MgZrOx / H-ZSM-5 composite bifunctional catalyst for preparing aromatic hydrocarbon from synthesis gas

Abstract

The invention discloses a MgZrOx / H-ZSM-5 composite bifunctional catalyst for preparing aromatic hydrocarbon from synthesis gas, the catalyst is formed by mixing a magnesium-zirconium-containing metal oxide-doped coupling molecular sieve, and the molecular sieve is H-ZSM-5 or an H-ZSM-5 molecular sieve modified by adding one or more of metal Mn, Ce or Fe; the selected magnesium-zirconium-containing doped metal oxide is one or more of a magnesium-zirconium-doped oxide, a zinc-magnesium-zirconium-doped oxide and an iron-magnesium-zirconium-doped oxide. The composite catalyst has the advantages of better catalytic performance, low selectivity of by-product CO2, high BTX component proportion in the product and simple preparation method.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and particularly relates to a catalyst for synthesizing aromatics from syngas. Background Art

[0002] Aromatics are important basic chemical raw materials, which are widely used in the synthesis of chemicals such as plastics, nylon, and spices. At present, they are mainly prepared by petroleum reforming and cracking. A large amount of aromatics can also be prepared from coal resources, but the products are complex, the aromatic content is low, and it is not easy to be further processed; while syngas (mainly composed of CO and H2) obtained from coal, natural gas, biomass, etc. can be highly selectively converted into aromatic products through catalytic action, which is a new non-petroleum route for preparing aromatics.

[0003] The direct conversion of syngas to aromatics via a bifunctional catalyst is abbreviated as STA. This process has a short flow, can effectively reduce the energy consumption and cost of the overall process, and enhance the market competitiveness of aromatic products. Among bifunctional catalysts, Zr-based catalysts have strong CO adsorption ability and relatively high aromatic selectivity (about 80%), but their hydrogen dissociation ability is weak. When catalyzing the conversion of syngas alone, the CO conversion rate is low (about 5%), and the required pressure is high. Hydrogen dissociation promoters such as Ce, Zn, and Cu are often added to improve their catalytic performance. Huang et al. prepared Ce 0.2 Zr 0.8 O2 / H-ZSM5-40 catalyst and applied it to the direct synthesis of aromatics from syngas. Under the conditions of 450 °C, 2 MPa, and H2 / CO = 1, the CO conversion rate was 22.4%, the aromatic selectivity was 56.3%, and the proportion of BTX components was 54.4%. Xiao et al. prepared CuZnAl-ZrO2 / Nb-ZSM5 catalyst and applied it to the reaction of synthesizing aromatics from syngas. Under the conditions of 360 °C, 4 MPa, H2 / CO = 2, and 1800 mLg -1 h -1 conditions, the CO conversion rate was 88.4%, the aromatic selectivity was 39.8%, and the proportion of pseudocumene in aromatic products was 60%. Patent CN113289677A discloses a heterogeneous catalyst for synthesizing aromatics from syngas, which is a bifunctional catalyst formed by mechanically mixing a CeZr-doped metal oxide catalyst and a ZnZt-doped metal oxide catalyst and then coupling with a molecular sieve. The CO conversion rate of this catalyst is 50%, the CO2 selectivity is 48%, and the aromatic selectivity is 80%. Patent CN112108179A discloses a heterogeneous catalyst for synthesizing aromatics from syngas, which is a bifunctional catalyst formed by coupling a chromium calcium titanate metal oxide catalyst containing Mn or Zn with a molecular sieve. The CO conversion rate of this catalyst is 23.5%, the CH4 selectivity is 1.4%, and the aromatic selectivity is 76%.

[0004] In summary, in the direct synthesis of aromatics from syngas, designing a catalyst with high CO conversion rate, low by-product selectivity, high proportion of light aromatic components in the liquid product, and suitable for industrial production with a simple preparation method is one of the current difficulties in this field. Summary of the Invention

[0005] In view of the above problems, the present invention provides a MgZrO x / H-ZSM-5 composite bifunctional catalyst for the synthesis of aromatics from syngas. The catalyst is composed of a doped metal oxide containing magnesium and zirconium coupled with a molecular sieve. This composite catalyst has the advantages of better catalytic performance, low by-product CO2 selectivity, high proportion of BTX (light aromatics) components in the product, and a simple preparation method.

