High-performance pt-based molecular sieve catalyst for dehydrogenation of low-carbon alkanes to olefins

Abstract

The application discloses a high-performance Pt-based molecular sieve catalyst for dehydrogenation of low-carbon alkanes to olefins and a preparation method and application thereof. The catalyst is mainly composed of a large single-crystal molecular sieve carrier, a main active component and a secondary active component. The b-axis length of the large single-crystal molecular sieve carrier is 1.20-4.50 microns. The main active component is Pt clusters with a particle size of 0.55-0.75 nm. The secondary active component is any one or several of Cu, Ga, Zn and Sn. The application controls the grain size of the molecular sieve by adding a certain amount of hydrogen halide acid in the crystallization process of the molecular sieve, and makes the formed Pt sub-nanometer clusters encapsulated in the micropores of the molecular sieve. The obtained catalyst is applied to the propane dehydrogenation reaction, shows high selectivity (more than 98%), and the catalyst is not deactivated after running for 6 months, thereby providing a new technical approach for developing a propane dehydrogenation fixed bed process with low energy consumption, low operation cost and no need for frequent regeneration.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of industrial catalyst preparation, and particularly relates to a high-performance Pt-based molecular sieve catalyst for dehydrogenation of low-carbon alkanes to olefins, and a preparation method and application thereof. BACKGROUND

[0002] Currently, compared with the traditional propylene production method, propane dehydrogenation (PDH) has become a highly competitive propylene production route. In the past decade, although the propylene production capacity has increased to a great extent worldwide, China's propane dehydrogenation to propylene device is still under construction and regulation, and the weak supply and demand relationship of propylene has not been balanced. With the discovery and successful development of shale gas around the world, it provides a cheap, sufficient and stable source of raw materials for propane dehydrogenation to propylene. However, the existing Pt-based catalysts generally have the disadvantages of high reaction temperature (>600 ℃), low single-pass conversion rate of propane, easy sintering and deactivation of the catalyst, frequent regeneration and complex regeneration process. Therefore, it is urgent to develop a new generation of high-performance propane dehydrogenation Pt-based catalyst.

[0003] Industrial catalysts use Al2O3 as the carrier of Pt-based catalysts, but such open carriers will undergo migration sintering and Orowan ripening at high temperatures, causing Pt nanoparticles to agglomerate and sinter, which requires frequent regeneration by oxygen-chlorine treatment of the moving bed process, not only consuming energy but also emitting a large amount of corrosive and harmful HCl and Cl2 gas. Encapsulating Pt nanoparticles in the ordered micropores of molecular sieves can greatly improve their thermal stability. Chinese Patent CN 110479353 A and Angew. Chem. Int. Ed., 2020, 59, 19450-19459、 J Catal., 2020, 385, 61-69 all reported the in-situ synthesis of sub-nanometer PtZn clusters in pure-silica MFI molecular sieves, and the encapsulation of the sub-nanometer clusters in the micropores of the molecular sieves. The catalyst showed good propane dehydrogenation catalytic performance, and its stability at high temperature was significantly improved compared with the Pt / Al2O3 catalyst used in industry. However, during the long-term reaction process, the Pt clusters can still migrate out of the pores of the molecular sieves and agglomerate on the surface of the molecular sieve crystals, leading to irreversible deactivation of the catalyst. Therefore, the Pt@molecular sieve catalyst is still difficult to meet the demand for catalytic performance of propane dehydrogenation to propylene in a fixed bed process.

[0004] In view of the above problems of the Pt@molecular sieve catalyst, the present application provides a Pt-based molecular sieve catalyst suitable for a fixed bed process, which adds an appropriate amount of hydrogen halide as an additive to control the grain size of the in-situ synthesized Pt-based molecular sieve catalyst, and for the first time proposes to encapsulate Pt sub-nanometer particles with different particle sizes in molecular sieves, thereby obtaining a high-stability propane dehydrogenation catalyst. SUMMARY

[0005] The present application is to solve the problem that Pt-based catalysts for dehydrogenation of low-carbon alkanes to olefins are prone to migration and sintering under high-temperature conditions, forming larger Pt nanoparticles and causing permanent deactivation of the Pt-based catalysts, and to provide a high-performance Pt-based molecular sieve catalyst for dehydrogenation of low-carbon alkanes to olefins, as well as a preparation method and application thereof. The catalyst uses an in-situ encapsulation method to encapsulate ultra-small Pt sub-nanoparticles in the micropore channels of the molecular sieve, so that the resulting catalyst has high propane conversion rate and high propylene selectivity, and exhibits excellent catalytic stability at high temperatures.

[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0007] A high-performance Pt-based molecular sieve catalyst for dehydrogenation of low-carbon alkanes to olefins, which is composed of a large single-crystal molecular sieve carrier, a main active component and a secondary active component, wherein the b-axis length of the large single-crystal molecular sieve carrier is 1.20-4.50 μm; the main active component is a Pt sub-nanocluster with a particle size of 0.55-0.75 nm; and the secondary active component is any one or several of Cu, Ga, Zn and Sn.

[0008] The loading amount of the main active component is 0.01-5.00 wt%, and the loading amount of the secondary active component is 0.01-5.00 wt%.

