Pt-Sn heteronuclear bimetallic catalyst and preparation method and application thereof

Abstract

The invention relates to the field of petrifaction, and discloses a Pt-Sn heteronuclear bimetallic catalyst and a preparation method and application thereof. The catalyst comprises a carrier with a three-dimensional ordered interperforated channel structure, and Pt-Sn heteronuclear bimetal which is uniformly dispersed and loaded on the carrier in situ, wherein Pt is dispersed in the form of Pt0 nanoclusters, Sn exists in the valence state of Sn < 4 + > and is anchored on a carrier framework through Sn-O bonds, and a Pt0-Sn (4 +)-O interface structure is formed by the Sn and the adjacent Pt0 nanoclusters. The carrier of the catalyst provided by the invention has a three-dimensional ordered interperforated channel structure, and is matched with the loaded Pt-Sn heteronuclear bimetallic, so that the catalyst has higher mass transfer efficiency, stronger carbon deposition resistance and better metal dispersity, and when the catalyst is applied to the reaction of isomerizing mixed C8 aromatic hydrocarbon to prepare xylene, the catalyst has higher catalytic activity and higher catalytic activity. The catalyst has the characteristics of high conversion rate, high PX selectivity and good stability.

Description

Technical Field

[0001] This invention relates to the petrochemical field, and more particularly to a Pt-Sn heteronuclear bimetallic catalyst, its preparation method, and its applications. Background Technology

[0002] C8 mixed aromatics isomerization is a core process in aromatics complexes, aiming to convert non-thermodynamically equilibrium C8 aromatics (o-xylene, m-xylene, ethylbenzene) into high-value-added para-xylene (PX). Traditional aromatics isomerization catalysts often use ZSM-5 zeolite as a support to support noble metals (such as Pt), but these catalysts have the following limitations: (1) Low mass transfer efficiency: The microporous structure of traditional carriers (such as ZSM-5 zeolite) is small, which on the one hand restricts the diffusion of reactants, and on the other hand easily leads to carbon deposition and deactivation (literature: J. Catal., 2020, 385, 112-123). (2) Insufficient metal dispersion: Traditional precious metals (such as Pt) are prone to sintering into large particles during catalyst preparation, which reduces the active sites and thus affects the catalytic efficiency; (3) Insufficient selectivity: The strong acid sites of traditional aromatic isomerization catalysts are prone to triggering side reactions (such as cracking and disproportionation), thereby reducing the yield of xylene; (4) Low ethylbenzene conversion: Existing aromatic isomerization catalysts have limited conversion capacity for ethylbenzene (usually <30%), and are accompanied by xylene loss.

[0003] In recent years, research has focused on the synergistic effect of bimetals. For example, bimetals (such as Pt-Sn) have been used to modulate acidic sites and suppress carbon deposition. However, problems such as uneven bimetal dispersion still exist, limiting further improvements in the catalytic performance of aromatic isomerization. Three-dimensional ordered macroporous materials, due to their high specific surface area and open pore structure, have been used as catalyst supports for different reaction types. However, there are no reports on the use of three-dimensional ordered macroporous materials as supports in aromatic isomerization catalysts, therefore, their specific effects as aromatic isomerization catalyst supports remain unclear.

[0004] Furthermore, in other reaction-type catalysts that have already used three-dimensional ordered macroporous materials as supports, a single active metal is often used, which cannot simultaneously take into account the density of acidic sites and the dispersion of metals, and the catalytic effect needs to be further improved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a Pt-Sn heteronuclear bimetallic catalyst, its preparation method, and its applications. The catalyst support of this invention possesses a three-dimensional ordered interpenetrating porous structure, combined with a supported Pt-Sn heteronuclear bimetal, resulting in high mass transfer efficiency, strong resistance to carbon deposition, and good metal dispersion. When applied to the isomerization of mixed C8 aromatics to xylene, it exhibits high conversion rate, high PX selectivity, and good stability.