[0006] The present invention provides a MgZrO x / H-ZSM-5 composite bifunctional catalyst, characterized in that it is composed of a doped metal oxide containing magnesium and zirconium coupled with a molecular sieve;

[0007] The molecular sieve is H-ZSM-5, or H-ZSM-5 molecular sieve modified by adding one or more of metals Mn, Ce, and Fe. Relative to the molecular sieve, the addition amount of the metal is 2%-10% by mass ratio;

[0008] The selected doped metal oxide containing magnesium and zirconium is one or more of magnesium-zirconium doped oxide, zinc-magnesium-zirconium doped oxide, and iron-magnesium-zirconium doped oxide. Relative to MgZrO x , 3%-10% of metal Zn or Fe is used to modify the MgZrO x / H-ZSM-5 composite bifunctional catalyst by mass ratio;

[0009] The mass ratio of the doped metal oxide containing magnesium and zirconium to the molecular sieve is 2:1 - 1:3.

[0010] Preferably, the particle size of the composite bifunctional catalyst is 20 - 100 mesh, preferably 30 - 40 mesh.

[0011] Preferably, the silica-alumina ratio of the molecular sieve is 80 - 200.

[0012] The present invention can further passivate the surface acidity of the molecular sieve by adding SiO2. The addition amount of silicon is 10%-20% by mass ratio (relative to the H-ZSM-5 molecular sieve). The molecular sieve is H-ZSM-5 molecular sieve modified by adding metal Mn, and the mass ratio of the doped metal oxide containing magnesium and zirconium to the molecular sieve is 1:1 - 1:2.

[0013] Further preferably, the composite bifunctional catalyst is 1Fe-MgZrOx / 2Mn-ZSM5-117 or 1Fe-MgZrOx / 2Mn-ZSM5-117@Si.

[0014] The MgZrO x / H-ZSM-5 composite bifunctional catalyst for synthesizing aromatics from syngas provided by the present invention has the following specific preparation steps:

[0015] (1) Preparation of doped metal oxide catalyst of MgZrO x The doped metal oxide catalyst of MgZrO is prepared by coprecipitation method or impregnation method.

[0016] The doped metal oxide catalyst of MgZrO is prepared by coprecipitation method or impregnation method. x The doped metal oxide catalyst;

[0017] Among them, for the preparation of the doped metal oxide of MgZrO by coprecipitation method x The doped metal oxide is as follows: zirconium salt and magnesium salt are added into water to form an aqueous solution, and then ammonia water solution is used as a precipitant, which is added into the above aqueous solution for precipitation at 80-90 °C. After the precipitation is complete at a stable temperature, it is aged for 2-4 h and then filtered, and washed with deionized water; then the solid product is dried overnight and calcined in air at 480-520 °C for 3-5 h to obtain the doped metal oxide catalyst of MgZrO. x The doped metal oxide catalyst;

[0018] Among them, for the preparation of the im-MgZrO x catalyst by impregnation method: first, magnesium salt is dissolved in deionized water, then ZrO2 powder carrier is added into the solution, stirred, dried, and then calcined in air at 480-520 °C for 3-5 h to obtain the im-MgZrO x catalyst;

[0019] (2) After the doped metal oxide catalyst of MgZrO prepared in step (1) is mechanically mixed with H-ZSM-5 molecular sieve, the catalyst is tableted and sieved to obtain the MgZrO x / H-ZSM-5 composite bifunctional catalyst. x / H-ZSM-5 composite bifunctional catalyst.

[0020] Further, on the basis of the doped metal oxide of MgZrO, the Fe-MgZrO x or Zn-MgZrO x doped metal oxide catalyst is further prepared by impregnation method, specifically: first, iron salt or magnesium salt is dissolved in deionized water, then MgZrO x powder carrier is added into the solution, stirred, dried, and then calcined in air at 480-520 °C for 3-5 h to obtain Fe-MgZrO x or Zn-MgZrO x or Zn-MgZrOx Doped metal oxide catalyst

[0021] Furthermore, on the basis of H-ZSM-5 molecular sieve, Ce-ZSM5 molecular sieve, Fe-ZSM5 molecular sieve or Mn-ZSM5 molecular sieve is further prepared by ion exchange method. Specifically: first, cerium salt, iron salt or manganese salt is dissolved in water, then H-ZSM5 molecular sieve carrier is added to the solution, stirred in a water bath for 3-5 h, dried, and then calcined in air at 480-520 °C for 3-5 h to obtain Ce-ZSM5 molecular sieve, Fe-ZSM5 molecular sieve or Mn-ZSM5 molecular sieve.

