HZSM-5 molecular sieve catalyst and application thereof

Abstract

The application discloses an HZSM-5 molecular sieve catalyst and application thereof, wherein the catalyst is a single-shell HZSM-5 molecular sieve catalyst or a double-shell monolithic HZSM-5 molecular sieve catalyst. The catalyst has high low-temperature catalytic activity and the characteristics of resistance to sulfur, water and chlorine poisoning when catalyzing oxidation of VOCs, improves the stability of the catalyst, has high HCl selectivity, and can reduce the generation of Cl2 and other organic by-products. The successful preparation of the catalyst can improve the low-temperature purification of complex organic waste gas, especially the efficient removal of heteroatom VOCs, and has certain economic and environmental benefits.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to an HZSM-5 molecular sieve catalyst and its applications. Background Technology

[0002] Compared to other VOCs treatment technologies, combustion methods offer higher VOCs removal efficiency and stability, making them popular among enterprises. However, compared to direct combustion, catalytic combustion technology offers advantages such as lower energy consumption and smaller footprint, making it more suitable for low-carbon development. The core of catalytic combustion technology is the catalyst; the quality of the catalyst directly determines the treatment efficiency, energy consumption, and secondary pollution issues. The properties of industrial waste gas also determine the applicability of catalytic combustion technology. Problems such as carbon buildup, poor water resistance, active component poisoning, and numerous toxic byproducts are key issues to be addressed in catalyst design and development. Many scholars have conducted extensive research on these issues, including studies on carbon buildup mechanisms, poisoning mechanisms, and the formation mechanisms of toxic byproducts. However, the complex composition of VOCs leads to poor matching between catalyst properties and waste gas properties, resulting in persistent problems such as carbon buildup and poisoning. Furthermore, while precious metal catalysts have high activity, they are prone to poisoning, while non-precious metal catalysts have strong resistance to chlorine poisoning but low activity and produce numerous byproducts. The catalytic oxidation of VOCs (including halogenated hydrocarbons and sulfur-containing VOCs) is subject to the synergistic effects of catalytic degradation and oxidation. Therefore, further enhancing the synergistic effect of catalyst surface acidity and redox properties, and improving their compatibility, is crucial for catalyst design and development. Furthermore, industrial waste gases contain a certain amount of water vapor, thus the developed catalysts must possess a certain degree of hydrothermal stability.

[0003] Research and investigation revealed that existing commercial catalysts have poor effectiveness and applicability to complex gases, mainly due to poor deep oxidation of reactants, numerous byproducts, and high catalytic temperatures.

[0004] HZSM-5 (Zeolite Socony Mobil–5) molecular sieves are preferred for the catalytic purification of VOCs and CVOCs due to their advantages such as tunable hydrophobicity, controllable surface acidity, and high thermal stability. However, traditional HZSM-5 sieves, with their small pore size and low oxidation performance, cannot completely oxidize organic transition states in a timely manner, leading to significant carbon and chlorine deposition, which greatly limits their practical application. Therefore, enhancing the low-temperature deep oxidation performance of HZSM-5 for VOCs, especially CVOCs, and improving its practical application is of great significance for enhancing the application of catalytic combustion technology in the field of organic waste gas purification.

[0005] To date, considerable research has been conducted on improving the catalytic oxidation performance of HZSM-5 for VOCs, mainly in the following aspects: (1) supporting metal oxides; (2) increasing the specific surface area and mesopore volume of molecular sieves; and (3) preparing novel composite catalysts. However, the problems of carbon and chlorine on the surface of molecular sieve catalysts and sulfur poisoning resistance have not been effectively solved.

[0006] Therefore, how to better improve the resistance of HZSM-5 catalyst to chlorine, sulfur, carbon deposition, and low-temperature deep oxidation is an important problem that needs to be solved. This has guiding significance for improving the practical application of HZSM-5 molecular sieves in the catalytic oxidation of CVOCs, and is of great significance and application value for enhancing the position of catalytic combustion technology in the field of heteroatom VOCs and achieving low-energy emission reduction and green development. Summary of the Invention

[0007] To address the aforementioned shortcomings in existing technologies and improve the removal efficiency of VOCs from complex gases, as well as enhance the catalytic activity and stability of VOCs, this invention develops an HZSM-5 molecular sieve catalyst co-modified with single-atom metals and heteronuclear metal oxide ultrafine nanoclusters. This catalyst not only improves the removal efficiency of VOCs from complex gases and reduces the generation of byproducts, but also enables the development of a low-carbon and green economy, which is of significant practical importance for improving the atmospheric environment.

[0008] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0009] In one aspect, an HZSM-5 molecular sieve catalyst is provided, which is a single-shell HZSM-5 molecular sieve catalyst or a double-shell monolithic HZSM-5 molecular sieve catalyst.

[0010] The general formula of the single-shell HZSM-5 molecular sieve catalyst is MOx ultrafine nanoclusters / N-HZSM-5 nanotubes, where N and M represent transition metals or rare metal elements, N-HZSM-5 is a hierarchical porous nanotube molecular sieve with an MFI structure, MOx ultrafine nanoclusters are ultrafine nanocluster oxides of metal M in a highly dispersed state, and N is a metal element with a metal ion radius higher than M. This catalyst is an integral nanotube molecular sieve catalyst co-modified with MOx ultrafine nanoclusters and framework metal N inside and outside. The MOx ultrafine nanoclusters are adjacent to the framework metal N and are highly dispersed on the surface of the HZSM-5 matrix, and are tightly bonded to the HZSM-5 matrix through interaction.

