Mesoporous nanosphere acid-base bifunctional catalyst for synthesizing methyl methacrylate and preparation method of mesoporous nanosphere acid-base bifunctional catalyst

Abstract

The invention provides a mesoporous nanosphere acid-base bifunctional catalyst for synthesizing methyl methacrylate and a preparation method of the mesoporous nanosphere acid-base bifunctional catalyst. The acidic metal ions are introduced into the skeleton of the mesoporous MCM-41 carrier as a modifier, the alkaline active site Cs species are loaded, and the good acid-base balance degree is achieved by regulating and controlling the proportion of the CS species and the acidic metal ions. The composition of the catalyst is Csa / Xb-MCM-41, X is selected from one or two of Zr, Ti, Al, La, Ce and Fe, and a is the mass fraction of Cs species calculated on the basis of a carrier and is 0.08-0.30 in terms of Cs2O; and b is the mass fraction of the oxide corresponding to the element X in the MCM-41 carrier, and is 0.04-0.20. When the catalyst provided by the invention is used for synthesizing methyl methacrylate through reaction of methyl propionate and formaldehyde, excellent catalytic activity and carbon deposition resistance are shown.

Description

Technical Field

[0001] The invention relates to a catalyst for aldol condensation reaction and a preparation method thereof, and in particular to a mesoporous nanosphere acid-base bifunctional catalyst for synthesizing methyl methacrylate from methyl propionate and formaldehyde and a preparation method thereof. Background Art

[0002] Methyl methacrylate (MMA) is an important chemical raw material and polymer intermediate, widely used in organic glass, plastic modifiers, lubricant additives, surface coatings, and printing and dyeing auxiliaries. Due to the rapid development of its application areas, global demand for MMA is growing, showing broad market prospects.

[0003] The main synthetic routes for MMA include the acetone cyanohydrin method (ACH method), the C4 route isobutylene / tert-butyl alcohol oxidation method, the C2 route ethylene carbonylation method (BASF method), and the ethylene-methyl propionate method (Alpha method). The traditional ACH method is simple, mature, and offers high yields. However, the raw material hydrocyanic acid used in this process is highly toxic, and it also produces a large amount of ammonium bisulfate waste liquid, which is expensive to handle. Furthermore, the process equipment corrodes severely, potentially causing environmental pollution. The isobutylene / tert-butyl alcohol oxidation method offers high MMA yields and few byproducts, but requires high catalyst preparation requirements, resulting in higher investment and production costs. The ethylene carbonylation method offers high atom utilization and a simpler process, but its catalyst life is short, product selectivity is poor, and production costs are higher than the isobutylene oxidation method. The Alpha method offers mild reaction conditions, non-corrosive raw materials and intermediates to equipment, and high atom economy. Compared with the ACH and isobutylene oxidation methods, it can reduce costs by 30-40%, demonstrating significant competitiveness.

[0004] The Alpha process uses ethylene, CO, and methanol as raw materials to react and produce methyl propionate (MP). MP then reacts with formaldehyde (FA) to produce MMA. The key to this technology lies in the development of a catalyst for the aldol condensation of MP and FA. The current industrial catalyst used is a supported catalyst developed by Lucite, which uses SiO2 as a carrier and Cs as the active component. However, this catalyst suffers from low catalytic activity and yield (MP conversion is 11%, and MMA yield is only around 10%). Furthermore, the presence of water in the reaction reduces the surface area of ​​the SiO2 carrier, leading to a continuous decline in activity. Furthermore, the presence of double-bond compounds such as methyl methacrylate and formaldehyde in this reaction system easily forms carbon deposits on the catalyst surface. The accumulation of carbon deposits ultimately leads to catalyst deactivation and a shortened lifespan.

[0005] In response to the above problems, researchers have conducted modification studies on the above catalysts. The main method is to introduce active additives and anti-carbon deposition additives into the active components. For example, Chinese patent CN106423159B discloses amorphous SiO2 as a carrier, and the addition of La, Ce, Nd, Pr and Pm active additives and Pt, Rh, Ru, Pd, Ir, Fe, Co and Ni oxides, chlorides, nitrates, carbonates and organic acid salts as anti-carbon deposition agents to the Cs active component. Chinese patent CN107175094B discloses a method using a composite carrier of amorphous SiO2 and TiO2 as a carrier, and the addition of Na, K, Mg, Ca, Ba and other active additives to the Cs active component. Chinese patent CN116262239B discloses a catalyst using bio-based amorphous SiO2 as a carrier, with active components consisting of one or more of Li, Na, K, Cs, Sr, and Ba, and additives consisting of one or more of V, Nb, La, Fe, W, Zr, and Sn. Compared to industrial catalysts, this catalyst exhibits improved catalytic activity and carbon deposition resistance. However, modification of these catalysts typically involves adding active additives or anti-carbon deposition agents to the catalyst surface. These added components occupy a certain number of active sites, thus limiting the improvement in catalytic activity. Furthermore, the added additives have a weak interaction with the active components, which can easily lead to loss of these components or additives, resulting in a decrease in catalytic performance. Furthermore, anti-carbon deposition agents have limited effectiveness in inhibiting the polymerization of substances such as methyl methacrylate and formaldehyde, and cannot fundamentally address the occurrence of carbon deposition. Therefore, developing highly active and stable aldol condensation catalysts for the synthesis of MMA from MP and FA remains a significant challenge. Summary of the Invention

[0006] The present invention aims to provide a mesoporous nanosphere acid-base bifunctional catalyst for the preparation of MMA by the aldol condensation of MP and FA, and a preparation method thereof. Based on the acid-base synergistic catalytic reaction mechanism of MMA synthesis and the assumption that the acid-base balance of a catalyst is the key to catalytic activity, the present invention introduces an acidic species into a carrier and regulates the addition amount to impart an acid strength suitable for FA activation. This catalyst is then combined with an alkaline active species of suitable base strength capable of activating MP to synthesize a bifunctional catalyst with acid-base synergistic catalysis. Furthermore, the innovative introduction of a mesoporous carrier into the reaction system increases the diffusion rate of reactants, intermediates, and products, essentially inhibiting deep condensation at active sites and thus preventing carbon deposition.

[0007] In order to achieve the above-mentioned purpose, the present invention introduces acidic metal ions as modifiers into the skeleton of the mesoporous MCM-41 carrier, and loads Cs species as alkaline active sites. SThe ratio of the species and the acidic metal ions is adjusted to achieve a good acid-base balance. By using templates of different chain lengths, the pore size of the mesopores can be regulated, thereby synthesizing an ordered mesoporous nanosphere acid-base bifunctional catalyst. The preparation method of the present invention is simple, the raw material cost is low, and the prepared catalyst has excellent catalytic activity and anti-carbon deposition performance.

