobalt nitrate, 5g of cesium nitrate, and 1g of nitric acid Lanthanum was stirred and dissolved to obtain material C; materials A and C were jointly added to material B placed in a 40°C water bath under rapid stirring to form a slurry, and aged and refluxed at 50°C for 8 hours to obtain the required catalyst slurry.

The obtained catalyst slurry was stirred and evaporated to dryness at 85° C., and the obtained solid was dried in a blast drying oven at 120° C. for 12 hours to obtain a catalyst precursor.

Then the dried catalyst was pulverized, and then roasted at 450°C for 4 hours in an air atmosphere to remove the surfactant, and then formed, pulverized and sieved to obtain the composite metal oxide catalyst to be evaluated with catalytic activity.

2.0 milliliters of the resulting composite metal oxide catalyst is mixed with quartz sand of equal particle size according to a volume ratio of 1:1 and packed in a fixed-bed reactor with an internal diameter of 10 mm, and the catalyst is filled with quartz sand of equal particle size up and down. Isobutene: Oxygen: Nitrogen: Water = 1:2.1:11:0.7 (molar ratio) mixed gas is used as the raw material, the space velocity is 2000h ^-1 , the reaction is carried out at 370°C under normal pressure, and the reaction is carried out continuously for 20 hours.

The conversion of isobutene was determined to be 99.4%, and the selectivity to methacrolein was 85.1%.

After continuous operation for 1000 hours, the conversion rate of isobutene was 99.1%, and the selectivity of methacrolein was 84.2%.

Example 2

10 g of hexadecyl-3-methylimidazolium tetrafluoroborate was weighed, stirred and dissolved in 300 ml of deionized water at 45° C. to obtain material A. Measure 100ml of deionized water, add 85g of ammonium molybdate, and dissolve to obtain material B; measure 50ml of deionized water, add 30g of bismuth nitrate, 15g of iron nitrate, 36g of cobalt nitrate, 4g of copper nitrate, 4g of cesium nitrate, and 4g of nitrate Cerium was stirred and dissolved to obtain material C; first, material B was added to material A placed in a 50°C water bath under rapid stirring, and then material C was added to the mixture of materials A and B placed in a 50°C water bath under rapid stirring In the mixed material, a slurry was formed, and aged and refluxed at 70° C. for 6 hours to obtain the desired catalyst slurry.

The obtained catalyst slurry was stirred and evaporated to dryness at 90° C., and the obtained solid was dried in a blast drying oven at 110° C. for 10 h to obtain a catalyst precursor.

Then the dried catalyst was pulverized, and then roasted at 400°C for 6 hours in an air atmosphere to remove the surfactant, and then formed, pulverized and sieved to obtain the composite metal oxide catalyst to be evaluated with catalytic activity.

The catalyst evaluation method is as in Example 1.

The conversion of isobutene was determined to be 95.8%, and the selectivity to methacrolein was 82.7%.

After continuous operation for 1000 hours, the conversion rate of isobutene was 95.4%, and the selectivity of methacrolein was 82.2%.

Example 3

Weigh 10 g of sodium dodecylbenzenesulfonate, stir and dissolve it in 200 ml of deionized water at 70° C. to obtain material A. Measure 90ml of deionized water, add 85g of ammonium molybdate, and dissolve to obtain material B; measure 50ml of deionized water, add 17g of bismuth nitrate, 10g of iron nitrate, 30g of cobalt nitrate, 4g of copper nitrate, 4g of cesium nitrate, and 2g of magnesium acetate , 2g of nickel nitrate and 4g of zirconium nitrate were stirred and dissolved to obtain material C; materials B and C were jointly added to material A placed in a 55°C water bath under rapid stirring to form a slurry, and aged and refluxed at 80°C for 16 hours, the desired catalyst slurry was obtained.

The obtained catalyst slurry was stirred and evaporated to dryness at 80° C., and the obtained solid was dried in a blast drying oven at 120° C. for 12 hours to obtain a catalyst precursor.

Then the dried catalyst was pulverized, and then roasted at 400°C for 6 hours in an air atmosphere to remove the surfactant, and then formed, pulverized and sieved to obtain the composite metal oxide catalyst to be evaluated with catalytic activity.

