Difunctional core-shell catalyst, preparation and CO2 hydrogenation coupling benzene alkylation reaction process

Abstract

The invention relates to a preparation method of a difunctional core-shell structure catalyst, the difunctional core-shell structure catalyst prepared by the method and application of the difunctional core-shell structure catalyst. The bifunctional core-shell catalyst is prepared by the following steps: mixing an aluminum source and a precipitator, crystallizing and washing to obtain Al2O3 precursor slurry; and then dispersing the Al2O3 precursor slurry and an HZSM-5 molecular sieve in deionized water, carrying out rotary evaporation drying, and roasting to obtain the HZSM-5-coated Al2O3 catalyst. The bifunctional core-shell catalyst has the advantages of simple preparation method and low cost. After being compounded with a ZnZrOx catalyst, the bifunctional core-shell catalyst disclosed by the invention is applied to CO2 hydrogenation coupling benzene alkylation reaction, and intermediate methanol is dehydrated and converted into DME on an Al2O3 shell layer, so that not only can the self-reaction of the intermediate methanol on an acid site of a core HZSM-5 molecular sieve be inhibited, but also the intermediate methanol is dehydrated in advance, and the reaction time is shortened; the poisoning effect of water molecules on acidic sites of the core HZSM-5 molecular sieve is reduced, so that the reaction process is high in benzene alkylation rate.

Description

Technical Field

[0001] The present invention belongs to the technical field of aromatic hydrocarbon preparation technology, and specifically relates to a bifunctional core-shell catalyst and a preparation method thereof, as well as a CO2 hydrogenation coupled benzene alkylation reaction process obtained by applying the bifunctional core-shell catalyst. Background Art

[0002] As the cornerstone of organic chemicals, polymer materials and fine chemicals, toluene plays a vital role in modern petrochemicals. At present, toluene mainly comes from the petroleum route aromatics complex and coal coking crude benzene hydrorefining. These production routes face serious challenges, such as being limited by fossil energy, low product yield and poor quality. With the rapid growth of market demand for toluene and the increasing depletion of fossil resources, countries around the world are actively developing new technologies for increasing toluene production through efficient non-fossil routes and expanding the source of raw materials for producing high-value aromatics. Based on the current strategic task of CO2 emission reduction and the current situation of overproduction of benzene, using CO2 / H2 as an alkylating agent and alkylating benzene to prepare high-value aromatics is undoubtedly of great significance for the conversion and utilization of CO2 and the quality improvement of benzene alkylation.

[0003] Chinese patent CN 110743609 B discloses a combined catalyst and its preparation method and a method for preparing xylene by coupling toluene alkylation with carbon dioxide hydrogenation. The catalyst in the first component is ZnZrO x1 (1<x1<2) metal oxide, the acidic molecular sieves in the second component include ZSM-5, MCM-22 and SAPO-34. Among them, the metal oxide is mainly used to reduce carbon dioxide to methanol, and the molecular sieve is mainly used to alkylate toluene and methanol to produce xylene. Compared with the traditional toluene methanol alkylation method, this process uses carbon dioxide and hydrogen as raw materials instead of methanol, which can inhibit the isomerization reaction of xylene and improve the selectivity of xylene in the product. However, the alkylation agent methanol has low alkylation activity on the acidic molecular sieve and tends to self-react and convert into low-carbon olefins, which reduces the utilization efficiency of the intermediate methanol and leads to lower benzene alkylation efficiency. Therefore, how to strengthen the efficient alkylation of oxygen-containing intermediates and raw benzene is the key to achieving high conversion rate and high selectivity of CO2 hydrogenation and benzene alkylation to produce toluene. Summary of the invention

[0004] On the basis of the prior art, the present invention aims at the fact that the intermediate or alkylating agent methanol in the process of CO2 hydrogenation coupled benzene alkylation reaction tends to self-react on the acidic molecular sieve, resulting in a low alkylation characteristic with the raw material benzene. Firstly, a new type of bifunctional core-shell catalyst is designed, and then it is combined with ZnZrO x The composite catalyst is applied to the CO2 hydrogenation coupled benzene alkylation reaction, which can greatly reduce the self-reaction of the intermediate methanol and improve the alkylation conversion efficiency of the raw benzene.

