Bimetal molecular sieve catalyst for toluene oxidation, preparation method and application

Abstract

The invention belongs to the technical field of volatile organic compound catalytic purification and nano catalytic materials, and discloses a bimetallic molecular sieve catalyst for toluene oxidation, and a preparation method and application thereof. According to the method, a'interface engineering 'strategy is adopted, a'protective impregnation method' is adopted to calcine second metal to obtain a bimetallic catalyst with strong interaction and a high dispersion interface, a synergistic effect on catalytic oxidation of toluene is achieved, and complete catalytic oxidation of toluene is achieved at a low temperature. The preparation method disclosed by the invention is controllable in process and good in repeatability, and the catalyst is widely applied to catalytic purification of VOCs (Volatile Organic Compounds) such as methylbenzene in industrial waste gas, CO2 hydrogenation and other processes and has a very good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of catalytic purification of volatile organic compounds and nanocatalytic materials, and relates to a bimetallic molecular sieve catalyst for toluene oxidation, its preparation method and application. Background Technology

[0002] Volatile organic compounds (VOCs) are key precursors to ozone (O3) and fine particulate matter (PM2.5) pollution in the atmosphere. Their emissions are widespread, covering multiple industrial sectors such as chemical, coating, and printing, posing serious threats to the ecological environment and human health. Catalytic oxidation technology, due to its outstanding advantages such as high purification efficiency, mild reaction conditions, and no secondary pollution, has become the mainstream technology for industrial VOCs treatment. The development of high-performance catalysts is the core key to the industrial application of this technology.

[0003] Among VOCs catalytic oxidation catalysts, noble metal catalysts (such as Pt, Pd, and Au-based catalysts) possess excellent low-temperature catalytic activity, but they suffer from resource scarcity, high cost, and susceptibility to Cl. - The inactivation due to poisoning by impurities such as sulfur (S) limits its large-scale industrial application. Transition metal oxides, due to their low cost, wide availability, and excellent redox properties, have become ideal alternatives to noble metal catalysts. Among them, Co3O4, with its unique spinel structure, efficient redox capabilities, and strong adsorption and activation of VOC molecules, has shown good application potential in the catalytic oxidation of VOCs such as toluene. However, unsupported or poorly dispersed Co3O4 nanoparticles are prone to agglomeration and sintering under high-temperature reaction conditions, leading to a decrease in active surface area, a reduction in oxygen vacancies, and a sharp decline in catalytic activity and stability.

[0004] To improve its dispersibility and thermal stability, Co3O4 is typically loaded onto supports with high specific surface area. Molecular sieve materials are considered ideal supports due to their high specific surface area, regular pore structure, good thermal stability, and shape-selective catalytic performance. However, the narrow channels (typically less than 2 nm) of traditional microporous molecular sieves severely restrict the internal diffusion of large molecular reactants such as toluene, generating significant mass transfer resistance and reducing the accessibility of active sites. Simultaneously, the limited pore space also restricts the high-dispersion loading of active components. Even with single-metal modification, high loading levels can easily lead to the aggregation of active components at the pore openings or outer surfaces, even clogging the pores. Introducing a second metal to construct a bimetallic system can alleviate this phenomenon to some extent and is expected to improve performance through synergistic effects, but it places higher demands on the loading method.

[0005] To address the aforementioned technical challenges, existing research focuses on optimization in two main directions: first, modifying the molecular sieve support by constructing a hierarchical porous structure to improve mass transfer and increase loading sites; second, introducing a second metal component to build a synergistic interface with Co species to enhance intrinsic activity and stability. However, existing technologies still face significant bottlenecks: First, traditional loading methods such as impregnation struggle to achieve high dispersion of active components, especially bimetallic components. During drying, precursor salts migrate with the solvent and crystallize and accumulate on the outer surface of the support or at large pores. After calcination, these salts easily form large, poorly dispersed metal oxide particles, resulting in limited active interfaces and poor synergistic effects (Nature. 1997, 389, 827). Second, when introducing a second metal (such as Cu), the strong acidity of the precursor solution can easily disrupt the structure of the pre-loaded metal-organic framework (MOF) precursor, such as ZIF-67, thereby impairing the dispersion of cobalt species and the integrity of the catalytic system.

