Metal oxide / metal-organic framework composite catalyst, preparation method therefor, and use thereof

Abstract

The application discloses a metal organic framework material composite catalyst and a preparation method and application thereof, and belongs to the technical field of industrial catalytic material preparation and CO2 catalytic conversion. The application takes metal organic framework material UIO-66 as a catalyst carrier and a reaction intermediate (methanol) for preparing aromatic hydrocarbon catalyst, obtains a metal oxide / metal organic framework material composite catalyst through metal oxide modification, realizes direct preparation of aromatic hydrocarbon through CO2 hydrogenation without HZSM-5 molecular sieve, effectively inhibits a side reaction, and can also obtain high selectivity of aromatic hydrocarbon under lower pressure. Compared with existing catalysts, the catalyst prepared in the application has great improvement in catalytic activity in the reaction of preparing aromatic hydrocarbon through CO2 hydrogenation, the preparation method of the catalyst is simple to operate, raw materials are cheap and easy to obtain, and the catalyst meets the demand of green industrial production.

Description

Technical Field

[0001] This invention relates to the fields of industrial catalytic material preparation and CO2 catalytic conversion technology, specifically to metal oxide / metal-organic framework composite catalysts, their preparation methods, and applications. Background Technology

[0002] With the rapid development of the energy industry and the large-scale extraction and use of fossil resources such as coal, oil, and natural gas, the total amount of CO2 emitted into the environment has been rising year by year. The massive emission of CO2 leads to the greenhouse effect, resulting in major problems such as glacial melting, sea-level rise, desertification, and reduced agricultural yields. Controlling and reducing CO2 emissions or reusing CO2 has become urgent. Research on the chemical conversion and utilization of CO2 is of great significance. CO2 possesses thermodynamic stability and kinetic inertness, and achieving the efficient conversion of carbon dioxide has always been a difficult problem that researchers have been striving to solve, and it is also one of the most challenging topics in the field of green chemistry and catalysis. Currently, research on the catalytic conversion of CO2 into high-value chemicals mainly focuses on developing a highly active, highly selective, and highly stable catalyst suitable for various chemical methods.

[0003] Currently, the main methods for producing aromatics from CO2 via hydrogenation are the CO2-modified Fischer-Tropsch synthesis (CO2-FTS) or the methanol-mediated (MeOH) route. However, these methods are often limited by low CO2 conversion rates, poor aromatic selectivity, and catalyst deactivation. All of these synthetic routes utilize composite catalysts composed of metal oxides and HZSM-5 molecular sieves. However, the narrow pores of the HZSM-5 molecular sieves used in existing composite catalysts severely restrict molecule transport, leading to catalyst deactivation due to coking and poor stability. Researchers are currently focusing on the pore structure and morphology of HZSM-5 molecular sieves. The preparation process of HZSM-5 molecular sieves is complex and costly. Therefore, finding novel catalysts that break free from the constraints of HZSM-5 molecular sieves remains a significant challenge. To address this, this invention provides a metal oxide / metal-organic framework composite catalyst, its preparation method, and its applications. Summary of the Invention

[0004] To address the above problems, this invention provides a metal oxide / metal-organic framework (MOF) composite catalyst, its preparation method, and its applications. The composite catalyst is obtained by modifying a metal oxide. Compared with existing catalysts, the composite catalyst prepared by this invention can directly extract aromatics from CO2 hydrogenation without HZSM-5 molecular sieves, while effectively suppressing side reactions and achieving high selectivity for aromatics even at lower pressures. Furthermore, the preparation method of the metal oxide / metal-organic framework catalyst in this invention is simple and inexpensive.

[0005] The first objective of this invention is to provide a method for preparing a metal oxide / metal-organic framework composite catalyst, comprising the following steps:

[0006] S1. The zirconium source, ligand and modifier are dissolved in a solvent and crystallized to synthesize UIO-66 metal-organic framework material;

[0007] S2. Mix the metal oxide with the UIO-66 metal-organic framework material from S1 to obtain the metal oxide / UIO-66 composite catalyst.

[0008] Preferably, in S2, the metal oxide is obtained by calcining zinc nitrate hydrate, indium nitrate hydrate, or gallium nitrate hydrate in a muffle furnace.

[0009] Preferably, the calcination temperature is 300-350°C and the time is 5-5.5 hours.

[0010] Preferably, in S2, the metal oxide accounts for 8% of the mass percentage of the composite catalyst.