[0005] The bifunctional core-shell catalyst of the present invention is represented by HZSM-5@Al2O3, wherein the core structure is an HZSM-5 molecular sieve with a silicon-aluminum ratio of 15 to 100, and the mass ratio of the core structure HZSM-5 molecular sieve to the shell layer Al2O3 is 1 to 10. The bifunctional core-shell catalyst has two functions of catalyzing alkylation reaction and methanol dehydration reaction, and by adjusting the mass ratio of the core structure to the shell layer in the core-shell catalyst, the product distribution after application can be adjusted.

[0006] The preparation method of the HZSM-5@Al2O3 core-shell catalyst of the present invention comprises the following steps:

[0007] (1) Preparation of Al2O3 precursor slurry: adding an aluminum source and a precipitant together into deionized water to obtain a uniformly mixed solution, stirring the obtained mixed solution uniformly, and then transferring it to a reactor for static crystallization; then, taking out the crystallized product, centrifuging it / washing it with water until it is neutral, and obtaining Al2O3 precursor slurry;

[0008] (2) Preparation of HZSM-5@Al2O3 core-shell catalyst: The Al2O3 precursor slurry prepared in step (1) and the HZSM-5 molecular sieve are dispersed in a certain amount of deionized water; after being stirred evenly, the mixture is placed on a rotary evaporator to remove the deionized water to obtain a mixture, and the mixture is dried, calcined, and ground to obtain a core-shell structure catalyst HZSM-5@Al2O3 with the HZSM-5 molecular sieve as the core structure and the Al2O3 catalyst as the shell layer, and the mass ratio of the core structure to the shell layer is 1 to 10.

[0009] Preferably, the aluminum source in step (1) includes aluminum nitrate, aluminum sulfate, and aluminum chloride.

[0010] Preferably, the precipitant in step (1) includes ammonium carbonate, sodium carbonate, sodium bicarbonate, or urea.

[0011] Preferably, the crystallization temperature in step (1) is 150-210°C.

[0012] Preferably, the crystallization time in step (1) is 1 h to 100 h.

[0013] Preferably, the silicon-aluminum ratio of the ZSM-5 molecular sieve in step (2) is 15 to 1000.

[0014] Preferably, the evaporation temperature of the rotary evaporation in step (2) is 20 to 100°C.

[0015] Preferably, the calcination temperature in step (2) is 450-600°C.

[0016] The present invention also relates to a method of combining the HZSM-5@Al2O3 core-shell catalyst with ZnZrO x After the catalyst is compounded, it is applied to the CO2 hydrogenation coupled benzene alkylation reaction, thereby obtaining a reaction process for the preparation of toluene by CO2 hydrogenation coupled benzene alkylation. x The particle size of the catalyst is preferably 20 to 40 meshes. Then the two are physically mixed according to a certain mass ratio and loaded into the catalytic bed of the reactor.

[0017] The reaction principle of the reaction process of the present invention is to firstly x CO2 is hydrogenated to methanol under the action of the catalyst, and methanol is catalytically converted to dimethyl ether in the Al2O3 shell of the multifunctional core-shell catalyst. Then benzene and dimethyl ether diffuse into the core HZSM-5 of the multifunctional core-shell catalyst and are catalytically converted to the target product in the internal pore structure of HZSM-5. In this process, by strengthening the conversion of the intermediate methanol to dimethyl ether, the directional conversion of CO2 hydrogenation to methanol intermediates is promoted, and the occurrence of reverse water gas reaction is inhibited; at the same time, the formation of alkylating agents is regulated to reduce the activation energy required for the alkylation reaction with benzene, and the local environment for the formation of in-situ water in the alkylation reaction is regulated, which weakens the competitive adsorption between it and the raw material / alkylating agent, thereby improving the alkylation efficiency of benzene.

