A trans-encapsulated catalyst, its preparation method and application

Abstract

This invention, for the first time, prepares a homogeneous and small-volume ZSM-5@ZnCr reverse capsule catalyst using a simple modified co-precipitation method and applies it to the direct conversion of carbon dioxide to isoalkanes. This capsule catalyst has a unique structure, with ZSM-5 zeolite as the core and zinc oxide chromium as the shell, and can be used to directly convert CO2 to isoalkanes. In terms of catalytic performance, the ZSM-5@ZnCr-3 capsule catalyst exhibits 75.6% isoalkanes selectivity based on a CO2 conversion rate of 17.3% under reaction conditions of 360℃ and 5 MPa. Furthermore, no deactivation was observed within 100 hours, and the high isoalkanes selectivity remained stable. The ZSM-5@ZnCr capsule catalyst not only opens up a new integration mode for oxide-zeolite composite catalysts but also provides a powerful catalyst for the directed conversion of carbon dioxide to isoalkanes.

Description

Technical Field

[0001] This invention relates to the field of capsule catalyst technology, and in particular to a trans-capsule catalyst, its preparation method, and its application. Background Technology

[0002] Environmental issues have garnered widespread attention over the past few decades. Carbon dioxide (CO2), the primary greenhouse gas, is mainly emitted excessively due to the extensive use of fossil fuels. However, from an energy perspective, CO2 is also the cheapest and most abundant carbon source, capable of producing high-value-added fuels and chemical products through chemical conversion. Direct CO2 conversion not only effectively utilizes carbon resources to create social benefits but also mitigates a range of environmental problems caused by CO2 emissions. Among all these methods, thermocatalytic conversion of carbon dioxide is the most promising due to its high CO2 conversion rate and controllable product distribution.

[0003] Liquid fuels, especially gasoline, play a crucial role in the global energy supply system. However, with dwindling oil resources, the production of gasoline from petroleum refining can no longer meet the growing global demand. While gasoline can be obtained directly from the hydrogenation of carbon dioxide via a modified Fischer-Tropsch synthesis, the resulting product is paraffin. Furthermore, as contributors to octane rating, olefins and aromatics are restricted from being added to gasoline due to their instability and carcinogenicity. Therefore, the direct conversion of CO2 into isoalkanes has attracted widespread attention.

[0004] In summary, achieving efficient activation of CO2 molecules to improve conversion efficiency and the energy efficiency of the conversion system is crucial in CO2 conversion and utilization. The development of highly active and stable catalysts has always been one of the core foundations of CO2 chemical conversion processes. Zeolite molecular sieves, with their uniform pore structure, high specific surface area, and high hydrothermal stability, are excellent supports for loading metal active sites and are widely used in CO2 conversion catalyst research.

[0005] Generally, there are two different methods for preparing capsule catalysts: chemical hydrothermal method and physical coating method. (1) In the physical method, the particle size of the capsule catalyst is large and non-uniform, between 1000-2000 μm. (2) In the chemical method, metal catalysts are corroded by the harsh hydrothermal environment. Directly synthesizing capsule catalysts with uniform and small particle size remains a serious challenge. Summary of the Invention

[0006] In view of this, the present invention provides a trans-encapsulated catalyst, which has high conversion rate and selectivity in the reaction of carbon dioxide directly converted into isoalkanes.

[0007] This invention provides a method for preparing a trans-encapsulated catalyst, comprising the following steps:

[0008] A) Zinc nitrate hexahydrate and chromium nitrate nonahydrate are mixed to obtain the first mixture;

[0009] B) Formamide and ZSM-5 zeolite are dissolved in water to obtain a second mixture;

[0010] C) The first mixture and the alkaline solution are added dropwise to the second mixture, precipitate, stand, dry, and calcine to obtain the ZSM-5@ZnCr trans capsule catalyst.

[0011] Preferably, the mass ratio of zinc nitrate hexahydrate and chromium nitrate nonahydrate in step A) is 2 to 4:2.

[0012] Preferably, the SiO2 / Al2O3 ratio of the ZSM-5 zeolite in step B) is 24 to 1500.

[0013] Preferably, the mass ratio of formamide, ZSM-5 zeolite and water in step B) is 0.1-0.5:2-6:100.

[0014] The mass ratio of zinc nitrate hexahydrate, chromium nitrate nonahydrate, and ZSM-5 zeolite is 1:5.

[0015] The concentration of the alkaline solution is 0.2M.

