Catalyst and preparation method therefor, and method for preparing olefinic unsaturated acid or ester thereof

Abstract

A catalyst and a preparation method therefor, and a method for preparing an olefinic unsaturated acid or an ester thereof. The catalyst comprises a carrier and catalytic metal loaded on the carrier, wherein the carrier is a composite of silicon dioxide and mesoporous boron nitride. Furthermore, in the presence of the catalyst, an alkanoic acid or alkanoate having a general formula of R1-CH2-COOR2 reacts with formaldehyde to obtain an olefinic unsaturated acid or an ester thereof, wherein R1 and R2 are independently selected from hydrogen or alkyl.

Description

Catalyst and preparation method thereof, and preparation method of ethylenically unsaturated acid or ester thereof

[0001] Related applications

[0002] This application claims priority to Chinese patent application No. 202410138931.1, filed on February 1, 2024, entitled “Catalyst and method for preparing same, method for preparing olefinically unsaturated acid or its ester”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of catalyst technology, and in particular to a catalyst and a preparation method thereof, and a preparation method of an ethylenically unsaturated acid or an ester thereof. Background Art

[0004] Methyl methacrylate (MMA) is an important fine chemical raw material and can be used as a monomer for the synthesis of polymethyl methacrylate (PMMA).

[0005] For the synthesis of methyl methacrylate via the aldol condensation reaction of formaldehyde and methyl propionate, existing catalysts use supports such as SiO2 and molecular sieves. The catalytic metals primarily consist of alkali metals such as Cs, Na, K, and Rb as active components, with Mg, Al, Zr, and Ba as co-active components. However, in these catalysts, a small number of active components, due to weak support, can become free alkali metal ions. These free alkali metal ions act as local hotspots during the reaction, generating carbon deposits and inhibiting catalyst performance.

[0006] Summary of the Invention

[0007] Based on this, it is necessary to provide a catalyst and a preparation method thereof, and a preparation method of an olefinically unsaturated acid or its ester to address the above-mentioned problems. The carrier of the catalyst has a stronger anchoring ability for the active component. When used in the reaction of preparing an olefinically unsaturated acid or its ester, the generation of free alkali metal ions can be reduced, thereby reducing carbon deposition on the catalyst surface, making the catalyst's selectivity and other properties more stable.

[0008] In order to achieve the above-mentioned purpose, the technical solution adopted in this application is: a catalyst for producing olefinically unsaturated acids or their esters, the catalyst comprising a carrier and a catalytic metal loaded on the carrier, wherein the carrier is a composite of silica and mesoporous boron nitride.

[0009] In one embodiment, the mass ratio of the mesoporous boron nitride to the silicon dioxide is 1:0.5-1:10.8.

[0010] In one embodiment, the catalytic metal includes an active component and a co-active component, wherein the active component is selected from salts or oxides of Cs, K, and Rb, and the co-active component is selected from salts or oxides of Zr, Ti, Mg, Al, Ba, and Hf.

[0011] In one embodiment, the mass of the active ingredient is 2.2%-15.8% of the mass of the carrier.

[0012] In one embodiment, the mass of the co-active component is 0.3%-4.1% of the mass of the carrier.

[0013] The present application also provides a method for preparing a catalyst, comprising the following steps:

[0014] preparing a mixture of mesoporous boron nitride and a silicon source;

[0015] mixing a salt solution of a co-active component with the mixture, followed by drying and calcining to obtain an intermediate;

[0016] The precursor of the active component is mixed with the intermediate and impregnated, and then dried and calcined to obtain a catalyst.

[0017] In one embodiment, the silicon source is selected from silica sol.

[0018] The present application also provides another method for preparing a catalyst, comprising the following steps:

[0019] Mesoporous boron nitride and silicon dioxide are dispersed in a solvent, and then dried and calcined to obtain a carrier;

[0020] The carrier is impregnated in a salt solution of a co-active component, and then dried and calcined to obtain an intermediate;

[0021] The intermediate is impregnated in a precursor of an active component and then dried to obtain a catalyst.