[0018] Preferably, the reaction process of the present invention adopts a fixed bed reactor. More preferably, the optimal reaction conditions are a reaction temperature of 300-500°C, a pressure of 0.1-6 MPa, and a flow rate of the raw material CO2 / CO / H2 gas of 10-200 mL·min -1 , the mass space velocity of raw material benzene is 1~6·h -1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Electron micrographs of the HZSM-5@Al2O3 catalyst prepared in Example 1 of the present invention, including: (a) TEM image of the shell Al2O3 catalyst, (b) TEM image of the core structure HZSM-5 molecular sieve, (c) and (d) are TEM and SEM images of the HZSM-5@Al2O3 catalyst, respectively. DETAILED DESCRIPTION

[0020] The specific implementation scheme of the present invention is further described in detail below through specific implementation cases.

[0021] In the following examples, Examples 1 to 4 are preferred implementation methods of the preparation process of some HZSM-5@Al2O3 core-shell catalysts of the present invention.

[0022] [Example 1]

[0023] Appropriate amounts of aluminum nitrate and urea in a molar ratio of 1:3 were dissolved in 500 ml of deionized water, and after being fully stirred, the mixture was transferred to a hydrothermal reactor and allowed to stand for crystallization at 210° C. for 2 h. The crystallized product was washed to obtain an Al2O3 precursor slurry.

[0024] An appropriate amount of tetrapropylammonium hydroxide (TPAOH), tetraethyl orthosilicate (TEOS, expressed as SiO2) and deionized water are mixed and aged in a water bath at 80°C for 12 hours, and then NaOH solution and Al(NO3)3 solution are simultaneously added to the mixed solution to obtain a mixed material, and then the mixed material is hydrothermally reacted at 170°C for 24 hours; wherein the molar ratio of each material in the mixed material is: 6SiO2:15TPAOH:1Al2O3:5Na2O:500H2O. After the hydrothermal reaction is completed, the reaction solution is cooled to room temperature and centrifuged. The solid product is washed, dried, ground, and calcined at 550°C for 6 hours to obtain a NaZSM-5 molecular sieve, which is then ion exchanged to obtain a HZSM-5 molecular sieve with a silicon-aluminum ratio of 85.

[0025] 10.8 g of the Al2O3 precursor slurry prepared in step (1) and 3 g of the HZSM-5 molecular sieve prepared in step (2) were dispersed in 50 ml of deionized water and stirred thoroughly. The deionized water was then evaporated away using a rotary evaporator. The obtained solid product was calcined at 550°C for 3 h and ground to 20 to 40 mesh to obtain a HZSM-5@Al2O3 core-shell catalyst, labeled Cat1.

[0026] [Example 2]

[0027] The preparation method of Al2O3 precursor slurry and the preparation method of HZSM-5 molecular sieve are the same as those in Example 1.

[0028] 3.6 g of Al2O3 precursor slurry and 3 g of HZSM-5 molecular sieve were dispersed in 30 mL of deionized water. After sufficient stirring, the water was removed by rotary evaporation. The obtained solid product was calcined at 550°C for 3 h and ground to 20 to 40 mesh to obtain a HZSM-5@Al2O3 core-shell structure catalyst, which was labeled as Cat2.

[0029] [Example 3]

[0030] The preparation method of Al2O3 precursor slurry and the preparation method of HZSM-5 molecular sieve are the same as those in Example 1.

[0031] 10.8 g of Al2O3 precursor slurry and 3 g of HZSM-5 molecular sieve prepared in step (2) were dispersed in 50 ml of deionized water and stirred thoroughly. The deionized water was then removed by rotary evaporation. The obtained solid product was calcined at 550°C for 3 h to obtain a HZSM-5@Al2O3 core-shell catalyst, which was labeled Cat3.

[0032] [Example 4]

[0033] The preparation method of Al2O3 precursor slurry and the preparation method of HZSM-5 molecular sieve are the same as those in Example 1.

