Pt-based molecular sieve dehydrogenation catalyst and preparation method thereof

Abstract

The invention discloses a Pt-based molecular sieve dehydrogenation catalyst as well as a preparation method and application thereof. According to the catalyst, a molecular sieve is used as a carrier, Pt is used as an active component, one of Fe, Co, Ni, Cu, Zn and the like is used as an auxiliary component, and one of Na, Mg, K, Ca and Cs is used as an alkali metal component. The preparation method comprises the following steps: firstly, carrying out thermal activation treatment on a carrier, then carrying out secondary ball milling treatment to improve the accessibility of metal particles and carrier defect sites, and further chemically inducing the carrier defect sites and the metal particles to form stable chemical bonds through high-energy mechanical force, so as to enhance the metal-carrier interaction. And stabilizing active metal sites through high-temperature oxidation and reduction treatment, thereby obtaining the dehydrogenation catalyst with high activity and high stability. According to the method, the use of a solvent is avoided, the synthesis steps are simplified, and the method is an environment-friendly, simple, economical and efficient catalyst synthesis method.

Description

Technical Field

[0001] The present invention belongs to the field of catalyst preparation, and particularly relates to a Pt-based molecular sieve dehydrogenation catalyst and a preparation method thereof. Background Art

[0002] With the rapid development of the global economy and the continuous advancement of the industrialization process, the demand for chemicals and energy continues to grow. Among many important chemical products, olefins, as basic raw materials, play a crucial role in fields such as plastics, rubbers, and synthetic fibers. Traditional olefin production mainly relies on petroleum resources and is achieved through processes such as steam cracking. However, with the increasing tension and price fluctuations of petroleum resources, as well as the continuous improvement of environmental protection requirements, it has become extremely urgent to find a more sustainable and efficient olefin production route. Low-carbon alkanes, such as propane and butane, are widely present in natural gas, associated petroleum gas, and light hydrocarbon fractions of refineries, with rich sources and relatively low prices. Converting these low-carbon alkanes into corresponding olefins through catalytic dehydrogenation technology can not only reduce the dependence on petroleum resources but also lower production costs and improve resource utilization efficiency. Therefore, in recent years, the low-carbon alkane catalytic dehydrogenation technology has received extensive attention as an important olefin production method, and the research and development of highly efficient dehydrogenation catalysts is its key core.

[0003] An ideal dehydrogenation catalyst needs to have high activity, high selectivity, high stability, and a long service life. In Pt-based catalysts, the size of metal Pt nanoparticles is a key factor affecting dehydrogenation performance. Reducing the particle size is beneficial to exposing more metal active sites, thereby increasing the conversion rate of alkanes. Currently, industrially, mainly Al2O3-supported noble metal Pt catalysts are used as low-carbon alkane dehydrogenation catalysts for production. However, during the high-temperature conversion of dehydrogenation, the interaction between the metal and the support is weak, and small-sized Pt nanoparticles will undergo severe sintering and rapidly reduce their activity.

[0004] Molecular sieves have characteristics such as regular pore structures, excellent thermal stability, and chemical stability, and are considered ideal carriers for anchoring metal nanoparticles. The preparation methods of metal-loaded molecular sieve catalysts mainly include impregnation methods, ion exchange methods, coprecipitation methods, and one-step synthesis methods, etc. However, their preparation processes are complex, require the use of a large amount of organic solvents, and the metal nanoparticles obtained in the resulting catalysts are uneven and have poor dispersion, resulting in poor catalytic performance. Therefore, it is of great significance to develop a simpler synthesis strategy to prepare metal cluster dehydrogenation molecular sieve catalysts with excellent catalytic performance. Patent CN119281369A uses a hydrothermal method to synthesize NS-1 molecular sieve containing a secondary active metal N, and then uses an ion exchange method to introduce the primary active metal M into the NS-1 molecular sieve carrier to obtain an M-NS-1 catalyst. The resulting catalyst has a propylene space-time yield three times higher than the literature value. Patent CN 117443433A uses a hydrothermal method to first prepare Silicalite-1 molecular sieve, then impregnates a metal source, and after drying, a dry gel crystallization reaction is carried out, and then dehydrogenation molecular sieve is obtained through calcination in nitrogen and air and hydrogen reduction. The resulting catalyst has good stability and high conversion and selectivity. Although the above methods can obtain dehydrogenation catalysts with high yields and high stabilities, their synthesis methods are complex and require the use of a large amount of solvents, so their industrial applications are limited.