[0006] The specific technical solution of the present invention includes: In a first aspect, the present invention provides a Pt-Sn heteronuclear bimetallic catalyst, comprising a support having a three-dimensional ordered interpenetrating pore structure, and a Pt-Sn heteronuclear bimetallic catalyst uniformly dispersed in situ and supported on the support; wherein: Pt with Pt 0 Sn is dispersed in the form of nanoclusters. 4+ The valence state exists, anchored to the carrier framework via Sn-O bonds, and associated with neighboring Pt. 0 Pt nanoclusters 0 -Sn (4+) -O interface structure. Pt 0 Provides hydrogenation / dehydrogenation active sites, Sn (4+) This can adjust the acidity of the support and stabilize the dispersion of Pt. Sn (4+) The carrier is connected via an oxygen bridge, while simultaneously interacting with Pt. 0 Nanoclusters generate electronic interactions, weakening the d-band centers of Pt and enhancing the adsorption capacity of reactants.

[0007] The catalyst of this invention has a three-dimensional ordered interpenetrating pore structure and is loaded with a Pt-Sn heteronuclear bimetal. Its advantages lie in the fact that the three-dimensional ordered interpenetrating pore structure allows the support to have a large-sized open pore structure, significantly improving mass transfer efficiency and enhancing reactant diffusion and intermediate adsorption capabilities. When this catalyst is applied to the isomerization reaction of mixed C8 aromatics to prepare xylene (PX), it exhibits high selectivity for p-xylene (≥92%) and long-term stability (>500 h), making it suitable for continuous industrial production.

[0008] Preferably, the loading of Pt is 0.1-1.5 wt%, and the loading of Sn is 0.5-3.0 wt%.

[0009] Based on the bimetallic synergistic catalysis mechanism and industrial practice, this invention controls the Pt and Sn loadings within the aforementioned ranges, corresponding to a Pt:Sn molar ratio of ≈1:1-1:5. This achieves an ideal bimetallic synergistic effect: Sn... 4+ Modulating the strong acid sites in the support can inhibit ethylbenzene cracking; Pt 0 -Sn 4+Interfacial electron transfer shifts the d-band center of Pt downwards, optimizing aromatic ring adsorption capacity and reducing carbon deposition rate. If the Pt loading is too low, the active site density is too low, resulting in insufficient active centers for hydrogenation / dehydrogenation, hindering effective catalysis of the isomerization cycle of C8 aromatics. If the Pt loading is too high, there is a risk of metal sintering, affecting the hydrogenation / dehydrogenation reaction. If the Sn loading is too low, due to Sn… 4+ Modifying the strong acid sites of the support with Sn-O-Al bonds can suppress cleavage side reactions, but this leads to the failure of acid modulation, while Sn 4+ For Pt 0 The anchoring effect weakens, accelerating Pt sintering. If the Sn loading is too high, it will clog the carrier channels, increasing mass transfer resistance. Simultaneously, Pt... 0 To Sn 4+ Excessive electron transfer weakens Pt's activation ability for H2.

[0010] Preferably, the pore size of the three-dimensional ordered interpenetrating pore structure is 50-250 nm, the pore wall thickness is 10-50 nm, and the specific surface area is 150-300 m². 2 / g.

[0011] Based on the principles of mass transfer kinetics and surface chemistry of porous materials, the limitations on the support parameters in this invention stem from the following scientific mechanisms: The pore size of the three-dimensional ordered interpenetrating pore structure described in this invention is within the aforementioned range, which can balance the diffusion frequency of reactant molecules within the pores and their collision frequency with active sites; the pore wall thickness is within the aforementioned range, which can form a continuous lattice network, strengthening Sn-O-Al bond anchoring and improving strength and dimensional stability; and the specific surface area is within the aforementioned range, resulting in a large proportion of mesopores, which can achieve spatial separation of metal sites (Pt-Sn interface) and acidic sites, thus improving the selectivity for xylene. Furthermore, this invention discovers that a support with the above-mentioned parameters and three-dimensional ordered interpenetrating pores can further enhance the mass transfer efficiency of the catalyst.