[0022] The present application also provides a method for preparing an olefinically unsaturated acid or an ester thereof, wherein an alkanoic acid or an alkanoic acid ester of the general formula R1-CH2-COOR2 is reacted with formaldehyde in the presence of the catalyst to obtain an olefinically unsaturated acid or an ester thereof, wherein R1 and R2 are independently selected from hydrogen or an alkyl group.

[0023] In one embodiment, the alkanoate is methyl propionate, and the methyl propionate reacts with formaldehyde to obtain methyl methacrylate.

[0024] The catalyst of the present application uses a complex of mesoporous boron nitride and silicon dioxide as a carrier. The polar boron-nitrogen bond in the mesoporous boron nitride can strengthen the charge interaction (SMSI effect) between the carrier surface and the active component, making the carrier's anchoring ability to the active component stronger, thereby improving the activity and stability of the catalyst. Therefore, when the catalyst of the present application is applied to the reaction of an alkanoic acid or an alkanoate of the general formula R1-CH2-COOR2 with formaldehyde to prepare an olefinically unsaturated acid or its ester, the generation of free alkali metal ions can be reduced, thereby reducing the carbon deposit formed on the catalyst surface due to high-temperature coking, making the selectivity and other properties of the catalyst more stable, and improving the service life of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the conventional technology, the following briefly introduces the drawings required for use in the embodiments or the conventional technology descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0026] FIG1 is a schematic flow chart of the method for preparing the catalyst of the present application. DETAILED DESCRIPTION

[0027] To facilitate understanding of the present application, the present application will be described in more detail below. However, it should be understood that the present application can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the technical field of the present application. The terms used herein in the specification of the present application are only for the purpose of describing specific embodiments or embodiments and are not intended to limit the present application. The optional scope of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0029] Patent CN112675830A discloses an aldol condensation catalyst, the preparation method of which is as follows: 1) preparing a foamed silica support containing a modifier element; 2) calcining the foamed silica support prepared in step 1) to obtain a modified silica support; 3) dissolving a water-soluble salt containing an alkali metal element in water and impregnating the modified silica support to obtain a catalyst precursor A; 4) drying and calcining catalyst precursor A to obtain a catalyst precursor B; 5) washing catalyst precursor B with a mixture of methanol and methyl propionate to remove free alkali metal elements to obtain a catalyst. During the preparation process, the catalyst precursor is calcined under certain water vapor conditions to expose free alkali metal elements that have a weaker interaction with the support. The free alkali metal elements are then washed away in a non-aqueous system to avoid side reactions catalyzed by the free alkali metal elements and reduce carbon deposits. However, the calcination under water vapor conditions mentioned in the preparation process and the flushing with the methyl propionate and methanol mixture after the preparation will inevitably damage the pore structure of the catalyst, resulting in adverse effects on the catalyst life and stability.

[0030] The present application provides a catalyst for producing olefinically unsaturated acids or esters thereof, wherein the catalyst comprises a carrier and a catalytic metal supported on the carrier, wherein the carrier is a composite of silicon dioxide and mesoporous boron nitride.

[0031] Because boron nitride has an sp2 hybridized hexagonal structure similar to graphene, it has excellent thermal conductivity, high-temperature stability, and resistance to acid and alkali corrosion. Even at high temperatures, its chemical and thermal properties change very little. At the same time, mesoporous boron nitride has interconnected channels and exceptional mechanical strength. Therefore, compared to silica supports, the catalyst of this application, which uses a composite of mesoporous boron nitride and silica as a support, has higher mechanical strength and thermal stability.