[0016] Preferably, the precipitation temperature in step C) is 60°C; and the pH value of the precipitate is 7-8.

[0017] Preferably, the settling time in step C) is 2-3 hours; after settling, the sediment is washed with water; the drying is carried out at 120°C for 10-30 hours; and the calcination is carried out at 450-500°C for 2-5 hours.

[0018] Preferably, step C) further includes:

[0019] The first mixture and the alkaline solution were added dropwise to the ZSM-5@ZnCr trans-capsule catalyst prepared in step C), precipitated, allowed to stand, dried, and calcined to obtain a re-coated trans-capsule catalyst, denoted as Na-ZSM-5@ZnCr-2; the above steps 1 to 2 were repeated to obtain multi-layered trans-capsule catalysts ZSM-5@ZnCr-x (x = 3 and 4).

[0020] This invention provides a trans-encapsulated catalyst, prepared by any one of the preparation methods described above.

[0021] This invention provides a method for preparing isoparaffins from CO2, using the trans-encapsulated catalyst described in the above technical solution.

[0022] Compared with existing technologies, this invention provides a method for preparing a trans-capsule catalyst, comprising the following steps: A) mixing zinc nitrate hexahydrate and chromium nitrate nonahydrate to obtain a first mixture; B) dissolving formamide and ZSM-5 zeolite in water to obtain a second mixture; C) adding the first mixture and an alkaline solution dropwise to the second mixture, precipitating, allowing to stand, drying, and calcining to obtain the ZSM-5@ZnCr trans-capsule catalyst. This invention is the first to prepare a uniform and small-volume ZSM-5@ZnCr trans-capsule catalyst using a simple modified co-precipitation method, and applies it to the reaction of direct conversion of carbon dioxide to isoalkanes. This capsule catalyst has a unique structure, with ZSM-5 zeolite as the core and zinc oxide chromium as the shell, and can be used to directly convert CO2 to isoalkanes. In terms of catalytic performance, the ZSM-5@ZnCr-3 capsule catalyst passed through in one pass at 360℃ and 5MPa, exhibiting 75.6% isoalkane selectivity based on a CO2 conversion rate of 17.3%. Furthermore, no deactivation was observed within 100 hours, and the high selectivity for isoalkanes remained stable. The ZSM-5@ZnCr capsule catalyst not only opens up a new integration method for oxide-zeolite composite catalysts but also provides a powerful candidate catalyst for the directed conversion of carbon dioxide to isoalkanes. Attached Figure Description

[0023] Figure 1 XRD pattern of the prepared catalyst;

[0024] Figure 2 XPS analysis of different catalysts;

[0025] Figure 3 (a and b) SEM images of the original ZSM-5 and (c and d) ZSM-5@ZnCr-2 capsule catalysts, and (eh) EDS spectra of the ZSM-5@ZnCr-2 capsule catalysts;

[0026] Figure 4 (a) Diffusion pathways of oxide@zeolite and (b) zeolite@oxide capsule catalysts;

[0027] Figure 5 Catalytic performance of different catalysts in converting CO2 to isoparaffins. Carbon dioxide hydrogenation reaction conditions: 360℃, 5.0 MPa (equilibrium of 23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar and H2), flow time (TOS) = 8 h, GHSV = 1200 mL / gcat / h;

[0028] Figure 6Catalytic performance of different catalysts (ZSM-5-ZnCr(24), ZSM-5@ZnCr(105), ZSM-5-ZnCr(300) and ZSM-5-ZnCr(1500)) in converting CO2 to isoparaffins. Carbon dioxide hydrogenation reaction conditions: 360℃, 5.0MPa, (equilibrium of 23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar and H2), flow time (TOS) = 8 h, GHSV = 1200 mL / gcat / h;

[0029] Figure 7 The performance of different ZSM-5@ZnCr-x catalysts in catalyzing the formation of isoparaffins from CO2. CO2 hydrogenation reaction conditions: 360℃, 5.0 MPa (equilibrium of 23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar and H2), flow time (TOS) = 8 h, GHSV = 1200 mL / gcat / h;

[0030] Figure 8 Stability of ZSM-5@ZnCr-3 capsule catalyst. CO2 hydrogenation reaction conditions: 360℃, 5.0MPa (equilibrium of 23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar and H2), GHSV = 1200 mL / gcat / h. Detailed Implementation

[0031] This invention provides a trans-encapsulated catalyst, its preparation method, and its application. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and fall within the scope of this invention. The method and application of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the method and application described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0032] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural.

