Mfi type molecular sieve confined noble metal ru-based catalyst, and preparation method and application thereof

Abstract

The application discloses an MFI type molecular sieve confined noble metal Ru-based catalyst and a preparation method and application thereof, and the preparation method comprises the following steps: mixing a silicon source, a template agent and water, stirring to hydrolyze the silicon source, and obtaining a mixed solution; mixing a precursor of Ru and a ligand, then adding the mixture into the mixed solution, and then performing hydrothermal reaction at 160-180 DEG C for 72-96 h to obtain a solid sample; and performing step-by-step calcination on the solid sample in a flowing atmosphere. The MFI type molecular sieve confined Ru-based catalyst realizes effective stabilization of the easily-migrated and agglomerated Ru. The catalyst is applied to a propane oxidation reaction, and compared with a supported catalyst directly impregnated on the surface of the MFI molecular sieve, the catalyst has better low-temperature propane oxidation performance and shows excellent high-temperature thermal stability.

Description

Technical Field

[0001] This invention belongs to the technical field of catalytic oxidation and elimination of low-carbon alkanes, specifically relating to an MFI-type molecular sieve-confined noble metal Ru-based catalyst, its preparation method, and its application. Background Technology

[0002] Volatile organic compounds (VOCs) occupy a central position in the global chemical industry as key industrial raw materials. However, with the expansion of industrial activities and the widespread use of fossil fuels, VOC emissions have increased dramatically globally, causing widespread environmental and health problems. These compounds in the atmosphere can not only participate in the formation of surface ozone (O3) and fine particulate matter (PM2.5) through photochemical reactions, exacerbating urban smog and air quality deterioration, but also affect regional and even global climate systems through long-distance transport. Therefore, to meet the needs of sustainable development, it is urgent to effectively treat VOCs to mitigate air pollution. Catalytic oxidation is considered one of the most effective VOC treatment methods due to its advantages of high cost-effectiveness, low energy consumption, and minimal secondary pollution. Faced with increasingly stringent environmental standards, current research and development of catalytic oxidation technology focuses on developing more efficient and stable catalysts to address the complex challenges of industrial emissions. Propane, as an abundant low-carbon VOC, has a long atmospheric lifetime and high CH bond energy and thermal / chemical stability, making the development of low-temperature, highly active propane combustion catalysts a current research hotspot and technical challenge.

[0003] Noble metal Pt and Pd-based catalysts have attracted much attention due to their high efficiency in catalytic deep oxidation. However, traditional heterogeneous catalyst preparation techniques typically involve directly impregnating noble metals onto the surface of a support. Under high-temperature reaction conditions, this method is prone to Ostwald ripening, leading to the aggregation of catalytic metal particles. In recent years, researchers have increasingly favored the method of encapsulating noble metals in molecular sieves (metal@zeolite). This method effectively prevents metal sintering and leaching and provides a unique microenvironment for reactants, thereby significantly improving the activity and stability of catalytic reactions. In particular, pure silica-based Silicalite-1 type MFI microporous materials have become a research focus due to their narrow pore size and excellent stability. Notably, numerous studies have successfully encapsulated small-particle Pt, Pd, and Rh in microporous or mesoporous molecular sieves using metal precursor stabilization strategies. However, the scarcity and high cost of these noble metals remain major obstacles to their widespread commercial application. Therefore, exploring inexpensive alternatives to noble metal catalysts that can maintain high activity and high stability is of great significance.

[0004] Ru, a platinum group metal, is considered one of the most promising alternatives to Pt due to its similar properties and relatively low cost (about one-third that of Pt / Pd). However, compared to Pt and Pd, Ru exhibits higher cohesive energy and lower solubility product, making it more prone to precipitation under the harsh conditions (high pH=12 and high temperature 170°C) during the hydrothermal crystallization of silicate gels into MFI frameworks. Furthermore, Ru shows higher mobility and aggregation tendency during the high-temperature redox removal of template agents. Based on existing synthetic methods, these factors typically result in a bimodal size distribution of Ru encapsulation in microporous molecular sieves, making stable encapsulation difficult. Therefore, developing new synthetic strategies to achieve uniform distribution and stable encapsulation of Ru in MFI-type zeolites is crucial for improving the oxidation efficiency of VOCs and the commercial application of catalysts. Summary of the Invention