[0011] Preferably, in step S2, the specific steps for preparing the UIO-66 metal-organic framework material are as follows:

[0012] Zirconium tetrachloride, terephthalic acid, and benzoic acid were dissolved in a solvent, and acetic acid and water were added sequentially for mixing. After the mixed solution was clarified, it was transferred to a high-pressure reactor lined with polytetrafluoroethylene for crystallization. After crystallization, the mixture was centrifuged, washed, and dried to obtain UIO-66 metal-organic framework material.

[0013] Preferably, the zirconium tetrachloride has a mass ratio of terephthalic acid, benzoic acid, and solvent of 0.32:0.23:0.1:27; a volume ratio of solvent, acetic acid, and water of 28:3:6; the solvent is N,N-dimethylformamide; the crystallization temperature is 100–120°C, and the time is 18–30 h; the detergent is N,N-dimethylformamide and methanol, and the washing is performed 2–4 times; the drying temperature is 80–120°C, and the time is 8–12 h.

[0014] A second objective of this invention is to provide a metal oxide / metal-organic framework composite catalyst prepared by the above-described method.

[0015] A third objective of this invention is to provide the application of the aforementioned metal oxide / metal-organic framework composite catalyst in the hydrogenation of CO2 to aromatics, wherein the catalytic reaction is carried out at a pressure of 0.5–3.5 MPa, a temperature of 320 °C, and a space velocity of 4800 mL·g. -1 ·h -1 The molar ratio of H2 to CO2 is 3:1.

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[0017] (1) This invention uses the metal-organic framework material UIO-66 as a catalyst support and reaction intermediate (methanol) to produce aromatics. A metal oxide / metal-organic framework composite catalyst is obtained through metal oxide modification, enabling direct CO2 hydrogenation to aromatics production without HZSM-5 molecular sieves. Simultaneously, side reactions are effectively suppressed, and high selectivity for aromatics is achieved even at lower pressures. Compared to existing catalysts, the catalyst prepared in this invention exhibits significantly improved catalytic activity in the CO2 hydrogenation to aromatics reaction. The catalyst preparation method is simple, and the raw materials are inexpensive and readily available, meeting the requirements of green industrial production.

[0018] (2) This invention designs the pore size and functionality of UIO-66 by selecting organic ligands, functional groups, and metal ion activation, thereby endowing it with special physicochemical properties. Zn-doped UIO-66 has the characteristics of multiple active sites, strong acidity, and fine catalytic interface, which can promote the formation of aromatics. It has excellent catalytic activity in the direct production of aromatics by CO2 hydrogenation. Under optimal reaction conditions, the CO2 conversion rate is as high as 25.03%, and the selectivity of aromatics is as high as 79.75%. At the same time, it achieves the efficient formation of light aromatics (benzene, toluene, p-xylene), with a selectivity as high as 76.46%. This catalyst can still obtain high selectivity of aromatics under different pressure conditions, and the selectivity of aromatics is still as high as 67.36% under normal pressure. Attached Figure Description

[0019] Figure 1 The X-ray diffraction patterns are shown for the metal oxide / metal-organic framework composite catalysts prepared in the embodiments and comparative examples of this invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0021] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased from the market or prepared by existing methods.

[0022] Example 1

[0023] A method for preparing a metal oxide / metal-organic framework composite catalyst includes the following steps:

[0024] S1, 1.60 g zirconium tetrachloride, 1.15 g terephthalic acid and 0.5 g benzoic acid were dissolved in 140 mL N,N-dimethylformamide, and 15 mL acetic acid and 30 mL water were added sequentially. After the mixture became clear, it was subjected to hydrothermal crystallization at 120 °C for 24 h in a polytetrafluoroethylene-lined autoclave. After crystallization, it was allowed to cool naturally to room temperature, centrifuged, and washed three times each with N,N-dimethylformamide and methanol solution. It was then dried at 100 °C for 12 h to obtain UIO-66 metal-organic framework material.

[0025] S2. 1g of gallium nitrate hydrate was placed in a muffle furnace and calcined at 350℃ for 5.5h to obtain Ga2O3.

[0026] The Ga / UIO-66 catalyst was obtained by uniformly mixing 0.04 g Ga2O3 and 0.46 g S1 to obtain the UIO-66 metal-organic framework material.

[0027] Catalytic reaction conditions: reaction pressure 3 MPa, reaction temperature 320 °C, space velocity 4800 mL·g -1 ·h -1 The molar ratio of H2 to CO2 is 3:1.