[0008] The technical solutions of the present invention are as follows:

[0009] A mesoporous nanosphere acid-base bifunctional catalyst for synthesizing methyl methacrylate, characterized in that the catalyst expression is Cs a / X b -MCM-41, wherein X is selected from one or two of the elements Zr, Ti, Al, La, Ce or Fe, a is the mass fraction of Cs species calculated based on the support, which is 0.08 to 0.30 in terms of Cs2O, and b is the mass fraction of the oxide corresponding to element X in the MCM-41 support, which is 0.04 to 0.20.

[0010] The mesoporous nanosphere acid-base dual-function catalyst has a catalyst particle size of 10 to 200 nm and a specific surface area of ​​500 to 1500 m 2 / g, and the mesopore diameter is 2 to 10 nm.

[0011] The mesoporous nanosphere acid-base dual-function catalyst includes one of the following structures:

[0012] Cs a / Zr b -MCM-41, Cs a / Ti b -MCM-41, Cs a / Al b -MCM-41, Cs a / La b -MCM-41, Cs a / Ce b -MCM-41, Cs a / Fe b -MCM-41, Cs a / Zr b -Ce b -MCM-41, Cs a / Fe b -La b -MCM-41.

[0013] The preparation method of the mesoporous nanosphere acid-base dual-function catalyst for synthesizing methyl methacrylate of the present invention comprises the following steps:

[0014] (1) Weigh trimethylamine halide C n H2n+1 N(CH3)3 + Y - The surfactant is used as a template and is dispersed in deionized water under magnetic stirring to form a trimethylamine halide dispersion, and then an alkali source is added to obtain an alkaline surfactant solution;

[0015] (2) Weighing an inorganic salt / organic salt containing acidic metal ions as an acidic metal ion precursor, dissolving it in deionized water or ethanol, and then introducing it dropwise into the alkaline surfactant solution obtained in step (1), and then adding a silicon source to react; transferring the resulting reaction solution to a stainless steel hydrothermal kettle with a polytetrafluoroethylene liner for hydrothermal aging; after the reaction is completed, filtering the reaction solution and washing it with deionized water and ethanol until it is neutral, and placing it in an oven to dry overnight to obtain an acidic metal ion-modified MCM-41 mesoporous molecular sieve precursor;

[0016] (3) calcining the precursor obtained in step (2) under air atmosphere to obtain a nano-spherical carrier having hexagonal ordered mesopores;

[0017] (4) Weighing a cesium source precursor and dissolving it in deionized water to form a cesium metal ion solution, weighing the nano-spherical support obtained in step (3) and impregnating it in the cesium metal ion solution, and performing shaking impregnation under heating conditions; after the reaction is completed, filtering the reaction solution and washing it with deionized water, and placing it in an oven to dry overnight to obtain a catalyst precursor with an acidic metal ion-modified MCM-41 as a support and a Cs active component loaded thereon;

[0018] (5) calcining the precursor obtained in step (4) under air atmosphere to obtain a mesoporous nanosphere acid-base dual-functional catalyst.

[0019] In the step (1), trimethylamine halide C n H 2n+1 N(CH3)3 + Y - wherein Y is Cl or Br, and n is 8 to 18; the inorganic salt / organic salt containing acidic metal ions is one or two of the nitrates, carbonates, acetates, propoxides, and fatty acid salts of the corresponding metals of Zr, Ti, Al, La, Ce, and Fe.

[0020] In the step (1), the alkali source is selected from sodium hydroxide, tetramethylammonium hydroxide or ammonia water; and the pH of the solution is adjusted to a range of 10 to 13.

[0021] In the step (2), the silicon source is selected from tetraethyl silicate and silica sol; the molar ratio of the silicon source to the trimethylamine halide template is 1:0.4 to 1:0.05, the hydrothermal temperature is 90 to 160° C., and the aging time is 6 to 72 hours.

[0022] In the step (3), the calcination temperature is 400-600° C., and the calcination time is 4-12 hours.

[0023] In the step (4), the cesium source precursor is selected from cesium carbonate, cesium nitrate, cesium acetate or cesium hydroxide; the reaction temperature is 25-60° C., and the reaction time is 4-12 hours.

[0024] The mass ratio of the amount of the cesium source precursor added in step (4) to the amount of the acidic metal ion precursor added in step (2) is in the range of 1:0.2 to 1:1.2.

[0025] In the step (5), the calcination temperature is 400-600° C., and the calcination time is 3-10 hours.

[0026] The present invention discloses a method for preparing a mesoporous nanosphere acid-base bifunctional catalyst for producing MMA by condensing MP and FA. The method comprises introducing an acidic metal ion additive into an MCM-41 precursor for modification, further hydrothermal aging the precursor to obtain a modified MCM-41 precursor, and then calcining the precursor at high temperature to obtain an MCM-41 support modified with acidic metal ions. The modified support is then immersed in a deionized aqueous solution containing cesium metal ions, and a Cs active species is loaded on the surface of the modified support to obtain a catalyst precursor. After the reaction is complete, the precursor is calcined at high temperature to obtain a supported catalyst with the acidic metal ion-modified MCM-41 as the support and the Cs species as the active component.

[0027] The MCM-41 precursor described above can be obtained by reacting a publicly reported template and a silicon source in an alkaline solution. The template can be a trimethylamine halide with different hydrophobic chain lengths.

[0028] The acidic metal ion-modified MCM-41 loaded Cs active component nanosphere acid-base bifunctional catalyst needs to be prepared through hydrothermal treatment and calcination, and the prepared nanoscale catalyst has ordered hexagonal mesopores.

[0029] The catalyst prepared by the present invention is specifically used in the condensation reaction of MP and FA to produce MMA. The method involves loading catalyst sample particles into the constant temperature zone in the middle of the tubular reactor, equipped with a preheater and a reactor, and embedding a temperature measuring point therein. N2 carrier gas is introduced from the preheater into the reactor. A mixed raw material of MP, FA, and CH3OH at a fixed molar ratio of 1:1:1.5 is then vaporized and mixed in the preheater using a micropump and injected into the reactor along with the carrier gas for reaction. The content of the product to be stabilized by the reaction is determined by chromatography. Calculations indicate that when the catalyst of the present invention is used in the MMA synthesis reaction, the conversion of MP exceeds 25% and the selectivity of MMA exceeds 85%.

