Methods for the synthesis of methyl methacrylate, bifunctional catalysts for oxidative esterification, their preparation methods and applications

Abstract

This invention provides a method for synthesizing methyl methacrylate, a bifunctional catalyst for oxidative esterification, its preparation method, and its application. The catalyst comprises catalysts having the general formula AuRh. a O n / MN b O x The active component, wherein N is selected from Group IIA elements, M is a carrier element; a = 0 to 1 and not 0; b = 0 to 1 and not 0; x and n are values ​​determined by the total valence of the elements other than oxygen in the general formula; the catalyst of the present invention has the advantages of high conversion rate and high yield, and its use in the synthesis of methyl methacrylate results in high yield and high raw material conversion rate.

Description

Technical Field

[0001] This invention belongs to the technical field of methyl methacrylate synthesis methods, specifically relating to a catalyst for methyl methacrylate synthesis, its preparation method, and its application. Background Technology

[0002] Methyl methacrylate (MMA) is an important organic chemical raw material, mainly used in the production of polymethyl methacrylate (PMMA), also known as acrylic glass. Acrylic glass is widely used in industries such as automobiles, construction, sanitary ware, and public works. As of 2020, China's MMA production capacity had reached 1.455 million tons per year.

[0003] Currently, the ACH process is the most prevalent in MMA production. It requires the use of acrylonitrile units to produce HCN as a byproduct, and is therefore greatly affected by their operating status. In addition, it produces a large amount of ammonium sulfate as a byproduct, resulting in high production costs. The government has already restricted this process route.

[0004] Compared with other processes, the direct oxidation method using C4 as a raw material has significant advantages in terms of abundant raw material sources and environmental friendliness. MMA production using C4 as a raw material is gradually being promoted in China. This process route is divided into a three-step method and a two-step method. The three-step method oxidizes isobutylene to methacrolein, further oxidizes it to methacrylic acid, and finally esterifies it with methanol to obtain methyl methacrylate. The two-step method, on the other hand, oxidizes and esterifies methacrolein in a single step to produce methacrylic acid. The two-step route has many advantages, including a shorter reaction route, higher atom utilization, better selectivity, milder reaction conditions, and environmental friendliness. It represents a significant revolution in C4 MMA production, and its catalyst is key to this technology.

[0005] Currently, oxide-supported noble metal catalysts are widely used, especially Au-supported catalysts, which have the advantage of high selectivity, but their cost is extremely high. For example, Suzuki et al. of Asahi Chemical Corporation in Japan supported 1.1 wt% Au nanoparticles on a composite oxide support such as SiO2-Al2O3-MgO, and the cost of their catalyst reached several million yuan per ton. How to improve catalyst performance and gradually reduce catalyst cost has become the biggest challenge. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of low catalyst conversion and low product yield in the one-step oxidative esterification synthesis reaction of the prior art, and to provide a bifunctional oxidative esterification catalyst with high conversion and high product yield.

[0007] Studies have shown that Au nanoparticles are highly beneficial for improving the selectivity of this reaction, and better auxiliaries and carriers need to be developed to promote the activity of gold nanoparticles.

[0008] To achieve the above objectives, the present invention provides an oxidative esterification bifunctional catalyst, the catalyst comprising having the general formula AuRh a O n / MN b O x The active component, wherein N is selected from Group IIA elements and M is a carrier element;

[0009] a = 0 to 1, and not 0;

[0010] b = 0 to 1, and is not 0;

[0011] x and n are numerical values ​​determined by the total valence of the elements other than oxygen in the general formula.

[0012] A second aspect of this invention provides a method for preparing an oxidative esterification bifunctional catalyst, the method comprising:

[0013] (1) Preparation of MN b O x The carrier element, N is selected from Group IIA elements, and M is the carrier element;

[0014] (2) MN b O x The support is mixed and contacted with Au and Rh sources in solution, and optionally dried and then calcined to obtain the catalyst.

[0015] A third aspect of the present invention provides an oxidative esterification bifunctional catalyst prepared by the method described herein.

[0016] The fourth aspect of this invention provides the application of the oxidative esterification bifunctional catalyst described herein in the synthesis of methyl methacrylate.

