A bimetallic Pt-based molecular sieve catalyst for dehydrogenation of light alkanes to olefins

Abstract

The present invention discloses a bimetallic Pt-based molecular sieve catalyst for the efficient dehydrogenation of light alkanes to olefins. The catalyst is formed by doping a secondary active metal component M into a large crystal size molecular sieve to form an M@ molecular sieve, and anchoring the main active metal component Pt in the form of nanoclusters on the molecular sieve framework. The secondary active metal component M is any one or more of Sn, Ga, and Zn. The present invention first uses a hydrothermal method to prepare the M@ molecular sieve, and regulates the crystal size of the molecular sieve by adding a chelating agent. Then, Pt is loaded on the obtained large grain size M@ molecular sieve by vacuum impregnation, so that the Pt nanoclusters are firmly stabilized on the molecular sieve framework, and finally reduced to obtain the bimetallic Pt-based molecular sieve catalyst. The bimetallic Pt-based molecular sieve catalyst prepared by the present invention has high temperature stability, metal particle anti-sintering and long-term cyclic regeneration performance, and can be applied to high-temperature dehydrogenation reactions of ethane, propane or butane.

Description

Technical Field

[0001] The present invention belongs to the field of industrial catalyst preparation, and in particular relates to a bimetallic Pt-based molecular sieve catalyst for efficient dehydrogenation of light alkanes to olefins, and a preparation method and application thereof. Background Art

[0002] Light olefins have become a primary raw material for the petrochemical industry, particularly products such as propylene and ethylene, which are widely used in various fields. In recent years, global olefin production has been experiencing a weak supply-demand relationship. Currently, the primary source of olefins is traditional petroleum production, but traditional production processes are complex and inefficient, and petroleum is a non-renewable resource. my country has abundant reserves of alkane feedstocks, which are often used as fuel in daily life. To convert propane into high-value-added olefins and overcome the shortcomings of traditional olefin production, direct alkane dehydrogenation is becoming an increasingly popular method for producing olefins in the global petrochemical industry.

[0003] Pt-based molecular sieve catalysts for the dehydrogenation of light alkanes to olefins have been widely reported, with the traditional impregnation method being the most commonly used. For example, the bimetallic Pt-based catalysts reported in patent applications with publication numbers CN 102389831A, CN 101972664A, CN 104307555A, and CN105056990A have high initial alkane conversion rates, but generally suffer from disadvantages such as large Pt nanocluster particles, poor catalyst stability, low olefin selectivity, and easy carbon deposition. Angew. Chem. Int. Ed., 2020, 59, 19450-19459, J Catal., 2020, 385, 61-69 all reported encapsulating the active Pt component within the pores of molecular sieves. The confinement effect of the molecular sieve pores not only improves the dispersion of the Pt species but also largely prevents the sintering and enlargement of the active platinum particles in the catalyst under high-temperature conditions, thereby improving catalyst stability and reducing environmental pollution caused by catalyst regeneration. However, the performance of these molecular sieve-encapsulated Pt catalysts still cannot meet the requirements of long-term industrial operation. These catalysts slowly deactivate during operation, and their stability at high activity rarely exceeds 20 days.

[0004] In response to the drawbacks of the aforementioned Pt-based molecular sieve catalysts, the present invention provides a bimetallic Pt-based molecular sieve catalyst for efficient dehydrogenation of low-carbon alkanes to olefins and its preparation method. This catalyst is prepared by simultaneously crystallizing a secondary active metal element (M) (Sn, Ga, Zn) and a molecular sieve raw material, and adding an appropriate amount of a chelating agent to adjust the size of the molecular sieve crystals. This produces an M@ molecular sieve with a shortest crystal axis length of 1.00 to 5.00 μm. The primary active component, Pt, is then loaded onto the M@ molecular sieve. Due to the doping of the secondary active metals into the molecular sieve framework, bimetallic Pt nanoclusters are firmly anchored to the molecular sieve. The resulting Pt / M@ molecular sieve catalyst exhibits excellent sintering resistance. High-temperature fixed-bed catalytic testing confirmed that, compared to smaller Pt-based molecular sieve catalysts, the large-crystal Pt / M@ molecular sieve catalyst prepared in this invention exhibits bimetallic nanoclusters firmly anchored to the molecular sieve surface, resulting in superior sintering resistance. After 4400 hours of reaction, the catalyst showed no significant catalytic deactivation, suggesting promising industrial application prospects. Summary of the Invention