[0006] Therefore, how to accurately construct an efficient and synergistic bimetallic interface while achieving high dispersion and loading of active components, and avoid damage to the structure of the active phase during the preparation process, has become a core technical challenge that urgently needs to be overcome in this field. Summary of the Invention

[0007] The first objective of this invention is to provide a bimetallic molecular sieve catalyst for toluene oxidation and its preparation method. This invention proposes an "interface engineering" design strategy, employing a "protective impregnation method" to precisely introduce a second metal species under mild conditions. This achieves the controllable construction of a highly dispersed and synergistic bimetallic interface, ultimately yielding a bimetallic molecular sieve catalyst with low-temperature catalytic activity, providing technical support for the efficient treatment of industrial VOCs.

[0008] The technical solution of this invention:

[0009] A bimetallic molecular sieve catalyst for toluene oxidation uses an alkali-etched modified hierarchical porous MFI-E molecular sieve as a support, and is loaded with active components of Co and a second metal. The Co support is dispersed on the support in the form of Co3O4 nanoparticles, with a loading of 4.0-10.0 wt%, preferably 5 wt%. The second metal forms a close bimetallic interface with Co, with a loading of 3.0-10.0 wt%, preferably 5 wt%.

[0010] The carrier is a B-MFI-E molecular sieve, a Si-MFI-E molecular sieve, or an Al-MFI-E molecular sieve.

[0011] The second metal is Cu, Ni, or Mn.

[0012] The mesopore volume of the alkaline-etched modified hierarchical B-MFI-E molecular sieve is 0.50 cm³. 3 / g, with an external specific surface area of ​​173 m² 2 / g.

[0013] A method for preparing a bimetallic molecular sieve catalyst for toluene oxidation involves introducing a second metal species using a "protective impregnation method," followed by heat treatment to obtain an M / Co / MFI-E supported bimetallic molecular sieve catalyst.

[0014] The steps include the following (taking M / Co / B-MFI-E molecular sieve catalyst as an example):

[0015] (1) Preparation of ZIF-67 / B-MFI-E precursor (Dalton Trans. 2024, 53, 5212): First, B-MFI molecular sieve was hydrothermally etched in an alkaline solution, washed, dried, and calcined to obtain B-MFI-E support; B-MFI-E support was ultrasonically dispersed in anhydrous ethanol, and cobalt source solution was added to obtain suspension A, which was ultrasonically centrifuged to obtain solid; the solid was redispersed in anhydrous ethanol, and ligand solution was added to obtain suspension B, which was ultrasonically centrifuged to obtain solid, and the obtained solid was dispersed in anhydrous ethanol, and ligand solution was added with stirring, followed by cobalt source solution with stirring to obtain suspension C, which was magnetically stirred, washed, and dried to obtain ZIF-67 / B-MFI-E precursor.

[0016] (2) Preparation of impregnation solution: Dissolve the second metal salt in anhydrous ethanol, stir and add ammonia water dropwise, adjust the pH of the solution to neutral, and prepare the metal ammonia complex impregnation solution;

[0017] (3) Preparation of catalyst: The ZIF-67 / B-MFI-E precursor was dispersed in a metal ammonia complex impregnation solution, stirred and impregnated, and calcined to obtain a bimetallic molecular sieve catalyst.

[0018] In step (1), the alkaline solution is a 0.4 mol / L tetrapropylammonium hydroxide aqueous solution; the cobalt source solution is a 0.12 mol / L cobalt nitrate hexahydrate ethanol solution; and the ligand solution is a 1.22 mol / L 2-methylimidazolium ethanol solution. The mass ratio of cobalt salt to carrier in suspension A is 3.5:1, and the molar ratio of ligand to cobalt salt in suspension A in suspension B is 10.1:1. The amounts of ligand solution and cobalt salt solution added to suspension C are the same as those added to suspension B.

