Core-shell structure catalyst for preparing xylene by coupling carbon dioxide hydrogenation with toluene alkylation as well as preparation method and application of core-shell structure catalyst

Abstract

The invention discloses a core-shell catalyst for preparing xylene through carbon dioxide hydrogenation coupled toluene alkylation, the catalyst is composed of a metal oxide, an adhesive and a molecular sieve, the metal oxide is formed by one or more of GaZrOx, InZrOx, ZnZrOx or CrZrOx; the molecular sieve is formed by combining one or two of a ZSM-5 molecular sieve and a ZSM-11 molecular sieve. The invention also discloses a preparation method of the catalyst, which comprises the following specific steps: 1) adding a precipitant into a metal salt aqueous solution while heating and stirring, and aging, washing, drying and roasting the obtained mixture to prepare composite metal oxide particles; 2) dropwise adding a silica sol aqueous solution into the composite metal oxide particles to wet the metal oxide particles, and then mixing with molecular sieve powder to prepare molecular sieve coated metal oxide particles; and 3) drying the molecular sieve coated metal oxide particles and then roasting. The catalyst provided by the invention has a special core-shell structure and can effectively improve the toluene conversion rate.

Description

Technical Field

[0001] The invention relates to the technical field of catalysts, in particular to a core-shell structure catalyst for preparing xylene by coupling carbon dioxide hydrogenation with toluene alkylation, and a preparation method and application thereof. Background Art

[0002] The preparation of high value-added chemicals from carbon dioxide is one of the effective means to improve the utilization rate of carbon dioxide and replace fossil energy (Wenhang Wang, Chunyang Zeng and Noritatsu Tsubak, Recent advancements and perspectives of the CO 2 hydrogenation reaction[J].Green Carbon,2023,1,133-145.;Jian Wei,Ruwei Yao,Yu Han,Qingjie Ge and Jian Sun,Towards the development of the emerging process of CO 2 Heterogeneous hydrogenation into high-value unsaturated heavy hydrocarbons[J].Chem.Soc.Rev.,2021,50,10764-10805.). Carbon dioxide can be hydrogenated to obtain a variety of products, among which aromatic products can be further processed for the production of fuels, medicines and fiber products. At present, the methods for preparing aromatics by hydrogenating carbon dioxide are mainly divided into two categories: direct hydrogenation and coupled aromatic alkylation. Among them, the method for directly hydrogenating carbon dioxide to prepare aromatics is usually to convert carbon dioxide to aromatics using an iron-based catalyst or a bifunctional catalyst composed of a composite of a metal oxide and a molecular sieve (Guo Tian, ​​Zhengwen Li, Chenxi Zhang and Xinyan Liu et al., Upgrading CO 2to sustainable aromatics via perovskite-mediated tandem catalysis[J].Nature Communications,2024,15,3037-3050.); while the method of carbon dioxide hydrogenation coupled toluene alkylation to produce aromatics is to use metal oxide catalysts to convert carbon dioxide and hydrogen to produce methanol intermediates, and then the obtained intermediates are alkylated with toluene to produce xylene. The direct hydrogenation method with iron-based catalysts has a high carbon dioxide conversion rate and a low carbon monoxide selectivity, but its final product distribution is wide and the selectivity of single aromatics is low; while the carbon dioxide hydrogenation coupled to aromatic alkylation method not only has a high atom economy, but also can obtain a higher single aromatic selectivity. In the presence of toluene, CO 2 As carbon source, ZnZrO x The toluene conversion rate was 10%, the xylene selectivity was 80%, and the para-xylene (PX) selectivity in xylene was 70%. (Jiachang Zuo, Weikun Chen, Jia Liu and Xinping Duan et al., Selective methylation of toluene using CO 2 and H 2 to para-xylene[J].Science Advance,2020,6,eaba5433.). In addition, the Aspen Plus simulation was used to simulate the CO 2 The direct (coupled alkylation) and indirect (hydrogenation to methanol, then methanol-toluene alkylation) processes for methylation production of PX were compared, and it was found that the direct process was superior to the indirect process in terms of element utilization, demand for cold and hot utilities, energy efficiency and economic benefits, and CO 2 The emissions are significantly lower. The direct process has strong environmental and economic advantages due to its low energy consumption, low fixed investment and high economic returns. (Ruonan Liu, Junqiang Zhang, Guizhu Zhang and Wei Zhang et al., Carbon dioxide methylation with toluene to para-xylene process: Technical, economic and environmental evaluation[J]. Chem. Eng. Process., 2024, 201, 109834-109847.)