[0005] Ball milling has advantages such as being solvent-free, having strong interfacial bonding, and refining particles, and is a simple, economical, and environmentally friendly method for loading metal catalysts. Patent CN 117205962A uses a coprecipitation method and a hydrothermal method to respectively prepare CuCoO x composite oxides and SAPO-34 molecular sieves, then uses a ball mill to mix them evenly, and finally obtains a CuCoO x -SAPO-34 oxide-molecular sieve composite catalyst, which has the characteristics of high activity and high stability. Patent CN 105413738A uses a high-energy ball milling method to evenly mix copper oxide, iron oxide, promoter metal oxide, and molecular sieve, then adds an active component introducing agent and a surface dispersant for impregnation, and through ball milling, drying, grinding, and calcination, a composite oxide molecular sieve SCR catalyst is obtained. The resulting catalyst has uniform metal dispersion and significantly improves its catalytic activity. The preparation processes of the above methods are still relatively complex, and solvents are still required in the precursor synthesis and ball milling processes, resulting in high production costs. In addition, the above ball milling method is limited to the preparation of non-noble metal catalysts. Since the interaction between noble metals and carriers is weak, it is difficult to disperse them into the structure of molecular sieves through a simple ball milling method. Summary of the Invention

[0006] In view of the above problems, the present invention provides a Pt-based molecular sieve dehydrogenation catalyst and a preparation method thereof. The preparation method does not require the addition of solvents, has a simple synthesis process, and high economic benefits. The obtained catalyst has advantages such as high activity, high stability, and renewability, and can solve the problems existing in the preparation of catalysts by traditional methods, such as complex preparation processes, poor metal dispersion, and high-temperature instability.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A Pt-based molecular sieve dehydrogenation catalyst is composed of a carrier, an active component, a promoter component, and an alkali metal component; wherein, the carrier is a molecular sieve; the active component is Pt; the promoter component is any one of Fe, Co, Ni, Cu, Zn, Ga, In, Ge, Sn, Mn, Zr, V, Cr, Ti, Nb, Mo, Y, W, Pb, Sc, Bi, Sb, La, Ce; the alkali metal component is one of Na, Mg, Ca, K, Cs.

[0008] Further, in the dehydrogenation catalyst, the content of the active component accounts for 0.1-10.0 wt.% of the total weight of the catalyst, the content of the promoter component accounts for 0.1-10.0 wt.% of the total weight of the catalyst, and the content of the alkali metal component accounts for 0.1-10.0 wt.% of the total weight of the catalyst.

[0009] The preparation of the Pt-based molecular sieve dehydrogenation catalyst is to first perform high-temperature thermal activation treatment on the carrier to form abundant defect sites, and then perform two ball-milling treatments on the activated carrier, the compound containing the active component, the compound containing the promoter component, and the compound containing the alkali metal component. The first ball-milling treatment breaks the molecular sieve and metal particles to increase the specific surface area of the molecular sieve and improve the accessibility of the metal particles and the defect sites of the molecular sieve. The second ball-milling treatment further induces the formation of a sufficient and stable chemical bond between the carrier defect sites and the metal particles through high-energy mechanochemical action. Finally, the ball-milled product is subjected to high-temperature oxidation and reduction treatments to stabilize the active metal sites and achieve the uniform dispersion and anchoring of the metal components on the carrier, thereby obtaining a dehydrogenation catalyst with high activity and high stability. It specifically includes the following steps: 1) High-temperature thermal activation of the molecular sieve in an active atmosphere to obtain the activated molecular sieve; 2) After the activated molecular sieve is preliminarily mixed with the compound containing the Pt active component, the compound containing the promoter component, and the compound containing the alkali metal component, add it together with an appropriate amount of agate grinding balls into a ball mill for the first ball-milling treatment, then screen out the grinding balls, and dry the mixture to obtain a uniform mixture of metal particles and the carrier; 3) Put the mixture obtained in step 2) into a ball mill again together with an appropriate amount of agate grinding balls for a second ball milling treatment, then screen out the grinding balls, and dry the ball-milled product to obtain a catalyst precursor; 4) Carry out a high-temperature oxidation treatment on the catalyst precursor obtained in step 3) in an oxygen-containing gas stream, and then carry out a reduction treatment under H2 to obtain a Pt-based molecular sieve dehydrogenation catalyst.

[0010] Further, the molecular sieve described in step 1) is any one or more of Silicalite-1, ZSM-5, ZSM-11, Beta, MCM-41, SSZ-13, ITQ-1.

[0011] Further, the active atmosphere described in step 1) is one or more of O2, H2O, CO, CO2, NO, NO2, etc.

[0012] Further, the temperature of the high-temperature thermal activation treatment in step 1) is 500-1000 °C, and the time is 0.5-10 h.

[0013] Further, the compound containing the active component described in step 2) is any one or more of metal particles, oxides, chlorides, nitrate compounds, sulfate compounds, and hydroxides of Pt.

[0014] Further, the compound containing the promoter component described in step 2) is one or more of oxides, chlorides, nitrates, sulfates, and acetates of any one of Fe, Co, Ni, Cu, Zn, Ga, In, Ge, Sn, Mn, Zr, V, Cr, Ti, Nb, Mo, Y, W, Pb, Sc, Bi, Sb, La, Ce.