[0011] The general formula of the monolithic double-shell HZSM-5 molecular sieve catalyst is MOx ultrafine nanoclusters / N-HZSM-5@ROx ultrafine nanoclusters / P-HZSM-5 nanotubes, where N, M, R, and P represent transition metals or rare metal elements, N-HZSM-5 and P-HZSM-5 are hierarchical porous molecular sieves with MFI structures, MOx and ROx ultrafine nanoclusters are ultrafine nanocluster oxides of transition metals in a highly dispersed state, and N and P are metal elements with ionic radii higher than M and R, respectively. This catalyst is a monolithic double-shell HZSM-5 catalyst co-modified with single-atom metals and heteronuclear metal oxide ultrafine nanoclusters. The catalyst consists of five molecular sieves, with the inner layer being an integral HZSM-5 molecular sieve catalyst co-modified by MOx ultrafine nanoclusters and framework metal N. The MOx ultrafine nanoclusters are adjacent to the framework metal N and highly dispersed on the surface of the HZSM-5 matrix, interacting and tightly bonded to the HZSM-5 matrix. The outer layer is an integral HZSM-5 hierarchical porous catalyst co-modified by ROx ultrafine nanoclusters and framework metal P. The ROx ultrafine nanoclusters are adjacent to the framework metal P and highly dispersed on the surface of the HZSM-5 matrix, interacting and tightly bonded to the HZSM-5 matrix. The two layers have strong interactions and are tightly bonded to form an integral catalyst.

[0012] Secondly, it provides applications for single-shell HZSM-5 molecular sieve catalysts or double-shell monolithic HZSM-5 molecular sieve catalysts for the removal of VOCs from complex gases.

[0013] The beneficial effects of this invention are as follows:

[0014] 1. This catalyst exhibits high low-temperature catalytic activity and resistance to sulfur, water, and chlorine poisoning when catalytically oxidizing VOCs, which improves the stability of the catalyst, has high HCl selectivity, and can reduce the generation of Cl2 and other organic byproducts.

[0015] 2. The successful preparation of this catalyst can improve the low-temperature purification of complex organic waste gases, especially the efficient removal of heteroatom VOCs, which has certain economic and environmental benefits. Attached Figure Description

[0016] Figure 1 The distribution of Cl2 production rate for each catalyst is shown in the diagram.

[0017] Figure 2 The distribution of HCl production rate for each catalyst is shown in the diagram.

[0018] Figure 3 The distribution of CH3Cl production rate for each catalyst at different reaction temperatures is shown in the figure.

[0019] Figure 4The distribution of organic products for each catalyst at different reaction temperatures is shown in the diagram.

[0020] Figure 5 The distribution of chlorine-containing intermediates for each catalyst at different reaction temperatures is shown in the diagram.

[0021] Figure 6 The images show SEM images and EDS-Cl images of each catalyst before and after the catalytic reaction.

[0022] Figure 7 EDS-Cl images before and after catalytic reactions with different modified molecular sieves;

[0023] Figure 8 The catalytic efficiency and chlorine-containing product distribution of 1.2% Cr-HZSM-5 molecular sieve catalysts with different Si / Al ratios are shown in the figure. Detailed Implementation

[0024] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0025] Example 1

[0026] A single-shell HZSM-5 molecular sieve catalyst with the general formula MOx ultrafine nanoclusters / N-HZSM-5 nanotubes, wherein N and M represent transition metals or rare metal elements.

[0027] The catalyst is a monolithic nanotube molecular sieve catalyst consisting of MOx ultrafine nanoclusters / N-HZSM-5 nanotubes. N-HZSM-5 is a hierarchical porous nanotube molecular sieve with an MFI structure. The MOx ultrafine nanoclusters are highly dispersed oxides of metal M (M = transition metals such as Mn, Ti, Fe, and Ni). N is a metal element with a ionic radius higher than M, and can be specifically selected based on the metal element M. The selection range of N includes transition metals such as Cu, Cr, and Co, or rare metal elements such as La and Ce. This catalyst is a monolithic nanotube molecular sieve catalyst co-modified with MOx ultrafine nanoclusters and framework metal N. The MOx ultrafine nanoclusters are adjacent to the framework metal N and highly dispersed on the surface of the HZSM-5 matrix, interacting tightly with the HZSM-5 matrix.

[0028] Its preparation method includes the following steps:

[0029] S1: Preparation of framework lattice metal M-HZSM-5 crystal nucleation solution A

[0030] S101: Mix the soluble salt of transition metal M and deionized water in a certain proportion, and stir with heat radiation, ultrasound and magnetic force. Then add a certain amount of tetrapropylammonium hydroxide or tetrapropylammonium bromide (TPAOH / TPABr), and stir with heat radiation, ultrasound and magnetic force again to obtain mixture a.

