A method for producing aromatics from carbon dioxide via bifunctional catalysts of zinc oxide-zirconia@C / hierarchical porous nano ZSM-5 molecular sieves.

Abstract

This invention discloses a method for producing aromatics from carbon dioxide via a bifunctional catalyst of zinc oxide-zirconia@C / hierarchical porous nano-ZSM-5 molecular sieve. The invention addresses the problems of low selectivity for aromatics and excessively high selectivity for byproducts in existing catalysts used in the carbon dioxide hydrogenation conversion reaction. The method involves pyrolyzing a zinc-modified organometallic complex under a nitrogen atmosphere to prepare a ZnO-ZrO2@C composite metal oxide, which is then mixed with a modified hierarchical porous nano-ZSM-5 molecular sieve to form a bifunctional catalyst. This catalyst is then loaded into a fixed-bed reactor, activated under a nitrogen atmosphere, and then a mixture of carbon dioxide and H2-Ar gas is introduced into the reactor. Aromatics are produced under controlled reaction conditions. The bifunctional catalyst used in this invention improves the diffusion performance of reaction intermediates and aromatic products, suppresses side reactions such as reverse water-gas shift and excessive hydrogenation, and significantly improves the carbon dioxide conversion rate and the selectivity for tetramethylene-rich aromatics.

Description

Technical Field

[0001] This invention relates to a method for the catalytic hydrogenation of carbon dioxide to aromatics on a bifunctional catalyst of ZnO-ZrO2@C / hierarchical porous nano ZSM-5 molecular sieve. Background Technology

[0002] With the rapid development of modern industry, the large-scale extraction and utilization of fossil fuels has led to a continuous increase in carbon dioxide emissions, resulting in a rising concentration of carbon dioxide in the atmosphere and causing a series of increasingly serious ecological and environmental problems. Currently, the main technological means to reduce atmospheric carbon dioxide concentration include carbon dioxide capture and storage (CCS) and carbon dioxide capture and utilization (CCU). Utilizing carbon dioxide as a C1 resource has better economic viability and is an effective way to achieve carbon peaking and carbon neutrality. Hydrogenating carbon dioxide into clean fuels and high-value-added chemicals can not only reduce the adverse effects of the greenhouse effect on the ecological environment but also reduce dependence on fossil fuels and establish new non-petroleum routes for producing fuels and chemicals.

[0003] Carbon dioxide can be converted into methanol, formic acid, C2-C4 low-carbon olefins, and C4 carbon dioxide through catalytic hydrogenation. 5+ Liquid fuels and aromatics: Aromatics production offers higher added value. Currently, aromatics are mainly produced from petroleum fractions through aromatization reactions. However, due to the continuous depletion of non-renewable petroleum resources, developing new technological routes for aromatics production via carbon dioxide hydrogenation is of great significance. In particular, utilizing renewable energy sources such as wind power for electricity generation, followed by the hydrogenation reaction of green hydrogen produced through water electrolysis with carbon dioxide, will enable green production of aromatics.

[0004] The hydrogenation of carbon dioxide to aromatics typically employs bifunctional catalysts with both metallic and acidic sites. The metallic active sites are usually provided by metal oxides, while the acidic sites are provided by zeolite molecular sieves. The production of aromatics from carbon dioxide is achieved through a series of reactions. If a bifunctional catalyst composed of an iron-based metal oxide and a molecular sieve is used, carbon dioxide first undergoes hydrogenation at the iron carbide active sites generated in situ from iron oxide to form a CO intermediate. The CO then diffuses to the acidic sites on the molecular sieve and reacts with hydrogen via a Fischer-Tropsch synthesis to yield hydrocarbon products, including aromatics (Fischer-Tropsch synthesis pathway). If a bifunctional catalyst composed of a non-ferrous metal oxide and a molecular sieve is used, carbon dioxide first undergoes hydrogenation at the metal oxide to form a methanol intermediate. The methanol intermediate diffuses to the acidic sites provided by the molecular sieve and undergoes dehydration, C / C bond construction, oligomerization of low-carbon olefins, cyclization, and dehydrogenation / hydrogen transfer reactions to produce aromatics (methanol intermediate pathway). The selectivity of the aromatic products is closely related to the type of metal oxide and the type and properties of the acidic sites provided by the molecular sieve. Composite metal oxides such as ZnZrOx, ZnAlOx, and ZnCrOx are suitable metal site donors. However, composite metal oxides prepared by co-precipitation, hydrothermal synthesis, and sol-gel methods typically have large grain sizes and few exposed active sites, especially low oxygen vacancy densities for activating carbon dioxide. Therefore, the conversion rate of carbon dioxide is low. To improve the conversion rate, the reaction needs to be carried out at higher temperatures, but this simultaneously exacerbates the reverse water-gas shift reaction (endothermic reaction), leading to increased selectivity for carbon monoxide byproducts and varying degrees of decreased selectivity for hydrocarbon products such as aromatics. Therefore, establishing new methods for preparing metal oxides, reducing their grain size to expose more active sites, and constructing more oxygen vacancies to improve the activation capacity for carbon dioxide and suppress the reverse water-gas shift reaction are crucial for developing highly efficient catalysts for carbon dioxide hydrogenation conversion.

