Reverse-encapsulated capsule catalyst, preparation method therefor, and use thereof

Abstract

According to the present invention, a uniform and small-size ZSM-5@ZnCr reverse-encapsulated capsule catalyst is prepared by a simple and convenient improved co-precipitation method for the first time, and is applied to a reaction for directly converting carbon dioxide into isoparaffin. The capsule catalyst has a unique structure, takes ZSM-5 zeolite as a core and zinc chromium oxide as a shell, and can be used for directly converting CO2 into isoparaffin. In terms of catalytic performance, a ZSM-5@ZnCr-3 capsule catalyst exhibits 75.6% isoparaffin selectivity at a 17.3% CO2 conversion rate under the reaction conditions of 360°C and 5 MPa. In addition, the deactivation phenomenon is not observed within 100 hours, and the high isoparaffin selectivity is kept stable. The ZSM-5@ZnCr capsule catalyst not only develops a new integration mode for an oxide-zeolite composite catalyst, but also provides a powerful catalyst for directional conversion of carbon dioxide to isoparaffin.

Description

A trans-capsule catalyst and its preparation method and application

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on February 27, 2024, with application number 202410214681.5 and invention name “A trans-capsule catalyst, its preparation method and application”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the technical field of capsule catalysts, in particular to a trans capsule catalyst and a preparation method and application thereof. Background Art

[0003] Environmental issues have attracted widespread attention over the past few decades. Carbon dioxide (CO2), a major greenhouse gas, is excessively emitted primarily due to the extensive use of fossil fuels. However, from an energy perspective, CO2 is also the cheapest and most abundant carbon source, which can be converted into high-value-added fuels and chemical products through chemical conversion. Direct conversion of CO2 not only effectively utilizes carbon resources to create benefits for society, but also alleviates a range of environmental issues caused by CO2 emissions. Among these methods, thermal catalytic conversion of CO2 is the most promising due to its high CO2 conversion rate and controllable product distribution.

[0004] Liquid fuels, especially gasoline, play a critical role in the global energy supply system. However, with the dwindling of petroleum resources, the production of petroleum-based gasoline is no longer able to meet the growing global demand. Although gasoline can be directly obtained from the hydrogenation of carbon dioxide via a modified Fischer-Tropsch synthesis, the resulting product is paraffin. Furthermore, olefins and aromatics, contributors to octane rating, are restricted from addition to gasoline due to their instability and carcinogenicity. Therefore, the direct conversion of CO2 into isoparaffins has attracted widespread attention.

[0005] In summary, efficient activation of CO2 molecules is crucial for improving both conversion efficiency and the energy efficiency of the conversion system during CO2 conversion and utilization. The development of highly active and stable catalysts has always been a core foundation of CO2 chemical conversion. Zeolite molecular sieves, with their uniform pore structure, high surface area, and high hydrothermal stability, are excellent supports for metal active sites and are widely used in CO2 conversion catalyst research.

[0006] Generally speaking, there are two different methods for preparing encapsulated catalysts: chemical hydrothermal and physical encapsulation. (1) In the physical method, the particle size of the encapsulated catalyst is large and uneven, ranging from 1000-2000 μm. (2) In the chemical method, the metal catalyst is corroded by the harsh hydrothermal environment. The direct synthesis of encapsulated catalysts with uniform and small particle size remains a serious challenge.

[0007] Summary of the Invention

[0008] In view of this, the present invention provides a trans-capsule catalyst. The catalyst provided by the present invention has high conversion rate and selectivity in the reaction of directly converting carbon dioxide into isoparaffins.

[0009] The present invention provides a method for preparing a trans-encapsulated catalyst, comprising the following steps:

[0010] A) mixing zinc nitrate hexahydrate and chromium nitrate nonahydrate to obtain a first mixed solution;

[0011] B) dissolving formamide and ZSM-5 zeolite in water to obtain a second mixed solution;

[0012] C) adding the first mixed solution and the alkaline solution dropwise to the second mixed solution, precipitating, standing, drying, and calcining to obtain a ZSM-5@ZnCr trans-capsule catalyst.