[0003] At present, most catalysts used for catalytic hydrogenation of carbon dioxide coupled to alkylation of toluene to produce xylene are composite catalysts prepared by grinding mixed metal oxides and molecular sieves. In such catalysts, the uniformly dispersed metal oxides are directly exposed to the toluene atmosphere during the reaction, which affects the performance of the metal oxides (Zhikai Xiao, Hai Huang, Chenxi Cao, Jing Xu and Zixu Yang, Designing abifunctional ZrCuO x / HZSM-5catalyst for selective methylation of toluene with carbondioxide to para-xylene[J].Fuel,2022,319,123848-123866.); Therefore, although this method can generally obtain 80% or more xylene selectivity, its carbon dioxide and toluene conversion rates are relatively low.

[0004] In summary, there are still many problems in the catalyst for preparing xylene by catalytic hydrogenation of carbon dioxide coupled with alkylation of toluene, such as how to design a catalyst with high stability and high selectivity. In view of this, this patent application is specially proposed. Summary of the invention

[0005] The purpose of the present invention is to provide a core-shell structure catalyst for the production of xylenes by coupling the hydrogenation of carbon dioxide to toluene and a preparation method thereof, and to successfully apply the prepared catalyst to the reaction of coupling the hydrogenation of carbon dioxide to toluene to produce xylene, thereby solving the problem that the performance of the existing catalysts is easily affected by the substrate toluene.

[0006] To achieve the above-mentioned purpose, the present invention provides a core-shell catalyst for the production of xylene by coupling the hydrogenation of carbon dioxide with the alkylation of toluene. The catalyst is composed of a metal oxide, a binder and a molecular sieve. The metal oxide is GaZrO x ,InZrO x 、ZnZrO x or CrZrO x The molecular sieve is composed of one or more of ZSM-5 molecular sieve or ZSM-11 molecular sieve.

[0007] Furthermore, the catalyst has a core-shell structure, and the core-shell structure is constructed by bonding the molecular sieve layer by layer on the metal oxide surface with the adhesive.

[0008] The preparation method of the core-shell catalyst for the production of xylene by coupling the hydrogenation of carbon dioxide with the alkylation of toluene specifically comprises the following steps:

[0009] 1) adding a precipitant to a metal salt aqueous solution under heating and stirring, and preparing composite metal oxide particles after aging, washing, drying and calcining the obtained mixture;

[0010] 2) adding a silica sol aqueous solution to the composite metal oxide particles obtained in step 1) to wet the metal oxide particles, then mixing the wetted metal oxide particles with molecular sieve powder, and shaking the resulting mixture until the molecular sieve powder completely covers the metal oxide particles to obtain molecular sieve-coated metal oxide particles;

[0011] 3) The metal oxide particles coated with the molecular sieve obtained in step 2) are dried and then calcined to obtain the core-shell catalyst for the carbon dioxide hydrogenation coupled toluene alkylation to produce xylene.

[0012] Furthermore, the metal salt described in step 1) is composed of one or more combinations of gallium nitrate, indium nitrate, zinc nitrate, chromium nitrate or zirconium nitrate; the precipitant is composed of one or more combinations of ammonium carbonate, sodium carbonate, ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate or potassium bicarbonate.

[0013] Furthermore, the heating and stirring temperature in step 1) is 60-80° C., and the heating and stirring time is 2-3 hours; the roasting temperature is 500-600° C., and the roasting time is 2-3 hours.

[0014] Furthermore, the mass ratio of silica sol to water in the silica sol aqueous solution described in step 2) is 1:1 to 1:2.5.

[0015] Furthermore, the mass ratio of the metal oxide particles to the molecular sieve in step 2) is 1:9 to 9:1.

[0016] Furthermore, the calcination temperature in step 3) is 500-600° C., and the calcination time is 2-3 hours.

