A catalyst with core-shell structure and its preparation method and application

Abstract

The application belongs to the technical field of catalyst preparation, and discloses a catalyst with a core-shell structure and a preparation method and application thereof. The catalyst is prepared by the following steps: mixing an ethanol solution, tetramethyl silicate, ammonia water and cetyltrimethylammonium bromide, and then sequentially performing drying and heat treatment to obtain mesoporous silica; mixing the mesoporous silica and a ferric nitrate solution, and then performing heat treatment to obtain Fe-mSiO2; mixing the Fe-mSiO2 and a chloroplatinic acid solution, and then performing heat treatment to obtain Fe / Pt-mSiO2; mixing the Fe / Pt-mSiO2, triethanolamine, cetyltrimethylammonium bromide and water, then sequentially adding cyclohexane and tetraethyl orthosilicate into the mixture, and performing heat treatment to obtain meso-SiO2@Fe / Pt-mSiO2. The catalyst obtained by the application can effectively inhibit carbon deposition and limit Pt migration, and has high stability.

Description

Technical Field

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

[0002] Propylene is an important chemical raw material, and its production technology and yield are among the indicators of the level of the chemical industry. Among the technologies for propylene production, propane dehydrogenation (PDH) is considered one of the most promising propylene production technologies due to its mature technology and economic and environmental benefits. Currently, Pt-based catalysts are commonly used, but they are prone to carbon deposition and active component agglomeration during high-temperature reactions. Carbon deposition affects the number of active sites and catalyst stability, while active component agglomeration promotes structure-sensitive side reactions, leading to reduced propylene selectivity. To develop catalysts that are both highly efficient and stable, extensive research has focused on the size effect of Pt particles, the promoting effect of bimetals, and the selection of zeolite and metal-free material supports.

[0003] The support can influence the dispersion, stability, and electronic properties of Pt to a certain extent. Pt can form Pt-M alloys with metal additives M, further enhancing the catalytic activity, selectivity, and stability of propane catalytic dehydrogenation. Zhang et al. (Catal Commun, 2006, 7(11): 860-866.) prepared a PtSn / ZSM-5 catalyst, but the ZSM-5 support has strong acidity, which easily leads to coking and deactivation of the Pt component. Currently, the mainstream catalysts that are widely studied have the following problems: ① The catalyst is affected by carbon deposition and deactivates quickly. ② The active component of the catalyst is prone to sintering, leading to an increase in side reactions and a decrease in propane selectivity.

[0004] Therefore, there is an urgent need in this field to develop a core-shell structure catalyst and its preparation method and application, so as to solve the problems of catalyst carbon deposition, easy deactivation, numerous side reactions and low selectivity for propane in the existing technology. Summary of the Invention

[0005] In view of this, the present invention provides a catalyst with a core-shell structure, its preparation method and application, the purpose of which is to obtain a highly stable core-shell structure catalyst that can inhibit carbon deposition and limit Pt migration.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] This invention provides a method for preparing a catalyst with a core-shell structure, comprising the following steps:

[0008] (1) After mixing ethanol solution, tetramethyl silicate, ammonia water and hexadecyltrimethylammonium bromide, the mixture was dried and heat-treated in sequence to obtain mesoporous silica.

[0009] (2) After mixing mesoporous silica and ferric nitrate solution, heat treatment was performed to obtain Fe-mSiO2;

[0010] (3) Fe-mSiO2 and chloroplatinic acid solution were mixed and then subjected to heat treatment to obtain Fe / Pt-mSiO2;

[0011] (4) After mixing Fe / Pt-mSiO2, triethanolamine, hexadecyltrimethylammonium bromide and water, cyclohexane and tetraethyl silicate are added sequentially and heat-treated to obtain meso-SiO2@Fe / Pt-mSiO2.

[0012] Preferably, in step (1), the volume ratio of alcohol to water in the ethanol solution is 40-45%, and the volume-to-mass ratio of ethanol solution, tetramethyl silicate, ammonia and hexadecyltrimethylammonium bromide is 78-82 mL: 0.8-1.2 mL: 0.8-1.2 mL: 0.13-0.18 g.