[0009] The preparation method of the high-performance Pt-based molecular sieve catalyst comprises the following steps:

[0010] (1) Under certain temperature conditions, a silicon source, a template agent, water, a Pt metal complex providing the main active component and a metal compound providing the secondary active component are fully stirred and mixed to obtain a uniform solution;

[0011] (2) The uniform solution obtained in step (1) is transferred to a polytetrafluoroethylene lining of a stainless steel crystallization kettle, a certain amount of hydrogen halide acid is added, and the mixture is fully stirred to obtain a uniform gel-like mixture;

[0012] (3) The gel-like mixture obtained in step (2) is statically hydrothermally crystallized at a certain temperature for a period of time, and then filtered, washed and dried to obtain a Pt-based compound molecular sieve catalyst precursor, which is finally reduced by H2 to obtain the high-performance Pt-based molecular sieve catalyst.

[0013] The molar ratio of the silicon source to the template agent, water, the Pt metal complex, the metal compound and the hydrogen halide acid is 1:(1-10):(0.01-1):(0.00001-0.01):(0.00001-0.01):(0.01-1).

[0014] Further, the silicon source is any one or several of tetraethyl orthosilicate, white carbon black, silica sol, water glass, and solid silica gel.

[0015] Further, the template agent is any one or several of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide, and tetrabutylammonium bromide.

[0016] Further, the Pt metal complex is composed of a Pt compound and an organic complex in a molar ratio of 1:2, wherein the Pt compound is any one or several of Pt(NH3)4(OH)2, Pt(NH3)4Cl2·H2O, Pt(NH3)4Cl2, [Pt(NH3)4](NO3)2, H2PtCl6·6H2O, PtCl2, and PtCl4; and the organic complex is any one or several of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine.

[0017] Further, when Cu is used as the secondary active component, the metal compound is any one or several of CuCl2·2H2O, CuCl2, and (NH4)2CuCl4·2H2O; when Ga is used as the secondary active component, the metal compound is any one or several of GaCl3, Ga2Cl4, and Ga(NO3)3·xH2O; when Zn is used as the secondary active component, the metal compound is any one or several of ZnCl2 and Zn(NO3)2·6H2O; and when Sn is used as the secondary active component, the metal compound is any one or several of SnCl2·2H2O and SnCl4.

[0018] Further, the hydrogen halide is any one or several of HCl, HBr, and HI.

[0019] Further, the temperature used in step (1) is 25-100 ℃.

[0020] Further, the temperature for the crystallization in step (3) is 100-200 ℃, and the time is 1-200 h.

[0021] Further, the temperature for the drying in step (3) is 60-180 ℃, and the time is 2-24 h.

[0022] Further, the temperature for the reduction in step (3) is 100-900 ℃, and the time is 2-24 h.

[0023] The b-axis size of the obtained Pt-based molecular sieve catalyst is 1.20-4.50 μm.

[0024] The high-performance Pt-based molecular sieve catalyst is suitable for dehydrogenation of low-carbon alkanes to olefins in a fixed bed reactor, and the specific application steps are as follows:

[0025] (1) The high-performance Pt-based molecular sieve catalyst is uniformly mixed with quartz sand and then filled in a quartz tube fixed bed reactor with an outer diameter of 12 mm, and the catalyst is ensured to be in the constant temperature zone of the heating furnace of the fixed bed reactor;

[0026] (2) Hydrogen is first introduced for pretreatment, then the temperature is lowered to room temperature, then the temperature is raised to the reaction temperature at a rate of 2 ℃ / min, and a certain amount of pure low-carbon alkane is introduced for catalytic dehydrogenation reaction.

[0027] Further, in step (1), the mass ratio of the high-performance Pt-based molecular sieve catalyst to quartz sand is 1:4, and the filling amount of the mixture in the quartz tube fixed bed reactor is 5-30 g.

[0028] Further, in step (2), the pretreatment temperature is 100-500 ℃, and the time is 1-10 h.

[0029] Further, in step (2), the reaction temperature is 500-700 ℃.

[0030] Further, in step (2), the mass space velocity of the introduced pure low-carbon alkane is 10-400 h -1 .

[0031] The applicant found in the research that in high-temperature reaction, Pt clusters can migrate in the pores of the molecular sieve, and then compete with surface aggregation and pore aggregation. When the size of the b-axis of the molecular sieve single crystal is less than 1.20 μm, the Pt clusters will diffuse and migrate to the outer surface of the molecular sieve and aggregate, eventually leading to irreversible sintering deactivation of the catalyst, so that the stability of the obtained catalyst is poor; when the size of the b-axis of the molecular sieve single crystal is greater than 1.20 μm, the Pt clusters will aggregate when migrating in the pores, forming a lock in the pores of the molecular sieve, and the Pt clusters have very high thermal stability, so that the stability of the obtained propane dehydrogenation catalyst is high.

[0032] According to the in-situ synthesis route, a certain amount of hydrogen halide is added during crystallization to form a gel complex with the silicon source, so that a large grain size Pt-based molecular sieve catalyst is first prepared. The sub-nanometer Pt clusters in the catalyst can still exist stably in the pores of the molecular sieve after high-temperature long-time reaction, so that the high-temperature catalytic performance and long-time stability of the Pt-based nanoclusters can be greatly improved, and the catalyst has great practical industrial application prospect.

