A lattice-confined bimetallic ZnCr@S-1 catalyst and a preparation method and application thereof

Abstract

This invention discloses a lattice-confined bimetallic ZnCr@S-1 catalyst, its preparation method, and its application, belonging to the field of catalytic material preparation technology. Using S-1 molecular sieves as a support, this invention employs a synergistic strategy of sol-gel combined with rotary evaporation for confined loading and in-situ calcination. This anchors Zn and Cr species in the lattice channels and framework defect sites of the S-1 molecular sieve in the form of bimetallic alloy clusters or heteronuclear coordination structures, thereby obtaining the catalyst. Through the bimetallic synergistic effect of Zn and Cr and the lattice confinement effect of the S-1 molecular sieve, this invention simultaneously improves the activity, selectivity, and stability of the catalyst, suppresses agglomeration and carbon deposition at high temperatures, and the obtained catalyst exhibits excellent catalytic performance in the propane / CO2 coupled dehydrogenation to propylene reaction. This provides a new approach for the design of highly efficient bifunctional propane dehydrogenation catalysts and has significant industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of catalytic material preparation technology, specifically relating to a lattice-confined bimetallic ZnCr@S-1 catalyst and its preparation method, as well as its application in the propane / CO2 coupled dehydrogenation to propylene reaction. Background Technology

[0002] As propylene serves as a core raw material in the basic chemical industry, its market demand continues to grow alongside the development of downstream industries such as polypropylene and acrylonitrile. Direct propane dehydrogenation (PDH) technology, due to its wide availability of raw materials and environmentally friendly process, has become the mainstream direction for increasing propylene production. However, this reaction suffers from problems such as thermodynamic equilibrium limitations and catalyst agglomeration and deactivation at high temperatures. Introducing CO2 as a weak oxidant to construct a coupled dehydrogenation system can consume the H2 generated by PDH through reverse water-gas reaction (RWGS), breaking the thermodynamic equilibrium and simultaneously achieving the resource utilization of CO2, aligning with the "dual carbon" goal.

[0003] Cr-based catalysts are a classic system for propane dehydrogenation, but single Cr-based catalysts suffer from drawbacks such as poor dispersion of active sites, easy formation of inactive Cr₂O₃ aggregates at high temperatures, and insufficient propylene selectivity. Bimetallic synergistic strategies are an effective way to improve catalyst performance. Zn, as a modifying metal, can regulate the electronic state, dispersion, and catalytic selectivity of the main active component through its electronic properties and geometric effects. However, in the preparation of traditional bimetallic catalysts, metal species are prone to phase separation or agglomeration, making it difficult to form stable bimetallic active sites and limiting the synergistic effect.

[0004] S-1 molecular sieves possess well-ordered MFI-type lattice channels (5.1 × 5.5 Å and 5.3 × 5.6 Å), high specific surface area, and good thermal stability. Their lattice channels and framework defect sites can anchor metal species through physical confinement and chemical coordination. Currently, there are no reports on constructing Zn-Cr bimetallic synergistic active sites using lattice confinement strategies for propane / CO2 coupled dehydrogenation reactions. Developing such catalysts is of great significance for solving the aggregation problem of traditional bimetallic catalysts and enhancing synergistic effects. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of existing Cr-based catalysts and bimetallic catalysts, and to provide a lattice-confined bimetallic ZnCr@S-1 catalyst, which fixes the Zn-Cr bimetallic active sites through the lattice confinement effect of S-1 molecular sieve, thereby improving the catalytic performance of the obtained catalyst for the propane / CO2 coupled dehydrogenation reaction.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: One objective of this invention is to protect a lattice-confined bimetallic ZnCr@S-1 catalyst, which uses a pure silicon S-1 molecular sieve with an MFI topology as a support. The catalyst utilizes the synergistic confinement effect of its lattice channels and framework defect sites to anchor bimetallic alloy clusters or heteronuclear coordination structures formed by Zn and Cr species. The introduction of Zn allows Cr to... 6+ Species increased, while Cr 6+ The species may be the active site for the propane dehydrogenation reaction.