[0030] Compared with the prior art, the advantages of the present invention are:

[0031] (1) The acidic metal ions are introduced into the mesoporous MCM-41 carrier by the sol-gel method. Compared with the specific surface area of ​​the SiO2 carrier in the industrial catalyst, the specific surface area of ​​the MCM-41 carrier is 200-400 m 2 / g increases to 900~1100m 2 / g, and effectively solves the problem of the carrier's specific surface area being reduced due to hydrolysis of water in the reaction system.

[0032] (2) Compared to catalysts modified by the impregnation method, the acid-base bifunctional catalyst prepared by the present invention, which is a modified MCM-41 with an acidic metal ion skeleton and loaded with an alkaline active component, can more effectively modulate the acid-base properties of the support, reduce the adsorption competition between the acidic metal ions and the alkaline active species on the support surface, and promote the high dispersion of the alkaline active species. In addition, the Si-OH groups in the modified MCM-41 support and the alkaline component Cs can form Si-O-Cs chemical bonds, thereby significantly enhancing the interaction between the active component and the support and improving the catalyst stability.

[0033] (3) The acid-base bifunctional catalyst prepared by the present invention has a hexagonal ordered mesoporous structure, which can significantly improve the mass transfer efficiency of reactants and products by regulating the confinement effect of the mesopores, thereby inhibiting the deep condensation of substances such as MMA and FA at the active sites of the catalyst to generate macromolecular substances such as aromatic hydrocarbons and alicyclic hydrocarbons, essentially inhibiting the occurrence of carbon deposition, achieving the purpose of improving the catalyst's anti-carbon deposition performance and extending the service life of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the XRD pattern of the catalyst prepared in Example 4.

[0035] Figure 2 This is the TEM image of the catalyst prepared in Example 4. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto:

[0037] The catalyst prepared by the present invention is an acidic metal ion modified mesoporous MCM-41 with adjustable pore size loaded with Cs active component nanosphere acid-base dual-function catalyst. a / X b-MCM-41, where X is selected from one or two elements of Zr, Ti, Al, La, Ce, and Fe; a is the mass fraction of the Cs species based on the support (calculated as Cs2O), which is 0.08-0.30; and b is the mass fraction of the oxide corresponding to element X in the MCM-41 support, which is 0.04-0.20. Based on the above composition, a more representative catalyst expression is as follows:

[0038] Cs a / Zr b -MCM-41

[0039] Cs a / Ti b -MCM-41

[0040] Cs a / Al b -MCM-41

[0041] Cs a / La b -MCM-41

[0042] Cs a / Ce b -MCM-41

[0043] Cs a / Fe b -MCM-41

[0044] Cs a / Zr b -Ce b -MCM-41

[0045] Cs a / Fe b -La b -MCM-41

[0046] The catalyst precursor is calcined and the Cs source precursor loaded on the carrier surface is decomposed to finally obtain an acidic metal ion modified MCM-41 loaded Cs active component nanosphere acid-base bifunctional catalyst with a particle size of 10 to 200 nm and a specific surface area of ​​500 to 1500 m 2 / g of ordered mesoporous nanosphere acid-base bifunctional catalyst.

[0047] The method for preparing an ordered mesoporous nanosphere acid-base bifunctional catalyst for preparing MMA by condensing MP and FA according to an embodiment of the present invention includes the following steps:

[0048] (1) Weigh trimethylamine halide C n H 2n+1 N(CH3)3 + Y- The surfactant is used as a template and is dispersed in deionized water under magnetic stirring to form a trimethylamine halide dispersion, and then an alkali source is added to obtain an alkaline surfactant solution;

[0049] (2) Weighing an inorganic salt / organic salt containing acidic metal ions as an acidic metal ion precursor, dissolving it in deionized water or ethanol, and then introducing it dropwise into the alkaline surfactant solution obtained in step (1), and then adding a silicon source to react; transferring the resulting reaction solution to a stainless steel hydrothermal kettle with a polytetrafluoroethylene liner for hydrothermal aging; after the reaction is completed, filtering the reaction solution and washing it with deionized water and ethanol until it is neutral, and placing it in an oven to dry overnight to obtain an acidic metal ion-modified MCM-41 mesoporous precursor;

[0050] (3) The precursor obtained in step (2) is calcined in an air atmosphere to obtain nanosphere carriers with hexagonal ordered mesopores, and the mesopore diameter can be controlled by changing the hydrophobic chain length of the trimethylamine halide template agent, and the pore diameter range is 2 to 10 nm, thereby achieving different confinement effects and regulating the diffusion rate of reactants and products.

[0051] (4) Weighing a cesium source precursor and dissolving it in ionized water to form a cesium metal ion solution, weighing the nano-spherical carrier obtained in step (3) and immersing it in the cesium metal ion solution, and shaking the immersion under heating conditions; after the reaction is completed, filtering the reaction solution and washing it with deionized water, and placing it in an oven to dry overnight, thereby obtaining a catalyst precursor with acidic metal ion-modified MCM-41 as a carrier and loaded with Cs active components.

[0052] (5) calcining the precursor obtained in step (4) in an air atmosphere to obtain an acid-base bifunctional catalyst having ordered mesoporous nanospheres.

[0053] Furthermore, in the step (1), trimethylamine halide C n H 2n+1 N(CH3)3 + Y - (Y=Cl or Br, n=8-18), the inorganic salt / organic salt containing acidic metal ions is one or two of the nitrates, carbonates, acetates, propoxides, and fatty acid salts of the corresponding metals of Zr, Ti, Al, La, Ce, and Fe.

[0054] Furthermore, in step (1), the alkali source is selected from sodium hydroxide, tetramethylammonium hydroxide, ammonia water, etc., and the pH of the solution is adjusted to a range of 10 to 13. In step (2), the silicon source is selected from tetraethyl silicate, silica sol, etc., the molar ratio of the silicon source to the trimethylamine halide template is 1:0.4 to 1:0.05, the hydrothermal temperature is 90 to 160° C., and the aging time is 6 to 72 hours.

[0055] Furthermore, in step (3), the calcination temperature is 400-600° C., and the calcination time is 4-12 hours.

[0056] Furthermore, in step (4), the cesium source precursor is selected from cesium carbonate, cesium nitrate, cesium acetate, cesium hydroxide, etc., the reaction temperature is 25-60° C., and the reaction time is 4-12 hours.

[0057] Furthermore, in step (5), the calcination temperature is 400-600° C., and the calcination time is 3-10 hours.

[0058] Furthermore, the acid-base balance is determined by analyzing the number of acidic sites and basic sites using NH3-TPD and CO2-TPD. In order to achieve a good acid-base balance effect, the mass ratio of the amount of the cesium source precursor added in step (4) to the amount of the acidic metal ion precursor added in step (2) is in the range of 1:0.2 to 1:1.2.

