Molecular sieve-based catalyst with MFI structure and application of molecular sieve-based catalyst in synthesis of 1, 3-butadiene

Abstract

The invention discloses a molecular sieve-based catalyst with an MFI structure and application of the molecular sieve-based catalyst in synthesis of 1, 3-butadiene. The catalyst consists of a crystallized short-range ordered molecular sieve carrier KPMFI with an MFI configuration, and Zn and Hf species which are loaded on the molecular sieve carrier KPMFI and interact with silicon hydroxyl on a molecular sieve. By regulating and controlling a large number of silicon hydroxyl defects on the carrier, active sites with the synergistic effect of the silicon hydroxyl defects and a metal active center are constructed, and the catalytic performance of the catalyst is remarkably improved. The catalyst disclosed by the invention is simple in preparation process, relatively low in energy consumption, relatively low in cost, free of environmental pollution, suitable for industrial large-scale production and relatively high in utilization value.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and particularly to a molecular sieve-based catalyst with an MFI structure and its application in the synthesis of 1,3-butadiene. Background Art

[0002] 1,3-Butadiene (referred to as butadiene for short), as one of the "three olefins", is an important raw material for petrochemical products. It has a broad downstream product market and can be used to produce various polymers and synthetic rubbers (such as nitrile rubber and styrene-butadiene rubber). Currently, most butadiene is separated from the C4 fraction, which is a by-product of the catalytic cracking of naphtha to produce ethylene. However, with the depletion of petroleum resources and the lightening of the feedstock of steam cracking units due to the increase in shale gas production, there has been a huge shortage of long-chain hydrocarbons including butadiene in the pyrolysis products, and the contradiction between supply and demand has become increasingly prominent. The traditional petroleum route production can no longer meet the needs of people and the development of the industry. Therefore, a new butadiene preparation process is urgently needed to replace it. In recent years, the technology of bioethanol has developed rapidly, and the production cost of ethanol has been greatly reduced. Using sustainable bioethanol to synthesize butadiene can not only reduce carbon emissions but also reduce the dependence on petroleum resources, which is a green and feasible butadiene production route.

[0003] The process of converting ethanol to butadiene can be carried out by the Lebedev process using a single ethanol feed or by the Ostromislensky process using a mixed feed of ethanol and acetaldehyde. Compared with the Ostromislensky process using a mixed feed of ethanol and acetaldehyde, the Lebedev process of directly converting ethanol to butadiene in one step is more concise, has better economic performance, and has higher industrial application value.

[0004] Molecular sieves have shown great brilliance in the field of acid catalysis due to their unique properties such as regular pore structures, large specific surface areas, high thermal stability, and hydrothermal stability. The research on molecular sieves in the reaction of ethanol to butadiene mainly focuses on molecular sieves with two configurations, namely Beta and MFI.

[0005] Dai et al. synthesized Zn-Y / Beta zeolite by using dealuminated Beta zeolite and applied it to the reaction of ethanol to butadiene. The conversion rate of ethanol was 82%, and the selectivity of butadiene was 63% [W.L. Dai, S.S. Zhang, Z.Y. Yu, T.T. Yan, G.J. Wu, N.J. Guan, L.D. Li, Zeolite Structural Confinement Effects Enhance One-Pot Catalytic Conversion of Ethanol to Butadiene, Acs Catalysis, 7 (2017) 3703-3706.]. However, the catalyst prepared by this method has poor stability, is easy to deactivate, and the preparation of the catalyst requires the use of concentrated nitric acid, which has high requirements for equipment, high energy consumption, and is not environmentally friendly. Patent application CN118491559A discloses a hierarchical pore nano-ZnZr / Si-Beta@Y / Si-Beta capsule catalyst synthesized by using dealuminated Beta zeolite as a seed. The conversion rate of ethanol is 97%, and the selectivity of butadiene is 62%. Although the selectivity of butadiene in this method is relatively high, this method requires the use of dealuminated Beta zeolite and still needs to use concentrated nitric acid that is not environmentally friendly. Moreover, the preparation process of this catalyst is cumbersome, has high energy consumption, and is not easy to scale up for industrial production. For Beta zeolite-based catalysts, they are mainly applied to the one-step preparation of butadiene from ethanol. The conversion rate of the catalyst is relatively high, but the selectivity of butadiene still has deficiencies. In addition, the preparation steps of Beta zeolite-based catalysts are cumbersome. Concentrated nitric acid needs to be used in the dealumination process, which is not environmentally friendly, has high equipment requirements, and is not conducive to industrial use.