[0034] 18 g of Al2O3 precursor slurry and 3 g of HZSM-5 molecular sieve were dispersed in 30 mL of deionized water; after stirring evenly, the deionized water was removed by rotary evaporation, and the obtained solid product was calcined at 600°C for 3 h to obtain a HZSM-5@Al2O3 core-shell structure catalyst, marked as Cat4.

[0035] The shell layer, core layer and HZSM-5@Al2O3 samples of the Cat1 to Cat4 catalysts prepared in Examples 1 to 4 were tested by TEM using a JEM-2100F transmission electron microscope. The test method is as follows: a small amount of sample is placed in an ethanol solution, and after ultrasonication for 40 minutes, a small amount of the upper mixture is sucked by a syringe and dripped onto a copper mesh covered with a carbon support film. After natural drying, the test is performed at an accelerating voltage of 200 kV. Since the characterization diagrams are basically the same, the test results of the Cat1 catalyst prepared in Example 1 (see Figure 1 ) as an example to illustrate.

[0036] Figure 1 Middle: (a) TEM image of shell Al2O3 catalyst, (b) TEM image of core structure HZSM-5 molecular sieve, (c) TEM image of HZSM-5@Al2O3 catalyst. Figure 1 It can be seen that the catalyst prepared by the method of the present invention has a shell Al2O3 sample that is nano-thin and rich in a large number of mesoporous structures, while the core structure HZSM-5 molecular sieve has a columnar structure. It is worth noting that the HZSM-5 molecular sieve is enriched with nano-thin Al2O3 (such as Figure 1 (c) shows that the thin Al2O3 flakes are bonded to the outer layer of the HZSM-5 molecular sieve to form a stable shell structure.

[0037] The core-shell structure HZSM-5@Al2O3 catalyst prepared by the method of the present invention was further characterized by a Czech TESCAN MIRA LMS scanning electron microscope. The test method is: a trace amount of sample is bonded to a conductive adhesive, and a Quorum SC7620 sputtering coater is used to spray gold for 180 seconds, and then the sample is placed in a scanning electron microscope for morphology testing. The results are shown in Figure 1 In (d). Because the TEM images of the aforementioned catalysts are basically similar, the SEM images of the catalysts prepared in Examples 1 to 4 of the present invention are also basically the same, so here only Example 1 is used as an example to illustrate the test results of the catalyst prepared by the method of the present invention.

[0038] Figure 1 (d) shows that the HZSM-5@Al2O3 catalyst prepared by the method of the present invention has a spherical structure and is covered with an Al2O3 nanosheet shell. Figure 1 The test results in (c) fully demonstrate that in the core-shell structured HZSM-5@Al2O3 catalyst prepared by the method of the present invention, the shell Al2O3 is firmly bonded to the outer layer of the HZSM-5 molecular sieve.

[0039] In the method of the present invention, ZnZrO is prepared by coprecipitation x Catalyst, since the coprecipitation method for preparing metal oxides is a common method in the art (see CN 110743609 B, CN113600229B, CN 115646537 A), the present invention does not provide a detailed exemplary description, and only some preferred embodiments of the present invention are listed below through Examples 5 and 6. The preferred coprecipitation method for preparing ZnZrO x The method of the metal oxide catalyst is: mixing the corresponding metal salt and the precipitant, causing a coprecipitation reaction to obtain a precipitate; washing and calcining the precipitate in sequence to obtain a metal oxide. In the present invention, the metal salt is a metal nitrate, the precipitant is ammonia water, the washing times are preferably 1 to 5 times, the washing detergent is preferably deionized water and / or ultrapure water, the calcination process is carried out in an air atmosphere, the calcination temperature is 400 to 700°C, and the calcination time is 2 to 12 hours.