[0031] S102: Dissolve a certain amount of sodium hydroxide in deionized water, add a certain amount of aluminum component, stir by thermal radiation combined with ultrasound and magnetic stirring, add a certain amount of silicon component, and stir by thermal radiation combined with ultrasound and magnetic stirring for a certain time to obtain mixture b;

[0032] S103: Slowly pour mixture a into mixture b while maintaining thermal radiation stirring and ultrasonic vibration for a certain period of time to obtain mixture c;

[0033] S104: The mixture c is transferred to a polytetrafluoroethylene reactor and nucleated for a certain time under a certain pressure and combined with microwave-assisted heating to obtain M-HZSM-5 crystal nucleus solution A.

[0034] S2: Preparation of N-HZSM-5 nucleation solution B with surface metal M dispersed and supported

[0035] S201: A certain amount of heteronuclear metal N soluble salt is added to the crystal nucleation solution A, and after thermal radiation combined with ultrasound and magnetic stirring, a mixture d is obtained;

[0036] S202: The mixture d is transferred to a polytetrafluoroethylene reactor and nucleated for a certain time under a certain pressure and combined with microwave-assisted heating of thermal radiation to obtain a crystal nucleus solution B of N-HZSM-5 with surface metal M dispersed and loaded.

[0037] S3: HZSM-5 nanotube hierarchical porous catalyst co-modified with MOx ultrafine nanoclusters and framework metal N on both the inner and outer surfaces.

[0038] S301: A certain amount of template agents such as carbon nanofibers and carbon nanotubes are added to the crystal nucleation solution B. After thermal radiation combined with ultrasound and magnetic stirring, a mixture f is obtained.

[0039] S302: Add a certain amount of solvents such as ethylenediaminetetraacetic acid (EDTA), hexadecyltrimethylammonium bromide (CTAB), and polyquaternary ammonium salt to mixture f, and then obtain mixture g after thermal radiation combined with ultrasound and magnetic stirring;

[0040] S303: After ultrasonic heating and drying of the mixture to dry gel, it is transferred to a polytetrafluoroethylene reactor and crystallized for a certain time under certain pressure and temperature. After calcination, HZSM-5 molecular sieve catalyst with framework lattice metal N and framework outer ultrafine nano clusters MOx co-modified on the inner and outer surfaces is obtained. N and M represent transition metal or rare metal elements.

[0041] Preferably, the soluble salt of transition metal M in step S101 can be a soluble salt of transition metals such as Mn, Ti, Fe, Ni nitrates, chlorides, or organic salts, or it can be one or a combination of different soluble salts.

[0042] Preferably, the aluminum component in step S102 can be one or more aluminum-containing substances such as aluminum chloride, sodium aluminate, aluminum hydroxide, and aluminum triethanolamine.

[0043] Preferably, the molar ratio of each component in mixture c of steps S103 and S104 is as follows:

[0044] SiO2:TPAOH or TPABr = 100:(10-35);

[0045] SiO2:H2O = 100:(1000-8000);

[0046] SiO2:Na2O=100:(10-30);

[0047] SiO2:M=100:(0.05-3);

[0048] SiO2:Al2O3 = 100:(10-600)

[0049] Preferably, the heteronuclear metal N soluble salt in step S201 can be a soluble salt such as an organic salt, nitrate, or chloride of transition metals such as Cu, Cr, and Co, or rare metal elements such as La and Ce, or it can be one or a combination of different soluble salts.

[0050] Preferably, the molar ratio of heteronuclear metal N to silicon component in mixture d of step S202 is:

[0051] SiO2:N = 100:(0.05-3);

[0052] Preferably, in step S301, the mass ratio of the amount of template agent such as carbon nanofibers and carbon nanotubes added to the mass ratio of SiO2 in the mixture is (0.5-1.5):1.

[0053] Preferably, in step S302, the mass ratio of the solvents such as ethylenediaminetetraacetic acid (EDTA), hexadecyltrimethylammonium bromide (CTAB), and polyquaternary ammonium salt to the mass of SiO2 in the mixture is (0.05-0.8):1.

[0054] Preferably, the polyquaternary ammonium salt in step S302 can be poly(dimethylammonium chloride), polyacrylamide, N-vinylpyrrolidone, or quaternized vinylimidazolium copolymer, etc.

[0055] As a preferred embodiment, during the crystallization process in step S303, a small amount of deionized water is added to the reactor, with the ratio of water to dry adhesive mass being (0.5-2):1, the crystallization temperature being 140-200℃, and the crystallization time being 24-48h.

[0056] Preferably, step S303, the calcination process in air atmosphere, is divided into three stages: in the first stage, the crystallized product is dried at 100-120℃ for 2-3 hours; in the second stage, the temperature is slowly increased from 100-120℃ to 300-400℃ at a heating rate of 1-5℃ and held at that temperature for 3-5 hours; in the third stage, the calcination temperature is slowly increased to 500-700℃ at a heating rate of 1-5℃ and held at that temperature for 4-6 hours.

[0057] As a preferred embodiment, in steps S1, S2 and S3, the ultrasonic power is 50-300W, the heating temperature is 50-80℃, the magnetic stirring speed is 400-800r / min, and the ultrasonic combined with thermal radiation magnetic stirring time is 60-120min.

[0058] Preferably, in steps S1 and S2, nucleation is carried out in a sealed reactor at a temperature of 80-120°C, with the pressure adjusted by the temperature, a microwave power of 300-600W, and a nucleation time of 8-20 hours.

