Preparation method of encapsulated ptsn cluster modified zeolite carrier catalyst and application thereof in propane dehydrogenation to propylene

Abstract

The application discloses a preparation method of a packaged PtSn cluster modified zeolite carrier catalyst and application of the catalyst in propane dehydrogenation to prepare propylene. The catalyst selects PtSn bimetal as an active component, the ratio of the two metals Pt and Sn is 1:3-9, a modified multi-stage structure Silicalite-1 molecular sieve is selected as a carrier, by regulating the metal ratio of Pt and Sn, a one-pot method is adopted to finally obtain a catalyst with different structures of PtSn encapsulated in the Silicalite-1 molecular sieve after stirring hydrolysis, high-temperature crystallization, centrifugal separation, washing and calcination reduction treatment; the application provides a simple and efficient idea for modification of the Silicalite-1 molecular sieve carrier, highly dispersed and limited metal active sites are utilized by using the special ordered microporous structure of the molecular sieve carrier, the obtained multi-stage structure improves the diffusion limitation problem of microporous zeolite, when applied to the propane dehydrogenation to prepare propylene reaction, the catalyst has excellent C-H bond activation capacity, high propane conversion rate and propylene selectivity, and good catalytic stability.

Description

Technical Field

[0001] This invention belongs to the field of thermocatalytic material preparation technology, specifically relating to a method for preparing an encapsulated PtSn cluster modified zeolite support catalyst and its application in propane dehydrogenation to propylene. Background Technology

[0002] Propylene is the second most consumed petrochemical intermediate after ethylene, and is a crucial raw material for the production of various high-value chemicals, commodities, and fuels. However, actual propylene production falls far short of market demand. Since shale gas provides abundant and inexpensive propane for large-scale extraction, propane dehydrogenation to propylene has become an important technology to meet global propylene demand. Supported Pt-based catalysts are widely used in industrial propane dehydrogenation due to their excellent CH bond selectivity and low CC cracking capacity, but they face the challenges of rapid deactivation and poor propylene selectivity. Meanwhile, because small-sized metal nanoparticles suffer severe sintering during high-temperature propane dehydrogenation, the confinement effect of the support and / or strong metal-support interactions is also critical.

[0003] Zeolites, due to their large specific surface area, uniform and ordered microporous structure, high thermal stability, and strong confinement ability, are considered ideal supports for anchoring smaller metal nanoparticles, better preventing the sintering of sub-nanometer metal catalysts, and are widely used in the propane dehydrogenation to propylene field. In addition, adding a second metal promoter to further enhance the selective activation of CH bonds in propane dehydrogenation catalysts, thereby improving the catalyst's activity, selectivity, and stability, is also a very effective strategy. However, traditional impregnation methods result in poorly dispersed and large metal nanoparticles on the zeolite support. Therefore, how to design bimetallic catalysts by combining Pt with a second metal using in-situ encapsulation methods, and relying on the support to stabilize the metal catalyst to prevent sintering and agglomeration during the high-temperature propane dehydrogenation reaction, thus constructing a high-performance propane dehydrogenation catalyst, is a key technical challenge that those skilled in the art need to solve. Summary of the Invention

[0004] To address the shortcomings of existing technologies and solve the problems of easy deactivation and poor propylene selectivity in Pt-based catalysts, this invention provides a method for preparing an encapsulated PtSn cluster-modified zeolite support catalyst, specifically including the following steps:

[0005] (1) After the template agent is dissolved in deionized water, a ligand-protected Pt precursor solution is added and stirred evenly. Then, a silicon source is added for hydrolysis. Finally, a ligand-protected Sn precursor solution is added and stirred evenly to obtain a mixed gel. The template agent, silicon source and deionized water react to obtain Silicalite-1 zeolite.

[0006] (2) The mixed gel in step (1) was subjected to hydrothermal crystallization, then cooled to room temperature, and then centrifuged to obtain a grayish-white solid precipitate;

[0007] (3) The grayish-white solid precipitate obtained in step (2) is washed and dried, and then the obtained powder is reduced and heated to obtain the encapsulated PtSn cluster modified zeolite support catalyst.