[0005] The present invention aims to address the problems of low Pt species dispersion, high-temperature sintering of Pt metal particles, and frequent catalyst regeneration in existing Pt-based catalysts for the dehydrogenation of alkanes to olefins. The present invention provides a bimetallic Pt-based molecular sieve catalyst for the efficient dehydrogenation of low-carbon alkanes to olefins, as well as its preparation method and application. During the eutecticization of the secondary active metal component and the molecular sieve raw material, the present invention adds a chelating agent to inhibit the nucleation rate of the molecular sieve, thereby regulating the size of the shortest crystal axis of the molecular sieve grains. The catalyst is then vacuum-impregnated with Pt species to produce a catalyst with bimetallic Pt-based nanoclusters anchored on the molecular sieve surface. This catalyst exhibits advantages such as sintering resistance, high alkane conversion, and recyclability.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A bimetallic Pt-based molecular sieve catalyst for efficient dehydrogenation of light alkanes to olefins, comprising a molecular sieve with a large crystal size doped with a secondary active metal component M to form an M@ molecular sieve, and a primary active metal component Pt anchored to the molecular sieve framework in the form of nanoclusters.

[0008] The secondary active metal component M is specifically any one or more of Sn, Ga, and Zn, and its loading amount is 0.10~10.0 wt%; the molecular sieve is any one of S-1 molecular sieve, Beta molecular sieve, and ZSM-11 molecular sieve, and the length of its shortest crystal axis is 1.00~5.00 μm; the particle size of the nanocluster is 0.40~0.80 nm, and its loading amount is 0.10~10.0wt%.

[0009] The preparation method of the bimetallic Pt-based molecular sieve catalyst is to first prepare a large-grain M@ molecular sieve by a hydrothermal method under the condition of adding a chelating agent, then load Pt on the M@ molecular sieve by a vacuum impregnation method, and finally obtain the bimetallic Pt-based molecular sieve catalyst by reduction; the method comprises the following steps:

[0010] (1) Preparation of M@ molecular sieve

[0011] Under room temperature, water, silicon source, structure-directing agent, secondary active metal salt and chelating agent are fully stirred and mixed to obtain a uniform gel solution. The solution is then placed in a polytetrafluoroethylene liner and hydrothermally crystallized at a certain temperature and time. The solution is then filtered, dried and calcined to obtain M@ molecular sieve with large crystal size.

[0012] (2) Synthesis of Pt / M@ molecular sieve catalyst

[0013] Under vacuum conditions, the prepared M@ molecular sieve is heated and then impregnated with an organic solution containing a Pt metal organic compound. The mixture is then filtered, washed, dried, and reduced to obtain a bimetallic Pt / M@ molecular sieve catalyst.

[0014] The molar ratio of the silicon source, water, structure directing agent, secondary active metal salt and chelating agent is 1:(0.01-1):(1-10):(0.00001-0.01):(0.01-1).

[0015] Furthermore, the silicon source is any one or more of solid silica gel, water glass, ethyl orthosilicate, white carbon black, and silica sol.

[0016] Furthermore, the structure directing agent is any one or more of tetrapropylammonium hydroxide, tetramethylammonium bromide, tetrabutylammonium bromide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, tetraethylammonium bromide, and tetrapropylammonium bromide.

[0017] Furthermore, when Sn is used as the secondary active metal, the secondary active metal salt used is any one or more of SnCl2·2H2O and SnCl4; when Ga is used as the secondary active metal, the secondary active metal salt used is any one or more of GaCl3, Ga2Cl4, and Ga(NO3)3·xH2O; when Zn is used as the secondary active metal, the secondary active metal salt used is any one or more of ZnCl2 and Zn(NO3)2·6H2O.

[0018] Furthermore, the chelating agent is any one or more of HF, HCl, HBr, and HI.

