Supported molecular sieve catalyst as well as preparation method and application thereof

Abstract

The invention provides a supported molecular sieve catalyst as well as a preparation method and application thereof, and belongs to the technical field of catalysts. According to the preparation method of the supported molecular sieve catalyst, framework aluminum can be removed through acid leaching treatment, so that the acid site of the molecular sieve is adjusted, and hydroxyl nest active sites are constructed; alkaline leaching can remove part of framework silicon and framework aluminum and broaden the pore structure in the molecular sieve to form rich hydroxyl nest active sites; the supported molecular sieve catalyst is prepared by combining an atomic layer deposition (ALD) technology and a molecular sieve, can keep metal nanoparticles not growing in a long time range under propane dehydrogenation reaction conditions, has good sintering resistance and long-period stability, can keep high catalytic activity in a long time, and has no obvious activity reduction.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts, and in particular relates to a supported molecular sieve catalyst and a preparation method and application thereof. Background Art

[0002] Propylene is an important chemical feedstock for the production of chemicals such as polypropylene, acrylonitrile, acrylic acid, and propylene oxide. It is primarily produced by naphtha steam cracking and petroleum fluidized catalytic cracking, but these processes suffer from high energy consumption and low propylene selectivity. Propane direct dehydrogenation (PDH) is an effective way to meet the growing global demand for propylene. The reaction equation for PDH is: This reaction is a highly endothermic reaction (ΔH = +124.3 kJ / mol) and needs to be carried out at high temperatures (550-650°C) and in the presence of a catalyst. Expensive platinum-based catalysts (such as Pt-Sn / Al2O3) or toxic chromium-based catalysts (such as Cr2O3 / Al2O3) are typically used for catalysis in the prior art. Platinum-based catalysts deactivate due to carbon deposition and sintering of the supported metal under high temperature conditions, which restricts the development of platinum-based catalysts. Therefore, how to achieve high dispersion of the catalyst under high temperature conditions is the key to solving this problem. Summary of the Invention

[0003] The purpose of the present invention is to provide a supported molecular sieve catalyst and its preparation method and application. The supported molecular sieve catalyst prepared by the present invention has excellent sintering resistance and can maintain high dispersion under high temperature conditions of propane dehydrogenation to propylene.

[0004] In order to achieve the purpose of the present invention, the present invention provides the following technical solutions:

[0005] A method for preparing a supported molecular sieve catalyst comprises the following steps:

[0006] acid leaching and / or alkali leaching of the molecular sieve matrix to obtain a pretreated molecular sieve matrix;

[0007] The precursor and the carrier gas are alternately pulsed into a deposition device to adsorb and react on the pretreated molecular sieve substrate to achieve metal loading, and the supported molecular sieve catalyst is obtained after reduction treatment; the precursor includes a metal precursor and an oxide;

[0008] The metal element in the metal precursor includes one or more of Pt, Fe, Co, Ni, Sn and Zn.

[0009] Preferably, the molecular sieve matrix includes one of an MFI molecular sieve, a BEA molecular sieve and an MWW molecular sieve.

[0010] Preferably, the deposition temperature of the deposition equipment is 120-280° C., the pressure is 10-200 Pa, the carrier gas is N 2 ; the number of depositions is 5-40; and the temperature of the metal precursor is 50-90° C.

[0011] Preferably, the reduction treatment is performed at a temperature of 400 to 600° C. and for a time of 4 to 10 hours.

[0012] The present invention also provides a supported molecular sieve catalyst prepared by the preparation method described in the above scheme, comprising a molecular sieve matrix and metal particles supported on the surface of the molecular sieve matrix; the particle size of the metal particles is 1.0 to 3.0 nm; the metal particles include one or more of Pt, Fe, Co, Ni, Sn and Zn.

[0013] Preferably, the loading amount of the metal particles is 0.01 to 1.5 wt%.

[0014] The present invention also provides the use of the supported molecular sieve catalyst described in the above scheme in catalyzing propane dehydrogenation.