[0012] If the pore size of the carrier is too small, it will lead to a surge in mass transfer resistance, a decrease in reactant diffusion rate, and a prolonged residence time of carbon deposit precursors. If the pore size is too large, the specific surface area will decrease sharply, resulting in insufficient density of Pt active sites and inadequate exposure of acidic sites. Furthermore, large pores weaken capillary forces, making it easier for metal precursors to migrate and aggregate during impregnation, leading to uneven dispersion. If the pore wall thickness of the carrier is too thin, it will reduce the mechanical strength and thermal stability of the carrier. If the pore wall thickness of the carrier is too thick, it will lead to compression of the effective pore volume, reduced pore connectivity, and easy shielding of active sites. If the specific surface area of ​​the carrier pores is too low, since the dispersion density of Pt-Sn nanoclusters is proportional to the specific surface area, it will reduce the loading of active components of Pt-Sn and decrease the density of L acid sites, resulting in a decrease in the rate of isomerization reaction. If the specific surface area of ​​the carrier pores is too high, the proportion of excessively small micropores will increase significantly, leading to obstructed diffusion of m-xylene and rapid clogging by carbon deposits.

[0013] Secondly, the present invention provides a method for preparing a Pt-Sn heteronuclear bimetallic catalyst, comprising: using aluminum sol as a carrier precursor and PS microspheres as templates, synthesizing a three-dimensional ordered macroporous structure carrier by template method, and then impregnating, drying and calcining, and reducing the loaded Pt-Sn heteronuclear bimetallic catalyst.

[0014] Preferably, the preparation method specifically includes: a) The PS microsphere suspension was centrifuged and assembled into a three-dimensional ordered template by centrifugation. The carrier precursor sol was transferred into the template and vacuum-filled. After molding, drying and calcination to remove the template, a carrier with a three-dimensional ordered macroporous structure was obtained.

[0015] b) The carrier is impregnated in a Pt salt or Sn salt solution for loading, dried, and calcined.

[0016] c) Reduction treatment to activate metal sites.

[0017] Preferably, in step a), the particle size of the PS microspheres is 150-300 nm.

[0018] In step a), centrifugal force drives the PS microspheres to pack tightly together, forming a face-centered cubic (FCC) template. The FCC provides highly interconnected channels, providing a low-resistance path for reactant diffusion.

[0019] Preferably, in step a), 1-3 wt% citric acid is added to the carrier precursor as a dispersant to improve the uniformity of the metal precursor.

[0020] Citric acid, as a dispersant, has a carboxyl group (-COOH) that reacts with Al. 3+ Formation of complexes (e.g., [Al(C6H6O7)]) + This inhibits premature gelation of aluminum sol and reduces the surface tension of the carrier precursor solution, thereby improving the template filling rate.

[0021] Preferably, in step a), the calcination includes: heating to 600-750°C at a rate of 2-5°C / min, holding at that temperature for 4-6 hours, and removing the PS template.

[0022] During calcination, a suitable heating rate can control the densification process of the framework, avoiding pore collapse (too fast) or excessively large grains (too slow). After holding at this temperature, the template is removed, which simultaneously promotes the formation of the Al2O3 crystalline phase.

[0023] Preferably, in step b), the load is subjected to ultrasonic treatment for 30-60 minutes.

[0024] In step b), during impregnation, the cavitation effect of ultrasound is used to break up precursor agglomerates, ensuring a narrow particle size distribution, while allowing metal salt ions to diffuse deeply into the pores.

[0025] Preferably, in step b), the drying conditions are: temperature 80-120℃, time 12-24h.

[0026] Preferably, in step b), the inert atmosphere for calcination is N2 and / or Ar, the temperature is 450-650℃, and the time is 2-4h.

[0027] During calcination, calcination under an inert atmosphere can suppress Sn. 2+ Excessive oxidation, avoid Sn 4+ Premature formation affects the formation of the Pt-Sn interface; a suitable calcination temperature can keep PtO2 highly dispersed while avoiding excessive growth of SnO2 crystals.

[0028] Preferably, in step c), the reduction treatment is carried out in an H2 / Ar (5-10% H2) atmosphere at a temperature of 350-400°C for 2-3 hours.

[0029] In step c), low-temperature reduction limits Pt atom migration and prevents excessively large particle size; an H2 concentration of 5-10% prevents strong reduction from causing Sn to migrate. 4+ Restore to Sn 0 Simultaneously construct Pt 0 -Sn 4+ Interface, Sn 4+ 5s 0 Empty orbit accepts Pt 0 The 5d electrons form Ptδ + -Snδ + key, Sn 4+ Pt sintering is suppressed by anchoring the support through Sn-O-Al bonds.