[0033] The Pt-based molecular sieve catalyst of the present application exhibits excellent catalytic activity and long-time stability in high-temperature propane dehydrogenation reaction. In particular, in the propane dehydrogenation reaction, the initial propane conversion rate of the Pt-based molecular sieve catalyst with different b-axis length is about 45% at 600 DEG C, and after 30 days of reaction, the propane conversion rate of the Pt-based molecular sieve catalyst with large grain size is in a very stable trend, and the carbon deposition amount is very small through the thermal analyzer test, indicating that the Pt-based molecular sieve catalyst with large grain size not only has the anti-sintering performance for long-time reaction, but also has the long-time anti-carbon deposition performance.

[0034] The present application has the beneficial effects that: the Pt-based molecular sieve catalyst with different b-axis length is synthesized in situ, wherein the sub-nano Pt clusters in the Pt-based molecular sieve catalyst with small grain size are sintered and aggregated at high temperature, causing permanent deactivation, and the sub-nano Pt clusters existing in the Pt-based molecular sieve catalyst with large grain size can still stably exist in the pore of the molecular sieve at high temperature for a long time. Based on the size effect of the molecular sieve itself, the present application not only improves the dispersion and utilization rate of the Pt active component, but most importantly, enhances the high-temperature stability of the sub-nano Pt clusters of the active component, greatly hinders the sintering and aggregation of the Pt nano clusters, and exhibits excellent catalytic performance and super-long high-temperature catalytic life when applied to the propane dehydrogenation reaction, which is far superior to the Pt-based catalysts reported so far. Therefore, the Pt-based molecular sieve with large grain size prepared by the present application has high conversion rate, high selectivity and high-temperature long-time stability, and provides a new route for preparing efficient and stable propane dehydrogenation molecular sieve catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 SEM image of the Pt-Sn@S-1(0.10) catalyst obtained for the comparative example.

[0036] Figure 2 SEM image of the Pt-Sn@S-1(0.50) catalyst obtained for example 1.

[0037] Figure 3 SEM image of the Pt-Sn@S-1(1.20) catalyst obtained for example 2.

[0038] Figure 4 SEM image of the Pt-Sn@S-1(2.50) catalyst obtained for example 3.

[0039] Figure 5 SEM image of the Pt-Sn@S-1(3.50) catalyst obtained for example 4.

[0040] Figure 6 SEM image of the Pt-Sn@S-1(4.50) catalyst obtained for example 5.

[0041] Figure 7 STEM image of Pt-Sn@S-1(4.50) catalyst obtained in Example 5.

[0042] Figure 8 Catalytic activity chart of Pt-Sn@S-1(4.50) catalyst obtained in Example 5 for propane dehydrogenation for 6 consecutive months. DETAILED DESCRIPTION

[0043] A high-performance Pt-based@molecular sieve catalyst for dehydrogenation of low-carbon alkanes to olefins, which is composed of a large single-crystal molecular sieve carrier, a main active component and a secondary active component, wherein the b-axis length of the large single-crystal molecular sieve carrier is 1.20-4.50 μm; the main active component is Pt sub-nanocluster with a particle size of 0.55-0.75 nm; and the secondary active component is any one or several of Cu, Ga, Zn and Sn.

[0044] The loading amount of the main active component is 0.01-5.00 wt%, and the loading amount of the secondary active component is 0.01-5.00 wt%.

[0045] The preparation method of the high-performance Pt-based@molecular sieve catalyst comprises the following steps:

[0046] (1) at 25-100 ℃, the silicon source, the template agent, the water, the Pt metal complex providing the main active component and the metal compound providing the secondary active component are fully stirred and mixed to obtain a uniform solution;

[0047] (2) the uniform solution obtained in step (1) is transferred to the polytetrafluoroethylene lining of the stainless steel crystallization kettle, a certain amount of hydrogen halide acid is added, and the mixture is fully stirred to obtain a uniform gel-like mixture;

[0048] (3) the gel-like mixture obtained in step (2) is statically hydrothermally crystallized at 100-200 ℃ for 1-200 h, and then filtered, washed, dried at 60-180 ℃ for 2-24 h to obtain a Pt-based compound@molecular sieve catalyst precursor, and finally reduced by H2 at 100-900 ℃ for 2-24 h to obtain a Pt-based@molecular sieve catalyst with a larger crystal size.

[0049] The molar ratio of the silicon source to the template agent, water, Pt metal complex, metal compound and hydrogen halide acid is 1:(1-10):(0.01-1):(0.00001-0.01):(0.00001-0.01):(0.01-1).

[0050] The silicon source is any one or several of tetraethyl orthosilicate, white carbon black, silica sol, water glass, and solid silica gel. The template agent is any one or several of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide, and tetrabutylammonium bromide. The Pt metal complex is composed of a Pt compound and an organic complex in a molar ratio of 1:2, wherein the Pt compound is any one or several of Pt(NH3)4(OH)2, Pt(NH3)4Cl2·H2O, Pt(NH3)4Cl2, [Pt(NH3)4](NO3)2, H2PtCl6·6H2O, PtCl2, and PtCl4; and the organic complex is any one or several of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine. When Cu is used as a secondary active component, the metal compound is any one or several of CuCl2·2H2O, CuCl2, and (NH4)2CuCl4·2H2O; when Ga is used as a secondary active component, the metal compound is any one or several of GaCl3, Ga2Cl4, and Ga(NO3)3·xH2O; when Zn is used as a secondary active component, the metal compound is any one or several of ZnCl2 and Zn(NO3)2·6H2O; and when Sn is used as a secondary active component, the metal compound is any one or several of SnCl2·2H2O and SnCl4. The hydrogen halide is any one or several of HCl, HBr, and HI.