[0013] Preferably, in step (1), the mixing speed is 600-800 rpm, the mixing time is 1.5-3.5 h, the drying temperature is 75-90℃, the drying time is 10-14 h, the heat treatment temperature is 500-700℃, the heat treatment time is 5-7 h, and the heating rate to reach the heat treatment temperature is 1.5-2.5℃ / min.

[0014] Preferably, in step (2), the mass concentration of the ferric nitrate solution is 0.03-0.06 g / mL, the mass-volume ratio of mesoporous silica to ferric nitrate solution is 0.5 g: 0.1-0.15 mL, the heat treatment temperature is 500-700 °C, the heat treatment time is 3-5 h, and the heating rate to reach the heat treatment temperature is 3-6 °C / min.

[0015] Preferably, in step (3), the mass concentration of the chloroplatinic acid solution is 0.005-0.015 g / mL, the mass-volume ratio of Fe-mSiO2 to the chloroplatinic acid solution is 0.5 g: 0.1-0.15 mL, the heat treatment temperature is 500-700 °C, the heat treatment time is 3-5 h, and the heating rate to reach the heat treatment temperature is 0.5-1.5 °C / min.

[0016] Preferably, in step (4), the mass-to-volume ratio of Fe / Pt-mSiO2, triethanolamine, hexadecyltrimethylammonium bromide and water is 0.08-0.15g:3-6mL:8-13g:160-200mL.

[0017] Preferably, in step (4), the mass-to-volume ratio of Fe / Pt-mSiO2 to cyclohexane is 0.08–0.15 g: 50 mL. After adding cyclohexane, the mixture is stirred for 50–70 min at a temperature of 55–67 °C. The mass-to-volume ratio of Fe / Pt-mSiO2 to tetraethyl silicate is 0.08–0.15 g: 1 mL. After adding tetraethyl silicate, the mixture is stirred for 22–26 h at a temperature of 55–67 °C.

[0018] Preferably, in step (4), the heat treatment temperature is 520-570℃, the heat treatment time is 3-5h, and the heating rate to reach the heat treatment temperature is 1.5-2.5℃ / min.

[0019] The present invention also provides a method for preparing a catalyst with a core-shell structure, which yields a catalyst with a core-shell structure.

[0020] The present invention also provides the application of the core-shell structured catalyst in propane dehydrogenation.

[0021] As can be seen from the above technical solution, compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] This invention significantly improves the carbon deposition of the catalyst by adding Fe as an auxiliary agent. Mesoporous SiO2 is selected as the catalyst support. The mesopores facilitate the entry of gas into the reaction. Furthermore, by encapsulating and confining the catalyst, a new layer of silica can be grown on the original catalyst to limit the aggregation of Pt particles, which is beneficial to improving the stability of the catalyst.

[0023] The catalyst obtained by this invention can effectively inhibit carbon deposition, limit Pt migration, and has high stability. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0025] Figure 1 The graph shows the propane conversion rates of the catalyst obtained in Example 1 and the catalysts obtained in Comparative Examples 1 and 2.

[0026] Figure 2 The propylene selectivity diagrams are shown for the catalysts obtained in Example 1 and Comparative Examples 1-2.

[0027] Figure 3The graph shows the propane conversion rates of the catalyst obtained in Example 1 and the catalysts obtained in Comparative Examples 3-4.

[0028] Figure 4 The graph shows the propylene selectivity of the catalyst obtained in Example 1 and the catalysts obtained in Comparative Examples 3-4. Detailed Implementation

[0029] This invention provides a method for preparing a catalyst with a core-shell structure, comprising the following steps:

[0030] (1) After mixing ethanol solution, tetramethyl silicate, ammonia water and hexadecyltrimethylammonium bromide, the mixture was dried and heat-treated in sequence to obtain mesoporous silica.

[0031] (2) After mixing mesoporous silica and ferric nitrate solution, heat treatment was performed to obtain Fe-mSiO2;

[0032] (3) Fe-mSiO2 and chloroplatinic acid solution were mixed and then subjected to heat treatment to obtain Fe / Pt-mSiO2;

[0033] (4) After mixing Fe / Pt-mSiO2, triethanolamine, hexadecyltrimethylammonium bromide and water, cyclohexane and tetraethyl silicate are added sequentially and heat-treated to obtain meso-SiO2@Fe / Pt-mSiO2.