[0059] Example 2

[0060] A monolithic HZSM-5 molecular sieve catalyst with a double-shell structure has the general formula MOx ultrafine nanoclusters / N-HZSM-5@ROx ultrafine nanoclusters / P-HZSM-5 nanotubes, wherein N, M, R and P represent transition metals or rare metal elements.

[0061] Among them, MOx ultrafine nanoclusters / N-HZSM-5@ROx ultrafine nanoclusters / P-HZSM-5 nanotubes are monolithic catalysts. N-HZSM-5 and P-HZSM-5 are hierarchical porous molecular sieves with MFI structure. MOx and ROx ultrafine nanoclusters are ultrafine nanocluster oxides of transition metals such as Mn, Ti, Fe, and Ni, and are in a highly dispersed state. N and P are metal elements with ionic radii higher than M and R, respectively, and can be specifically selected according to the metal elements M and R. The selection range of N and P is transition metals such as Cu, Cr, and Co, or rare metal elements such as La and Ce. This catalyst is a monolithic HZSM-5 molecular sieve catalyst with a double shell, co-modified by single-atom metal and heteronuclear metal oxide ultrafine nanoclusters. The inner layer is a monolithic HZSM-5 molecular sieve catalyst co-modified by MOx ultrafine nanoclusters and framework metal N. The MOx ultrafine nanoclusters are adjacent to the framework metal N and highly dispersed on the surface of the HZSM-5 matrix, interacting and tightly bonded to the HZSM-5 matrix. The outer layer is a monolithic HZSM-5 hierarchical porous catalyst co-modified by ROx ultrafine nanoclusters and framework metal P. The ROx ultrafine nanoclusters are adjacent to the framework metal P and highly dispersed on the surface of the HZSM-5 matrix, interacting and tightly bonded to the HZSM-5 matrix. The inner and outer layers have strong interactions and are tightly bonded to form a monolithic catalyst.

[0062] Its preparation method includes the following steps:

[0063] S1: Preparation of framework lattice metal M-HZSM-5 crystal nucleation solution A

[0064] S101: Mix the soluble salt of transition metal M and deionized water in a certain proportion, and stir with heat radiation, ultrasound and magnetic force. Then add a certain amount of tetrapropylammonium hydroxide or tetrapropylammonium bromide (TPAOH / TPABr), and stir with heat radiation, ultrasound and magnetic force again to obtain mixture a.

[0065] S102: Dissolve a certain amount of sodium hydroxide in deionized water, add a certain amount of aluminum component, stir by thermal radiation combined with ultrasound and magnetic stirring, add a certain amount of silicon component, and stir by thermal radiation combined with ultrasound and magnetic stirring for a certain time to obtain mixture b;

[0066] S103: Slowly pour mixture a into mixture b while maintaining thermal radiation stirring and ultrasonic vibration for a certain period of time to obtain mixture c;

[0067] S104: The mixture c is transferred to a polytetrafluoroethylene reactor and nucleated for a certain time under a certain pressure and combined with microwave-assisted heating to obtain M-HZSM-5 crystal nucleus solution A.

[0068] S2: Preparation of N-HZSM-5 nucleation solution B with surface metal M dispersed and supported

[0069] S201: A certain amount of heteronuclear metal N soluble salt is added to the crystal nucleation solution A, and after thermal radiation combined with ultrasound and magnetic stirring, a mixture d is obtained;

[0070] S202: The mixture d is transferred to a polytetrafluoroethylene reactor and nucleated for a certain time under a certain pressure and combined with microwave-assisted heating of thermal radiation to obtain a crystal nucleus solution B of N-HZSM-5 with surface metal M dispersed and loaded.

[0071] S3: HZSM-5 nanotube hierarchical porous catalyst co-modified with MOx ultrafine nanoclusters and framework metal N on both the inner and outer surfaces.

[0072] S301: A certain amount of template agents such as carbon nanofibers and carbon nanotubes are added to the crystal nucleation solution B. After thermal radiation combined with ultrasound and magnetic stirring, a mixture f is obtained.

[0073] S302: Add a certain amount of solvents such as ethylenediaminetetraacetic acid (EDTA), hexadecyltrimethylammonium bromide (CTAB), and polyquaternary ammonium salt to mixture f, and then obtain mixture g after thermal radiation combined with ultrasound and magnetic stirring;

[0074] S303: After ultrasonic heating and drying of the mixture to dry gel, it is transferred to a polytetrafluoroethylene reactor and crystallized for a certain time under certain pressure and temperature. After calcination, HZSM-5 molecular sieve catalyst with framework lattice metal N and framework outer ultrafine nano clusters MOx co-modified on the inner and outer surfaces is obtained. N and M represent transition metal or rare metal elements.

[0075] S4: Preparation of crystal nucleation solution C

[0076] S401: Prepare the nucleation solution C according to the steps of S1 and S2, where metal M in S1 is represented by the letter R and metal N in S2 is represented by the letter P.

[0077] S402: The HZSM-5 molecular sieve catalyst obtained from S303 is added to the crystal nucleus solution C, and a certain amount of solvents such as ethylenediaminetetraacetic acid (EDTA), hexadecyltrimethylammonium bromide (CTAB), and polyquaternary ammonium salt are added. After thermal radiation combined with ultrasound and magnetic stirring, a mixture h is obtained.