[0006] Patent application CN117500592A discloses a molecular sieve with MFI configuration as a carrier to load ZnO and Zr for the reaction of ethanol to butadiene. The evaluation results show that the conversion rate of ethanol is 97.9%, and the selectivity is 38.7%. There is still room for improvement in the butadiene selectivity of this catalyst. Chinese patent CN113996330B discloses a Zr-based MFI molecular sieve catalyst prepared by ball milling method. At 350 °C, WHSV is 1.44 h -1 , when the aldehyde-alcohol ratio is 1:2, the conversion rate of ethanol and acetaldehyde is 40%, and the selectivity of butadiene is 70%. The stability of this catalyst is good, but the conversion rate of ethanol and acetaldehyde is low, and the selectivity of butadiene still needs to be improved. Chinese patent application CN112958146B discloses the use of MFI molecular sieve nanosheets to load zirconium for the preparation of butadiene from ethanol and acetaldehyde. At 350 °C, WHSV is 1.8 h -1, when the aldehyde-alcohol ratio is 1:2, the conversion rate of ethanol and acetaldehyde is 45%, and the selectivity of butadiene is 80%. There is a slight improvement in the performance compared to the previous catalyst, but the conversion rate of ethanol and acetaldehyde and the selectivity of butadiene are still insufficient. Moreover, the two-step method using acetaldehyde as a raw material is not easy to scale up industrially. Patent application CN117500592A discloses a method of using a molecular sieve with MFI configuration as a carrier to load ZnO and Zr for the one-step preparation of butadiene from ethanol. The evaluation results show that the conversion rate of ethanol is 97.9%, and the selectivity is only 38.7%. There is still a high room for improvement in the butadiene selectivity of the catalyst.

[0007] Li et al. developed a Mg-Zr / MFI(NS) bimetallic catalyst based on MFI nanosheets as a carrier for the conversion of ethanol and acetaldehyde to butadiene. The abundant silanol nests on the surface of the nanosheets provide highly dispersed sites for Zr species. At 350 °C, WHSV = 1.44 h -1 , under the reaction conditions of ethanol / acetaldehyde = 2:1, the selectivity of butadiene is 74.6%. However, the conversion rate of ethanol and acetaldehyde of this catalyst is only 41.5%, and there is a problem of poor catalyst stability. Moreover, acetaldehyde needs to be used as a raw material, which is not easy to scale up industrially [X.Q. Li, J.F. Pang, C. Wang, L. Li, X.L. Pan, M.Y. Zheng, T. Zhang, Conversion of ethanolto 1,3-butadiene over high-performance Mg-ZrO x / MFI nanosheet catalysts viathe two-step method, Green Chemistry, 22(2020)2852-2861.].

[0008] Wang et al. used two-dimensional nanosheet MFI molecular sieve to prepare a LiZnHf-MFI(NS) catalyst by impregnation method for the one-step preparation of butadiene from ethanol. The doping of Li effectively eliminates acid sites, reduces the side reaction of ethanol dehydration; the nanosheet structure shortens the diffusion path of reactants, reduces the residence time of intermediates (such as acetaldehyde, 3-hydroxybutyraldehyde), and inhibits carbon deposition formation. At 320 °C, WHSV is 0.47 h -1Under the reaction conditions, the ethanol conversion rate was 64.6%, and the butadiene selectivity was 73%. Due to the addition of Li, the ethanol conversion rate of this catalyst was relatively low, and there was still room for improvement in the butadiene selectivity. Moreover, the preparation process of the catalyst nanosheet structure was cumbersome, with high energy consumption and low mechanical strength, which was not conducive to industrial production [C. Wang, M. Y. Zheng, X. S. Li, X. Q. Li, T. Zhang, Catalytic conversion of ethanol into butadiene over high performance LiZnHf-MFI zeolite nanosheets, Green Chemistry, 21 (2019) 1006-1010].