[0008] Preferably, the template agent in step (1) is one of tetrapropylammonium hydroxide, tetrapropylbromine hydroxide, and tetrapropylchlorine hydroxide;

[0009] The silicon source mentioned in step (1) is one of tetraethyl orthosilicate, silica sol, and sodium silicate;

[0010] The Pt metal salt used in the ligand-protected Pt precursor solution in step (1) is one of chloroplatinic acid and platinum chloride;

[0011] The Sn metal salt used in the ligand-protected Sn precursor solution in step (1) is one of tin nitrate, tin chloride, and tin sulfate;

[0012] The ligand mentioned in step (1) is a ligand that can react with Pt metal salt and Sn metal salt to form a metal complex, and is one of ethylenediamine, acetylacetone, disodium ethylenediaminetetraacetate and triethylamine.

[0013] Preferably, the ligand-protected Pt precursor solution and the ligand-protected Sn precursor solution in step (1) are prepared by dissolving Pt metal salt and Sn metal salt in a deionized aqueous solution containing ligands, respectively, and stirring for 6-24 hours.

[0014] Preferably, the template agent in step (1) is tetrapropylammonium hydroxide, and the silicon source is tetraethyl orthosilicate; the molar ratio of tetrapropylammonium hydroxide, tetraethyl orthosilicate and deionized water in the mixed gel is 1:0.4:35;

[0015] The ligand in step (1) is specifically ethylenediamine, which reacts with the Pt metal salt and the Sn metal salt to obtain [Pt(NH2CH2CH2NH2)]Cl2 and [Sn(NH2CH2CH2NH2)]Cl2 metal precursor solutions.

[0016] Preferably, the mass fraction of Pt encapsulated in Silicalite-1 zeolite is 0.7 wt%-0.8 wt%, the mass fraction of Sn encapsulated in Silicalite-1 zeolite is 2.1 wt%-7.2 wt%, and the mass ratio of metallic Pt to metallic Sn is 1:3-9;

[0017] When the mass ratio of metal Pt to metal Sn is 1:6, a multi-level fin-like Silicalite-1 zeolite structure with smooth and flat fins on the surface is obtained.

[0018] Preferably, the hydrolysis in step (1) is carried out at room temperature and the stirring time is 6-12 h.

[0019] Preferably, the hydrothermal temperature in step (2) is 170°C and the hydrothermal time is 48-72 h.

[0020] Preferably, the drying temperature in step (3) is 60°C; the reduction heating temperature in step (3) is 400°C, the heating time is 2 h, the holding time is 2 h, pure hydrogen is used for reduction, and the gas flow rate is 60 ml / min, wherein the ligand and template act as metal protectants and gradually decompose as the metal is reduced.

[0021] The present invention also provides an encapsulated PtSn cluster modified zeolite support catalyst obtained by any of the above preparation methods.

[0022] The present invention also provides the application of encapsulated PtSn cluster-modified zeolite supported catalyst in propane dehydrogenation to propylene. 0.3 g of the encapsulated PtSn cluster-modified zeolite supported catalyst is diluted with 0.5 g of 40-60 mesh quartz sand and then loaded into a fixed bed reactor. Under argon atmosphere protection, the temperature is raised to the reaction temperature of 550°C for 1 h, and gaseous reactants are introduced. The ratio of propane to argon is 10:50 (ml / min).

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) The ligand protection method used in this invention can realize the confinement of the metal active phase in the micropores of the molecular sieve during the hydrothermal synthesis of zeolite, thereby avoiding the agglomeration, growth and sintering of metal active sites during high-temperature catalysis to a certain extent, while also enhancing the interaction between the metal sites and the support and improving the stability of the catalyst.

[0025] (2) The ligand protection method used in this invention can improve the mismatch between the fast crystallization process of metal ions and the long crystallization time of zeolite support, by using organometallic complexes to slow down the crystallization and precipitation rate of metal ions during the hydrothermal process. Compared with traditional preparation methods such as impregnation and ion exchange, this method of in-situ encapsulation using organometallic complexes has advantages such as strong metal-support interaction and tunable coordination state of metal sites, which is beneficial to improving the activity and stability of the catalyst.

[0026] (3) This invention provides a simple and efficient approach to modifying Silicalite-1 molecular sieve supports. It can utilize the highly dispersed and confined metal active sites of the ordered microporous structure of molecular sieve supports. By adjusting the ratio of Pt and Sn, different structures of Silicalite-1 zeolites can be obtained. In particular, the unique multi-level fin structure obtained when the implantation amount of Pt and Sn is kept at 1:6 improves the limitation of the microporous zeolite in the mass transfer process, ensures a short diffusion length and a smooth surface, helps to accelerate the diffusion rate and provide high surface permeability, enhances the propane adsorption and propylene desorption process, may reduce coke deposition, and extend the service life of the catalyst. Finally, a propane dehydrogenation to propylene catalyst with high conversion rate, high selectivity and high stability is obtained.