[0015] The present invention also provides a method for producing propylene by dehydrogenating propane, comprising the following steps:

[0016] A mixed gas containing N2, H2 and propane is introduced into a reactor containing a catalyst to carry out a dehydrogenation reaction to obtain propylene; the catalyst is the supported molecular sieve catalyst described in the above scheme.

[0017] The present invention provides a preparation method of a supported molecular sieve catalyst, comprising the following steps: subjecting the molecular sieve substrate to acid leaching and / or alkali leaching to obtain a pretreated molecular sieve substrate; passing a precursor and a carrier gas into a deposition device in alternating pulses, adsorbing and reacting on the pretreated molecular sieve substrate to achieve metal loading, and obtaining the supported molecular sieve catalyst after reduction treatment; the precursor comprises a metal precursor and an oxide; and the metal element in the metal precursor comprises one or more of Pt, Fe, Co, Ni, Sn and Zn. In the present invention, the framework aluminum can be removed by acid leaching, thereby adjusting the acidic sites of the molecular sieve and constructing hydroxyl nests; alkaline leaching can remove part of the framework silicon and framework aluminum and widen the pore structure inside the molecular sieve, forming rich hydroxyl nest sites; atomic layer deposition technology (ALD) is used to prepare a loaded molecular sieve catalyst on the surface of the molecular sieve substrate, wherein during the exposure, diffusion and purification of the metal precursor, the metal precursor is adsorbed (including physical adsorption and chemical adsorption) and desorbed on the surface of the molecular sieve support, and the metal precursor reacts chemically with the hydroxyl nest active sites on these molecular sieve substrates or undergoes strong physical adsorption to selectively place the metal source at the active sites, completing a cycle after the oxide is oxidized. After multiple cycles, highly dispersed metals can be loaded on the surface of the molecular sieve substrate, and the metal nanoparticles formed after the reduction treatment can keep the metal particles from growing for a long time at the propane dehydrogenation reaction temperature, have good sintering resistance and long-term stability, and can maintain a high catalytic activity for a long time without obvious activity decline. In addition, the present invention pre-treats the molecular sieve matrix and constructs more hydroxyl nest active sites by dealumination or desiliconization, which is beneficial to the deposition of nano-metal particles.

[0018] Furthermore, the metal loading of the supported molecular sieve catalyst prepared by the present invention is 0.01 to 1.5 wt %, which is extremely low. The preparation method of the present invention is suitable for preparing sintering-resistant noble metal catalysts. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 This is a transmission electron microscope (TEM) image of the Pt-Beta catalyst obtained in Example 1 before catalyzing propane dehydrogenation;

[0021] Figure 2 This is a TEM image of the Pt-Beta catalyst obtained in Example 1 after catalyzing propane dehydrogenation for 6 hours;

[0022] Figure 3 This is a TEM image of the PtZn-Beta catalyst obtained in Example 2 after catalyzing propane dehydrogenation for 100 hours;

[0023] Figure 4 This is a TEM image of the Pt-IWI catalyst obtained in Comparative Example 1 before catalyzing propane dehydrogenation. DETAILED DESCRIPTION

[0024] The present invention provides a method for preparing a supported molecular sieve catalyst, comprising the following steps:

[0025] acid leaching and / or alkali leaching of the molecular sieve matrix to obtain a pretreated molecular sieve matrix;

[0026] The precursor and the carrier gas are alternately pulsed into a deposition device to adsorb and react on the pretreated molecular sieve substrate to achieve metal loading, and the supported molecular sieve catalyst is obtained after reduction treatment; the precursor includes a metal precursor and an oxide;

[0027] The metal element in the metal precursor includes one or more of Pt, Fe, Co, Ni, Sn and Zn.

[0028] In the present invention, unless otherwise specified, all preparation raw materials are commercially available products well known to those skilled in the art.