[0022] Furthermore, on the basis of Mn-ZSM5 molecular sieve, Ce-ZSM5 molecular sieve or Fe-ZSM5 molecular sieve, the molecular sieve is silanized by chemical liquid deposition method (CLD). Specifically: H-ZSM5 molecular sieve and tetraethyl orthosilicate are added to n-hexane for hydrothermal reaction, dried, and then calcined in air at 480-520 °C for 3-5 h.

[0023] The technical effects of the present invention are as follows: the doped metal oxide catalyst is simple and economical to prepare, and is easy to be industrially produced; it has the advantages of high catalytic activity, low by-product selectivity, high proportion of light aromatics in the product and high stability in the direct synthesis of aromatics from syngas through the oxygen-containing intermediate route. Description of the Drawings

[0024] Figure 1 For MgZrO x Doped metal oxide catalyst and ZrO x XRD pattern of the catalyst;

[0025] Figure 2 For MgZrO x Doped metal oxide catalyst and ZrO x CO2-TPD pattern of the catalyst. Detailed Embodiments

[0026] Hereinafter, the present invention will be further described in detail by examples and drawings, but it is not limited thereto. The H-ZSM-5 molecular sieve of the present invention is purchased from Tianjin Nankai Catalyst Co., Ltd.

[0027] Example 1

[0028] MgZrO doped metal oxide catalyst is prepared by co-precipitation method. Specifically: x

[0029] ​(1) Dissolve 27.9 g of Zr(NO3)4·5H2O and 12.7 g of Mg(NO3)2·6H2O in 100 mL of water to form a solution;

[0030] (2) Using 25% aqueous ammonia solution as a precipitating agent, add it to the mixed aqueous solution prepared in step (1) at 85 °C for precipitation. After complete precipitation at a stable temperature, age for 3 h, filter, and wash with deionized water;

[0031] (3) Then dry the solid product overnight at 110 °C and calcine it in air at 500 °C for 4 h to obtain the MgZrO x doped metal oxide catalyst. The XRD pattern is as Figure 1 shown, and the CO2-TPD pattern is as Figure 2 shown. It can be seen from the figure that: the MgZrO x doped metal oxide catalyst and the ZrO x catalyst have obvious differences in the pattern.

[0032] Then grind and mix the MgZrO x doped metal oxide catalyst and the H-ZSM5 zeolite with a silica-alumina ratio of 117 in an agate mortar at a mass ratio of 1:1, denoted as 1MgZrO x / 1H-ZSM5-117. Press the catalyst into tablets and screen it to a particle size of 30-40 mesh.

[0033] Use the above bifunctional catalyst in the direct synthesis of aromatics from syngas via an oxygen-containing intermediate route. Specifically: First, load the catalyst into a fixed-bed reactor, introduce syngas (H2 / CO = 2), and conduct experiments at 400 °C and 3 MPa. The products are analyzed by a gas chromatograph.

[0034] It should be noted that: The catalyst evaluation experiments are always carried out under conditions that exclude the influence of internal and external diffusion of catalyst particles and under non-equilibrium conditions. A certain amount of catalyst particles are loaded in the reactor and activated under optimal activation conditions to make the catalyst in the best working state; then slowly introduce a certain pressure of syngas into the reactor and gradually adjust the pressure and temperature to the reaction pressure and reaction temperature respectively. During the reaction process, the effluent from the reactor outlet passes through a cold trap and a backpressure valve, and the liquid products generated by the reaction can be collected through a condensation device. The remaining small-molecule gases are collected with gas bags at certain intervals and the gas products are analyzed by a gas chromatograph.

[0035] Example 2

[0036] Prepare the MgZrO x doped metal oxide catalyst by the co-precipitation method. The specific preparation method is the same as that in Example 1. Then the MgZrO xThe doped metal oxide catalyst and H-ZSM5-117 molecular sieve were ground and mixed in an agate mortar at a mass ratio of 1:2, denoted as 1MgZrO x / 2H-ZSM5-117. The catalyst was pressed and sieved to a particle size of 30-40 mesh.