[0019] Furthermore, in step (1), the temperature of the hydrothermal crystallization is 100-200°C, and the time is 1-196 hours; the temperature of the drying is 50-150°C, and the time is 1-20 hours; and the temperature of the calcination is 450-650°C, and the time is 1-20 hours.

[0020] Furthermore, the Pt metal organic compound in step (2) is any one or more of Pt(COD)(Me)2, Pt(COD)Cl2, and Pt(HACAC)2.

[0021] Furthermore, the heating treatment in step (2) is carried out at a temperature of 100-500°C for 1-20 hours; and the reduction is carried out in a H2 atmosphere at a temperature of 100-700°C for 1-20 hours.

[0022] The bimetallic Pt-based molecular sieve catalyst is suitable for high-temperature and high-efficiency dehydrogenation of ethane, propane or butane in a fixed bed. The dehydrogenation reaction conditions are: pure alkane feed, mass space velocity of 2-12 h -1 The reaction temperature is 450~700 ℃ and the reaction pressure is 0.1~0.2 MPa.

[0023] The beneficial effects of the present invention are:

[0024] The present invention first simultaneously crystallizes secondary active metal components such as Sn, Ga, and Zn and molecular sieve raw materials to dope the secondary active metals into the molecular sieve framework, and then controls the grain size of the molecular sieve by adding a chelating agent to obtain a large-grain M@ molecular sieve. Then, under vacuum conditions, the main active metal component Pt element is loaded on the large-grain M@ molecular sieve to improve the dispersion and utilization rate of the Pt active component and firmly anchor the bimetallic Pt nanoclusters on the molecular sieve.

[0025] The large-grain bimetallic Pt-based molecular sieve catalyst obtained by the present invention exhibits advantages such as high Pt species dispersion, good high-temperature stability, strong sintering resistance of Pt metal nanoclusters, high alkane conversion rate, and recyclability in the high-temperature dehydrogenation reaction of alkanes. The strong interaction between the active Pt species and the molecular sieve enhances the Pt species' sintering resistance, resulting in no significant deactivation after 4400 hours of high-temperature reaction. This reduces the catalyst's regeneration frequency and minimizes environmental pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the SEM image of the Pt / Sn@S-1(0.10) catalyst prepared in Comparative Example 1.

[0027] Figure 2 This is the SEM image of the Pt / Sn@S-1(1.00) catalyst prepared in Example 1.

[0028] Figure 3 This is the SEM image of the Pt / Sn@S-1(2.00) catalyst prepared in Example 2.

[0029] Figure 4 This is the SEM image of the Pt / Sn@S-1(3.00) catalyst prepared in Example 3.

[0030] Figure 5 This is the SEM image of the Pt / Sn@S-1(5.00) catalyst prepared in Example 4.

[0031] Figure 6 This is the STEM image of the Pt / Sn@S-1(5.00) catalyst prepared in Example 4.

[0032] Figure 7 This is a diagram showing the catalytic activity of the Pt / Sn@S-1 (5.00) catalyst prepared in Example 4 for propane dehydrogenation for 6 consecutive months. DETAILED DESCRIPTION

[0033] A bimetallic Pt-based molecular sieve catalyst for efficient dehydrogenation of light alkanes to olefins, the preparation method of which comprises the following steps:

[0034] (1) Preparation of M@ molecular sieve

[0035] At room temperature, water, a silicon source, a structure-directing agent, a secondary active metal salt, and a chelating agent are thoroughly stirred and mixed to obtain a uniform gel solution. The solution is then placed in a polytetrafluoroethylene liner and hydrothermally crystallized at 100-200°C for 1-196 hours. The solution is then filtered, dried at 50-150°C for 1-20 hours, and calcined at 450-650°C for 1-20 hours to obtain M@ molecular sieve with large crystal size.

[0036] (2) Synthesis of Pt / M@ molecular sieve catalyst

[0037] Under vacuum conditions, the prepared M@ molecular sieve was heated at 100-500 °C for 1-20 h, then impregnated with an organic solution containing a Pt metal organic compound. The mixture was then filtered, washed, and dried, and reduced at 100-700 °C for 1-20 h in a H2 atmosphere to obtain a bimetallic Pt / M@ molecular sieve catalyst.