[0028] Example 2

[0029] A method for preparing a metal oxide / metal-organic framework composite catalyst includes the following steps:

[0030] S1, same as in Example 1

[0031] S2. 1g of indium nitrate hydrate was placed in a muffle furnace and calcined at 350℃ for 5.5h to obtain In2O3.

[0032] The In / UIO-66 metal-organic framework material obtained by uniformly mixing 0.04g In2O3 and 0.46g S1 was obtained to obtain the In / UIO-66 composite catalyst.

[0033] Catalytic reaction conditions: reaction pressure 3 MPa, reaction temperature 320 °C, space velocity 4800 mL·g -1 ·h -1 The molar ratio of H2 to CO2 is 3:1.

[0034] Example 3

[0035] A method for preparing a metal oxide / metal-organic framework composite catalyst includes the following steps:

[0036] S1, Same as Example 1;

[0037] S2. 1g of zinc nitrate hydrate was placed in a muffle furnace and calcined at 350℃ for 5.5h to obtain ZnO.

[0038] The Zn / UIO-66 composite catalyst was obtained by uniformly mixing 0.04g ZnO and 0.46g S1 to obtain the UIO-66 metal-organic framework material.

[0039] Catalytic reaction conditions: reaction pressure 0.5 MPa, reaction temperature 320 °C, space velocity 4800 mL·g⁻¹ -1 ·h -1 The molar ratio of H2 to CO2 is 3:1.

[0040] Example 4

[0041] A method for preparing a metal oxide / metal-organic framework catalyst includes the following steps:

[0042] S1, Same as Example 1;

[0043] S2. 1g of zinc nitrate hydrate was placed in a muffle furnace and calcined at 350℃ for 5.5h to obtain ZnO.

[0044] The Zn / UIO-66 composite catalyst was obtained by uniformly mixing 0.04g ZnO and 0.46g S1 to obtain the UIO-66 metal-organic framework material.

[0045] Catalytic reaction conditions: reaction pressure 1 MPa, reaction temperature 320 °C, space velocity 4800 mL·g -1 ·h -1 The molar ratio of H2 to CO2 is 3:1.

[0046] Example 5

[0047] A method for preparing a metal oxide / metal-organic framework composite catalyst includes the following steps:

[0048] S1, Same as Example 1;

[0049] S2. 1g of zinc nitrate hydrate was placed in a muffle furnace and calcined at 350℃ for 5.5h to obtain ZnO.

[0050] The Zn / UIO-66 composite catalyst was obtained by uniformly mixing 0.04g ZnO and 0.46g S1.

[0051] Catalytic reaction conditions: reaction pressure 1.5 MPa, reaction temperature 320 °C, space velocity 4800 mL·g⁻¹ -1 ·h -1 The molar ratio of H2 to CO2 is 3:1.

[0052] Example 6

[0053] A method for preparing a metal oxide / metal-organic framework composite catalyst includes the following steps:

[0054] S1, Same as Example 1;

[0055] S2. 1g of zinc nitrate hydrate was placed in a muffle furnace and calcined at 350℃ for 5.5h to obtain ZnO.

[0056] The Zn / UIO-66 composite catalyst was obtained by uniformly mixing 0.04g ZnO and 0.46g S1 to obtain the UIO-66 metal-organic framework material.

[0057] Catalytic reaction conditions: reaction pressure 2 MPa, reaction temperature 320 °C, space velocity 4800 mL·g -1 ·h -1 The molar ratio of H2 to CO2 is 3:1.

[0058] Example 7

[0059] A method for preparing a metal oxide / metal-organic framework composite catalyst includes the following steps:

[0060] S1, Same as Example 1;

[0061] S2. 1g of zinc nitrate hydrate was placed in a muffle furnace and calcined at 350℃ for 5.5h to obtain ZnO.

[0062] The Zn / UIO-66 composite catalyst was obtained by uniformly mixing 0.04g ZnO and 0.46g S1 to obtain the UIO-66 metal-organic framework material.

[0063] Catalytic reaction conditions: reaction pressure 2.5 MPa, reaction temperature 320 °C, space velocity 4800 mL·g⁻¹ -1 ·h -1 The molar ratio of H2 to CO2 is 3:1.

[0064] Example 8

[0065] A method for preparing a metal oxide / metal-organic framework catalyst includes the following steps:

[0066] S1, Same as Example 1;

[0067] S2. 1g of zinc nitrate hydrate was placed in a muffle furnace and calcined at 350℃ for 5.5h to obtain ZnO.