[0019] In step (1), the ultrasonic dispersion time is 1 hour and the stirring growth time is 2 hours.

[0020] In step (2), the metal ammonia complex impregnation solution is a metal ammonia complex impregnation solution with a second metal concentration of 0.015-0.05 mol / L, preferably 0.025 mol / L; the second metal salt is a copper salt (copper nitrate trihydrate, copper acetate), a nickel salt (nickel nitrate hexahydrate, nickel acetate) or a manganese salt (manganese nitrate hexahydrate, manganese levulinate).

[0021] In step (3), the stirring and soaking time is 2-12 hours, with the preferred soaking time being 2 hours.

[0022] In step (3), the calcination temperature is 350-500 ℃, the calcination time is 2-4 hours, and the heating rate is 1-5 ℃ / min; preferably, the calcination temperature is 400 ℃, the calcination time is 3 hours, and the heating rate is 3 ℃ / min.

[0023] An application of the bimetallic molecular sieve catalyst prepared by the above method in the oxidation of toluene utilizes the close contact between Co supported on the surface of the bimetallic molecular sieve catalyst and a second metal to form a bimetallic interface. The reaction is carried out at a temperature of 200-300℃ and a space velocity of 30000-90000 mL·g. -1 ·h -1 The experiment was conducted under the following conditions: toluene concentration of 500-2000 ppm, O2 concentration of 10-25 vol%, and N2 balance gas.

[0024] The bimetallic molecular sieve catalyst achieved a toluene conversion rate of over 90% at 249 °C. It has advantages such as high catalytic activity, simple preparation method, and low cost, and can be used in industrial and environmental remediation fields.

[0025] The beneficial effects of this invention are:

[0026] (1) Precise and controllable construction of bimetallic interface: By adopting the "protective impregnation" strategy, an appropriate amount of ammonia water is added to adjust the pH value of the solution to neutral, and a second metal ammonia complex impregnation solution is prepared to create a mild environment, avoid the acidic precursor from destroying the dispersion of Co species, and achieve close contact between Co species and the second metal species to form a strongly interacting bimetallic interface.

[0027] (2) The preparation process is green, controllable and easy to industrialize: the preparation steps are simple, the parameters are easy to adjust and the repeatability is excellent; the protective impregnation method has mild conditions and does not require toxic reagents, which is in line with the concept of green chemical industry. Attached Figure Description

[0028] Figure 1These are transmission electron microscope (TEM) images of the B-MFI molecular sieve and B-MFI-E support prepared in this invention, wherein (a) is a TEM image of the B-MFI molecular sieve and (b) is a TEM image of the B-MFI-E support.

[0029] Figure 2 This is a transmission electron microscope image of the Cu / Co / B-MFI-E bimetallic molecular sieve catalyst prepared in Example 1 of this invention.

[0030] Figure 3 The images show the XRD patterns of the bimetallic molecular sieve catalysts prepared in Examples 1-3 of this invention.

[0031] Figure 4 The toluene oxidation activity curves are for the bimetallic molecular sieve catalysts prepared in Examples 1-3 of this invention. Detailed Implementation

[0032] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0033] The precursor in this application is prepared using the following method:

[0034] (1) Preparation of B-MFI molecular sieves:

[0035] Weigh 8.6401 g of 40 wt% TPAOH aqueous solution into a beaker, add 10.029 g of deionized water, and stir until homogeneous. Add 0.655 g of boric acid and stir magnetically at room temperature for 30 min until completely dissolved. Then slowly add 11.25 g of TEOS dropwise, continuing to stir until a clear solution is formed. Transfer the solution to a 50 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene, seal, and hydrothermally react at 140℃ for 5 days. After the reaction, allow it to cool naturally to room temperature, centrifuge to separate the product, wash repeatedly with deionized water, and dry in an oven at 70℃ overnight. Transfer the dried powder to a muffle furnace and calcine at 550℃ for 6 hours to obtain B-MFI molecular sieve.

