Preparation method and application of aldol condensation catalyst with Si-O-Zr framework constructed through in-situ doping

Abstract

The invention discloses a preparation method and application of an aldol condensation catalyst with a Si-O-Zr framework constructed through in-situ doping. The preparation method mainly comprises preparation and application of the Si-O-Zr framework constructed through in-situ doping and the aldol condensation catalyst. Wherein the in-situ doping construction of the Si-O-Zr framework mainly utilizes the pre-hydrolysis matching of a silicon source and the hydrolysis / polycondensation rate between a zirconium source to realize the atomic-scale dispersion of the active component, a proper pore structure can be provided for the subsequent loading of the active component, the possibility of clustering of the active component is reduced, the catalytic activity is further improved, and the method is simple in preparation and low in cost. The method is suitable for subsequent large-scale industrial application.

Description

Technical Field

[0001] The present invention belongs to the technical field of heterogeneous catalytic materials, and specifically relates to a preparation method and application of an in-situ doped Si-O-Zr skeleton for an aldol condensation catalyst, and is particularly suitable for a Cs-based acid-base bifunctional catalyst system for synthesizing methyl methacrylate (MMA) from methyl propionate and formaldehyde. Background Art

[0002] Methyl methacrylate (MMA), as a core monomer for the preparation of polymethyl methacrylate (PMMA), specialty coatings, and high-performance adhesives, has attracted considerable attention for its industrial production technology. Current mainstream processes include the acetone cyanohydrin method (ACH), the isobutylene oxidation method, the ethylene method, and the coal-based ethylene method. The coal-based method has become a key development direction due to its readily available raw materials and environmentally friendly advantages. The aldol condensation reaction of methyl propionate and formaldehyde is a key step in this process, and its catalytic system still faces significant technical challenges: the reaction is essentially an acid-base synergistic catalytic process, requiring the construction of a bifunctional catalyst with both high active site exposure and structural stability.

[0003] In terms of catalytic system optimization, existing research focuses on the dispersion and regulation of active components. For example, patent CN117205909A innovatively proposes the use of a polymer modification strategy. By introducing polymer additives during the impregnation process, the distribution state of active components on the carrier surface is effectively regulated to achieve a dynamic balance of acid-base sites. This catalyst system has excellent performance in terms of reaction activity, selectivity and regeneration stability, and the preparation process has the potential for industrial scale-up. Patent CN117563577A approaches this from the perspective of carrier modification. Through a specific treatment process, the content of silanol groups on the carrier surface is regulated to construct an interfacial microenvironment suitable for the anchoring of active components, significantly inhibiting the clustering of active components, thereby improving catalytic performance.

[0004] It is worth noting that while catalytic performance has made some progress through component regulation and support modification, the traditional isovolumetric impregnation method still has essential defects: it relies on the physical adsorption of metal precursors and hydroxyl groups on the support surface. During the subsequent drying and calcination processes, the active components are prone to surface migration and form agglomerates. This irreversible structural degradation will lead to a mismatch in the spatial distribution of acid-base active sites, shortening the catalyst life, and restricting further improvement in catalytic performance. Therefore, breaking through the technical bottleneck of the existing impregnation method and developing a new catalyst construction strategy that can achieve atomic-level dispersion of active components and has a strong anchoring effect has become a key scientific issue for improving the efficiency of the aldol condensation reaction and promoting the industrialization of coal-based MMA processes. Summary of the Invention

[0005] The purpose of the present invention is to address the deficiencies of the prior art. The present invention provides a preparation method and application of an in-situ doping-constructed Si-O-Zr skeleton for an aldol condensation catalyst. The method is characterized in that the in-situ doping-constructed Si-O-Zr skeleton is achieved by matching the hydrolysis / polycondensation rates of a silicon source and a metal precursor, and embedding Zr atoms into the skeleton in a Si-O-Zr structure during the formation of a gel network to achieve atomic-level dispersion. The aldol condensation catalyst is a catalyst prepared by loading Cs on the obtained carrier by an equal volume impregnation method, and is used for the one-step synthesis of methyl methacrylate from methyl propionate and formaldehyde.

[0006] Based on the above concept, the present invention provides a method for preparing an aldol condensation catalyst by in-situ doping to construct a Si-O-Zr framework and its application, comprising the following steps:

[0007] (1) mixing a silicon source compound with a solvent and pre-hydrolyzing the mixture under acidic conditions for 3-12 hours to obtain a silica sol; then adding a zirconium source compound solution dropwise to the obtained silica sol, adjusting the pH of the system to 3-4, and forming a zirconium-silicon composite gel; aging the composite gel at 40-80° C. for 3-24 hours, drying the composite gel, and calcining the composite gel at 400-600° C. in a muffle furnace for 4-6 hours;

[0008] (2) Weigh a certain amount of cesium salt and place it in a blue-capped bottle. Add the corresponding amount of solvent to prepare a salt solution.