[0007] Furthermore, the Cr loading in the catalyst is 0.5~10wt% (preferably 1~5wt%).

[0008] Furthermore, the specific surface area of ​​the catalyst is 135~307 m². 2 / g, pore volume 0.18~0.27cm³ 3 / g, with a pore size of 1.9~10nm.

[0009] The second objective of this invention is to protect the preparation method of the lattice-confined bimetallic ZnCr@S-1 catalyst, which includes the following steps: 1) Preparation of S-1 molecular sieve: Using tetraethyl orthosilicate (TEOS) as silicon source, tetrapropylammonium hydroxide (TPAOH) as template agent, and urea as structure regulator, the precursor of S-1 molecular sieve was synthesized by hydrothermal crystallization, and then the template agent was removed by calcination to obtain S-1 molecular sieve. 2) Preparation of Zn-Cr composite metal sol: Cr source compound and Zn source compound were added to a mixed solvent of anhydrous ethanol and deionized water. After stirring until the solid was completely dissolved, chelating agent citric acid was added, and the pH of the system was adjusted to 3-5 with dilute nitric acid. Then, the chelation and hydrolysis reaction was carried out under constant temperature conditions to obtain a transparent and uniform Zn-Cr composite metal sol. 3) Confined loading: The Zn-Cr composite metal sol prepared in step 2) is added dropwise to the S-1 molecular sieve prepared in step 1), and the bimetallic ions are uniformly penetrated into the lattice channels and framework defect sites of the S-1 molecular sieve by rotation impregnation. 4) In-situ calcination anchoring: The sample impregnated in step 3) is dried and calcined sequentially. During the calcination process, the Cr source compound and the Zn source compound decompose to generate Cr. 6+ Zn 2+ The species react with hydroxyl and oxygen atoms on the surface of the S-1 molecular sieve framework to form Zn-O-Cr-Si coordination bonds, thereby confining and fixing the bimetallic species by the lattice channels and defect sites, thus obtaining the lattice-confined bimetallic ZnCr@S-1 catalyst.

[0010] Furthermore, the mass ratio of tetraethyl orthosilicate, tetrapropylammonium hydroxide, and urea used in step 1) is 1:1.31:0.18.

[0011] Furthermore, the hydrothermal crystallization temperature in step 1) is 170~190 ℃, and the time is 48~72 h.

[0012] Furthermore, the calcination described in step 1) involves heating to 550-600°C at a rate of 3-5°C / min and holding at that temperature for 6-8 hours.

[0013] Further, the Cr source compound mentioned in step 2) is one or more of chromium nitrate nonahydrate, chromic anhydride, and chromium acetylacetonate, preferably chromium nitrate nonahydrate.

[0014] Further, the Zn source compound mentioned in step 2) is one or more of zinc nitrate hexahydrate, zinc acetate, and zinc oxide, preferably zinc nitrate hexahydrate.

[0015] Further, in step 2), the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 2:1.

[0016] Furthermore, in step 2), the molar ratio of the Cr source compound, the Zn source compound, and citric acid is 1:(0.5~2):1.2.

[0017] Furthermore, the chelation hydrolysis reaction described in step 2) is carried out at a temperature of 40~60℃ for 2~4 h.

[0018] Furthermore, the total volume of the Zn-Cr composite metal sol added in step 3) is equal to the pore volume of the S-1 molecular sieve to ensure that the sol can fully penetrate into the pores of the carrier.

[0019] Furthermore, in step 3), the temperature of the rotary impregnation is 60~80℃, the rotation speed is 100~200 r / min, and the impregnation time is 1~3h.

[0020] Furthermore, during the rotary impregnation process described in step 3), a dispersing agent may be added to reduce the agglomeration tendency of bimetallic ions and promote the uniform dispersion of bimetallic ions in the carrier pores.

[0021] Furthermore, the dispersing agent is ethylene glycol or glycerol.

[0022] Further, the drying temperature in step 4) is 80~100℃, and the time is 4~6h.