[0013] Preferably, in step A), the mass ratio of zinc nitrate hexahydrate to chromium nitrate nonahydrate is 2 to 4:2.

[0014] Preferably, the SiO2 / Al2O3 ratio of the ZSM-5 zeolite in step B) is 24-1500.

[0015] Preferably, in step B), the mass ratio of formamide, ZSM-5 zeolite and water is 0.1-0.5:2-6:100.

[0016] The mass ratio of the zinc nitrate hexahydrate, the chromium nitrate nonahydrate and the ZSM-5 zeolite is 1:5.

[0017] The concentration of the alkaline solution is 0.2M.

[0018] Preferably, the precipitation temperature in step C) is 60° C.; and the pH value of the precipitation is 7-8.

[0019] Preferably, in step C), the standing time is 2 to 3 hours; after the standing, the precipitate is washed with water; the drying is performed at 120° C. for 10 to 30 hours; and the calcination is performed at 450 to 500° C. for 2 to 5 hours.

[0020] Preferably, the step C) further comprises:

[0021] The first mixed solution and the alkaline solution are 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, recorded as Na-ZSM-5@ZnCr-2; the above steps are repeated 1 to 2 times to obtain a multi-layer coated trans capsule catalyst ZSM-5@ZnCr-x (x=3 and 4).

[0022] The present invention provides a trans-capsule catalyst, which is prepared by the preparation method described in any one of the above technical solutions.

[0023] The present invention provides a method for preparing isoalkanes from CO2, using the trans-capsule catalyst described in the above technical solution as catalysis.

[0024] Compared to the prior art, the present invention provides a method for preparing a reverse encapsulated catalyst, comprising the following steps: A) mixing zinc nitrate hexahydrate and chromium nitrate nonahydrate to obtain a first mixed solution; B) dissolving formamide and ZSM-5 zeolite in water to obtain a second mixed solution; and C) dropwise adding the first mixed solution and an alkaline solution to the second mixed solution, allowing precipitation, allowing to stand, drying, and calcining to obtain a ZSM-5@ZnCr reverse encapsulated catalyst. This invention, for the first time, prepares a uniform and compact ZSM-5@ZnCr reverse encapsulated catalyst using a simple, improved co-precipitation method and applies it to the direct conversion of carbon dioxide to isoparaffins. This encapsulated catalyst has a unique structure, consisting of a ZSM-5 zeolite core and a zinc chromium oxide shell, and can be used for the direct conversion of CO2 to isoparaffins. In terms of catalytic performance, the ZSM-5@ZnCr-3 encapsulated catalyst exhibits a 75.6% isoparaffin selectivity based on a 17.3% CO2 conversion in a single pass at 360°C and 5 MPa. Furthermore, no deactivation was observed over 100 h, and the high isoparaffin selectivity remained stable. The ZSM-5@ZnCr capsule catalyst not only opens up a new integration approach for oxide-zeolite composite catalysts but also provides a strong candidate catalyst for the targeted conversion of CO2 to isoparaffins. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 shows the XRD pattern of the catalyst prepared;

[0026] Figure 2 XPS analysis of different catalysts;

[0027] Figure 3. (a and b) SEM images of pristine ZSM-5 and (c and d) ZSM-5@ZnCr-2 capsule catalysts, (eh) EDS spectra of ZSM-5@ZnCr-2 capsule catalysts.

[0028] Figure 4. Diffusion pathways of (a) oxide@zeolite and (b) zeolite@oxide capsule catalysts.

[0029] Figure 5. Catalytic performance of different catalysts for the conversion of CO₂ to isoparaffins. CO₂ hydrogenation reaction conditions: 360°C, 5.0 MPa, (23.02 vol% CO₂, 3.01 vol% CO, 3.01 vol% Ar and H₂ balance), time of operation (TOS) = 8 h, GHSV = 1200 mL / gcat / h.