[0068] The Zn / UIO-66 composite catalyst was obtained by uniformly mixing 0.04g ZnO and 0.46g S1 to obtain the UIO-66 metal-organic framework material.

[0069] Catalytic reaction conditions: reaction pressure 3.0 MPa, reaction temperature 320 °C, space velocity 4800 mL·g⁻¹ -1 ·h -1 The molar ratio of H2 to CO2 is 3:1.

[0070] Example 9

[0071] A method for preparing a metal oxide / metal-organic framework catalyst includes the following steps:

[0072] S1, Same as Example 1;

[0073] S2. 1g of zinc nitrate hydrate was placed in a muffle furnace and calcined at 350℃ for 5.5h to obtain ZnO.

[0074] The Zn / UIO-66 composite catalyst was obtained by uniformly mixing 0.04g ZnO and 0.46g S1 to obtain the UIO-66 metal-organic framework material.

[0075] Catalytic reaction conditions: reaction pressure 3.5 MPa, reaction temperature 320 °C, space velocity 4800 mL·g⁻¹ -1 ·h -1 The molar ratio of H2 to CO2 is 3:1.

[0076] To further illustrate the technical effects of the present invention, a comparative example is also provided, as follows:

[0077] Comparative Example 1

[0078] A method for preparing a metal oxide / metal-organic framework catalyst includes the following steps:

[0079] S1. Dissolve 1.60 g zirconium tetrachloride, 1.15 g terephthalic acid and 0.5 g benzoic acid in 140 mL N,N-dimethylformamide, add 15 mL acetic acid and 30 mL water in sequence, and after the mixture is clear, perform hydrothermal crystallization at 120 °C for 24 h in a polytetrafluoroethylene-lined autoclave. After crystallization, allow it to cool naturally to room temperature, centrifuge, and wash three times each with N,N-dimethylformamide and methanol solution. Dry at 100 °C for 12 h to obtain UIO-66 metal-organic framework material.

[0080] Catalytic reaction conditions: reaction pressure 3.0 MPa, reaction temperature 320 °C, space velocity 4800 mL·g⁻¹ -1 ·h -1 The molar ratio of H2 to CO2 is 3:1.

[0081] Comparative Example 2

[0082] A method for preparing metal oxide / metal-organic framework catalysts includes the following steps:

[0083] S1, 1.60 g zirconium tetrachloride, 1.15 g terephthalic acid and 0.5 g benzoic acid were dissolved in 140 mL N,N-dimethylformamide, and 15 mL acetic acid and 30 mL water were added sequentially. After the mixture became clear, it was subjected to hydrothermal crystallization at 120 °C for 24 h in a polytetrafluoroethylene-lined autoclave. After crystallization, it was allowed to cool naturally to room temperature, centrifuged, and washed three times each with N,N-dimethylformamide and methanol solution. It was then dried at 100 °C for 12 h to obtain UIO-66 metal-organic framework material.

[0084] S2. 1g of zinc nitrate hydrate was placed in a muffle furnace and calcined at 350℃ for 5.5h to obtain ZnO.

[0085] The Zn / UIO-66 composite catalyst was obtained by uniformly mixing 0.04g ZnO and 0.46g S1 to obtain the UIO-66 metal-organic framework material.

[0086] Catalytic reaction conditions: reaction pressure 0 MPa, reaction temperature 320 °C, space velocity 4800 mL·g -1 ·h -1 The molar ratio of H2 to CO2 is 3:1.

[0087] Figure 1 The XRD patterns of the catalysts prepared in Examples 1, 2, 8 and Comparative Example 1 are shown below. Figure 1 It can be seen that all samples possess the characteristic diffraction peaks of UIO-66 metal-organic framework materials, indicating that UIO-66 metal-organic framework materials were successfully prepared via the hydrothermal method. After mixing different metal oxides with the metal-organic framework materials, the metal oxides retained their characteristic diffraction peaks; and a composite phase structure consisting of two phases, metal oxides and metal-organic framework materials, was formed. Furthermore, the interface between the metal oxides and the metal-organic framework materials is a physical interaction, with each component retaining its unique structure.