[0029] In the present invention, the metal element in the metal precursor includes one or more of Pt, Fe, Co, Ni, Sn and Zn. In specific embodiments, it can be Pt, Pt and Zn, or Pt and Fe. In specific embodiments, the metal precursor can be trimethylcyclopentadienylplatinum or diethylzinc.

[0030] In the present invention, the molecular sieve matrix includes one of MFI type molecular sieve, BEA type molecular sieve and MWW type molecular sieve; the MFI type molecular sieve is one of ZSM-5 molecular sieve, TS-1 molecular sieve and Silicalite-1 molecular sieve; the BEA type molecular sieve is Beta molecular sieve, and the particle size of the Beta molecular sieve is 20 to 100 nm; the MWW type molecular sieve is MCM-22; in a specific embodiment, the molecular sieve matrix can be Beta molecular sieve.

[0031] In the present invention, the acid reagent used for the acid leaching includes one or more of a strong acid, a weak acid and an acid salt; the strong acid is one of hydrochloric acid, a sulfuric acid solution and a nitric acid solution; the weak acid is an acetic acid solution or a carbonic acid solution; the acid salt is an ammonium chloride solution; the alkaline reagent used for the alkali leaching is one or more of a strong base, a weak base and an alkaline salt, the strong base is a sodium hydroxide solution or a potassium hydroxide solution, the weak base is ammonia water, and the alkaline salt is a sodium carbonate solution or a sodium acetate solution; in a specific embodiment, it can be a nitric acid solution or a sodium hydroxide solution; in a specific embodiment, it can be 13M concentrated nitric acid; the temperature of the acid leaching and / or alkali leaching is 100-120°C and the time is 12-24h; after the acid leaching and / or alkali leaching, the obtained molecular sieve is further washed and dried; the washing can be washing with water until neutral; the drying temperature is 0-100°C and the time is 6-8h.

[0032] In the present invention, the oxide is ozone or water.

[0033] In the present invention, the reaction temperature of the reactor is 120-280°C, and in specific embodiments, it can be 125°C, 150 or 230°C; the pressure is 10-200 Pa, and in specific embodiments, it can be 50 or 133 Pa; the carrier is nitrogen, and the amount of carrier gas introduced is 20-300 mL / min, and in specific embodiments, it can be 50, 100 or 200 mL / min; the number of depositions is 5-40, and in specific embodiments, it can be 10 or 15 times; the temperature of the gaseous precursor is 50-90°C, and in specific embodiments, it can be 60 or 80°C.

[0034] The present invention does not specifically limit other parameters in the atomic layer deposition process, and adjusts them according to the types of molecular sieve substrate and gas phase precursor; in a specific embodiment, when the molecular sieve substrate is Beta molecular sieve, the pulse, exposure and purge times of the Pt precursor are 1s, 18s, and 25s respectively, the pulse, exposure and purge times of ozone are 1s, 12s, and 25s respectively, and the deposition temperature of the cavity is 200-280°C. The present invention adopts atomic layer deposition technology (ALD) combined with molecular sieve to prepare loaded molecular sieve catalysts. During the exposure, diffusion and purification process of the metal precursor, the metal precursor is adsorbed (including physical adsorption and chemical adsorption) and desorbed on the surface of the molecular sieve carrier. The metal precursor reacts chemically with the active sites on these molecular sieve matrices or undergoes strong physical adsorption to selectively place the metal source on the active sites. A cycle is completed in an oxidizing atmosphere. Multiple cycles can load highly dispersed metals on the surface of the molecular sieve matrix. The metal nanoparticles formed after reduction have a weaker interaction with the carrier than the metal particles prepared by the traditional impregnation method. The preparation method provided by the present invention can keep the metal nanoparticles from growing for a long time at the propane dehydrogenation reaction temperature, has good sintering resistance and long-term stability, can maintain a high catalytic activity for a long time, and there is no obvious decrease in activity.

[0035] In the present invention, the reduction treatment further includes granulating the product obtained by atomic layer deposition; the instruments used for granulation are tableting molds and screens.