[0037] The above bifunctional catalyst was used in the reaction process of directly synthesizing aromatics from syngas. Specifically: First, the catalyst was loaded into a fixed-bed reaction device, and the reaction conditions and product analysis were the same as in Example 1.

[0038] Example 3

[0039] The MgZrO x doped metal oxide catalyst was prepared by the impregnation method. Specifically:

[0040] (1) First, 27.9 g of Mg(NO3)2·6H2O was dissolved in an appropriate amount of deionized water, and then 12.7 g of ZrO2 powder carrier was added to the solution and stirred for 30 min;

[0041] (2) After stirring, it was dried overnight at 100 °C and then calcined at 500 °C for 4 h to obtain im-MgZrO x catalyst.

[0042] The im-MgZrO x catalyst and H-ZSM5-117 molecular sieve were ground and mixed in an agate mortar at a mass ratio of 1:2, denoted as 1im-MgZrO x / 2H-ZSM5-117. The catalyst was pressed and sieved to a particle size of 30-40 mesh.

[0043] The above bifunctional catalyst was used in the reaction process of directly synthesizing aromatics from syngas. Specifically: The catalyst was loaded into a fixed-bed reaction device, and the reaction conditions and product analysis were the same as in Example 1.

[0044] Example 4

[0045] The MgZrO x doped metal oxide catalyst was prepared by the co-precipitation method, and the specific preparation method was the same as in Example 1. Then, the MgZrO x doped metal oxide catalyst and H-ZSM5-80 molecular sieve were ground and mixed in an agate mortar at a mass ratio of 1:2, denoted as 1MgZrO x / 2H-ZSM5-80. The catalyst was pressed and sieved to a particle size of 30-40 mesh.

[0046] The above bifunctional catalyst was used in the reaction process of directly synthesizing aromatics from syngas. Specifically: The catalyst was loaded into a fixed-bed reaction device, and the reaction conditions and product analysis were the same as in Example 1.

[0047] Example 5

[0048] Using MgZrO x solid solution as the carrier, an Fe-MgZrO x doped metal oxide catalyst was prepared by the impregnation method, specifically:

[0049] (1) First, 0.7 g of Fe(NO3)3·9H2O was dissolved in an appropriate amount of deionized water, and then 3 g of MgZrO x powder carrier (the preparation method refers to Example 1) was added to the solution and stirred for 30 min;

[0050] (2) After stirring, it was dried overnight at 100 °C and then calcined at 500 °C for 4 h to obtain Fe-MgZrO x catalyst.

[0051] The Fe-MgZrO x catalyst and H-ZSM5-117 molecular sieve were ground and mixed in an agate mortar at a mass ratio of 1:2, denoted as 1Fe-MgZrO x / 2H-ZSM5-117, and the catalyst was tableted and sieved to a particle size of 30-40 mesh.

[0052] The above bifunctional catalyst was used in the direct synthesis of aromatics from syngas reaction process, specifically: The catalyst was loaded into a fixed-bed reaction device, and the reaction conditions and product analysis were the same as in Example 1.

[0053] Example 6

[0054] Using MgZrO x solid solution as the carrier, a Zn-MgZrO x doped metal oxide catalyst was prepared by the impregnation method, specifically:

[0055] (1) First, 0.46 g of Zn(NO3)2·6H2O was dissolved in an appropriate amount of deionized water, and then 3 g of MgZrO x powder carrier (the preparation method refers to Example 1) was added to the solution and stirred for 30 min;

[0056] (2) After stirring, it was dried overnight at 100 °C and then calcined at 500 °C for 4 h to obtain Zn-MgZrO x catalyst.

[0057] The Zn-MgZrO x catalyst and H-ZSM5-117 molecular sieve were ground and mixed in an agate mortar at a mass ratio of 1:2, denoted as 1Zn-MgZrO x / 2H-ZSM5-117, and the catalyst was tableted and sieved to a particle size of 30-40 mesh.

[0058] The above bifunctional catalyst was used in the reaction process of directly synthesizing aromatics from syngas. Specifically, the catalyst was loaded into a fixed-bed reaction device, and the reaction conditions and product analysis were the same as those in Example 1.