[0038] The molar ratio of the silicon source, water, structure directing agent, secondary active metal salt and chelating agent is 1:(0.01-1):(1-10):(0.00001-0.01):(0.01-1).

[0039] The silicon source is any one or more of solid silica gel, water glass, tetraethyl orthosilicate, white carbon black, and silica sol. The structure-directing agent is any one or more of tetrapropylammonium hydroxide, tetramethylammonium bromide, tetrabutylammonium bromide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, tetraethylammonium bromide, and tetrapropylammonium bromide. When Sn is used as the secondary active metal, the secondary active metal salt used is any one or more of SnCl2·2H2O and SnCl4; when Ga is used as the secondary active metal, the secondary active metal salt used is any one or more of GaCl3, Ga2Cl4, and Ga(NO3)3·xH2O; when Zn is used as the secondary active metal, the secondary active metal salt used is any one or more of ZnCl2 and Zn(NO3)2·6H2O. The chelating agent is any one or more of HF, HCl, HBr, and HI.

[0040] The Pt metal organic compound is any one or more of Pt(COD)(Me)2, Pt(COD)Cl2, and Pt(HACAC)2.

[0041] The loading amount of the secondary active metal component in the obtained catalyst is 0.10-10.0 wt%; the particle size of the nanoclusters is 0.40-0.80 nm, and the loading amount thereof is 0.10-10.0 wt%.

[0042] In order to make the contents of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0043] Unless otherwise specified, the chemicals used in the following examples were purchased commercially and were not processed. Tetraethyl orthosilicate (TEOS), tetrapropylammonium hydroxide (TPAOH), (1,5-cyclooctadiene)dimethylplatinum (Pt(COD)(Me)2), tin tetrachloride (SnCl4), gallium chloride (GaCl3), zinc chloride (ZnCl2), ethylenediamine (NH2CH2CH2NH2), HF, HCl, HBr, and HI were all purchased from Aladdin Reagent Co., Ltd. Deionized water used in the experiments was obtained from the laboratory's high-purity water system.

[0044] The catalysts in the comparative examples and examples are named Pt / Sn@S-1(x), where Pt represents the primary active component, approximately 0.30 wt.%, S represents the secondary active component, approximately 0.50 wt.%, and x represents the shortest axis size of the molecular sieve crystals (μm). For example, an S-1 molecular sieve catalyst with a shortest axis size of 2.00 μm is named Pt / Sn@S-1(2.00).

[0045] Comparative Example (without adding chelating agent)

[0046] At room temperature, 16.2 g of TEOS, 16.6 g of TPAOH, and 9.3 g of deionized water were weighed into a beaker and stirred for 5 h. After complete hydrolysis, a homogeneous solution was obtained. 55.2 mg of SnCl4 was then weighed and dissolved in the homogeneous solution. Stirring was continued for 1 h to form a mixed solution. The mixed solution was then loaded into the polytetrafluoroethylene lining of a stainless steel crystallization kettle. The stainless steel crystallization kettle was placed in an oven, heated from room temperature to 175 °C, and maintained for static hydrothermal crystallization for 120 h. After the crystallization was completed, the mixture was cooled, centrifuged, washed, dried at 110 °C for 14 h, and calcined at 600 °C for 5 h to obtain small-grain Sn@S-1(0.10) molecular sieve.

[0047] 1.0 g of Sn@S-1(0.10) molecular sieve was weighed and placed in a vacuum box, heat treated at 270 °C and maintained for 12 h; then an organic solution containing 5.2 mg of Pt(COD)(Me)2 was added and impregnated for 1 h. The mixture was then filtered, washed, dried, and reduced in a hydrogen atmosphere at 200 °C for 4 h to finally obtain small-grain Pt / Sn@S-1(0.10) molecular sieve.