[0023] Further, in step 4), the calcination is carried out by heating to 500-600℃ at a rate of 5-10℃ / min and holding at that temperature for 3-5 hours.

[0024] A third objective of this invention is to protect the lattice-confined bimetallic ZnCr@S-1 catalyst in its application in the catalytic dehydrogenation of propane / CO2 to propylene.

[0025] During the reaction, the lattice-confined Zn-O-Cr active sites are the main catalytic centers. Zn species regulate the electronic state of Cr through electron transfer, reducing the activation energy of CH bonds and inhibiting Cr species aggregation. Cr species enhance CO2 adsorption and activation, consuming H2 generated by PDH through the reverse water-gas reaction and breaking the thermodynamic equilibrium. CO2 can further eliminate carbon deposits on the catalyst surface through the Boudouard reaction. Therefore, the synergistic effect of bimetals and the weak oxidation effect of CO2 can jointly inhibit carbon deposition and extend catalyst life.

[0026] Furthermore, the reaction conditions are as follows: reaction temperature 500~600℃ (preferably 550℃), reaction pressure 0.1~0.5MPa, reaction gas volume ratio C3H8:CO2:Ar=1:(1~2):0.04 (preferably 1:2:0.04), and gas hourly space velocity (WHSV)=10000~15000mL·g -1 ·h -1 .

[0027] Compared with the prior art, the present invention has the following significant advantages: (1) The present invention anchors Zn-Cr bimetallic species in the form of alloy clusters or heteronuclear coordination structures to the lattice channels and defect sites of S-1 molecular sieve through the lattice confinement effect, forming a stable Zn-O-Cr-Si coordination network, which effectively inhibits the phase separation and aggregation of bimetallic species in high-temperature reactions and significantly improves the stability of the catalyst.

[0028] (2) The bimetallic synergistic effect of Zn and Cr significantly optimizes the catalytic performance: Zn species regulate the electronic state and dispersion of Cr, and improve the activation efficiency of CH bond; Cr species enhance CO2 activation and RWGS reaction. The synergistic effect of the two can increase the propane conversion rate to more than 48.1% and the propylene selectivity to more than 91%, which is better than the performance of single metal Cr-based catalysts.

[0029] (3) The present invention uses a combination of sol-gel and rotary evaporation for lattice confinement loading and in-situ calcination as a synergistic strategy to achieve high uniformity loading of bimetals. The process is simple, easy to operate, requires no complex equipment, has low cost, and is easy to scale up industrially. The resulting catalyst exhibits excellent comprehensive performance in propane / CO2 coupled dehydrogenation reaction and has broad prospects for industrial application. Attached Figure Description

[0030] Figure 1XRD patterns (A) and magnified views (B) of the S-1 support, ZnCr@S-1 catalyst, and Cr / S-1 catalyst prepared in Example 1, respectively. As shown in the figures, the diffraction peaks of the S-1 support significantly decreased after loading the active metal, indicating that the loading of the active metal affects the crystallinity of the S-1 support (A). Meanwhile, obvious Cr2O3 diffraction peaks are visible on the XRD pattern of the Cr / S-1 catalyst, while only weak Cr2O3 diffraction peaks are observed on the ZnCr@S-1 catalyst. In addition, a small amount of ZnCr2O4 spinel phase was detected, indicating that the introduction of Zn promotes the dispersion of Cr species on the S-1 support, thereby greatly improving the catalytic activity of the samples (B).

[0031] Figure 2 The adsorption isotherms (A) and pore size distribution diagrams (B) of the S-1 support, ZnCr@S-1 catalyst prepared in Example 1, and the Cr / S-1 catalyst prepared in Comparative Example 1 are shown. As can be seen from the figures, the obtained catalysts all exhibit the characteristics of a mesoporous type IV isotherm and all have H3 type hysteresis loops.