[0059] Example 7

[0060] Using H-ZSM5-117 molecular sieve as the carrier, Ce-ZSM5-117 molecular sieve was prepared by the ion exchange method. Specifically:

[0061] (1) First, 0.31 g of Ce(NO3)3·6H2O was dissolved in an appropriate amount of deionized water, and then 2 g of H-ZSM5-117 molecular sieve carrier was added to the solution, followed by stirring in a water bath for 4 h.

[0062] (2) After hydrothermal stirring, it was dried overnight at 100 °C and then calcined at 500 °C for 4 h to obtain Ce-ZSM5-117 molecular sieve.

[0063] The Fe-MgZrO x doped metal oxide catalyst (the preparation method was referred to Example 5) and Ce-ZSM5-117 molecular sieve were ground and mixed in a mortar in a mass ratio of 1:2, denoted as 1Fe-MgZrO x / 2Ce-ZSM5-117. The catalyst was pressed and sieved to a particle size of 30-40 mesh.

[0064] The above bifunctional catalyst was used in the reaction process of directly synthesizing aromatics from syngas. Specifically, the catalyst was loaded into a fixed-bed reaction device, and the reaction conditions and product analysis were the same as those in Example 1.

[0065] Example 8

[0066] Using H-ZSM5-117 molecular sieve as the carrier, Mn-ZSM5-117 molecular sieve was prepared by the ion exchange method. Specifically:

[0067] (1) First, 0.46 g of Mn(NO3)2·4H2O was dissolved in an appropriate amount of deionized water, and then 2 g of H-ZSM5-117 molecular sieve carrier was added to the solution, followed by stirring in a water bath for 4 h.

[0068] (2) After hydrothermal stirring, it was dried overnight at 100 °C and then calcined at 500 °C for 4 h to obtain Mn-ZSM5-117 molecular sieve.

[0069] The Fe-MgZrO x doped metal oxide catalyst (the preparation method was referred to Example 5) and Mn-ZSM5-117 molecular sieve were ground and mixed in a mortar in a mass ratio of 1:2, denoted as 1Fe-MgZrO x / 2Mn-ZSM5-117, the catalyst was tableted and sieved to a particle size of 30-40 mesh.

[0070] The above bifunctional catalyst was used in the direct synthesis of aromatics from syngas. The catalyst was loaded into a fixed-bed reactor, and the reaction conditions and product analysis were the same as in Example 1.

[0071] Example 9

[0072] Using H-ZSM5-117 zeolite as a support, Mn-ZSM5-117@Si zeolite was prepared by the ion exchange method, specifically:

[0073] (1) First, 1.4 g of tetraethyl orthosilicate was dissolved in an appropriate amount of n-hexane, and then 2 g of Mn-ZSM5-117 zeolite support (the preparation method is referred to Example 8) was added to the solution, and the mixture was stirred for 4 h under water bath heating;

[0074] (2) After hydrothermal stirring, it was dried overnight at 100 °C, and then calcined at 500 °C for 4 h to obtain Mn-ZSM5-117@Si zeolite.

[0075] Mix the Fe-MgZrO x doped metal oxide catalyst (the preparation method refers to Example 5) and Mn-ZSM5-117@Si zeolite in a mass ratio of 1:2 and grind them in an agate mortar, denoted as 1Fe-MgZrO x / 2Mn-ZSM5-117@Si, the catalyst was tableted and sieved to a particle size of 30-40 mesh.

[0076] The above bifunctional catalyst was used in the direct synthesis of aromatics from syngas, specifically: The catalyst was loaded into a fixed-bed reactor, and the reaction conditions and product analysis were the same as in Example 1.

[0077] Comparative Example 1:

[0078] A ZrO2-doped metal oxide catalyst was prepared by the co-precipitation method. Specifically, 34.9 g of Zr(NO3)4·5H2O was added to 100 mL of water to form a solution. Then, an ammonia water solution with a certain ratio was prepared, and 25% ammonia water solution was used as a precipitant and added to the 85 °C mixed aqueous solution for precipitation. After complete precipitation at a stable temperature, it was aged for 3 h and filtered, and washed with deionized water. Then, the solid product was dried overnight at 110 °C and calcined in air at 500 °C for 4 h to obtain a ZrO2 metal oxide catalyst. The ZrO2 metal oxide catalyst and H-ZSM5-117 zeolite were ground and mixed in an agate mortar in a mass ratio of 1:1, denoted as 1ZrO x / 1H-ZSM5-117, the catalyst was tableted and sieved to 30-40 mesh.