[0078] S403: After ultrasonic heating and drying of the mixture to dry gel, it is transferred to a polytetrafluoroethylene reactor and crystallized for a certain time under certain pressure and temperature. After calcination, MOx ultrafine nanoclusters / N-HZSM-5@ROx ultrafine nanoclusters / P-HZSM-5 nanotube catalyst is obtained, where N, M, R and P represent transition metals or rare metal elements.

[0079] Preferably, the soluble salt of transition metal M in step S101 can be a soluble salt of transition metals such as Mn, Ti, Fe, Ni nitrates, chlorides, or organic salts, or it can be one or a combination of different soluble salts.

[0080] Preferably, the aluminum component in step S102 can be one or more aluminum-containing substances such as aluminum chloride, sodium aluminate, aluminum hydroxide, and aluminum triethanolamine.

[0081] Preferably, the molar ratio of each component in mixture c of steps S103 and S104 is as follows:

[0082] SiO2:TPAOH or TPABr = 100:(10-35);

[0083] SiO2:H2O = 100:(1000-8000);

[0084] SiO2:Na2O=100:(10-30);

[0085] SiO2:M=100:(0.05-3);

[0086] SiO2:Al2O3 = 100:(10-600);

[0087] Preferably, the heteronuclear metal N soluble salt in step S201 can be a soluble salt such as an organic salt, nitrate, or chloride of transition metals such as Cu, Cr, and Co, or rare metal elements such as La and Ce, or it can be one or a combination of different soluble salts.

[0088] Preferably, the molar ratio of heteronuclear metal N to silicon component in mixture d of step S202 is: SiO2:N=100:(0.05-3);

[0089] Preferably, in step S301, the mass ratio of the amount of template agent such as carbon nanofibers and carbon nanotubes added to the mass ratio of SiO2 in the mixture is (0.5-1.5):1.

[0090] Preferably, the mass ratio of the solvents such as ethylenediaminetetraacetic acid (EDTA), hexadecyltrimethylammonium bromide (CTAB), and polyquaternary ammonium salt added in steps S302 and S402 to the mass ratio of SiO2 in the mixture is (0.05-0.8):1.

[0091] Preferably, the polyquaternary ammonium salt in step S302 can be poly(dimethylammonium chloride), polyacrylamide, N-vinylpyrrolidone, or quaternized vinylimidazolium copolymer, etc.

[0092] As a preferred embodiment, during the crystallization process in steps S303 and S402, a small amount of deionized water is added to the reactor, with the ratio of water added to dry adhesive mass being (0.5-2):1, the crystallization temperature being 140-200℃, and the crystallization time being 24-48h.

[0093] Preferably, the calcination process in steps S303 and S403 under air atmosphere is divided into three stages: in the first stage, the crystallized product is dried at 100-120℃ for 2-3 hours; in the second stage, the temperature is slowly increased from 100-120℃ to 300-400℃ at a heating rate of 1-5℃ and held at the temperature for 3-5 hours; in the third stage, the calcination temperature is slowly increased to 500-700℃ at a heating rate of 1-5℃ and held at the temperature for 4-6 hours.

[0094] Preferably, in step S401, metals R and P can be the same as or different from metals M and N in S1 and S2, respectively, or they can be one or more combinations of different soluble salts.

[0095] Preferably, in step S402, the mass ratio of the amount of HZSM-5 molecular sieve catalyst added to the mass of SiO2 in the mixture is (0.5-2):1;

[0096] Preferably, in steps S1, S2, S3 and S4, the ultrasonic power is 50-300W, the heating temperature is 50-80℃, the magnetic stirring speed is 400-800r / min, and the ultrasonic combined with thermal radiation magnetic stirring time is 60-120min.

[0097] Preferably, in steps S1, S2 and S4, nucleation is carried out in a sealed reactor at a temperature of 80-120°C, with the pressure adjusted by the temperature, a microwave power of 300-600W, and a nucleation time of 8-20 hours.

[0098] Example 3

[0099] from Figure 1As can be seen, no Cl2 was detected in the DCM products of Co-HZSM-5, Cu-HZSM-5, Fe-HZSM-5, and HZSM-5 molecular sieve catalysts. The Cr-doped HZSM-5 catalyst formed the most oxygen vacancies, and its surface adsorbed oxygen and surface lattice oxygen content were higher than other catalysts. Mobility-rich lattice oxygen can diffuse to the outer surface of the catalyst, replacing Cl species adsorbed on oxygen vacancies and promoting Cl2 formation, resulting in the highest Cl2 formation rate. Furthermore, the Cl2 formation temperature of Cr-HZSM-5 was 300℃, lower than Ce-HZSM-5 and Mn-HZSM-5, which is related to the higher surface active oxygen content of Cr-HZSM-5. The Cl2 formation temperature of Mn-HZSM-5 was 400℃, increasing the Cl2 formation temperature. No Cl2 formation was detected in Fe-HZSM-5, and combined with the Cl balance, it can be seen that Fe-HZSM-5 also exhibits good HCl selectivity.