[0048] Example 1

[0049] At room temperature, 16.2 g of TEOS, 16.6 g of TPAOH, and 9.3 g of deionized water were weighed into a beaker and stirred for 5 h to obtain a homogeneous solution after complete hydrolysis. 56.2 mg of SnCl4 was then weighed and dissolved in the homogeneous solution and stirred for 1 h to form a mixed solution. The mixed solution was then placed in the polytetrafluoroethylene liner of a stainless steel crystallization kettle, and 0.42 g of HBr was added and stirred for 2 h to form a gel-like solid mixture. Finally, the stainless steel crystallization kettle was placed in an oven, heated from room temperature to 175 °C, and maintained for static hydrothermal crystallization for 120 h. After the crystallization was completed, the mixture was cooled, centrifuged, washed, dried at 110 °C for 14 h, and calcined at 600 °C for 5 h to obtain large-grain Sn@S-1(1.00) molecular sieve.

[0050] 1.0 g of Sn@S-1(1.00) molecular sieve was weighed and placed in a vacuum box, heat treated at 270 °C and maintained for 12 h; then an organic solution containing 5.2 mg of Pt(COD)(Me)2 was added and impregnated for 1 h. The mixture was then filtered, washed, dried, and reduced in a hydrogen atmosphere at 200 °C for 4 h to finally obtain Pt / Sn@S-1(1.00) molecular sieve.

[0051] Example 2

[0052] At room temperature, 16.7 g TEOS, 16.9 g TPAOH, and 9.2 g deionized water were weighed into a beaker and stirred for 5 h to obtain a homogeneous solution after complete hydrolysis. 56.4 mg SnCl4 was then weighed and dissolved in the homogeneous solution and stirred for 1 h to form a mixed solution. The mixed solution was then placed in the polytetrafluoroethylene liner of a stainless steel crystallization kettle, and 0.64 g HBr was added and stirred for 2 h to form a gel-like solid mixture. Finally, the stainless steel crystallization kettle was placed in an oven, heated from room temperature to 175 °C, and maintained for static hydrothermal crystallization for 120 h. After the crystallization was completed, the mixture was cooled, centrifuged, washed, dried at 100 °C for 12 h, and calcined at 600 °C for 4 h to obtain large-grain Sn@S-1(2.00) molecular sieve.

[0053] 1.0 g of Sn@S-1(2.00) molecular sieve was weighed and placed in a vacuum box, heat treated at 260 °C and maintained for 12 h; then an organic solution containing 5.7 mg of Pt(COD)(Me)2 was added and impregnated for 1 h. The mixture was then filtered, washed, dried, and reduced in a hydrogen atmosphere at 200 °C for 4 h to finally obtain Pt / Sn@S-1(2.00) molecular sieve.

[0054] Example 3

[0055] At room temperature, 16.5 g of TEOS, 16.9 g of TPAOH, and 9.4 g of deionized water were weighed into a beaker and stirred for 5 h to obtain a homogeneous solution after complete hydrolysis. 66.7 mg of GaCl3 was then weighed and dissolved in the homogeneous solution and stirred for 1 h to form a mixed solution. The mixed solution was then placed in the polytetrafluoroethylene liner of a stainless steel crystallization kettle, and 0.81 g of HBr was added and stirred for 2.5 h to form a gel-like solid mixture. Finally, the stainless steel crystallization kettle was placed in an oven, heated from room temperature to 175 °C, and maintained for static hydrothermal crystallization for 130 h. After the crystallization was completed, the mixture was cooled, centrifuged, washed, dried at 100 °C for 12 h, and calcined at 600 °C for 4 h to obtain large-grain Sn@S-1(3.00) molecular sieve.

[0056] 1.0 g of Sn@S-1(3.00) molecular sieve was weighed and placed in a vacuum box, heat treated at 280 °C and maintained for 12 h; then an organic solution containing 5.4 mg of Pt(COD)(Me)2 was added and impregnated for 1 h. The mixture was then filtered, washed, dried, and reduced in a hydrogen atmosphere at 200 °C for 4 h to finally obtain Pt / Sn@S-1(3.00) molecular sieve.