[0051] In order to make the content of the present application more convenient to understand, the technical solutions of the present application are further described below in combination with specific embodiments, but the present application is not limited thereto.

[0052] The medicines used in the examples are all purchased through commercial channels and are not treated, unless otherwise specified. Among them, tetraethyl orthosilicate (TEOS), tetrapropylammonium hydroxide (TPAOH), stannous chloride dihydrate (SnCl2·2H2O), chloroplatinic acid hexahydrate (H2PtCl6·6H2O), platinum tetrachloride (PtCl4), zinc chloride (ZnCl2), gallium chloride (GaCl3), ethylenediamine (NH2CH2CH2NH2), hydrochloric acid (HCl), hydrogen bromide (HBr), and hydrogen iodide (HI) are all purchased from Aladdin Reagent Co., Ltd. The deionized water used in the experimental process is obtained from a high-purity water machine system in the laboratory.

[0053] The catalyst in the example is named as Pt-x@S-1 (y), wherein Pt represents the main active component, the content of which is 0.3 wt.%; x represents the secondary active component, the content of which is 0.5 wt.%; S-1 represents Silicalite-1 molecular sieve; y represents the length of the b axis of the crystal grain in the Silicalite-1 molecular sieve (μm). For example, the single crystal b axis length of the Pt-Sn@S-1 molecular sieve catalyst is 3.00 μm, and the catalyst is named as Pt-Sn@S-1 (3.00).

[0054] Comparative example (without adding hydrohalic acid)

[0055] (1) 16.2 g of TEOS was weighed and dissolved in 7.6 g of deionized water, and stirred in a water bath at 25 °C for 6.1 h to completely hydrolyze and obtain a uniform solution;

[0056] (2) 15.6 g of TPAOH solution was weighed and added to the uniform solution of step (1), and continued to be stirred for 2.3 h to obtain a uniform mixed solution;

[0057] (3) 40.1 mg of H2PtCl6·6H2O was weighed and dissolved in 2.0 g of deionized water, and a uniform solution was formed after stirring in a water bath at 30 °C for 1 h, then 0.5 mL of ethylenediamine was slowly added and continued to be stirred for 2.1 h to obtain a uniform solution containing Pt organic amine complex;

[0058] (4) 35.2 mg of SnCl2·2H2O was weighed and dissolved in 2.3 g of deionized water, and a uniform solution was formed after stirring in a water bath at 30 °C for 1 h;

[0059] (5) The solutions obtained in steps (2), (3), and (4) were mixed, and continued to be stirred for 2.2 h to form a uniform mixed solution, which was then loaded into the polytetrafluoroethylene inner liner of a stainless steel crystallization kettle;

[0060] (6) The stainless steel crystallization kettle was placed in an oven, and the temperature was increased from room temperature to 170 °C and kept static hydrothermal crystallization for 2 days. After the crystallization was completed, the catalyst powder precursor was obtained after cooling, centrifugation, washing, and drying at 100 °C for 12 h;

[0061] (7) The obtained catalyst powder precursor was placed in a tube furnace, and the temperature was increased to 600 °C at a rate of 2 °C / min in a high-purity H2 atmosphere and reduced for 5 h to finally obtain the Pt-Sn@S-1 (0.10) catalyst.

[0062] Example 1

[0063] (1) 16.2 g of TEOS was weighed and dissolved in 7.6 g of deionized water, and stirred in a water bath at 25 °C for 6.1 h to completely hydrolyze and obtain a uniform solution;

[0064] (2) 15.6 g of TPAOH solution was weighed and added to the uniform solution of step (1), and stirring was continued for 2.3 h to obtain a uniform mixed solution;

[0065] (3) 40.1 mg of H2PtCl6·6H2O was weighed and dissolved in 2.0 g of deionized water, and a uniform solution was formed after stirring for 1 h under a 30 °C water bath. Then 0.5 mL of ethylenediamine was slowly added and stirring was continued for 2.1 h to obtain a uniform solution of Pt-containing organic amine complex;

[0066] (4) 35.2 mg of SnCl2·2H2O was weighed and dissolved in 2.20 g of deionized water, and a uniform solution was formed after stirring for 2 h under a 35 °C water bath;

[0067] (5) The solutions obtained in steps (2), (3), and (4) were mixed, and stirring was continued for 3 h to form a uniform mixed solution. Then 0.3 g of HI was added and stirred thoroughly for 2 h. Finally, it was loaded into the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0068] (6) The stainless steel crystallization kettle was placed in an oven and heated from room temperature to 170 °C and kept static hydrothermal crystallization for 2 days. After the crystallization was completed, it was cooled, centrifuged, washed, and dried at 100 °C for 12 h to obtain a catalyst powder precursor;

[0069] (7) The obtained catalyst powder precursor was placed in a tube furnace and reduced at 600 °C for 5 h at a rate of 2 °C / min in a high-purity H2 atmosphere to obtain a Pt-Sn@S-1(0.50) catalyst.