[0005] Zeolite molecular sieves, with their specific pore structure and tunable acidic sites, have been widely used in various fields such as petroleum refining, petrochemicals, and fine chemicals. Compared with other zeolites, ZSM-5 molecular sieves, with their three-dimensional ten-membered ring intersecting channels and tunable acidic sites over a wider range, exhibit superior catalytic activity and aromatic selectivity in the aromatization reactions of methanol and olefins. They also show potential for use as bifunctional catalysts with composite metal oxides in the hydrogenation conversion of carbon dioxide to aromatics. However, traditionally synthesized micron-sized ZSM-5 molecular sieves suffer from limitations in the generation and diffusion of aromatic products within the sieve channels due to their single micropore structure and relatively large particle size. Therefore, synthesizing nano-sized ZSM-5 molecular sieves using a simple method and constructing mesoporous structures within the crystals to prepare hierarchical ZSM-5 molecular sieves with both micropores and mesopores will enhance the accessibility of acidic sites, promote the generation of aromatic products, shorten their diffusion distance within the molecular sieve channels, thereby improving aromatic selectivity, inhibiting carbon deposition, and extending catalyst lifespan.

[0006] Using Zn-modified ZrO2 with higher oxygen vacancy density and smaller crystallites as metal sites, and combining it with nano-ZSM-5 molecular sieves with intracrystalline and intercrystalline mesopores to form a bifunctional catalyst for carbon dioxide hydrogenation reaction, can promote synergistic catalysis of metal sites and acidic sites. It is expected to simultaneously improve carbon dioxide conversion rate, aromatic selectivity and catalytic stability, and has broad application potential in the fields of carbon dioxide resource utilization, production of high-value-added fine chemicals and clean fuels. Summary of the Invention

[0007] The purpose of this invention is to address the problems of existing bifunctional catalysts used in the hydrogenation of carbon dioxide to aromatics, such as large crystal size of metal oxides, low reactivity, excessively high carbon monoxide selectivity and low hydrocarbon product selectivity due to the intensified reverse water-gas shift reaction at higher temperatures. It also addresses the problems of reduced aromatic selectivity caused by the large crystal size and single-pore structure of micron-sized ZSM-5 molecular sieves providing acidic sites, which hinders the formation and diffusion of aromatic products within the sieve pores, and the catalyst's tendency to carbon buildup and deactivation. Therefore, this invention provides a method for preparing a highly efficient bifunctional catalyst for the hydrogenation of carbon dioxide to aromatics, combining carbon-confined nano-ZnO-ZrO2@C composite metal oxides with hierarchical porous nano-ZSM-5 molecular sieves.

[0008] The method for producing aromatics by carbon dioxide hydrogenation on a bifunctional catalyst of zinc oxide-zirconium dioxide@C / hierarchical porous nano ZSM-5 molecular sieve is implemented according to the following steps:

[0009] A bifunctional catalyst, ZnO-ZrO2@C / hierarchical porous nano-ZSM-5 molecular sieve, was loaded into the isothermal zone of a fixed-bed reactor and activated at 300–500 °C under a nitrogen atmosphere. After cooling to the reaction temperature, a mixture of carbon dioxide and H2-Ar was introduced into the fixed-bed reactor. The reaction temperature was controlled at 260–360 °C, the reaction pressure at 1.0–4.0 MPa, and the total space velocity of the H2-Ar (95% H2, 5% Ar) mixture and CO2 mixture at 1000–5000 h⁻¹. -1 The volume ratio of H2 to CO2 is 1 to 4:1, and the reaction yields aromatic products mainly composed of tetramethylbenzene.

[0010] The ZnO-ZrO2@C / hierarchical porous nano ZSM-5 molecular sieve bifunctional catalyst is prepared by mixing, pressing, and sieving ZnO-ZrO2@C composite metal oxide and modified hierarchical porous nano ZSM-5 molecular sieve in a mass ratio of 1:2 to 2:1; the ZnO-ZrO2@C composite metal oxide is prepared by pyrolysis of Zn-modified organometallic complex UIO-66 under a nitrogen atmosphere; and the modified hierarchical porous nano ZSM-5 molecular sieve is prepared by ammonium fluoride pretreatment followed by desilication modification with sodium hydroxide solution.

[0011] The method for producing aromatics by carbon dioxide hydrogenation on a bifunctional catalyst of ZnO-ZrO2@C / hierarchical porous nano ZSM-5 molecular sieve described in this invention has the following beneficial effects:

[0012] 1. This invention involves zinc modification of a zirconium-based organometallic complex UIO-66 with zinc acetate solutions of varying concentrations, followed by pyrolysis under a nitrogen atmosphere to prepare a series of carbon-confined composite metal oxides, ZnO-ZrO2@C, with ZnO accounting for 2.0–10.0 wt.% of ZnO. These are highly dispersed nanocrystals rich in oxygen vacancies. By changing the concentration of the zinc acetate solution and the treatment time of UIO-66, the amount of ZnO introduced and the hydrogenation capacity of the prepared ZnO-ZrO2@C oxides can be precisely modulated.