[0027] (4) The present invention uses a one-step direct hydrogen reduction calcination method, which avoids the problem of metal active site aggregation caused by calcination in air. The organic ligands and templates can act as metal protectants and gradually decompose as the metal is reduced. Moreover, the direct reduction method makes the reduction step more convenient and energy-saving. Attached Figure Description

[0028] Figure 1 This invention provides the synthetic route for the encapsulated PtSn cluster-modified zeolite-supported catalyst PtSn@S-1.

[0029] Figure 2 These are aberration-corrected high-angle annular dark-field scanning transmission electron microscope (TEM) images of the encapsulated PtSn cluster-modified zeolite support catalyst PtSn@S-1 provided by this invention, where ad is an aberration-corrected high-angle annular dark-field scanning transmission electron microscope image of the Pt@S-1 catalyst, eh is an aberration-corrected high-angle annular dark-field scanning transmission electron microscope image of the PtSn3@S-1 catalyst, il is an aberration-corrected high-angle annular dark-field scanning transmission electron microscope image of the PtSn6@S-1-Fin catalyst, and mp is an aberration-corrected high-angle annular dark-field scanning transmission electron microscope image of the PtSn9@S-1 catalyst.

[0030] Figure 3 This is a powder X-ray diffraction image of the encapsulated PtSn cluster modified zeolite support catalyst PtSn@S-1 provided by the present invention.

[0031] Figure 4 The nitrogen adsorption-desorption curves of the encapsulated PtSn cluster modified zeolite support catalyst PtSn@S-1 provided by this invention are shown.

[0032] Figure 5The X-ray photoelectron spectra of the encapsulated PtSn cluster-modified zeolite support catalyst PtSn@S-1 provided by this invention are shown in Figure a. Figure a shows the X-ray photoelectron spectra of the Pt 4f orbitals of the three catalysts: PtSn3@S-1, PtSn6@S-1-Fin, and PtSn9@S-1. Figure b shows the X-ray photoelectron spectra of the Sn 3d orbitals of the three catalysts: PtSn3@S-1, PtSn6@S-1-Fin, and PtSn9@S-1.

[0033] Figure 6 This is the hydrogen temperature-programmed reduction curve of the encapsulated PtSn cluster modified zeolite support catalyst PtSn@S-1 provided by the present invention.

[0034] Figure 7 This is the propane temperature-programmed desorption curve of the encapsulated PtSn cluster modified zeolite support catalyst PtSn@S-1 provided by the present invention.

[0035] Figure 8 These are scanning electron microscope images of the Pt@S-1 catalyst at different magnifications provided by this invention.

[0036] Figure 9 These are scanning electron microscope images of the PtSn3@S-1 catalyst provided by this invention at different magnifications.

[0037] Figure 10 These are scanning electron microscope images of the PtSn6@S-1 catalyst provided by this invention at different magnifications.

[0038] Figure 11 These are scanning electron microscope images of the Sn@S-1 catalyst provided by this invention at different magnifications.

[0039] Figure 12 This invention presents the propane conversion and propylene selectivity of the encapsulated PtSn cluster-modified zeolite support catalyst PtSn@S-1 during propane catalysis. Figure a shows the propane conversion of PtSn@S-1 with different metal ratios during propane catalysis, and figure b shows the propylene selectivity of PtSn@S-1 with different metal ratios during propane catalysis.

[0040] Figure 13 The present invention describes the propane conversion and propylene selectivity of the encapsulated PtSn cluster modified zeolite support catalysts PtSn3@S-1 and PtSn6@S-1-Fin during long-term propane catalytic reactions. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are also within the scope of protection of this disclosure.

[0042] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this subject matter pertains. It will be further understood that terms such as those defined in commonly used dictionaries shall be interpreted as having the meaning consistent with their meaning in the context of the specification and in the relevant art, and shall not be interpreted in an idealized or overly formal form unless otherwise explicitly defined herein.