[0033] The present invention aims to design and develop capsule catalysts with high selectivity, especially for isoalkane, and high stability to directly convert CO2 into isoalkane, thereby developing a technology for producing liquid fuels from non-petroleum resources.

[0034] This invention provides a method for preparing a trans-encapsulated catalyst, comprising the following steps:

[0035] A) Zinc nitrate hexahydrate and chromium nitrate nonahydrate are mixed to obtain the first mixture;

[0036] B) Formamide and ZSM-5 zeolite are dissolved in water to obtain a second mixture;

[0037] C) The first mixture and the alkaline solution are added dropwise to the second mixture, precipitate, stand, dry, and calcine to obtain the ZSM-5@ZnCr trans capsule catalyst.

[0038] The method for preparing the trans-encapsulated catalyst provided by the present invention first involves mixing zinc nitrate hexahydrate and chromium nitrate nonahydrate to obtain a first mixture.

[0039] The mass ratio of zinc nitrate hexahydrate and chromium nitrate nonahydrate in this invention is 2 to 4:2.

[0040] In some embodiments, the mass ratio of zinc nitrate hexahydrate to chromium nitrate nonahydrate is 2.5 to 3.5:2.

[0041] In some embodiments, the mass ratio of zinc nitrate hexahydrate to chromium nitrate nonahydrate is 2.6 to 3.2:2.

[0042] In some embodiments, the mass ratio of zinc nitrate hexahydrate to chromium nitrate nonahydrate is 2.97:2.

[0043] Formamide and ZSM-5 zeolite were dissolved in water to obtain a second mixture.

[0044] According to the present invention, the mass ratio of formamide, ZSM-5 zeolite and water is 0.1-0.5:2-6:100.

[0045] In some embodiments, the mass ratio of formamide, ZSM-5 zeolite, and water is 0.1–0.3:2–5:100.

[0046] In some embodiments, the mass ratio of formamide, ZSM-5 zeolite, and water is 0.1–0.2:2–4:100.

[0047] In some embodiments, the mass ratio of formamide, ZSM-5 zeolite, and water is 0.1:2:100.

[0048] According to the present invention, the SiO2 / Al2O3 ratio of the ZSM-5 zeolite is 24 to 1500. Specifically, it can be 24, 100, 105, 200, 250, 300, 500, 800, 900, 1000 or 1500.

[0049] This invention investigated the effect of ZSM-5 zeolite with different SiO2 / Al2O3 ratios on catalytic performance, such as different catalysts (ZSM-5-ZnCr (24), ZSM-5@ZnCr (105), ZSM-5-ZnCr (300), and ZSM-5-ZnCr (1500). As the SiO2 / Al2O3 ratio of ZSM-5 zeolite increased from 24 to 1500, the CO2 conversion rate slightly decreased from 19.6% to 17.0%; the CO selectivity first decreased and then increased. The CH4 selectivity decreased from 1... The selectivity for methanol decreased from 1.3% to 1.6%, while the selectivity for MeOH / DME increased sharply from 1.7% to 96.5%. The selectivity for isoparaffins initially increased from 32.1% to 70.0%, then decreased significantly to 0.6%. When the SiO2 / Al2O3 ratio was 24, the large number of acidic sites led to side reactions such as methanation. When the SiO2 / Al2O3 ratio was 1500, the number of acidic sites was insufficient to further convert methanol into hydrocarbons, resulting in higher selectivity for CO and MeOH / DME.

[0050] The present invention also provides an alkaline solution with a concentration of 0.2M.

[0051] The alkaline solution includes, but is not limited to, sodium hydroxide solution.

[0052] The first mixture and the alkaline solution are added dropwise to the second mixture.

[0053] After the addition was complete, the precipitate was allowed to stand, dried, and calcined to obtain the ZSM-5@ZnCr trans-capsule catalyst.

[0054] The precipitation temperature of the present invention is 60°C; the pH value of the precipitate is 7-8.

[0055] In this invention, precipitation is carried out at 60°C, and the pH value is controlled at 7.0–8.0 with stirring. After standing for 2–3 hours at the same temperature, the precipitate is washed three times with distilled water and collected by filtration.

[0056] The product was dried at 120℃ for 10–30 h and then calcined at 450–500℃ for 2–5 h. The sample was labeled as Na-ZSM-5@ZnCr-1 capsule catalyst.

[0057] In some embodiments, the product was dried at 120°C for 24–26 h and then calcined at 480–500°C for 2–5 h, and the sample was labeled as Na-ZSM-5@ZnCr-1 capsule catalyst.