[0013] 2. The multi-level porous nano ZSM-5 molecular sieve prepared by the present invention using a combination of ammonium fluoride pretreatment and alkali desilication modification has abundant intercrystalline and intracrystalline mesopores, which can significantly shorten the diffusion distance of the product.

[0014] 3. This invention prepares a bifunctional catalyst by mixing ZnO-ZrO2@C with hierarchical porous nano-ZSM-5 molecular sieves in a certain proportion. Because ZnO-ZrO2@C has a larger specific surface area and more active sites (oxygen vacancies) for adsorbing and activating carbon dioxide, it exhibits strong carbon dioxide conversion capability during carbon dioxide hydrogenation conversion while effectively inhibiting the reverse water-gas shift reaction to generate carbon monoxide and / or the over-hydrogenation to generate methane. Simultaneously, the hierarchical porous nano-ZSM-5 molecular sieves significantly improve the generation and diffusion of aromatic products within the sieve channels, promoting the diffusion of methanol intermediates generated on ZnO-ZrO2@C to the acidic sites of the molecular sieve for further conversion into aromatics—a tandem reaction. This achieves synergistic catalysis of metal and acidic sites, simultaneously improving carbon dioxide conversion rate, aromatic selectivity, and the proportion of tetramethylbenzene in aromatic products. Attached Figure Description

[0015] Figure 1 This is the XRD pattern of 4.0ZnO-ZrO2@C in catalyst A used in Examples 1 and 2;

[0016] Figure 2 These are SEM images of 4.0 ZnO-ZrO2@C in catalyst A used in Examples 1 and 2;

[0017] Figure 3 This is the XRD pattern of 8.1ZnO-ZrO2@C in catalyst B used in Examples 3 and 4;

[0018] Figure 4 These are SEM images of 8.1 ZnO-ZrO2@C in catalyst B used in Examples 3 and 4;

[0019] Figure 5 The XRD pattern of 5.9ZnO-ZrO2-MW@C in catalyst C used in Examples 5 and 6;

[0020] Figure 6 These are SEM images of 5.9ZnO-ZrO2-MW@C in catalyst C used in Examples 5 and 6;

[0021] Figure 7 This is the XRD pattern of 4.6ZnO-ZrO2-MW1@C in catalyst D used in Examples 7 and 8;

[0022] Figure 8 These are SEM images of 4.6ZnO-ZrO2-MW1@C in catalyst C used in Examples 7 and 8;

[0023] Figure 9These are SEM images of the hierarchical porous nano ZSM-5 molecular sieves used in the catalysts employed in Examples 1-8;

[0024] Figure 10 These are TEM images of the hierarchical porous nano ZSM-5 molecular sieves used in the catalysts employed in Examples 1-8;

[0025] Figure 11 This is a pore size distribution curve of the hierarchical porous nano ZSM-5 molecular sieve in the catalysts used in Examples 1-8. Detailed Implementation

[0026] Specific Implementation Method 1: The method for producing aromatics by carbon dioxide hydrogenation on a bifunctional catalyst of zinc oxide-zirconium dioxide@C / hierarchical porous nano ZSM-5 molecular sieve is implemented according to the following steps:

[0027] A bifunctional catalyst, ZnO-ZrO2@C / hierarchical porous nano-ZSM-5 molecular sieve, was loaded into the isothermal zone of a fixed-bed reactor and activated at 300–500 °C under a nitrogen atmosphere. After cooling to the reaction temperature, a mixture of carbon dioxide and H2-Ar was introduced into the fixed-bed reactor. The reaction temperature was controlled at 260–360 °C, the reaction pressure at 1.0–4.0 MPa, and the total space velocity of the H2-Ar (95% H2, 5% Ar) mixture and CO2 mixture at 1000–5000 h⁻¹. -1 The volume ratio of H2 to CO2 is 1 to 4:1, and the reaction yields aromatic products mainly composed of tetramethylbenzene.

[0028] The ZnO-ZrO2@C / hierarchical porous nano ZSM-5 molecular sieve bifunctional catalyst is prepared by mixing, pressing, and sieving ZnO-ZrO2@C composite metal oxide and modified hierarchical porous nano ZSM-5 molecular sieve in a mass ratio of 1:2 to 2:1; the ZnO-ZrO2@C composite metal oxide is prepared by pyrolysis of Zn-modified organometallic complex UIO-66 under a nitrogen atmosphere; and the modified hierarchical porous nano ZSM-5 molecular sieve is prepared by ammonium fluoride pretreatment followed by desilication modification with sodium hydroxide solution.