[0009] Wang et al. prepared a hierarchical nanostructured ZnZr-Silicalite-1 (MFI configuration) catalyst by a one-pot crystallization method for the conversion of ethanol to butadiene. The hierarchical nanostructure (coexistence of micropores and mesopores) shortened the diffusion path of reactants, improved the mass transfer efficiency, and enhanced the catalyst stability. At 350 °C and WHSV = 0.38 h -1 Under the conditions, the ethanol conversion rate reached 89.8%, and the butadiene selectivity reached 61.4%. The selectivity of butadiene of this catalyst was still insufficient, and the preparation process was complex with high energy consumption, which was not conducive to industrial scale-up [K. Z. Wang, W. Z. Gao, F. Chen, G. B. Liu, J. H. Wu, N. Liu, Y. Kawabata, X. Y. Guo, Y. L. He, P. P. Zhang, G. H. Yang, N. Tsubaki, Hierarchical nano-sized ZnZr-Silicalite-1 multifunctional catalyst for selective conversion of ethanol to butadiene, Applied Catalysis B-Environment and Energy, 301 (2022)]. For MFI zeolite-based catalysts, the current catalysts are mainly suitable for the two-step process of ethanol and acetaldehyde for the preparation of butadiene with complex processes, and there is still a large room for improvement in the ethanol conversion rate and the butadiene selectivity; the catalyst preparation process is complex, with high energy consumption, and there are still problems with poor stability.

[0010] In summary, the current catalysts for the production of butadiene from ethanol mainly have the following problems: (1) The combination between the catalyst support and the metal is poor, resulting in few active sites for the reaction, especially few coordinatively unsaturated metal active sites with high activity, insufficient activity, and there is still a high room for improvement in the selectivity and yield of butadiene; (2) The stability of the catalyst is poor; (3) The preparation process of the catalyst is complex, with high energy consumption and easy to pollute the environment, and it is not easy to scale up for industrial production. Summary of the Invention

[0011] Aiming at the problems of the existing catalysts, the present invention provides a molecular sieve-based catalyst with an MFI structure and its application in the synthesis of 1,3-butadiene. First, a molecular sieve support with a large number of silanol defects is synthesized, and then metals Zn and Hf are loaded onto the support by an impregnation method to prepare a catalyst active center with the synergistic effect of a large number of coordinatively unsaturated metal centers and silanol defects. The catalyst has high ethanol conversion and high butadiene selectivity in the reaction of ethanol to butadiene, and has good industrial application prospects.

[0012] In order to achieve the above object, the technical scheme adopted by the present invention is as follows:

[0013] A molecular sieve-based catalyst with an MFI structure, which is composed of a crystalline short-range ordered molecular sieve support with an MFI configuration, and Zn and Hf species loaded on the molecular sieve support and interacting with the silanols on the molecular sieve. The catalyst has a microporous structure.

[0014] The preparation method of the molecular sieve-based catalyst with an MFI structure includes the preparation of the catalyst support and the loading of the metal, and the steps are as follows:

[0015] 1) Mix the template agent and the silicon source, and stir for 8 - 14 h under a water bath heating at 30 - 50 °C to form solution A;

[0016] 2) Dissolve the amino acid and the K metal precursor in water to form solution B;

[0017] 3) Slowly drip solution B into solution A, and continuously stir for 8 - 16 h to obtain a mixed solution;

[0018] 4) Transfer the above mixed solution to a polytetrafluoroethylene inner liner, and then put the polytetrafluoroethylene inner liner into a stainless steel hydrothermal synthesis kettle, and crystallize at 70 - 120 °C for 8 - 24 h;

[0019] 5) Wash, dry, and calcine the crystallized product to obtain the catalyst support, that is, KPMFI molecular sieve (incompletely crystallized MFI);

[0020] 6) Dissolve the Hf metal precursor and the Zn metal precursor in water to form solution C. Add solution C to the KPMFI molecular sieve, stir evenly, let it stand at room temperature for 3 - 6 h, then place it in a constant temperature oven and dry at 80 - 100 °C for 6 - 12 h. Put the obtained solid into a muffle furnace and calcine at 300 - 600 °C for 3 - 8 h to obtain the Zn-Hf-KPMFI catalyst.