[0030] Figure 6. Catalytic performance of different catalysts (ZSM-5-ZnCr(24), ZSM-5@ZnCr(105), ZSM-5-ZnCr(300), and ZSM-5-ZnCr(1500)) for the conversion of CO2 to isoparaffins. CO2 hydrogenation reaction conditions: 360°C, 5.0 MPa, (23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar, and H2 in balance), flow time (TOS) = 8 h, GHSV = 1200 mL / gcat / h;

[0031] Figure 7. Catalytic performance of different ZSM-5@ZnCr-x catalysts for CO2 to isoparaffin formation. CO2 hydrogenation reaction conditions: 360°C, 5.0 MPa, (23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar, and H2 in balance), time of operation (TOS) = 8 h, GHSV = 1200 mL / gcat / h.

[0032] Figure 8. Stability of ZSM-5@ZnCr-3 capsule catalyst. CO2 hydrogenation reaction conditions: 360°C, 5.0 MPa, (23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar and H2 in balance), GHSV = 1200 mL / gcat / h. DETAILED DESCRIPTION

[0033] The present invention provides a trans-encapsulated catalyst, its preparation method, and application. Those skilled in the art can refer to the contents herein and appropriately modify the process parameters to achieve the desired results. It is particularly important to note that all similar substitutions and modifications will be apparent to those skilled in the art and fall within the scope of protection of the present invention. The methods and applications of the present invention have been described through preferred embodiments, and it is apparent that those skilled in the art can modify or appropriately alter and combine the methods and applications herein to implement and apply the technology of the present invention without departing from the content, spirit, and scope of the present invention.

[0034] In this application, the term "and / or" describes the association relationship between associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

[0035] The present invention aims to design and develop a capsule catalyst with high selectivity, especially isoparaffin selectivity, and high stability, to directly convert CO2 into isoparaffins and develop a technology for preparing liquid fuels from non-petroleum resources.

[0036] The present invention provides a method for preparing a trans-encapsulated catalyst, comprising the following steps:

[0037] A) mixing zinc nitrate hexahydrate and chromium nitrate nonahydrate to obtain a first mixed solution;

[0038] B) dissolving formamide and ZSM-5 zeolite in water to obtain a second mixed solution;

[0039] C) adding the first mixed solution and the alkaline solution dropwise to the second mixed solution, precipitating, standing, drying, and calcining to obtain a ZSM-5@ZnCr trans-capsule catalyst.

[0040] The preparation method of the trans-capsule catalyst provided by the present invention comprises the following steps: firstly mixing zinc nitrate hexahydrate and chromium nitrate nonahydrate to obtain a first mixed solution.

[0041] The mass ratio of the zinc nitrate hexahydrate to the chromium nitrate nonahydrate is 2-4:2.

[0042] In some embodiments, the mass ratio of the zinc nitrate hexahydrate to the chromium nitrate nonahydrate is 2.5-3.5:2.

[0043] In some embodiments, the mass ratio of the zinc nitrate hexahydrate to the chromium nitrate nonahydrate is 2.6-3.2:2.

[0044] In some embodiments, the mass ratio of the zinc nitrate hexahydrate to the chromium nitrate nonahydrate is 2.97:2.

[0045] Formamide and ZSM-5 zeolite are dissolved in water to obtain a second mixed solution.

[0046] According to the present invention, the mass ratio of formamide, ZSM-5 zeolite and water is 0.1-0.5:2-6:100.

[0047] In some embodiments, the mass ratio of formamide, ZSM-5 zeolite and water is 0.1-0.3:2-5:100.

[0048] In some embodiments, the mass ratio of formamide, ZSM-5 zeolite and water is 0.1-0.2:2-4:100.

[0049] In some embodiments, the mass ratio of formamide, ZSM-5 zeolite and water is 0.1:2:100.

[0050] According to the present invention, the SiO2 / Al2O3 ratio of the ZSM-5 zeolite is 24 to 1500, and can be specifically 24, 100, 105, 200, 250, 300, 500, 800, 900, 1000 or 1500.

[0051] The present invention studies the effect of ZSM-5 zeolite with different SiO2 / Al2O3 ratios on catalytic performance. For example, for 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 increases from 24 to 1500, the CO2 conversion rate decreases slightly from 19.6% to 17.0%; the CO selectivity first decreases and then increases. The CH4 selectivity increases from 1 The selectivity of methanol to CO decreased from 1.3% to 1.6%, while the MeOH / DME selectivity increased dramatically from 1.7% to 96.5%. The selectivity of isoparaffins first increased from 32.1% to 70.0%, then dropped sharply 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 to hydrocarbons, resulting in high CO and MeOH / DME selectivity.