[0017] The application of the core-shell catalyst for the production of xylene by hydrogenation of carbon dioxide coupled to toluene alkylation comprises the following specific steps: the catalyst is reduced by a reducing gas and then mixed with the reaction raw materials to carry out the hydrogenation of carbon dioxide coupled to toluene alkylation reaction to produce xylene, wherein the reaction raw materials are a mixture of carbon dioxide, hydrogen, toluene and an inert gas.

[0018] Furthermore, the reducing gas is a hydrogen-argon mixed gas containing 5% hydrogen, the inert gas is one of argon or nitrogen; the reaction temperature is 320-360°C, the reaction pressure is 0.5-3MPa, and the space velocity of the reaction raw materials is 6000-12000mL·g -1 ·h -1, the space velocity of toluene is 0.1~0.9h- 1 .

[0019] The design principle of the present invention is as follows:

[0020] The preparation method of the catalyst provided by the present invention is to use silica sol aqueous solution as a binder to bond molecular sieve (for example, ZSM-5) powder layer by layer on the surface of metal oxide to construct a core-shell catalyst with a core-shell structure. Such a catalyst can perform diffusion control on the reaction intermediate and substrate when conducting a carbon dioxide hydrogenation coupled toluene alkylation reaction, thereby successfully avoiding the influence of the substrate toluene on the carbon dioxide hydrogenation performance of the core metal oxide. Specifically, the catalyst provided by the present invention utilizes the pore size of the shell molecular sieve ZSM-5, which is larger than the kinetic diameter of carbon dioxide and hydrogen molecules and close to the substrate toluene molecule, thereby avoiding toluene from directly contacting the metal oxide to affect the metal oxide catalytic carbon dioxide hydrogenation; this can not only give full play to the carbon dioxide hydrogenation performance of the metal oxide, but also further improve the alkylation conversion rate of toluene.

[0021] Compared with the existing carbon dioxide hydrogenation coupled toluene alkylation catalyst to produce xylene, the beneficial effects of the present invention are as follows:

[0022] (1) The catalyst provided by the present invention has a core-shell structure, and the special spatial confinement effect of the core-shell structure can effectively prevent the metal oxide from contacting the substrate toluene, reduce the interference of the substrate toluene on the catalytic performance of the metal oxide, thereby increasing the supply of alkylation intermediates and promoting toluene conversion.

[0023] (2) The method for preparing the core-shell catalyst for the carbon dioxide hydrogenation coupled toluene alkylation to produce xylene provided by the present invention has the advantages of simple operation method, short preparation time and mild reaction conditions. In addition, the catalyst preparation method provided by the present invention also has the advantage of a wide range of applications, and can be used to combine different metal oxides and molecular sieves to construct different core-shell catalysts.

[0024] (3) The catalyst provided by the present invention can be used for the reaction of carbon dioxide hydrogenation coupled to toluene alkylation to produce xylene. The results show that the catalyst provided by the present invention not only has good stability, but also has high conversion rate and selectivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The catalyst GaZrO prepared by the present invention x / ZSM-5 and GaZrO x @ZSM-5 stability test chart;

[0026] Figure 2 This is a SEM image of the core-shell structure catalyst provided by the present invention;

[0027] Figure 3 This is a schematic diagram of the reaction mechanism of the catalyst provided by the present invention catalyzing the hydrogenation of carbon dioxide coupled with the alkylation of toluene to produce xylene. DETAILED DESCRIPTION

[0028] The present application is further described in detail below through the accompanying drawings and embodiments. Through these descriptions, the characteristics and advantages of the present application will become clearer and more specific.

[0029] The reaction of the partial catalytic carbon dioxide hydrogenation coupled toluene alkylation to produce xylene in the embodiment of the present invention is carried out in a high-temperature and high-pressure fixed-bed continuous flow reactor, and the reaction tail gas is detected by online analysis using gas chromatography. Before the reaction, the catalyst needs to be pretreated with a reducing gas, and then the raw gas and substrate are introduced, and the carbon dioxide hydrogenation coupled toluene alkylation test is carried out at a certain pressure and temperature. The reaction product is analyzed online by gas chromatography, and the product is quantitatively analyzed using TCD and FID detectors.