[0017] The fifth aspect of the present invention provides a method for synthesizing methyl methacrylate, the method comprising: contacting methanol with methacrolein in the presence of a catalyst to carry out an oxidative esterification reaction, wherein the catalyst comprises the oxidative esterification bifunctional catalyst of the present invention.

[0018] The catalyst of this invention has the advantages of high conversion rate and high yield. When used to synthesize methyl methacrylate, it results in high yield and high feed conversion rate. Detailed Implementation

[0019] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] This invention provides an oxidative esterification bifunctional catalyst, the catalyst comprising having the general formula AuRh a O n / MN b O x The active component, wherein N is selected from Group IIA elements and M is a carrier element;

[0021] a = 0 to 1, and not 0;

[0022] b = 0 to 1, and is not 0;

[0023] x and n are values ​​determined by the total valence of the elements other than oxygen in the general formula. The catalyst of the present invention has the advantages of high conversion rate and high yield, and its use in the synthesis of methyl methacrylate results in high yield and high feed conversion rate.

[0024] According to a preferred embodiment of the present invention, a = 0.01-0.5, preferably 0.12-0.19; b = 0.01-0.3, preferably 0.1-0.2.

[0025] According to a preferred embodiment of the present invention, the content of Group IIA elements, calculated as oxides, ranges from 1 to 50 wt%, preferably 5 to 20 wt%.

[0026] According to a preferred embodiment of the present invention, the Au content, calculated as oxides, ranges from 0.1 to 0.9 wt%, preferably 0.5 to 0.8 wt%. According to a preferred embodiment of the present invention, the Rh content, calculated as oxides, ranges from 0.01 to 0.2 wt%, preferably 0.04 to 0.06 wt%.

[0027] According to a preferred embodiment of the present invention, any Group IIA element can be used in the present invention. The Group IIA element of the present invention is selected from at least one of Be, Mg, Ca, Sr, Ba and Rr, preferably Ca and / or Sr.

[0028] According to a preferred embodiment of the present invention, commonly used carriers can be used in the present invention, and the range of carrier element M is relatively wide. For the present invention, M is preferably one or more of Si, Al, Ce and Ti, and preferably Si.

[0029] According to a preferred embodiment of the present invention, the size of the Au particles ranges from 1 to 10 nm. Using the aforementioned preferred catalyst, the oxidative esterification conversion rate and selectivity of the catalyst can be further improved.

[0030] According to a preferred embodiment of the present invention, the specific surface area of ​​the catalyst is in the range of 100-500 m². 2 / g.

[0031] Catalysts possessing the aforementioned characteristics of this invention can all be used in this invention, and there are no special requirements for their preparation methods. Specifically, this invention provides a method for preparing an oxidative esterification bifunctional catalyst, the method comprising:

[0032] (1) Preparation of MN b O x The carrier element, N is selected from Group IIA elements, and M is the carrier element;

[0033] (2) MN b O x The support is mixed and contacted with Au and Rh sources in solution, and optionally dried and then calcined to obtain the catalyst.

[0034] In this invention, MN is prepared b O x There are no special requirements for the method of preparing the carrier; any commonly used method for preparing carriers containing active metals can be used in this invention. For this invention, the preferred method is to prepare MN. b O x Methods for using carriers include impregnation and co-precipitation.

[0035] According to a preferred embodiment of the present invention, preferably, MN is prepared b O x The method for preparing the carrier includes: dissolving an N source in water to obtain solution A, adding solution A to a sol of M, spray drying to obtain the carrier precursor, and then calcining to obtain MN. b O x Support. The aforementioned preferred technical solution can further improve the oxidative esterification activity and selectivity of the catalyst.

[0036] According to a preferred embodiment of the present invention, the sol of M is a silica sol, more preferably an ammonium silica sol, and more preferably a silica sol with a solid content of 5-50% by weight, preferably 35-45% by weight, for example 35% by weight, 40% by weight, or 45% by weight. The aforementioned preferred technical solution can further improve the oxidative esterification activity and selectivity of the catalyst.

[0037] In this invention, there are no special requirements for the spray drying conditions; commonly used spray drying conditions can be used, and will not be described in detail here. The embodiments using spray drying conditions including an inlet temperature of 300°C, an outlet temperature of 150°C, and a rotation speed of 2 W / min are provided as examples to illustrate the advantages of this invention, but do not limit the scope of the invention.