[0036] (2) Preparation of hierarchical porous B-MFI-E support:

[0037] Weigh 0.3 g of the B-MFI molecular sieve prepared in step (1) and place it in a flask. Add 3.75 g of tetrapropylammonium hydroxide aqueous solution (TPAOH concentration of 0.4 mol / L) and stir magnetically at room temperature for 2 hours. Transfer the mixture to a 50 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene and perform hydrothermal etching at 140℃ for 3 days. After etching, allow it to cool naturally, centrifuge to separate the product, and wash with deionized water until the pH of the filtrate is 7. Dry the product in a 70℃ oven overnight, and then transfer it to a muffle furnace and calcine at 550℃ for 6 hours to obtain a hierarchical porous B-MFI-E support.

[0038] (3) Preparation of ZIF-67 / B-MFI-E precursor:

[0039] Weigh 0.1 g of the B-MFI-E support prepared in step (2), disperse it in 10 mL of anhydrous ethanol, and sonicate for half an hour to obtain a uniform suspension. Separately weigh 0.35 g of Co(NO3)2·6H2O, dissolve it in 10 mL of anhydrous ethanol, stir to dissolve, and slowly add it dropwise to the above suspension. After sonication for 1 hour, centrifuge to obtain a solid precipitate. Redisperse the solid in 10 mL of anhydrous ethanol, add 10 mL of ethanol solution containing 1.0 g of 2-methylimidazole, sonicate for 1 hour, and centrifuge. Disperse the obtained solid in 10 mL of anhydrous ethanol again, stir and add 10 mL of ethanol solution containing 0.25 g of 2-methylimidazole, then stir and add 10 mL of ethanol solution containing 0.35 g of Co(NO3)2·6H2O. Stir magnetically at room temperature for 2 hours. After the reaction is complete, centrifuge, wash three times with anhydrous ethanol, and dry in an oven at 80℃ for 12 hours to obtain the ZIF-67 / B-MFI-E precursor.

[0040] Example 1

[0041] Weigh 0.060 g of Cu(NO3)2·3H2O and dissolve it in 10 mL of anhydrous ethanol. Add an appropriate amount of ammonia water to adjust the pH to ≈7. Stir magnetically until the solution turns deep blue to obtain Cu. 2+ A 0.025 mol / L copper-ammonia complex impregnation solution was prepared. 0.3 g of the ZIF-67 / B-MFI-E precursor prepared above was weighed and dispersed in the impregnation solution. The mixture was magnetically stirred at room temperature for 2 hours. After impregnation, the mixture was centrifuged, washed twice with deionized water, and dried in an oven at 80°C for 12 hours. The dried solid was transferred to a tube furnace and calcined at 3°C / min to 400°C for 3 hours to obtain the Cu / Co / B-MFI-E bimetallic molecular sieve catalyst.

[0042] Weigh 0.10 g of the above catalyst, compressed into tablets of 40-60 mesh, and place them in a quartz tube of a fixed-bed reactor. The catalyst is placed in the isothermal zone of the reaction gas. Before the reaction, heat to 300 °C at a rate of 10 °C / min under air atmosphere for 1 hour to remove various impurities adsorbed on the catalyst surface, and then cool to 200 °C. Reaction conditions: toluene concentration 1000 ppm, O2 concentration 21 vol%, N2 balance gas, space velocity 60000 mL·g -1 ·h -1Catalytic oxidation tests were conducted by controlling the temperature controller to raise the temperature from room temperature to 200-290 °C at a rate of 5-20 °C / min under normal pressure. At a reaction temperature of 249 °C, a toluene removal rate of over 90% was achieved.