[0040] [Example 5]

[0041] 100 mL of industrial ammonia water, an appropriate amount of 0.01 mol / L zinc nitrate solution and an appropriate amount of 0.08 mol / L zirconium nitrate solution were simultaneously added dropwise into a three-necked flask for coprecipitation reaction. During the reaction, the temperature of the mixed liquid in the flask was kept at 70°C and pH = 7. After the reaction was complete, it was aged for 3 hours, filtered and washed. The obtained solid product was dried at 100°C for 12 hours and then ground. After grinding, it was placed in a muffle furnace and heated to 500°C at a heating rate of 5°C / min and then kept for 3 hours to obtain ZnZrO 0.13 catalyst.

[0042] [Example 6]

[0043] 100 mL of industrial ammonia solution, an appropriate amount of 0.01 mol / L zinc nitrate and an appropriate amount of 0.04 mol / L zirconium nitrate solution were simultaneously added dropwise to a three-necked flask for coprecipitation reaction. During the reaction, the temperature of the mixed liquid in the flask was kept at 70°C and pH = 7. After the reaction was complete, it was aged for 3 hours, filtered and washed. The obtained solid product was dried at 100°C for 12 hours, then ground, and heated to 500°C in a muffle furnace at a heating rate of 5°C / min for 3 hours to obtain ZnZrO 0.23 Oxide.

[0044] It should be noted that in the embodiments of the present invention, x in ZnZrOx oxide is not limited. In the preparation methods of Examples 5 and 6, the reaction conditions are controlled so that x in ZnZrOx oxide is 0.13 and 0.23 respectively, only for performance comparison with the catalyst provided in CN110743609B. Therefore, Examples 5 and 6 are only exemplary descriptions and cannot be understood as limiting the scope of protection of the present invention.

[0045] The following examples 7 to 10 and comparative examples 1 to 3 further illustrate the HZSM-5@Al2O3 core-shell structure catalyst prepared by the method of the present invention and the ZnZrO prepared by the coprecipitation method. x The catalysts are connected in series and applied to a fixed bed reactor to produce toluene by coupling CO2 hydrogenation with benzene alkylation and the technical effect thereof.

[0046] [Example 7]

[0047] 0.1 g ZnZrO 0.13 The catalyst was mixed with 0.9 g of Cat1 catalyst and then placed in a fixed bed reactor for evaluation of CO2 hydrogenation coupled with benzene alkylation reaction. The reaction conditions were: temperature 350 °C, pressure 3 MPa, and mixed gas flow rate 80 ml min -1 , the mass space velocity of benzene is 1h -1 The gas phase products of the reaction were directly analyzed by online chromatography, and the liquid phase products were analyzed by offline chromatography.

[0048] [Example 8]

[0049] 0.1 g ZnZrO 0.23 The catalyst was mixed evenly with 0.75g Cat2 catalyst and placed in a fixed bed reactor for evaluation of CO2 hydrogenation coupled benzene alkylation reaction. The reaction conditions were: temperature 350℃, pressure 3MPa, mixed gas flow rate 100ml·min -1 The mass space velocity of benzene is 1.5h -1 The gas phase products of the reaction were directly analyzed by online chromatography, and the liquid phase products were analyzed by offline chromatography.

[0050] [Example 9]

[0051] 0.1 g ZnZrO 0.13 The catalyst was mixed evenly with 0.9 g of Cat3 catalyst and then placed in a fixed bed reactor for evaluation of CO2 hydrogenation coupled benzene alkylation reaction. The reaction conditions were: temperature 350 °C, pressure 3 MPa, mixed gas flow rate 80 ml min -1 , the mass space velocity of benzene is 1h -1 The gas phase products of the reaction were directly analyzed by online chromatography, and the liquid phase products were analyzed by offline chromatography.