[0021] Furthermore, the template agent is one of tetrabutylammonium hydroxide, tetrapropylammonium hydroxide, and tetrapropylammonium bromide; the silicon source is one of fumed silica, tetraethyl orthosilicate, and silica sol; the amino acid is one of L-tyrosine, L-lysine, arginine, and histidine; the K metal precursor is one of KCl, KOH, and KBr.

[0022] Furthermore, the molar ratio of the template agent to the silicon source is 0.35 - 0.55, the molar ratio of the amino acid to the silicon source is 0.3 - 0.45, the molar ratio of the K metal precursor to the silicon source is 0.01 - 0.0001, and the molar ratio of water to the silicon source in step 2) is 6 - 15.

[0023] Furthermore, the Zn metal precursor is one of zinc nitrate, zinc chloride, and zinc acetate; the Hf metal precursor is one of hafnium oxynitrate, hafnium chloride, and hafnium oxyhydroxide.

[0024] Preferably, the loading amount of Zn element in the catalyst is 1 wt% - 2 wt% (based on the mass of the carrier), and the loading amount of Hf element in the catalyst is 4 wt% - 6 wt% (based on the mass of the carrier).

[0025] Furthermore, the molecular sieve-based catalyst with MFI structure can be used in the synthesis of 1,3-butadiene. The method is as follows: Place the Zn-Hf-KPMFI catalyst in a tablet press to make tablets, granulate to 40 - 60 mesh, then put it into a quartz tube reactor for reaction evaluation, fix both ends with quartz wool, and place the quartz tube into an ethanol-to-butadiene fixed bed reactor. Use nitrogen as the carrier gas, with a nitrogen flow rate of 30 - 50 ml / min. First, pre-treat the catalyst under the conditions: heat the catalyst to 300 - 500 °C in a nitrogen atmosphere and keep it for 0.5 - 2 h, then cool it down to the reaction temperature for reaction. The reaction raw material ethanol is introduced into the catalyst by nitrogen bubbling for reaction. The reaction temperature is 300 - 400 °C, and the reaction weight hourly space velocity is 0.05 - 1 h -1 . The reaction products are analyzed online on a gas chromatograph (GC) equipped with a flame ionization detector (FID).

[0026] The present invention has the following beneficial effects:

[0027] 1. The present invention uses amino acids to slow down the crystallization rate of molecular sieves. By regulating the crystallization temperature and crystallization time, a molecular sieve support with a large number of silanol defects is synthesized. By adding K metal to the support, the silanols on the molecular sieve support are consumed, realizing the regulation of silanols and enabling better bonding between the metal and the support.

[0028] 2. Based on the anchoring effect of a large number of silanol defects on the support on the metal, by regulating the silanol defects on the support, a catalyst active center with the synergistic effect of a large number of coordinatively unsaturated metal centers and silanol defects is synthesized. Moreover, the active centers are well-dispersed and have high ethanol conversion and high butadiene selectivity in the reaction of ethanol to butadiene.

[0029] 3. This method avoids the use of concentrated nitric acid or ammonia water, and there is no emission of acidic waste gas (such as NO x ) or alkaline wastewater (such as NH3) during the preparation process, without polluting the environment.

[0030] 4. The catalyst preparation process of the present invention is simple, fast, low in energy consumption, and low in cost, and can be used for large-scale industrial production.

[0031] 5. The catalyst of the present invention can be used for the one-step preparation of butadiene from ethanol. This catalyst has high ethanol conversion and high butadiene selectivity in the reaction of ethanol to butadiene, and the preparation process is simple and fast, which is beneficial to large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 XRD pattern of the catalyst prepared in Example 6.