[0059] Example 1

[0060] Under magnetic stirring, 6.0 g of cationic surfactant hexadecyltrimethylammonium bromide was first weighed and dissolved in 280 mL of water. After complete dissolution, 24 mL of ammonia water was introduced to adjust the pH value of the solution to 11 to obtain an alkaline surfactant solution.

[0061] 1.44 g of zirconium n-propoxide was weighed and dispersed in 30 mL of ethanol. After ultrasonication for 30 min, stirring was continued at room temperature for 2 h. The obtained solution was added dropwise to the alkaline surfactant solution. After stirring for 15 min, 25 mL of tetraethyl silicate was added dropwise. The reaction was maintained at a constant speed at 35 ° C for 4 h and then transferred to a stainless steel hydrothermal autoclave with a polytetrafluoroethylene liner. After hydrothermal aging at 100 ° C for 18 h, the obtained product was filtered and washed until neutral and then dried in an oven at 120 ° C overnight to obtain a Zr metal ion-modified MCM-41 precursor.

[0062] The precursor was calcined at 550 °C in air atmosphere for 6 h to obtain Zr metal ion modified Zr 0.08 -MCM-41 vector.

[0063] 1.80 g of cesium nitrate was weighed and dissolved in deionized water to form a cesium nitrate solution. 10.0 g of Zr-MCM-41 carrier was impregnated into the cesium nitrate solution and shaken at 25 ° C for 12 h. After the reaction was completed, the reaction solution was filtered, washed and placed in an oven at 120 ° C overnight to obtain Cs active component loaded Cs 0.13 / Zr 0.08 -MCM-41 catalyst precursor.

[0064] The precursor was calcined at 550 ° C in air atmosphere for 5 h to obtain a nano-spherical acid-base bifunctional catalyst with ordered mesopores. After grinding, tableting and screening, the catalyst Cs 0.13 / Zr 0.08 -MCM-41.

[0065] In an atmospheric-pressure tubular fixed-bed reactor equipped with a preheater and reactor, approximately 5.0 g (10.0 mL) of catalyst sample pellets were loaded into the constant temperature zone in the middle of the tubular reactor, where a temperature measuring point was embedded. N₂ at 100 mL / min was introduced from the preheater into the reactor. A mixture of methyl propionate, formaldehyde, and methanol in a molar ratio of 1:1:1.5 was then vaporized and mixed in the preheater using a micropump and injected into the reactor along with a carrier gas. After the reaction system stabilized, the gaseous products were liquefied via a circulating condensation system and analyzed by gas chromatography (FID). The low-boiling tail gas was analyzed by gas chromatography (TCD). Catalytic performance evaluation of the catalyst revealed a 26.8% conversion of MP and an 88.2% selectivity for MMA. The catalyst activity remained unchanged after 300 hours of continuous operation.

[0066] Example 2

[0067] Under magnetic stirring, 6.0 g of cationic surfactant hexadecyltrimethylammonium bromide was first weighed and dissolved in 280 mL of water. After complete dissolution, 24 mL of ammonia water was introduced to adjust the pH value of the solution to 11 to obtain an alkaline surfactant solution.

[0068] 2.16 g of zirconium n-propoxide was weighed and dispersed in 40 mL of ethanol. After ultrasonication for 45 minutes, stirring was continued at room temperature for 2 hours. The obtained solution was added dropwise to the alkaline surfactant solution. After stirring for 15 minutes, 25 mL of tetraethyl silicate was added dropwise. The reaction was maintained at a constant speed at 35 ° C for 4 hours and then transferred to a stainless steel hydrothermal autoclave with a polytetrafluoroethylene liner. After hydrothermal aging at 100 ° C for 18 hours, the obtained product was filtered and washed until neutral and then dried in an oven at 120 ° C overnight to obtain a Zr metal ion-modified MCM-41 precursor.

[0069] The precursor was calcined at 400 °C in air atmosphere for 12 h to obtain Zr metal ion modified Zr 0.12 -MCM-41 vector.

[0070] Weigh 2.49 g of cesium nitrate and dissolve it in deionized water to form a cesium nitrate solution. Then, 10.0 g of Zr-MCM-41 carrier was impregnated into the cesium nitrate solution and shaken at 60 ° C for 8 h. After the reaction was completed, the reaction solution was filtered, washed, and dried in an oven at 120 ° C overnight to obtain Cs active component loaded Cs. 0.18 / Zr 0.12-MCM-41 catalyst precursor.

[0071] The precursor was calcined at 600 ° C in air atmosphere for 3 h to obtain a nano-spherical acid-base bifunctional catalyst with ordered mesopores. After grinding, tableting and screening, the catalyst Cs 0.18 / Zr 0.12 -MCM-41.

[0072] The evaluation method of the prepared catalyst was the same as that in Example 1. The catalytic performance evaluation of the catalyst showed that the conversion rate of MP was 31.6%, the selectivity of MMA was 86.8%, and the activity of the catalyst remained unchanged after 300 hours of continuous operation.

[0073] Example 3

[0074] Under magnetic stirring, 3.6 g of cationic surfactant octadecyltrimethylammonium bromide was first weighed and dissolved in 300 mL of water. After complete dissolution, 1.2 g of sodium hydroxide was introduced to adjust the pH value of the solution to 13 to obtain an alkaline surfactant solution.

[0075] 1.43 g of titanium isopropoxide was weighed and dispersed in 40 mL of ethanol. After ultrasonication for 30 min, stirring was continued at room temperature for 1 h. The obtained solution was added dropwise to the alkaline surfactant solution. After stirring for 15 min, 25.4 g of silica sol industrial reagent (mass fraction 26.5%) was added dropwise. The reaction was maintained at a constant speed at 35 ° C for 6 h and then transferred to a stainless steel hydrothermal autoclave with a polytetrafluoroethylene liner. After hydrothermal aging at 90 ° C for 72 h, the obtained product was filtered and washed until neutral and then dried in an oven at 120 ° C overnight to obtain a Ti metal ion-modified MCM-41 precursor.

[0076] The precursor was calcined at 550 °C in air atmosphere for 8 h to obtain Ti metal ion modified Ti 0.06 -MCM-41 vector.

[0077] Weigh 1.38g of cesium hydroxide and dissolve it in deionized water to form a cesium hydroxide solution. 0.06 -MCM-41 support was impregnated into cesium hydroxide solution and shaken at 45℃ for 6h. After the reaction was completed, the reaction solution was filtered and washed and placed in an oven at 120℃ to dry overnight to obtain Cs active component loaded Cs 0.13 / Ti 0.06 -MCM-41 catalyst precursor.