[0088] The catalysts prepared in Examples 1-9 and Comparative Examples 1-2 were used in the process of CO2 hydrogenation to produce aromatics. The catalytic reaction was carried out in a fixed-bed stainless steel reactor (outer diameter 20 mm, inner diameter 9 mm, length 290 mm). Before the reaction, the catalyst was activated for 3 h in a reducing atmosphere (H2). The amount of catalyst used was 0.5 g, the catalytic reaction pressure was 0.5–3.5 MPa, the reaction temperature was 320 °C, and the space velocity was 4800 ml·g. -1 ·h -1The molar ratio of H2 to CO2 is 3:1. The conversion rate of carbon dioxide (X) is tested. CO2 ), Aromatic selectivity (S Aro. ) and the selectivity of BTX (S BTX The results are shown in Table 1.

[0089] Table 1 Catalytic performance of the composite catalyst prepared in this invention

[0090]

[0091]

[0092] As shown in Table 1, when metal oxides and metal-organic framework materials are mixed (Example 8), the catalyst exhibits high CO2 conversion, BTX, and total aromatic selectivity. This is because the metal system can serve as an active site for the CO2 hydrogenation reaction. The UIO-66 metal-organic framework material has numerous acidic sites, which can promote the aromatization of methanol intermediates. ZnO is widely used as an effective catalyst for CO2 hydrogenation to aromatics. When ZnO nanoparticles are dispersed on the surface of the UIO-66 metal-organic framework material, they exhibit good physical interactions, promoting the formation of aromatics. ZnO promotes the dissociation of H2, and the addition of an appropriate amount of Zn is beneficial for the formation of intermediate products, thereby improving CO2 conversion and BTX selectivity. High aromatic selectivity can still be obtained on this catalyst under different reaction pressures. As the pressure increases, the aromatic selectivity gradually increases; high pressure is thermodynamically favorable for the CO2 aromatization reaction. When the reaction pressure increased by 3.0 MPa from atmospheric pressure, the CO selectivity on the Zn / UIO-66 composite catalyst decreased significantly from 37.2% to 16.1%, indicating that increased pressure can significantly promote the conversion of CO to hydrocarbons. Simultaneously, higher pressure accelerated the conversion of carbon dioxide and promoted the formation of aromatics.

[0093] Under optimal reaction conditions, such as the composite catalyst prepared in Example 8, the CO2 conversion rate after catalytic reaction is as high as 25.03%, the selectivity of aromatics is as high as 79.75%, and the efficient generation of light aromatics (benzene, toluene, p-xylene) is achieved with a selectivity of up to 76.46%, and the selectivity of aromatics is still as high as 67.36% at 0 MPa.

[0094] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0095] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. The application of a metal oxide / metal-organic framework composite catalyst in the hydrogenation of CO2 to aromatics, characterized in that, The catalytic reaction was carried out at a pressure of 0.5–3.5 MPa, a temperature of 320 °C, and a space velocity of 4800 mL·g. -1 ·h -1 The molar ratio of H2 to CO2 is 3:1; The metal oxide / metal-organic framework composite catalyst is prepared according to the following steps: S1. A zirconium source, ligand, and modifier are dissolved in a solvent and crystallized to synthesize UIO-66 metal-organic framework material; the modifier is benzoic acid. S2. Mix the metal oxide with the UIO-66 metal-organic framework material from S1 to obtain a metal oxide / UIO-66 composite catalyst. The metal oxide is obtained by calcining zinc nitrate hydrate, indium nitrate hydrate, or gallium nitrate hydrate in a muffle furnace; the calcination temperature is 300~350℃ and the time is 5~5.5 h; the metal oxide accounts for 8% of the mass of the composite catalyst.

2. The application according to claim 1, characterized in that, In S1, the specific steps for preparing the UIO-66 metal-organic framework material are as follows: Zirconium tetrachloride, terephthalic acid, and benzoic acid were dissolved in a solvent, and acetic acid and water were added sequentially for mixing. After the mixed solution was clarified, it was transferred to a high-pressure reactor lined with polytetrafluoroethylene for crystallization. After crystallization, the mixture was centrifuged, washed, and dried to obtain UIO-66 metal-organic framework material.

3. The application according to claim 2, characterized in that, The mass ratio of zirconium tetrachloride, terephthalic acid, benzoic acid, and solvent is 0.32:0.23:0.1:27; the volume ratio of solvent, acetic acid, and water is 28:3:6; the solvent is N,N-dimethylformamide; the crystallization temperature is 100~120℃, and the time is 18~30h; the detergent is N,N-dimethylformamide and methanol, and the washing is performed 2~4 times; the drying temperature is 80~120℃, and the time is 8~12h.

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