[0030] Example 1

[0031] The specific preparation steps of the core-shell catalyst for carbon dioxide hydrogenation coupled toluene alkylation to produce xylene are as follows:

[0032] 1) Under stirring in an oil bath at 70°C, 3.06 g of ammonium carbonate was used as a precipitant and completely dissolved in 100 mL of water. The resulting solution was slowly added dropwise to the 0.60 g Zn(NO 3 ) 2 6H 2 O, 5.80 g Zr(NO 3 ) 4 ·5H 2 O and 100 mL of water; after the dropwise addition, the obtained mixture was stirred at 70°C for 2 h and then aged at room temperature for 2 h. After the aging, the obtained solid was washed 5 times with 200 mL of deionized water; the washed solid was dried at 105°C for 10 h; the dried solid was placed in a muffle furnace and calcined at 500°C for 3 h; the calcined solid was granulated and sieved to 30-40 mesh to obtain ZnZrO x Metal oxide particles;

[0033] 2) Weigh 0.25 g of ZnZrO obtained in step 1) x The metal oxide particles and 0.25 g ZSM-5 molecular sieve powder were set aside; 0.25 g ZnZrO x0.04 mL of a 0.12 wt% silica sol solution was added dropwise to the metal oxide particles until the metal oxide particles were completely wetted, and then the wetted metal oxide particles were transferred to a container pre-filled with 0.02 g of ZSM-5 molecular sieve powder, and shaken until the ZSM-5 molecular sieve powder in the container was completely coated on the surface of the metal oxide particles, and then sieved with a 60-mesh sieve to remove the ZSM-5 molecular sieve powder that was easily detached; the sieved particles were wetted again with a 0.12 wt% silica sol solution, and after complete wetting, the particles were transferred to a container pre-filled with 0.025 g of ZSM-5 molecular sieve powder, and shaken until the ZSM-5 molecular sieve powder in the container was completely coated on the surface of the particles, and then sieved with a 60-mesh sieve to remove the ZSM-5 molecular sieve powder that was easily detached; the above process was repeated many times until 0.25 g of ZSM-5 molecular sieve powder was used up to obtain ZSM-5 molecular sieve-coated ZnZrO x Metal oxide particles; in the process of coating the metal oxide particles, the amount of 0.12wt% silica sol solution used to wet the obtained particles each time is increased by 0.02mL compared with the previous time, and the ZSM-5 molecular sieve powder loaded into the container is increased by 0.005g compared with the previous time;

[0034] 3) The ZSM-5 molecular sieve coated ZnZrO obtained in step 2) x The metal oxide particles were placed in an oven and dried at 50°C for 12 hours. The dried particles were placed in a muffle furnace and calcined in air at 500°C for 2 hours to obtain the core-shell catalyst for carbon dioxide hydrogenation coupled to toluene alkylation to produce xylene. The obtained core-shell catalyst was recorded as ZnZrO x @ZSM-5.

[0035] The specific steps of carbon dioxide hydrogenation coupled toluene alkylation to produce xylene are as follows:

[0036] 0.2 g ZnZrO x The ZSM-5 core-shell catalyst was placed in a quartz reaction tube, and then the catalyst was pretreated with a hydrogen-argon mixture containing 5% hydrogen at 400°C for 2 h, and then heated at 12000 mL·g- 1 ·h- 1A reaction raw material mixed gas consisting of carbon dioxide, hydrogen, toluene and nitrogen (wherein the volume fraction of nitrogen is 1-10%, serving as an internal standard) is introduced at an air velocity of , wherein the molar ratio of hydrogen to carbon dioxide is 3:1, the molar ratio of carbon dioxide to gaseous toluene is 13:1, toluene is sampled using a bubbling tank at 90°C, the temperature of the catalytic reaction is 360°C, the pressure is 3MPa, and the reaction time is 15h; the reaction products are divided and then enter a gas chromatograph (GC) equipped with a flame ionization detector (FID) and a thermal conductivity detector (TCD) for online analysis, the conversion rate of carbon dioxide and the selectivity of the reaction products are calculated using a C-based normalization method, and the results are shown in Table 1.

[0037] Example 2

[0038] The preparation steps of the core-shell catalyst for the coupling of carbon dioxide hydrogenation with toluene alkylation to produce xylene are as described in Example 1, except that the amount of ammonium carbonate used in step 1) is changed to 2.98 g, and Zn(NO 3 ) 2 6H 2 O to Ga(NO 3 ) 3 ·xH 2 O, and Ga(NO 3 ) 3 ·xH 2 The amount of O used was 0.51 g; the remaining steps were the same as in Example 1; the prepared core-shell catalyst was recorded as GaZrO x @ZSM-5.