[0078] The precursor was calcined at 500 ° C in air atmosphere for 6 h to obtain a nano-spherical acid-base bifunctional catalyst with ordered mesopores. After grinding, tableting and screening, the catalyst Cs 0.13 / Ti0.06 -MCM-41.

[0079] The evaluation method of the prepared catalyst was the same as that in Example 1. The catalytic performance evaluation of the catalyst showed that the conversion rate of MP was 25.3%, the selectivity of MMA was 85.8%, and the activity of the catalyst remained unchanged after 300 hours of continuous operation.

[0080] Example 4

[0081] Under magnetic stirring, 6.0 g of cationic surfactant hexadecyltrimethylammonium bromide was first weighed and dissolved in 260 mL of water. After complete dissolution, 24 mL of ammonia water was introduced to adjust the pH value of the solution to 12 to obtain an alkaline surfactant solution.

[0082] 1.08 g of aluminum isopropoxide was weighed and dispersed in 28 mL of ethanol. After ultrasonication for 15 min, stirring was continued at room temperature for 1 h. The obtained solution was added dropwise to the alkaline surfactant solution. After stirring for 15 min, 25 mL of tetraethyl silicate was added dropwise. The reaction was maintained at a constant speed at 35 ° C for 3 h and then transferred to a stainless steel hydrothermal autoclave with a polytetrafluoroethylene liner. After hydrothermal aging at 100 ° C for 56 h, the obtained product was filtered and washed until neutral and then dried in an oven at 120 ° C overnight to obtain an Al metal ion-modified MCM-41 precursor.

[0083] The precursor was calcined at 600℃ in air atmosphere for 5h to obtain Al metal ion modified Al 0.04 -MCM-41 vector.

[0084] 1.74 g of cesium carbonate was weighed and dissolved in deionized water to form a cesium carbonate solution. 10.0 g of Al-MCM-41 support was impregnated into the cesium carbonate solution and shaken at 30 ° C for 12 h. After the reaction was completed, the reaction solution was filtered, washed, and dried in an oven at 120 ° C overnight to obtain Cs active component loaded Cs 0.15 / Al 0.04 -MCM-41 catalyst precursor.

[0085] The precursor was calcined at 550 ° C in air atmosphere for 8 h to obtain a nano-spherical acid-base bifunctional catalyst with ordered mesopores. After grinding, tableting and screening, the catalyst Cs 0.15 / Al 0.04 -MCM-41. XRD and TEM of the prepared catalyst are as follows Figure 1 、 Figure 2 shown.

[0086] The evaluation method of the prepared catalyst was the same as that in Example 1. The catalytic performance evaluation of the catalyst showed that the MP conversion rate was 30.2% and the MMA selectivity was 91.3%. After continuous operation for 300 hours, the activity of the catalyst remained unchanged.

[0087] Example 5

[0088] Under magnetic stirring, 6.0 g of cationic surfactant hexadecyltrimethylammonium bromide was first weighed and dissolved in 260 mL of water. After complete dissolution, 24 mL of ammonia water was introduced to adjust the pH value of the solution to 11 to obtain an alkaline surfactant solution.

[0089] 2.6 g of aluminum isopropoxide was weighed and dispersed in 40 mL of ethanol. After ultrasonication for 30 min, stirring was continued at room temperature for 1 h. The obtained solution was added dropwise to the alkaline surfactant solution. After stirring for 15 min, 25 mL of tetraethyl silicate was added dropwise. The reaction was maintained at a constant speed at 35 ° C for 3 h and then transferred to a stainless steel hydrothermal autoclave with a polytetrafluoroethylene liner. After hydrothermal aging at 160 ° C for 6 h, the obtained product was filtered and washed until neutral and then dried in an oven at 120 ° C overnight to obtain an Al metal ion-modified MCM-41 precursor.

[0090] The precursor was calcined at 600℃ in air atmosphere for 10h to obtain Al metal ion modified Al 0.1 -MCM-41 vector.

[0091] 2.31 g of cesium carbonate was weighed and dissolved in deionized water to form a cesium carbonate solution. 10.0 g of Al-MCM-41 support was impregnated into the cesium carbonate solution and shaken at 50 ° C for 6 h. After the reaction was completed, the reaction solution was filtered and washed and placed in an oven at 120 ° C overnight to obtain Cs active component loaded Cs 0.2 / Al 0.1 -MCM-41 catalyst precursor.

[0092] The precursor was calcined at 550 ° C in air atmosphere for 8 h to obtain a nano-spherical acid-base bifunctional catalyst with ordered mesopores. After grinding, tableting and screening, the catalyst Cs 0.2 / Al 0.1 -MCM-41.

[0093] The evaluation method of the prepared catalyst was the same as that in Example 1. The catalytic performance evaluation of the catalyst showed that the MP conversion rate was 31.9% and the MMA selectivity was 90.4%. After continuous operation for 300 hours, the activity of the catalyst remained unchanged.

[0094] Example 6

[0095] Under magnetic stirring, first weigh 1.8 g of cationic surfactant dodecyltrimethylammonium bromide and dissolve it in 300 mL of water. After complete dissolution, introduce 1.2 mL of tetramethylammonium hydroxide solution (25 wt %) and adjust the pH value of the surfactant aqueous solution to 12 to obtain an alkaline surfactant solution.

[0096] 0.54 g of lanthanum nitrate was weighed and dispersed in 40 mL of deionized water. After ultrasonication for 15 minutes, stirring was continued at room temperature for 1 hour. The obtained solution was added dropwise to the alkaline surfactant solution. After stirring for 15 minutes, 25 mL of tetraethyl silicate was added dropwise. The reaction was maintained at a constant speed at 35 ° C for 3 hours and then transferred to a stainless steel hydrothermal autoclave with a polytetrafluoroethylene liner. After hydrothermal aging at 90 ° C for 72 hours, the obtained product was filtered and washed until neutral and then dried in an oven at 120 ° C overnight to obtain a La metal ion-modified MCM-41 precursor.

[0097] The precursor was calcined at 450 °C in air atmosphere for 12 h to obtain La metal ion modified mesoporous La 0.04 -MCM-41 vector.

[0098] Weigh 2.18g of cesium acetate and dissolve it in deionized water to form a cesium acetate solution. 0.04 -MCM-41 support was immersed in cesium acetate solution and shaken at 25℃ for 12h. After the reaction was completed, the reaction solution was filtered and washed and placed in an oven at 120℃ to dry overnight to obtain Cs active component loaded Cs 0.16 / La 0.04 -MCM-41 catalyst precursor.