[0043] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of the phrase "embodiment" in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0044] To address the issues of easy deactivation and poor propylene selectivity in Pt-based catalysts, this invention provides a catalyst, its preparation method, and applications using an encapsulated PtSn bimetallic cluster-modified zeolite support. A ligand-protected direct hydrogen reduction method is employed, where sub-nanometer Pt-Sn bimetallic clusters are in-situ encapsulated in Silicalite-1 zeolite under hydrothermal conditions at 170 °C. This effectively prevents the sintering of the metal nanoclusters during traditional calcination reduction. Furthermore, by controlling the ratio of Pt to Sn, a multi-level finned zeolite structure is obtained. The mass fraction of Pt encapsulated within the Silicalite-1 zeolite is 0.7 wt%–0.8 wt%, and the mass fraction of Sn encapsulated within the Silicalite-1 zeolite is 2.1 wt%–7.2 wt%, with a platinum to tin mass ratio of 1:3–9. In addition, during the direct hydrogen reduction process, the organic ligands and template act as metal protectants, gradually decomposing as the metal is reduced. The direct reduction method also makes the reduction step more convenient and energy-efficient. The multi-level finned zeolite structure provided by this invention has a shorter diffusion length, which helps to improve the diffusion rate of reactants and the surface permeability of catalyst materials, accelerate the adsorption of propane and the desorption of propylene, and obtain a highly active, highly selective and highly stable propane dehydrogenation catalyst.

[0045] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments: Example 1

[0046] 1. Dissolve 0.12 g of platinum chloride in a deionized aqueous solution containing ethylenediamine (including 0.5 ml of ethylenediamine and 4.5 ml of deionized water).

[0047] 2. Weigh 13 g of tetrapropylammonium hydroxide and dissolve it in 15 g of deionized water. Stir it for 10 min until it is uniform, then add 1.2 ml of the Pt precursor solution obtained in step (1), stir for 30 min, then add 8.32 g of tetraethyl orthosilicate, and stir for 6 h until it is completely hydrolyzed to obtain a uniformly mixed gel.

[0048] 3. The mixed gel obtained in step (2) is loaded into the liner of a polytetrafluoroethylene reactor, and then into a stainless steel high-pressure reactor. It is hydrothermally crystallized at 170°C for 72 h to form a grayish-white solid precipitate.

[0049] 4. After cooling the product obtained in step (3) to room temperature, centrifuge it at 7000 rpm, wash it three times with deionized water, and dry it at 60°C for 12 h.

[0050] 5. The powder obtained in step (3) is heated from room temperature to 400℃ in a pure hydrogen atmosphere (flow rate of 60 ml / min) for 2 h, and then kept at that temperature for 2 h. After cooling down, a light gray powder is obtained, which is the PtSn bimetallic cluster encapsulated in the multi-level fin structure Silicalite-1 zeolite catalyst. Example 2

[0051] 1. Dissolve 0.12 g of platinum chloride in a deionized aqueous solution containing ethylenediamine (including 0.5 ml of ethylenediamine and 4.5 ml of deionized water); similarly, dissolve 1.05 g of tin chloride in a deionized aqueous solution containing ethylenediamine (including 3 ml of ethylenediamine and 12 ml of deionized water).

[0052] 2. Weigh 13 g of tetrapropylammonium hydroxide and dissolve it in 15 g of deionized water. Stir it for 10 min until it is uniform, then add 1.2 ml of the Pt precursor solution obtained in step (1), stir for 30 min, then add 8.32 g of tetraethyl orthosilicate, stir for 6 h until it is completely hydrolyzed, then add 1.8 ml of the Sn precursor solution obtained in step (1), and stir again for 30 min to obtain a uniformly mixed gel.

[0053] 3. The mixed gel obtained in step (2) is loaded into the liner of a polytetrafluoroethylene reactor, and then into a stainless steel high-pressure reactor. It is hydrothermally crystallized at 170°C for 72 h to form a grayish-white solid precipitate.

[0054] 4. After cooling the product obtained in step (3) to room temperature, centrifuge it at 7000 rpm, wash it three times with deionized water, and dry it at 60°C for 12 h.