[0036] In the present invention, the temperature of the reduction treatment is 400-600°C, and in a specific embodiment, it can be 500 or 550°C, and the time is 4-10 hours, and in a specific embodiment, it can be 6 or 8 hours; the reducing gas used in the reduction treatment is a hydrogen-argon mixture, and the volume ratio of hydrogen is 5-10%.

[0037] The present invention also provides a supported molecular sieve catalyst prepared by the preparation method described in the above technical solution, comprising a molecular sieve matrix and metal particles loaded on the surface of the molecular sieve matrix; the particle size of the metal particles is 1.0 to 3.0 nm; the metal particles include one or more of Pt, Fe, Co, Ni, Sn and Zn.

[0038] In the present invention, the loading amount of the metal particles is 0.01 to 1.5 wt %. In specific embodiments, it can be 0.06, 0.16, 0.3, 0.5 or 1.0 wt %.

[0039] In the present invention, the size of the metal particles is 1.0 to 3.0 nm, and in specific embodiments, may be 1.34, 1.59, 2.06 or 2.18 nm.

[0040] The present invention also provides the use of the supported molecular sieve catalyst described in the above technical solution in catalyzing propane dehydrogenation.

[0041] The present invention also provides a method for producing propylene by dehydrogenating propane, comprising the following steps:

[0042] A mixed gas containing N2, H2 and propane is introduced into a reactor containing a catalyst to carry out a dehydrogenation reaction to obtain propylene; the catalyst is the supported molecular sieve catalyst described in the above technical solution;

[0043] In the present invention, the volumes of the N2, H2 and propane gases may be 2:1:1.

[0044] In the present invention, the space velocity of the mixed gas can be 10 to 100 mL / min, and in specific embodiments, can be 20 or 50 mL / min; the temperature of the dehydrogenation reaction is 550 to 650° C., and in specific embodiments, can be 600° C.; and the time is 5 to 200 h, and in specific embodiments, can be 6, 10, 50 or 100 h.

[0045] To further illustrate the present invention, the supported molecular sieve catalyst, its preparation method and application provided by the present invention are described in detail below with reference to the accompanying drawings and examples, but they should not be construed as limiting the scope of protection of the present invention.

[0046] Example 1

[0047] Weigh 10 g of hydrogen-type Beta molecular sieve and 20 mL of concentrated nitric acid (13 M) in a round-bottom flask, stir at a constant temperature of 100-120°C for 12-24 hours, centrifuge several times and wash with deionized water until the supernatant is neutral, and dry at 80-100°C for 6-8 hours to obtain dealuminated Beta molecular sieve;

[0048] 30 mg of the above-mentioned dealuminated Beta molecular sieve was weighed and placed on the surface of a quartz plate of 80 mm * 80 mm * 2 mm, dissolved with anhydrous ethanol and smeared to make it evenly distributed on the entire surface of the quartz plate. After the surface was dried, it was placed in the vacuum reaction chamber of the atomic layer deposition equipment. Trimethylcyclopentadienyl platinum and ozone were used as gas phase precursors. 10 cycles of Pt were deposited on the surface of the dealuminated Beta molecular sieve using atomic layer deposition technology to obtain unreduced single metal catalyst Pt-Beta powder. The ALD deposition parameters were: trimethylcyclopentadienyl platinum was kept at a constant temperature of 60 ° C, and the vacuum reaction chamber temperature was 20 ° C. The temperature was 280°C, the pressure was 10 Pa, and a carrier gas (high-purity nitrogen) was introduced at a rate of 100 mL / min; an appropriate amount of Pt-Beta powder was taken and granulated using a tableting mold and a screen, the granulated Pt-Beta catalyst was placed in a quartz tube with an inner diameter of 6 mm, fixed with quartz wool, and 5% hydrogen-argon mixed gas was started to pass (at a flow rate of 20 mL / min) and the temperature was gradually increased to 550°C and maintained for 6 h to obtain a single metal catalyst Pt-Beta, in which the Pt loading was 0.06 wt%, the Pt existed in the form of small metal clusters, and the average particle size was 1.34 nm.