[0099] The precursor was calcined at 400 ° C in air atmosphere for 10 h to obtain a nano-spherical acid-base bifunctional catalyst with ordered mesopores. After grinding, tableting and screening, the catalyst Cs 0.16 / La 0.04 -MCM-41.

[0100] The evaluation method of the prepared catalyst was the same as that in Example 1. The catalytic performance evaluation of the catalyst showed that the conversion rate of MP was 28.8%, the selectivity of MMA was 90.8%, and the activity of the catalyst remained unchanged after 300 hours of continuous operation.

[0101] Example 7

[0102] Under magnetic stirring, 14.5 g of cationic surfactant hexadecyltrimethylammonium bromide was first weighed and dissolved in 260 mL of water. After complete dissolution, 1.1 g of sodium hydroxide was added to adjust the pH value of the solution to 13 to obtain an alkaline surfactant solution.

[0103] 2.55 g of cerium nitrate was weighed and dispersed in 40 mL of deionized water. After ultrasonication for 30 min, stirring was continued at room temperature for 1 h. The obtained solution was added dropwise to the alkaline surfactant solution. After stirring for 15 min, 25.4 g of silica sol industrial reagent (mass fraction 26.5%) was gradually added. The reaction was maintained at a constant speed at 35 ° C for 3 h and then transferred to a stainless steel hydrothermal autoclave with a polytetrafluoroethylene liner. After hydrothermal aging at 120 ° C for 24 h, the obtained product was filtered and washed until neutral and then dried in an oven at 100 ° C overnight to obtain a Ce metal ion-modified MCM-41 precursor.

[0104] The precursor was calcined at 550 °C in air atmosphere for 6 h to obtain Ce metal ion modified mesoporous Ce 0.20 -MCM-41 vector.

[0105] Weigh 3.47g of cesium carbonate and dissolve it in deionized water to form a cesium carbonate solution. 0.20 -MCM-41 support was immersed in cesium carbonate solution and shaken at 30℃ for 6h. After the reaction was completed, the reaction solution was filtered and washed and placed in an oven at 100℃ to dry overnight to obtain Cs active component loaded Cs 0.30 / Ce 0.20 -MCM-41 catalyst precursor.

[0106] The precursor was calcined at 600 ° C in air atmosphere for 3 h to obtain a nano-spherical acid-base bifunctional catalyst with ordered mesopores. After grinding, tableting and screening, the catalyst Cs 0.30 / Ce 0.20 -MCM-41.

[0107] The evaluation method of the prepared catalyst was the same as that in Example 1. The catalytic performance evaluation of the catalyst showed that the conversion rate of MP was 34.3%, the selectivity of MMA was 87.5%, and the activity of the catalyst remained unchanged after 300 hours of continuous operation.

[0108] Example 8

[0109] Under magnetic stirring, 6.0 g of cationic surfactant hexadecyltrimethylammonium bromide was first weighed and dissolved in 300 mL of water. After complete dissolution, 1 mL of ammonia water was introduced to adjust the pH value of the solution to 10 to obtain an alkaline surfactant solution.

[0110] 2.04 g of ferric nitrate was weighed and dispersed in 40 mL of ethanol. After ultrasonication for 20 minutes, stirring was continued at room temperature for 1 hour. The obtained solution was added dropwise to the alkaline surfactant solution. After stirring for 15 minutes, 25 mL of tetraethyl silicate was added dropwise. The reaction was maintained at a constant speed at 35°C for 3 hours and then transferred to a stainless steel hydrothermal autoclave with a polytetrafluoroethylene liner. After hydrothermal aging at 120°C for 36 hours, the obtained product was filtered and washed until neutral and then dried in an oven at 120°C overnight to obtain an Fe metal ion-modified MCM-41 precursor.

[0111] The precursor was calcined at 600℃ in air atmosphere for 4h to obtain Fe metal ion modified mesoporous Fe 0.10 -MCM-41 vector.

[0112] Weigh 2.21g of cesium nitrate and dissolve it in deionized water to form a cesium nitrate solution. 0.10 -MCM-41 carrier was immersed in cesium nitrate solution and shaken at 40℃ for 6h. After the reaction was completed, the reaction solution was filtered and washed and placed in an oven at 120℃ to dry overnight to obtain Cs active component loaded Cs 0.16 / Fe 0.10 -MCM-41 catalyst precursor.

[0113] The precursor was calcined at 400 ° C in air atmosphere for 10 h to obtain a nano-spherical acid-base bifunctional catalyst with ordered mesopores. The catalyst Cs was obtained by grinding, tableting and screening. 0.16 / Fe 0.10 -MCM-41.

[0114] The evaluation method of the prepared catalyst was the same as that in Example 1. The catalytic performance evaluation of the catalyst showed that the conversion rate of MP was 31.3%, the selectivity of MMA was 86.9%, and the activity of the catalyst remained unchanged after 300 hours of continuous operation.

[0115] Example 9

[0116] Under magnetic stirring, 6.4 g of cationic surfactant hexadecyltrimethylammonium bromide was first weighed and dissolved in 340 mL of water. After complete dissolution, 33 mL of ammonia water was introduced to adjust the pH value of the solution to 11 to obtain an alkaline surfactant solution.

[0117] 0.72 g of zirconium n-propoxide and 1.18 g of cerium nitrate were weighed and dispersed in 45 mL of ethanol. After ultrasonication for 30 min, stirring was continued at room temperature for 1 h. The obtained solution was added dropwise to the alkaline surfactant solution. After stirring for 20 min, 25 mL of tetraethyl silicate was added dropwise. The reaction was maintained at a constant speed at 35 ° C for 4 h and then transferred to a stainless steel hydrothermal autoclave with a polytetrafluoroethylene liner. After hydrothermal aging at 120 ° C for 24 h, the obtained product was filtered and washed until neutral and then dried in an oven at 120 ° C overnight to obtain a Zr-Ce bimetallic ion modified MCM-41 precursor.

[0118] The precursor was calcined at 400℃ in air atmosphere for 12h to obtain Zr-Ce double metal ion modified mesoporous Zr 0.04 -Ce 0.1 -MCM-41 vector.

[0119] Weigh 2.49g of cesium nitrate and dissolve it in deionized water to form a cesium nitrate solution. 0.04 -Ce 0.1 -MCM-41 carrier was immersed in cesium nitrate solution and shaken at 60℃ for 4h. After the reaction was completed, the reaction solution was filtered and washed and placed in an oven at 120℃ to dry overnight to obtain Cs active component loaded Cs 0.18 / Zr 0.04 -Ce 0.1 -MCM-41 catalyst precursor.