[0052] The present invention also provides an alkaline solution, wherein the concentration of the alkaline solution is 0.2M.

[0053] The alkaline solution includes but is not limited to sodium hydroxide solution.

[0054] The first mixed solution and the alkaline solution are added dropwise to the second mixed solution.

[0055] After the addition is completed, the mixture is precipitated, allowed to stand, dried, and calcined to obtain the ZSM-5@ZnCr trans-capsule catalyst.

[0056] The precipitation temperature of the present invention is 60° C.; the pH value of the precipitation is 7-8.

[0057] The present invention is to precipitate at 60 DEG C and control the pH value to be 7.0-8.0 under stirring. After standing at the same temperature for 2-3 hours, the precipitate is washed three times with distilled water and collected by filtration.

[0058] The product was dried at 120°C for 10-30 h and then calcined at 450-500°C for 2-5 h. The sample was labeled as Na-ZSM-5@ZnCr-1 capsule catalyst.

[0059] In some embodiments, the product is dried at 120° C. for 24 to 26 hours and then calcined at 480 to 500° C. for 2 to 5 hours. The sample is labeled as Na-ZSM-5@ZnCr-1 capsule catalyst.

[0060] In some embodiments, the product was dried at 120° C. for 24 h and then calcined at 500° C. for 3 h. The sample was labeled as Na-ZSM-5@ZnCr-1 capsule catalyst.

[0061] In order to obtain ZnCr capsule catalysts with different thicknesses, the above synthesis process was repeated.

[0062] According to the present invention, the above steps further include:

[0063] The first mixed solution and the alkaline solution are 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, recorded as Na-ZSM-5@ZnCr-2.

[0064] Repeat the above steps 1 to 2 times to obtain a multi-layered trans-encapsulated catalyst ZSM-5@ZnCr-x (x=3 and 4).

[0065] The first mixed solution and the alkaline solution were added dropwise to the Na-ZSM-5@ZnCr-2 trans capsule catalyst, precipitated, allowed to stand, dried, and calcined to obtain a re-coated trans capsule catalyst, which was recorded as Na-ZSM-5@ZnCr-3.

[0066] The first mixed solution and the alkaline solution were added dropwise to the Na-ZSM-5@ZnCr-3 trans capsule catalyst, precipitated, allowed to stand, dried, and calcined to obtain a re-coated trans capsule catalyst, which was recorded as Na-ZSM-5@ZnCr-4.

[0067] The different SiO2 / Al2O3 ratios of the zeolite of the present invention affect the number of acid sites on the catalyst surface and thus the selectivity of the catalyst. For the ZSM-5@ZnCr capsule catalyst, the membrane thickness plays a key role in the catalytic system.

[0068] This study, published in Nature Communications, reports the preparation of a uniform and compact ZSM-5@ZnCr capsule catalyst for the direct conversion of carbon dioxide to isoparaffins. This capsule catalyst possesses a unique structure, consisting of a ZSM-5 zeolite core and a zinc chromium oxide shell. Furthermore, it is produced using a previously unreported modified co-precipitation method. The ZSM-5@ZnCr capsule catalyst exhibited a selectivity of 75.6% for isoparaffins, which remained stable for 100 hours.

[0069] The present invention provides a trans-capsule catalyst, which is prepared by the preparation method described in any one of the above technical solutions.

[0070] The present invention has clearly described the above preparation method, which will not be repeated here.

[0071] The present invention also provides a use of the trans-capsule catalyst described in the above technical solution as a catalyst for preparing isoparaffins from CO2.

[0072] The present invention provides a method for preparing isoalkanes from CO2, using the trans-capsule catalyst described in the above technical solution as catalysis.