[0005] In order to overcome the problems of high migration and aggregation of Ru in the hydrothermal crystallization process of silicate gel in the prior art, the purpose of this invention is to provide an MFI-type molecular sieve confined noble metal Ru-based catalyst, its preparation method and application.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for preparing an MFI-type molecular sieve-confined noble metal Ru-based catalyst includes the following steps:

[0008] Mix the silicon source, stencil agent, and water, and stir until the silicon source hydrolyzes to obtain a mixed solution;

[0009] The precursor and ligand of Ru were mixed and added to the mixed solution, and then a hydrothermal reaction was carried out at 160~180 °C for 72~96 h to obtain a solid sample.

[0010] The solid sample was calcined in a flowing atmosphere in steps to obtain an MFI-type molecular sieve-confined noble metal Ru-based catalyst.

[0011] A further improvement of the present invention is that the silicon source is one of tetraethyl orthosilicate, silica sol, silica gel and amorphous SiO2 powder.

[0012] A further improvement of the present invention is that the template agent is an aqueous solution of tetrapropylammonium hydroxide.

[0013] A further improvement of this invention is that the amounts of silicon source, stencil agent and water are in the molar ratio of SiO2:TPAOH:H2O=1:0.4:35, and TPAOH is tetrapropylammonium hydroxide.

[0014] A further improvement of the present invention is that the precursor of Ru is RuCl3 or RuCl3∙ 3H2O.

[0015] A further improvement of the present invention is that the ligand is ethylenediamine.

[0016] A further improvement of the present invention is that the flowing atmosphere is dry air, and the flow rate of the dry air is 120~150 mL / min.

[0017] A further improvement of the present invention is that the stepwise calcination is specifically as follows: first, the temperature is maintained at 250-300 °C for 1 h to 3 h and then cooled to 25 °C. Then, the temperature is increased from 25 °C to 300-350 °C and maintained for 1 h to 3 h. Then, the temperature is increased to 350-400 °C and maintained for 1 h to 3 h. Then, the temperature is increased to 560 °C and maintained for 2 h to 5 h.

[0018] A noble metal Ru-based catalyst confined within an MFI-type molecular sieve.

[0019] Application of an MFI-type molecular sieve-confined noble metal Ru-based catalyst in the catalytic oxidation of propane.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] This invention successfully achieved stable encapsulation of Ru clusters in MFI-type zeolites through an innovative strategy combining hydrothermal in-situ ligand protection with stepwise calcination in flowing air. During the hydrothermal synthesis process, the protective effect of ethylenediamine on the metal precursor inhibits the precipitation, aggregation, and migration of Ru under the high-alkalinity and high-temperature hydrothermal conditions of silicate synthesis. Subsequently, the stepwise calcination strategy in flowing air avoids the agglomeration of Ru clusters caused by localized exothermic reactions during the high-temperature combustion of the structure-directing agent, thus ensuring uniform dispersion and stable encapsulation of Ru in MFI. This synthetic strategy is simple, feasible, and highly scalable, providing a new approach for the encapsulation of other unstable metals in molecular sieves.

[0022] The MFI-type molecular sieve-confined noble metal Ru catalyst prepared in this invention exhibits superior catalytic performance in the deep oxidation of propane. The interaction between the encapsulated Ru and the microenvironment of the MFI effectively promotes the activation of propane and oxygen. Under low-temperature conditions, it accelerates the breaking of CH and CC bonds, thereby achieving efficient deep oxidation of propane. Furthermore, the MFI-type molecular sieve-confined Ru catalyst prepared in this invention demonstrates excellent thermal stability, maintaining its geometric and electronic structure stability at temperatures up to 1000 °C. This is attributed to the stable encapsulation of Ru clusters within the MFI zeolite, overcoming the defects of traditional catalysts that are prone to sintering, aggregation, and deactivation under high-temperature reaction conditions, thus extending the catalyst's lifespan. This performance is difficult to achieve in traditional noble metal catalysts, highlighting the unique advantages of the catalyst of this invention. This invention has significant application prospects in the field of volatile organic pollutant purification. Attached Figure Description

[0023] Figure 1 The images show the scanning electron microscope (SEM) results of the Ru@MFI and Ru / MFI catalysts of this invention.