[0015] Further, the compound containing the alkali metal component described in step 2) is any one of chlorides, hydroxides, sulfates and / or nitrates of Na, Mg, K, Ca, Cs.

[0016] Further, the mass ratio of balls to materials in the first ball milling treatment described in step 2) is (5-20):1, the ball milling speed is 100-500 rpm, and the ball milling time is 1-12 h.

[0017] Further, the mass ratio of balls to materials in the second ball milling treatment described in step 3) is (10-30):1, the ball milling speed is 500-2000 rpm, and the ball milling time is 5-20 h.

[0018] Further, the drying temperature in steps 2) and 3) is 60-120 °C, and the drying time is 1-12 h.

[0019] Further, the oxygen content of the oxygen-containing gas stream described in step 4) is 2 to 100%.

[0020] Further, the temperature of the high-temperature oxidation treatment described in step 4) is 450 to 900 °C, and the time is 5 to 720 min.

[0021] Further, the temperature of the reduction treatment described in step 4) is 300 to 900 °C, and the time is 0.5 to 10 h.

[0022] The Pt-based molecular sieve dehydrogenation catalyst can be used for the dehydrogenation reaction of light alkanes and the efficient dehydrogenation of organic compounds such as cycloalkanes.

[0023] Further, its application method is as follows: After mixing the catalyst powder with quartz sand, it is fixed in a tubular reactor with quartz wool. The conditions for the dehydrogenation reaction are: pure alkane feed, mass space velocity of 2 to 30 h -1 , reaction temperature of 500 to 700 °C, and reaction pressure of 0.05 to 0.2 MPa.

[0024] The design idea of the present invention is to pre-treat the molecular sieve carrier by high-temperature activation heat treatment to generate abundant defect sites, and then use two ball-milling treatments to mix and grind the activated carrier with the active component, the promoter component, and the alkali metal component. First, the accessibility of metal particles and molecular sieve defect sites is improved, and stable chemical bonding is induced between the carrier defect sites and metal particles through high-energy mechanical force chemistry. Finally, the ball-milled product is subjected to high-temperature oxidation and reduction treatments to achieve uniform dispersion and anchoring of the metal on the carrier, and a dehydrogenation catalyst with high activity and high stability is obtained. Compared with the traditional catalyst preparation method, this method has the advantages of solvent-free synthesis, economic efficiency, simple operation, and environmental friendliness, and the obtained catalyst exhibits excellent dehydrogenation catalytic performance.

[0025] The beneficial effects of the present invention are as follows: 1) In the present invention, the molecular sieve is first activated by heat treatment to promote the generation of abundant defect sites, and then through two ball-milling treatments, the accessibility of metal particles and molecular sieve defect sites is improved, and stable chemical bonding is induced between the carrier defect sites and metal particles by high-energy mechanical force chemistry, realizing uniform dispersion and anchoring of the metal on the carrier, and obtaining a dehydrogenation catalyst with high activity and high stability.

[0026] 2) The dehydrogenation catalyst obtained in the present invention has excellent stability and regenerability. In the propane dehydrogenation reaction, its propane conversion rate is 47 to 49%, the propylene selectivity is 96 to 99%, it can stably react for 200 hours without obvious deactivation, and can be successfully regenerated at least 50 times, having great industrial application prospects.

[0027] 3) The ball milling method adopted in the present invention directly uses metal salts as raw materials, and its solvent-free synthesis completely avoids the use of organic solvents, simplifies the synthesis steps, reduces the production cost, and is an environmentally friendly, simple and efficient catalyst synthesis method, providing a new technology for the preparation of highly efficient and stable dehydrogenation molecular sieve catalysts. Description of the Drawings

[0028] Figure 1 TEM and STEM images of the PtSnK / S-1 catalyst prepared in Example 1.

[0029] Figure 2 TEM image of the PtSnK@S-1 catalyst prepared in Comparative Example 1.

[0030] Figure 3 TEM image of the PtSnK / S-1-imp catalyst prepared in Comparative Example 2.

[0031] Figure 4 For the PtSnK / S-1 prepared in Comparative Example 3 unactivated TEM image of the catalyst.

[0032] Figure 5 Catalytic activity diagram of the PtSnK / S-1 catalyst prepared in Example 1 for propane dehydrogenation reaction for 200 hours.