[0033] Figure 2 TEM image of the catalyst prepared in Example 6. DETAILED DESCRIPTION OF THE INVENTION

[0034] The present invention will be further described in detail and completely below in conjunction with specific examples. The following description is only for illustrative purposes in essence and is not a limitation to the present disclosure, application, or use.

[0035] Example 1

[0036] In this example, tetraethyl orthosilicate (TEOS) is selected as the silicon source, tetrapropylammonium hydroxide (TPAOH) as the template agent, hafnium chloride, and zinc nitrate hexahydrate as the metal precursors. The specific steps are as follows:

[0037] 1): Mix 25 g of TPAOH and 15 g of TEOS, place them in a water bath at 30 °C, stir and age for 12 h to form solution A.

[0038] 2) Dissolve 3 g of L-lysine in 10 g of water to form solution B.

[0039] 3) Add solution B to solution A, and continue stirring and aging for 10 h under a water bath at 30 °C to obtain a mixed solution.

[0040] 4) Transfer the above mixed solution to a polytetrafluoroethylene liner, and then place the polytetrafluoroethylene liner into a stainless-steel hydrothermal synthesis autoclave for crystallization at 90 °C for 10 h.

[0041] 5) Wash the dry gel obtained in step 4), dry it in a constant-temperature oven at 100 °C for 10 h, and then calcine it in a muffle furnace at 550 °C for 6 h to obtain PMFI / 10 h molecular sieve.

[0042] 6) Weigh 0.2 g of hafnium chloride and 0.07 g of zinc nitrate hexahydrate, dissolve them in 1 g of water to form solution C. Add solution C to 2 g of PMFI / 10 h molecular sieve, stir evenly, let it stand at room temperature for 4 h, then dry it in a constant-temperature oven at 100 °C for 4 h. Put the obtained solid into a muffle furnace and calcine it at 550 °C for 4 h to obtain Zn-Hf-PMFI / 10 h catalyst.

[0043] Press the Zn-Hf-PMFI / 10 h catalyst into tablets, granulate it to 40 - 60 mesh, and then put it into a quartz tube, and fix both ends with quartz wool. Place the quartz tube into an ethanol-to-butadiene fixed-bed reactor for reaction evaluation. First, pre-treat the catalyst under the conditions: heat the catalyst to 400 °C in a nitrogen atmosphere at 40 ml / min and keep it for 30 min, then cool it down to the reaction temperature for reaction. The raw material ethanol for the reaction is brought into the catalyst by nitrogen bubbling for reaction, and the reaction products are analyzed online on a gas chromatograph (GC) equipped with a flame ionization detector (FID). The reaction temperature is 380 °C, and the space velocity WHSV is 0.7 h -1 . The reaction results are shown in Table 1.

[0044] Example 2

[0045] Change the crystallization time in step 4) of Example 1 to 12 h, and keep the other steps unchanged to prepare Zn-Hf-PMFI / 12 h catalyst.

[0046] The reaction evaluation conditions of Zn-Hf-PMFI / 12 h catalyst are the same as those in Example 1, and the reaction results are shown in Table 1.

[0047] Example 3

[0048] Change the crystallization time in step 4) of Example 1 to 12 h, and keep the other steps unchanged to prepare Zn-Hf-PMFI / 14 h catalyst.

[0049] The reaction evaluation conditions of Zn-Hf-PMFI / 14 h catalyst are the same as those in Example 1, and the reaction results are shown in Table 1.

[0050] Table 1 Reaction Evaluation Results

[0051]

[0052] The evaluation results of the catalyst show that too long crystallization time (14 h) leads to excessive reduction of silanol defects, insufficient metal anchoring sites, and decreased dispersion of active centers. Too short crystallization time (10 h) leads to excessive silanol defects, resulting in an increase in ethylene by-products. By modulating the crystallization time of the support, the silanols on the support are regulated. When the crystallization time is 12 h, the Zn, Hf-loaded catalyst has the best catalytic effect for the conversion of ethanol to butadiene, with an ethanol conversion of 92.3% and a butadiene selectivity of 50.3%.