[0057] Example 4

[0058] At room temperature, 16.4 g TEOS, 16.8 g TPAOH, and 9.4 g deionized water were weighed into a beaker and stirred for 5 h to obtain a homogeneous solution after complete hydrolysis. 58.4 mg SnCl4 was then weighed and dissolved in the homogeneous solution and stirred for 2 h to form a mixed solution. The mixed solution was then placed in the polytetrafluoroethylene liner of a stainless steel crystallization kettle, and 0.95 g HBr was added and stirred for 2 h to form a gel-like solid mixture. Finally, the stainless steel crystallization kettle was placed in an oven, heated from room temperature to 175 °C, and maintained for static hydrothermal crystallization for 110 h. After the crystallization was completed, the mixture was cooled, centrifuged, washed, dried at 100 °C for 12 h, and calcined at 600 °C for 4 h to obtain large-grain Sn@S-1(5.00) molecular sieve.

[0059] 1.0 g of Sn@S-1(5.00) molecular sieve was weighed and placed in a vacuum box, heat treated at 260 °C and maintained for 12 h; then an organic solution containing 4.95 mg of Pt(COD)(Me)2 was added and impregnated for 1 h, and then filtered, washed, dried, and reduced in a hydrogen atmosphere at 200 °C for 4 h to finally obtain Pt / Sn@S-1(5.00) molecular sieve.

[0060] Example 5

[0061] At room temperature, 16.2 g of TEOS, 16.6 g of TPAOH, and 9.3 g of deionized water were weighed into a beaker and stirred for 5 h to obtain a homogeneous solution after complete hydrolysis. 56.2 mg of SnCl4 was then weighed and dissolved in the homogeneous solution and stirred for 1 h to form a mixed solution. The mixed solution was then placed in the polytetrafluoroethylene liner of a stainless steel crystallization kettle, and 0.95 g of HI was added and stirred for 2 h to form a gel-like solid mixture. Finally, the stainless steel crystallization kettle was placed in an oven, heated from room temperature to 175 °C, and maintained for static hydrothermal crystallization for 120 h. After the crystallization was completed, the mixture was cooled, centrifuged, washed, dried at 110 °C for 14 h, and calcined at 600 °C for 5 h to obtain large-grain Sn@ZSM-11 (5.00) molecular sieve.

[0062] 1.0 g of Sn@ZSM-11(1.00) molecular sieve was weighed and placed in a vacuum oven, heat treated at 270 °C and maintained for 12 h; then an organic solution containing 5.2 mg of Pt(COD)(Me)2 was added and impregnated for 1 h. The mixture was then filtered, washed, dried, and reduced in a hydrogen atmosphere at 200 °C for 4 h to finally obtain Pt / Sn@ZSM-11(5.00) molecular sieve.

[0063] Example 6

[0064] At room temperature, 16.4 g of TEOS, 16.8 g of TPAOH, and 9.4 g of deionized water were weighed into a beaker and stirred for 5 h to obtain a homogeneous solution after complete hydrolysis. 58.4 mg of SnCl4 was then weighed and dissolved in the homogeneous solution and stirred for another 2 h to form a mixed solution. The mixed solution was then placed into the polytetrafluoroethylene liner of a stainless steel crystallization kettle, and 0.95 g of HF was added and stirred for 2 h to form a gel-like solid mixture. Finally, the stainless steel crystallization kettle was placed in an oven, heated from room temperature to 175 °C, and maintained for static hydrothermal crystallization for 110 h. After the crystallization was completed, the mixture was cooled, centrifuged, washed, dried at 100 °C for 12 h, and calcined at 600 °C for 4 h to obtain large-grain Sn@Beta(5.00) molecular sieve.

[0065] 1.0 g of Sn@Beta(5.00) molecular sieve was weighed and placed in a vacuum box, heat treated at 260 °C and maintained for 12 h; then an organic solution containing 4.95 mg of Pt(COD)(Me)2 was added and impregnated for 1 h. The mixture was then filtered, washed, dried, and reduced in a hydrogen atmosphere at 200 °C for 4 h to finally obtain Pt / Sn@Beta(5.00) molecular sieve.