[0033] Figure 6 Catalytic activity diagram of the PtSnK / S-1 catalyst prepared in Example 1 for propane dehydrogenation reaction-regeneration cycle 50 times. Detailed Description of the Invention

[0034] A Pt-based molecular sieve dehydrogenation catalyst, the preparation of which includes the following steps: 1) Thermally activate the molecular sieve in an active atmosphere at a high temperature of 500-1000 °C for 0.5-10 h to obtain the activated molecular sieve; 2) After the activated molecular sieve is preliminarily mixed with the compound containing the Pt active component, the compound containing the promoter component and the compound containing the alkali metal component, add them into the ball mill together with agate grinding balls according to the ball-to-material mass ratio of (5-20):1, and mechanically ball mill at a rotation speed of 100-500 rpm for 1-12 h. Then screen out the grinding balls and dry at 60-120 °C for 1-12 h to obtain a uniform mixture of metal particles and the carrier; 3) Put the mixture obtained in step 2) and agate grinding balls into the ball mill again according to the ball-to-material mass ratio of (10-30):1, and mechanically ball mill at a rotation speed of 500-2000 rpm for 5-20 h. Then screen out the grinding balls and dry at 60-120 °C for 1-12 h to obtain the catalyst precursor; 4) The catalyst precursor obtained in step 3) is subjected to high-temperature oxidation treatment in an oxygen-containing gas stream with an oxygen content of 2-100% at 450-900 °C for 5-720 min, and then reduced under H2 at 300-900 °C for 0.5-10 h to obtain a Pt-based molecular sieve dehydrogenation catalyst. Among them, based on the total weight of the catalyst, the loading amount of the active component is 0.1-10.0 wt.%, the loading amount of the promoter component is 0.1-10.0 wt.%, and the loading amount of the alkali metal component is 0.1-10.0 wt.%.

[0035] Among them, the molecular sieve in step 1) is any one or more of Silicalite-1, ZSM-5, ZSM-11, Beta, MCM-41, SSZ-13, ITQ-1. The active atmosphere is one or more of O2, H2O, CO, CO2, NO, NO2, etc.

[0036] The compound containing the active component in step 2) is selected from any one or more of metal particles, oxides, chlorides, nitrate compounds, sulfate compounds, and hydroxides of Pt. The compound containing the promoter component is an oxide, chloride, nitrate, sulfate, and / or acetate of any one of Fe, Co, Ni, Cu, Zn, Ga, In, Ge, Sn, Mn, Zr, V, Cr, Ti, Nb, Mo, Y, W, Pb, Sc, Bi, Sb, La, Ce. The compound containing the alkali metal component is a chloride, hydroxide, sulfate, and / or nitrate of any one of Na, Mg, K, Ca, Cs.

[0037] To make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0038] The diameter of the agate grinding balls used in the examples is 3-20 mm.

[0039] Example 1 Preparation of a Pt-based molecular sieve dehydrogenation catalyst (1) Place 2.5 g of the S-1 molecular sieve carrier in a tubular furnace, introduce CO2, and heat-treat at 800 °C for 2 h to obtain an activated S-1 molecular sieve carrier; (2) Add the activated S-1 molecular sieve carrier obtained in step (1), 25 mg of H2PtCl6·6H2O, 50 mg of SnCl4·5H2O, and 20 mg of KCl to a ball mill, add agate grinding balls according to a ball-to-material mass ratio of 10:1, mechanically ball-mill at 300 rpm for 2 h, then screen out the grinding balls, and dry at 80 °C for 2 h to obtain a mixture; (3) Add the mixture obtained in step (2) and agate grinding balls into the ball mill again at a ball-to-material mass ratio of 20:1, and mechanically ball mill for 8 h at a rotation speed of 1000 rpm. Then, sieve out the grinding balls and dry at 100 °C for 4 h to obtain the catalyst precursor. (4) Oxidize the obtained catalyst precursor in an air stream with an oxygen content of 21% at 700 °C for 4 h, and then reduce it in a hydrogen stream at 600 °C for 2 h to obtain the PtSnK / S-1 catalyst. Among them, the loading amount of the active metal Pt is 0.38 wt.%, the loading amount of the promoter metal Sn is 0.68 wt.%, and the loading amount of the alkali metal K is 0.42 wt.%.

[0040] Figure 1 The TEM and STEM images of the obtained PtSnK / S-1 catalyst are shown as follows. As shown in the figure, Pt clusters with a particle size of ~1 nm are uniformly dispersed on the molecular sieve support, indicating that activating the support and ball milling bonding can effectively disperse and anchor the active metal clusters.

[0041] Example 2 Preparation of a dehydrogenation Pt-based molecular sieve catalyst (1) Place 2.5 g of ZSM-11 molecular sieve support in a tubular furnace, introduce CO2, and heat-treat at 800 °C for 2 h to obtain the activated ZSM-11 molecular sieve support. (2) Add the activated ZSM-11 molecular sieve support obtained in step (1), 25 mg of H2PtCl6·6H2O, 50 mg of SnCl4·5H2O, and 20 mg of KCl into the ball mill, and add agate grinding balls at a ball-to-material mass ratio of 10:1. Mechanically ball mill at a rotation speed of 300 rpm for 2 h, then sieve out the grinding balls and dry at 80 °C for 2 h to obtain a mixture. (3) Add the mixture obtained in step (2) and agate grinding balls into the ball mill again at a ball-to-material mass ratio of 20:1, and mechanically ball mill for 8 h at a rotation speed of 1000 rpm. Then, sieve out the grinding balls and dry at 100 °C for 4 h to obtain the catalyst precursor. (4) Oxidize the obtained catalyst precursor in an air stream with an oxygen content of 21% at 700 °C for 4 h, and then reduce it in a hydrogen stream at 600 °C for 2 h to obtain the PtSnK / ZSM-11 catalyst. Among them, the loading amount of the active metal Pt is 0.38 wt.%, the loading amount of the promoter metal Sn is 0.68 wt.%, and the loading amount of the alkali metal K is 0.42 wt.%.