[0029] In this embodiment, the highly dispersed ZnO-ZrO2@C catalyst possesses more active sites (oxygen vacancies) for adsorbing and activating carbon dioxide, thus exhibiting strong carbon dioxide conversion capacity during carbon dioxide hydrogenation. It can effectively suppress the reverse water-gas shift reaction to generate carbon monoxide and / or the over-hydrogenation to generate methane. Furthermore, the hierarchical porous nano-ZSM-5 molecular sieve significantly improves the formation and diffusion of aromatic products within the molecular sieve channels, promoting the diffusion of methanol intermediates generated on ZnO-ZrO2@C to the acidic sites of the molecular sieve for further conversion into aromatics. Therefore, it can simultaneously improve both carbon dioxide conversion rate and aromatic selectivity. This solves the problems of large particle size, low oxygen vacancy density, poor mass transfer performance, long product diffusion distance, easy carbon deposition and deactivation, and low aromatic selectivity inherent in existing catalysts prepared by methods such as co-precipitation of composite metal oxides.

[0030] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the preparation method of the ZnO-ZrO2@C composite metal oxide is as follows:

[0031] (1) Weigh 1-2 parts zirconium tetrachloride, 1-6 parts terephthalic acid, 1-12 parts hydrochloric acid and 40-170 parts N,N-dimethylformamide by weight, mix them evenly, transfer them to a microwave digester, crystallize them at 120-200℃ for 10-180 minutes, and obtain the organometallic complex UIO-66 prepared by microwave radiation heating after centrifugation, washing, solvent exchange and drying.

[0032] (2) Mix UIO-66 with zinc acetate solution and stir at room temperature for 12-24 hours. After centrifugation, washing with deionized water, solvent exchange with anhydrous ethanol, and drying, zinc-modified UIO-66 is obtained. Then, it is pyrolyzed at 400-800℃ for 4-10 hours under nitrogen atmosphere to obtain ZnO-ZrO2@C composite metal oxide, denoted as ZnO-ZrO2@C.

[0033] In this embodiment, the ZnO-ZrO2@C composite metal oxide is obtained by pyrolysis of zinc-modified UIO-66 under a nitrogen atmosphere.

[0034] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 2 in that step (1) is replaced by: weighing 1-2 parts zirconium tetrachloride, 1-6 parts terephthalic acid, 1-12 parts hydrochloric acid and 40-170 parts N,N-dimethylformamide by weight, mixing them evenly, crystallizing them at 180-240°C for 20-24 hours, and then centrifuging, washing, solvent exchange and drying to obtain the organometallic complex UIO-66.

[0035] This embodiment uses a solvothermal synthesis method to prepare the organometallic complex UIO-66.

[0036] Specific Implementation Method 4: This implementation method differs from Specific Implementation Method 2 in that in step (2), the nitrogen gas is pyrolyzed at 500-600℃ for 5-10 hours under a nitrogen atmosphere, and the volume flow rate of nitrogen gas during pyrolysis is controlled to be 10-60 mL / min.

[0037] Specific Implementation Method 5: This implementation method differs from Specific Implementation Method 2 in that the particle size of the ZnO-ZrO2@C composite metal oxide is 150-550 nm, and the mass percentage of ZnO in the ZnO-ZrO2@C composite metal oxide is 2.0-10.0 wt.%.

[0038] Specific Implementation Method Six: The preparation method of the modified hierarchical porous nano ZSM-5 molecular sieve in this implementation method is as follows:

[0039] (1) Mix 0.1-0.2 parts of aluminum isopropoxide, 7-11 parts of tetrapropylammonium hydroxide (tetrapropylammonium hydroxide TPAOH has a mass percentage of 55%), 9-14 parts of deionized water and 12-18 parts of tetraethyl orthosilicate evenly, stir at room temperature for 0.5-4 hours, and then treat in a microwave digester at 165-185℃ for 10-60 minutes to obtain a seed suspension;

[0040] (2) Weigh 1-4 parts of sodium hydroxide, 0.1-0.4 parts of sodium aluminate, 20-80 parts of silica sol (SiO2 mass percentage of 30%) and 30-120 parts of deionized water according to the weight percentage, mix them evenly, add seed suspension accounting for 0.1%-0.9% of gel mass percentage, stir thoroughly to obtain initial gel, then transfer to stainless steel crystallization kettle with polytetrafluoroethylene liner, crystallize at 150-158℃ for 8-14 hours, then centrifuge, wash, dry and calcine to obtain sodium-type nano ZSM-5 molecular sieve;

[0041] (3) Sodium-type nano ZSM-5 molecular sieve is mixed with ammonium fluoride solution with a concentration of 0.1-0.5 mol / L and stirred at room temperature. After centrifugation, washing, drying and calcination, it is mixed with sodium hydroxide solution with a concentration of 0.05-2 mol / L and stirred at 70-90℃ for 10-60 minutes. After centrifugation, washing, drying and calcination, it is mixed with ammonium nitrate solution with a concentration of 0.5-1.5 mol / L and stirred at 70℃ for 1-10 hours for two ion exchanges. After centrifugation, washing, drying and calcination, modified hierarchical porous nano ZSM-5 molecular sieve (Hi-NZ5) is obtained.

[0042] In step (3) of this embodiment, sodium-type nano ZSM-5 molecular sieve is mixed with 0.1-1 mol / L ammonium fluoride solution at a liquid-solid ratio of 3:1. After centrifugation, washing, drying and calcination, it is mixed with 0.05-2 mol / L sodium hydroxide solution at a liquid-solid ratio of 30:1. The mixture is stirred at 70-90°C for 10-60 minutes. After centrifugation, washing, drying and calcination, it is mixed with 0.5-1.5 mol / L ammonium nitrate solution at a liquid-solid ratio of 30:1.