[0070] Example 2

[0071] (1) 20.2 g of TEOS was weighed and dissolved in 9.9 g of deionized water, and a uniform solution was obtained after stirring for 9.1 h under a 40 °C water bath to completely hydrolyze it;

[0072] (2) 18.9 g of TPAOH solution was weighed and added to the uniform solution of step (1), and stirring was continued for 4 h to obtain a uniform mixed solution;

[0073] (3) 48 mg of H2PtCl6·6H2O was weighed and dissolved in 2.90 g of deionized water, and a uniform solution was formed after stirring for 3.3 h under a 45 °C water bath. Then 0.72 mL of ethylenediamine was slowly added and stirring was continued for 3 h to obtain a uniform solution of Pt-containing organic amine complex;

[0074] (4) 35.0 mg SnCl2 2H2O was weighed into 2.80 g deionized water, and a uniform solution was formed after stirring for 2 h in a 45 °C water bath;

[0075] (5) The solutions obtained in steps (2), (3), and (4) were mixed, and stirring was continued for 3 h to form a uniform mixed solution. Then, 0.6 g HI was added, and stirring was continued for 2 h. Finally, the mixture was loaded into a polytetrafluoroethylene liner of a stainless steel crystallization kettle;

[0076] (6) The stainless steel crystallization kettle was placed in an oven, and the temperature was increased from room temperature to 165 °C and kept static for hydrothermal crystallization for 6 days. After the crystallization was completed, the catalyst powder precursor was obtained by cooling, centrifugation, washing, and drying at 100 °C for 12 h;

[0077] (7) The catalyst powder precursor obtained was placed in a tube furnace, and the temperature was increased to 600 °C at a rate of 2 °C / min under a high-purity H2 atmosphere and reduced for 6 h to obtain the Pt-Sn@S-1 (1.20) catalyst.

[0078] Example 3

[0079] (1) 10.3 g TEOS was weighed into 5.9 g deionized water, and a uniform solution was obtained after stirring for 5.2 h in a 25 °C water bath;

[0080] (2) 9.9 g TPAOH solution was weighed into the uniform solution obtained in step (1), and stirring was continued for 2.7 h to obtain a uniform mixed solution;

[0081] (3) 28 mg PtCl4 was weighed into 1.90 g deionized water, and a uniform solution was formed after stirring for 3 h in a 25 °C water bath. Then, 0.36 mL ethylenediamine was slowly added, and stirring was continued for 3 h to obtain a uniform solution of a Pt-containing organic amine complex;

[0082] (4) 25 mg SnCl2 2H2O was weighed into 1.80 g deionized water, and a uniform solution was formed after stirring for 2 h in a 25 °C water bath;

[0083] (5) The solutions obtained in steps (2), (3), and (4) were mixed, and stirring was continued for 3 h to form a uniform mixed solution. Then, 0.75 g HI was added, and stirring was continued for 2.5 h. Finally, the mixture was loaded into a polytetrafluoroethylene liner of a stainless steel crystallization kettle;

[0084] (6) The stainless steel crystallization kettle was placed in an oven, and the temperature was increased from room temperature to 175 °C and kept static for hydrothermal crystallization for 5 days. After the crystallization was completed, the catalyst powder precursor was obtained by cooling, centrifugation, washing, and drying at 100 °C for 12 h;

[0085] (7) The obtained catalyst powder precursor was placed in a tube furnace, and was heated to 600 ℃ at a rate of 2 ℃ / min in a high-purity H2 atmosphere and reduced for 7 h, to finally obtain a Pt-Sn@S-1(2.50) catalyst.

[0086] Example 4

[0087] (1) 13.3 g of TEOS was weighed and dissolved in 7.9 g of deionized water, and stirred in a 35 ℃ water bath for 6.4 h to obtain a uniform solution after complete hydrolysis;

[0088] (2) 12.8 g of TPAOH solution was weighed and added to the uniform solution of step (1), and stirring was continued for 3.2 h to obtain a uniform mixed solution;

[0089] (3) 29.5 mg of H2PtCl6·6H2O was weighed and dissolved in 2.7 g of deionized water, and a uniform solution was formed after stirring in a 35 ℃ water bath for 3.5 h, then 0.44 mL of ethylenediamine was slowly added and stirring was continued for 3 h to obtain a uniform solution containing a Pt-containing organic amine complex;

[0090] (4) 28.5 mg of SnCl4 was weighed and dissolved in 2.4 g of deionized water, and a uniform solution was formed after stirring in a 35 ℃ water bath for 2 h;

[0091] (5) The solutions obtained in steps (2), (3), and (4) were mixed, stirring was continued for 3 h to form a uniform mixed solution, then 0.89 g of HI was added and fully stirred for 2.5 h, and finally it was loaded into the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0092] (6) The stainless steel crystallization kettle was placed in an oven and heated from room temperature to 174 ℃ and kept static hydrothermal crystallization for 5.5 days, after the crystallization was completed, it was cooled, centrifuged, washed, and dried at 100 ℃ for 12 h to obtain a catalyst powder precursor;

[0093] (7) The obtained catalyst powder precursor was placed in a tube furnace, and was heated to 600 ℃ at a rate of 2 ℃ / min in a high-purity H2 atmosphere and reduced for 4 h, to finally obtain a Pt-Sn@S-1(3.50) catalyst.