The catalyst evaluation method is as in Example 1.

The conversion of isobutene was determined to be 98.2%, and the selectivity to methacrolein was 86.7%.

Example 4

Weigh 20 g of sodium octadecyl sulfate, stir and dissolve in 100 ml of deionized water at room temperature to obtain material A. Measure 100ml of deionized water, add 90g of ammonium molybdate, and dissolve to obtain material B; measure 50ml of deionized water, add 20g of bismuth nitrate, 13g of iron nitrate, 65g of cobalt nitrate, 6g of copper nitrate, 4g of cesium nitrate, and 5g of manganese acetate , 1g of strontium nitrate and 3g of lanthanum nitrate were stirred and dissolved to obtain material C; materials A and B were jointly added to material C placed in a water bath at 60°C under rapid stirring to form a slurry, and aged and refluxed at 80°C for 6 hours, the desired catalyst slurry was obtained.

The obtained catalyst slurry was stirred and evaporated to dryness at 90° C., and the obtained solid was dried in a blast drying oven at 120° C. for 12 hours to obtain a catalyst precursor.

Then the dried catalyst was pulverized, and then roasted at 450°C for 8 hours in an air atmosphere to remove the surfactant, and the composite metal oxide catalyst to be evaluated with catalytic activity was obtained through molding, pulverization and sieving.

The catalyst evaluation method is as in Example 1.

The conversion of isobutene was determined to be 99.3%, and the selectivity to methacrolein was 85.2%.

Example 5

50 g of polyethylene glycol was weighed, stirred and dissolved in 100 ml of deionized water at 50° C. to obtain material A. Measure 120ml of deionized water, add 95g of ammonium molybdate, and dissolve to obtain material B; measure 50ml of deionized water, add 41g of bismuth nitrate, 13g of iron nitrate, 65g of cobalt nitrate, 6g of copper nitrate, 6g of potassium nitrate, and 7g of zinc nitrate , 1g of chromium nitrate and 5g of cerium nitrate were stirred and dissolved to obtain material C; materials A and B were jointly added to material C placed in a water bath at 35°C under rapid stirring to form a slurry, and stirred and aged at 80°C for 3 hours , to obtain the desired catalyst slurry.

The obtained catalyst slurry was stirred and evaporated to dryness at 100° C., and the obtained solid was dried in a blast drying oven at 140° C. for 6 hours to obtain a catalyst precursor.

Then the dried catalyst was pulverized, and then roasted at 400°C for 10 hours in an air atmosphere to remove the surfactant, and then formed, pulverized and sieved to obtain the composite metal oxide catalyst to be evaluated with catalytic activity.

The catalyst evaluation method is as in Example 1.

The conversion of isobutene was measured to be 98.0%, and the selectivity to methacrolein was 88.9%.

Example 6

5g of tetraethylammonium acetate was weighed, stirred and dissolved in 100ml of deionized water at 85°C to obtain material A. Measure 100ml of deionized water, add 80g of ammonium molybdate, and dissolve to obtain material B; measure 50ml of deionized water, add 16g of bismuth nitrate, 13g of iron nitrate, 39g of cobalt nitrate, 6g of copper nitrate, 4g of cesium nitrate, and 1g of zirconium nitrate and 6g of cerium nitrate, stirred and dissolved to obtain material C; materials A and B were jointly added to material C placed in a 60°C water bath under rapid stirring to form a slurry, and stirred and aged at 60°C for reflux for 4 hours to obtain the obtained Catalyst slurry is required.

The obtained catalyst slurry was stirred and evaporated to dryness at 100° C., and the obtained solid was dried in a blast drying oven at 100° C. for 20 h to obtain a catalyst precursor.

Then the dried catalyst was pulverized, and then roasted at 450°C for 6 hours in an air atmosphere to remove the surfactant, and then formed, pulverized and sieved to obtain the composite metal oxide catalyst to be evaluated with catalytic activity.

The catalyst evaluation method is as in Example 1.

The conversion of isobutene was measured to be 97.0%, and the selectivity to methacrolein was 86.6%.