[0032] Moreover, the polar boron-nitrogen bond in mesoporous boron nitride can strengthen the charge interaction (SMSI effect) between the carrier surface and the active component, so that the carrier has a stronger anchoring ability to the active component, thereby improving the activity and stability of the catalyst. Therefore, when the catalyst of the present application is applied to the reaction of preparing olefinically unsaturated acids or their esters, the generation of free alkali metal ions can be reduced, thereby reducing the carbon deposit formed by high-temperature coking on the catalyst surface, making the selectivity of the catalyst more stable, and improving the service life of the catalyst.

[0033] It should be noted that the carrier is a composite of silicon dioxide and mesoporous boron nitride, which means that silicon dioxide and mesoporous boron nitride form an integral structure, not a mixture, and a -O-Si-[NB] n -or-O-Si-[BN] n -Bonded structure.

[0034] Optionally, the mass ratio of the mesoporous boron nitride to the silicon dioxide is 1:0.5-1:10.8, further preferably 1:1.4-1:7.3, and more preferably 1:2.3-1:5.1, thereby ensuring the anchoring ability of the carrier to the active component without causing polymerization of the active component.

[0035] In the catalyst for producing olefinically unsaturated acids or esters thereof, the catalytic metal primarily comprises an alkali metal salt or oxide as the active component. In some embodiments, a metal salt or metal oxide other than an alkali metal may also be employed as a co-active component. This application does not limit the catalytic metal of the catalyst. In some embodiments, the catalytic metal comprises an active component and a co-active component.

[0036] Optionally, the active component is selected from salts or oxides of Cs, K, and Rb, preferably a salt or oxide of Cs, wherein the salt may be a nitrate, a hydrochloride, a carbonate, etc. Optionally, the mass of the active component is 2.2%-15.8% of the mass of the carrier, more preferably 3.6%-14.1%, and even more preferably 5.2%-12.5%.

[0037] Optionally, the co-active component is selected from salts or oxides of Zr, Ti, Mg, Al, Ba, and Hf, preferably salts or oxides of Zr, Ti, and Al, wherein the salt may be a nitrate, hydrochloride, carbonate, or organic salt. Optionally, the mass of the co-active component is 0.3% to 4.1% of the mass of the carrier, more preferably 0.5% to 3.4%, and even more preferably 0.8% to 2.5%.

[0038] The present application does not limit the preparation method of the catalyst. A composite body can be prepared first as a carrier, and then the catalytic metal can be loaded on the carrier by impregnation or the like. Alternatively, the catalytic metal can be directly formed in situ in the composite body when preparing the composite body. Specifically, when preparing a composite body of silicon dioxide and mesoporous boron nitride, a silicon source can be mixed with mesoporous boron nitride to prepare the composite body, or silicon dioxide can be mixed with a precursor of mesoporous boron nitride such as borane or borazine to prepare the composite body, or a silicon source and a precursor of mesoporous boron nitride can be mixed to prepare the composite body.

[0039] The present application also provides a method for preparing the catalyst. When preparing the complex, the co-active component is directly loaded on the carrier in situ, which not only ensures that the co-active component can be loaded on the carrier uniformly and dispersedly, but also avoids the competition effect of the active component on the loading site.

[0040] Specifically, referring to FIG1 , the preparation method includes the following steps, wherein, in order to fully contact the solid and the solvent and reduce the number of preparation steps, a rotary evaporator is preferably used in the impregnation and drying processes during the preparation process.

[0041] S11, preparing a mixture of mesoporous boron nitride and a silicon source;

[0042] S12, mixing a salt solution of a co-active component with the mixture, followed by drying and calcining to obtain an intermediate;

[0043] S13, mixing the precursor of the active component with the intermediate, impregnating the mixture, and then drying and calcining the mixture to obtain a catalyst.

[0044] In step S11, the silicon source is selected from silica sol, water glass, etc., preferably silica sol, which not only simplifies the preparation process but also acts as a binder. Furthermore, to reduce the sodium content in the carrier, the selected silica sol is preferably neutral silica sol, and the silicon dioxide content is preferably 20%-30%.