[0058] In some embodiments, the product was dried at 120°C for 24 hours and then calcined at 500°C for 3 hours, and the sample was labeled as Na-ZSM-5@ZnCr-1 capsule catalyst.

[0059] To obtain capsule catalysts with different ZnCr thicknesses, the above synthesis process was repeated.

[0060] According to the present invention, the above steps are followed by:

[0061] The first mixture and the alkaline solution were added dropwise to the ZSM-5@ZnCr trans-capsule catalyst prepared in step C), precipitated, allowed to stand, dried, and calcined to obtain the re-coated trans-capsule catalyst, denoted as Na-ZSM-5@ZnCr-2.

[0062] Repeat steps 1-2 above to obtain the multi-layered trans-encapsulated catalyst ZSM-5@ZnCr-x (x = 3 and 4). Specifically:

[0063] The first mixture and the alkaline solution were added dropwise to the Na-ZSM-5@ZnCr-2 trans-encapsulated catalyst, precipitated, allowed to stand, dried, and calcined to obtain the re-encapsulated trans-encapsulated catalyst, denoted as Na-ZSM-5@ZnCr-3.

[0064] The first mixture and the alkaline solution were added dropwise to the Na-ZSM-5@ZnCr-3 trans-encapsulated catalyst, precipitated, allowed to stand, dried, and calcined to obtain a re-encapsulated trans-encapsulated catalyst, denoted as Na-ZSM-5@ZnCr-4.

[0065] The different SiO2 / Al2O3 ratios of the zeolite in this invention affect the number of acidic sites on the catalyst surface, thus affecting the selectivity of the catalyst; for the ZSM-5@ZnCr capsule catalyst, the film thickness plays a key role in the catalytic system.

[0066] This invention presents the first preparation of a homogeneous and small-volume ZSM-5@ZnCr capsule catalyst, which is then applied to the direct conversion of carbon dioxide to isoalkanes. This capsule catalyst features a unique structure, with ZSM-5 zeolite as the core and zinc chromium oxide as the shell. Furthermore, it can be achieved via a previously unreported modified co-precipitation method. The ZSM-5@ZnCr capsule catalyst exhibits a selectivity of 75.6% for isoalkanes and remains stable over 100 hours.

[0067] This invention provides a trans-encapsulated catalyst, prepared by any one of the preparation methods described above.

[0068] The preparation method described above has been clearly described in this invention, and will not be repeated here.

[0069] The present invention also provides the application of the trans-encapsulated catalyst described above as a catalyst for the preparation of isoalkanes from CO2.

[0070] This invention provides a method for preparing isoparaffins from CO2, using the trans-encapsulated catalyst described in the above technical solution.

[0071] This invention provides a method for preparing a trans-capsule catalyst, comprising the following steps: A) mixing zinc nitrate hexahydrate and chromium nitrate nonahydrate to obtain a first mixture; B) dissolving formamide and ZSM-5 zeolite in water to obtain a second mixture; C) adding the first mixture and an alkaline solution dropwise to the second mixture, allowing precipitation, standing, drying, and calcining to obtain the ZSM-5@ZnCr trans-capsule catalyst. This invention is the first to prepare a uniform and small-volume ZSM-5@ZnCr trans-capsule catalyst using a simple modified co-precipitation method, and applies it to the reaction of direct conversion of carbon dioxide to isoalkanes. This capsule catalyst has a unique structure, with ZSM-5 zeolite as the core and zinc oxide chromium as the shell, and can be used to directly convert CO2 to isoalkanes. In terms of catalytic performance, the ZSM-5@ZnCr-3 capsule catalyst passed through in one pass at 360℃ and 5MPa, exhibiting 75.6% isoalkane selectivity based on a CO2 conversion rate of 17.3%. Furthermore, no deactivation was observed within 100 hours, and the high isoalkane selectivity remained stable. The ZSM-5@ZnCr capsule catalyst not only opens up a new integration method for oxide-zeolite composite catalysts, but also provides a powerful candidate catalyst for the directional conversion of carbon dioxide to isoalkanes.

[0072] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0073] The numerical ranges and parameters involved in this invention have been presented as accurately as possible to the relevant values ​​in the specific embodiments. However, any numerical value inevitably contains standard deviations due to individual test methods. Therefore, unless otherwise expressly stated, it should be understood that all numerical ranges or specific data used in this disclosure may have a reasonable deviation within a certain range, for example, within 1% or 0.5%.