Comparative Example 1

Except changing 5g of undecyltrimethylammonium acetate into 15g of undecyltrimethylammonium acetate in Example 1, others were all prepared according to the method of Example 1 to obtain a composite metal oxide catalyst.

The catalyst evaluation method is as in Example 1.

The conversion of isobutene was determined to be 99.5%, and the selectivity to methacrolein was 89.1%.

After continuous operation for 1000 hours, the conversion rate of isobutene was 99.3%, and the selectivity of methacrolein was 88.7%.

Comparative Example 2

Measure 100ml of deionized water, add 85g of ammonium molybdate, and dissolve to obtain material A; measure 50ml of deionized water, add 30g of bismuth nitrate, 15g of iron nitrate, 36g of cobalt nitrate, 4g of copper nitrate, 4g of cesium nitrate, and 4g of nitrate Cerium, stirred and dissolved to obtain material B; first, material B was added to material A placed in a water bath at 50°C under rapid stirring to form a slurry, and aged and refluxed at 70°C for 6 hours to obtain the required catalyst slurry .

The drying and roasting method of catalyst are as embodiment 2.

Example 1 is implemented as the catalyst evaluation method.

The conversion of isobutene was determined to be 93.6%, and the selectivity to methacrolein was 79.5%.

After continuous operation for 1000 hours, the conversion rate of isobutene was 84.0%, and the selectivity of methacrolein was 73.9%.

Comparative Example 3

Except that 10 g of sodium dodecylbenzenesulfonate in Example 3 was changed to 4 g of tetradecyltrimethylammonium bromide, the others were prepared according to the method of Example 3 to obtain a composite metal oxide catalyst.

The catalyst evaluation method is as in Example 1.

The conversion of isobutene was determined to be 99.7%, and the selectivity to methacrolein was 90.3%.

Comparative Example 4

Materials A and B were jointly added to material C under rapid stirring to form a slurry, and stirred and aged at 80° C. for an hour to obtain the desired catalyst slurry.

Measure 100ml of deionized water, add 90g of ammonium molybdate, and dissolve to obtain material A; measure 50ml of deionized water, add 20g of bismuth nitrate, 13g of iron nitrate, 65g of cobalt nitrate, 6g of copper nitrate, 4g of cesium nitrate, and 5g of manganese acetate , 1g of strontium nitrate and 3g of lanthanum nitrate were stirred and dissolved to obtain material B; material B was added to material A placed in a 60°C water bath under rapid stirring to form a slurry, and aged and refluxed at 80°C for 6 hours to obtain required catalyst slurry.

Example 4 of the drying and roasting method of catalysts.

The catalyst evaluation method is as in Example 1.

The conversion of isobutene was measured to be 93.0%, and the selectivity to methacrolein was 81.1%.

Comparative Example 5

Except for changing 50g of polyethylene glycol in Example 3 to 10g of Polyethylene Glycol, the others were prepared according to the method of Example 5 to obtain a composite metal oxide catalyst.

The catalyst evaluation method is as in Example 1.

The conversion of isobutene was determined to be 94.3%, and the selectivity to methacrolein was 82.1%.

Comparative Example 6

Except changing 5g of tetraethylammonium acetate into 5g of tetra-n-butylammonium acetate in embodiment 6, others were all prepared according to the method of embodiment 6 to obtain composite metal oxide catalyst.

The catalyst evaluation method is as in Example 1.

The conversion of isobutene was determined to be 99.1%, and the selectivity to methacrolein was 89.8%.

Claims (12)

1. The catalyst is characterized in that a surfactant is used as a template agent, the catalyst reacts with metal salt, and the catalyst is dried and roasted to prepare the composite metal oxide catalyst with the pore diameter of 2-7 nanometers, the diameter of about 0.3-8 micrometers, and the specific surface area of 30-300 m²A composite metal oxide catalyst of the formula:

Mo₁₂Bi_aFe_bCu_cX_dY_eZ_fO_m-N_n

wherein,

x is at least one selected from Co, Mg, Ni, V, Ti, Cr, W and Zn;

y is at least one selected from alkaline earth metals or alkali metals;

z is at least one selected from La, Ce, Nd, Zr, Nb, Yb, Er, Sb, Sr and Ag;

n is at least one selected from surfactants with 5-25 carbon atoms;

a. b, c, d, e, f, g, m, n represent the atomic ratio of each element in one catalyst cluster, respectively, wherein,

the range of a is selected from 0.5-5;

b is selected from 0.4-4;

c is selected from 0.05-2;

d is selected from 0.1-8;

e is selected from 0.1-6;

f is selected from 0.1-4;

n is selected from 0.02-5;

m is the number of oxygen atoms satisfying the oxidation state of the above elements.