[0049] The hydrogen-argon mixture was switched to a mixed gas (nitrogen, hydrogen, and propane in a volume ratio of 2:1:1 at a flow rate of 16 mL / min) and detected and recorded continuously by gas chromatography to evaluate the activity of the Pt-Beta catalyst for propane dehydrogenation.

[0050] The results showed that the initial propane conversion rate was 26.86% and the selectivity was 93.64%. After 6 hours, the conversion rate was 26.85% and the selectivity was 89.43%. The Pt-Beta catalyst before and after the reaction was characterized. Figure 1 This is a TEM image of the Pt-Beta catalyst obtained in Example 1 before catalyzing propane dehydrogenation. Figure 2 This is a TEM image of the Pt-Beta catalyst obtained in Example 1 after catalyzing propane dehydrogenation for 6 hours. Figures 1-2 It can be seen that before and after the catalytic propane dehydrogenation reaction, the metal nanoparticles did not grow significantly, and the average particle size remained at 1.34 nm, proving that they have excellent sintering resistance.

[0051] Example 2

[0052] Weigh 30 mg of the above-mentioned dealuminated Beta molecular sieve and place it on the surface of an 80 mm * 80 mm * 2 mm quartz sheet, dissolve it with anhydrous ethanol and apply it to make it evenly distributed on the entire surface of the quartz sheet. After the surface is dried, place it in the vacuum deposition chamber of the atomic layer deposition equipment, and use trimethylcyclopentadienyl platinum and ozone as gas phase precursors to use atomic layer deposition technology to deposit 10 cycles of Pt on the surface of the dealuminated Beta molecular sieve. Then, use diethyl zinc and water as gas phase precursors to continue to deposit Zn on the surface of the molecular sieve for 10 cycles to obtain an unreduced bimetallic catalyst PtZn-Beta powder; the ALD deposition parameters are: trimethylcyclopentadienyl platinum and diethyl zinc at a constant temperature At 60°C, the vacuum deposition chamber temperature was 280°C, the pressure was 10Pa, and a carrier gas (high-purity nitrogen) was introduced at 100mL / min; an appropriate amount of Pt-Beta powder was taken and granulated using a tableting mold and a screen, and the granulated Pt-Beta catalyst was placed in a quartz tube with an inner diameter of 6mm and fixed with quartz wool. A 5% hydrogen-argon mixture was started (flow rate of 20mL / min) and the temperature was gradually increased to 550°C and maintained for 6h to obtain a bimetallic catalyst Pt-Beta, in which the Pt loading was 0.06wt%, the Zn loading was 0.16wt%, and Pt existed in the form of small metal clusters with an average particle size of 1.34nm.

[0053] The hydrogen-argon mixture was switched to a reaction gas mixture (nitrogen, hydrogen, and propane in a volume ratio of 2:1:1 at a flow rate of 16 mL / min) and detected and recorded continuously by gas chromatography to evaluate the activity of the PtZn-Beta catalyst for propane dehydrogenation.

[0054] The results are as follows: the initial propane conversion rate is 26.16%, the selectivity is 98.24%, the conversion rate after 6 hours is 25.86%, the selectivity is 98.98%, and after 100 hours, the propane conversion rate is still 24.82% and the selectivity is 99.13%. Figure 3 As shown, after 100 h, the metal nanoparticles of the PtZn-Beta catalyst had no obvious sintering and the average particle size was 1.36 nm.