[0030] Thirdly, the present invention provides the application of the above-mentioned Pt-Sn heteronuclear bimetallic catalyst in the isomerization reaction of C8 mixed aromatics to produce xylene.

[0031] Preferably, the reaction conditions are as follows: a fixed-bed reactor is used; o-xylene, m-xylene, and ethylbenzene are used as C8 mixed aromatic feedstocks in a mass ratio of 1:2-4:1-2; the reaction temperature is 360-380℃, the pressure is 2-3 MPa, the H2 / hydrocarbon molar ratio is 3-5:1, and the weight hourly space velocity (WHSV) is 4-6 h⁻¹. -1 .

[0032] Compared with the prior art, the beneficial effects of the present invention are: (1) Three-dimensional ordered interpenetrating pore structure design: A carrier with a three-dimensional ordered interpenetrating pore structure is constructed by PS microsphere template method. The pore size is uniform and controllable (50-250nm) and the pore wall thickness is 10-50nm, which can significantly improve mass transfer efficiency and inhibit carbon deposition.

[0033] (2) Bimetallic synergistic mechanism: by constructing Pt 0 -Sn 4+ -O interface, Pt provides hydrogenation / dehydrogenation activity, promoting xylene isomerization cycle, Sn (4+) Modulating the acidity of the support and stabilizing the Pt dispersion, and Sn (4·) The carrier is connected via an oxygen bridge, while simultaneously interacting with Pt. 0 Nanoclusters generate electronic interactions, weakening the d-band centers of Pt and enhancing the adsorption capacity of reactants. Detailed Implementation

[0034] The present invention will be further described below with reference to embodiments.

[0035] General Implementation Examples In a first aspect, a Pt-Sn heteronuclear bimetallic catalyst comprises a support having a three-dimensional ordered interpenetrating pore structure, and a Pt-Sn heteronuclear bimetallic catalyst uniformly dispersed in situ on the support; wherein: Pt is Pt 0 Sn is dispersed in the form of nanoclusters. 4+ The valence state exists, anchored to the carrier framework via Sn-O bonds, and associated with neighboring Pt. 0 Pt nanoclusters 0 -Sn (4 +) -O interface structure.

[0036] In some preferred embodiments, the loading of Pt is 0.1-1.5 wt%, and the loading of Sn is 0.5-3.0 wt%.

[0037] In some preferred embodiments, the pore size of the three-dimensional ordered interpenetrating pore structure is 50-250 nm, the pore wall thickness is 10-50 nm, and the specific surface area is 150-300 m². 2 / g.

[0038] Secondly, a method for preparing a Pt-Sn heteronuclear bimetallic catalyst includes: using aluminum sol as a carrier precursor and PS microspheres as a template, synthesizing a three-dimensional ordered macroporous structure carrier by template method, and then impregnating, drying and calcining, and reducing the loaded Pt-Sn heteronuclear bimetallic catalyst.

[0039] In some preferred embodiments, the preparation method specifically includes: a) The PS microsphere suspension was centrifuged and assembled into a three-dimensional ordered template by centrifugation. The carrier precursor sol was transferred into the template and vacuum-filled. After molding, drying and calcination to remove the template, a carrier with a three-dimensional ordered macroporous structure was obtained.

[0040] In some preferred embodiments, in step a), the particle size of the PS microspheres is 150-300 nm.

[0041] In some preferred embodiments, in step a), the concentration of the PS microsphere suspension is 5-10 wt%.

[0042] In some preferred embodiments, in step a), 1-3 wt% citric acid is added to the carrier precursor as a dispersant to improve the uniformity of the metal precursor.

[0043] In some preferred embodiments, step a) includes: heating to 600-750°C at a rate of 2-5°C / min, holding at that temperature for 4-6 hours, and removing the PS template.

[0044] b) The carrier is impregnated in a Pt salt or Sn salt solution for loading, dried, and calcined.

[0045] In some preferred embodiments, in step b), the load is subjected to ultrasonic treatment for 30-60 minutes.

[0046] In some preferred embodiments, in step b), the Pt salt is H2PtCl6; and the Sn salt is SnCl2.

[0047] In some preferred embodiments, in step b), the drying conditions are: temperature 80-120°C, time 12-24h.

[0048] In some preferred embodiments, in step b), the inert atmosphere for calcination is N2 and / or Ar, the temperature is 450-650℃, and the time is 2-4h.