[0055] 5. The powder obtained in step (3) is heated from room temperature to 400℃ in a pure hydrogen atmosphere (flow rate of 60 ml / min) for 2 h, and then kept at that temperature for 2 h. After cooling down, a light gray powder is obtained, which is the PtSn bimetallic cluster encapsulated in the multi-level fin structure Silicalite-1 zeolite catalyst. Example 3

[0056] 1. Dissolve 0.12 g of chloroplatinic acid in a deionized aqueous solution containing ethylenediamine (including 0.5 ml of ethylenediamine and 4.5 ml of deionized water); similarly, dissolve 1.05 g of tin chloride in a deionized aqueous solution containing ethylenediamine (including 3 ml of ethylenediamine and 12 ml of deionized water).

[0057] 2. Weigh 13 g of tetrapropylammonium hydroxide and dissolve it in 15 g of deionized water. Stir it for 10 min until it is uniform, then add 1.2 ml of the Pt precursor solution obtained in step (1), stir for 30 min, then add 8.32 g of tetraethyl orthosilicate, stir for 6 h until it is completely hydrolyzed, then add 3.6 ml of the Sn precursor solution obtained in step (1), and stir again for 30 min to obtain a uniformly mixed gel.

[0058] 3. The mixed gel obtained in step (2) is loaded into the PTFE reactor liner and then into a stainless steel high-pressure reactor. It is then hydrothermally crystallized at 170°C for 72 h to form a grayish-white solid precipitate.

[0059] 4. After cooling the product obtained in step (3) to room temperature, centrifuge it at 7000 rpm, wash it three times with deionized water, and dry it at 60°C for 12 h.

[0060] 5. The powder obtained in step (3) is heated from room temperature to 400℃ in a pure hydrogen atmosphere (flow rate of 60 ml / min) for 2 h, and then kept at that temperature for 2 h. After cooling down, a light gray powder is obtained, which is the PtSn bimetallic cluster encapsulated in the multi-level fin structure Silicalite-1 zeolite catalyst. Example 4

[0061] 1. Dissolve 0.12 g of platinum chloride in a deionized aqueous solution containing ethylenediamine (including 0.5 ml of ethylenediamine and 4.5 ml of deionized water); similarly, dissolve 1.05 g of tin chloride in a deionized aqueous solution containing ethylenediamine (including 0.5 ml of ethylenediamine and 4.5 ml of deionized water).

[0062] 2. Weigh 13 g of tetrapropylammonium hydroxide and dissolve it in 15 g of deionized water. Stir it for 10 min until it is uniform, then add 1.2 ml of the Pt precursor solution obtained in step (1), stir for 30 min, then add 8.32 g of tetraethyl orthosilicate, stir for 6 h until it is completely hydrolyzed, then add 5.4 ml of the Sn precursor solution obtained in step (1), and stir again for 30 min to obtain a uniformly mixed gel.

[0063] 3. The mixed gel obtained in step (2) is loaded into the liner of a polytetrafluoroethylene reactor, and then into a stainless steel high-pressure reactor. It is hydrothermally crystallized at 170°C for 72 h to form a grayish-white solid precipitate.

[0064] 4. After cooling the product obtained in step (3) to room temperature, centrifuge it at 7000 rpm, wash it three times with deionized water, and dry it at 60°C for 12 h.

[0065] 5. The powder obtained in step (3) is heated from room temperature to 400℃ in a pure hydrogen atmosphere (flow rate of 60 ml / min) for 2 h, and then kept at that temperature for 2 h. After cooling down, a light gray powder is obtained, which is the PtSn bimetallic cluster encapsulated in the multi-level fin structure Silicalite-1 zeolite catalyst. Example 5

[0066] 1. Dissolve 1.05 g of tin chloride in a deionized aqueous solution containing ethylenediamine (including 0.5 ml of ethylenediamine and 4.5 ml of deionized water).

[0067] 2. Weigh 13 g of tetrapropylammonium hydroxide and dissolve it in 15 g of deionized water. Stir it for 10 min until it is uniform, then add 8.32 g of tetraethyl orthosilicate and stir it for 6 h until it is completely hydrolyzed. Then add 3.6 ml of the Sn precursor solution obtained in step (1) and stir it again for 30 min to obtain a uniformly mixed gel.

[0068] 3. The mixed gel obtained in step (2) is loaded into the liner of a polytetrafluoroethylene reactor, and then into a stainless steel high-pressure reactor. It is hydrothermally crystallized at 170°C for 72 h to form a grayish-white solid precipitate.

[0069] 4. After cooling the product obtained in step (3) to room temperature, centrifuge it at 7000 rpm, wash it three times with deionized water, and dry it at 60°C for 12 h.