[0034] In step (1) of the present invention, the volume ratio of alcohol to water in the ethanol solution is preferably 40-45%, more preferably 41-44%, and even more preferably 42-43%. The volume-to-mass ratio of ethanol solution, tetramethyl silicate, ammonia, and hexadecyltrimethylammonium bromide is preferably 78-82 mL: 0.8-1.2 mL: 0.8-1.2 mL: 0.13-0.18 g, more preferably 79-81 mL: 0.9-1.1 mL: 0.9-1.1 mL: 0.14-0.17 g, and even more preferably 80 mL: 1.0 mL: 1.0 mL: 0.15-0.16 g.

[0035] In step (1) of the present invention, the mixing speed is preferably 600-800 rpm, more preferably 650-750 rpm, and even more preferably 680-700 rpm; the mixing time is preferably 1.5-3.5 h, more preferably 2.0-3.0 h, and even more preferably 2.5 h; the drying temperature is preferably 75-90℃, more preferably 78-85℃, and even more preferably 80-83℃; the drying time is preferably 10-14 h, more preferably 11-13 h, and even more preferably 12 h; the heat treatment temperature is preferably 500-700℃, more preferably 550-650℃, and even more preferably 580-600℃; the heat treatment time is preferably 5-7 h, more preferably 5.5-6.5 h, and even more preferably 6 h; and the heating rate to reach the heat treatment temperature is preferably 1.5-2.5℃ / min, and even more preferably 2℃ / min.

[0036] In step (1) of the present invention, the mixed solution is preferably centrifuged and washed before drying. The centrifugation time is preferably 1 to 5 min, more preferably 2 to 4 min, and more preferably 3 min. The centrifugation speed is preferably 8000 to 12000 rpm, more preferably 9000 to 11000 rpm, and more preferably 10000 rpm. Deionized water is preferably used for washing, and the number of washings is preferably 1 to 5 times, more preferably 2 to 4 times, and more preferably 3 times. After drying, the product is preferably ground before heat treatment. The particle size of the ground product is preferably 180 to 220 mesh, more preferably 190 to 210 mesh, and more preferably 200 mesh.

[0037] In step (2) of this invention, the preferred mass concentration of the ferric nitrate solution is 0.03–0.06 g / mL, more preferably 0.04–0.05 g / mL; the preferred mass-to-volume ratio of mesoporous silica to ferric nitrate solution is 0.5 g: 0.1–0.15 mL, more preferably 0.5 g: 0.11–0.14 mL, more preferably 0.5 g: 0.12–0.13 mL; the preferred heat treatment temperature is 500–700 °C, more preferably 550–650 °C, more preferably 580–600 °C; the preferred heat treatment time is 3–5 h, more preferably 4 h; and the preferred heating rate to reach the heat treatment temperature is 3–6 °C / min, more preferably 4–5 °C / min.

[0038] In step (2) of the present invention, after mixing, it is preferable to dry and grind the mixture before heat treatment. The drying is preferably evaporation, and the evaporation temperature is preferably 75-85°C, more preferably 78-82°C, and even more preferably 80°C. The particle size after grinding is preferably greater than or equal to 200 mesh, more preferably greater than or equal to 240 mesh, and even more preferably greater than or equal to 300 mesh.

[0039] In step (3) of the present invention, the mass concentration of the chloroplatinic acid solution is preferably 0.005-0.015 g / mL, more preferably 0.08-0.012 g / mL, and even more preferably 0.01 g / mL; the mass-volume ratio of Fe-mSiO2 to chloroplatinic acid solution is preferably 0.5 g:0.1-0.15 mL, more preferably 0.5 g:0.11-0.14 mL, and even more preferably 0.5 g:0.12-0.13 mL; the heat treatment temperature is preferably 500-700 °C, more preferably 550-650 °C, and even more preferably 600 °C; the heat treatment time is preferably 3-5 h, more preferably 3.5-4.5 h, and even more preferably 4 h; and the heating rate to reach the heat treatment temperature is preferably 0.5-1.5 °C / min, more preferably 0.8-1.2 °C / min, and even more preferably 1 °C / min.