[0094] Example 5

[0095] (1) 13.5 g of TEOS was weighed and dissolved in 7.5 g of deionized water, and stirred in a 35 ℃ water bath for 6.4 h to obtain a uniform solution after complete hydrolysis;

[0096] (2) 12.9 g of TPAOH solution was weighed and added to the uniform solution of step (1), and stirring was continued for 3.2 h to obtain a uniform mixed solution;

[0097] (3) 29.8 mg of H2PtCl6·6H2O was dissolved in 2.7 g of deionized water, and a uniform solution was formed after stirring for 3.5 h under a 35 ℃ water bath. Then 0.44 mL of ethylenediamine was slowly added, and stirring was continued for 3 h to obtain a uniform solution of Pt-containing organic amine complex;

[0098] (4) 28.9 mg of SnCl4 was dissolved in 2.4 g of deionized water, and a uniform solution was formed after stirring for 2 h under a 35 ℃ water bath;

[0099] (5) The solutions obtained in steps (2), (3), and (4) were mixed, and stirring was continued for 3 h to form a uniform mixed solution. Then 0.97 g of HI was added, and stirring was continued for 2.5 h. Finally, it was loaded into the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0100] (6) The stainless steel crystallization kettle was placed in an oven, and the temperature was increased from room temperature to 174 ℃ and kept static hydrothermal crystallization for 6.5 days. After the crystallization was completed, cooling, centrifugation, washing, and drying at 100 ℃ for 12 h were performed to obtain a catalyst powder precursor;

[0101] (7) The obtained catalyst powder precursor was placed in a tube furnace, and the temperature was increased to 600 ℃ at a rate of 2 ℃ / min under a high-purity H2 atmosphere and reduced for 4 h to finally obtain a Pt-Sn@S-1(4.50) catalyst.

[0102] Example 6

[0103] (1) 16.2 g of TEOS was dissolved in 7.6 g of deionized water, and stirring was performed under a 25 ℃ water bath for 6.1 h to completely hydrolyze it and obtain a uniform solution;

[0104] (2) 15.6 g of TPAOH solution was weighed and added to the uniform solution of step (1), and stirring was continued for 2.3 h to obtain a uniform mixed solution;

[0105] (3) 40.1 mg of H2PtCl6·6H2O was dissolved in 2.0 g of deionized water, and a uniform solution was formed after stirring for 1 h under a 30 ℃ water bath. Then 0.5 mL of ethylenediamine was slowly added, and stirring was continued for 2.1 h to obtain a uniform solution of Pt-containing organic amine complex;

[0106] (4) 35.2 mg of GaCl3 was dissolved in 2.20 g of deionized water, and a uniform solution was formed after stirring for 2 h under a 35 ℃ water bath;

[0107] (5) The solutions obtained in steps (2), (3), and (4) are mixed, and stirring is continued for 3 h to form a uniform mixed solution. Then, 0.97 g of HBr is added, and stirring is continued for 2 h. Finally, the mixture is loaded into a polytetrafluoroethylene liner of a stainless steel crystallization kettle;

[0108] (6) The stainless steel crystallization kettle is placed in an oven, and the temperature is increased from room temperature to 170 °C and kept for static hydrothermal crystallization for 2 days. After the crystallization is completed, the catalyst powder precursor is obtained by cooling, centrifugation, washing, and drying at 100 °C for 12 h;

[0109] (7) The catalyst powder precursor obtained is placed in a tube furnace, and the temperature is increased to 600 °C at a rate of 2 °C / min under a high-purity H2 atmosphere and reduced for 5 h to obtain the Pt-Ga@S-1(4.50) catalyst.

[0110] Example 7

[0111] (1) 20.2 g of TEOS is dissolved in 9.9 g of deionized water, and stirring is performed at 40 °C for 9.1 h to obtain a uniform solution after complete hydrolysis;

[0112] (2) 18.9 g of a TPAOH solution is added to the uniform solution obtained in step (1), and stirring is continued for 4 h to obtain a uniform mixed solution;

[0113] (3) 48 mg of H2PtCl6·6H2O is dissolved in 2.90 g of deionized water, and stirring is performed at 45 °C for 3.3 h to form a uniform solution. Then, 0.72 mL of ethylenediamine is slowly added, and stirring is continued for 3 h to obtain a uniform solution of a Pt-containing organic amine complex;

[0114] (4) 35.0 mg of ZnCl2 is dissolved in 2.80 g of deionized water, and stirring is performed at 45 °C for 2 h to form a uniform solution;

[0115] (5) The solutions obtained in steps (2), (3), and (4) are mixed, and stirring is continued for 3 h to form a uniform mixed solution. Then, 0.97 g of HBr is added, and stirring is continued for 2 h. Finally, the mixture is loaded into a polytetrafluoroethylene liner of a stainless steel crystallization kettle;

[0116] (6) The stainless steel crystallization kettle is placed in an oven, and the temperature is increased from room temperature to 165 °C and kept for static hydrothermal crystallization for 6 days. After the crystallization is completed, the catalyst powder precursor is obtained by cooling, centrifugation, washing, and drying at 100 °C for 12 h;

[0117] (7) The obtained catalyst powder precursor was placed in a tube furnace, and was heated to 600 ℃ at a rate of 2 ℃ / min in a high-purity H2 atmosphere and reduced for 6 h, to finally obtain a Pt-Zn@S-1(4.50) catalyst.