[0055] Example 3

[0056] 30 mg of the above-mentioned dealuminated Beta molecular sieve was weighed and placed on the surface of an 80 mm * 80 mm * 2 mm quartz plate, dissolved with anhydrous ethanol and smeared to evenly distribute it on the entire surface of the quartz plate. After the surface was dried, it was placed in the vacuum deposition chamber of the atomic layer deposition equipment. Co was deposited on the surface of the dealuminated Beta molecular sieve using cobalt cyclopentadienyl and ozone as gas phase precursors by atomic layer deposition technology for 10 cycles to obtain unreduced single metal catalyst Co-Beta powder. The ALD deposition parameters were: cobalt cyclopentadienyl was kept at a constant temperature of 60 ° C, The temperature of the vacuum reaction chamber was 280°C, the pressure was 10 Pa, and a carrier gas (high-purity nitrogen) was introduced at 100 mL / min. An appropriate amount of Co-Beta powder was granulated using a tableting mold and a screen. The granulated Co-Beta catalyst was placed in a quartz tube with an inner diameter of 6 mm and fixed with quartz wool. A 5% hydrogen-argon mixture was started (at a flow rate of 20 mL / min) and the temperature was gradually increased to 550°C and maintained for 6 hours to obtain a single-metal catalyst Co-Beta with an average particle size of 2.18 nm.

[0057] The activity of the Co-Beta catalyst for catalytic propane dehydrogenation was evaluated according to the method described in Example 1. After 12 hours of reaction, the average particle size of Co was 2.50 nm.

[0058] Example 4

[0059] 30 mg of the above-mentioned dealuminated Beta molecular sieve was weighed and placed on the surface of an 80 mm * 80 mm * 2 mm quartz plate, dissolved with anhydrous ethanol and smeared to evenly distribute it on the entire surface of the quartz plate. After the surface was dried, it was placed in the vacuum reaction chamber of the atomic layer deposition equipment. Nickelocene and ozone were used as gas phase precursors. Atomic layer deposition technology was used to deposit Ni on the surface of the dealuminated Beta molecular sieve for 10 cycles to obtain unreduced single metal catalyst Ni-Beta powder. The ALD deposition parameters were: nickelocene was kept at a constant temperature of 60 ° C, The temperature of the vacuum reaction chamber was 280°C, the pressure was 10 Pa, and a carrier gas (high-purity nitrogen) was introduced at 100 mL / min. An appropriate amount of Ni-Beta powder was granulated using a tableting mold and a screen. The granulated Ni-Beta catalyst was placed in a quartz tube with an inner diameter of 6 mm and fixed with quartz wool. A 5% hydrogen-argon mixture was initially introduced (at a flow rate of 20 mL / min) and the temperature was gradually increased to 550°C and maintained for 6 hours to obtain a monometallic catalyst Ni-Beta with an average Ni particle size of 1.97 nm.

[0060] The activity of Ni-Beta catalyst in catalyzing propane dehydrogenation was evaluated according to the method described in Example 1. After 12 hours of reaction, the average particle size of Ni was 2.06 nm.

[0061] Comparative Example 1

[0062] 1 g of the dealuminated Beta molecular sieve obtained in Example 1 was continuously added dropwise to the dealuminated Beta molecular sieve while stirring continuously with a glass rod until the dealuminated Beta molecular sieve was completely soaked. The amount of deionized water used at this point was recorded. Ten times the amount of deionized water used was placed in a container, 20.5 mg of chloroplatinic acid hexahydrate was added, and the mixture was stirred with a glass rod and ultrasonicated to obtain a chloroplatinic acid standard solution.

[0063] A standard solution of chloroplatinic acid (CPIA) was added dropwise to 1 g of dealuminated Beta molecular sieve using a pipette, stirring continuously until the solid powder was completely wetted. The impregnated sample was allowed to stand at room temperature for 6 hours, then dried in an 80°C oven for 6 hours. The sample was then reduced with a 5% hydrogen-argon mixture at 550°C for 6 hours to obtain the Pt-IWI catalyst. The actual platinum loading on Pt-IWI was 0.06 wt%, consistent with Example 1.

[0064] Figure 4 TEM image of the Pt-IWI catalyst obtained in Comparative Example 1 before catalytic propane dehydrogenation. Figure 1 and Figure 4 It can be seen that the catalyst prepared by the ALD method in the present invention has a smaller metal particle size.