[0074] The embodiments and comparative examples of this invention describe some examples, in which the embodiments illustrate certain implementations of the invention. However, this does not mean that the effects of the invention can only be achieved in these examples.

[0075] To further illustrate the present invention, the following detailed description of a trans-encapsulated catalyst, its preparation method, and its application, in conjunction with embodiments, is provided by the present invention.

[0076] Materials in the Examples

[0077] Chromium nitrate nonahydrate (Cr(NO3)3-9H2O, Strem, 99%); zinc nitrate hexahydrate (Zn(NO3)2-6H2O, Wako, 99%); sodium hydroxide (NaOH, Wako); formamide (FA, HCONH2, Wako); ammonium carbonate ((NH4)2CO3, Wako); deionized water (homemade); commercial ZSM-5 zeolite (SiO2 / Al2O3 = 105, Mizusawa Industrial Chemicals Co., Ltd.); commercial Beta and Y zeolite (SiO2 / Al2O3 = 100, Tosoh Co.); and commercial ZSM-22 zeolite (SiO2 / Al2O3 = 65-80, ACS Material). All chemicals were used without any further purification steps.

[0078] Example 1: Synthesis of ZSM-5@ZnCr capsule catalyst

[0079] Solution A: Dissolve 2.97 g Zn(NO3)2·6H2O and 2.00 g Cr(NO3)3·9H2O in 100 mL of deionized water. Solution B: Dissolve 1.6 g NaOH in 200 mL of deionized water. Solution C: Dissolve 0.1 g formamide and 2 g ZSM-5 zeolite in 100 mL of deionized water. Simultaneously, add solutions A and B dropwise to solution C, precipitate at 60 °C, and maintain the pH at 7.0-8.0 with stirring. After standing for 3 hours at the same temperature, wash the precipitate three times with distilled water, filter, and collect. Dry the product overnight at 120 °C, then calcine at 500 °C for 3 hours. The sample is labeled as Na-ZSM-5@ZnCr-1 capsule catalyst.

[0080] To obtain capsule catalysts with different ZnCr thicknesses, the above synthesis process was repeated. However, 2 grams of ZSM-5 zeolite were replaced with 2 grams of Na-ZSM-5@ZnCr-1. The resulting samples were labeled as Na-ZSM-5@ZnCr-2 capsule catalysts.

[0081] Replace 2 grams of Na-ZSM-5@ZnCr-1 with 2 grams of Na-ZSM-5@ZnCr-2, and repeat the above synthesis process to obtain the Na-ZSM-5@ZnCr-3 capsule catalyst.

[0082] ZSM-5@ZnCr-x (x = 1, 2, and 3) samples were obtained from Na-ZSM-5@ZnCr-x samples by ion exchange. 2 g of Na-ZSM-5@ZnCr-x sample was dispersed in 200 mL of NH4NO3 aqueous solution (1 mol / L) and stirred at 80 °C for 5 h. This process was repeated three times, followed by drying at 120 °C overnight, and then calcining at 500 °C for 3 h.

[0083] Synthesis of ZSM-5 / ZnCr catalyst

[0084] Solution A: Dissolve 2.97 g of Zn(NO3)2·6H2O and 2.00 g of Cr(NO3)3·9H2O in 100 mL of deionized water. Solution B: Dissolve 1.6 g of NaOH in 200 mL of deionized water. Solution C: Dissolve 0.1 g of formamide in 100 mL of deionized water. Simultaneously, solutions A and B are added dropwise to solution C, and precipitation is carried out at 60 °C, with the pH controlled at 7.0-8.0 under stirring. After standing for 3 hours at the same temperature, the precipitate is washed three times with distilled water and collected by filtration. The product is dried overnight at 120 °C and then calcined at 500 °C for 3 hours; the sample is labeled as a ZnCr catalyst.

[0085] ZnCr oxide and ZSM-5 molecular sieve were physically ground to obtain ZSM-5 / ZnCr catalyst with a mass ratio of ZnCr:ZSM-5 = 1.56:1.

[0086] The preparation process of Beta-ZnCr-2, Y-ZnCr-2, and ZSM-22-ZnCr-2 catalysts is the same as that of ZSM-5@ZnCr-2, except that the type of molecular sieve is changed.