[0043] In this embodiment, the nano-ZSM-5 molecular sieve modified by alkali desilication is first pretreated with a certain concentration of ammonium fluoride solution, and then desilication treated with sodium hydroxide solutions of different concentrations.

[0044] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Method Six in that in step (3), sodium-type nano ZSM-5 molecular sieve is mixed with ammonium fluoride solution with a concentration of 0.1 to 0.5 mol / L, and the stirring treatment time at room temperature is 6 to 10 hours.

[0045] Specific Implementation Method 8: This implementation method differs from Specific Implementation Method 6 in that the concentration of sodium hydroxide solution in step (3) is 0.05-0.1 mol / L.

[0046] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Method Six in that the intracrystalline mesopore size range of the modified hierarchical porous nano ZSM-5 molecular sieve is 5–20 nm.

[0047] Specific Implementation Method 10: This implementation method differs from Specific Implementation Method 1 in that the ZnO-ZrO2@C / hierarchical porous nano ZSM-5 molecular sieve bifunctional catalyst is prepared by mixing ZnO-ZrO2@C composite metal oxide and modified hierarchical porous nano ZSM-5 molecular sieve in a 1:1 mass ratio, followed by tableting and sieving to 20-40 mesh.

[0048] Specific Implementation Method Eleven: This implementation method differs from Specific Implementation Method One in that the activation treatment at 300-500℃ under a nitrogen atmosphere is carried out for 1.0-3.0 hours.

[0049] Specific Implementation Method Twelve: This implementation method differs from Specific Implementation Method One in that the reaction temperature is controlled at 280–320°C and the reaction pressure is controlled at 2.5–3.5 MPa.

[0050] Specific Implementation Method Thirteen: This implementation method differs from Specific Implementation Method One in that the total volumetric space velocity of the H2-Ar (95% H2, 5% Ar) mixture and the CO2 mixture is 3000–4000 h⁻¹. -1 The volume ratio of H2 to CO2 is 2 to 3:1.

[0051] Example 1: This example describes a method for producing aromatics from carbon dioxide via hydrogenation using a bifunctional catalyst of 4.0 ZnO-ZrO2@C / hierarchical porous nano ZSM-5 molecular sieve (Hi-NZ5). The method is implemented according to the following steps:

[0052] A bifunctional catalyst of 4.0 ZnO-ZrO2@C / hierarchical porous nano ZSM-5 molecular sieve was loaded into the isothermal zone of a fixed-bed reactor and activated at 320℃ for 2 hours under a nitrogen atmosphere. After cooling to the reaction temperature, a mixture of carbon dioxide and H2-Ar (H2 / CO2 = 3:1 (volume ratio)) was introduced into the fixed-bed reactor. The reaction temperature was controlled at 320℃, the reaction pressure at 3.0 MPa, and the total space velocity of the H2-Ar (95% H2, 5% Ar) mixture and CO2 mixture at 4000 h⁻¹. -1 The reaction yields aromatic products, primarily tetramethylbenzene.

[0053] The 4.0ZnO-ZrO2@C / hierarchical porous nano ZSM-5 molecular sieve bifunctional catalyst is prepared by mixing 4.0ZnO-ZrO2@C composite metal oxide and modified hierarchical porous nano ZSM-5 molecular sieve in a 1:1 mass ratio, followed by tableting and sieving to 20-40 mesh, and is denoted as catalyst A.

[0054] The preparation method of the 4.0ZnO-ZrO2@C / hierarchical porous nano ZSM-5 molecular sieve bifunctional catalyst described in this embodiment is as follows:

[0055] 1.9 parts by weight of zirconium tetrachloride, 2.6 parts by weight of terephthalic acid, 1.7 parts by weight of 37 wt.% hydrochloric acid, and 47.4 parts by weight of N,N-dimethylformamide were weighed, mixed, and stirred evenly. The mixture was then transferred to a stainless steel crystallization autoclave lined with polytetrafluoroethylene and crystallized at 220°C for 24 hours. After centrifugation, washing, solvent exchange, and drying, the solvothermal synthesized organometallic complex UIO-66 was obtained. UIO-66 was mixed with a 0.02 mol / L zinc acetate solution at a solid-liquid ratio of 1:300 and stirred at room temperature for 24 hours. After centrifugation, washing with deionized water, solvent exchange with anhydrous ethanol, and overnight drying in a vacuum oven at 60°C, zinc-modified UIO-66 was obtained. The mixture was then heat-treated at 600°C for 6 hours under a nitrogen atmosphere to obtain a composite metal oxide sample with a ZnO content of 4.0 wt.%, denoted as 4.0ZnO-ZrO2@C.

[0056] 0.14 parts of aluminum isopropoxide, 9.1 parts of tetrapropylammonium hydroxide (tetrapropylammonium hydroxide mass percentage is 55%), 10.0 parts of deionized water and 14.6 parts of tetraethyl orthosilicate were mixed evenly and stirred at room temperature for 1 hour. Then the mixture was treated in a microwave digester at 175°C for 40 minutes to obtain a seed suspension.