[0032] Figure 3 The UV-Vis spectra of the Cr / S-1 catalyst prepared in Comparative Example 1 and the ZnCr@S-1 catalyst prepared in Example 1 before and after the reaction are shown in the figure. As can be seen from the figure, the fresh Cr / S-1 catalyst exhibits adsorption bands at 274 nm and 376 nm, which are attributed to O2 in the chromate via tetrahedral coordination. 2- Cr 6+ The charge transfer transitions, with adsorption bands at 460 nm and 600 nm, are attributed to Cr2O3 or CrO. x Octahedral Cr in clusters 3+ Species transition; however, the fresh ZnCr@S-1 catalyst only exhibits adsorption bands at 274 nm and 376 nm, and the band strength is stronger than that of the Cr / S-1 catalyst. This indicates that the introduction of Zn enables Cr to undergo adsorption. 6+ Species increase, Cr 3+ The reduction in species concentration led to a significant decrease in the Cr2O3 diffraction peak, which is consistent with the XRD results. Furthermore, observation of the UV-Vis spectra of the ZnCr@S-1 catalyst before and after the reaction revealed the disappearance of the band structure at 376 nm after the reaction, indicating the isolation of Cr species during the reaction. 6+ A change has occurred, indicating that Cr 6+ It is very likely the active site for the propane dehydrogenation reaction. Detailed Implementation

[0033] A lattice-confined bimetallic ZnCr@S-1 catalyst is constructed using a pure silica S-1 molecular sieve with an MFI topology as a support. The catalyst utilizes the synergistic confinement effect of its lattice channels and framework defect sites to anchor bimetallic alloy clusters or heteronuclear coordination structures formed by Zn and Cr species, thereby constituting the catalyst. Its preparation includes the following steps: 1) Preparation of S-1 molecular sieve: Urea was dissolved in deionized water, and then tetrapropylammonium hydroxide (TPAOH) was added. The mixture was stirred at 900 r / min for 2 h at room temperature. Then, under continued stirring, tetraethyl orthosilicate (TEOS) was added dropwise to the above solution. After the addition was complete, isopropanol was added and stirred for 30 min. The mixed solution was then hydrothermally crystallized at 170~190℃ for 48~72 h. After crystallization, the mixture was filtered, washed until neutral, dried at 80℃ overnight, ground, and then heated to 550~600℃ in a muffle furnace at a rate of 3~5℃ / min and held for 6~8 h to remove the template agent, thus obtaining pure silicon S-1 molecular sieve with MFI lattice structure. The mass ratio of tetraethyl orthosilicate, tetrapropylammonium hydroxide, and urea used was 1:1.31:0.18. 2) Preparation of Zn-Cr composite metal sol: The Cr source compound and the Zn source compound were added to a mixed solvent of anhydrous ethanol and deionized water (2:1, v / v), and stirred until the solid was completely dissolved. Then, citric acid was added as a chelating agent, and the pH of the system was adjusted to 3-5 with dilute nitric acid. The chelation and hydrolysis reaction was then carried out by stirring at a constant temperature of 40-60℃ for 2-4 h to obtain a transparent and homogeneous Zn-Cr composite metal sol. The molar ratio of the Cr source compound, Zn source compound and citric acid used was 1:(0.5-2):1.2. 3) Confined loading: Add the Zn-Cr composite metal sol prepared in step 2) dropwise to the S-1 molecular sieve prepared in step 1), with an equal pore volume to it, and then rotate and impregnate at 60~80℃ and 100~200 r / min for 1~3h to allow the bimetallic ions to uniformly penetrate into the lattice channels and framework defect sites of the S-1 molecular sieve. 4) In-situ calcination anchoring: The sample impregnated in step 3) is dried at 80~100℃ for 4~6h, and then heated to 500~600℃ at a rate of 5~10℃ / min and calcined for 3~5h to obtain a lattice-confined bimetallic ZnCr@S-1 catalyst, wherein the Cr loading is 0.5~10wt%.

[0034] In step 2), the Cr source compound is one or more of chromium nitrate nonahydrate, chromic anhydride, and chromium acetylacetone. The Zn source compound is one or more of zinc nitrate hexahydrate, zinc acetate, and zinc oxide.