[0045] In step S12, the co-active component salt is selected from nitrates, hydrochlorides, carbonates, organic salts, etc. The solvent selected for the co-active component salt solution is not particularly limited, and water and organic solvents can be used. In order to better remove the solvent during the drying stage, an alcohol with 1 to 6 carbon atoms is preferred, and methanol is particularly preferred.

[0046] In step S12, the drying temperature is 65°C-95°C, the time is 1 hour-3 hours, and the calcination temperature is 450°C-600°C, the time is 3 hours-6 hours.

[0047] In step S13, the precursor of the active component is selected from nitrates, hydrochlorides, carbonates, alkalis, etc. In the step of mixing and impregnating the precursor of the active component with the intermediate, there is no special restriction on the selected solvent, and both water and organic solvents can be used. In order to better remove the solvent during the drying stage, alcohols with 1 to 6 carbon atoms are preferred, and methanol is particularly preferred.

[0048] In step S13, the drying temperature is 65° C.-95° C., the time is 1 hour-3 hours, and the calcination temperature is 450° C.-600° C., the time is 3 hours-6 hours.

[0049] The present application also provides another method for preparing the catalyst, in which a composite is first prepared as a carrier, and then the co-active component and the active component are respectively loaded on the carrier by impregnation.

[0050] Specifically, the preparation method includes the following steps, wherein, in order to fully contact the solid and the solvent and reduce the number of preparation steps, a rotary evaporator is preferably used in the impregnation and drying processes during the preparation process.

[0051] S21, dispersing mesoporous boron nitride and silicon dioxide in a solvent, followed by drying and calcining to obtain a support;

[0052] S22, impregnating the support in a salt solution of a co-active component, followed by drying and calcining to obtain an intermediate;

[0053] S23, impregnating the intermediate in an active component salt solution, and then drying and calcining to obtain a catalyst.

[0054] In step S21, the solvent is selected from n-hexane, the drying temperature is 65°C-95°C, the time is 1 hour-3 hours, and the calcination temperature is 650°C-800°C, and the time is 4 hours-6 hours.

[0055] In step S22, the auxiliary active component salt is selected from nitrate, hydrochloride, carbonate, organic salt, etc., the drying temperature is 65°C-95°C, the time is 1h-3h, and the calcination temperature is 450°C-600°C, and the time is 3h-6h.

[0056] In step S23, the precursor of the active component is selected from nitrate, hydrochloride, carbonate, alkali, etc., and the drying temperature is 65° C.-95° C. and the drying time is 1 hour-3 hours.

[0057] In step S23, calcination may be performed after drying, with the calcination temperature being 450°C-600°C and the calcination time being 3h-6h.

[0058] The present application also provides a method for preparing an olefinically unsaturated acid or an ester thereof, wherein an alkanoic acid or an alkanoic acid ester of the general formula R1-CH2-COOR2 is reacted with formaldehyde in the presence of the catalyst to obtain an olefinically unsaturated acid or an ester thereof, wherein R1 and R2 are independently selected from hydrogen or an alkyl group.

[0059] In one embodiment, the alkanoate is methyl propionate, and the methyl propionate reacts with formaldehyde to obtain methyl methacrylate.

[0060] Because the carrier in the catalyst of the present application has a stronger ability to anchor the active component, the activity and stability of the catalyst are improved. Therefore, when the catalyst is used in the reaction of preparing ethylenically unsaturated acids or esters thereof in the present application, the catalyst's selectivity and other properties are more stable, and the yield and selectivity of the ethylenically unsaturated acids or esters thereof are also more stable.

[0061] Hereinafter, the catalyst and its preparation method, and the preparation method of the ethylenically unsaturated acid or its ester will be further described through the following specific examples.