[0118] Example 8

[0119] (1) 10.3 g of TEOS was weighed and dissolved in 5.9 g of deionized water, and stirred in a 25 ℃ water bath for 5.2 h to completely hydrolyze it to obtain a uniform solution;

[0120] (2) 9.9 g of TPAOH solution was weighed and added to the uniform solution of step (1), and continued to be stirred for 2.7 h to obtain a uniform mixed solution;

[0121] (3) 28 mg of PtCl4 was weighed and dissolved in 1.90 g of deionized water, and stirred in a 25 ℃ water bath for 3 h to form a uniform solution, then 0.36 mL of ethylenediamine was slowly added and continued to be stirred for 3 h to obtain a uniform solution containing a Pt-containing organic amine complex;

[0122] (4) 25 mg of SnCl2·2H2O was weighed and dissolved in 1.80 g of deionized water, and stirred in a 25 ℃ water bath for 2 h to form a uniform solution;

[0123] (5) The solutions obtained in steps (2), (3), and (4) were mixed, and continued to be stirred for 3 h to form a uniform mixed solution, then 0.97 g of HCl was added and fully stirred for 2.5 h, and finally it was loaded into the polytetrafluoroethylene inner liner of a stainless steel crystallization kettle;

[0124] (6) The stainless steel crystallization kettle was placed in an oven, and was heated from room temperature to 175 ℃ and kept static hydrothermal crystallization for 5 days, after the crystallization was completed, it was cooled, centrifuged, washed, and dried at 100 ℃ for 12 h to obtain a catalyst powder precursor;

[0125] (7) The obtained catalyst powder precursor was placed in a tube furnace, and was heated to 600 ℃ at a rate of 2 ℃ / min in a high-purity H2 atmosphere and reduced for 7 h, to finally obtain a Pt-Sn@Beta(4.50) catalyst.

[0126] Example 9

[0127] (1) 13.3 g of TEOS was weighed and dissolved in 7.9 g of deionized water, and stirred in a 35 ℃ water bath for 6.4 h to completely hydrolyze it to obtain a uniform solution;

[0128] (2) 12.8 g of TPAOH solution was weighed and added to the uniform solution of step (1), and continued to be stirred for 3.2 h to obtain a uniform mixed solution;

[0129] (3) 29.5 mg of H2PtCl6·6H2O was weighed and dissolved in 2.7 g of deionized water, and a uniform solution was formed after stirring for 3.5 h under a 35 °C water bath. Then 0.44 mL of ethylenediamine was slowly added and stirred for 3 h to obtain a uniform solution of Pt-containing organic amine complex;

[0130] (4) 28.5 mg of SnCl4 was weighed and dissolved in 2.4 g of deionized water, and a uniform solution was formed after stirring for 2 h under a 35 °C water bath;

[0131] (5) The solutions obtained in steps (2), (3), and (4) were mixed and stirred for 3 h to form a uniform mixed solution. Then 0.97 g of HI was added and stirred for 2.5 h. Finally, it was loaded into the polytetrafluoroethylene lining of a stainless steel crystallization kettle;

[0132] (6) The stainless steel crystallization kettle was placed in an oven and heated from room temperature to 174 °C and kept static hydrothermal crystallization for 5.5 days. After the crystallization was completed, it was cooled, centrifuged, washed, and dried at 100 °C for 12 h to obtain a catalyst powder precursor;

[0133] (7) The obtained catalyst powder precursor was placed in a tube furnace and reduced at 600 °C for 4 h at a rate of 2 °C / min in a high-purity H2 atmosphere to obtain a Pt-Sn@ZSM-5(4.50) catalyst.

[0134] Example 10

[0135] (1) 13.5 g of TEOS was weighed and dissolved in 7.5 g of deionized water, and a uniform solution was obtained after stirring for 6.4 h under a 35 °C water bath to completely hydrolyze it;

[0136] (2) 12.9 g of TPAOH solution was added to the uniform solution of step (1) and stirred for 3.2 h to obtain a uniform mixed solution;

[0137] (3) 29.8 mg of H2PtCl6·6H2O was weighed and dissolved in 2.7 g of deionized water, and a uniform solution was formed after stirring for 3.5 h under a 35 °C water bath. Then 0.44 mL of ethylenediamine was slowly added and stirred for 3 h to obtain a uniform solution of Pt-containing organic amine complex;

[0138] (4) 28.9 mg of SnCl4 was weighed and dissolved in 2.4 g of deionized water, and a uniform solution was formed after stirring for 2 h under a 35 °C water bath;

[0139] (5) The solutions obtained in steps (2), (3), and (4) were mixed, and stirring was continued for 3 h to form a uniform mixed solution. Then, 0.97 g of HBr was added, and the mixture was stirred thoroughly for 2.5 h. Finally, the mixture was loaded into a polytetrafluoroethylene liner of a stainless steel crystallization kettle;

[0140] (6) The stainless steel crystallization kettle was placed in an oven, and the temperature was increased from room temperature to 174 °C and kept static hydrothermal crystallization for 6.5 days. After the crystallization was completed, the mixture was cooled, centrifuged, washed, and dried at 100 °C for 12 h to obtain a catalyst powder precursor;

[0141] (7) The catalyst powder precursor obtained was placed in a tube furnace, and the temperature was increased to 600 °C at a rate of 2 °C / min under a high-purity H2 atmosphere and reduced for 4 h to obtain a Pt-Sn@ZSM-11(4.50) catalyst finally.

[0142] Figures 1-6 The SEM images of the Pt-based molecular sieve catalysts obtained in the comparative example and examples 1-5 are shown in FIGS. 1-5, respectively. As can be seen from the figures, by changing the amount of hydrohalic acid HI, the b-axis length of the catalyst crystal grains can be controlled, and catalysts with different b-axis lengths can be obtained.

[0143] Figure 7 The STEM image of the Pt-Sn@S-1 catalyst obtained in example 5 is shown in FIG. 6. As can be seen from the figure, the size of the PtSn nanoclusters in the catalyst is about 0.65 nm.