[0066] Example 7

[0067] At room temperature, 16.7 g TEOS, 16.9 g TPAOH, and 9.2 g deionized water were weighed into a beaker and stirred for 5 h to obtain a homogeneous solution after complete hydrolysis. 56.9 mg ZnCl2 was then weighed and dissolved in the homogeneous solution and stirred for 1 h to form a mixed solution. The mixed solution was then placed in the polytetrafluoroethylene liner of a stainless steel crystallization kettle, and 0.95 g HBr was added and stirred for 2 h to form a gel-like solid mixture. Finally, the stainless steel crystallization kettle was placed in an oven, heated from room temperature to 175 °C, and maintained for static hydrothermal crystallization for 120 h. After the crystallization was completed, the mixture was cooled, centrifuged, washed, dried at 100 °C for 12 h, and calcined at 600 °C for 4 h to obtain large-grain Zn@S-1(5.00) molecular sieve.

[0068] 1.0 g of Zn@S-1(2.00) molecular sieve was weighed and placed in a vacuum box, heat treated at 260 °C and maintained for 12 h; then an organic solution containing 5.7 mg of Pt(COD)(Me)2 was added and impregnated for 1 h. The mixture was then filtered, washed, dried, and reduced in a hydrogen atmosphere at 200 °C for 4 h to finally obtain Pt / Zn@S-1(5.00) molecular sieve.

[0069] Example 8

[0070] At room temperature, 16.5 g of TEOS, 16.9 g of TPAOH, and 9.4 g of deionized water were weighed into a beaker and stirred for 5 h to obtain a homogeneous solution after complete hydrolysis. 66.7 mg of GaCl3 was then weighed and dissolved in the homogeneous solution and stirred for 1 h to form a mixed solution. The mixed solution was then placed in the polytetrafluoroethylene liner of a stainless steel crystallization kettle, and 0.95 g of HBr was added and stirred for 2.5 h to form a gel-like solid mixture. Finally, the stainless steel crystallization kettle was placed in an oven, heated from room temperature to 175 °C, and maintained for static hydrothermal crystallization for 130 h. After the crystallization was completed, the mixture was cooled, centrifuged, washed, dried at 100 °C for 12 h, and calcined at 600 °C for 4 h to obtain large-grain Ga@S-1(5.00) molecular sieve.

[0071] 1.0 g of Ga@S-1(5.00) molecular sieve was weighed and placed in a vacuum box, heat treated at 280 °C and maintained for 12 h; then an organic solution containing 5.4 mg of Pt(COD)(Me)2 was added and impregnated for 1 h, and then filtered, washed, dried, and reduced in a hydrogen atmosphere at 200 °C for 4 h to finally obtain Pt / Ga@S-1(5.00) molecular sieve.

[0072] Figure 1-5 The SEM images of the Pt-based molecular sieve catalysts prepared in the comparative example and Examples 1 to 4 are shown. As can be seen from the figure, by changing the amount of chelating agent HBr, the length of the shortest crystallite of the molecular sieve can be adjusted to obtain M@ molecular sieves with different crystallite lengths.

[0073] Figure 6 This is the STEM image of the Pt / Sn@S-1(5.00) catalyst prepared in Example 4. As can be seen from the figure, the size of the PtSn nanoclusters in the catalyst is about 0.66 nm.

[0074] 0.3 g of the Pt / Sn@S-1 catalyst (20-40 mesh) prepared in the comparative example and the example was loaded into a 6 mm quartz tube fixed bed reactor, and propane was used as the reactant at a WHSV of 7 h. -1 The mass space velocity was 1.5 wt % and the reaction was carried out at 600 ℃ and normal pressure. The results are shown in Table 1.

[0075] Table 1 Comparison of catalytic performance of different Pt / M@S-1 catalysts

[0076]

[0077] As can be seen from the results in Table 1, the stability of the catalyst obtained in the examples is significantly improved compared to the comparative examples, and the catalyst maintains excellent comprehensive catalytic performance under high temperature conditions, with essentially no deactivation of the catalyst. A comparison of Examples 1-4 shows that increasing the amount of chelating agent HBr can increase the shortest crystal axis size of the catalyst; and a comparison of Examples 4-8 shows that, under conditions of the same shortest crystal axis size, catalysts prepared using different types of metal as secondary active metal components or using different types of molecular sieves all exhibit strong stability. This demonstrates that increasing the size of the catalyst's shortest crystal axis can fundamentally stabilize the migration of Pt-based nanoclusters in the catalyst, avoiding high-temperature sintering, and obtaining a Pt-based catalyst with excellent comprehensive catalytic performance for propane dehydrogenation and high-temperature stability.