[0120] The precursor was calcined at 500 ° C in air atmosphere for 8 h to obtain a nano-spherical acid-base bifunctional catalyst with ordered mesopores. After grinding, tableting and screening, the catalyst Cs 0.18 / Zr 0.04 -Ce 0.1 -MCM-41.

[0121] The evaluation method of the prepared catalyst was the same as that in Example 1. The catalytic performance evaluation of the catalyst showed that the conversion rate of MP was 32.1%, the selectivity of MMA was 87.3%, and the activity of the catalyst remained unchanged after 300 hours of continuous operation.

[0122] Example 10

[0123] Under magnetic stirring, 6.2 g of cationic surfactant hexadecyltrimethylammonium bromide was first weighed and dissolved in 310 mL of water. After complete dissolution, 30 mL of ammonia water was introduced to adjust the pH value of the solution to 11 to obtain an alkaline surfactant solution.

[0124] 1.43 g of ferric nitrate and 0.54 g of lanthanum nitrate were weighed and dispersed in 40 mL of ethanol. After ultrasonication for 25 minutes, stirring was continued at room temperature for 1 hour. The obtained solution was added dropwise to the alkaline surfactant solution. After stirring for 15 minutes, 25.4 g of silica sol industrial reagent (mass fraction 26.5%) was gradually added. The reaction was maintained at a constant speed at 35°C for 3 hours and then transferred to a stainless steel hydrothermal autoclave with a polytetrafluoroethylene liner. After hydrothermal aging at 160°C for 24 hours, the obtained product was filtered and washed until neutral and then dried in an oven at 120°C overnight to obtain an Fe-La bimetallic ion modified MCM-41 precursor.

[0125] The precursor was calcined at 550℃ in air atmosphere for 8h to obtain Fe-La bimetallic ion modified mesoporous Fe 0.07 -La 0.04 -MCM-41 vector.

[0126] Weigh 2.21g of cesium nitrate and dissolve it in deionized water to form a cesium nitrate solution. 0.07 -La 0.04 -MCM-41 carrier was immersed in cesium nitrate solution and shaken at 45℃ for 6h. After the reaction was completed, the reaction solution was filtered and washed and placed in an oven at 120℃ to dry overnight to obtain Cs active component loaded Cs 0.16 / Fe 0.07 -La 0.04 -MCM-41 catalyst precursor.

[0127] The precursor was calcined at 550 ° C in air atmosphere for 5 h to obtain a nano-spherical acid-base bifunctional catalyst with ordered mesopores. After grinding, tableting and screening, the catalyst Cs 0.16 / Fe 0.07 -La 0.04 -MCM-41.

[0128] The evaluation method of the prepared catalyst was the same as that in Example 1. The catalytic performance evaluation of the catalyst showed that the conversion rate of MP was 29.6%, the selectivity of MMA was 88.0%, and the activity of the catalyst remained unchanged after 300 hours of continuous operation.

[0129] Comparative Example 1

[0130] The ethanol dispersion of aluminum isopropoxide was not added in the preparation process of the carrier, and the other conditions were the same as those in Example 4.

[0131] The process of supporting Cs active component was the same as that in Example 4, and the amount of cesium carbonate used was 1.40 g to obtain catalyst Cs 0.12 / MCM-41.

[0132] The evaluation method of the prepared catalyst was the same as that in Example 1. Analysis showed that the MP conversion was 22.6% and the MMA selectivity was 80.9%. After 300 hours of continuous operation, the MP conversion dropped to 15.6% and the MMA selectivity was around 75%.

[0133] Comparative Example 2

[0134] The preparation process of the carrier does not include cetyltrimethylammonium bromide surfactant, and the other conditions are the same as those in Example 4.

[0135] The process of supporting the Cs active component was the same as that in Example 4, and the amount of cesium carbonate used was 0.93 g to obtain the catalyst Cs 0.08 / Silica.

[0136] The evaluation method of the prepared catalyst was the same as that in Example 1. The catalytic performance evaluation of the catalyst showed that the MP conversion rate was 15.8% and the MMA selectivity was 70.3%. After 300 hours of continuous operation, the MP conversion rate dropped to 8.4% and the MMA selectivity was around 62%.

[0137] The MP conversion rate and MMA selectivity of the acid-base bifunctional catalyst prepared in the embodiment of the present invention are shown in Table 1:

[0138] Table 1 Catalytic performance of catalysts in comparative examples and different examples

[0139]

[0140]

[0141] As can be seen from Table 1, the Cs 0.15 / Al 0.04 -MCM-41 catalyst is used in the reaction of MP and FA condensation to prepare MMA. Under the optimized conditions, the conversion rate of MP can reach 30.2% and the selectivity of MMA can reach 91.3%. In addition, in order to prove the effect of introducing acidic metal ions into the MCM-41 framework, the present invention prepared unmodified Cs 0.12 / MCM-41 catalyst. By comparing the differences between the two catalysts, it was found that the skeleton-doped Al ions can significantly enhance the acidic properties of the catalyst, increase the optimal loading amount of the Cs active component, and promote the dispersion of the active component, thereby enhancing the synergistic effect of the acid-base sites of the catalyst. In addition, in order to prove that the introduction of a mesoporous carrier in the present invention is beneficial to improving the catalytic activity and anti-carbon deposition performance, the present invention did not add a pore-forming template during the preparation process, and prepared an amorphous porous silicon carrier-supported Cs / Silica catalyst. It can be seen that the optimal loading amount of the Cs active component and the initial activity of the Cs / Silica catalyst are significantly lower than those of the Cs with ordered mesopores. a / X b-MCM-41 catalyst, and showed a significant decrease in activity during the long-term experiment. This result proves the advantage of mesoporous carriers in improving the dispersion of active components and enhancing catalyst performance and stability. In addition, the Cs / Silica catalyst showed a black color after 300h of evaluation, which means that it had serious carbon deposition and reduced activity, while the Cs a / X b -MCM-41 catalyst showed light gray after evaluation, and no obvious carbon deposition was observed, further proving that the mesoporous support can essentially inhibit the formation of carbon deposition.

[0142] Comparison of the present invention with the catalysts reported in the literature shows that the catalytic performance of the present invention has good advantages in both conversion rate and selectivity. However, the catalysts reported in the literature often sacrifice conversion rate (selectivity) in order to improve selectivity (conversion rate), which does not meet the high conversion rate and high selectivity requirements for the efficient synthesis of MMA.