[0052] [Example 10]

[0053] 0.1 g ZnZrO 0.13 The catalyst was tableted and sieved to obtain a granular catalyst with a size of 20 to 40 meshes. At the same time, 1.05g of Cat4 catalyst was tableted and sieved to obtain a granular catalyst with a size of 20 to 40 meshes. Then, the two kinds of particles were mixed and evaluated in a fixed bed reactor for the CO2 hydrogenation coupled benzene alkylation reaction. The reaction conditions were: temperature 350°C, pressure 3MPa, and mixed gas flow rate 80ml·min -1 , the mass space velocity of benzene is 1h -1 The gas phase products of the reaction were directly analyzed by online chromatography, and the liquid phase products were analyzed by offline chromatography.

[0054] [Comparative Example 1]

[0055] 0.1 g ZnZrO 0.13 The catalyst was pelletized and sieved with 0.9g HZSM-5 molecular sieve to obtain a granular catalyst with a size of 20 to 40 meshes. The two particles were evenly mixed. The CO2 hydrogenation coupled benzene alkylation reaction was evaluated in a fixed bed reactor. The reaction conditions were: temperature 350°C, pressure 3MPa, and mixed gas flow rate 80ml·min -1 , the mass space velocity of benzene is 1h -1The gas phase products of the reaction were directly analyzed by online chromatography, and the liquid phase products were analyzed by offline chromatography.

[0056] [Comparative Example 2]

[0057] 0.1 g ZnZrO 0.13 The catalyst was tableted and sieved separately to obtain a granular catalyst with a size of 20 to 40 meshes. At the same time, 0.3g Al2O3 and 0.9g HZSM-5 molecular sieve were ground clockwise in an agate mortar for 20 minutes, and the mixed catalyst was tableted and sieved using a tablet press to obtain a granular catalyst with a size of 20 to 40 meshes. The two kinds of particles were evenly mixed and evaluated in a fixed bed reactor for CO2 hydrogenation coupled benzene alkylation reaction. The reaction conditions were: temperature 350°C, pressure 3MPa, and mixed gas flow rate 80ml·min -1 , the mass space velocity of benzene is 1h -1 The gas phase products of the reaction were directly analyzed by online chromatography, and the liquid phase products were analyzed by offline chromatography.

[0058] The evaluation results of the catalytic performance of the series-connected catalysts in Examples 7 to 10 and Comparative Examples 1 to 2 are shown in Table 1.

[0059] Table 1 Evaluation of catalytic effects of Examples 7 to 10 and Comparative Examples 1 to 2

[0060]

[0061] It can be seen from Table 1 that under the same reaction conditions, compared with the method of Example 1, ZnZrO X (Comparative Examples 1 and 2, X=0.13) The catalyst and H-ZSM-5 molecular sieve (Cat1) were ground and mixed at a mass ratio of 0.1:0.9 and then used for catalytic reaction. In Example 7 of the present invention, 0.1 g ZnZrO 0.13 The catalyst was mixed with 0.9 g HZSM-5@Al2O3 core-shell catalyst for catalytic reaction. The benzene conversion rate and CO selectivity were significantly improved, and the toluene yield increased from 105.6 mg·g -1 zeolite ·h -1 Increased to 122.1 mg g -1 zeolite ·h -1 , an increase of 15.6%. When the H-ZSM-5 molecular sieve (Cat3) prepared by Example 3 of the preferred embodiment of the present invention was tested for tandem catalyst performance under the same conditions (i.e. Example 9), the benzene conversion rate and CO selectivity were further improved, and the corresponding toluene yield was increased to 162.8 mg·g -1 zeolite ·h -1, an increase of 54.2%. However, if the amount of HZSM-5@Al2O3 core-shell structure catalyst is reduced during the catalytic process (see Example 8), the benzene conversion rate, CO selectivity and toluene yield will decrease slightly, but the catalytic performance of the tandem catalyst is still significantly better than that of Comparative Example 1. Under the same conditions, the benzene conversion rate, CO selectivity and toluene yield did not change significantly by increasing the amount of Al2O3 in Comparative Document 2, indicating that the HZSM-5@Al2O3 core-shell structure catalyst prepared by the present invention is better than that of ZnZrO X The oxide catalysts were mixed and applied to the CO2 hydrogenation coupled benzene alkylation reaction, which can significantly improve the conversion rate of raw CO2 and benzene and improve the toluene selectivity. Among them, the improvement of toluene yield is related to the fact that the HZSM-5@Al2O3 core-shell catalyst inhibits the formation of light hydrocarbons to a certain extent and strengthens the catalytic performance of methanol dehydration to dimethyl ether.