[0100] Figure 2 The HCl selectivity of all the metal-doped molecular sieve catalysts was higher than that of the HZSM-5 catalyst, indicating that metal doping increased the acid strength and the number of acidic sites on the catalyst surface, enhancing the initial C-Cl cracking ability in DCM. Specifically, the Mn-HZSM-5 molecular sieve catalyst began to produce HCl from 200℃, reaching 80% at 400℃, indicating a high selectivity for HCl. This may be due to the strong acidity of the Mn-HZSM-5 catalyst and the abundance of Brønsted acid on its surface. The HCl production rate of the Cr-HZSM-5 molecular sieve catalyst at 400℃ was second only to Mn-HZSM-5 and higher than other catalysts, suggesting that appropriate acidity is beneficial to HCl production. Notably, at temperatures of 200-250℃, the catalytic degradation activity curves of Cu-HZSM-5, Cr-HZSM-5, and HZSM-5 for DCM were relatively flat across all catalysts. Figure 2 Analysis of HCl production rate and H2-TPR revealed that, before 250℃, only Mn-HZSM-5 and Co-HZSM-5 molecular sieves produced small amounts of HCl; other catalysts did not produce HCl. This is likely because the desorption temperature of HCl was not reached before 250℃, and because the decomposition rate of DCM was greater than the oxidation rate, many intermediate products were not further oxidized and occupied active sites, leading to a decrease in catalytic activity. When the temperature rose to 300℃, the slope of the DCM degradation curves of all metal-doped molecular sieve catalysts increased significantly, and was greater than that of the HZSM-5 catalyst. This indicates that metal doping improves the low-temperature redox performance of the molecular sieve catalyst surface, exhibiting higher catalytic oxidation activity from 300℃ onwards.

[0101] from Figure 3 It can be concluded that CH3Cl was the only detected byproduct during the DCM degradation process. Some scholars believe that DCM first reacts with OH species on the catalyst surface, continuously dechlorinating to produce HCl, while simultaneously forming the HCHO intermediate. The HCHO intermediate undergoes a disproportionation reaction to generate methoxy and formate esters. The formate species are further oxidized to COx, and the methoxy and HCl react to generate CH3Cl. The above results indicate that at low temperatures, DCM can be catalytically cracked at the strong acid sites of the molecular sieve catalyst, producing a large amount of intermediate methoxy species and HCl. These react on the molecular sieve surface to generate CH3Cl. As the temperature increases, the activity of surface oxygen species gradually increases, and the intermediate products are further oxidized, thus reducing the production rate of CH3Cl. In addition, as the temperature increases, the cracking ability of surface acid sites increases, enhancing the dechlorination of CH3Cl and thus weakening the production capacity of CH3Cl. No CH3Cl was detected in the catalytic oxidation products of DCM on Cr-HZSM-5, Ce-HZSM-5, and Cu-HZSM-5 catalysts, indicating that the surface oxygen activity is relatively high at low temperatures after doping with Cr, Ce, and Cu, effectively inhibiting the formation of CH3Cl. Furthermore, Cr-HZSM-5 possesses relatively strong acidity and numerous acidic sites, which to some extent enhances the dechlorination of CH3Cl and weakens its formation. Mn-HZSM-5, Co-HZSM-5, Fe-HZSM-5, and HZSM-5 molecular sieve catalysts produced CH3Cl during the catalytic oxidation of DCM. It is worth noting that the CH3Cl production rate of the Mn-HZSM-5 molecular sieve catalyst showed a trend of first increasing and then decreasing in the range of 250-450℃. The CH3Cl production rate reached a maximum of 20% at 350℃, and then decreased to 0% at 400℃. In addition, the CH3Cl production rates of Co-HZSM-5 and HZSM-5 began to decrease at 350℃ and 400℃, respectively.

[0102] Figure 4-5The HZSM-5 molecular sieve exhibits significantly higher levels of chlorine-containing intermediates than other metal-doped molecular sieve catalysts, along with a greater quantity of intermediate organic byproducts. This is likely because, at 100-250°C, the molecular sieve catalyst itself possesses numerous acidic sites, leading to rapid adsorption of DCM onto the active sites and the breaking of C-Cl bonds, resulting in a large amount of intermediates. These intermediates further react with Cl to generate chlorine-containing intermediates. The relatively low oxidizing power of HZSM-5 itself is insufficient to oxidize the other organic byproducts and chlorine-containing intermediates generated by the catalytic degradation of DCM, resulting in a significantly higher level of intermediates produced by HZSM-5 compared to metal-doped molecular sieves. Furthermore, the Cl content on the surface of the HZSM-5 molecular sieve reaches a high value at 250°C, subsequently decreasing and producing HCl. Simultaneously, the surface organic byproducts also begin to decrease. This demonstrates that the plateau in the activity of HZSM-5 between 200-250°C is due to the deposition of Cl components (including HCl, Cl atoms, and organic chlorines) and the presence of numerous intermediate non-chlorine organic transition products that were not promptly removed. At higher temperatures, the formation rates of intermediate organic products and chlorine-containing byproducts were low for both Cr-HZSM-5 and Mn-HZSM-5 at 450℃, indicating that the coupling of metals Cr and Mn can promote the formation of less carbon and chlorine deposition in ZSM-5 molecular sieves, which is related to their redox properties and acidity. Combined with the yield results of HCl, Cl2, and CH3Cl, it can be seen that metal-coupled HZSM-5 exhibits a higher Cl removal capacity, improving the chlorine poisoning resistance of ZSM-5, consistent with the SEM-EDS results. Except for Cu-HZSM-5, Mn-HZSM-5, Co-HZSM-5, Cr-HZSM-5, Fe-HZSM-5, and Ce-HZSM-5 all showed low surface chlorine deposition at 350-450℃, with Cr-HZSM-5 showing the lowest surface chlorine deposition compared to other catalysts, indicating that Cr-HZSM-5 has better chlorine poisoning resistance. Before 450℃, Mn-HZSM-5 exhibits some chlorine deposition, but shows a low chlorine deposition rate, indicating that Mn-HZSM-5 can achieve good chlorine resistance at high temperatures. This is related to the synergy between its enhanced surface acidity and redox properties at high temperatures.