[0049] c) Reduction treatment to activate metal sites.

[0050] In some preferred embodiments, in step c), the reduction process is carried out in an H2 / Ar (5-10% H2) atmosphere at a temperature of 350-400°C for 2-3 hours.

[0051] Thirdly, the application of the above-mentioned Pt-Sn heteronuclear bimetallic catalyst in the isomerization reaction of C8 mixed aromatics to produce xylene.

[0052] In some preferred embodiments, the reaction conditions are as follows: a fixed-bed reactor is used; o-xylene, m-xylene, and ethylbenzene are used as C8 mixed aromatic feedstocks in a mass ratio of 1:2-4:1-2; the reaction temperature is 360-380℃, the pressure is 2-3 MPa, the H2 / hydrocarbon molar ratio is 3-5:1, and the weight hourly space velocity (WHSV) is 4-6 h⁻¹. -1 .

[0053] Specific Examples and Comparative Examples (I) The Influence of Different Supports on the Catalytic Efficiency of Catalysts Example 1: Pt-Sn / Al2O3 catalyst supported by a three-dimensional ordered interpenetrating porous structure (1) Synthesis of Al2O3 with three-dimensional ordered interpenetrating channel structure Monodisperse PS microspheres (200 nm in diameter, 10 wt% ethanol suspension) were assembled into a three-dimensional ordered template by centrifugation; aluminum sol was prepared by mixing aluminum nitrate and deionized water at a mass ratio of 1:5, adding 1 wt% citric acid as a dispersant, and stirring for 2 h; the aluminum sol was vacuum impregnated into the PS template, and dried at 60 °C for 12 h after molding. The temperature was increased to 650℃ at 3℃ / min, and calcined in air for 5 hours. The template was then removed to obtain an Al2O3 support with a three-dimensional ordered interpenetrating pore structure.

[0054] (2) Preparation of Pt-Sn / Al2O3 The Al2O3 prepared above was impregnated in a mixed solution of H2PtCl6 and SnCl2; Dry at 100℃ for 15 hours, then calcine at 500℃ for 3 hours under N2 atmosphere; Pt-Sn / Al2O3 was obtained by reduction in H2 / Ar (5% H2) at 380℃ for 2 h.

[0055] The resulting catalyst includes a three-dimensional ordered interpenetrating pore structure (specific surface area 182 m²). 2 A support with a pore size of approximately 60-200 nm and a pore wall thickness of approximately 40 nm ( / g), and a Pt-Sn heteronuclear bimetallic material uniformly dispersed in situ on the support (Pt loading is 0.6 wt%, Sn loading is 1 wt%); wherein: Pt is in the form of Pt 0 Sn is dispersed in the form of nanoclusters. 4+ The valence state exists, anchored to the carrier framework via Sn-O bonds, and associated with neighboring Pt. 0 Pt nanoclusters 0 -Sn (4+) -O interface structure.

[0056] Comparative Example 1: Pt-Sn / Al2O3 catalyst without a three-dimensional ordered interpenetrating porous support (1) Synthesis of Al2O3 Preparation of aluminum sol: Aluminum nitrate and deionized water are mixed at a mass ratio of 1:5, and 1 wt% citric acid is added as a dispersant. The mixture is stirred for 2 hours. After molding, it is dried at 60°C for 12 hours. The Al2O3 support was obtained by heating to 650℃ at a rate of 3℃ / min and calcining in air for 5 hours.

[0057] (2) Preparation of Pt-Sn / Al2O3 Al2O3 was impregnated in a mixed solution of H2PtCl6 and SnCl2; Dry at 100℃ for 15 hours, then calcine at 500℃ for 3 hours under N2 atmosphere; Pt-Sn / Al2O3 was obtained by reduction in H2 / Ar (5% H2) at 380℃ for 2 h.

[0058] The resulting catalyst includes a support (without a three-dimensional ordered interpenetrating pore structure and a specific surface area of ​​156 m²). 2 / g, with a pore size of approximately 10-50 nm and a pore wall thickness of approximately 23 nm), and a Pt-Sn heteronuclear bimetallic material uniformly dispersed in situ on the support (Pt loading is 0.6 wt%, Sn loading is 1 wt%); wherein: Pt is in the form of Pt 0 Sn is dispersed in the form of nanoclusters. 4+ The valence state exists, anchored to the carrier framework via Sn-O bonds, and associated with neighboring Pt. 0 Pt nanoclusters 0 -Sn (4+) -O interface structure.