[0070] 5. The powder obtained in step (3) is heated from room temperature to 400℃ in a pure hydrogen atmosphere (flow rate of 60 ml / min) for 2 h, and then kept at that temperature for 2 h. After cooling down, a light gray powder is obtained, which is the PtSn bimetallic cluster encapsulated in the multi-level fin structure Silicalite-1 zeolite catalyst. Example 6

[0071] 1. Dissolve 0.12 g of platinum chloride in a deionized aqueous solution containing disodium ethylenediaminetetraacetate (including 1 ml of disodium ethylenediaminetetraacetate and 4 ml of deionized water) and stir for 6 h; similarly, dissolve 1.05 g of tin chloride in a deionized aqueous solution containing disodium ethylenediaminetetraacetate (including 4 ml of disodium ethylenediaminetetraacetate and 11 ml of deionized water) and stir for 3 h.

[0072] 2. Weigh 13 g of tetrapropylammonium hydroxide and dissolve it in 15 g of deionized water. Stir it for 10 min until it is uniform, then add 1 ml of the Pt precursor solution obtained in step (1), stir for 30 min, then add 8.32 g of tetraethyl orthosilicate, stir for 8 h until it is completely hydrolyzed, then add 3 ml of the Sn precursor solution obtained in step (1), and stir again for 30 min to obtain a uniformly mixed gel.

[0073] 3. The mixed gel obtained in step (2) is loaded into the liner of a polytetrafluoroethylene reactor, and then into a stainless steel high-pressure reactor. It is hydrothermally crystallized at 170°C for 48 h to form a grayish-white solid precipitate.

[0074] 4. After cooling the product obtained in step (3) to room temperature, centrifuge it at 7000 rpm, wash it three times with deionized water, and dry it at 60°C for 12 h.

[0075] 5. The powder obtained in step (3) is heated from room temperature to 400℃ in a pure hydrogen atmosphere (flow rate of 40 ml / min) for 2 h, and then kept at that temperature for 2 h. After cooling down, a light gray powder is obtained, which is the PtSn bimetallic cluster encapsulated in the multi-level fin structure Silicalite-1 zeolite catalyst.

[0076] Examples 1-5 prepared PtxSny@S-catalysts with metal clusters encapsulated in Silicalite-1 zeolite. The samples from Examples 1-4 were used as examples to characterize the monometallic catalysts Pt@S-1 and Sn@S-1 and the bimetallic catalysts PtSn3@S-1, PtSn6@S-1-Fin and PtSn9@S-1 prepared in Examples 1-4, and propane dehydrogenation catalysis was tested.

[0077] Figure 1This is the synthesis route of PtSn bimetallic cluster implanted zeolite composite material (PtSn@S-1) in the embodiments of the present invention.

[0078] Figure 2 These are aberration-corrected high-angle annular dark-field scanning transmission electron microscope images of the monometallic and bimetallic catalytic materials prepared in Examples 1-4 of this invention, such as... Figure 2 As shown in the diagram, metal nanoclusters were uniformly observed inside the Pt@S-1 catalyst, but not in the "shell". The elemental distribution and chemical composition were determined by energy-dispersive X-ray spectroscopy, showing that Pt was uniformly distributed within the zeolite. For the PtSn3@S-1 sample, EDX analysis revealed that Pt and Sn were uniformly distributed within the zeolite and located almost in the same position, indicating the establishment of a bimetallic system. Figure 2 (eh). It can be obtained from... Figure 2 It was learned that the fins of PtSn6@S-1-Fin are uniformly and regularly sized, and PtSn sub-nanometer bimetallic clusters are uniformly distributed on the fins inside and outside the zeolite. This novel fin structure has a shorter diffusion length. Therefore, the unique fin structure of Pt1Sn6@S-1-Fin will improve mass transport characteristics by ensuring both high surface permeability and short diffusion length.

[0079] Figure 3 The powder X-ray diffraction images of the single-metal and bimetallic catalytic materials prepared in Examples 1-4 of this invention show that the obtained samples all have typical MFI-type framework structures, and no diffraction peaks of Pt and / or Sn crystal phases were observed, indicating that Pt and / or Sn are highly dispersed on the S-1 support.