[0087] Comparative Example 1: Synthesis of Zinc Chromium Oxide

[0088] Solution A: Dissolve 2.97 g of Zn(NO3)2·6H2O and 2.00 g of Cr(NO3)3·9H2O in 100 mL of deionized water. Solution B: Dissolve 1.6 g of NaOH in 200 mL of deionized water. Solution C: Dissolve 0.1 g of formamide in 100 mL of deionized water. Add solutions A and B simultaneously to solution C, precipitate at 60 °C, and maintain the pH at 7.0-8.0 with stirring. After standing for 3 hours at the same temperature, wash the precipitate three times with distilled water, filter, and collect. Dry the product at 120 °C overnight, then calcine at 500 °C for 3 hours.

[0089] ZnCr sample was obtained from Na-ZnCr sample by ion exchange. 2 g of Na-ZnCr sample was dispersed in 200 mL of NH4NO3 aqueous solution (1 mol / L) and stirred at 80 °C for 5 hours. This process was repeated three times, followed by drying at 120 °C overnight, and then calcining at 500 °C for 3 hours.

[0090] Verification Example

[0091] 1.1 Figure 1The XRD patterns of the catalyst prepared in Example 1 are shown. First, zinc chromium oxide (Zn / Cr molar ratio of 2) and ZSM-5 zeolite (SiO2 / Al2O3 ratio of 105) from Comparative Example 1 were analyzed. Zinc chromium oxide exhibited typical characteristic peaks, belonging to the ZnCr2O4 and ZnO phases. ZSM-5 zeolite showed characteristic peaks of the MFI structure. After encapsulation of ZSM-5 zeolite with ZnCr oxide, the ZSM-5@ZnCr-x catalyst simultaneously exhibited characteristic peaks of both ZSM-5 zeolite and ZnCr oxide. With increasing encapsulation times, the peak intensity of ZSM-5 zeolite decreased, while the peak intensity of zinc chromium oxide increased.

[0092] 1.2 With increasing encapsulation times, the content of ZnCr oxide gradually increased. To further reveal the capsule structure of the synthesized catalyst, XPS technology was used, and the results are as follows: Figure 2 As shown. Figure 2 XPS analysis of different catalysts. It can be seen that with increasing encapsulation times, the characteristic peaks of Si and Al species in the molecular sieve disappear, indicating that ZnCr metal oxides are successfully coated on the surface of ZSM-5 zeolite. Figure 3 SEM characterization revealed that the original ZSM-5 zeolite was elliptical. Meanwhile, the shape of the ZSM-5@ZnCr-2 capsule catalyst was similar to that of the ZSM-5 zeolite. Figure 3 (c and 3d). Compared with the original ZSM-5 zeolite, the ZSM-5@ZnCr-2 capsule catalyst has a larger particle size and a rougher outer surface. These results indicate that zinc oxide can be effectively deposited on the outer surface of ZSM-5 zeolite via this modified co-precipitation method. Furthermore, the ZSM-5@ZnCr-2 capsule catalyst exhibits uniform particle size.

[0093] However, a small portion of ZnCr oxide was observed to separate from the ZSM-5@ZnCr-2 capsule catalyst. Figure 3 c). This may be due to the shedding of ZnCr oxide during preparation and calcination. The external elemental distribution of the ZSM-5@ZnCr-2 capsule catalyst was studied using EDS spectra, such as... Figure 3 As shown in (eh), Si, Al, Cr, and Zn elements are mainly distributed in the capsule catalyst region. Furthermore, the signal intensity of Zn increases as the signal intensity of Si decreases. These results indicate that ZSM-5 zeolite can be coated with zinc oxide chromium, but the distribution of zinc oxide chromium on the outer surface of ZSM-5 zeolite is not symmetrical. Figure 3 (a and b) SEM images of the original ZSM-5 and (c and d) ZSM-5@ZnCr-2 capsule catalysts, and (eh) EDS spectra of the ZSM-5@ZnCr-2 capsule catalysts.

[0094] 1.3 Figure 5 The catalytic performance of different catalysts in converting CO2 to isoparaffins. The ZSM-5@ZnCr-2 catalyst was prepared according to the method described above. The ZSM-5 / ZnCr catalyst was prepared by physically mixing ZSM-5 and ZnCr oxide by grinding (the mass ratio of metal oxide to molecular sieve was 1.5:1). The Beta-ZnCr-2, Y-ZnCr-2, and ZSM-22-ZnCr-2 catalysts were prepared using the same method as the ZSM-5@ZnCr-2 catalyst, except that ZSM-5 was replaced with Beta or ZSM-22.