[0024] Figure 2 This is a schematic diagram of the device structure used when applying the catalyst of the present invention.

[0025] In the diagram, 1 is a propane cylinder, 2 is an air cylinder, 3 is the first mass flow meter, 4 is the second mass flow meter, 5 is the third mass flow meter, 6 is the premixing device, 7 is the catalytic reactor, and 8 is the gas chromatograph.

[0026] Figure 3 The diagram shows the propane oxidation activity of the fresh catalysts Ru@MFI, Ru / MFI, and Ru@MFI-1000 and Ru / MFI-1000 catalysts calcined at 1000 °C according to the present invention.

[0027] Figure 4 The graph shows the hydrothermal stability results of propane oxidation for the Ru@MFI and Ru / MFI catalysts of this invention.

[0028] Figure 5 The graph shows the propane oxidation cycle stability results of the Ru@MFI catalyst of the present invention. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. It should be noted that the embodiments described are only a part of the present invention, and not all of them. All other implementations obtained by those skilled in the art based on these embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0030] The MFI-type molecular sieve-confined noble metal Ru-based catalyst of the present invention is Ru@MFI, with a Ru loading (Ru accounting for 0.6% of the total mass of the catalyst), and its preparation method includes the following steps:

[0031] A. Mix the silicon source, template agent, and water according to the general molar ratio of MFI molecular sieve (the gel composition of MFI molecular sieve is SiO2:TPAOH:H2O=1:0.4:35, molar ratio), and stir at 500 rpm / min for 6-8 h at room temperature until the silicon source is completely hydrolyzed; wherein, the silicon source is one of tetraethyl orthosilicate, silica sol, silica gel, and amorphous SiO2 powder; the template agent is a mixture of 40 wt.% tetrapropylammonium hydroxide aqueous solution (Alfa-Aesar (China) Chemical Co., Ltd., code 17456.22) and 20 wt.% tetrapropylammonium hydroxide aqueous solution (Sigma-Aldrich (Shanghai) Trading Co., Ltd., containing ~0.6 wt% K, product code 254533–100 G) in a mass ratio of 15.00:18.72.

[0032] B. Thoroughly mix the Ru precursor and ligand, and while the solution in A is being vigorously stirred, add the Ru precursor and ligand complex dropwise; wherein the Ru precursor is RuCl3 or RuCl 3∙ 3H2O; the ligand is ethylenediamine.

[0033] C. Transfer the obtained solution to a Teflon-lined autoclave and place it in an oven. Perform a hydrothermal reaction at 160-180 °C for 72-96 h. Wash repeatedly with acetone and water until pH≈7. Centrifuge at 8000 rpm / min for 10-20 min each time, and freeze dry.

[0034] D. Finally, the obtained solid sample was calcined in a flowing atmosphere in stages to obtain the MFI-stabilized Ru cluster catalyst. The flowing atmosphere refers to high-purity dry air (99.999%, ALPHAGAZ™ 1 Air) at a flow rate of 120–150 mL / min. Specifically, the staged calcination was carried out within a temperature range of 25–560°C, with a heating rate of 1–2 °C / min for each stage, and a calcination time of 8–12 h. Specifically: first, the temperature was maintained at 250–300 °C for 1–3 h, then cooled to 25 °C; then, the temperature was increased from 25 °C to 300–350 °C, maintained for 1–3 h, then increased again to 350–400 °C, maintained for 1–3 h, and then increased again to 560 °C and maintained for 2–5 h.

[0035] The application of the MFI-type molecular sieve-confined noble metal Ru-based catalyst Ru@MFI, as described above, in the catalytic oxidation of propane. Specifically, 0.3 g of the molecular sieve-confined noble metal Ru-based catalyst was placed in a quartz reaction tube. The total flow rate of the introduced reaction gas was precisely controlled at 100 mL / min, and the reaction space velocity was 20000 mL / h / gcat. The experiment was conducted within a temperature range of 150-600 °C. During this process, the volume ratio of propane in the reaction gas mixture was 0.1%, oxygen was 20%, and nitrogen was used as the balance gas.