[0062] Example 1

[0063] Weigh 10g of mesoporous boron nitride and 80g of 30% silica sol, mix them into a mixture, weigh 1.41g of zirconium nitrate and dissolve them in 65ml of methanol solution to obtain a mixed solution, add the mixed solution to the mixture while stirring, put it into a rotary evaporator and rotate it at 40°C for 12h, then dry it under reduced pressure at 90°C for 2h, and calcine it in a muffle furnace at 550°C for 4h to obtain an intermediate.

[0064] 2.65 g of cesium carbonate was weighed and dissolved in 65 ml of methanol solution. The intermediate was added to the mixture while stirring. The mixture was placed in a rotary evaporator and rotated at 40°C for 12 hours. It was then dried under reduced pressure at 90°C for 2 hours and calcined in a muffle furnace at 550°C for 4 hours. The catalyst was pressed into tablets to obtain a catalyst, which was recorded as C-1.

[0065] 2 g of the prepared catalyst was soaked in deionized solution for 1 h, then rinsed three times with a certain amount of water, and all the solutions were collected for ICP analysis.

[0066] Example 2

[0067] The only difference between Example 2 and Example 1 is that the amount of mesoporous boron nitride used is 6.49 g, the amount of zirconium nitrate used is 1.27 g, and the amount of cesium carbonate used is 2.37 g. The obtained catalyst is recorded as C-2.

[0068] Example 3

[0069] The only difference between Example 3 and Example 1 is that the amount of mesoporous boron nitride used is 4.8 g, the amount of zirconium nitrate used is 1.2 g, and the amount of cesium carbonate used is 2.24 g. The obtained catalyst is recorded as C-3.

[0070] Example 4

[0071] The only difference between Example 4 and Example 1 is that the amount of mesoporous boron nitride used is 7.74 g, the amount of zirconium nitrate used is 1 g, and the amount of cesium carbonate used is 2.46 g. The obtained catalyst is recorded as C-4.

[0072] Example 5

[0073] The difference between Example 5 and Example 1 is that when preparing the intermediate, the amount of mesoporous boron nitride used is 6.67 g, and the amount of zirconium nitrate used is 1.8 g; when preparing the catalyst, 2.79 g of cesium hydroxide monohydrate (99%) is used instead of cesium carbonate, and the catalyst is calcined in a muffle furnace at 550°C for 6 hours. The obtained catalyst is recorded as C-5.

[0074] Example 6

[0075] Weigh 5.45g of mesoporous boron nitride and 80g of 30% silica sol, mix them into a mixture, weigh 3.32g of zirconium acetylacetonate and dissolve them in 90ml of methanol solution to obtain a mixed solution, add the mixed solution to the mixture while stirring, put it into a rotary evaporator and rotate it at 40°C for 12h, then dry it under reduced pressure at 90°C for 2h, and calcine it in a muffle furnace at 550°C for 4h to obtain an intermediate.

[0076] 3.1 g of cesium hydroxide monohydrate (99%) was weighed and dissolved in 65 g of methanol solution. The intermediate was added to the mixture while stirring. The mixture was placed in a rotary evaporator and rotated at 40°C for 12 hours. It was then dried under reduced pressure at 90°C for 2 hours and calcined in a muffle furnace at 550°C for 6 hours. The catalyst was pressed into tablets to obtain a catalyst, which was recorded as C-6.

[0077] 2 g of the prepared catalyst was soaked in deionized solution for 1 h, then rinsed three times with a certain amount of water, and all the solutions were collected for ICP analysis.

[0078] Example 7

[0079] 5 g of mesoporous boron nitride and 26 g of silica (Q10) (Fuji Silysia CARiACT Q10) were added to 110 g of n-hexane solution and stirred continuously. The mixture was dried under reduced pressure on a rotary evaporator at 70°C for 2 h to remove the solvent. The remaining solid was placed in a muffle furnace and calcined at 750°C for 6 h under an argon or nitrogen atmosphere to obtain a composite of mesoporous boron nitride and silica.