[0095] The carbon dioxide hydrogenation reaction conditions were 360℃, 5.0 MPa (equilibrium of 23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar and H2), flow time (TOS) = 8 h, GHSV = 1200 mL / gcat / h. Table 1. Product distribution for different catalysts. a ;Depend on Figure 5 As shown in Table 1, the ZSM-5@ZnCr-2 capsule catalyst achieved 70.0% isoparaffin selectivity under conditions of 17.5% CO2 conversion and 63.8% CO selectivity. Specifically, the byproduct CH4 selectivity was only 3.1%. The MeOH / DME selectivity was 1.4%, indicating that the methanol intermediate was almost completely converted. Furthermore, the C2-3 selectivity was controlled below 20%, and the Ciso / Cp ratio (the molar ratio of C in isoparaffins to paraffin) was 3.22. In addition, a comparison was made with the ZSM-5 / ZnCr composite catalyst, which was prepared using a conventional powder mixing method. Under the same zeolite / oxide weight ratio and reaction conditions, the ZSM-5 / ZnCr catalyst achieved a CO2 conversion of 19.4%, a CO selectivity of 39.8%, and an isoparaffin selectivity of 59.6%. Compared to these two integrated methods, the powder-mixed catalyst showed a higher N-C4+ selectivity (18.2%) than the capsule catalyst (6.5%). This is because in the powder mixing method, zinc oxide chromium cannot completely cover the outer surface of ZSM-5 zeolite, allowing light aromatic hydrocarbons (benzene, toluene, and p-xylene) and long-chain hydrocarbons to escape smoothly from the zeolite. However, for the ZSM-5@ZnCr-2 capsule catalyst, due to the obstruction of zinc oxide, products formed in the pores of ZSM-5 zeolite may not be able to escape smoothly. Figure 4 b). Conversely, due to the limitations of thermodynamic equilibrium, the products cannot leave the catalyst in a timely manner, which leads to fluctuations in CO2 conversion, CO, and MeOH / DME selectivity. Therefore, compared with the ZSM-5 / ZnCr catalyst, the ZSM-5@ZnCr-2 capsule catalyst exhibits lower CO2 conversion and higher CO and MeOH / DME selectivity.

[0096] This invention investigated the effects of different types of zeolites on catalytic performance. The selectivity for isoparaffins was, in descending order: ZSM-5@ZnCr-2 (70.0%) > Beta-ZnCr-2 (64.7%) > Y-ZnCr-2 (48.8%) > ZSM-22-ZnCr-2 (20.7%). Although these zeolites had similar SiO2 / Al2O3 ratios, different types of zeolites produced different carbon dioxide conversion rates and product distributions. This is due to the different channel structures and the varying number of acidic sites.

[0097] Beta, Y, and ZSM-22 were all commercially available, and their preparation methods were the same as those for ZSM-5.

[0098] Table 1. Product distribution of different catalysts a

[0099]

[0100]

[0101] a Reaction conditions: 360℃, 5.0MPa (equilibrium of 23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar and H2), flow time (TOS) = 8 h, GHSV = 1200 mL / g cat / h.

[0102] b NC 4+ :C 4+ Products, excluding isoparaffins.

[0103] c iso: Isoalkane.

[0104] d Ciso / C p It is the C molar ratio of all isoalkanes to all paraffins with n>1.

[0105] 1.4 This patent investigated the effect of ZSM-5 zeolite with different SiO2 / Al2O3 ratios on catalytic performance. The catalytic performance is shown in [reference needed]. Figure 6See Table 2. As the SiO2 / Al2O3 ratio of ZSM-5 zeolite increased from 24 to 1500, the CO2 conversion rate slightly decreased from 19.6% to 17.0%; CO selectivity first decreased and then increased. CH4 selectivity decreased from 11.3% to 1.6%, while MeOH / DME selectivity increased sharply from 1.7% to 96.5%. The selectivity of isoparaffins first increased from 32.1% to 70.0%, then decreased significantly to 0.6%. When the SiO2 / Al2O3 ratio was 24, a large number of acidic sites led to side reactions such as methanation. When the SiO2 / Al2O3 ratio was 1500, the number of acidic sites was insufficient to further convert methanol into hydrocarbons, resulting in higher CO and MeOH / DME selectivities. Figure 6 Catalytic performance of different catalysts (ZSM-5-ZnCr(24), ZSM-5@ZnCr(105), ZSM-5-ZnCr(300) and ZSM-5-ZnCr(1500)) in converting CO2 to isoparaffins. Carbon dioxide hydrogenation reaction conditions: 360℃, 5.0MPa (equilibrium of 23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar and H2), flow time (TOS) = 8 h, GHSV = 1200 mL / gcat / h; Table 2. Product distribution of different catalysts. a .