[0009] (3) adding the carrier in step (1) to the salt solution in step (2) and fully immersing at room temperature for 4-8 hours;

[0010] (4) drying the wet catalyst in step (3) in an oven at 80-120°C for 4-12 hours, and then calcining in a muffle furnace at a heating rate of 10°C / min to 400-600°C for 4-6 hours;

[0011] The silicon source is selected from at least one of ethyl orthosilicate and methyl orthosilicate; the solvent is selected from at least one of anhydrous ethanol and anhydrous methanol; and the acidic condition is adjusted by nitric acid, hydrochloric acid or acetic acid.

[0012] The zirconium source compound is selected from one of zirconium nitrate, zirconium oxychloride, zirconium oxynitrate and zirconium acetylacetonate, and its addition amount is determined according to the molar ratio of Si in the silicon source compound to Zr in the zirconium source of 40-100.

[0013] The main sources of the cesium salt are cesium nitrate, cesium acetate, cesium carbonate and cesium hydroxide; the amount of cesium is calculated based on cesium oxide, and the loading amount is 1-15wt.%.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] A method for preparing an in-situ doping Si-O-Zr framework for use as an aldol condensation catalyst and its application are disclosed. This method effectively suppresses metal oxide phase separation by matching the hydrolysis / polycondensation rates of a silicon-source precursor with a zirconium-source precursor, enabling the embedding of Zr into the SiO2 framework in a tetracoordinated manner, forming moderately strong acidic sites dominated by Lewis acids. Subsequently, Cs is loaded as the primary active component via an isovolumetric impregnation method to obtain an aldol condensation catalyst, resulting in improved catalytic activity. This method achieves atomic-level dispersion of the active components, reduces the likelihood of clustering, and enhances catalytic activity. Its ease of operation makes it suitable for large-scale catalyst preparation. DETAILED DESCRIPTION

[0016] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0017] Example 1:

[0018] 20ml of tetraethyl orthosilicate was mixed with 20ml of ethanol, 10ml of acetic acid, and 5ml of deionized water, placed in a flask equipped with a condenser and mechanical stirring, and pre-hydrolyzed under vigorous stirring and reflux for 6 hours. Subsequently, an aqueous solution containing 0.35g of zirconyl nitrate was added dropwise to the above solution, and the reaction was completed until a gel was formed. The gel was aged at 50°C overnight, then dried at 100°C for 12 hours, and calcined at 500°C in a static air atmosphere for 4 hours to obtain the corresponding SG-1 carrier;

[0019] Example 2:

[0020] 20ml of tetraethyl orthosilicate was mixed with 20ml of ethanol, 10m of acetic acid, and 5ml of deionized water, placed in a flask equipped with a condenser and mechanical stirring, and pre-hydrolyzed under vigorous stirring and reflux for 6 hours. Subsequently, an aqueous solution containing 0.3g of zirconyl nitrate was added dropwise to the above solution, and the reaction was completed until a gel was formed. The gel was aged at 50°C overnight, then dried at 100°C for 12 hours, and calcined at 500°C in a static air atmosphere for 4 hours to obtain the corresponding SG-2 carrier;

[0021] Example 3:

[0022] 20ml of tetraethyl orthosilicate was mixed with 20ml of ethanol, 10m of acetic acid, and 5ml of deionized water, placed in a flask equipped with a condenser and mechanical stirring, and pre-hydrolyzed under vigorous stirring and reflux for 6 hours. Subsequently, an aqueous solution containing 0.26g of zirconyl nitrate was added dropwise to the above solution, and the reaction was completed until a gel was formed. The gel was aged at 50°C overnight, then dried at 100°C for 12 hours, and calcined at 500°C in a static air atmosphere for 4 hours to obtain the corresponding SG-3 carrier;

[0023] Example 4:

[0024] 20ml of tetraethyl orthosilicate was mixed with 20ml of ethanol, 10m of acetic acid, and 5ml of deionized water, placed in a flask equipped with a condenser and mechanical stirring, and pre-hydrolyzed under vigorous stirring and reflux for 6 hours. Subsequently, an aqueous solution containing 0.23g of zirconyl nitrate was added dropwise to the above solution, and the reaction was completed until a gel was formed. The gel was aged at 50°C overnight, then dried at 100°C for 12 hours, and calcined at 500°C in a static air atmosphere for 4 hours to obtain the corresponding SG-4 carrier;

[0025] Example 5:

[0026] 20ml of tetraethyl orthosilicate was mixed with 20ml of ethanol, 10m of acetic acid, and 5ml of deionized water, placed in a flask equipped with a condenser and mechanical stirring, and pre-hydrolyzed under vigorous stirring and reflux for 6 hours. Subsequently, an aqueous solution containing 0.20g of zirconyl nitrate was added dropwise to the above solution, and the reaction was completed until a gel was formed. The gel was aged at 50°C overnight, then dried at 100°C for 12 hours, and calcined at 500°C in a static air atmosphere for 4 hours to obtain the corresponding SG-5 carrier;

[0027] Example 6:

[0028] (1) Weigh 1.38 g of cesium nitrate and dissolve it in deionized water to obtain an active component impregnation solution. Sieve the carrier in Example (1) into 20-40 mesh particles, weigh 10 g of the 20-40 mesh carrier, pour it into the active component impregnation solution, stir thoroughly, and let it stand at room temperature for 4 hours;

[0029] (2) After impregnation, the catalyst precursor in (1) was transferred to an oven and dried at 120°C for 4 h. The dried catalyst precursor was then transferred to a muffle furnace and calcined at 500°C for 4 h to obtain the corresponding catalyst, which was designated as Cat-1.

[0030] Example 7:

[0031] (1) Weigh 1.38 g of cesium nitrate and dissolve it in deionized water to obtain an active ingredient impregnation solution. Sieve the carrier in Example (2) into 20-40 mesh particles, weigh 10 g of the 20-40 mesh carrier, pour it into the active ingredient impregnation solution, stir thoroughly, and let it stand at room temperature for 4 hours;

[0032] (2) After impregnation, the catalyst precursor in (1) was transferred to an oven and dried at 120°C for 4 h. The dried catalyst precursor was then transferred to a muffle furnace and calcined at 500°C for 4 h to obtain the corresponding catalyst, which was designated as Cat-2.

[0033] Example 8:

[0034] (1) Weigh 1.38 g of cesium nitrate and dissolve it in deionized water to obtain an active ingredient impregnation solution. Sieve the carrier in Example (3) into 20-40 mesh particles, weigh 10 g of the 20-40 mesh carrier, pour it into the active ingredient impregnation solution, stir thoroughly, and let it stand at room temperature for 4 hours;

[0035] (2) After impregnation, the catalyst precursor in (1) was transferred to an oven and dried at 120°C for 4 h. The dried catalyst precursor was then transferred to a muffle furnace and calcined at 500°C for 4 h to obtain the corresponding catalyst, which was designated as Cat-3.

[0036] Example 9:

[0037] (1) Weigh 1.38 g of cesium nitrate and dissolve it in deionized water to obtain an active ingredient impregnation solution. Sieve the carrier in Example (4) into 20-40 mesh particles, weigh 10 g of the 20-40 mesh carrier, pour it into the active ingredient impregnation solution, stir thoroughly, and let it stand at room temperature for 4 hours;

[0038] (2) After impregnation, the catalyst precursor in (1) was transferred to an oven and dried at 120°C for 4 h. The dried catalyst precursor was then transferred to a muffle furnace and calcined at 500°C for 4 h to obtain the corresponding catalyst, which was designated as Cat-4.

[0039] Example 10:

[0040] (1) Weigh 1.38 g of cesium nitrate and dissolve it in deionized water to obtain an active component impregnation solution. Sieve the carrier in Example (1) into 20-40 mesh particles, weigh 10 g of the 20-40 mesh carrier, pour it into the active component impregnation solution, stir thoroughly, and let it stand at room temperature for 4 hours;

[0041] (2) After impregnation, the catalyst precursor in (1) was transferred to an oven and dried at 120°C for 4 h. The dried catalyst precursor was then transferred to a muffle furnace and calcined at 500°C for 4 h to obtain the corresponding catalyst, which was designated as Cat-5.

[0042] Comparative Example 1:

[0043] (1) Weigh 0.56 g of zirconium oxynitrate and add it to 9 mL of deionized water and stir to dissolve it to obtain impregnation solution A;

[0044] (2) Weigh 10 g of 20-40 mesh SiO2 carrier, add it to the impregnation solution prepared in (1), shake it evenly, and then let it stand at room temperature for 4-6 hours; after the impregnation is completed, transfer it to a blast drying oven, dry it at 120°C for 4 hours, and then transfer it to a muffle furnace, raise the temperature to 500°C at a heating rate of 10°C / min and calcine it for 4 hours to obtain SG-6 catalyst precursor;

[0045] Comparative Example 2:

[0046] (1) Weigh 1.38 g of cesium nitrate and add it to 9 mL of deionized water, stirring and dissolving to obtain impregnation solution B;