[0040] In step (3) of the present invention, after mixing, it is preferable to dry and grind the mixture before heat treatment. The drying is preferably evaporation, and the evaporation temperature is preferably 75-85°C, more preferably 78-82°C, and even more preferably 80°C. The particle size after grinding is preferably greater than or equal to 200 mesh, more preferably greater than or equal to 240 mesh, and even more preferably greater than or equal to 300 mesh.

[0041] In step (4) of the present invention, the preferred mass-to-volume ratio of Fe / Pt-mSiO2, triethanolamine, hexadecyltrimethylammonium bromide and water is 0.08-0.15g:3-6mL:8-13g:160-200mL, more preferably 0.1-0.12g:5mL:10-12g:180-190mL, and even more preferably 0.11g:5mL:11g:195mL. The mixing is preferably ultrasonic mixing, the preferred ultrasonic mixing frequency is 35-45kHz, more preferably 38-42kHz, and even more preferably 40kHz. The preferred ultrasonic mixing time is 1.5-2.5h, and even more preferably 2h.

[0042] In step (4) of this invention, the preferred mass-to-volume ratio of Fe / Pt-mSiO2 to cyclohexane is 0.08–0.15 g:50 mL, more preferably 0.1–0.14 g:50 mL, and even more preferably 0.12–0.13:50 mL. After adding cyclohexane, stirring is performed for a preferred stirring time of 50–70 min, more preferably 55–65 min, and even more preferably 60 min. The preferred stirring temperature is 55–67 °C, more preferably 58–65 °C, and even more preferably 60–62 °C. The preferred mass-to-volume ratio of Fe / Pt-mSiO2 to tetraethyl orthosilicate is 0.08–0.15 g:1 mL, more preferably 0.1–0.12 g:1 mL. After adding tetraethyl orthosilicate, stirring is performed for a preferred stirring time of 22–26 h, more preferably 23–25 h, and even more preferably 24 h. The preferred stirring temperature is 55–67 °C, more preferably 58–64 °C, and even more preferably 60–62 °C.

[0043] In step (4) of this invention, the heat treatment temperature is preferably 520–570°C, more preferably 530–560°C, and even more preferably 540–550°C. The heat treatment time is preferably 3–5 h, more preferably 4 h. The heating rate to reach the heat treatment temperature is preferably 1.5–2.5°C / min, and even more preferably 2°C / min.

[0044] In step (4) of the present invention, centrifugation, washing, drying and grinding are preferably performed before heat treatment. The centrifugation speed is preferably 8000-12000 rpm, more preferably 9000-11000 rpm, and more preferably 10000 rpm. The centrifugation time is preferably 1-5 min, more preferably 2-4 min, and more preferably 3 min. The washing is preferably done sequentially with water and anhydrous ethanol. The number of washings is preferably 1-5 times, more preferably 2-4 times, and more preferably 3 times. The drying temperature is preferably 75-85℃, more preferably 78-82℃, and more preferably 80℃. The drying time is preferably 10-14 h, more preferably 11-13 h, and more preferably 12 h. The particle size after grinding is preferably greater than or equal to 200 mesh, more preferably greater than or equal to 240 mesh, and more preferably greater than or equal to 300 mesh.

[0045] In this invention, the core-shell structure is preferably based on a layer of silica as the core, with PtFe bimetal loaded on the silica surface, and then another layer of silica is prepared on the outer surface for covering. This structure can fix the position of PtFe clusters and inhibit the aggregation and sintering of Pt. The silica on the outer surface is mesoporous silica, and the performance of the catalyst can be adjusted by adjusting the size of the mesopores.

[0046] Propane dehydrogenation catalysts are prone to carbon deposition and deactivation at high temperatures, and the active components are easily sintered, resulting in a decrease in propane dehydrogenation performance. Therefore, by using PtFe as the active center and adding promoters to change the electron cloud density of Pt, carbon deposition is prevented from settling on the Pt surface, thereby reducing carbon buildup.

[0047] The present invention also provides a method for preparing a catalyst with a core-shell structure, which yields a catalyst with a core-shell structure.

[0048] The present invention also provides the application of the core-shell structured catalyst in propane dehydrogenation.