[0144] 5 g of the catalyst prepared in the comparative example and examples was mixed with 20 g of quartz sand thoroughly, and then filled into a quartz tube fixed bed reactor with a diameter of 12 mm and ensured to be in the constant temperature zone of the heating furnace of the fixed bed reactor. Then, hydrogen was introduced, and the mixture was pretreated at 500 °C for 9 h. Then, the temperature was increased to 600 °C at a rate of 2 °C / min, and pure propane was introduced at a mass space velocity of WHSV = 10.2 h-1to carry out the reaction. The results are shown in Table 1. -1

[0145] Table 1 Comparison of the catalytic properties of different Pt-x@S-1 catalysts obtained in the comparative example and examples

[0146]

[0147] ​From the comparison of the comparative example and examples 1-5 in Table 1, it can be seen that in the preparation of the Pt-based molecular sieve, the b-axis size of the catalyst crystal grains can be increased by increasing the amount of hydrogen halide HI added, and the stability of the catalyst is obviously improved, which indicates that increasing the size of the b-axis of the catalyst crystal grains can effectively slow down the sintering of Pt nanoclusters in the catalyst; from the comparison of examples 5-10, it can be seen that under the condition that the b-axis size of the crystal grains is the same, the Pt-based molecular sieve catalyst prepared by using different types of metals as the secondary active component or by using different types of molecular sieves as the carrier all have strong stability, which further proves that increasing the size of the b-axis of the catalyst crystal grains is an important factor for improving the stability of the Pt-based molecular sieve catalyst.

[0148] Figure 8 The figure shows the catalytic activity effect of the Pt-Sn / S-1(4.50) catalyst obtained in example 5 on propane dehydrogenation for 6 months in succession. It can be seen from the figure that after a long time of propane dehydrogenation reaction, the propane conversion rate of the catalyst almost does not decrease, which further proves that the catalyst with a long b-axis size has excellent stability.

[0149] The above only describes the preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the patent application of the present application shall be included in the scope of the present application.

Claims

1. A method for preparing a high-performance Pt-based molecular sieve catalyst for the dehydrogenation of low-carbon alkanes to olefins, characterized in that: The catalyst is composed of a large single crystal molecular sieve carrier, a main active component and a secondary active component, wherein the b-axis length of the large single crystal molecular sieve carrier is 1.20-4.50 μm; the main active component is Pt sub-nanometer clusters with a particle size of 0.55-0.75 nm; and the secondary active component is any one or several of Cu, Ga and Sn; The preparation of the catalyst comprises the following steps: (1) under certain temperature conditions, a silicon source, a template agent, water, a Pt metal complex providing the main active component and a metal compound providing the secondary active component are fully stirred and mixed to obtain a uniform solution; (2) a certain amount of a hydrogen halide acid is added to the uniform solution obtained in step (1) and fully stirred and mixed to obtain a uniform gel-like mixture; (3) the gel-like mixture obtained in step (2) is statically hydrothermally crystallized at a certain temperature for a period of time, and then filtered, washed and dried to obtain a Pt-based compound@molecular sieve catalyst precursor, which is finally reduced by H2 to obtain the high-performance Pt-based molecular sieve catalyst; The hydrogen halide acid is any one or several of HCl, HBr and HI.

2. The method for preparing a high performance Pt-based molecular sieve catalyst according to claim 1, characterized in that: The loading amount of the main active component in the catalyst is 0.01-5.00 wt%, and the loading amount of the secondary active component is 0.01-5.00 wt%.

3. The method for preparing the high-performance Pt-based@molecular sieve catalyst according to claim 1, characterized in that: The molar ratio of the silicon source to the template agent, water, the Pt metal complex, the metal compound and the hydrogen halide acid in the system is 1:(1-10):(0.01-1):(0.00001-0.01):(0.00001-0.01):(0.01-1).

4. The method for preparing a high-performance Pt-based molecular sieve catalyst according to claim 1 or 3, characterized in that: The silicon source is any one or several of tetraethyl orthosilicate, white carbon black, silica sol, water glass and solid silica gel; The template agent is any one or several of tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, tetramethylammonium bromide, tetraethylammonium bromide, tetrapropylammonium bromide and tetrabutylammonium bromide; The Pt metal complex is composed of a Pt compound and an organic complex in a molar ratio of 1:2, wherein the Pt compound is any one or several of Pt(NH3)4(OH)2, Pt(NH3)4Cl2·H2O, Pt(NH3)4Cl2, [Pt(NH3)4](NO3)2, H2PtCl6·6H2O, PtCl2 and PtCl4; and the organic complex is any one or several of ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine and pentaethylenehexamine; When Cu is used as the secondary active component, the metal compound is any one or several of CuCl2·2H2O, CuCl2 and (NH4)2CuCl4·2H2O; when Ga is used as the secondary active component, the metal compound is any one or several of GaCl3, Ga2Cl4 and Ga(NO3)3·xH2O; and when Sn is used as the secondary active component, the metal compound is any one or several of SnCl2·2H2O and SnCl4.

5. The method for preparing the high-performance Pt-based@molecular sieve catalyst according to claim 1, characterized in that: The temperature used in step (1) is 25-100 ℃. The temperature of the crystallization in step (3) is 100-200 ℃, and the time is 1-200 h; the temperature of the drying is 60-180 ℃, and the time is 2-24 h; the temperature of the reduction is 100-900 ℃, and the time is 2-24 h.

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