[0073] The present invention provides a method for preparing a reverse encapsulated catalyst, comprising the following steps: A) mixing zinc nitrate hexahydrate and chromium nitrate nonahydrate to obtain a first mixed solution; B) dissolving formamide and ZSM-5 zeolite in water to obtain a second mixed solution; and C) dropwise adding the first mixed solution and an alkaline solution to the second mixed solution, allowing precipitation, allowing to stand, drying, and calcining to obtain a ZSM-5@ZnCr reverse encapsulated catalyst. This invention, for the first time, prepares a uniform and compact ZSM-5@ZnCr reverse encapsulated catalyst using a simple, improved co-precipitation method and applies it to the direct conversion of carbon dioxide to isoparaffins. This encapsulated catalyst has a unique structure, consisting of a ZSM-5 zeolite core and a zinc chromium oxide shell, and can be used for the direct conversion of CO2 to isoparaffins. In terms of catalytic performance, the ZSM-5@ZnCr-3 encapsulated catalyst exhibited a 75.6% isoparaffin selectivity based on a 17.3% CO2 conversion rate in a single pass at 360°C and 5 MPa. Furthermore, no deactivation was observed over 100 hours, and the high isoparaffin selectivity remained stable. The ZSM-5@ZnCr capsule catalyst not only opens up a new integration approach for oxide-zeolite composite catalysts but also provides a strong candidate catalyst for the targeted conversion of carbon dioxide to isoparaffins.

[0074] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can 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 the present application.

[0075] The numerical ranges and parameters used in this disclosure are presented as precisely as possible to represent the relevant numerical values ​​of the specific embodiments. However, any numerical value inherently and inevitably contains standard deviations resulting from individual testing methods. Therefore, unless otherwise expressly stated, it should be understood that all numerical ranges or specific data used in this disclosure are subject to reasonable deviation within a certain range, for example, within 1% or 0.5%.

[0076] Some cases are described in the embodiments and comparative examples of the present invention, wherein the embodiments illustrate certain implementations of the present invention. However, this does not mean that the effects of the present invention can only be achieved in these cases.

[0077] In order to further illustrate the present invention, a trans-capsule catalyst provided by the present invention, its preparation method and application are described in detail below with reference to examples.

[0078] Materials of Examples

[0079] 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 zeolites (SiO2 / Al2O3=100, Tosoh Co.), and commercial ZSM-22 zeolite (SiO2 / Al2O3=65-80, ACS Materials). All chemicals were used without any further purification steps.

[0080] Example 1 Synthesis of ZSM-5@ZnCr Capsule Catalyst

[0081] 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 and 2 g of ZSM-5 zeolite in 100 ml of deionized water. Solutions A and B were added dropwise to Solution C simultaneously, precipitated at 60°C, and the pH was controlled between 7.0 and 8.0 while stirring. After standing at the same temperature for 3 hours, the precipitate was washed three times with distilled water and collected by filtration. The product was dried at 120°C overnight and then calcined at 500°C for 3 hours. The sample was labeled as Na-ZSM-5@ZnCr-1 capsule catalyst.

[0082] To obtain ZnCr capsule catalysts with varying thicknesses, the above synthesis process was repeated, except that 2 g of ZSM-5 zeolite was replaced with 2 g of Na-ZSM-5@ZnCr-1. The resulting samples were labeled Na-ZSM-5@ZnCr-2 capsule catalysts.

[0083] Replace 2 g of Na-ZSM-5@ZnCr-1 with 2 g of Na-ZSM-5@ZnCr-2 and repeat the above synthesis process to obtain Na-ZSM-5@ZnCr-3 capsule catalyst.

[0084] ZSM-5@ZnCr-x (x = 1, 2, and 3) samples were obtained from Na-ZSM-5@ZnCr-x samples via ion exchange. 2 g of Na-ZSM-5@ZnCr-x sample was dispersed in 200 mL of 1 mol / L aqueous NH₄NO₃ solution and stirred at 80°C for 5 h. This process was repeated three times, followed by drying at 120°C overnight and calcination at 500°C for 3 h.

[0085] Synthesis of ZSM-5 / ZnCr Catalyst

[0086] 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. Solutions A and B were added dropwise to Solution C simultaneously, precipitated at 60°C, and the pH was controlled at 7.0-8.0 while stirring. After standing at the same temperature for 3 hours, the precipitate was washed three times with distilled water and collected by filtration. The product was dried at 120°C overnight and then calcined at 500°C for 3 hours. The sample was labeled as ZnCr catalyst.