[0053] Example 4

[0054] Change the crystallization time in step 4) of Example 1 to 12 h and the crystallization temperature to 100 °C, and keep the other steps unchanged to obtain the Zn-Hf-100PMFI catalyst.

[0055] The reaction evaluation conditions of the Zn-Hf-100PMFI catalyst are the same as those of Example 1, and the reaction results are shown in Table 2.

[0056] Example 5

[0057] Change the crystallization time in step 4) of Example 1 to 12 h and the crystallization temperature to 110 °C, and keep the other steps unchanged to obtain the Zn-Hf-110PMFI catalyst.

[0058] The reaction evaluation conditions of the Zn-Hf-110PMFI catalyst are the same as those of Example 1, and the reaction results are shown in Table 2.

[0059] Table 2 Reaction Evaluation Results

[0060]

[0061] The evaluation results of the catalyst show that by modulating the crystallization temperature of the support to regulate the silanols on the support, the performance of the catalyst loaded with Zn and Hf metals is improved. When the crystallization temperature is 100 °C, the catalyst has the best performance, with a support conversion of 92.4% and a butadiene selectivity of 61.3%.

[0062] Example 6

[0063] 1) Mix 25 g of TPAOH and 15 g of TEOS, place it in a water bath at 30 °C and stir and age for 12 h to form solution A.

[0064] 2) Dissolve 3 g of L-lysine in 10 g of water, and then add 0.003 g of KOH to form solution B.

[0065] 3) Add solution B to solution A, and continue stirring and aging for 10 h under a water bath at 30 °C to obtain a mixed solution.

[0066] 4) Transfer the above mixed solution to a polytetrafluoroethylene liner, and then place the polytetrafluoroethylene liner into a stainless-steel hydrothermal synthesis autoclave, and crystallize at 100 °C for 12 h.

[0067] 5) Wash the dry gel obtained in step 4), dry it in a constant-temperature oven at 100 °C for 10 h, and then calcine it in a muffle furnace at 550 °C for 6 h to obtain KPMFI molecular sieve.

[0068] 6) Weigh 0.2 g of hafnium chloride and 0.07 g of zinc nitrate hexahydrate, dissolve them in 1 g of water to form solution C, add solution C to 2 g of KPMFI molecular sieve, stir evenly, let it stand at room temperature for 4 h, then dry it in a constant-temperature oven at 100 °C for 4 h, and put the obtained solid into a muffle furnace and calcine it at 550 °C for 4 h to obtain Zn-Hf-100-3KPMFI catalyst.

[0069] The reaction evaluation conditions of the Zn-Hf-100-3KPMFI catalyst are the same as those in Example 1, and the reaction results are shown in Table 2.

[0070] Example 7

[0071] Change the addition amount of KOH in step 2) of Example 6 to 0.002 g, and keep the other steps unchanged to prepare Zn-Hf-100-2KPMFI catalyst.

[0072] The reaction evaluation conditions of the Zn-Hf-100-2KPMFI catalyst are the same as those in Example 1, and the reaction results are shown in Table 2.

[0073] Example 8

[0074] Change the addition amount of KOH in step 2) of Example 6 to 0.001 g, and keep the other steps unchanged to prepare Zn-Hf-100-1KPMFI catalyst.

[0075] The reaction evaluation conditions of the Zn-Hf-100-1KPMFI catalyst are the same as those in Example 1, and the reaction results are shown in Table 3.

[0076] Table 3 Reaction evaluation results

[0077]

[0078] The evaluation results of the catalyst show that by adding K metal to react with the silanol groups on the support, the silanol groups on the support are regulated. After loading Zn and Hf metals, the performance of the catalyst is further improved. When the addition amount of K is 0.002, the performance of the catalyst is the best, the conversion rate of the support is 92.4%, and the selectivity for butadiene is 70.0%.

[0079] Comparative Example 1

[0080] Weigh 0.2 g of hafnium chloride, 0.07 g of zinc nitrate hexahydrate and 0.003 g of KOH and dissolve them in 1 g of water to form solution C. Add solution C to 2 g of S-1 molecular sieve, stir evenly, let it stand at room temperature for 4 h, then put it in a constant temperature oven at 100 °C and dry for 4 h. Put the obtained solid into a muffle furnace and calcine it at 550 °C for 4 h to obtain the Zn-Hf-KS-1 catalyst.