[0059] Application Example 1 The catalysts from Example 1 and Comparative Example 1 were applied to the isomerization of mixed C8 aromatics to prepare xylene under the following conditions: a fixed-bed reactor was used, the feedstock was C8 aromatics (ortho:meta:para mass ratio = 20:60:20), the temperature was 360°C, the pressure was 2 MPa, the H2 / hydrocarbon molar ratio was 4:1, and the weight hourly space velocity (WHSV) was 4 h⁻¹. After 10 h of stable operation, samples were taken to test the feedstock conversion and PX selectivity, and the amount of carbon deposited on the catalyst was measured after 500 h. The results are shown in the table below: catalyst Conversion rate (%) PX selectivity (%) Carbon deposits (500h, wt%) Example 1 48.7 92.5 2.4 Comparative Example 1 39.8 81.2 9.2 The data comparison in the table above shows that the three-dimensional ordered interpenetrating pore structure of the catalyst in Example 1, combined with the Pt-Sn bimetallic synergistic effect, can significantly improve the conversion rate and PX selectivity of the reaction, and reduce the amount of carbon deposits.

[0060] (II) Effect of Pt / Sn loading on catalyst performance The catalyst preparation method differs from that in Example 1 in that the loading amounts of Pt and Sn are adjusted as shown in the table below.

[0061] The prepared catalyst was applied to the isomerization of mixed C8 aromatics to prepare xylene under the following conditions: a fixed-bed reactor was used, the feedstock was C8 aromatics (ortho:meta:para mass ratio = 20:60:20), the temperature was 360℃, the pressure was 2 MPa, the H2 / hydrocarbon molar ratio was 4:1, and the weight hourly space velocity (WHSV) was 4 h⁻¹. After 10 h of stable operation, samples were taken to detect the conversion rate of the feedstock and the selectivity of PX. The results are shown in the table below: Pt loading (wt%) Sn loading (wt%) PX selectivity (%) Conversion rate (%) 0.6 0 81.8 53.2 0.6 0.5 89.7 52.1 0.6 1 92.5 51.4 0.6 3.0 91.8 45.2 0.6 5.0 89.3 43.5 0 1 85.7 41.4 0.1 1 88.1 47.5 0.6 1 92.5 51.4 1.5 1 90.3 52.1 3 1 87.6 53.3 The data comparison in the table above shows that when the Pt loading in the catalyst is 0.6 wt%, the feed conversion rate gradually decreases with increasing Sn loading, while the PX selectivity initially increases and then decreases. This is because the strong acidic sites of the Sn-modified support can suppress some cracking side reactions. When the Sn loading in the catalyst is 1 wt%, the feed conversion rate gradually increases with increasing Pt loading, while the PX selectivity also initially increases and then decreases. This is because excessive Pt content can lead to... Excessive hydrogen / dehydrogenation reaction leads to increased side reactions and a higher risk of carbon deposition. The optimal catalytic effect is achieved with a Pt loading of 0.6 wt% and a Sn loading of 1 wt%. This indicates that the loading of Pt and Sn significantly impacts the catalytic performance of the isomerization of mixed C8 aromatics to xylene, thus requiring optimization of their content.

[0062] (III) The Influence of Support Pore Size on Catalytic Efficiency The difference between the catalyst preparation method and Example 1 is that the support pore size is different (i.e., the PS microsphere size is different), as shown in the table below.