[0042] Example 3 Preparation of a dehydrogenation Pt-based molecular sieve catalyst (1) Place 2.5 g of Beta zeolite support in a tubular furnace, introduce CO2, and heat-treat at 800 °C for 2 h to obtain the activated Beta zeolite support; (2) Add the activated Beta zeolite support obtained in step (1), 25 mg of H2PtCl6·6H2O, 50 mg of SnCl4·5H2O, and 20 mg of KCl to a ball mill together, add agate grinding balls according to a ball-to-material mass ratio of 10:1, mechanically ball-mill at 300 rpm for 2 h, then sieve out the grinding balls, and dry at 80 °C for 2 h to obtain a mixture; (3) Add the mixture obtained in step (2) and agate grinding balls to the ball mill again according to a ball-to-material mass ratio of 20:1, mechanically ball-mill at 1000 rpm for 8 h, then sieve out the grinding balls, and dry at 100 °C for 4 h to obtain a catalyst precursor; (4) Oxidize the obtained catalyst precursor in an air stream with an oxygen content of 21% at 700 °C for 4 h, and then reduce it in a hydrogen stream at 600 °C for 2 h to obtain the PtSnK / Beta catalyst, where the loading of the active metal Pt is 0.38 wt.%, the loading of the promoter metal Sn is 0.68 wt.%, and the loading of the alkali metal K is 0.42 wt.%.

[0043] Example 4 Preparation of a dehydrogenation Pt-based zeolite catalyst (1) Place 2.5 g of S-1 zeolite support in a tubular furnace, introduce CO2, and heat-treat at 800 °C for 2 h to obtain the activated S-1 zeolite support; (2) Add the activated S-1 zeolite support obtained in step (1), 25 mg of H2PtCl6·6H2O, 20 mg of GeO2, and 20 mg of KCl to a ball mill together, add agate grinding balls according to a ball-to-material mass ratio of 10:1, mechanically ball-mill at 300 rpm for 2 h, then sieve out the grinding balls, and dry at 80 °C for 2 h to obtain a mixture; (3) Add the mixture obtained in step (2) and agate grinding balls to the ball mill again according to a ball-to-material mass ratio of 20:1, mechanically ball-mill at 1000 rpm for 8 h, then sieve out the grinding balls, and dry at 100 °C for 4 h to obtain a catalyst precursor; (4) Oxidize the obtained catalyst precursor in an air stream with an oxygen content of 21% at 700 °C for 4 h, and then reduce it in a hydrogen stream at 600 °C for 2 h to obtain the PtGeK / S-1 catalyst, where the loading of the active metal Pt is 0.38 wt.%, the loading of the promoter metal Ge is 0.55 wt.%, and the loading of the alkali metal K is 0.42 wt.%.

[0044] Example 5 Preparation of a dehydrogenation Pt-based molecular sieve catalyst (1) Place 2.5 g of S-1 molecular sieve support in a tubular furnace, introduce CO2, and heat-treat at 800 °C for 2 h to obtain the activated S-1 molecular sieve support; (2) Add the activated S-1 molecular sieve support obtained in step (1), 25 mg of H2PtCl6·6H2O, 50 mg of SnCl4·5H2O, and 20 mg of NaCl to a ball mill, add agate grinding balls according to a ball-to-material mass ratio of 10:1, and mechanically ball mill at 300 rpm for 2 h. Then sieve out the grinding balls and dry at 80 °C for 2 h to obtain a mixture; (3) Add the mixture obtained in step (2) and agate grinding balls to the ball mill again according to a ball-to-material mass ratio of 20:1, mechanically ball mill at 1000 rpm for 8 h, then sieve out the grinding balls and dry at 100 °C for 4 h to obtain a catalyst precursor; (4) Oxidize the obtained catalyst precursor in an air stream with an oxygen content of 21% at 700 °C for 4 h, and then reduce it in a hydrogen stream at 600 °C for 2 h to obtain the PtSnNa / S-1 catalyst, where the loading of the active metal Pt is 0.38 wt.%, the loading of the promoter metal Sn is 0.68 wt.%, and the loading of the alkali metal Na is 0.31 wt.%.