[0039] The steps of carbon dioxide hydrogenation coupled toluene alkylation to produce xylene are referred to Example 1, except that the catalyst ZnZrO x @ZSM-5 replaced by GaZrO x @ZSM-5, the results are shown in Table 1.

[0040] Example 3

[0041] The preparation steps of the core-shell catalyst for the coupling of carbon dioxide hydrogenation with toluene alkylation to produce xylene are as described in Example 1, except that the amount of ammonium carbonate used in step 1) is changed to 2.98 g, and Zn(NO 3 ) 2 6H 2 O becomes In(NO 3 ) 3 ·xH 2 O,In(NO 3 ) 3 ·xH 2 The amount of O used was 0.56 g; the remaining steps were the same as in Example 1; the prepared core-shell catalyst was recorded as InZrO x@ZSM-5. Here, the catalyst InZrO x @ZSM-5 was characterized by SEM, and the results are as follows Figure 2 As shown: Figure 2 InZrO after cutting x @ZSM-5 SEM spectrum, no Zr element signal was found in its core-shell layer, which indicates that the ZSM-5 molecular sieve powder is coated with InZrO x The metal oxide surface forms a core-shell structure catalyst.

[0042] The steps of carbon dioxide hydrogenation coupled toluene alkylation to produce xylene are referred to Example 1, except that the catalyst ZnZrO x @ZSM-5 replaced by InZrO x @ZSM-5, the results are shown in Table 1.

[0043] Example 4

[0044] The preparation steps of the core-shell catalyst for the coupling of carbon dioxide hydrogenation with toluene alkylation to produce xylene are as described in Example 1, except that the amount of ammonium carbonate used in step 1) is changed to 2.98 g, and Zn(NO 3 ) 2 6H 2 O turns into Cr(NO 3 ) 3 9H 2 O,Cr(NO 3 ) 3 9H 2 The amount of O used was 0.80 g; the remaining steps were the same as in Example 1; the prepared core-shell catalyst was recorded as CrZrO x @ZSM-5.

[0045] The steps of carbon dioxide hydrogenation coupled toluene alkylation to produce xylene are referred to Example 1, except that the catalyst ZnZrO x @ZSM-5 replaced by CrZrO x @ZSM-5, the results are shown in Table 1.

[0046] Comparative Example 1

[0047] The specific preparation steps of the powdered mixed catalyst for carbon dioxide hydrogenation coupled toluene alkylation to produce xylene are as follows:

[0048] 1) Under stirring in an oil bath at 70°C, 3.06 g of ammonium carbonate was used as a precipitant and completely dissolved in 100 mL of water. The resulting solution was slowly added dropwise to the 0.60 g Zn(NO 3 ) 2 6H 2 O, 5.80 g Zr(NO 3) 4 ·5H 2 O and 100 mL of water; after the addition, the mixture was stirred at 70 ° C for 2 h and then aged at room temperature for 2 h. After the aging, the solid was washed 5 times with 200 mL of deionized water; the washed solid was dried at 105 ° C for 10 h; the dried solid was placed in a muffle furnace and calcined at 500 ° C for 3 h to obtain ZnZrO x Metal oxides;

[0049] 2) 0.25 g of ZnZrO obtained in step 1) was added x The metal oxide and 0.25 g ZSM-5 molecular sieve were ground and mixed, granulated and sieved to 60 mesh to obtain the catalyst for carbon dioxide hydrogenation coupled to toluene alkylation to produce xylene; the obtained catalyst was recorded as ZnZrO x / ZSM-5.

[0050] The steps of carbon dioxide hydrogenation coupled toluene alkylation to produce xylene are referred to Example 1, except that the catalyst ZnZrO x @ZSM-5 replaced by ZnZrO x / ZSM-5, the results are shown in Table 1.

[0051] Comparative Example 2

[0052] The preparation steps of the powdered mixed catalyst for the hydrogenation of carbon dioxide coupled to the alkylation of toluene to produce xylene are as follows: 3 ) 2 6H 2 O to Ga(NO 3 ) 3 ·xH 2 O, and Ga(NO 3 ) 3 ·xH 2 The amount of O used was 0.51 g; the remaining steps were the same as in Example 1; the prepared catalyst was recorded as GaZrO x / ZSM-5.