[0057] Weigh out 3.0 parts by weight of sodium hydroxide, 0.3 parts by weight of sodium aluminate, 60.0 parts by weight of silica sol (SiO2 mass percentage of 30.0%) and 90.0 parts by weight of deionized water, mix them evenly, add 0.8% by weight of pre-prepared seed suspension, stir thoroughly to obtain initial gel, then transfer to a stainless steel crystallization kettle with a polytetrafluoroethylene liner, crystallize at 155℃ for 10 hours, then centrifuge, wash, dry and calcine to obtain sodium-type nano ZSM-5 molecular sieve;

[0058] Sodium-type nano ZSM-5 molecular sieve was mixed with 0.3 mol / L ammonium fluoride solution at a liquid-solid ratio of 3:1 and stirred at room temperature for 7 hours. After centrifugation, washing, drying and calcination, it was mixed with 0.1 mol / L sodium hydroxide solution at a liquid-solid ratio of 30:1 and stirred at 85℃ for 30 minutes. After centrifugation, washing, drying and calcination, it was mixed with 1 mol / L ammonium nitrate solution at a liquid-solid ratio of 30:1 and stirred at 70℃ for 5 hours for two ion exchanges. After centrifugation, washing, drying and calcination, a hierarchical porous nano ZSM-5 molecular sieve (Hi-NZ5) modified by ammonium fluoride pretreatment and sodium hydroxide solution alkaline desilication was obtained.

[0059] The properties of the organometallic complex UIO-66 prepared in Example 1 are shown in Table 1, and the name and composition of the bifunctional catalyst A are shown in Table 2. The composition of the products from the hydrogenation of carbon dioxide to aromatics was analyzed by gas chromatography, and the results are shown in Table 3. The conversion rate of carbon dioxide was 13.6%, the selectivity for carbon monoxide was 14.6%, and the selectivity for aromatics was 93.0%.

[0060] Example 2: This example differs from Example 1 in that the reaction temperature in the fixed-bed reactor is controlled at 280°C, while the bifunctional catalyst and other reaction conditions are the same as in Example 1. Gas chromatography was used to analyze the composition of the carbon dioxide hydrogenation reaction products, and the results are shown in Table 3. The carbon dioxide conversion rate was 11.1%, the carbon monoxide selectivity was 9.2%, and the aromatic hydrocarbon selectivity was 95.3%.

[0061] Example 3: This example differs from Example 1 in that the zinc acetate solution concentration used for Zn impregnation modification of UIO-66 is 0.05 mol / L. The sample was treated at 600°C for 4 hours under nitrogen protection at a flow rate of 20 mL / min to obtain a composite metal oxide sample 8.1ZnO-ZrO2-@C with a ZnO content of 8.1 wt.%. This sample was then mixed with Hi-NZ5 prepared according to the method in Example 1 at a mass ratio of 1:1, pressed into tablets, and sieved to 20-40 mesh to obtain a bifunctional catalyst, denoted as Catalyst B. The reaction temperature in the fixed-bed reactor was controlled at 300°C, and other reaction conditions were the same as in Example 1. The composition of the carbon dioxide hydrogenation reaction products was analyzed by gas chromatography, and the results are shown in Table 3. The carbon dioxide conversion rate was 10.4%, the carbon monoxide selectivity was 17.5%, and the aromatic hydrocarbon selectivity was 96.9%.

[0062] Example 4: This example differs from Example 3 in that the reaction temperature in the fixed-bed reactor is controlled at 290°C. The bifunctional catalyst used is the same as in Example 3, and other reaction conditions are the same as in Example 1. Gas chromatography was used to analyze the composition of the carbon dioxide hydrogenation reaction products, and the results are shown in Table 3. The carbon dioxide conversion rate was 9.0%, the carbon monoxide selectivity was 15.9%, and the aromatic hydrocarbon selectivity was 94.8%.

[0063] Example 5: This example differs from Example 1 in that ZrCl4, terephthalic acid, hydrochloric acid, and DMF were mixed evenly and then microwave-assisted crystallized at 180°C for 2 hours in a microwave digester to obtain UIO-66. Following the method in Example 1, this UIO-66 was modified with Zn and heat-treated under a nitrogen atmosphere to obtain sample 5.9ZnO-ZrO2-MW@C (MW represents microwave heating). This sample was then mixed with Hi-NZ5 at a mass ratio of 1:1 to obtain a bifunctional catalyst, denoted as catalyst C. The reaction temperature in the fixed-bed reactor was controlled at 340°C, and other reaction conditions were the same as in Example 1. The composition of the carbon dioxide hydrogenation reaction products was analyzed by gas chromatography, and the results are shown in Table 3. The carbon dioxide conversion rate was 11.8%, the carbon monoxide selectivity was 14.4%, and the aromatic hydrocarbon selectivity was 95.1%.