[0045] Example 6 Preparation of a dehydrogenation Pt-based molecular sieve catalyst (1) Place 2.5 g of S-1 molecular sieve support in a tubular furnace, introduce CO2, and heat-treat at 800 °C for 2 h to obtain the activated S-1 molecular sieve support; (2) Add the activated S-1 molecular sieve support obtained in step (1), 10 mg of Pt metal particles, 20 mg of GeO2, and 20 mg of NaCl to a ball mill, add agate grinding balls according to a ball-to-material mass ratio of 10:1, and mechanically ball mill at 300 rpm for 2 h. Then sieve out the grinding balls and dry at 80 °C for 2 h to obtain a mixture; (3) Add the mixture obtained in step (2) and agate grinding balls to the ball mill again according to a ball-to-material mass ratio of 20:1, mechanically ball mill at 1000 rpm for 8 h, then sieve out the grinding balls and dry at 100 °C for 4 h to obtain a catalyst precursor; (4) The obtained catalyst precursor was oxidized in an air stream with an oxygen content of 21% at 700 °C for 4 h, and then reduced in a hydrogen stream at 600 °C for 2 h to obtain the PtGeNa / S-1 catalyst. Among them, the loading amount of the active metal Pt was 0.40 wt.%, the loading amount of the promoter metal Ge was 0.55 wt.%, and the loading amount of the alkali metal Na was 0.31 wt.%.

[0046] Comparative Example 1 Preparation of Pt-based molecular sieve catalyst by in-situ synthesis method (1) At room temperature, 8.2 g of tetraethyl orthosilicate, 8.5 g of tetrapropylammonium hydroxide, 3.5 g of deionized water, 50 mg of SnCl4·5H2O and 20 mg of KCl were weighed and mixed in a beaker, and stirred for 8 h until complete hydrolysis to obtain a homogeneous gel-like mixed solution.

[0047] (2) Separately, 25 mg of H2PtCl6·6H2O and 0.5 mL of ethylenediamine were added to 2.0 g of deionized water and stirred evenly to obtain a homogeneous Pt chelating solution.

[0048] (3) The Pt chelating solution obtained in step (2) was added to step (1) and stirred for 2 h. The obtained solution was transferred to the inner lining of a crystallization kettle and crystallized in an oven at 170 °C for 48 h. After cooling, centrifuging, and washing, a crystallized product was obtained.

[0049] (4) The crystallized product obtained in step (3) was dried at 100 °C for 6 h, calcined at 550 °C for 4 h, and finally reduced in hydrogen at 600 °C for 2 h to obtain the PtSnK@S-1 catalyst. Among them, the loading amount of the active metal Pt was 0.38 wt.%, the loading amount of the promoter metal Sn was 0.68 wt.%, and the loading amount of the alkali metal K was 0.42 wt.%.

[0050] Figure 2 This is the TEM image of the PtSnK@S-1 catalyst obtained in this comparative example. As shown in the figure, Pt clusters with a particle size of 2 - 4 nm exist on the molecular sieve support, indicating that the Pt clusters obtained by the in-situ synthesis method are relatively evenly dispersed, but are still slightly larger than those obtained by the ball milling method. Some larger clusters cannot enter the pores and are more likely to deactivate and agglomerate, and there are fewer active sites under the same Pt loading.

[0051] Comparative Example 2 Preparation of Pt-based molecular sieve catalyst by impregnation method (1) 25 mg of H2PtCl6·6H2O, 50 mg of SnCl4·5H2O, and 20 mg of KCl were dissolved in 2.0 g of deionized water and stirred evenly to form a homogeneous solution.

[0052] (2) Immerse 2.5 g of S-1 molecular sieve support with the homogeneous solution obtained in step (1), and let it stand for 4 h.

[0053] (3) Dry the impregnated sample obtained in step (2) in an oven at 80 °C for 6 h, calcine it in a muffle furnace at 550 °C for 4 h, and finally reduce it with hydrogen at 600 °C in a tubular furnace for 2 h to obtain the PtSnK / S-1-imp catalyst. Among them, the loading of active metal Pt is 0.38 wt.%, the loading of promoter metal Sn is 0.68 wt.%, and the loading of alkali metal K is 0.42 wt.%.

[0054] Figure 3 This is the TEM image of the PtSnK / S-1-imp catalyst obtained in this comparative example. As shown in the figure, Pt clusters and particles with particle sizes of ~2 nm and ~20 nm coexist on the molecular sieve support, indicating that the Pt clusters obtained by the impregnation method are less uniformly dispersed, and are larger than the Pt clusters obtained by the ball milling method. Some clusters and particles cannot enter the pores and are more likely to deactivate and agglomerate, and there are fewer active sites at the same Pt loading.

[0055] Comparative Example 3 Preparation of Pt-based molecular sieve catalyst by directly ball milling the molecular sieve without activation (1) Add 2.5 g of S-1 molecular sieve support, 25 mg of H2PtCl6·6H2O, 50 mg of SnCl4·5H2O, and 20 mg of KCl to a ball mill, add agate grinding balls according to a ball-to-material mass ratio of 10:1, and mechanically ball mill at 300 rpm for 2 h. Then screen out the grinding balls and dry at 80 °C for 2 h to obtain a mixture.