[0062] From the perspective of catalytic principle, ZnZrO X After the catalyst was connected in series with the HZSM-5@Al2O3 core-shell structure catalyst, in the process of CO2 hydrogenation coupled with benzene alkylation reaction, the raw materials CO2 and H2 were x The intermediate methanol diffuses to the Al2O3 shell of the HZSM-5@Al2O3 catalyst and is dehydrated to DME via Lewis acid sites, which diffuses to the HZSM-5 core and is converted to DME via The site participates in the benzene alkylation reaction. Compared with the traditional alkylation process (using the intermediate methanol as the alkylation agent), the alkylation agent DME formed in the process has a higher alkylation activity. At the same time, the intermediate methanol is dehydrated on the Al2O3 shell layer and converted into DME, which can not only inhibit the self-reaction of the intermediate methanol on the acidic site of the core HZSM-5 molecular sieve, but also the intermediate methanol is dehydrated in advance, reducing the poisoning effect of water molecules on the acidic site of the core HZSM-5 molecular sieve. Therefore, the reaction process of the present invention shows a higher benzene alkylation efficiency.

[0063] The above is only a preferred embodiment of the present invention. It should be pointed out that for those skilled in the art, several improvements and process combinations can be made without departing from the principles of the present invention. Any improvements and modifications made under the guidance of the spirit of the present invention should be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a bifunctional core-shell catalyst, comprising the following steps: a) dissolving an appropriate amount of aluminum source and precipitant in deionized water, transferring the obtained mixed solution to a hydrothermal reactor for static crystallization, and washing the crystallized product with water until it is neutral to obtain an Al2O3 precursor slurry; b) The Al2O3 precursor slurry prepared in step a) and the HZSM-5 molecular sieve are dispersed in deionized water according to a certain mass ratio, fully stirred, and then the water is removed by rotary evaporation. The obtained solid product is calcined at high temperature and ground to obtain a HZSM-5@Al2O3 core-shell structure catalyst.

2. The preparation method according to claim 1, characterized in that: The aluminum source includes any one or more of aluminum nitrate, aluminum sulfate and aluminum chloride.

3. The preparation method according to claim 1, characterized in that: The precipitant includes any one or more of ammonium carbonate, sodium carbonate, sodium bicarbonate and urea.

4. The preparation method according to claim 1, characterized in that: During the static crystallization process, the crystallization temperature is 150-210°C and the crystallization time is 1h-10h.

5. The preparation method according to claim 1, characterized in that: The calcination temperature is 450-600° C. and the calcination time is 4-6 hours.

6. A bifunctional core-shell structure catalyst prepared by the preparation method according to any one of claims 1 to 5.

7. The bifunctional core-shell structure catalyst according to claim 6, characterized in that: The core structure of the catalyst is a HZSM-5 molecular sieve with a silicon-aluminum ratio of 15-100, and the mass ratio of the core structure HZSM-5 molecular sieve to the shell Al2O3 is 1-10.

8. The bifunctional core-shell structure catalyst according to claim 6, characterized in that: The particle size of the catalyst is 20 to 40 meshes.

9. A bifunctional core-shell catalyst according to any one of claims 7 or 8 and ZnZrO x The catalysts are connected in series and applied to the reaction process of CO2 hydrogenation coupled with benzene alkylation to produce toluene.

10. The reaction process according to claim 9, characterized in that: The reactor adopts a fixed bed reactor, and the reaction process conditions are: reaction temperature 300-500°C, pressure 0.1-6MPa, raw material mixed gas flow rate 10-200mL·min -1 , the mass space velocity of benzene is 1~6h -1 .

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