[0079] The above bifunctional catalyst was used in the reaction process of directly synthesizing aromatics from syngas, specifically as follows: The catalyst was loaded into a fixed-bed reaction device, and the reaction conditions and product analysis were the same as those in Example 1.

[0080] The activities of the catalysts in each example are shown in Table 1 below.

[0081] Table 1 shows the catalytic activities of the catalysts in each example of the bifunctional catalyst of the present invention.

[0082]

[0083]

[0084] The specific examples of the present invention elaborate in detail the principle and implementation method of the catalyst preparation of the present invention and its application in the reaction process of directly synthesizing aromatics from syngas through an oxygen-containing intermediate route. The results show that the bifunctional catalysts of Example 8 (1Fe-MgZrOx / 2Mn-ZSM5-117) and Example 9 (1Fe-MgZrOx / 2Mn-ZSM5-117@Si) have the best performance. Compared with the unmodified bifunctional catalyst (Comparative Example 1), the 1Fe-MgZrOx / 2Mn-ZSM5-117 catalyst of Example 8 has an increase in CO conversion from 20.2% to 25.8%, a decrease in CO2 selectivity from 21% to 17.3%, and a significant increase in the proportion of light aromatics from 21.8% to 33.9%.

[0085] Through the detailed description of the reaction conditions and modification methods, other researchers in this field can practice the present invention and make other changes or modifications based on the modification of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A MgZrO x / H-ZSM-5 composite bifunctional catalyst for synthesizing aromatics from syngas, characterized in that, It is composed of a mixture of a magnesium-zirconium-containing doped metal oxide and a molecular sieve; The molecular sieve is H-ZSM-5, or an H-ZSM-5 molecular sieve modified by adding one or more of metals Mn, Ce, or Fe; The selected magnesium-zirconium-containing doped metal oxide is one or more of magnesium-zirconium doped oxide, zinc-magnesium-zirconium doped oxide, and iron-magnesium-zirconium doped oxide.

2. The composite bifunctional catalyst according to claim 1, wherein The silicon-aluminum ratio of the molecular sieve is 80-200.

3. The composite bifunctional catalyst according to claim 1, characterized in that, Relative to the H-ZSM-5 molecular sieve, the addition amount of the metal used in the modified H-ZSM-5 molecular sieve is 2%-10% by mass ratio.

4. The composite bifunctional catalyst according to claim 1, characterized in that, Relative to MgZrO x , the MgZrO x / H-ZSM-5 composite bifunctional catalyst is modified with 3%-10% of metallic Zn or Fe by mass ratio.

5. The composite bifunctional catalyst according to claim 1, characterized in that, The mass ratio of the magnesium-zirconium-containing doped metal oxide to the molecular sieve is 2:1-1:

3.

6. The composite bifunctional catalyst according to claim 1, characterized in that, The molecular sieve is passivated by adding SiO2, and the molecular sieve is an H-ZSM-5 molecular sieve modified by adding metal Mn.

7. The preparation method of the composite bifunctional catalyst according to claim 1 or 2, characterized in that, The specific steps are as follows: (1)MgZrO x Preparation of doped metal oxide catalyst Prepare the MgZrO x doped metal oxide catalyst by coprecipitation method or impregnation method; (2) Mix the doped metal oxide catalyst prepared in step (1) with H-ZSM-5 zeolite mechanically, then tablet and screen the catalyst to obtain the MgZrO x / H-ZSM-5 composite bifunctional catalyst. x ​ 8. The preparation method of the composite bifunctional catalyst according to claim 7, characterized in that, Based on MgZrO x doped metal oxide, the Fe-MgZrO x or Zn-MgZrO x doped metal oxide catalyst is further prepared by the impregnation method.

9. The preparation method of the composite bifunctional catalyst according to claim 7, characterized in that, On the basis of the H-ZSM-5 molecular sieve, Ce-ZSM5 molecular sieve, Fe-ZSM5 molecular sieve or Mn-ZSM5 molecular sieve is further prepared by the ion exchange method.

10. The preparation method of the composite bifunctional catalyst according to claim 9, characterized in that, On the basis of Mn-ZSM5 molecular sieve, Ce-ZSM5 molecular sieve or Fe-ZSM5 molecular sieve, the molecular sieve is silanized by the chemical liquid phase precipitation method.

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