[0063] The prepared catalyst was applied to the isomerization of mixed C8 aromatics to prepare xylene under the following conditions: a fixed-bed reactor was used, the feedstock was C8 aromatics (ortho:meta:para mass ratio = 20:60:20), the temperature was 360℃, the pressure was 2 MPa, the H2 / hydrocarbon molar ratio was 4:1, and the weight hourly space velocity (WHSV) was 4 h⁻¹. After 10 h of stable operation, samples were taken to detect the feedstock conversion and PX selectivity, and the amount of carbon deposited on the catalyst was measured after 500 h. The results are shown in the table below: Carrier pore size (nm) Conversion rate (%) PX selectivity (%) Carbon deposits (500h, wt%) 30-100 41.2 86.5 5.8 50-150 48.9 94.1 3.4 60-200 51.4 92.5 2.4 80-250 46.5 92.7 2.2 100-350 39.7 90.2 2.1 The data comparison in the table above shows that when the pore size of the support in the catalyst is between 50-250 nm, the conversion rate of aromatics and the selectivity of PX are both high, and the amount of carbon deposited after 500 h of catalyst use is low. Among them, the catalytic effect is the best when the pore size is 60-200 nm. However, when the pore size of the support is too large, the catalytic effect deteriorates. This indicates that the pore size of the support has a significant impact on the catalytic effect of the isomerization of mixed C8 aromatics to prepare xylene, and that a larger pore size is not always better. Therefore, it is necessary to optimize the pore size of the support.

Claims

1. A Pt-Sn heteronuclear bimetallic catalyst, characterized in that: It includes a carrier with a three-dimensional ordered interpenetrating channel structure, and a Pt-Sn heteronuclear bimetallic material uniformly dispersed in situ on the carrier; wherein: Pt with Pt 0 Sn is dispersed in the form of nanoclusters. 4+ The valence state exists, anchored to the carrier framework via Sn-O bonds, and associated with neighboring Pt. 0 Pt nanoclusters 0 -Sn (4+) -O Interface structure.

2. The Pt-Sn heteronuclear bimetallic catalyst according to claim 1, characterized in that: The loading of Pt is 0.1-1.5 wt%, and the loading of Sn is 0.5-3.0 wt%.

3. The Pt-Sn heteronuclear bimetallic catalyst according to claim 1 or 2, characterized in that: The three-dimensional ordered interpenetrating pore structure has a pore size of 50-250 nm, a pore wall thickness of 10-50 nm, and a specific surface area of ​​150-300 m². 2 / g.

4. A method for preparing a Pt-Sn heteronuclear bimetallic catalyst according to any one of claims 1-3, characterized in that... include: Using aluminum sol as a carrier precursor and PS microspheres as templates, a three-dimensional ordered macroporous structure carrier was synthesized by template method, and then impregnated, dried and calcined, and reduced to load Pt-Sn heteronuclear bimetals.

5. The preparation method according to claim 4, characterized in that... Specifically, it includes: a) Centrifuge the PS microsphere suspension, assemble it into a three-dimensional ordered template by centrifugation, transfer the carrier precursor sol into the template, and fill it under vacuum; After molding, drying, and calcination to remove the template, a carrier with a three-dimensional ordered macroporous structure is obtained; b) The carrier is impregnated in a Pt salt or Sn salt solution for loading, dried, and calcined; c) Reduction treatment to activate metal sites.

6. The preparation method according to claim 5, characterized in that: In step a), The PS microspheres have a particle size of 150-300 nm; The carrier precursor also contains 1-3 wt% citric acid as a dispersant; The calcination process includes: heating to 600-750℃ at a rate of 2-5℃ / min, holding at that temperature for 4-6 hours, and then removing the PS template.

7. The preparation method according to claim 5, characterized in that: In step b), The load is subjected to ultrasonic treatment for 30-60 minutes. The drying conditions are: temperature 80-120℃, time 12-24h; The inert atmosphere for calcination is N2 and / or Ar, the temperature is 450-650℃, and the time is 2-4h.

8. The preparation method according to claim 5, characterized in that: In step c), The reduction process is carried out in an H2 / Ar atmosphere at a temperature of 350-400℃ for 2-3 hours.

9. The application of the Pt-Sn heteronuclear bimetallic catalyst according to any one of claims 1-3 or the Pt-Sn heteronuclear bimetallic catalyst obtained by the preparation method according to any one of claims 4-8 in the isomerization reaction of C8 mixed aromatics to produce xylene.

10. The application according to claim 9, characterized in that: The conditions for the reaction are: A fixed-bed reactor was used. o-xylene, m-xylene, and ethylbenzene in a mass ratio of 1:2-4:1-2 were used as C8 mixed aromatics feedstock; Reaction temperature 360-380℃, pressure 2-3 MPa, H2 / hydrocarbon molar ratio 3-5:1, weight hourly space velocity 4-6 h⁻¹ -1 .