[0064] Example 6: This example differs from Example 5 in that the reaction temperature in the fixed-bed reactor is controlled at 280°C. The catalyst used is the same as in Example 5, and other reaction conditions are the same as in Example 1. Gas chromatography was used to analyze the composition of the carbon dioxide hydrogenation reaction products, and the results are shown in Table 3. The carbon dioxide conversion rate was 9.2%, the carbon monoxide selectivity was 9.7%, and the aromatic hydrocarbon selectivity was 94.3%.

[0065] Example 7: This example differs from Example 5 in that a mixed solution containing ZrCl4, terephthalic acid, hydrochloric acid, and DMF was crystallized at 180°C for 10 minutes in a microwave digester to obtain UIO-66. This UIO-66 was then modified with Zn and heat-treated under a nitrogen atmosphere according to the method in Example 1 to obtain sample 4.6ZnO-ZrO2-MW1@C. This sample was then mixed with Hi-NZ5 at a mass ratio of 1:1, pressed into tablets, and sieved to 20-40 mesh to obtain a bifunctional catalyst, denoted as catalyst D. The reaction temperature in the fixed-bed reactor was controlled at 260°C, and other reaction conditions were the same as in Example 1. The composition of the carbon dioxide hydrogenation reaction products was analyzed by gas chromatography, and the results are shown in Table 3. The carbon dioxide conversion rate was 13.6%, the carbon monoxide selectivity was 11.1%, and the aromatic hydrocarbon selectivity was 94.4%.

[0066] Example 8: This example differs from Example 7 in that the reaction temperature in the fixed-bed reactor is controlled at 320°C. The catalyst used is the same as in Example 7, and other reaction conditions are the same as in Example 1. The composition of the carbon dioxide hydrogenation reaction products was analyzed by gas chromatography, and the results are shown in Table 3. The carbon dioxide conversion rate was 10.8%, the carbon monoxide selectivity was 7.7%, and the aromatic hydrocarbon selectivity was 93.4%.

[0067] Table 1. Characteristics of UIO-66 used in the preparation of catalysts for each example.

[0068]

[0069] Table 2. List of catalysts for each embodiment

[0070]

[0071] Table 2 shows the reaction results for the carbon dioxide hydrogenation to aromatics production in each example.

[0072]

[0073]

[0074] Reaction conditions: reaction pressure 3 MPa, H2 / CO2 = 3:1 (volume ratio), total volume hourly space velocity 4000 h⁻¹ -1 *Liquid hydrocarbon selectivity refers to the percentage of liquid hydrocarbons in the product relative to all hydrocarbon products.

[0075] # Aromatic selectivity refers to the percentage of aromatic hydrocarbons in the product relative to all hydrocarbon products.

Claims

1. A method for the hydrogenation of carbon dioxide to arenes on a zinc oxide-zirconium dioxide@C / hierarchical-pore nano-ZSM-5 molecular sieve bifunctional catalyst, characterized in that The method for preparing aromatic hydrocarbon by carbon dioxide hydrogenation on the ZnO-ZrO2@C / hierarchical porous nano ZSM-5 molecular sieve bifunctional catalyst is realized according to the following steps: The ZnO-ZrO2@C / hierarchical nano ZSM-5 molecular sieve bifunctional catalyst is loaded into a constant temperature zone of a fixed bed reactor, activated at 300-500 DEG C under a nitrogen atmosphere, after being reduced to a reaction temperature, carbon dioxide and H2-Ar mixed gas are introduced into the fixed bed reactor, the reaction temperature is controlled at 260-360 DEG C, the reaction pressure is 1.0-4.0 MPa, the total space velocity of the H2-Ar mixed gas and CO2 mixed gas is 1000-5000 h -1 -1, the volume ratio of H2 to CO2 is 1-4:1, and after the reaction, an aromatic hydrocarbon product mainly composed of tetramethylbenzene is obtained. The ZnO-ZrO2@C / hierarchical porous nano ZSM-5 molecular sieve bifunctional catalyst is prepared by mixing, tabletting, and sieving ZnO-ZrO2@C composite metal oxide and modified hierarchical porous nano ZSM-5 molecular sieve at a mass ratio of 1:2-2:1; the ZnO-ZrO2@C composite metal oxide is prepared by pyrolyzing Zn-modified metal organic complex UIO-66 under a nitrogen atmosphere; and the modified hierarchical porous nano ZSM-5 molecular sieve is prepared by pretreating with ammonium fluoride and desiliconizing modification with a sodium hydroxide solution; The preparation method of the ZnO-ZrO2@C composite metal oxide is as follows: (1) 1-2 parts of zirconium tetrachloride, 1-6 parts of terephthalic acid, 1-12 parts of hydrochloric acid, and 40-170 parts of N,N-dimethylformamide are weighed and mixed and stirred uniformly, and then transferred into a microwave digestion instrument, crystallized at 120-200 DEG C for 10-180 minutes, centrifuged, washed, solvent exchanged, and dried to obtain metal organic complex UIO-66 prepared by microwave radiation heating; (2) UIO-66 is mixed with zinc acetate solution, stirred at room temperature for 12-24 hours, centrifuged, washed with deionized water, solvent exchanged with anhydrous ethanol, dried to obtain Zn-modified UIO-66, and then pyrolyzed at 400-800 DEG C for 4-10 hours under a nitrogen atmosphere to obtain ZnO-ZrO2@C composite metal oxide; The preparation method of the modified hierarchical porous nano ZSM-5 molecular sieve is as follows: (1) 0.1-0.2 parts of aluminum isopropoxide, 7-11 parts of tetrapropylammonium hydroxide, 9-14 parts of deionized water, and 12-18 parts of tetraethyl orthosilicate are mixed uniformly, stirred at room temperature for 0.5-4 hours, and then treated in a microwave digestion instrument at 165-185 DEG C for 10-60 minutes to obtain a crystal seed suspension; (2) 1-4 parts of sodium hydroxide, 0.1-0.4 parts of sodium metaaluminate, 20-80 parts of silica sol, and 30-120 parts of deionized water are mixed uniformly, and then 0.1%-0.9% of the crystal seed suspension based on the mass percentage of the gel is added, and the initial gel is obtained after being stirred thoroughly, and then transferred into a stainless steel crystallization kettle with a polytetrafluoroethylene liner, crystallized at 150-158 DEG C for 8-14 hours, and then centrifuged, washed, dried, and calcined to obtain sodium nano ZSM-5 molecular sieve; (3) mixing the sodium type nano ZSM-5 molecular sieve with an ammonium fluoride solution with a concentration of 0.1-0.5 mol / L, stirring at room temperature, centrifugal separation, washing, drying and calcination, and then mixing with a sodium hydroxide solution with a concentration of 0.05-2 mol / L, stirring at 70-90 ℃ for 10-60 minutes, centrifugal separation, washing, drying and calcination, and then mixing with an ammonium nitrate solution with a concentration of 0.5-1.5 mol / L, stirring at 70 ℃ for 1-10 hours for twice ion exchange, centrifugal separation, washing, drying and calcination, to obtain the modified hierarchical nano ZSM-5 molecular sieve, and the intracrystalline mesopore of the modified hierarchical nano ZSM-5 molecular sieve has a pore size range of 5-20 nm.