[0080] 2.11 g of zirconium nitrate was weighed and dissolved in 65 ml of methanol solution. After standing for 16 hours, the above-obtained complex was poured into the zirconium nitrate solution under stirring conditions. After immersion in a rotary evaporator for 16 hours, the solvent was removed by drying under reduced pressure at 70°C for 2 hours. Subsequently, the zirconium-loaded complex was placed in a muffle furnace and calcined at 550°C for 4 hours to obtain an intermediate.

[0081] 2.77 g of cesium carbonate was weighed and dissolved in 90 ml of methanol solution. The intermediate was poured into the cesium carbonate solution under stirring and immersed in a rotary evaporator for 16 h. The solvent was evaporated under reduced pressure at 70°C and then placed in an oven at 120°C for 16 h to obtain a catalyst, which was recorded as C-7.

[0082] 2 g of the prepared catalyst was soaked in deionized solution for 1 h, then rinsed three times with a certain amount of water, and all the solutions were collected for ICP analysis.

[0083] Example 8

[0084] The only difference between Example 8 and Example 7 is that the amount of mesoporous boron nitride used is 6.31 g, the amount of zirconium nitrate used is 2.6 g, and the amount of cesium carbonate used is 3.4 g. The obtained catalyst is recorded as C-8.

[0085] Comparative Example 1

[0086] The only difference between Comparative Example 1 and Example 7 is that only 24 g of silica (Q10) is used as a carrier, and mesoporous boron nitride is not used. In addition, the amount of zirconium nitrate used is 1.06 g, and the amount of cesium carbonate used is 1.59 g. The obtained catalyst is recorded as D-1.

[0087] Comparative Example 2

[0088] The only difference between Comparative Example 2 and Example 1 is that ordinary boron nitride (basically macroporous) is used instead of mesoporous boron nitride, and the obtained catalyst is recorded as D-2.

[0089] Comparative Example 3

[0090] The only difference between Comparative Example 3 and Example 1 is that microporous boron nitride is used instead of mesoporous boron nitride. The obtained catalyst is recorded as D-3.

[0091] Comparative Example 4

[0092] The only difference between Comparative Example 4 and Example 1 is that mesoporous alumina (γ-alumina) is used instead of mesoporous boron nitride. The obtained catalyst is recorded as D-4.

[0093] Comparative Example 5

[0094] The only difference between Comparative Example 5 and Example 7 is that α-alumina prepared by high-temperature calcination is used instead of silicon dioxide. The obtained catalyst is recorded as D-5.

[0095] Comparative Example 6

[0096] The only difference between Comparative Example 6 and Example 7 is that a composite prepared from 5 g of mesoporous boron nitride, 24 g of silica (Q10) (Fuji Silysia CARiACT Q10) and 5 g of α-alumina is used as a carrier. The resulting catalyst is designated D-6.

[0097] Application Examples

[0098] 5 g of the catalysts prepared in Examples 1 to 8 and Comparative Examples 1 to 6 were respectively placed in a fixed bed reactor, and glass beads were added to the top of the catalyst for better heat transfer. A mixed raw material consisting of formaldehyde, methyl propionate and methanol with a mass fraction of 10%:70%:20% was injected into the fixed bed reactor through a metering pump, and the pressure was controlled to 0.1 mPa with nitrogen. The temperature was raised to 300 ° C, and the mass space velocity of the mixed raw material was 2 h -1, methyl methacrylate was prepared by continuous feeding, and the results are shown in Table 1.

[0099] Table 1

[0100] It can be seen from the examples and comparative examples that the catalyst made of a carrier without mesoporous boron nitride doping will produce relatively more free alkali metals. At the same time, the content of mesoporous boron nitride in the catalyst is negatively correlated with the amount of free alkali metals generated, which indicates that the embedding of mesoporous boron nitride can indeed improve the anchoring ability of the catalyst to the active components, thereby reducing the local hot spot phenomenon caused by particle coking, and then reducing the production of by-products, so that the selectivity of the catalyst is improved.