[0043] Example 2

[0044] 0.073 g of Ni(NO3)2·6H2O was dissolved in 10 mL of anhydrous ethanol, and an appropriate amount of ammonia was added to adjust the pH to approximately 7 to prepare a nickel-ammonia complex impregnation solution with a Ni²⁺ concentration of 0.025 mol / L. 0.3 g of the ZIF-67 / B-MFI-E precursor prepared above was weighed and dispersed in the impregnation solution, and impregnated with magnetic stirring at room temperature for 2 hours. After impregnation, the mixture was centrifuged, washed twice with deionized water, and dried in an oven at 80℃ for 12 hours. The dried solid was transferred to a tube furnace and calcined at a rate of 3℃ / min to 400℃ for 3 hours to obtain the Ni / Co / B-MFI-E bimetallic molecular sieve catalyst.

[0045] Weigh 0.10 g of the above catalyst, compressed into tablets of 40-60 mesh, and place them in a quartz tube of a fixed-bed reactor. The catalyst is placed in the isothermal zone of the reaction gas. Before the reaction, heat to 300 °C at a rate of 10 °C / min under air atmosphere for 1 hour to remove various impurities adsorbed on the catalyst surface, and then cool to 200 °C. Reaction conditions: toluene concentration 1000 ppm, O2 concentration 21 vol%, N2 balance gas, space velocity 60000 mL·g -1 ·h -1 Catalytic oxidation tests were conducted by controlling the temperature controller to raise the temperature from room temperature to 200-290 °C at a rate of 5-20 °C / min under normal pressure. At a reaction temperature of 269 °C, a toluene removal rate of over 90% was achieved.

[0046] Example 3

[0047] Weigh 0.072 g of Mn(NO3)2·6H2O and dissolve it in 10 mL of anhydrous ethanol. Add an appropriate amount of ammonia water to adjust the pH to ≈7, and stir magnetically to prepare Mn 2+ An anhydrous ethanol impregnation solution with a concentration of 0.025 mol / L was prepared. 0.3 g of the ZIF-67 / B-MFI-E precursor prepared above was weighed and dispersed in the impregnation solution, and impregnated with magnetic stirring at room temperature for 2 hours. After impregnation, the mixture was centrifuged, washed twice with deionized water, and dried in an oven at 80 ℃ for 12 hours. The dried solid was transferred to a tube furnace and calcined at a heating rate of 3 ℃ / min to 400 ℃ for 3 hours to obtain the Mn / Co / B-MFI-E bimetallic molecular sieve catalyst.

[0048] Weigh 0.10 g of the above catalyst, compressed into tablets of 40-60 mesh, and place them in a quartz tube of a fixed-bed reactor. The catalyst is placed in the isothermal zone of the reaction gas. Before the reaction, heat to 300 °C at a rate of 10 °C / min under air atmosphere for 1 hour to remove various impurities adsorbed on the catalyst surface, and then cool to 200 °C. Reaction conditions: toluene concentration 1000 ppm, O2 concentration 21 vol%, N2 balance gas, space velocity 60000 mL·g -1 ·h -1 Catalytic oxidation tests were conducted by controlling the temperature controller to raise the temperature from room temperature to 200-290 °C at a rate of 5-20 °C / min under normal pressure. At a reaction temperature of 269 °C, a toluene removal rate of over 90% was achieved.

[0049] The ZIF-67 / Si-MFI-E precursor in this application was prepared using the following method:

[0050] (1) Preparation of Si-MFI molecular sieves:

[0051] Weigh 1.324 g of 40 wt% TPAOH aqueous solution into a beaker, add 12.676 g of deionized water, and stir until homogeneous. Then, slowly add 3.2655 g of TEOS dropwise, stirring continuously for 1 day. Transfer the solution to a 50 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene, seal, and react hydrothermally at 150℃ for 4 days. After the reaction, allow it to cool naturally to room temperature, centrifuge to separate the product, wash repeatedly with deionized water, and dry in a 70℃ oven overnight. Transfer the dried powder to a muffle furnace and calcine at 550℃ for 6 hours to obtain Si-MFI molecular sieve.