[0038] According to a preferred embodiment of the present invention, preferably, MN is prepared b O xThe method for using a carrier includes: dissolving an N source in water to obtain a solution A, impregnating and contacting solution A with a solid compound of M, and optionally drying and then calcining.

[0039] In this invention, there are no special requirements for the drying conditions; commonly used drying conditions can be used, and will not be described in detail here. The embodiments use vacuum drying conditions at 80-100°C as an example to illustrate the advantages of this invention, but this does not limit the scope of the invention.

[0040] According to a preferred embodiment of the present invention, preferably, the N source includes an oxygen-containing salt and / or an oxygen-containing salt hydrate selected from one or more elements selected from Be, Mg, Ca, Sr, Ba and Rr.

[0041] In this invention, there are no special requirements for the calcination method and conditions. Preferably, for this invention, calcination yields MN. b O x The conditions for the carrier include a temperature of 450-700℃, preferably 500-600℃. In the embodiments, 550℃ is used as an example to illustrate the advantages of the present invention, but this does not limit the scope of the present invention.

[0042] In this invention, there are no special requirements for the calcination method and conditions. Preferably, for this invention, calcination yields MN. b O x The conditions for the carrier include a time of 2 to 100 hours, preferably 3 to 6 hours. In the embodiments, 4 hours is used as an example to illustrate the advantages of the present invention, but this does not limit the scope of the present invention.

[0043] In this invention, there are no special requirements for the calcination conditions and steps in step (2). For this invention, the preferred conditions for obtaining the catalyst by calcination include: a calcination temperature of 150-550℃.

[0044] In this invention, there are no special requirements for the calcination conditions and steps in step (2). For this invention, the preferred conditions for calcining to obtain the catalyst include: a calcination temperature of 150-550°C and a calcination time of 2-200 hours, preferably 3-10 hours. In the examples, 4 hours is used as an example to illustrate the advantages of this invention, but this does not limit the scope of this invention.

[0045] According to a preferred embodiment of the present invention, preferably, the conditions for obtaining the catalyst in step (2) include: a first calcination in an oxygen-deficient atmosphere, followed by a second calcination in a pure oxygen atmosphere. The aforementioned preferred technical solution can further improve the oxidative esterification activity and selectivity of the catalyst.

[0046] According to a preferred embodiment of the present invention, preferably, the oxygen volume concentration in the oxygen-deficient atmosphere is 2-7%, and the other inert gas is at least one selected from argon, nitrogen, neon, and helium. The aforementioned preferred technical solution can further improve the oxidative esterification activity and selectivity of the catalyst.

[0047] According to a preferred embodiment of the present invention, preferably, the temperature of the first calcination is 20-300°C higher than the temperature of the second calcination, more preferably 100-200°C higher, for example, 100°C, 150°C, or 200°C higher. Using the aforementioned preferred technical solution can further improve the oxidative esterification activity and selectivity of the catalyst.

[0048] According to a preferred embodiment of the present invention, more preferably, the first calcination temperature is 250-550°C, preferably 300-400°C. In the examples, 350°C is used as an example to illustrate the advantages of the present invention, but this does not limit the scope of the present invention. The second calcination temperature is 150-350°C, preferably 200-250°C. In the examples, 250°C is used as an example to illustrate the advantages of the present invention, but this does not limit the scope of the present invention. The aforementioned preferred technical solutions can further improve the oxidative esterification activity and selectivity of the catalyst.

[0049] According to a preferred embodiment of the present invention, the first roasting time is 1-5 hours. In the example, 2 hours is used as an example to illustrate the advantages of the present invention, but this does not limit the scope of the present invention.

[0050] According to a preferred embodiment of the present invention, the second calcination time is 1-5 hours. In the example, 2 hours is used as an example to illustrate the advantages of the present invention, but this does not limit the scope of the present invention.

[0051] This invention provides a bifunctional oxidative esterification catalyst prepared by the method described in this invention.

[0052] This invention provides the application of the oxidative esterification bifunctional catalyst described herein in the synthesis of methyl methacrylate. The oxidative esterification bifunctional catalyst of this invention exhibits high activity and selectivity.

[0053] This invention provides a method for synthesizing methyl methacrylate, the method comprising: contacting methanol with methacrolein in the presence of a catalyst to carry out an oxidative esterification reaction, wherein the catalyst comprises the oxidative esterification bifunctional catalyst of this invention.