[0049] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0050] Example 1

[0051] Take 81 mL of ethanol-water solution (ethanol-water volume ratio of 42%), 1 mL of tetramethyl silicate, 1 mL of ammonia water and 0.16 g of hexadecyltrimethylammonium bromide and mix them at 700 rpm for 3 h at room temperature to obtain a mixed solution. After centrifuging the mixed solution at 10000 rpm for 3 min, wash the obtained powder with deionized water 3 times, dry it at 80℃ for 12 h and grind it to obtain sample powder with a particle size of 200 mesh. Place the sample powder in a muffle furnace and heat it to 600℃ at a heating rate of 2℃ / min. After heat treatment for 6 h, mesoporous silica is obtained.

[0052] Take 0.5g of mesoporous silica and mix it with 0.126mL of ferric nitrate solution (mass concentration of 0.05g / mL). Evaporate the resulting mixture to dryness at 80℃. After evaporation, grind the product and pass it through a 200-mesh sieve to obtain powder. Place the powder in a muffle furnace and heat it to 600℃ at a heating rate of 4℃ / min. After heat treatment for 4h, Fe-mSiO2 is obtained.

[0053] Take 0.5g Fe-mSiO2 and mix it with 0.126mL chloroplatinic acid solution (mass concentration of 0.01g / mL). Evaporate the resulting mixed solution to dryness at 80℃. After evaporation, grind the product and pass it through a 200-mesh sieve to obtain powder. Place the powder in a muffle furnace and heat it to 600℃ at a heating rate of 1℃ / min. After heat treatment for 4h, Fe / Pt-mSiO2 is obtained.

[0054] 0.1 g Fe / Pt-mSiO2, 4 mL triethanolamine, 10 g hexadecyltrimethylammonium bromide, and 180 mL water were ultrasonically mixed at 40 kHz for 2 h. Then, 50 mL cyclohexane was added and stirred at 60 °C for 60 min. Next, 1 mL tetraethyl silicate was added and stirred at 60 °C for 24 h to obtain a mixed solution. The mixed solution was centrifuged at 10000 rpm for 3 min and washed sequentially with water and anhydrous ethanol three times to obtain a powder. The powder was dried at 80 °C for 12 h and then ground. The ground powder was passed through a 200-mesh sieve and placed in a muffle furnace. The temperature was increased to 550 °C at a heating rate of 2 °C / min and heat-treated for 4 h to obtain the catalyst meso-SiO2@Fe / Pt-mSiO2.

[0055] Example 2

[0056] Take 80 mL of ethanol-water solution (ethanol-water volume ratio of 43%), 0.8 mL of tetramethyl silicate, 0.8 mL of ammonia water and 0.13 g of hexadecyltrimethylammonium bromide and mix them at 650 rpm for 1.5 h at room temperature to obtain a mixed solution. After centrifuging the mixed solution at 8000 rpm for 2 min, wash the obtained powder with deionized water 3 times, dry it at 75℃ for 10 h and grind it to obtain sample powder with a particle size of 200 mesh. Place the sample powder in a muffle furnace and heat it to 550℃ at a heating rate of 1.5℃ / min. After heat treatment for 5 h, mesoporous silica is obtained.

[0057] Take 0.5g of mesoporous silica and mix it with 0.1mL of ferric nitrate solution (mass concentration of 0.03g / mL). Evaporate the resulting mixture to dryness at 75℃. After evaporation, grind the product and pass it through a 200-mesh sieve to obtain powder. Place the powder in a muffle furnace and heat it to 550℃ at a heating rate of 3℃ / min. After heat treatment for 3h, Fe-mSiO2 is obtained.

[0058] Take 0.5g Fe-mSiO2 and mix it with 0.1mL chloroplatinic acid solution (mass concentration of 0.005g / mL). Evaporate the resulting mixed solution to dryness at 75℃. After evaporation, grind the product and pass it through a 200-mesh sieve to obtain powder. Place the powder in a muffle furnace and heat it to 600℃ at a heating rate of 0.5℃ / min. After heat treatment for 3h, Fe / Pt-mSiO2 is obtained.