[0052] (2) Preparation of hierarchical porous Si-MFI-E support:

[0053] Weigh 0.3 g of the Si-MFI molecular sieve prepared in step (1) and place it in a flask. Add 3.75 g of tetrapropylammonium hydroxide aqueous solution (TPAOH concentration of 0.4 mol / L) and stir magnetically at room temperature for 2 hours. Transfer the mixture to a 50 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene and perform hydrothermal etching at 140℃ for 3 days. After etching, allow it to cool naturally, centrifuge to separate the product, and wash with deionized water until the pH of the filtrate is 7. Dry the product in a 70℃ oven overnight, and then transfer it to a muffle furnace and calcine at 550℃ for 6 hours to obtain a hierarchical porous Si-MFI-E support.

[0054] (3) Preparation of ZIF-67 / Si-MFI-E precursor:

[0055] Weigh 0.1 g of the Si-MFI-E support prepared in step (2), disperse it in 10 mL of anhydrous ethanol, and sonicate it for half an hour to obtain a uniform suspension. Separately weigh 0.35 g of Co(NO3)2·6H2O, dissolve it in 10 mL of anhydrous ethanol, stir to dissolve, and slowly add it dropwise to the above suspension. After sonication for 1 hour, centrifuge to obtain a solid precipitate. Redisperse the solid in 10 mL of anhydrous ethanol, add 10 mL of ethanol solution containing 1.0 g of 2-methylimidazole, sonicate for 1 hour, and centrifuge. Disperse the obtained solid in 10 mL of anhydrous ethanol again, stir and add 10 mL of ethanol solution containing 0.25 g of 2-methylimidazole, then stir and add 10 mL of ethanol solution containing 0.35 g of Co(NO3)2·6H2O. Stir magnetically at room temperature for 2 hours. After the reaction is complete, centrifuge, wash three times with anhydrous ethanol, and dry in an oven at 80℃ for 12 hours to obtain the ZIF-67 / Si-MFI-E precursor.

[0056] Example 4

[0057] Based on Example 1, only the precursor was replaced with ZIF-67 / Si-MFI-E, while the composition, amount and operation steps of the other raw materials were the same, to prepare Cu / Co / Si-MFI-E bimetallic molecular sieve catalyst.

[0058] The experimental results of the Cu / Co / Si-MFI-E catalyst prepared in this embodiment show that a toluene removal rate of over 90% can be achieved at a reaction temperature of 255 °C.

[0059] Example 5

[0060] Based on Example 2, only the precursor was replaced with ZIF-67 / Si-MFI-E, while the composition, amount and operation steps of the other raw materials were the same, to prepare Ni / Co / Si-MFI-E bimetallic molecular sieve catalyst.

[0061] The experimental results of the Ni / Co / Si-MFI-E catalyst prepared in this embodiment show that a toluene removal rate of over 90% can be achieved at a reaction temperature of 272 °C.

[0062] Example 6

[0063] Based on Example 3, only the precursor was replaced with ZIF-67 / Si-MFI-E, while the composition, amount and operation steps of the other raw materials were the same, to prepare the Mn / Co / Si-MFI-E bimetallic molecular sieve catalyst.

[0064] The experimental results of the Mn / Co / Si-MFI-E catalyst prepared in this embodiment show that a toluene removal rate of over 90% can be achieved at a reaction temperature of 270 °C.

[0065] The ZIF-67 / Al-MFI-E precursor in this application was prepared using the following method:

[0066] (1) Preparation of Al-MFI molecular sieves:

[0067] Weigh 0.13 g of NaAlO2 into a beaker, add 7.9715 g of deionized water and 10.4 g of TEOS, and stir until homogeneous. Then add 5.447 g of 40 wt% TPAOH aqueous solution and stir magnetically at room temperature for 7 hours. Transfer the solution to a 50 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene, seal, and hydrothermally react at 180℃ for 7 days. After the reaction, allow it to cool naturally to room temperature, centrifuge to separate the product, wash repeatedly with deionized water, and dry in an oven at 70℃ overnight. Transfer the dried powder to a muffle furnace and calcine at 550℃ for 6 hours to obtain Al-MFI molecular sieve.