[0054] According to a preferred embodiment of the present invention, the method preferably includes: being carried out in a batch reactor.

[0055] According to a preferred embodiment of the present invention, the reaction temperature is 60-90°C.

[0056] According to a preferred embodiment of the present invention, the partial pressure of O2 is 0.02-3 MPa.

[0057] According to a preferred embodiment of the present invention, the molar ratio of methanol to methacrolein is 10-40.

[0058] According to a preferred embodiment of the present invention, the reaction time is 0.5-24h.

[0059] The present invention will now be described in detail with reference to embodiments. It should be understood that the embodiments and examples described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0060] The catalyst evaluation method used in the following examples is as follows:

[0061] Methacrolein and methanol were added to a batch reactor containing the catalyst to be tested. After heating to the required temperature, a certain amount of air was introduced, and the mixture was analyzed by gas chromatography. During the analysis, the carbon balance was calculated, and data with a carbon balance of 95%–105% were selected as valid data. The reaction conditions were as follows:

[0062] Reactor: Stirred tank reactor, 200ml volume;

[0063] Catalyst loading: 2 grams;

[0064] Reaction temperature: 90℃;

[0065] Reaction time: 3 hours;

[0066] Raw materials: Methanol: 58.2g, Methacrolein: 6.4g

[0067] Air pressure: 3.5 MPa.

[0068] Conversion rate of methacrolein = (Methacrolein consumed in the reaction / Methacrolein added to the reaction) * 100%;

[0069] Selectivity of methyl methacrylate = (number of moles of methyl methacrylate produced in the reaction) / (theoretically number of moles of methyl methacrylate produced) * 100%;

[0070] Methyl methacrylate yield = conversion of methacrolein * selectivity of methyl methacrylate.

[0071] The concentrations of each component in the reaction solution were determined using gas chromatography and internal standard method.

[0072] Example 1

[0073] (1) Dissolve 20g of strontium nitrate (Sr(NO3)2) in water to obtain solution A, then add solution A to 140.4g of silica sol (SiO2 40wt%), mix evenly, and spray dry (conditions include: inlet temperature 300℃, outlet temperature 150℃, rotation speed 2w / min) to obtain the carrier precursor.

[0074] (2) The obtained carrier precursor was calcined in air at 550°C for 4 hours to obtain the carrier.

[0075] (3) Mix 50 ml of gold chloride solution (Au content 0.005 g / ml) and 5 ml of rhodium chloride aqueous solution (Rh content 0.005 g / ml) to obtain mixed salt solution B. Add it to 50 g of carrier and stir for a period of time. When the color of solution B becomes transparent, filter and wash it, and dry it in a vacuum oven at 100°C to obtain the catalyst precursor.

[0076] (4) The obtained precursor was first calcined at 350°C for 2 h in an oxygen-deficient atmosphere (the remainder being nitrogen) with an oxygen content of 2% (V / V), and then calcined a second time at 250°C for 2 h in pure oxygen to obtain a catalyst for the synthesis of methyl methacrylate.

[0077] Example 2

[0078] (1) Dissolve 22.3g of calcium nitrate (Ca(NO3)2·4H2O) in water to obtain solution A, then add solution A to 140.4g of silica sol (SiO2 40wt%), mix evenly, and spray dry (conditions include: inlet temperature 300℃, outlet temperature 150℃, rotation speed 2w / min) to obtain the carrier precursor.

[0079] (2) The obtained carrier precursor was calcined in air at 550°C for 4 hours to obtain the carrier.

[0080] (3) Mix 50 ml of gold chloride solution (Au content 0.005 g / ml) and 5 ml of rhodium chloride aqueous solution (Rh content 0.005 g / ml) to obtain mixed salt solution B. Add it to 50 g of carrier and stir for a period of time. When the color of solution B becomes transparent, filter and wash it, and dry it in a vacuum oven at 100°C to obtain the catalyst precursor.

[0081] (4) The obtained precursor was first calcined at 350°C for 2 h in an oxygen-deficient atmosphere (the remainder being nitrogen) with an oxygen content of 2% (V / V), and then calcined a second time at 250°C for 2 h in pure oxygen to obtain a catalyst for the synthesis of methyl methacrylate.