[0087] ZnCr oxide and ZSM-5 molecular sieve were physically ground to obtain a ZSM-5 / ZnCr catalyst, with a mass ratio of ZnCr:ZSM-5=1.56:1.

[0088] 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.

[0089] Comparative Example 1 Synthesis of zinc chromium oxide

[0090] 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 dropwise to Solution C simultaneously, precipitate at 60°C, and control the pH between 7.0 and 8.0 while stirring. After standing at the same temperature for 3 hours, wash the precipitate three times with distilled water and collect by filtration. The product is dried at 120°C overnight and then calcined at 500°C for 3 hours.

[0091] The ZnCr sample was obtained from the Na-ZnCr sample by ion exchange. 2 g of the Na-ZnCr sample was dispersed in 200 ml of an aqueous NH4NO3 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 calcination at 500°C for 3 hours.

[0092] Verification Example

[0093] 1.1 Figure 1 shows the XRD pattern of the catalyst prepared in Example 1. First, the zinc chromium oxide (Zn / Cr molar ratio of 2) and ZSM-5 zeolite (SiO2 / Al2O3 ratio of 105) of Comparative Example 1 were detected. Zinc chromium oxide showed typical characteristic peaks, belonging to ZnCr2O4 and ZnO phases. ZSM-5 zeolite showed characteristic peaks of MFI structure. After ZSM-5 zeolite was encapsulated with ZnCr oxide, the ZSM-5@ZnCr-x catalyst simultaneously showed characteristic peaks of ZSM-5 zeolite and ZnCr oxide. As the number of coatings increased, the peak intensity of ZSM-5 zeolite decreased, while the peak intensity of zinc chromium oxide increased.

[0094] 1.2 The content of ZnCr oxide gradually increases with increasing encapsulation times. To further reveal the encapsulation structure of the synthesized catalysts, XPS technology was used, and the results are shown in Figure 2. Figure 2. XPS analysis of different catalysts. It can be seen that the characteristic peaks of Si and Al species of the molecular sieve disappear with increasing encapsulation times, indicating that the ZnCr metal oxide is successfully encapsulated on the surface of the ZSM-5 zeolite. The SEM characterization in Figure 3 shows that the original ZSM-5 zeolite is oval in shape. Meanwhile, the shape of the ZSM-5@ZnCr-2 encapsulated catalyst is similar to that of the ZSM-5 zeolite (Figures 3c and 3d). Compared with the original ZSM-5 zeolite, the ZSM-5@ZnCr-2 encapsulated 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 the ZSM-5 zeolite through this improved co-precipitation method. In addition, the particle size of the ZSM-5@ZnCr-2 encapsulated catalyst is uniform.

[0095] However, a small amount of ZnCr oxide was observed to separate from the ZSM-5@ZnCr-2 capsule catalyst (Figure 3c). This may be due to the shedding of ZnCr oxide during the preparation and calcination process. The external element distribution of the ZSM-5@ZnCr-2 capsule catalyst was studied using EDS spectra, as shown in Figure 3(eh). It can be seen that Si, Al, Cr, and Zn elements are mainly distributed in the capsule catalyst area. In addition, the signal intensity of the Zn element increases with the decrease of the Si element signal intensity. These results indicate that ZSM-5 zeolite can be coated with zinc chromium oxide, but the distribution of zinc chromium oxide on the outer surface of ZSM-5 zeolite is not symmetrical. Figure 3 (a and b) SEM images of pristine ZSM-5 and (c and d) ZSM-5@ZnCr-2 capsule catalysts, (eh) EDS spectrum of ZSM-5@ZnCr-2 capsule catalyst.

[0096] 1.3 Figure 5. Catalytic performance of different catalysts for the conversion of CO2 to isoparaffins. The ZSM-5@ZnCr-2 catalyst was prepared as 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 by the same method as the ZSM-5@ZnCr-2 catalyst, except that the ZSM-5 was replaced by Beta or ZSM-22.