[0036] Example 1

[0037] 15.00 g of tetrapropylammonium hydroxide (40 wt.%) and 18.72 g of tetrapropylammonium hydroxide (20 wt.%, containing about 0.6 wt.% K) were mixed with 50.77 mL of deionized water at room temperature. Then, 24.72 g of tetraethyl orthosilicate was added to the above solution with stirring at room temperature. The mixture was then stirred at 500 rpm / min for 6 h until the tetraethyl orthosilicate was completely hydrolyzed to obtain a mixed solution.

[0038] A solution containing n(Ru) / n(ethylenediamine) = 6 was then added dropwise to the above mixture under vigorous stirring. The resulting solution was transferred to a Teflon-lined stainless steel reactor and placed in a constant-temperature oven for hydrothermal reaction at 170 °C for 96 h. After the reaction, the sample was washed with distilled water and acetone until pH ≈ 7. The sample was centrifuged at 8000 rpm for 10 min, and finally freeze-dried to obtain a solid powder.

[0039] The solid powder was first exposed to flowing air (150 mL / min), and the temperature was increased from 25 °C to 275 °C at a rate of 2 °C / min, held for 2 h, and then cooled to 25 °C. The temperature was then increased from 25 °C to 300 °C at a rate of 1 °C / min, held for 2 h, then increased to 375 °C at a rate of 1 °C / min, held for 2 h, and then increased to 560 °C at a rate of 1 °C / min. This high temperature was maintained for 4 h to obtain a stable MFI-type molecular sieve-confined noble metal Ru-based catalyst, namely the Ru@MFI catalyst.

[0040] See Figure 1 As can be seen from (a) in the present invention, the Ru@MFI catalyst prepared by the present invention is very clean, and almost all of the Ru is encapsulated inside the pores of the MFI.

[0041] Comparative Example 1

[0042] First, 24.36 g of tetrapropylammonium hydroxide (40 wt.%) was mixed with 60.13 mL of deionized water at room temperature. Then, 24.72 g of tetraethyl orthosilicate was added to the solution with stirring at room temperature, and the mixture was stirred at 500 rpm / min for 6 h until the tetraethyl orthosilicate was completely hydrolyzed. The resulting solution was transferred to a Teflon-lined stainless steel reactor and placed in a constant-temperature oven for hydrothermal reaction at 170 °C for 96 h. After the reaction, the resulting sample was washed with distilled water and acetone until pH≈7. Finally, the washed and centrifuged sample was dried to obtain a white solid powder. The white solid powder was then calcined in a muffle furnace at a heating rate of 5 °C / min to 560 °C and held for 8 h to obtain the MFI molecular sieve support sample.

[0043] 0.39 mL of RuCl3·3H2O aqueous solution (0.38 mol / L), 0.38 mL of ethylenediamine, and 2.5 g of MFI were added to 25 mL of water, and the mixture was stirred for 3 h. After impregnation, the solution was dried overnight in a conventional oven at 80°C, and then calcined in an airflow at 560°C for 8 h to finally obtain the Ru / MFI catalyst.

[0044] See Figure 1 As shown in (b), the surface of the Ru / MFI catalyst prepared in this invention is covered with a large number of white bright spots, indicating that Ru is mainly distributed on the surface of the MFI molecular sieve and has a large particle size.

[0045] The difference from Example 1 is that the catalyst obtained in Comparative Example 1 is a Ru-supported catalyst on the surface of MFI.