[0103] Example 4

[0104] In catalytic oxidation, incomplete oxidation products may remain on the catalyst surface, causing chlorine and carbon deposition on the molecular sieve surface. To investigate the effect of metal atom doping on the chlorine and carbon deposition resistance of molecular sieve catalysts, thermogravimetric analysis and energy dispersive spectroscopy (EDS) analysis of surface Cl were performed on three catalysts with good catalytic performance: Cr-HZSM-5, Mn-HZSM-5, Co-HZSM-5, and HZSM-5 molecular sieve catalysts before and after 12 h of catalytic reaction at 360℃. Figure 6(ah) shows that the catalyst morphology consists of regular hexagonal particles ranging from 0.5 to 1 μm. The morphology of all catalysts did not change significantly before and after the catalytic reaction, and no obvious impurity accumulation appeared on the surface. This indicates that the catalysts have good thermal stability and are not easily deactivated by sintering at high temperatures. Figure 6 (ip) shows that the surface Cl distribution of Mn-HZSM-5 and Cr-HZSM-5 catalysts did not change significantly before and after the catalytic reaction, while the HZSM-5 catalyst showed obvious bright yellow spots on its surface after the catalytic reaction, and the Cl on the surface of the Co-HZSM-5 catalyst also increased slightly, indicating that there was a large accumulation of Cl on the surface of the HZSM-5 molecular sieve catalyst. Figure 5 In terms of the generation rate of chlorine-containing byproducts of each catalyst, the Mn-HZSM-5 and Cr-HZSM-5 catalysts, due to their stronger acidity and oxidizing properties, promoted the decomposition and oxidation of chlorine-containing organic matter during catalysis. Simultaneously, they enhanced the ability of surface Cl to be removed in the form of HCl and Cl2, significantly reducing chlorine deposition on the molecular sieve catalyst surface and improving chlorine resistance. Comparing the chlorine accumulation before and after catalysis for the four catalysts indicates that the coupling of metals Cr, Mn, and Co can enhance the chlorine resistance of the molecular sieve catalysts and reduce the occurrence of deactivation due to Cl poisoning during catalysis, which is consistent with the results of the previous section.

[0105] Example 5

[0106] HZSM-5 was modified using both doping and supporting methods with the same metal content. Although similar catalytic activities were observed at higher temperatures, the distribution of catalytic products showed that the supported catalyst (1.2% Cr / HZSM-5) had lower CO2 production and chlorine-containing inorganic product production rates than the doped catalyst (1.2% Cr-HZSM-5). This example characterized the Cl distribution on the catalyst surface before and after the reaction. Figure 7The results clearly show the difference in the changes of Cl species on the surface of the molecular sieve catalysts before and after catalysis under two different modification methods. The change in Cl species on the surface of the doped molecular sieve was not significant, while the supported modified molecular sieve catalyst showed dense enrichment of Cl on its surface after the catalytic reaction. This indicates that the 1.2% Cr-HZSM-5 molecular sieve has a higher acidity, which facilitates the initial cracking and subsequent oxidation of C-Cl in CVOCs, allowing surface Cl species to be removed from the catalyst surface. In contrast, the 1.2% Cr / HZSM-5 molecular sieve catalyst has a weaker acidity, which is not conducive to the removal of surface Cl, resulting in dense adsorption on the catalyst surface. This is also consistent with the finding that the HCl production rate of the 1.2% Cr / HZSM-5 molecular sieve decreased after 400℃. The total energy spectrum also shows that the Cr content in the 1.2% Cr-HZSM-5 molecular sieve catalyst before and after the catalytic reaction is relatively small, indicating that Cr loss during the reaction is minimal. This is consistent with the result that a very small amount of chlorine-containing intermediate byproducts (metal chloride oxides, organochlorides) were formed in the Cl equilibrium of the 1.2% Cr-HZSM-5 molecular sieve. Furthermore, after the catalytic reaction, the Cr content of the 1.2% Cr / HZSM-5 molecular sieve catalyst dispersed from one energy peak to three smaller peaks, indicating that Cr species existed in different forms during the reaction, and the overall content decreased significantly.