[0053] The steps of carbon dioxide hydrogenation coupled toluene alkylation to produce xylene are referred to Example 1, except that the catalyst ZnZrO x @ZSM-5 replaced by GaZrO x / ZSM-5, the results are shown in Table 1.

[0054] Comparative Example 3

[0055] The preparation steps of the powdered mixed catalyst for the hydrogenation of carbon dioxide coupled to the alkylation of toluene to produce xylene are as follows: 3 ) 2 6H 2 O becomes In(NO 3 ) 3 ·xH 2 O,In(NO 3 ) 3 ·xH 2 The amount of O used was 0.56 g; the remaining steps were the same as in Example 1; the prepared catalyst was recorded as InZrO x / ZSM-5.

[0056] The steps of carbon dioxide hydrogenation coupled toluene alkylation to produce xylene are referred to Example 1, except that the catalyst ZnZrO x @ZSM-5 replaced by InZrO x / ZSM-5, the results are shown in Table 1.

[0057] Comparative Example 4

[0058] The preparation steps of the powdered mixed catalyst for the hydrogenation of carbon dioxide coupled to the alkylation of toluene to produce xylene are as follows: 3 ) 2 6H 2 O turns into Cr(NO 3 ) 3 9H 2 O,Cr(NO 3 ) 3 9H 2 The amount of O used was 0.80 g; the remaining steps were the same as in Example 1; the prepared catalyst was recorded as CrZrO x / ZSM-5.

[0059] The steps of carbon dioxide hydrogenation coupled toluene alkylation to produce xylene are referred to Example 1, except that the catalyst ZnZrO x @ZSM-5 replaced by CrZrO x / ZSM-5, the results are shown in Table 1.

[0060] Table 1 Results of the reaction of carbon dioxide hydrogenation coupled toluene alkylation to produce xylene

[0061]

[0062] Example 5

[0063] For the catalyst GaZrOx / ZSM-5 and GaZrO x / ZSM-5 stability test, the specific steps are as follows: 0.2gGaZrO x / ZSM-5 or GaZrO x The ZSM-5 catalyst was placed in a quartz reaction tube, and then the catalyst was pretreated with a hydrogen-argon mixture containing 5% hydrogen at 400°C for 2 h, and then heated at 12000 mL·g- 1 ·h- 1 A reaction raw material mixed gas consisting of carbon dioxide, hydrogen, toluene and nitrogen (wherein the volume fraction of nitrogen is 1-10%, used as an internal standard) is introduced at an air velocity of 1:1, wherein the molar ratio of hydrogen to carbon dioxide is 3:1, the molar ratio of carbon dioxide to gaseous toluene is 13:1, toluene is sampled using a bubbling tank at 90°C, the temperature of the catalytic reaction is 360°C, the pressure is 3MPa, and the reaction time is 100h; the reaction products are divided and then enter a gas chromatograph (GC) equipped with a flame ionization detector (FID) and a thermal conductivity detector (TCD) for online analysis, the conversion rate of carbon dioxide and the selectivity of the reaction products are calculated using a C-based normalization method, and the results of the stability test are shown in FIG. Figure 1 As shown. Figure 1 It can be seen that the core-shell structure catalyst GaZrO x @ZSM-5 and milled mixed catalyst GaZrO x / ZSM-5 showed high stability within 100 h. The toluene and CO 2 The conversion rate is much higher than that of the ground mixed catalyst, but the xylene selectivity of the core-shell catalyst is slightly lower than that of the ground mixed catalyst.

[0064] also, Figure 3 The schematic diagram of the reaction mechanism of the catalyst provided by the present invention for the catalytic hydrogenation of carbon dioxide coupled to the alkylation of toluene to produce xylene. In the ground mixed catalyst, the metal oxide will be more exposed to the substrate toluene atmosphere, causing its catalytic performance to be disturbed; while the core-shell structure catalyst can effectively avoid the contact between the metal oxide and the substrate toluene by using its special spatial confinement effect, reducing the interference of the substrate aromatic hydrocarbons on the catalytic performance of the metal oxide, thereby increasing the supply of alkylation intermediates and promoting toluene conversion; therefore, the toluene and CO of the core-shell structure catalyst are 2 The conversion rate can be higher than that of the ground mixed catalyst.