[0081] The reaction evaluation conditions of the Zn-Hf-KS-1 catalyst are the same as those in Example 1, and the reaction results are shown in Table 4.

[0082] Table 4 Reaction evaluation results

[0083]

[0084] The evaluation results of the catalyst show that due to the significant difference in the pore structure or active site distribution of the S-1 support from that of the KPMFI support of the present invention, the metal-support synergy is insufficient, and the catalytic performance is significantly inferior to that of the catalyst of the present invention.

Claims

1. A method for preparing a molecular sieve-based catalyst with an MFI structure, characterized in that, It includes the following steps: 1) Mix the template agent with the silicon source, and stir for 8 - 14 h under water bath heating at 30 - 50 °C to form solution A; 2) Dissolve the amino acid and the K metal precursor in water to form solution B; 3) Slowly add solution B dropwise to solution A, and continuously stir for 8 - 16 h to obtain a mixed solution; 4) Transfer the above - mentioned mixed solution into a polytetrafluoroethylene liner, then put the polytetrafluoroethylene liner into a stainless - steel hydrothermal synthesis autoclave, and crystallize at 70 - 120 °C for 8 - 24 h; 5) Wash, dry, and calcine the crystallized product to obtain a catalyst support, namely KPMFI molecular sieve; 6) Dissolve the Hf metal precursor and the Zn metal precursor in water to form solution C, add solution C to the KPMFI molecular sieve, stir evenly, let it stand, dry, and then calcine in a muffle furnace to obtain the Zn - Hf - KPMFI catalyst.

2. The preparation method of a molecular sieve-based catalyst with an MFI structure according to claim 1, characterized in that, The template agent is one of tetrabutylammonium hydroxide, tetrapropylammonium hydroxide, and tetrapropylammonium bromide; the silicon source is one of fumed silica, tetraethyl orthosilicate, and silica sol; the amino acid is one of L - tyrosine, L - lysine, arginine, and histidine; the K metal precursor is one of KCl, KOH, and KBr.

3. The preparation method of a molecular sieve-based catalyst with an MFI structure according to claim 1, characterized in that, The molar ratio of the template agent to the silicon source is 0.35 - 0.55, the molar ratio of the amino acid to the silicon source is 0.3 - 0.45, and the molar ratio of the K metal precursor to the silicon source is 0.01 - 0.0001.

4. The preparation method of a molecular sieve-based catalyst with an MFI structure according to claim 1, characterized in that, In step 2), the molar ratio of water to the silicon source is 6 - 15.

5. The preparation method of a molecular sieve-based catalyst with an MFI structure according to claim 1, characterized in that, The Zn metal precursor is one of zinc nitrate, zinc chloride, and zinc acetate; the Hf metal precursor is one of hafnium oxynitrate, hafnium chloride, and hafnium oxyhydroxide.

6. The preparation method of a molecular sieve-based catalyst with an MFI structure according to claim 4, characterized in that, The loading amount of Zn element in the catalyst is 1wt% - 2wt%, and the loading amount of Hf element in the catalyst is 4wt% - 6wt%.

7. The preparation method of a molecular sieve-based catalyst with an MFI structure according to claim 1, characterized in that, In step 6), the standing time is 3 - 6 h, the drying condition is drying at 80 - 100 °C for 6 - 12 h, and the calcination condition is calcination at 300 - 600 °C for 3 - 8 h.

8. A molecular sieve - based catalyst with an MFI structure obtained by the preparation method according to any one of claims 1 - 7.

9. The molecular sieve-based catalyst with an MFI structure according to claim 8, characterized in that, It consists of a short - range ordered molecular sieve support with an MFI configuration, and Zn and Hf species loaded on the molecular sieve support and interacting with the silicon hydroxyl groups on the molecular sieve. The catalyst has a microporous structure.

10. Use of the molecular sieve - based catalyst with an MFI structure as claimed in claim 8 in the direct conversion of ethanol to 1,3 - butadiene.

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