[0097] The reaction conditions for CO2 hydrogenation were 360°C, 5.0 MPa, (23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar and H2 balance), flow time (TOS) = 8 h, GHSV = 1200 mL / gcat / h. Table 1. Product distribution of different catalysts aAs shown in Figure 5 and Table 1, the ZSM-5@ZnCr-2 capsule catalyst achieved an isoparaffin selectivity of 70.0% at a CO conversion of 17.5% and a CO selectivity of 63.8%. Specifically, the byproduct CH selectivity was only 3.1%. The MeOH / DME selectivity was 1.4%, indicating near-complete conversion of the methanol intermediate. Furthermore, the C2-3 selectivity was kept below 20%, and the Ciso / Cp ratio (the C molar ratio of isoparaffins to paraffins) was 3.22. A ZSM-5 / ZnCr composite catalyst, prepared using a conventional powder mixing method, was also compared. Under the same zeolite / oxide weight ratio and reaction conditions, the ZSM-5 / ZnCr catalyst achieved a CO conversion of 19.4%, a CO selectivity of 39.8%, and an isoparaffin selectivity of 59.6%. Compared to the two integrated methods, the powder mixing catalyst exhibited a higher N-C4+ selectivity (18.2%) than the capsule catalyst (6.5%). This is because in the powder mixing method, zinc chromium oxide cannot completely cover the outer surface of the ZSM-5 zeolite, and light aromatics (benzene, toluene and paraxylene) and long-chain hydrocarbons can leave the zeolite smoothly. For the ZSM-5@ZnCr-2 capsule catalyst, due to the obstruction of zinc oxide, the products formed in the pores of the ZSM-5 zeolite may not be able to escape smoothly (Figure 4b). In turn, due to the limitations of thermodynamic equilibrium, the products cannot leave the catalyst in time, which will lead 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.

[0098] This study investigated the effects of different zeolite types on catalytic performance. The selectivity for isoparaffins was ranked in the order ZSM-5@ZnCr-2 (70.0%), Beta-ZnCr-2 (64.7%), Y-ZnCr-2 (48.8%), and ZSM-22-ZnCr-2 (20.7%). Although these zeolites had similar SiO2 / Al2O3 ratios, the different zeolite types produced varying CO2 conversions and product distributions. This is attributed to their different channel structures and varying numbers of acidic sites.

[0099] Beta, Y, and ZSM-22 are all commercially available, and their preparation methods are the same as those for ZSM-5.

[0100] Table 1. Product distribution of different catalysts a

[0101] aReaction conditions: 360°C, 5.0 MPa, (23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar and H2 balance), flow time (TOS) = 8 h, GHSV = 1200 mL / g cat / h.

[0102] b NC 4+ :C 4+ products, except isoparaffins.

[0103] c iso: isoparaffin.

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

[0105] 1.4 This patent studies the effects of different SiO2 / Al2O3 ratios on the catalytic performance of ZSM-5 zeolites. The catalytic performance is shown in Figure 6 and Table 2. As the SiO2 / Al2O3 ratio of ZSM-5 zeolite increases from 24 to 1500, the CO2 conversion decreases slightly from 19.6% to 17.0%; CO selectivity initially decreases and then increases. CH4 selectivity decreases from 11.3% to 1.6%, while MeOH / DME selectivity increases sharply from 1.7% to 96.5%. Isoparaffin selectivity first increases from 32.1% to 70.0%, then drops sharply to 0.6%. When the SiO2 / Al2O3 ratio is 24, the large number of acidic sites leads to side reactions such as methanation. When the SiO2 / Al2O3 ratio is 1500, the number of acidic sites is insufficient to further convert methanol into hydrocarbons, resulting in high CO and MeOH / DME selectivity. Figure 6. Catalytic performance of different catalysts (ZSM-5-ZnCr(24), ZSM-5@ZnCr(105), ZSM-5-ZnCr(300), and ZSM-5-ZnCr(1500)) for the conversion of CO2 to isoparaffins. CO2 hydrogenation reaction conditions: 360°C, 5.0 MPa, (23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar and H2 balance), 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] aReaction conditions: 360° C., 5.0 MPa, (23.02 vol% CO 2 , 3.01 vol% CO, 3.01 vol% Ar and H 2 balance), flow time (TOS) = 8 h, GHSV = 1200 mL / gcat / h.