[0059] 0.1 g Fe / Pt-mSiO2, 3 mL triethanolamine, 8 g hexadecyltrimethylammonium bromide, and 160 mL water were ultrasonically mixed at 40 kHz for 1.5 h. Then, 50 mL cyclohexane was added and stirred at 55 °C for 50 min. Next, 1 mL tetraethyl silicate was added and stirred at 55 °C for 22 h to obtain a mixed solution. The mixed solution was centrifuged at 8000 rpm for 1 min and washed sequentially with water and anhydrous ethanol three times to obtain a powder. The powder was dried at 75 °C for 10 h and then ground. The ground powder was passed through a 200-mesh sieve and placed in a muffle furnace. The temperature was increased to 520 °C at a heating rate of 1.5 °C / min and heat-treated for 4 h to obtain the catalyst meso-SiO2@Fe / Pt-mSiO2.

[0060] Example 3

[0061] Take 82 mL of ethanol-water solution (ethanol-water volume ratio of 45%), 1.2 mL of tetramethyl silicate, 1.2 mL of ammonia water and 0.18 g of hexadecyltrimethylammonium bromide and mix them at 800 rpm for 3.5 h at room temperature to obtain a mixed solution. After centrifuging the mixed solution at 12000 rpm for 5 min, wash the obtained powder with deionized water 5 times, dry it at 90℃ for 14 h and grind it to obtain sample powder with a particle size of 220 mesh. Place the sample powder in a muffle furnace and heat it to 650℃ at a heating rate of 2.5℃ / min. After heat treatment for 7 h, mesoporous silica is obtained.

[0062] Take 0.5g of mesoporous silica and mix it with 0.15mL of ferric nitrate solution (mass concentration of 0.06g / mL). Evaporate the resulting mixture to dryness at 85℃. After evaporation, grind the product and pass it through a 200-mesh sieve to obtain powder. Place the powder in a muffle furnace and heat it to 700℃ at a heating rate of 6℃ / min. After heat treatment for 5h, Fe-mSiO2 is obtained.

[0063] Take 0.5g Fe-mSiO2 and mix it with 0.15mL chloroplatinic acid solution (mass concentration of 0.015g / mL). Evaporate the resulting mixture to dryness at 85℃. After evaporation, grind the product and pass it through a 200-mesh sieve to obtain powder. Place the powder in a muffle furnace and heat it to 650℃ at a heating rate of 1.5℃ / min. After heat treatment for 5h, Fe / Pt-mSiO2 is obtained.

[0064] 0.1 g Fe / Pt-mSiO2, 6 mL triethanolamine, 13 g hexadecyltrimethylammonium bromide, and 200 mL water were ultrasonically mixed at 40 kHz for 2.5 h. Then, 50 mL cyclohexane was added and stirred at 67 °C for 70 min. Next, 1 mL tetraethyl silicate was added and stirred at 67 °C for 26 h to obtain a mixed solution. The mixed solution was centrifuged at 12000 rpm for 5 min and washed sequentially with water and anhydrous ethanol three times to obtain a powder. The powder was dried at 85 °C for 14 h and then ground. The ground powder was passed through a 200-mesh sieve and placed in a muffle furnace. The temperature was increased to 570 °C at a heating rate of 2.5 °C / min and heat-treated for 5 h to obtain the catalyst meso-SiO2@Fe / Pt-mSiO2.

[0065] Comparative Example 1

[0066] 22.5 mL of ethanol, 1 mL of ammonia and 1 g of tetraethyl silicate were mixed at 80 °C for 4 h to obtain SiO2 support;

[0067] 0.5 g of SiO2 support was mixed with 0.15 mL of ferric nitrate solution (mass concentration of 0.06 g / mL). The resulting mixed solution was evaporated to dryness at 85 °C. After evaporation, the product was ground and passed through a 200-mesh sieve to obtain powder. The powder was placed in a muffle furnace and heated to 700 °C at a heating rate of 6 °C / min. After heat treatment for 5 h, Fe-SiO2 was obtained.

[0068] 0.5 g Fe-SiO2 was mixed with 0.15 mL chloroplatinic acid solution (mass concentration of 0.015 g / mL), and the resulting mixed solution was evaporated to dryness at 85 °C. After evaporation, the product was ground and passed through a 200-mesh sieve to obtain powder. The powder was placed in a muffle furnace and heated to 650 °C at a heating rate of 1.5 °C / min. After heat treatment for 5 h, the catalyst Fe / Pt-SiO2 was obtained.