[0056] (2) Add the mixture obtained in step (1) and agate grinding balls to the ball mill again according to a ball-to-material mass ratio of 20:1, mechanically ball mill at 1000 rpm for 8 h, then screen out the grinding balls and dry at 100 °C for 4 h to obtain a catalyst precursor.

[0057] (3) Oxidize the obtained catalyst precursor in an air stream with an oxygen content of 21% at 700 °C for 4 h, and then reduce it in a hydrogen stream at 600 °C for 2 h to obtain PtSnK / S-1 unactivated catalyst, where the loading of active metal Pt is 0.38 wt.%, the loading of promoter metal Sn is 0.68 wt.%, and the loading of alkali metal K is 0.42 wt.%.

[0058] Figure 4 This is the PtSnK / S-1 obtained in this comparative example unactivatedTEM image of the catalyst. As shown in the figure, Pt clusters and particles with a particle size of 2 - 15 nm exist on the molecular sieve support, indicating that the unactivated molecular sieve support cannot effectively anchor the active metal Pt.

[0059] Comparative Example 4 Preparation of Pt-based molecular sieve catalyst by one-step ball milling method (1) Place 2.5 g of S-1 molecular sieve support in a tube furnace, introduce CO2, and heat-treat at 800 °C for 2 h to obtain the activated S-1 molecular sieve support; (2) Add the activated S-1 molecular sieve support obtained in step (1), 25 mg of H2PtCl6·6H2O, 50 mg of SnCl4·5H2O, and 20 mg of KCl to a ball mill, add agate grinding balls according to a ball-to-material mass ratio of 10:1, mechanically ball mill at 1000 rpm for 10 h, then sieve out the grinding balls, and dry at 100 °C for 4 h to obtain the catalyst precursor; (3) Oxidize the obtained catalyst precursor in an air stream with an oxygen content of 21% at 700 °C for 4 h, and then reduce it in a hydrogen stream at 600 °C for 2 h to obtain PtSnK / S-1 BM-1 catalyst, where the loading of active metal Pt is 0.38 wt.%, the loading of promoter metal Sn is 0.68 wt.%, and the loading of alkali metal K is 0.42 wt.%.

[0060] Use the propane dehydrogenation reaction as a model reaction to evaluate the performance of the prepared dehydrogenation catalyst. The experimental process is as follows: Mix 0.25 g of the catalyst with 2 g of quartz sand and load it into a fixed-bed tube reactor (the inner diameter of the used tube reactor is 6 mm, the catalyst loading height is about 10 cm, and quartz wool is filled at the top and bottom for fixation). The reactant is propane, the reaction temperature is 600 °C, the reaction pressure is atmospheric pressure, and the propane weight hourly space velocity is 12 h -1 dehydrogenation reaction is carried out under the conditions, and the products are analyzed by a gas chromatograph. The propane conversion and propylene selectivity of the catalyst are shown in Table 1.

[0061] Table 1 Comparison of propane dehydrogenation catalytic performance of different catalysts

[0062] As can be seen from the results in Table 1, under the condition of the same composition, the activity and stability of the catalyst PtSnK / S-1 obtained in Example 1 are higher than those of the catalysts obtained in Comparative Examples 1-4, indicating that the obtained catalyst has excellent propane conversion and propylene selectivity, as well as a significant stabilizing effect of carrier activation and ball-milling bonding on the dehydrogenation catalyst. Among them, from the comparison with Comparative Example 3, it can be seen that without heat treatment activation of the molecular sieve carrier, there will not be enough defect sites to anchor the active metal Pt, resulting in a significant decrease in the catalyst activity; while from the comparison with Comparative Example 4, it can be seen that the one-stage ball-milling method cannot form a stable chemical bond between the active metal Pt and the defect sites of the molecular sieve, resulting in a rapid decrease in the catalyst activity.

[0063] Meanwhile, from the comparison of Examples 1-6, it can be seen that this method has good universality. By changing the types of carriers, promoters, alkali metals, and Pt species, stable and efficient dehydrogenation catalysts can be obtained. More importantly, this solvent-free synthesis method avoids environmental pollution caused by organic solvents, simplifies the synthesis steps, and reduces the production cost. It is an environmentally friendly, simple, and efficient catalyst synthesis method, providing strong support for the future design and application fields of high-temperature catalysts.