[0082] Example 3

[0083] (1) Dissolve 22.3g of calcium nitrate (Ca(NO3)2·4H2O) in water to obtain solution A, then add solution A to an aqueous solution containing 354.1g of aluminum nitrate (Al(NO3)3·9H2O), continue stirring for a period of time, and spray dry (conditions include: inlet temperature 300℃, outlet temperature 150℃, rotation speed 2w / min) to obtain the carrier precursor.

[0084] (2) The obtained carrier precursor was calcined in air at 550°C for 4 hours to obtain the carrier.

[0085] (3) Mix 50 ml of gold chloride solution (Au content 0.005 g / ml) and 5 ml of rhodium chloride aqueous solution (Rh content 0.005 g / ml) to obtain mixed salt solution B. Add it to 50 g of carrier and stir for a period of time. When the color of solution B becomes transparent, filter and wash it, and dry it in a vacuum oven at 100°C to obtain the catalyst precursor.

[0086] (4) The obtained precursor was first calcined at 350°C for 2 h in an oxygen-deficient atmosphere (the remainder being nitrogen) with an oxygen content of 2% (V / V), and then calcined a second time at 250°C for 2 h in pure oxygen to obtain a catalyst for the synthesis of methyl methacrylate.

[0087] Example 4

[0088] (1) Dissolve 20g of strontium nitrate (Sr(NO3)2) in water to obtain solution A, then add solution A to 140.4g of silica sol (SiO2 40wt%), continue stirring for a period of time, and spray dry (conditions include: inlet temperature 300℃, outlet temperature 150℃, rotation speed 2w / min) to obtain the carrier precursor.

[0089] (2) The obtained carrier precursor was calcined in air at 550°C for 4 hours to obtain the carrier.

[0090] (3) Mix 80 ml of gold chloride solution (Au content 0.005 g / ml) and 5 ml of rhodium chloride aqueous solution (Rh content 0.005 g / ml) to obtain mixed salt solution B. Add it to 50 g of carrier and stir for a period of time. When the color of solution B becomes transparent, filter and wash it, and dry it in a vacuum oven at 100°C to obtain the catalyst precursor.

[0091] (4) The obtained precursor was first calcined at 350°C for 2 h in an oxygen-deficient atmosphere (the remainder being nitrogen) with an oxygen content of 2% (V / V), and then calcined a second time at 250°C for 2 h in pure oxygen to obtain a catalyst for the synthesis of methyl methacrylate.

[0092] Example 5

[0093] The method is the same as in Example 1, except that the second roasting temperature is 350°C.

[0094] Example 6

[0095] The method is the same as in Example 1, except that the initial roasting temperature is 250°C.

[0096] Example 7

[0097] The method is the same as in Example 1, except that the initial roasting temperature is 250°C and the secondary roasting temperature is 350°C.

[0098] Example 8

[0099] The method is the same as in Example 1, except that both calcinations are performed in an oxygen-deficient atmosphere with an oxygen content of 2% (V / V) (the remainder being nitrogen).

[0100] Comparative Example 1

[0101] (1) 140.4g of silica sol (SiO2 40wt%) was spray-dried (conditions included: inlet temperature 300℃, outlet temperature 150℃, rotation speed 2w / min) to obtain the carrier precursor.

[0102] (2) The obtained carrier precursor was calcined in air at 550°C for 4 hours to obtain the carrier.

[0103] (3) Add 100ml of gold chloride solution (Au content 0.005g / ml) to 50g of carrier, stir for a period of time, wait until the color of solution B becomes transparent, filter and wash, and dry in a vacuum oven at 100℃ to obtain the catalyst precursor.

[0104] (4) The obtained precursor was calcined in air at 350°C for 2 hours to obtain a catalyst for the synthesis of methyl methacrylate.

[0105] Table 1

[0106]

[0107] By employing the preferred embodiments of the present invention, high target selectivity can be maintained under conditions of high conversion rate.

[0108] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A bifunctional catalyst for oxidative esterification, characterized in that, The catalyst comprises having the general formula AuRh a O n / MN b O x The active component, wherein N is selected from Group IIA elements and M is a carrier element; a=0.01-0.5; b=0.01-0.3; x and n are numerical values ​​determined by the total valence of the elements other than oxygen in the general formula. The Au content ranges from 0.1 to 0.9 wt%, and the Rh content ranges from 0.01 to 0.2 wt%. Group IIA elements are selected from Ca and / or Sr, and M is one or more of Si, Al, Ce and Ti.