[0069] Comparative Example 2

[0070] Take 81 mL of ethanol aqueous solution (ethanol-water volume ratio of 42%), 1 mL of tetramethyl silicate, 1 mL of ammonia water and 0.16 g of hexadecyltrimethylammonium bromide and mix them at 700 rpm for 2 h at room temperature to obtain a mixed solution. After centrifuging the mixed solution at 10000 rpm for 3 min, wash the obtained powder with deionized water 3 times, dry it at 80℃ for 12 h and grind it to obtain sample powder with a particle size of 200 mesh. Place the sample powder in a muffle furnace and heat it to 600℃ at a heating rate of 2℃ / min. After heat treatment for 6 h, mesoporous silica is obtained.

[0071] Take 0.5g of mesoporous silica and mix it with 0.126mL of ferric nitrate solution (mass concentration of 0.05g / mL). Evaporate the resulting mixture to dryness at 80℃. After evaporation, grind the product and pass it through a 200-mesh sieve to obtain powder. Place the powder in a muffle furnace and heat it to 600℃ at a heating rate of 4℃ / min. After heat treatment for 4h, Fe-mSiO2 is obtained.

[0072] 0.5 g Fe-mSiO2 was mixed with 0.126 mL of chloroplatinic acid solution (mass concentration of 0.01 g / mL), and the resulting mixed solution was evaporated to dryness at 80 °C. After evaporation, the product was ground and passed through a 200-mesh sieve to obtain powder. The powder was placed in a muffle furnace and heated to 600 °C at a heating rate of 1 °C / min. After heat treatment for 4 h, the catalyst Fe / Pt-mSiO2 was obtained.

[0073] Comparative Example 3

[0074] Take 57 mL of water, 24 mL of ethanol, 0.1 g of Fe / Pt-mSiO2 obtained in Example 1, 1 mL of tetraethyl silicate, 1 mL of ammonia water, and 0.16 g of hexadecyltrimethylammonium bromide and mix them at 700 rpm for 3 h at room temperature to obtain a mixed solution. Centrifuge the mixed solution at 10000 rpm for 3 min to obtain powder. Wash the powder three times with deionized water and dry it at 80 °C for 12 h. Place the dried product in a muffle furnace and heat it to 600 °C at a heating rate of 2 °C / min. After heat treatment for 6 h, Fe / Pt-mSiO2 coated with microporous silica is obtained.

[0075] Comparative Example 4

[0076] Take 36 mL of water, 24 mL of hexadecyltrimethylammonium chloride, 0.1 g of Fe / Pt-mSiO2 obtained in Example 1, and 0.18 g of triethanolamine and ultrasonically mix them at 500 W for 2 h at room temperature to obtain a mixed solution. Pour the mixed solution into a round-bottom flask and stir at 60 °C for 1 h. Then add 20 mL of tetraethyl silicate solution (using cyclohexane as solvent, with a volume fraction of 10% tetraethyl silicate) and stir at 60 °C for 12 h. Centrifuge the resulting solution at 10,000 rpm for 3 h, wash it three times with anhydrous ethanol, and extract it twice with 0.6 wt% ammonium nitrate ethanol solution at 60 °C for 6 h each time to obtain macroporous silica-coated Fe / Pt-mSiO2.

[0077] The propane conversion and propylene selectivity of the catalysts obtained in Examples 1-3 and Comparative Examples 1-4 are shown in Table 1:

[0078] Table 1. Propane conversion and propylene selectivity of the catalysts obtained in Examples 1-3 and Comparative Examples 1-4

[0079]

[0080] Combining Table 1 and Figures 1-4 Comparing the catalysts obtained in Example 1 with those in Comparative Examples 1-2, it is evident that the metal-supported single silica spheres are prone to deactivation due to high-temperature reactions, resulting in low conversion rates and selectivity. Confined structures can suppress the sintering of Pt clusters, thereby improving the conversion rate and stability of the reaction. Comparing the catalysts obtained in Example 1 with those in Comparative Examples 3-4, it is clear that although the selectivity for propane is not significantly different between the meso-SiO2@Fe / Pt-mSiO2 catalyst obtained in this invention and the microporous silica-coated Fe / Pt-mSiO2 catalyst obtained in Comparative Example 3, the former catalyst exhibits better stability than the microporous silica-coated Fe / Pt-mSiO2. Furthermore, the microporous silica-coated Fe / Pt-mSiO2, due to its small silica pore size, cannot allow propylene to pass through, easily leading to carbon deposition. Conversely, the macroporous silica-coated Fe / Pt-mSiO2 catalyst has significantly lower propane selectivity than the meso-SiO2@Fe / Pt-mSiO2 catalyst obtained in this invention.