[0080] Figure 4 The nitrogen adsorption-desorption curves of the monometallic and bimetallic catalytic materials prepared in Examples 1-4 of this invention show that the obtained catalysts all have microporous structures. Compared with the PtSn3@S-1 sample, the measured external surface area ratio of PtSn6@S-1-Fin is higher, which may prove that the fin structure can increase the accessibility of active sites. The external surface area of ​​Pt1Sn6@S-1-Fin is 102.97 m². 2 / g, significantly higher than Pt1Sn3@S-1 (89.33 m 2 / g), while the total surface area of ​​the two samples was almost the same (338.77 and 335.13 m²). 2 / g).

[0081] Figure 5The X-ray photoelectron spectroscopy (XPS) spectra of the single-metal and bimetallic catalytic materials prepared in Examples 1-4 of this invention characterize the detailed electronic structure of the PtSn bimetallic clusters. The two principal binding energies in the Pt@S-1 sample are 70.7 eV and 74.51 eV, respectively, corresponding to Pt 0 Furthermore, the XPS signal is relatively weak, indicating that most of the dispersed Pt nanoclusters in Pt@S-1 are confined within the zeolite crystals. With the introduction of Sn, the main peak of Pt 4f (70.7 eV) blue-shifts to 70.9 eV (PtSn3@S-1) and 71.3 eV (PtSn6@S-1-Fin), respectively. The main peak of PtSn6@S-1 is 0.4 eV higher than that of Pt1Sn3@S-1, while the Sn 3d values ​​corresponding to the two catalysts are similar, at 486.9 eV and 495.3 eV, respectively. 2+ This indicates that the valence state is slightly higher than that of metallic Pt, but still close to that of metallic Pt. 0 This may be attributed to the change in the density of states of Pt 5d near the Fermi level after the neighboring Sn atoms perturb the electronic structure of the Pt atoms on the surface.

[0082] Figure 6 The figures show the hydrogen temperature-programmed reduction curves of the bimetallic catalytic materials prepared in Examples 1-4 of this invention. As can be seen from the figures, the reduction peak of the PtSn6@S-1-Fin catalyst is higher than that of the PtSn3@S-1 catalyst, which proves that there is a stronger interaction between the metal and the support of the PtSn6@S-1-Fin catalyst. Therefore, the PtSn6@S-1-Fin catalyst has stronger propane dehydrogenation stability.

[0083] Figure 7 The figures show the propane temperature-programmed desorption curves of the bimetallic catalytic materials prepared in Examples 1-4 of this invention. As can be seen from the figures, the propane desorption temperatures of the two catalysts are basically the same, which proves that the two catalysts have similar active sites. However, the PtSn6@S-1-Fin catalyst has a larger propane desorption area, which proves that it has a stronger adsorption capacity for propane. Therefore, its propane dehydrogenation conversion rate is higher.

[0084] Figure 8-11 The images shown are scanning electron microscope images of Pt@S-1, PtSn3@S-1, PtSn6@S-1, and Sn@S-1 prepared in Examples 1-4 of this invention, respectively. Figure 8 The Pt@S-1 catalyst shown in the figure has a typical hexagonal structure. With the addition of Sn, the morphology of the PtSn3@S-1 sample changes from hexagonal to elliptical. Figure 9 Interestingly, from Figure 10It was observed that with further increases in the amount of Sn added, the hexagonal zeolite structure transformed into a finned zeolite with smooth surface fins. This novel finned structure exhibits a shorter diffusion length, potentially disrupting the trade-off between crystallinity and diffusion efficiency. However, for the Sn@S-1 sample containing only Sn monometal, from... Figure 11 It was observed that its outer surface was rough and its shape was unclear, which would lead to a decrease in the surface permeability of the material and affect the mass transfer process of the reactants.

[0085] Figure 12-13 The propane conversion and propylene selectivity of the single-metal and bimetallic catalytic materials prepared in Examples 1-4 of this invention are based on the following: Figure 13 It is evident that the initial propane conversion of the PtSn6@S-1-Fin catalyst is as high as ~65%. After continuous propane dehydrogenation catalysis for ~233 h, its propane conversion remains at ~45%, and its propylene selectivity remains at ~100%. Compared to the finned PtSn6@S-1-Fin catalyst, the smooth PtSn3@S-1 catalyst deactivates more rapidly, with its performance decreasing to ~40% after 66 h of continuous catalysis, although its selectivity remains at ~100%. Clearly, the unique finned structure of PtSn6@S-1-Fin improves the limitations of microporous zeolite in the mass transport process, ensuring a short diffusion length and a smooth surface, which helps to accelerate the diffusion rate and provide high surface permeability, enhancing the propane adsorption and propylene desorption processes, potentially reducing coke deposition, and extending the catalyst's lifespan.