2. The catalyst according to claim 1, wherein, a=0.12-0.19; b=0.1-0.

2.

3. The catalyst according to claim 1 or 2, wherein, In terms of oxides, The content of Group IIA metals ranges from 1 to 50 wt%; and / or Au content ranges from 0.5 to 0.8 wt%; and / or The Rh content ranges from 0.04 to 0.06 wt%.

4. The catalyst according to claim 3, wherein, In terms of oxides, The content of Group IIA metals ranges from 5 to 20 wt%.

5. The catalyst according to claim 1 or 2, wherein, M represents Si.

6. A method for preparing an oxidative esterification bifunctional catalyst according to any one of claims 1-5, characterized in that, The preparation method includes: (1) Preparation of MN b O x The carrier element, N is selected from Group IIA elements, and M is the carrier element; (2) MN b O x The carrier is mixed and contacted with the Au source and Rh source in solution.

7. The preparation method according to claim 6, wherein, Step (2) is followed by a drying and roasting step.

8. The preparation method according to claim 6 or 7, wherein, Preparation of MN b O x The carrier method includes one or more of the following: impregnation method and co-precipitation method.

9. The preparation method according to claim 8, wherein, Preparation of MN b O x The carrier method includes: N source is dissolved in water to obtain solution A. Solution A is then added to the sol of M, and spray-dried to obtain the carrier precursor, which is then calcined to obtain MN. b O x carrier; or, The N source is dissolved in water to obtain solution A. Solution A is then impregnated with a solid compound of M, followed by drying and calcination.

10. The preparation method according to claim 9, wherein, The sol of M is a silica sol; and / or N sources include oxygen-containing salts and / or oxygen-containing salt hydrates selected from one or more elements selected from Ca and Sr; and / or Calcination yields MN b O x The conditions for the carrier include: a temperature of 450-750℃ and a time of 2-100 hours.

11. The preparation method according to claim 10, wherein, The silica sol is an ammonium-type silica sol; and / or The solid content of the silica sol is 5-50% by weight; and / or Calcination yields MN b O x The conditions for the carrier include: a temperature of 500-600℃ and a time of 3-6 hours.

12. The preparation method according to claim 11, wherein, The solid content of the silica sol is 35-45% by weight.

13. The preparation method according to claim 6 or 7, wherein, The conditions for obtaining the catalyst by calcination in step (2) include: calcination temperature of 150-550℃ and calcination time of 2-200 hours.

14. The preparation method according to claim 13, wherein, The conditions for obtaining the catalyst by calcination in step (2) include: first calcination in an oxygen-deficient atmosphere, followed by a second calcination in a pure oxygen atmosphere.

15. The preparation method according to claim 14, wherein, The oxygen volume concentration in the oxygen-deficient atmosphere is 2-7%, and the other inert gases are at least one of argon, nitrogen, neon, and helium; and / or The temperature of the first roasting is 20-300℃ higher than the temperature of the second roasting; and / or The first roasting temperature is 250-550℃, and the second roasting temperature is 150-350℃; and / or The first roasting time is 1-5 hours, and the second roasting time is 1-5 hours.

16. The preparation method according to claim 15, wherein, The temperature of the first roasting is 100-200°C higher than the temperature of the second roasting; and / or The first roasting temperature is 300-400℃, and the second roasting temperature is 200-250℃.

17. The oxidative esterification bifunctional catalyst prepared by the method of any one of claims 6-16.

18. The use of the oxidative esterification bifunctional catalyst according to any one of claims 1-5 and 17 in the synthesis of methyl methacrylate.

19. A method for synthesizing methyl methacrylate, characterized in that, The method includes: contacting methanol with methacrolein in the presence of a catalyst to carry out an oxidative esterification reaction, said catalyst comprising the oxidative esterification bifunctional catalyst according to any one of claims 1-5 and 17.

20. The preparation method according to claim 19, wherein, The method includes: In a batch reactor, and / or Reaction temperature 60-90℃, and / or O2 partial pressure 0.02-3 MPa, and / or The molar ratio of methanol to methacrolein is 10-40, and / or Reaction time: 0.5-24 hours.

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