[0081] 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 producing a catalyst having a core-shell structure, characterized by, It comprises the following steps: (1) mixing ethanol solution, tetramethyl silicate, ammonia water and cetyl trimethyl ammonium bromide, and then sequentially drying and heat treating to obtain mesoporous silica; (2) mixing mesoporous silica and iron nitrate solution, and then heat treating to obtain Fe-mSiO2; (3) mixing Fe-mSiO2 and chloroplatinic acid solution, and then heat treating to obtain Fe / Pt-mSiO2; (4) mixing Fe / Pt-mSiO2, triethanolamine, cetyl trimethyl ammonium bromide and water, and then sequentially adding cyclohexane and tetraethyl silicate and heat treating to obtain meso-SiO2@Fe / Pt-mSiO2. In the step (1), the heat treating temperature is 500-700℃, the heat treating time is 5-7h, and the temperature rising rate reaching the heat treating temperature is 1.5-2.5℃ / min; In the step (2), the heat treating temperature is 500-700℃, the heat treating time is 3-5h, and the temperature rising rate reaching the heat treating temperature is 3-6℃ / min; In the step (3), the heat treating temperature is 500-700℃, the heat treating time is 3-5h, and the temperature rising rate reaching the heat treating temperature is 0.5-1.5℃ / min; In the step (4), the heat treating temperature is 520-570℃, the heat treating time is 3-5h, and the temperature rising rate reaching the heat treating temperature is 1.5-2.5℃ / min.

2. The method for preparing a catalyst with a core-shell structure according to claim 1, characterized in that, In the step (1), the alcohol water volume ratio of the ethanol solution is 40-45%, and the volume mass ratio of the ethanol solution, tetramethyl silicate, ammonia water and cetyl trimethyl ammonium bromide is 78-82mL:0.8-1.2mL:0.8-1.2mL:0.13-0.18g.

3. A method for preparing a catalyst with a core-shell structure according to claim 1 or 2, characterized in that, In the step (1), the mixing rotation speed is 600-800rpm, the mixing time is 1.5-3.5h, the drying temperature is 75-90℃, and the drying time is 10-14h.

4. The method for preparing a catalyst with a core-shell structure according to claim 1, characterized in that, In the step (2), the mass concentration of the iron nitrate solution is 0.03-0.06g / mL, and the mass volume ratio of the mesoporous silica and the iron nitrate solution is 0.5g:0.1-0.15mL.

5. The method for preparing a catalyst with a core-shell structure according to claim 4, characterized in that, In the step (3), the mass concentration of the chloroplatinic acid solution is 0.005-0.015g / mL, and the mass volume ratio of the Fe-mSiO2 and the chloroplatinic acid solution is 0.5g:0.1-0.15mL.

6. The method for preparing a catalyst with a core-shell structure according to claim 5, characterized in that, In the step (4), the mass volume ratio of the Fe / Pt-mSiO2, triethanolamine, cetyl trimethyl ammonium bromide and water is 0.08-0.15g:3-6mL:8-13g:160-200mL.

7. The method for preparing a catalyst with a core-shell structure according to claim 6, characterized in that, In the step (4), the mass-volume ratio of Fe / Pt-mSiO2 to cyclohexane is 0.08-0.15 g:50 mL, stirring is performed after the addition of cyclohexane, the stirring time is 50-70 min, and the stirring temperature is 55-67 ℃; the mass-volume ratio of Fe / Pt-mSiO2 to tetraethyl silicate is 0.08-0.15 g:1 mL, stirring is performed after the addition of tetraethyl silicate, the stirring time is 22-26 h, and the stirring temperature is 55-67 ℃.

8. The catalyst with core-shell structure prepared by the method according to any one of claims 1-7.

9. The use of the catalyst with core-shell structure according to claim 8 in the dehydrogenation of propane.

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