2. The composite metal oxide catalyst according to claim 1, wherein the catalyst uses a surfactant as a template to perform structural regulation, and finally forms a nanoscale spherical cluster structure, thereby obtaining a composite metal oxide having a high specific surface area and a mesoporous structure, and having a higher product yield and a longer life than other catalysts.

3. The method for producing a composite metal oxide catalyst according to claim 1, comprising the steps of:

a) under certain conditions, dissolving a certain amount of surfactant in water, mixing with a mixed metal salt aqueous solution in a certain proportion, stirring at a certain temperature, aging and refluxing to form required suspension slurry;

b) drying the suspension slurry formed after the aging reflux under a certain condition to obtain a catalyst precursor;

c) and (3) roasting the precursor prepared in the step under a certain condition to obtain the composite metal oxide catalyst.

4. The method for preparing a composite metal oxide catalyst according to claim, wherein the surfactant is at least one selected from the group consisting of ionic liquid surfactants and nonionic liquid surfactants, and the ionic liquid surfactants are preferably, but not limited to, imidazole ionic liquid surfactants, quaternary ammonium salt ionic liquid surfactants, pyridine ionic liquid surfactants, tetrafluoroborate ionic liquid surfactants, hexafluorophosphate ionic liquid surfactants, and dication ionic liquid surfactants.

5. The method for preparing a composite metal oxide catalyst according to claim 4, wherein the ionic liquid surfactant contains 5 to 25 carbon atoms, and the nonionic liquid surfactant is preferably, but not limited to, a compound containing 8 to 35 carbon atoms.

6. The method for preparing a composite metal oxide catalyst according to claim 5, wherein the ionic liquid type surfactant is preferably, but not limited to, 1-hexyl-3-methylimidazolium ion, 1-hexanoic acid-3-methylimidazolium ion, octylpyridinium ion, undecyltrimethylammonium ion, acetate, chloride, nitrate, carbonate of 1-octyl-3-methylimidazolium pyridinium ion, and the non-ionic liquid type surfactant is preferably, but not limited to, sodium stearate, sodium stearyl sulfate, polyethylene glycol, sodium dodecylbenzenesulfonate, polysorbate-80, sodium laurate, sodium lauroyl glutamate.

7. The method for preparing a composite metal oxide catalyst according to claim 3, wherein the part ratio of the surfactant to water in the surfactant dissolution process is 1:1 to 100, and the dissolution temperature is not particularly limited.

8. The method for preparing a composite metal oxide catalyst according to claim 3, wherein the mass ratio of the surfactant to the mixed metal salt is 1:2 to 200.

9. The method for preparing a composite metal oxide catalyst according to claim 3, wherein the surfactant solution is mixed with the mixed metal salt aqueous solution in a manner selected from at least one of: dropping the surfactant, dropping the surfactant into the mixed metal salt solution, dropping the mixed metal salt solution into the surfactant solution, and directly mixing.

10. The method for preparing a composite metal oxide catalyst according to claim 3, wherein the mixing temperature of the surfactant and the mixed metal salt aqueous solution in the step (a) is 30 to 90 ℃, the aging reflux temperature is 30 to 100 ℃, and the aging reflux time is 0.5 to 24 hours.

11. The method for preparing a composite metal oxide catalyst according to claim 3, wherein the drying method in the step (b) is at least one of stirring evaporation drying under normal pressure, centrifugal spray drying, rotary evaporation drying, vacuum drying, suction filtration drying and microwave drying.

12. A process for synthesizing methacrolein by oxidizing isobutylene or tert-butanol, characterized by using the composite metal oxide as recited in claims 1 to 10 as a catalyst.