[0107] Molecular sieve catalysts with a Si / Al ratio of 50 exhibit strong acidity, resulting in the highest HCl and CO2 production rates. Figure 8 Molecular sieve catalysts with different Si / Al ratios all exhibited 100% selectivity for HCl at low temperatures. However, as the temperature rose to 350℃, Cl2 began to be generated, and the selectivity for HCl decreased with increasing Si / Al ratio. Notably, no Cl2 or HCl was detected in the tail gas from the catalytic oxidation of DCM using pure silicon ZSM-5 molecular sieve. As shown in the figure, the generation rate of intermediate chlorine-containing byproducts decreased with increasing temperature for all aluminum-containing molecular sieve catalysts, but the generation rate of intermediate chlorine-containing byproducts for pure silicon ZSM-5 molecular sieve showed the opposite trend. This indicates that the acidic sites on the surface of the molecular sieve catalyst play a decisive role in the breaking of the C-Cl bonds in CVOCs. In summary, when Si / Al = 50, its catalytic activity is second only to Si / Al = 25. However, its CO2 and HCl yields in the high-temperature range are higher than other catalysts. At the same time, it exhibits lower Cl deposition and CO yields, indicating that appropriate acid amount and acid strength are beneficial to the synergistic effect between acidity and oxidizing power, giving the catalyst good resistance to chlorine poisoning and deep oxidation performance.

[0108] The catalyst provided by this invention exhibits high low-temperature catalytic activity and resistance to sulfur, water, and chlorine poisoning during the catalytic oxidation of VOCs, thus improving catalyst stability. It also demonstrates high HCl selectivity and reduces the generation of Cl2 and other organic byproducts. The successful preparation of this catalyst can improve the low-temperature purification of complex organic waste gases, especially the efficient removal of heteroatom VOCs, offering both economic and environmental benefits.

[0109] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

[0110] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A single-shell HZSM-5 molecular sieve catalyst, characterized in that, The general formula of the single-shell HZSM-5 molecular sieve catalyst is MOx ultrafine nanoclusters / N-HZSM-5 nanotubes, where M is Mn and N is Cu, Cr, La or Ce; N-HZSM-5 is a hierarchical porous nanotube molecular sieve with MFI structure, MOx ultrafine nanoclusters are ultrafine nanocluster oxides of metal M in a highly dispersed state, and N is a metal element with a metal ion radius higher than M; this catalyst is an integral nanotube molecular sieve catalyst co-modified with MOx ultrafine nanoclusters and framework metal N inside and outside, the MOx ultrafine nanoclusters are close to the framework metal N and highly dispersed on the surface of HZSM-5 matrix, and tightly bonded to HZSM-5 matrix through interaction; The preparation method of single-shell HZSM-5 molecular sieve catalyst includes the following steps: S1: Preparation of framework lattice metal M-HZSM-5 crystal nucleation solution A S101: Mix a certain proportion of soluble salt of transition metal M and deionized water, and stir with thermal radiation, ultrasound and magnetic force. Then add a certain amount of tetrapropylammonium hydroxide or tetrapropylammonium bromide, and stir with thermal radiation, ultrasound and magnetic force again to obtain mixture a. S102: Dissolve a certain amount of sodium hydroxide in deionized water, add a certain amount of aluminum component, stir by thermal radiation combined with ultrasound and magnetic stirring, add a certain amount of silicon component, and stir by thermal radiation combined with ultrasound and magnetic stirring for a certain time to obtain mixture b; S103: Slowly pour mixture a into mixture b while maintaining thermal radiation stirring and ultrasonic vibration for a certain period of time to obtain mixture c; S104: The mixture c is transferred to a polytetrafluoroethylene reactor and nucleated for a certain time under a certain pressure and combined thermal radiation and microwave-assisted heating to obtain M-HZSM-5 crystal nucleus solution A; S2: Preparation of N-HZSM-5 nucleation solution B with surface metal M dispersed and supported S201: A certain amount of heteronuclear metal N soluble salt is added to the crystal nucleation solution A, and after thermal radiation combined with ultrasound and magnetic stirring, a mixture d is obtained; S202: The mixture d is transferred to a polytetrafluoroethylene reactor and nucleated for a certain time under a certain pressure and combined thermal radiation and microwave-assisted heating to obtain a crystal nucleus solution B of N-HZSM-5 with surface metal M dispersed and loaded. S3: HZSM-5 nanotube hierarchical porous catalyst co-modified with MOx ultrafine nanoclusters and framework metal N inner and outer surfaces. S301: A certain amount of carbon nanofibers and carbon nanotube template agents are added to the crystal nucleation solution B, and after thermal radiation combined with ultrasound and magnetic stirring, a mixture f is obtained; S302: Add a certain amount of ethylenediaminetetraacetic acid, hexadecyltrimethylammonium bromide and polyquaternary ammonium salt solvent to mixture f, and after thermal radiation combined with ultrasound and magnetic stirring, obtain mixture g; S303: After ultrasonic heating and drying of the mixture to dry gel, it is transferred to a polytetrafluoroethylene reactor and crystallized for a certain time under certain pressure and temperature. After calcination, HZSM-5 molecular sieve catalyst with framework lattice metal N and framework outer ultrafine nano clusters MOx co-modified on the inner and outer surfaces is obtained.

2. The application of the single-shell HZSM-5 molecular sieve catalyst according to claim 1, characterized in that, Used to remove VOCs from complex gases.

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