[0046] Activity tests of propane oxidation catalysts confined by MFI molecular sieves and supported on Ru:

[0047] Figure 2 The structure of a solid reactor apparatus for a catalytic reaction is demonstrated. The apparatus includes an oxygen cylinder and a propane cylinder. The propane cylinder is connected to a mixing tank via a first mass flow meter 1. The oxygen cylinder outlet is split into two streams: one stream is connected to a water tank inlet via a second mass flow meter 2, and the water tank outlet is connected to the mixing tank; the other stream is connected to the mixing tank via a third mass flow meter 3. The mixing tank is connected to the catalytic reactor, which is then connected to a gas chromatograph. The catalysts obtained in Example 1 and Comparative Example 1 were compressed into tablets, sieved to 40-60 mesh, and 0.3 g was accurately weighed and placed in a quartz tube. Then, a reaction gas of 1000 ppm propane + 20% O2 / N2 (100 mL / min, GHSV = 20000 mL / h / gcat) was introduced, with the test temperature ranging from 150-600 °C. The reaction products were monitored and analyzed using online gas chromatography-mass spectrometry.

[0048] Figure 3 The results of propane oxidation activity and high-temperature thermal stability in Example 1 and Comparative Example 1 are presented. Through the analysis of... Figure 2 Analysis shows that the MFI-confined catalyst Ru@MFI prepared in this invention exhibits significant activity in the low-temperature oxidation of propane, achieving a 90% propane conversion rate at 260°C, while the Ru / MFI catalyst in the comparative example requires 300°C to achieve the same conversion rate. The stability and durability of the catalyst are key indicators of its long-term performance in practical applications. To evaluate the stability of the catalyst under extreme conditions, this invention subjected the Ru@MFI and Ru / MFI catalysts to a high-temperature aging treatment at 1000°C and tested their propane oxidation performance. The results show that the Ru@MFI-1000 catalyst, after high-temperature aging, showed almost no change in the temperatures required to achieve 90% and 100% propane conversion rates compared to the fresh catalyst. Conversely, the Ru / MFI-1000 catalyst achieved a 90% propane conversion rate at 490°C and a 100% conversion rate at 600°C, representing temperature increases of 190°C and 300°C, respectively, compared to the fresh catalyst. The above results indicate that the confined catalyst Ru@MFI exhibits excellent high-temperature thermal stability, which offers promising prospects for industrial applications.

[0049] Water resistance test of propane oxidation catalysts confined by MFI molecular sieves and supported on Ru.

[0050] The catalysts obtained in Example 1 and Comparative Example 1 were compressed into tablets, sieved to 40-60 mesh, and 0.3 g were accurately weighed and placed into a quartz tube. Then, a reaction gas of 1000 ppm propane + 20% O2 / N2 (100 mL / min, GHSV=20000 mL / h / gcat) was introduced. After the Ru@MFI and Ru / MFI catalysts stabilized at their respective 100% propane conversion temperatures, 5 vol.% H2O water vapor was introduced, and the catalytic activity of the catalysts under mixed component atmosphere conditions was continuously tested for 48 h.

[0051] Figure 4 The water resistance results for propane oxidation activity in Example 1 and Comparative Example 1 are shown. According to... Figure 4 Analysis shows that the MFI-confined catalyst Ru@MFI prepared in this invention exhibits excellent water resistance. During a continuous 48-hour test, the oxidation activity of propane remained stable without significant decrease. In contrast, the supported catalyst Ru / MFI showed a 16.7% decrease in propane oxidation conversion under the same conditions. This water resistance test result fully demonstrates the excellent hydrothermal stability of the MFI-type molecular sieve-confined Ru-based catalyst.

[0052] Cyclic stability test of MFI-type molecular sieve-confined Ru-based catalyst for propane oxidation

[0053] The catalyst of Example 1 was subjected to a cyclic stability test for propane oxidation. Figure 5 The diagram shows the propane conversion obtained from five cycles of testing the Ru@MFI catalyst. In each cycle, the propane conversion at different temperatures was recorded to examine the performance changes of the catalyst during repeated use. The results show that the propane conversion curves almost overlapped in the five cycles, indicating that the performance of the Ru@MFI catalyst did not significantly decrease even after repeated use, demonstrating good cycle stability under these reaction conditions. The MFI-type confined Ru@MFI catalyst prepared in this invention, which combines high stability and high activity, holds significant promise for its industrial application.