[0078] Figure 7 This figure shows the catalytic activity of the Pt / Sn@S-1(5.00) catalyst prepared in Example 4 for six consecutive months of propane dehydrogenation. As can be seen from the figure, the propane conversion rate of the catalyst barely decreases after the long propane dehydrogenation reaction, further demonstrating the excellent stability of the catalyst with a long crystal axis size.

[0079] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a bimetallic Pt-based molecular sieve catalyst for the efficient dehydrogenation of light alkanes to olefins. The catalyst comprises a large-crystal molecular sieve doped with a secondary active metal component, M, to form an M@ molecular sieve, and a primary active metal component, Pt, anchored to the molecular sieve framework in the form of nanoclusters. The catalyst is characterized by: The following steps are involved: (1) Preparation of M@ molecular sieve Under room temperature, water, silicon source, structure-directing agent, secondary active metal salt and chelating agent are fully stirred and mixed to obtain a uniform gel solution. The solution is then placed in a polytetrafluoroethylene liner and subjected to hydrothermal crystallization at a certain temperature and time. The solution is then filtered, dried and calcined to obtain the M@ molecular sieve. (2) Synthesis of Pt / M@ molecular sieve catalyst Under vacuum conditions, the prepared M@ molecular sieve is heated and then impregnated with an organic solution containing a Pt metal organic compound, followed by filtration, washing, drying, and reduction to obtain the bimetallic Pt-based molecular sieve catalyst; The secondary active metal component M is specifically any one or more of Sn, Ga, and Zn, and its loading amount is 0.10-10.0 wt%; the molecular sieve is any one of S-1 molecular sieve, Beta molecular sieve, and ZSM-11 molecular sieve, and its shortest crystal axis length is 1.00-5.00 μm; the particle size of the nanocluster is 0.40-0.80 nm, and its loading amount is 0.10-10.0 wt%; The chelating agent is any one or more of HF, HCl, HBr, and HI.

2. The method for preparing a bimetallic Pt-based molecular sieve catalyst according to claim 1, wherein: The molar ratio of the silicon source, water, structure directing agent, secondary active metal salt and chelating agent is 1:(0.01-1):(1-10):(0.00001-0.01):(0.01-1).

3. The method for preparing a bimetallic Pt-based molecular sieve catalyst according to claim 1 or 2, characterized in that: The silicon source is any one or more of solid silica gel, water glass, ethyl orthosilicate, white carbon black, and silica sol; The structure directing agent is any one or more of tetrapropylammonium hydroxide, tetramethylammonium bromide, tetrabutylammonium bromide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, tetraethylammonium bromide, and tetrapropylammonium bromide; When Sn is used as the secondary active metal, the secondary active metal salt used is any one or more of SnCl2·2H2O and SnCl4; when Ga is used as the secondary active metal, the secondary active metal salt used is any one or more of GaCl3, Ga2Cl4, and Ga(NO3)3·xH2O; when Zn is used as the secondary active metal, the secondary active metal salt used is any one or more of ZnCl2 and Zn(NO3)2·6H2O.

4. The method for preparing a bimetallic Pt-based molecular sieve catalyst according to claim 1, wherein: The hydrothermal crystallization temperature in step (1) is 100-200°C and the time is 1-196 h; The drying temperature is 50-150°C and the drying time is 1-20 hours; The calcination temperature is 450-650° C., and the calcination time is 1-20 h.

5. The method for preparing a bimetallic Pt-based molecular sieve catalyst according to claim 1, wherein: The Pt metal organic compound in step (2) is any one or more of Pt(COD)(Me)2, Pt(COD)Cl2, and Pt(HACAC)2; The heating treatment temperature is 100-500°C and the time is 1-20 h; The reduction is carried out in a H2 atmosphere at 100-700°C for 1-20 h.

Images