[0064] The reaction stability of the PtSnK / S-1 catalyst prepared in Example 1 was further investigated. The experimental process is as follows: 0.25 g of the catalyst powder was mixed with 2.0 g of quartz sand and loaded into a fixed-bed tubular reactor (the inner diameter of the used tubular reactor is 6 mm, the catalyst loading height is about 10 cm, and quartz wool was filled at the top and bottom for fixation). The reactant was propane, the reaction temperature was 600 °C, the reaction pressure was atmospheric pressure, and the propane weight hourly space velocity was 12 h -1 Under the conditions, the dehydrogenation reaction was carried out for 24 h. After the reaction, in an air (O2 / N2 = 21 / 79) atmosphere, the reactor was heated to 600 °C, calcined for 4 h and then cooled, and the atmosphere was switched to nitrogen for purging for 30 min, then switched to a hydrogen atmosphere, reduced at 600 °C for 2 h, and finally the atmosphere was switched to pure propane gas to carry out the dehydrogenation reaction again. The products were analyzed by a gas chromatograph, and the results are shown in Figure 5 、 6 。As can be seen from Figure 5 、 6 ,the PtSnK / S-1 catalyst can be successfully regenerated by simple calcination and reduction, and can be reused at least 50 times with basically no deactivation, showing significant reaction stability and recyclability.

[0065] The above are only the preferred embodiments of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A Pt-based molecular sieve dehydrogenation catalyst, characterized in that: The dehydrogenation catalyst is composed of a support, an active component, a promoter component, and an alkali metal component; wherein, the support is a molecular sieve; the active component is Pt; the promoter component is any one of Fe, Co, Ni, Cu, Zn, Ga, In, Ge, Sn, Mn, Zr, V, Cr, Ti, Nb, Mo, Y, W, Pb, Sc, Bi, Sb, La, Ce; and the alkali metal component is one of Na, Mg, Ca, K, Cs.

2. The Pt-based molecular sieve dehydrogenation catalyst according to claim 1, characterized in that: In the dehydrogenation catalyst, the content of the active component accounts for 0.1 - 10.0 wt.% of the total weight of the catalyst, the content of the promoter component accounts for 0.1 - 10.0 wt.% of the total weight of the catalyst, and the content of the alkali metal component accounts for 0.1 - 10.0 wt.% of the total weight of the catalyst.

3. A preparation method of the Pt-based molecular sieve dehydrogenation catalyst as described in claim 1, characterized in that: First, the molecular sieve is subjected to high-temperature thermal activation treatment to form abundant defect sites, and then the activated molecular sieve is subjected to two ball-milling treatments with a compound containing an active component, a compound containing a promoter component, and a compound containing an alkali metal component. Finally, the ball-milled product is subjected to high-temperature oxidation and reduction treatments to prepare a dehydrogenation catalyst with high activity and high stability.

4. The preparation method of the Pt-based molecular sieve dehydrogenation catalyst according to claim 3, characterized in that: The molecular sieve is any one or several of Silicalite-1, ZSM-5, ZSM-11, Beta, MCM-41, SSZ-13, ITQ-1.

5. The preparation method of the Pt-based molecular sieve dehydrogenation catalyst according to claim 3, characterized in that: The thermal activation treatment is carried out in an atmosphere of one or several of O2, H2O, CO, CO2, NO, NO2; the treatment temperature is 500 - 1000 °C, and the treatment time is 0.5 - 10 h.

6. The preparation method of the Pt-based molecular sieve dehydrogenation catalyst according to claim 3, characterized in that: The compound containing the active component is selected from any one or several of metal particles, oxides, chlorides, nitrate compounds, sulfate compounds, and hydroxides of Pt; The compound containing the promoter component is an oxide, chloride, nitrate, sulfate, and / or acetate of any one of Fe, Co, Ni, Cu, Zn, Ga, In, Ge, Sn, Mn, Zr, V, Cr, Ti, Nb, Mo, Y, W, Pb, Sc, Bi, Sb, La, Ce; The compound containing the alkali metal component is a chloride, hydroxide, sulfate, and / or nitrate of any one of Na, Mg, K, Ca, Cs.

7. The preparation method of the Pt-based molecular sieve dehydrogenation catalyst according to claim 3, wherein: In the two ball-milling treatments, the mass ratio of balls to materials in the first ball-milling treatment is (5 - 20):1, the ball-milling speed is 100 - 500 rpm, and the ball-milling time is 1 - 12 h; The mass ratio of balls to materials in the second ball-milling treatment is (10 - 30):1, the ball-milling speed is 500 - 2000 rpm, and the ball-milling time is 5 - 20 h.

8. The preparation method of the Pt-based molecular sieve dehydrogenation catalyst according to claim 3, characterized in that: The high-temperature oxidation is carried out in a gas stream with an oxygen content of 2 - 100%, the treatment temperature is 450 - 900 °C, and the treatment time is 5 - 720 min.

9. The preparation method of the Pt-based molecular sieve dehydrogenation catalyst according to claim 3, characterized in that: The reduction treatment is carried out in a H2 atmosphere, the treatment temperature is 300 - 900 °C, and the treatment time is 0.5 - 10 h.

10. Application of the Pt-based molecular sieve dehydrogenation catalyst as described in claim 1 in the dehydrogenation of light alkanes.

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