[0143] It can be seen that the method provided by the present invention can obtain a catalyst with both high conversion rate and high selectivity for the synthesis of MMA, and has a longer service life.

[0144] The present invention combines the sol-gel method with the wet impregnation method to prepare an ordered mesoporous nano-spherical acid-base bifunctional catalyst. The acidic metal ion modification auxiliary agent can be introduced into the skeleton of the carrier, achieving a good acid-base balance with the alkaline active component Cs and promoting the high dispersion of the active component, thereby greatly improving the catalytic activity of the catalyst. At the same time, a strong bonding interaction is formed between the alkaline active component Cs and the modified MCM-41 carrier, which improves the stability of the catalyst. In addition, after the acidic metal ions replace the Si atoms of the MCM-41 skeleton, they still exhibit a hexagonal ordered mesoporous structure. While adjusting the acidity and alkalinity, they utilize the confinement effect of the mesopores to significantly improve the mass transfer efficiency of reactants and products, thereby suppressing the occurrence of carbon deposition. The preparation method of the present invention using the sol-gel method and the impregnation method is simple to operate and has a short preparation process. In summary, this ordered mesoporous nano-spherical acid-base bifunctional catalyst meets the requirements of high efficiency, cleanliness and industrial production in terms of performance, service life and economy.

[0145] The technical solutions disclosed and proposed by the present invention can be implemented by those skilled in the art by drawing on the content of this document and appropriately changing the conditions, routes, and other aspects. Although the methods and preparation techniques of the present invention have been described through preferred embodiments, it is obvious that those skilled in the art can modify or recombine the methods and technical routes described herein without departing from the content, spirit, and scope of the present invention to achieve the ultimate preparation technology. It is particularly important to point out that all similar substitutions and modifications that are obvious to those skilled in the art are considered to be included in the spirit, scope, and content of the present invention.

Claims

1. A mesoporous nanosphere acid-base bifunctional catalyst for synthesizing methyl methacrylate, characterized in that: The catalyst expression is Cs a / X b -MCM-41, wherein X is selected from one or two of the elements Zr, Ti, Al, La, Ce or Fe, a is the mass fraction of Cs species calculated based on the support, which is 0.08 to 0.30 in terms of Cs2O, and b is the mass fraction of the oxide corresponding to element X in the MCM-41 support, which is 0.04 to 0.

20.

2. The mesoporous nanosphere acid-base dual-function catalyst according to claim 1, characterized in that: The catalyst particle size is 10-200nm and the specific surface area is 500-1500m 2 / g, and the mesopore diameter is 2 to 10 nm.

3. The mesoporous nanosphere acid-base dual-function catalyst according to claim 1, characterized in that it comprises One of the following structures: Cs a / Zr b -MCM-41, Cs a / Ti b -MCM-41, Cs a / Al b -MCM-41, Cs a / La b -MCM-41, Cs a / Ce b -MCM-41, Cs a / Fe b -MCM-41, Cs a / Zr b -Ce b -MCM-41, Cs a / Fe b -La b -MCM-41.

4. The method for preparing the mesoporous nanosphere acid-base dual-function catalyst for synthesizing methyl methacrylate according to claim 1, characterized in that: The steps include: (1) Weigh trimethylamine halide C n H 2n+1 N(CH3)3 + Y - The surfactant is used as a template and is dispersed in deionized water under magnetic stirring to form a trimethylamine halide dispersion, and then an alkali source is added to obtain an alkaline surfactant solution; (2) Weighing an inorganic salt / organic salt containing acidic metal ions as an acidic metal ion precursor, dissolving it in deionized water or ethanol, and then introducing it dropwise into the alkaline surfactant solution obtained in step (1), and then adding a silicon source to react; transferring the resulting reaction solution to a stainless steel hydrothermal kettle with a polytetrafluoroethylene liner for hydrothermal aging; after the reaction is completed, filtering the reaction solution and washing it with deionized water and ethanol until it is neutral, and placing it in an oven to dry overnight to obtain an acidic metal ion-modified MCM-41 mesoporous molecular sieve precursor; (3) calcining the precursor obtained in step (2) under air atmosphere to obtain a nano-spherical carrier having hexagonal ordered mesopores; (4) Weighing a cesium source precursor and dissolving it in deionized water to form a cesium metal ion solution, weighing the nano-spherical support obtained in step (3) and impregnating it in the cesium metal ion solution, and performing shaking impregnation under heating conditions; after the reaction is completed, filtering the reaction solution and washing it with deionized water, and placing it in an oven to dry overnight to obtain a catalyst precursor with an acidic metal ion-modified MCM-41 as a support and a Cs active component loaded thereon; (5) calcining the precursor obtained in step (4) under air atmosphere to obtain a mesoporous nanosphere acid-base dual-functional catalyst.

5. The method for preparing a bifunctional catalyst as claimed in claim 4, wherein: In the step (1), trimethylamine halide C n H 2n+1 N(CH3)3 + Y - wherein Y is Cl or Br, and n is 8 to 18; the inorganic salt / organic salt containing acidic metal ions is one or two of the nitrates, carbonates, acetates, propoxides, and fatty acid salts of the corresponding metals of Zr, Ti, Al, La, Ce, and Fe.

6. The method for preparing a bifunctional catalyst as claimed in claim 4, wherein: In step (1), the alkali source is selected from sodium hydroxide, tetramethylammonium hydroxide or ammonia water; the pH of the solution is adjusted to a range of 10 to 13; in step (2), the silicon source is selected from tetraethyl silicate and silica sol; the molar ratio of the silicon source to the trimethylamine halide template is 1:0.4 to 1:0.05, the hydrothermal temperature is 90 to 160° C., and the aging time is 6 to 72 hours.

7. The method for preparing a bifunctional catalyst as claimed in claim 4, wherein: In the step (3), the calcination temperature is 400-600° C., and the calcination time is 4-12 hours.

8. The method for preparing a bifunctional catalyst as claimed in claim 4, wherein: In the step (4), the cesium source precursor is selected from cesium carbonate, cesium nitrate, cesium acetate or cesium hydroxide; the reaction temperature is 25-60° C., and the reaction time is 4-12 hours.

9. The method for preparing a bifunctional catalyst as claimed in claim 4, wherein: The mass ratio of the amount of the cesium source precursor added in step (4) to the amount of the acidic metal ion precursor added in step (2) is in the range of 1:0.2 to 1:1.

2.

10. The method for preparing a bifunctional catalyst as claimed in claim 4, wherein: In the step (5), the calcination temperature is 400-600° C., and the calcination time is 3-10 hours.

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