Claims

1. A core-shell catalyst for the production of xylene by coupling the hydrogenation of carbon dioxide with the alkylation of toluene, characterized in that: The catalyst is composed of metal oxide, adhesive and molecular sieve, and the metal oxide is GaZrO x ,InZrO x 、ZnZrO x or CrZrO x The molecular sieve is composed of one or more of ZSM-5 molecular sieve or ZSM-11 molecular sieve.

2. The catalyst for preparing xylene by coupling toluene alkylation with carbon dioxide hydrogenation according to claim 1, characterized in that: The catalyst has a core-shell structure, and the core-shell structure is constructed by bonding the molecular sieve layer by layer on the metal oxide surface with the adhesive.

3. The method for preparing a core-shell catalyst for preparing xylene by coupling toluene alkylation with carbon dioxide hydrogenation according to claim 1, characterized in that: The specific steps include: 1) adding a precipitant to a metal salt aqueous solution under heating and stirring, and preparing composite metal oxide particles after aging, washing, drying and calcining the obtained mixture; 2) adding a silica sol aqueous solution to the composite metal oxide particles obtained in step 1) to wet the metal oxide particles, then mixing the wetted metal oxide particles with molecular sieve powder, and shaking the resulting mixture until the molecular sieve powder completely covers the metal oxide particles to obtain molecular sieve-coated metal oxide particles; 3) The metal oxide particles coated with the molecular sieve obtained in step 2) are dried and then calcined to obtain the core-shell catalyst for the carbon dioxide hydrogenation coupled toluene alkylation to produce xylene.

4. The method for preparing a core-shell catalyst for preparing xylene by coupling toluene alkylation with carbon dioxide hydrogenation according to claim 3, characterized in that: The metal salt in step 1) is composed of one or more of gallium nitrate, indium nitrate, zinc nitrate, chromium nitrate or zirconium nitrate; the precipitant is composed of one or more of ammonium carbonate, sodium carbonate, ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate or potassium bicarbonate.

5. The method for preparing a core-shell catalyst for preparing xylene by coupling toluene alkylation with carbon dioxide hydrogenation according to claim 3, characterized in that: The heating and stirring temperature in step 1) is 60-80° C., and the heating and stirring time is 2-3 hours; the roasting temperature is 500-600° C., and the roasting time is 2-3 hours.

6. The method for preparing a core-shell catalyst for preparing xylene by coupling toluene alkylation with carbon dioxide hydrogenation according to claim 3, characterized in that: The mass ratio of silica sol to water in the silica sol aqueous solution described in step 2) is 1:1 to 1:2.

5.

7. The method for preparing a core-shell catalyst for preparing xylene by coupling toluene alkylation with carbon dioxide hydrogenation according to claim 3, characterized in that: The mass ratio of the metal oxide particles to the molecular sieve in step 2) is 1:9 to 9:

1.

8. The method for preparing a core-shell catalyst for preparing xylene by coupling toluene alkylation with carbon dioxide hydrogenation according to claim 3, characterized in that: The calcination temperature in step 3) is 500-600°C, and the calcination time is 2-3h.

9. Use of the core-shell catalyst for preparing xylene by coupling toluene alkylation with carbon dioxide hydrogenation as claimed in claims 1-2 or the catalyst obtained by the preparation method as claimed in claims 3-8, characterized in that: The specific steps are as follows: the catalyst is reduced by a reducing gas and then mixed with a reaction raw material to carry out a carbon dioxide hydrogenation coupling toluene alkylation reaction to prepare xylene, wherein the reaction raw material is a mixture of carbon dioxide, hydrogen, toluene and an inert gas.

10. The use of the core-shell catalyst for preparing xylene by coupling toluene alkylation with carbon dioxide hydrogenation according to claim 9, characterized in that: The reducing gas is a hydrogen-argon mixed gas containing 5% hydrogen, and the inert gas is one of argon or nitrogen; the reaction temperature is 320-360°C, the reaction pressure is 0.5-3MPa, and the space velocity of the reaction raw materials is 6000-12000mL·g -1 ·h -1 , the space velocity of toluene is 0.1~0.9h- 1 .

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