[0106] Table 2. Product distribution of different catalysts a

[0107]

[0108]

[0109] a Reaction conditions: 360℃, 5.0MPa (equilibrium of 23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar and H2), flow time (TOS) = 8 h, GHSV = 1200 mL / gcat / h.

[0110] b NC 4+ :C 4+ Products, excluding isoparaffins.

[0111] c iso: Isoalkane.

[0112] d Ciso / Cp is the molar ratio of C for all isoalkanes to all paraffins with n>1.

[0113] 1.5 For the ZSM-5@ZnCr capsule catalyst, film thickness plays a crucial role in this catalytic system. Catalytic performance is detailed in [link to relevant documentation]. Figure 7 See Table 3. With increasing encapsulation times, CO2 conversion decreased slightly from 20.7% to 17.3%; CO selectivity decreased from 66.2% to 55.0%; and isoparaffin selectivity increased from 61.9% to 75.6%. Notably, the Ciso / Cp ratio increased from 2.39 to 4.78. Figure 7 The performance of different ZSM-5@ZnCr-x catalysts in catalyzing the formation of isoparaffins from CO2. The CO2 hydrogenation reaction conditions were 360℃, 5.0MPa (equilibrium of 23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar and H2), flow time (TOS) = 8 h, GHSV = 1200 mL / gcat / h.

[0114] Table 3. Product distribution of different catalysts a

[0115]

[0116] a Reaction conditions: 360℃, 5.0MPa (equilibrium of 23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar and H2), flow time (TOS) = 8 h, GHSV = 1200 mL / g cat / h.

[0117] b NC 4+ :C 4+ Products, excluding isoparaffins.

[0118] c iso: Isoalkane.

[0119] d Ciso / Cp is the molar ratio of C for all isoalkanes to all paraffins with n>1.

[0120] 1.6 The stability of ZSM-5@ZnCr-3 under conditions of 360℃ and 5MPa was investigated in this invention. Figure 8 Clearly, the carbon dioxide conversion rate and isoalkane selectivity remained stable over 100 hours. Figure 8 Stability of ZSM-5@ZnCr-3 capsule catalyst. CO2 hydrogenation reaction conditions: 360℃, 5.0MPa (equilibrium of 23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar and H2), GHSV = 1200 mL / gcat / h.

[0121] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a trans-encapsulated catalyst, characterized in that, Includes the following steps: A) Zinc nitrate hexahydrate and chromium nitrate nonahydrate are mixed to obtain the first mixture; B) Formamide and ZSM-5 zeolite are dissolved in water to obtain a second mixture; the SiO2 / Al2O3 ratio of the ZSM-5 zeolite is 24~300; C) The first mixture and the alkaline solution are added dropwise to the second mixture, precipitate, stand, dry, and calcine to obtain the ZSM-5@ZnCr trans capsule catalyst.

2. The preparation method according to claim 1, characterized in that, In step A), the mass ratio of zinc nitrate hexahydrate to chromium nitrate nonahydrate is 0.01 to 5.

95.

3. The preparation method according to claim 1, characterized in that, In step B), the mass ratio of formamide, ZSM-5 zeolite, and water is 0.1~0.5:2~6:

100.

4. The preparation method according to claim 1, characterized in that, The concentration of the alkaline solution in step C) is 0.2M.

5. The preparation method according to claim 1, characterized in that, The precipitation temperature in step C) is 60°C; the pH value of the precipitate is 7~8.

6. The preparation method according to claim 1, characterized in that, Step C) The settling time is 2-3 hours; after settling, the sediment is washed with water; the drying is done at 120°C for 10-30 hours; the calcination is done at 450-500°C for 2-5 hours.

7. The preparation method according to claim 1, characterized in that, Step C) is followed by: The first mixture and the alkaline solution were added dropwise to the ZSM-5@ZnCr trans-capsule catalyst prepared in step C), precipitated, allowed to stand, dried, and calcined to obtain a re-coated trans-capsule catalyst, denoted as Na-ZSM-5@ZnCr-2; the above steps 1 to 2 times were repeated to obtain multi-layered trans-capsule catalysts ZSM-5@ZnCr-x, where x = 3 and 4.

8. A trans-encapsulated catalyst, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.

9. A method for preparing isoparaffins from CO2, characterized in that, Catalysis is performed using the trans-encapsulated catalyst as described in claim 8.

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