[0054] Example 2

[0055] 15.00 g of tetrapropylammonium hydroxide (40 wt.%) and 18.72 g of tetrapropylammonium hydroxide (20 wt.%, containing about 0.6 wt.% K) were mixed with 50.77 mL of deionized water at room temperature. Then, 24.72 g of silica sol was added to the above solution with stirring at room temperature. The mixture was then stirred at 500 rpm / min for 6 h until tetraethyl orthosilicate was completely hydrolyzed to obtain a mixed solution.

[0056] RuCl3 was thoroughly mixed with the ligand (ethylenediamine) to obtain a solution with a molar ratio of n(Ru) / n(ethylenediamine) = 6. This solution was then added dropwise to the mixture under vigorous stirring. The resulting solution was transferred to a Teflon-lined stainless steel reactor and placed in a constant-temperature oven for hydrothermal reaction at 160 °C for 96 h. After the reaction, the sample was washed with distilled water and acetone until pH ≈ 7. The sample was centrifuged at 8000 rpm for 15 min, and finally freeze-dried to obtain a solid powder.

[0057] The solid powder was first exposed to flowing air (120 mL / min), and the temperature was increased from 25 °C to 275 °C at a rate of 2 °C / min, held for 2 h, and then cooled to 25 °C. It was then held at 250 °C for 3 h and cooled to 25 °C, then increased to 320 °C, held for 2 h, then increased to 350 °C, held for 1 h, and then increased to 560 °C and held for 3 h to obtain a stable MFI-type molecular sieve-confined noble metal Ru-based catalyst, i.e., the Ru@MFI catalyst.

[0058] Example 3

[0059] 15.00 g of tetrapropylammonium hydroxide (40 wt.%) and 18.72 g of tetrapropylammonium hydroxide (20 wt.%, containing about 0.6 wt.% K) were mixed with 50.77 mL of deionized water at room temperature. Then, 24.72 g of silica gel was added to the above solution with stirring at room temperature. The mixture was then stirred at 500 rpm / min for 6 h until tetraethyl orthosilicate was completely hydrolyzed to obtain a mixed solution.

[0060] RuCl3 was thoroughly mixed with the ligand (ethylenediamine) to obtain a solution with a molar ratio of n(Ru) / n(ethylenediamine) = 6. This solution was then added dropwise to the mixture under vigorous stirring. The resulting solution was transferred to a Teflon-lined stainless steel reactor and placed in a constant-temperature oven for hydrothermal reaction at 170 °C for 85 h. After the reaction, the sample was washed with distilled water and acetone until pH ≈ 7. The sample was centrifuged at 8000 rpm for 20 min, and finally freeze-dried to obtain a solid powder.

[0061] The solid powder was first exposed to flowing air (130 mL / min), and the temperature was increased from 25 °C to 275 °C at a rate of 2 °C / min, held for 2 h, and then cooled to 25 °C. It was then held at 300 °C for 1 h and cooled to 25 °C, then increased to 350 °C, held for 1 h, then increased to 400 °C, held for 1 h, and then increased to 560 °C and held for 5 h to obtain a stable MFI-type molecular sieve-confined noble metal Ru-based catalyst, i.e., the Ru@MFI catalyst.

[0062] Example 4

[0063] 15.00 g of tetrapropylammonium hydroxide (40 wt.%) and 18.72 g of tetrapropylammonium hydroxide (20 wt.%, containing about 0.6 wt.% K) were mixed with 50.77 mL of deionized water at room temperature. Then, 24.72 g of amorphous SiO2 powder was added to the above solution with stirring at room temperature. The mixture was then stirred at 500 rpm / min for 6 h until tetraethyl orthosilicate was completely hydrolyzed to obtain a mixed solution.

[0064] RuCl 3∙3H₂O was thoroughly mixed with the ligand (ethylenediamine) to obtain a solution with a molar ratio of n(Ru) / n(ethylenediamine) = 6. This solution was then added dropwise to the above mixture under vigorous stirring. The final solution was transferred to a Teflon-lined stainless steel reactor and placed in a constant-temperature oven for hydrothermal reaction at 190 °C for 72 h. After the reaction, the resulting sample was washed with distilled water and acetone until pH ≈ 7. The sample was centrifuged at 8000 rpm for 10 min, and finally freeze-dried to obtain a solid powder.