[0101] Stability testing

[0102] Hydrothermal experiments were conducted on the catalysts from Examples 1 to 8 and Comparative Examples 1 to 6. A 5% water content nitrogen gas at 93°C was passed over the catalysts, which were maintained at 350°C, for 28 days. Following the degradation experiments, the catalysts were removed and evaluated under the same conditions as described in the previous application examples. The catalyst particle strength was also tested using a particle strength meter. The results are shown in Table 2.

[0103] Table 2

[0104] As can be seen from Tables 1 and 2, in the catalyst of the present application, the carrier has a stronger anchoring ability for the active component, and when used, it can reduce the generation of free alkali metal ions. At the same time, the catalyst has excellent selectivity and a stable structure.

[0105] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0106] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of patent protection for the present application shall be determined by the appended claims.

Claims

1. A catalyst for producing an olefinically unsaturated acid or an ester thereof, comprising a carrier and a catalytic metal supported on the carrier, characterized in that: The carrier is a composite of silicon dioxide and mesoporous boron nitride.

2. The catalyst according to claim 1, wherein The mass ratio of the mesoporous boron nitride to the silicon dioxide is 1:0.5-1:10.

8.

3. The catalyst according to claim 1, wherein The catalytic metal includes an active component and a co-active component, wherein the active component is selected from salts or oxides of Cs, K, and Rb, and the co-active component is selected from salts or oxides of Zr, Ti, Mg, Al, Ba, and Hf.

4. The catalyst according to claim 3, wherein The mass of the active component is 2.2%-15.8% of the mass of the carrier.

5. The catalyst according to claim 3, wherein The mass of the co-active component is 0.3%-4.1% of the mass of the carrier.

6. A method for preparing a catalyst, characterized in that: The following steps are involved: preparing a mixture of mesoporous boron nitride and a silicon source; mixing a salt solution of a co-active component with the mixture, followed by drying and calcining to obtain an intermediate; The precursor of the active component is mixed with the intermediate and impregnated, and then dried and calcined to obtain a catalyst.

7. The method for preparing the catalyst according to claim 6, wherein: The silicon source is selected from silica sol.

8. A method for preparing a catalyst, characterized in that: The following steps are involved: Mesoporous boron nitride and silicon dioxide are dispersed in a solvent, and then dried and calcined to obtain a carrier; The carrier is impregnated in a salt solution of a co-active component, and then dried and calcined to obtain an intermediate; The intermediate is impregnated in a precursor of an active component and then dried to obtain a catalyst.

9. A method for preparing an ethylenically unsaturated acid or an ester thereof, wherein: In the presence of the catalyst as claimed in claim 1, an alkanoic acid or alkanoate of the general formula R1-CH2-COOR2 is reacted with formaldehyde to obtain an ethylenically unsaturated acid or ester thereof, wherein R1 and R2 are independently selected from hydrogen or alkyl.

10. The method for preparing an ethylenically unsaturated acid or an ester thereof according to claim 9, wherein The alkanoate is methyl propionate, and the methyl propionate reacts with formaldehyde to obtain methyl methacrylate.

11. The method for preparing an ethylenically unsaturated acid or an ester thereof according to claim 9, wherein The mass ratio of the mesoporous boron nitride to the silicon dioxide is 1:0.5-1:10.

8.

12. The method for preparing an ethylenically unsaturated acid or an ester thereof according to claim 9, wherein The catalytic metal includes an active component and a co-active component, wherein the active component is selected from salts or oxides of Cs, K, and Rb, and the co-active component is selected from salts or oxides of Zr, Ti, Mg, Al, Ba, and Hf.

13. The method for preparing an ethylenically unsaturated acid or an ester thereof according to claim 12, wherein The mass of the active component is 2.2%-15.8% of the mass of the carrier.

14. The method for preparing an ethylenically unsaturated acid or an ester thereof according to claim 12, wherein The mass of the co-active component is 0.3%-4.1% of the mass of the carrier.

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