[0035] In step 3), dispersing agents such as ethylene glycol or glycerol may be added during the rotary impregnation process.

[0036] The specific surface area of ​​the obtained catalyst is 135~307 m². 2 / g, pore volume 0.18~0.27cm³ 3 / g, with a pore size of 1.9~10nm.

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

[0038] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods. Example 1

[0039] S1. Preparation of S-1 molecular sieve support: Weigh 3g of urea and dissolve it in 19.137g of deionized water; add 21.963g of TPAOH and stir at 900r / min for 2h at room temperature. Then, while continuing to stir, add 16.8g of TEOS dropwise to the above solution using a peristaltic pump; after the addition is complete, add 0.168g of isopropanol and stir for 30min; then transfer the mixed solution to a 200mL hydrothermal reactor and hydrothermally crystallize at 180℃ for 48h; after crystallization, filter, wash until neutral, dry at 80℃ overnight, grind, and then heat to 550℃ in a muffle furnace at a rate of 3℃ / min for 6h to remove the template agent, obtaining the S-1 support (pore volume 0.17cm). 3 / g).

[0040] S2. Preparation of Zn-Cr composite metal sol: Weigh 0.05 g of chromium nitrate nonahydrate and 0.103 g of zinc nitrate hexahydrate, dissolve them in a mixed solvent of 0.17 mL of anhydrous ethanol and deionized water (2:1, v / v), stir for 30 min until the solid is completely dissolved, then add 0.001 g of ethylene glycol as a dispersant and 0.068 g of citric acid as a chelating agent, and adjust the pH of the system to 3-5 with dilute nitric acid. Then, stir at a constant temperature of 50 ℃ for 2.5 h to carry out the chelation hydrolysis reaction to obtain a transparent and stable Zn-Cr composite metal sol; S3. Lattice-confined bimetallic support: 1 g of S-1 support was placed in a rotary evaporator, and 0.17 mL of the above Zn-Cr composite metal sol was added dropwise. The mixture was then rotated and impregnated for 2 h at 70 °C and 150 r / min. S4. In-situ calcination anchoring: The impregnated sample was dried at 80℃ for 5h, and then placed in a muffle furnace and heated to 500℃ at a rate of 5℃ / min for calcination for 4h to obtain a lattice-confined bimetallic ZnCr@S-1 catalyst, wherein the theoretical loading of Cr is 5 wt% and the theoretical loading of Zn is 10 wt%. Example 2

[0041] The preparation of S1. S-1 molecular sieve support is the same as in Example 1.

[0042] S2. Preparation of Zn-Cr composite metal sol: Weigh 0.05 g of chromium nitrate nonahydrate and 0.05 g of zinc nitrate hexahydrate, dissolve them in a mixed solvent of 0.17 mL of anhydrous ethanol and deionized water (2:1, v / v), stir for 30 min until the solid is completely dissolved, then add 0.0005 g of glycerol as a dispersant, then add 0.068 g of citric acid as a chelating agent, and adjust the pH of the solution to 3-5 with dilute nitric acid. Then carry out the chelation hydrolysis reaction by stirring at 50 ℃ for 2 h to obtain a transparent, uniform and stable Zn-Cr composite metal sol; S3. Lattice-confined bimetallic support: 1 g of S-1 support was placed in a rotary evaporator, and 0.17 mL of the above Zn-Cr composite metal sol was added dropwise. The mixture was then rotated and impregnated for 3 h at 60 °C and 120 r / min. S4. In-situ calcination anchoring: The impregnated sample was dried at 90℃ for 4h, placed in a muffle furnace and heated to 550℃ at 8℃ / min, and calcined for 3h to obtain a lattice-confined bimetallic ZnCr@S-1 catalyst, wherein the theoretical loading of Cr and Zn is 5wt%.

[0043] Comparative Example 1 The preparation of S1. S-1 molecular sieve support is the same as in Example 1.