Claims

1. A method for preparing an encapsulated PtSn cluster-modified zeolite supported catalyst, characterized in that, Includes the following steps: (1) After the template agent is dissolved in deionized water, a ligand-protected Pt precursor solution is added and stirred evenly. Then, a silicon source is added for hydrolysis. Then, a ligand-protected Sn precursor solution is added and stirred evenly to obtain a mixed gel. The template agent is tetrapropylammonium hydroxide. The ligand is a ligand that can react with Pt metal salt and Sn metal salt to form a metal complex. It is one of ethylenediamine, acetylacetone, disodium ethylenediaminetetraacetate and triethylamine. The template agent, silicon source and deionized water react to obtain Silicalite-1 zeolite. (2) The mixed gel in step (1) was subjected to hydrothermal crystallization at a temperature of 170°C for 48-72 h. After cooling to room temperature, it was then centrifuged to obtain a grayish-white solid precipitate. (3) The grayish-white solid precipitate obtained in step (2) is washed and dried, and then the powder is reduced and heated to obtain an encapsulated PtSn cluster modified zeolite support catalyst. The mass fraction of Pt encapsulated in Silicalite-1 zeolite is 0.7wt%-0.8wt%, and the mass ratio of metal Pt to metal Sn is 1:

6. The surface of the catalyst has a multi-level fin-like Silicalite-1 zeolite structure with smooth and flat fins.

2. The preparation method of the encapsulated PtSn cluster modified zeolite support catalyst according to claim 1, characterized in that, The silicon source mentioned in step (1) is one of tetraethyl orthosilicate, silica sol, and sodium silicate; The Pt metal salt used in the ligand-protected Pt precursor solution in step (1) is one of chloroplatinic acid and platinum chloride; The Sn metal salt used in the ligand-protected Sn precursor solution in step (1) is one of tin nitrate, tin chloride, and tin sulfate.

3. The method for preparing an encapsulated PtSn cluster-modified zeolite supported catalyst according to claim 1, characterized in that, The ligand-protected Pt precursor solution and the ligand-protected Sn precursor solution in step (1) are prepared by dissolving Pt metal salt and Sn metal salt in a deionized aqueous solution containing ligands, respectively, and stirring for 6-24 hours.

4. The preparation method of an encapsulated PtSn cluster-modified zeolite supported catalyst according to claim 1, characterized in that, The template agent mentioned in step (1) is specifically tetrapropylammonium hydroxide, and the silicon source is specifically tetraethyl orthosilicate; the molar ratio of tetrapropylammonium hydroxide, tetraethyl orthosilicate and deionized water in the mixed gel is 1:0.4:35; The ligand in step (1) is specifically ethylenediamine, which reacts with the Pt metal salt and the Sn metal salt to obtain [Pt(NH2CH2CH2NH2)]Cl2 and [Sn(NH2CH2CH2NH2)]Cl2 metal precursor solutions.

5. The method for preparing an encapsulated PtSn cluster-modified zeolite supported catalyst according to claim 1, characterized in that, The hydrolysis in step (1) is carried out at room temperature and the stirring time is 6-12 h.

6. The method for preparing an encapsulated PtSn cluster-modified zeolite supported catalyst according to claim 1, characterized in that, The drying temperature in step (3) is 60°C; The reduction heating temperature in step (3) is 400℃, the heating time is 2 h, the holding time is 2 h, pure hydrogen is used for reduction, and the gas flow rate is 60 ml / min. The ligand and template act as metal protectants and gradually decompose as the metal is reduced.

7. The encapsulated PtSn cluster modified zeolite support catalyst obtained by the preparation method according to any one of claims 1-6.

8. The application of the encapsulated PtSn cluster-modified zeolite supported catalyst according to claim 7 in propane dehydrogenation to propylene, characterized in that, 0.3 g of the encapsulated PtSn cluster-modified zeolite support catalyst was diluted with 0.5 g of 40-60 mesh quartz sand and then loaded into a fixed-bed reactor. Under argon atmosphere protection, the temperature was raised to the reaction temperature of 550°C in 1 h, and gaseous reactants were introduced. The ratio of propane to argon was 10:50.

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