[0065] The activity of the Pt-IWI catalyst in catalyzing propane dehydrogenation was evaluated according to the method described in Example 1. The average particle sizes of the metal particles before and after 6 hours of propane dehydrogenation reaction were 3.35 nm and 4.53 nm, respectively, which were both larger than the Pt-Beta catalyst obtained in Example 1. At the same loading amount, the propane dehydrogenation reaction conversion rate of the catalyst obtained in Comparative Document 1 was 17.59%, and the selectivity was 86.94%, both lower than that in Example 1. This demonstrates that the supported molecular sieve catalyst obtained in the present invention can achieve higher catalytic activity at a lower loading amount.

[0066] Comparative Example 2

[0067] 20.5 mg of chloroplatinic acid hexahydrate and 9.1 mg of zinc nitrate hexahydrate were dissolved in 10 times the amount of deionized water and mixed evenly. 1 g of dealuminated Beta molecular sieve was taken and a half amount of the standard mixture of chloroplatinic acid and zinc nitrate was added dropwise to the dealuminated Beta using a pipette and stirred continuously until the solid powder was completely wetted. The impregnated sample was placed at room temperature for 6 hours, then dried in an 80°C oven for 6 hours, and reduced with a 5% hydrogen-argon mixture at 550°C for 6 hours to obtain the catalyst PtZn-IWI.

[0068] Compared with Example 2, the metal contents of platinum and zinc in PtZn-IWI are similar to those of PtZn-Beta obtained in Example 2. The activity of Pt-IWI catalyst in catalytic propane dehydrogenation was evaluated according to the method described in Example 1. After 6 hours of propane dehydrogenation reaction, the average particle sizes of the metal nanoparticles before and after were 1.59 nm and 2.00 nm, respectively, both larger than those of PtZn-Beta. The propane conversion rate was 11.95%, which was significantly lower than that of PtZn-ALD.

[0069] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a supported molecular sieve catalyst, characterized in that: The following steps are involved: acid leaching and / or alkali leaching of the molecular sieve matrix to obtain a pretreated molecular sieve matrix; The precursor and the carrier gas are alternately pulsed into a deposition device to adsorb and react on the pretreated molecular sieve substrate to achieve metal loading, and the supported molecular sieve catalyst is obtained after reduction treatment; the precursor includes a metal precursor and an oxide; The metal element in the metal precursor includes one or more of Pt, Fe, Co, Ni, Sn and Zn.

2. The preparation method according to claim 1, characterized in that The molecular sieve matrix includes one of an MFI type molecular sieve, a BEA type molecular sieve and an MWW type molecular sieve.

3. The preparation method according to claim 1, characterized in that The deposition temperature of the deposition equipment is 120-280° C., the pressure is 10-200 Pa, the carrier gas is N 2 ; the number of depositions is 5-40; and the temperature of the metal precursor is 50-90° C.

4. The preparation method according to claim 1, characterized in that The reduction treatment is performed at a temperature of 400 to 600° C. and for a time of 4 to 10 hours.

5. The supported molecular sieve catalyst prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The invention comprises a molecular sieve matrix and metal particles loaded on the surface of the molecular sieve matrix; the particle size of the metal particles is 1.0 to 3.0 nm; the metal particles comprise one or more of Pt, Fe, Co, Ni, Sn and Zn.

6. The supported molecular sieve catalyst according to claim 6, characterized in that The loading amount of the metal particles is 0.01 to 1.5 wt%.

7. Use of the supported molecular sieve catalyst according to claim 5 or 6 in catalytic propane dehydrogenation.

8. A method for preparing propylene by dehydrogenating propane, characterized in that: The following steps are involved: A mixed gas containing N2, H2 and propane is introduced into a reactor containing a catalyst to carry out a dehydrogenation reaction to obtain propylene; the catalyst is the supported molecular sieve catalyst according to claim 5 or 6.

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