[0044] S2. Preparation of Cr metal sol: Weigh 0.05 g of chromium nitrate nonahydrate and dissolve it in a mixed solvent of 0.17 mL of anhydrous ethanol and deionized water (2:1, v / v). Stir for 30 min until the solid is completely dissolved. Then, add 0.001 g of ethylene glycol as a dispersant and 0.068 g of citric acid as a chelating agent. Adjust the pH of the system to 3-5 with dilute nitric acid. Then, stir at a constant temperature of 50 ℃ for 2.5 h to carry out the chelation and hydrolysis reaction to obtain a transparent and stable Cr metal sol. S3. Lattice-confined metal loading: 1 g of S-1 support was placed in a rotary evaporator, and 0.17 mL of the above Cr metal sol was added dropwise. The mixture was then rotated and impregnated at 70 °C and 150 r / min for 2 h. S4. In-situ calcination anchoring: The impregnated sample was dried at 80℃ overnight and calcined at 500℃ for 4 hours to obtain a single metal Cr@S-1 catalyst with a theoretical Cr loading of 5wt%.

[0045] Comparative Example 2 The preparation of S1. S-1 molecular sieve support is the same as in Example 1.

[0046] S2. Preparation of Zn-Cr bimetallic impregnation solution: Weigh 0.05 g of chromium nitrate nonahydrate and 0.05 g of zinc nitrate hexahydrate, dissolve them in 0.17 mL of deionized water, stir for 30 min until completely dissolved, and then add 0.001 g of ethylene glycol as a dispersing agent to obtain the bimetallic impregnation solution; S3. Lattice-confined bimetallic support: 1 g of S-1 support was placed in a rotary evaporator, and 0.17 mL of the above bimetallic impregnation solution was added dropwise. The mixture was then rotated and impregnated for 2 h at 70 ℃ and 150 r / min. S4. In-situ calcination anchoring: The impregnated sample was dried at 80 °C for 5 h, and then placed in a muffle furnace and heated to 500 °C at a rate of 5 °C / min for calcination for 4 h to obtain a lattice-confined bimetallic ZnCr@S-1 catalyst, wherein the theoretical loading of Cr and Zn is 5 wt%.

[0047] Comparative Example 3 The preparation of S1. S-1 molecular sieve support is the same as in Example 1.

[0048] S2. Preparation of ZnCr / S-1 catalyst by physical mixing method: 0.05g of chromium nitrate nonahydrate, 0.05g of zinc nitrate hexahydrate and 1g of S-1 support were physically mixed and ground for 20min, dried at 80℃ for 5h and calcined at 500℃ for 4h to obtain ZnCr / S-1 catalyst, wherein the theoretical loading of Cr and Zn is 5wt%.

[0049] Comparative Example 4 The preparation of S1. S-1 molecular sieve support is the same as in Example 1.

[0050] S2. Preparation of Cr-Ga composite metal sol: Weigh 0.05 g of chromium nitrate nonahydrate and 0.05 g of gallium nitrate, dissolve them in a mixed solvent of 0.17 mL of anhydrous ethanol and deionized water (2:1, v / v), stir for 30 min until the solid is completely dissolved, then add 0.001 g of ethylene glycol as a dispersant and 0.068 g of citric acid as a chelating agent, and adjust the pH of the system to 3-5 with dilute nitric acid. Then, stir at a constant temperature of 50 ℃ for 2.5 h to carry out the chelation hydrolysis reaction, and obtain a transparent and stable Cr-Ga composite metal sol to obtain a bimetallic impregnation solution; S3. Lattice-confined bimetallic support: 1 g of S-1 support was placed in a rotary evaporator, and 0.17 mL of the above Cr-Ga composite metal sol was added dropwise. The mixture was then rotated and impregnated for 2 h at 70 ℃ and 150 r / min. S4. In-situ calcination anchoring: The impregnated sample was dried at 80 °C for 5 h, and then placed in a muffle furnace and heated to 500 °C at a rate of 5 °C / min for calcination for 4 h to obtain a lattice-confined bimetallic GaCr@S-1 catalyst, wherein the theoretical loading of Cr and Ga is 5 wt%.