[0047] (5) Weigh 10 g of the catalyst precursor of Comparative Example (1), add it to the impregnation solution prepared in (1), shake it evenly, and then let it stand at room temperature for 4-6 hours, then transfer it to a forced air drying oven at 120°C for 4 hours, and finally calcine it in a muffle furnace at 500°C for 4 hours to obtain a catalyst, which is recorded as Cat-6;

[0048] Application Example: Micromeritics ASAP 2460 automatic physical adsorption instrument was used to characterize the specific surface area and pore structure characteristics of the sample. The conventional operation steps are as follows: First, 100 mg of catalyst (particle size 20-40 mesh) was placed in a BET sample tube and heated at 300 ° C and vacuum degree 10 -3 The samples were pretreated under Pa conditions for 4 hours to completely remove surface adsorbed water and volatile impurities. Subsequently, the samples were subjected to N2 adsorption-desorption experiments in a liquid nitrogen tank. The specific surface area, pore volume and pore size distribution of the samples were calculated by BET and BJH methods. The detailed data are shown in Table 1. The activity of different catalysts was evaluated by a fixed bed reactor with a catalyst loading of 6 ml, a molar ratio of methyl propionate / formaldehyde / methanol of 2:1:2, and an air velocity of 0.8 h -1 , the reaction temperature was 370℃, the results are shown in Table 2

[0049] Table 1: Carrier structural properties

[0050]

[0051] Table 2: Catalyst activity evaluation results

[0052]

[0053]

[0054] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing an aldol condensation catalyst by in-situ doping to construct a Si-O-Zr framework, characterized in that: The following steps are involved: (1) mixing a silicon source compound with a solvent and pre-hydrolyzing the mixture under acidic conditions of pH 1-3 for 3-12 hours to obtain a silica sol; adding a zirconium source compound solution dropwise to adjust the pH of the system to 3-4 to form a zirconium-silicon composite gel; The hydrolysis / condensation rates of the zirconium source and the silicon source are matched, so that the Zr atoms are embedded in the silica skeleton through Si-O-Zr bonds to form an atomic-level dispersed structure; (2) aging the composite gel obtained in step (1) at 40-80° C. for 3-24 hours, drying, and calcining at 400-600° C. for 4-6 hours to obtain a Zr-doped SiO2 carrier; (3) dissolving the cesium salt in deionized water to prepare an impregnation solution, loading the solution onto the support obtained in step (2) by an equal volume impregnation method, and drying and calcining at 400-600° C. to obtain a Cs-based acid-base bifunctional catalyst.

2. The method according to claim 1, characterized in that In step (1), the silicon source is selected from at least one of ethyl orthosilicate and methyl orthosilicate; the solvent is selected from at least one of anhydrous ethanol and methanol; and the acidic condition is adjusted by nitric acid, hydrochloric acid or acetic acid.

3. The method according to claim 1, characterized in that In step (1), the zirconium source compound is selected from one of zirconium nitrate, zirconium oxychloride, zirconium oxynitrate and zirconium acetylacetonate, and its addition amount is determined based on the molar ratio of Si in the silicon source compound to Zr in the zirconium source being 40-100.

4. The method according to claim 1, wherein In step (3), the cesium salt is selected from one of cesium nitrate, cesium acetate, cesium carbonate and cesium hydroxide, and the loading amount is 1-15 wt.% based on cesium oxide.

5. The method according to claim 1, characterized in that In step (1), the pre-hydrolysis temperature is 50-80° C., and the aging time is 6-12 hours.

6. The method according to claim 1, characterized in that In step (3), the immersion time is 4-8 hours, and the calcination heating rate is 2-10°C / min.

7. An aldol condensation catalyst prepared by the method according to any one of claims 1 to 6, characterized in that The catalyst comprises: (1) Zr is embedded in the SiO2 framework in a four-coordinated manner to form Lewis acid sites; (2) Cs reacts with surface silanol groups to form basic sites on the support surface; (3) Specific surface area is 300-600m 2 / g, and the pore size distribution is 0.5-1.5nm.

8. The use of the aldol condensation catalyst according to claim 1, characterized in that: For the preparation of methyl methacrylate from formaldehyde and methyl propionate, a fixed-bed reaction tube is loaded with an aldol condensation catalyst, the reaction temperature is 300-400°C, the reaction pressure is atmospheric pressure, and a mixed liquid of methyl propionate, methanol and formaldehyde source in a certain molar ratio is passed into the fixed bed, wherein the formaldehyde source is trioxymethylene, the propionic acid / formaldehyde ratio is 1:1-8:1, and the methanol / formaldehyde ratio is 1:1-5:

1. The liquid hourly space velocity of the feed is 0.2-1.5h -1 .

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