2. The method for preparing aromatic hydrocarbon by carbon dioxide hydrogenation on the zinc oxide-zirconium dioxide@C / hierarchical porous nanometer ZSM-5 molecular sieve bifunctional catalyst according to claim 1, characterized in that The step (1) in the preparation method of the ZnO-ZrO2@C composite metal oxide is replaced by: taking 1-2 parts of zirconium tetrachloride, 1-6 parts of terephthalic acid, 1-12 parts of hydrochloric acid and 40-170 parts of N,N-dimethylformamide by weight fraction, mixing and stirring uniformly, crystallizing at 180-240 ℃ for 20-24 hours, and then performing centrifugal separation, washing, solvent exchange and drying treatment to obtain a metal organic complex UIO-66.

3. The method for preparing aromatic hydrocarbon by carbon dioxide hydrogenation on the zinc oxide-zirconium dioxide@C / hierarchical porous nanometer ZSM-5 molecular sieve bifunctional catalyst according to claim 1, characterized in that The particle size of the ZnO-ZrO2@C composite metal oxide is 150-550 nm, and the mass percentage content of ZnO in the ZnO-ZrO2@C composite metal oxide is 2.0-10.0 wt.%.

4. The method for preparing aromatic hydrocarbon by carbon dioxide hydrogenation on the zinc oxide-zirconium dioxide@C / hierarchical porous nanometer ZSM-5 molecular sieve bifunctional catalyst according to claim 1, characterized in that In the preparation method of the modified hierarchical nano ZSM-5 molecular sieve, the sodium type nano ZSM-5 molecular sieve is mixed with an ammonium fluoride solution with a concentration of 0.1-0.5 mol / L in step (3), and the stirring treatment time at room temperature is 6-10 hours.

5. The method for preparing aromatic hydrocarbon by carbon dioxide hydrogenation on the zinc oxide-zirconium dioxide@C / hierarchical porous nanometer ZSM-5 molecular sieve bifunctional catalyst according to claim 1, characterized in that The ZnO-ZrO2@C / hierarchical nano ZSM-5 molecular sieve bifunctional catalyst is mixed, tabletted, and sieved into 20-40 mesh according to a mass ratio of 1:

1.

6. The method for preparing aromatic hydrocarbon by carbon dioxide hydrogenation on the zinc oxide-zirconium dioxide@C / hierarchical porous nanometer ZSM-5 molecular sieve bifunctional catalyst according to claim 1, characterized in that The reaction temperature is controlled at 280-320 ℃, and the reaction pressure is controlled at 2.5-3.5 MPa.

7. The method for preparing aromatic hydrocarbon by carbon dioxide hydrogenation on the zinc oxide-zirconium dioxide@C / hierarchical porous nanometer ZSM-5 molecular sieve bifunctional catalyst according to claim 1, characterized in that The total volume space velocity of the mixed gas of H2-Ar and CO2 is 3000-4000 h -1 , and the volume ratio of H2 to CO2 is 2-3:1.

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