[0051] Comparative Example 5 The preparation of S1. S-1 molecular sieve support is the same as in Example 1.

[0052] S2. Preparation of Zn-Fe composite metal sol: Weigh 0.05 g zinc nitrate hexahydrate and 0.05 g ferric nitrate nonahydrate, dissolve them in a mixed solvent of 0.17 mL anhydrous ethanol and deionized water (2:1, v / v), stir for 30 min until the solid is completely dissolved, then add 0.001 g ethylene glycol as a dispersant and 0.068 g citric acid as a chelating agent, and adjust the pH of the system to 3-5 with dilute nitric acid. Then, stir at a constant temperature of 50 ℃ for 2 h to carry out the chelation hydrolysis reaction, and obtain a transparent and stable Zn-Fe composite metal sol to obtain a bimetallic impregnation solution; S3. Lattice-confined bimetallic loading: 1 g of S-1 support was placed in a rotary evaporator, and 0.17 mL of the above Zn-Fe composite metal sol was added dropwise. The mixture was then rotated and impregnated for 2 h at 70 ℃ and 150 r / min. S4. In-situ calcination anchoring: The impregnated sample was dried at 80 °C for 5 h, and then placed in a muffle furnace and heated to 500 °C at a rate of 5 °C / min for calcination for 4 h to obtain a lattice-confined bimetallic ZnFe@S-1 catalyst, wherein the theoretical loading of Zn and Fe is 5 wt%.

[0053] The specific surface area, pore volume, and pore size of the S-1 support, Cr / S-1, and CrZn / S-1 catalysts were measured using BET. The results are shown in […]. Figure 2 And Table 1.

[0054] Table 1. Basic physical properties of catalysts

[0055] As can be seen from Table 1, the specific surface area of ​​the catalysts loaded with active metals is lower than that of the S-1 support. The higher the loading, the more significant the decrease in specific surface area, indicating that the introduction of active metals occupies part of the pores of the support, thus leading to a decrease in specific surface area. The pore volume and pore size of the catalysts also show an increasing trend with the increase of loading, indicating that the introduction of active metals has, to some extent, disrupted the pore structure of the S-1 support.

[0056] Performance testing The catalysts prepared in the examples and comparative examples were used in the propane / CO2 coupled dehydrogenation reaction under the following conditions: 550 °C, 0.1 MPa, C3H8:CO2:Ar = 1:2:0.04 (v / v / v), WHSV = 13500 mL·g -1 ·h -1 The results are shown in Table 2.

[0057] Table 2

[0058] As shown in Table 2, the ZnCr@S-1 catalyst prepared by the present invention through a lattice confinement and bimetallic synergistic strategy significantly outperforms the single-metal Cr-based catalyst (Comparative Example 1), the impregnated bimetallic catalyst (Comparative Example 2), and the physically mixed bimetallic catalyst (Comparative Example 3) in terms of catalytic activity, selectivity, and stability, demonstrating the synergistic effect of lattice confinement and bimetallic interaction. Furthermore, the Zn-Cr bimetallic composition of the present invention is also superior to Cr-Ga and Zn-Fe bimetallic compositions. The Cr-Ga system suffers from poor metal ion radius matching, making it difficult to construct a stable coordination network within the molecular sieve lattice, resulting in weak bimetallic electronic interactions, limited improvement in catalytic activity, and easy loss of gallium components at high temperatures, leading to poor stability over long periods. The Zn-Fe bimetallic system exhibits weak CO2 activation ability, poor bimetallic synergistic effect, and is prone to metal particle sintering and agglomeration during the reaction, resulting in severe carbon deposition (up to 5.6 wt% after 20 hours of continuous reaction). This demonstrates that the selection of the Zn-Cr bimetallic composition in this invention has achieved unexpected technical results.