[0065] The solid powder was first exposed to flowing air (140 mL / min), held at 270 °C for 2 h, then cooled to 25 °C, and then heated from 25 °C to 300 °C and held for 3 h. The temperature was then further increased to 380 °C and held for 2 h, and then further increased to 560 °C and held for 2 h to obtain a stable MFI-type molecular sieve confined noble metal Ru-based catalyst, namely Ru@MFI catalyst.

[0066] This invention employs an in-situ synthesis method, in which a Ru precursor and an ethylenediamine ligand are added dropwise to a mixed solution of tetraethyl orthosilicate, tetrapropylammonium hydroxide, and water under vigorous stirring. The solution is then transferred to a Teflon-lined autoclave and hydrothermally heated at 160–180 °C for 72–96 h. After the reaction, the resulting solution is washed and freeze-dried. The resulting solid sample is then calcined stepwise in flowing dry air to obtain a highly dispersed Ru sub-nanometer catalyst confined within the pores of an MFI-type molecular sieve. This invention's MFI-type molecular sieve-confined Ru-based catalyst achieves effective stabilization of easily migrating and agglomerated Ru. When applied to propane oxidation, this catalyst exhibits superior low-temperature propane oxidation performance and excellent high-temperature thermal stability compared to supported catalysts directly impregnated on the surface of the MFI molecular sieve. The MFI-type molecular sieve-confined noble metal Ru-based catalyst prepared by this invention offers relatively high economic benefits, and its improved performance and stability significantly enhance its potential for industrial applications.

[0067] The above description is only of the preferred embodiment of the present invention and should not be construed as limiting the scope of the claims. The present invention is not limited to the above embodiments, and variations in its specific structure are permitted. All variations made within the scope of the independent claims of the present invention are also within the scope of protection of the present invention.

[0068] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

Claims

1. A method for preparing an MFI-type molecular sieve-confined noble metal Ru-based catalyst for propane catalytic oxidation, characterized in that, Includes the following steps: A. Mix the silicon source, template agent, and water according to the molar ratio of the general formula of MFI molecular sieve. The gel composition of the MFI molecular sieve is SiO2:TPAOH:H2O = 1:0.4:

35. Stir at 500 rpm for 6-8 h at room temperature until the silicon source is completely hydrolyzed. The silicon source is one of tetraethyl orthosilicate, silica sol, silica gel, and amorphous SiO2 powder. The template agent is 40 wt.% tetrapropylammonium hydroxide aqueous solution and 20 wt.% tetrapropylammonium hydroxide aqueous solution containing 0.6 wt% K in a mass ratio of 15.00:18.

72. B. Thoroughly mix the Ru precursor and ligand, and while the solution in A is being vigorously stirred, add the Ru precursor and ligand complex dropwise; wherein the Ru precursor is RuCl3 or RuCl 3∙ 3H2O; the ligand is ethylenediamine; C. Transfer the obtained solution to a Teflon-lined autoclave and place it in an oven. Perform a hydrothermal reaction at 160-180 °C for 72-96 h. Wash repeatedly with acetone and water until pH=7. Centrifuge at 8000 rpm for 10-20 min each time and freeze dry. D. Finally, the obtained solid sample is calcined in a flowing atmosphere in stages to obtain the catalyst with MFI-stabilized Ru clusters. The flowing atmosphere refers to high-purity dry air, 99.999%, ALPHAGAZ™ 1 Air, with a flow rate of 120~150 mL / min. The staged calcination is carried out in stages within a temperature range of 25~560°C, with a heating rate of 1~2 °C / min for each stage and a calcination time of 8~12 h. Specifically, the temperature is first maintained at 250-300 °C for 1~3 h and then cooled to 25 °C. Then, the temperature is increased from 25 °C to 300~350 °C and maintained for 1~3 h. Then, the temperature is increased to 350~400 °C and maintained for 1~3 h. Then, the temperature is increased to 560 °C and maintained for 2~5 h.

2. An MFI-type molecular sieve-confined noble metal Ru-based catalyst prepared according to the method of claim 1.

3. The application of an MFI-type molecular sieve-confined noble metal Ru-based catalyst prepared according to the method of claim 1 in the catalytic oxidation of propane.

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