[0108] b NC 4+ :C 4+ products, except isoparaffins.

[0109] c iso: isoparaffin.

[0110] d Ciso / Cp is the molar ratio of all isoparaffins to all paraffins with n > 1.

[0111] 1.5 For the ZSM-5@ZnCr encapsulated catalyst, membrane thickness plays a key role in this catalytic system. The catalytic performance is shown in Figure 7 and Table 3. With the increase in the number of encapsulations, the CO2 conversion rate decreased slightly from 20.7% to 17.3%; the CO selectivity decreased from 66.2% to 55.0%; and the isoparaffin selectivity increased from 61.9% to 75.6%. Notably, the Ciso / Cp ratio increased from 2.39 to 4.78. Figure 7. Catalytic performance of different ZSM-5@ZnCr-x catalysts for CO2 to isoparaffin formation. The CO2 hydrogenation reaction conditions were 360°C, 5.0 MPa, (23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar and H2 in balance), flow time (TOS) = 8 h, and GHSV = 1200 mL / gcat / h.

[0112] Table 3. Product distribution of different catalysts a

[0113] a Reaction conditions: 360°C, 5.0 MPa, (23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar and H2 balance), flow time (TOS) = 8 h, GHSV = 1200 mL / g cat / h.

[0114] b NC 4+ :C 4+ products, except isoparaffins.

[0115] c iso: isoparaffin.

[0116] d Ciso / Cp is the molar ratio of C of all isoparaffins to all paraffins with n>1.

[0117] 1.6 The present invention investigated the stability of ZSM-5@ZnCr-3 at 360°C and 5 MPa (Figure 8). Clearly, the CO2 conversion and isoparaffin selectivity remained stable over 100 hours. Figure 8: Stability of ZSM-5@ZnCr-3 capsule catalyst. The CO2 hydrogenation reaction conditions were 360°C, 5.0 MPa (23.02 vol% CO2, 3.01 vol% CO, 3.01 vol% Ar, and H2 in balance), with a GHSV of 1200 mL / gcat / h.

[0118] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be construed as limiting the present invention, and the scope of protection of the present invention should be determined by the scope defined in the claims. Persons skilled in the art will appreciate that improvements and modifications may be made without departing from the spirit and scope of the present invention, and such improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a trans-capsule catalyst, characterized in that: The steps include: A) mixing zinc nitrate hexahydrate and chromium nitrate nonahydrate to obtain a first mixed solution; B) dissolving formamide and ZSM-5 zeolite in water to obtain a second mixed solution; C) adding the first mixed solution and the alkaline solution dropwise to the second mixed solution, precipitating, standing, drying, and calcining to obtain a 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 Step B) The SiO2 / Al2O3 ratio of the ZSM-5 zeolite is 24-1500.

4. 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. The mass ratio of the zinc nitrate hexahydrate, the chromium nitrate nonahydrate and the ZSM-5 zeolite is 1:

5.

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

6. The preparation method according to claim 1, characterized in that Step C) The precipitation temperature is 60° C.; the pH value of the precipitation is 7-8.

7. The preparation method according to claim 1, characterized in that In step C), the standing time is 2 to 3 hours; after the standing, the precipitate is washed with water; the drying is performed at 120° C. for 10 to 30 hours; and the calcination is performed at 450 to 500° C. for 2 to 5 hours.

8. The preparation method according to claim 1, characterized in that The step C) further comprises: The first mixed solution and the alkaline solution are 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, recorded as Na-ZSM-5@ZnCr-2; the above steps are repeated 1 to 2 times to obtain a multi-layer coated trans capsule catalyst ZSM-5@ZnCr-x (x=3 and 4).

9. A trans-capsule catalyst, characterized in that: The compound is prepared by the preparation method according to any one of claims 1 to 8.

10. A method for preparing isoalkanes from CO2, characterized in that: The trans-capsule catalyst according to claim 9 is used for catalysis.

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