[0059] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A lattice-confined bimetallic ZnCr@S-1 catalyst, characterized in that, Using S-1 molecular sieve as a support, the catalyst is constructed by anchoring bimetallic alloy clusters or heteronuclear coordination structures formed by Zn and Cr species through the synergistic confinement effect of its lattice channels and framework defect sites; the loading of Cr in the catalyst is 0.5~10wt%.

2. The lattice-confined bimetallic ZnCr@S-1 catalyst according to claim 1, characterized in that, The catalyst has a specific surface area of ​​135~307 m². 2 / g, pore volume 0.18~0.27cm³ 3 / g, with a pore size of 1.9~10nm.

3. A method for preparing the lattice-confined bimetallic ZnCr@S-1 catalyst as described in claim 1, characterized in that, Includes the following steps: 1) Preparation of S-1 molecular sieve: Using tetraethyl orthosilicate as silicon source, tetrapropylammonium hydroxide as template agent, and urea as structure regulator, the precursor of S-1 molecular sieve was synthesized by hydrothermal crystallization, and then the template agent was removed by calcination to obtain S-1 molecular sieve. 2) Preparation of Zn-Cr composite metal sol: Cr source compound and Zn source compound were added to a mixed solvent of anhydrous ethanol and deionized water. After stirring until the solid was completely dissolved, chelating agent citric acid was added, and the pH of the system was adjusted to 3-5 with dilute nitric acid. Then, the chelation and hydrolysis reaction was carried out under constant temperature conditions to obtain a transparent and uniform Zn-Cr composite metal sol. 3) Confined loading: The Zn-Cr composite metal sol prepared in step 2) is added dropwise to the S-1 molecular sieve prepared in step 1), and the bimetallic ions are uniformly penetrated into the lattice channels and framework defect sites of the S-1 molecular sieve by rotation impregnation. 4) In-situ calcination anchoring: The sample impregnated in step 3) is dried and calcined to obtain the lattice-confined bimetallic ZnCr@S-1 catalyst.

4. The preparation method according to claim 3, characterized in that, In step 1), the mass ratio of tetraethyl orthosilicate, tetrapropylammonium hydroxide, and urea is 1:1.31:0.18; the hydrothermal crystallization temperature is 170~190 ℃ and the time is 48~72h; the calcination is carried out by heating to 550~600℃ at a rate of 3~5℃ / min and holding for 6~8h.

5. The preparation method according to claim 3, characterized in that, In step 2), the Cr source compound is one or more of chromium nitrate nonahydrate, chromic anhydride, and chromium acetylacetone; the Zn source compound is one or more of zinc nitrate hexahydrate, zinc acetate, and zinc oxide; the volume ratio of anhydrous ethanol to deionized water in the mixed solvent is 2:1; the molar ratio of the Cr source compound, Zn source compound, and citric acid used is 1:(0.5~2):1.2; the temperature of the chelation hydrolysis reaction is 40~60℃, and the time is 2~4 h.

6. The preparation method according to claim 3, characterized in that, The total volume of the Zn-Cr composite metal sol added in step 3) is equal to the pore volume of the S-1 molecular sieve; the temperature of the rotary impregnation is 60~80℃, the rotation speed is 100~200 r / min, and the impregnation time is 1~3h.

7. The preparation method according to claim 3, characterized in that, Step 3) A dispersing agent is added during the rotary impregnation process; the dispersing agent is ethylene glycol or glycerol.

8. The preparation method according to claim 3, characterized in that, Step 4) The drying temperature is 80~100℃ and the time is 4~6h; the calcination is to raise the temperature to 500~600℃ at a rate of 5~10℃ / min and hold it for 3~5h.

9. The application of the lattice-confined bimetallic ZnCr@S-1 catalyst as described in claim 1 in the catalytic dehydrogenation of propane / CO2 to propylene.

10. The application according to claim 9, characterized in that, The reaction conditions are as follows: reaction temperature 500~600℃, reaction pressure 0.1~0.5MPa, gas volume ratio of C3H8:CO2:Ar = 1:(1~2):0.04, and gas hourly space velocity (WHSV) = 10000~15000mL·g. -1 ·h -1 .

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