[0068] (2) Preparation of hierarchical porous Al-MFI-E support:

[0069] Weigh 0.3 g of the Al-MFI molecular sieve prepared in step (1) and place it in a flask. Add 3.75 g of tetrapropylammonium hydroxide aqueous solution (TPAOH concentration of 0.4 mol / L) and stir magnetically at room temperature for 2 hours. Transfer the mixture to a 50 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene and perform hydrothermal etching at 140℃ for 3 days. After etching, allow it to cool naturally, centrifuge to separate the product, and wash with deionized water until the pH of the filtrate is 7. Dry the product in a 70℃ oven overnight, and then transfer it to a muffle furnace and calcine at 550℃ for 6 hours to obtain a hierarchical porous Al-MFI-E support.

[0070] (3) Preparation of ZIF-67 / Al-MFI-E precursor:

[0071] Weigh 0.1 g of the Al-MFI-E support prepared in step (2), disperse it in 10 mL of anhydrous ethanol, and sonicate for half an hour to obtain a uniform suspension. Separately weigh 0.35 g of Co(NO3)2·6H2O, dissolve it in 10 mL of anhydrous ethanol, stir to dissolve, and slowly add it dropwise to the above suspension. After sonication for 1 hour, centrifuge to obtain a solid precipitate. Redisperse the solid in 10 mL of anhydrous ethanol, add 10 mL of ethanol solution containing 1.0 g of 2-methylimidazole, sonicate for 1 hour, and centrifuge. Disperse the obtained solid in 10 mL of anhydrous ethanol again, stir and add 10 mL of ethanol solution containing 0.25 g of 2-methylimidazole, then stir and add 10 mL of ethanol solution containing 0.35 g of Co(NO3)2·6H2O. Stir magnetically at room temperature for 2 hours. After the reaction is complete, centrifuge, wash three times with anhydrous ethanol, and dry in an oven at 80℃ for 12 hours to obtain the ZIF-67 / Al-MFI-E precursor.

[0072] Example 7

[0073] Based on Example 1, only the precursor was replaced with ZIF-67 / Al-MFI-E, while the composition, amount and operation steps of the other raw materials were the same, to prepare Cu / Co / Al-MFI-E bimetallic molecular sieve catalyst.

[0074] The experimental results of the Cu / Co / Al-MFI-E catalyst prepared in this embodiment show that a toluene removal rate of over 90% can be achieved at a reaction temperature of 258 °C.

[0075] Example 8

[0076] Based on Example 2, only the precursor was replaced with ZIF-67 / Al-MFI-E, while the composition, amount and operation steps of the other raw materials were the same, to prepare Ni / Co / Al-MFI-E bimetallic molecular sieve catalyst.

[0077] The experimental results of the Ni / Co / Al-MFI-E catalyst prepared in this embodiment show that a toluene removal rate of over 90% can be achieved at a reaction temperature of 268 °C.

[0078] Example 9

[0079] Based on Example 3, only the precursor was replaced with ZIF-67 / Al-MFI-E, while the composition, amount and operation steps of the other raw materials were the same, to prepare the Mn / Co / Al-MFI-E bimetallic molecular sieve catalyst.

[0080] The experimental results of the Mn / Co / Al-MFI-E catalyst prepared in this embodiment show that a toluene removal rate of over 90% can be achieved at a reaction temperature of 270 °C.

[0081] Comparative Example 1

[0082] 0.060 g of Cu(NO3)2·3H2O was weighed and dissolved in 10 mL of anhydrous ethanol, and stirred until dissolved. 0.3 g of the ZIF-67 / B-MFI-E precursor prepared above was weighed and dispersed in the above impregnation solution, and impregnated with magnetic stirring at room temperature for 2 hours. After impregnation, the mixture was centrifuged, washed twice with deionized water, and dried in an oven at 80℃ for 12 hours. The dried solid was transferred to a tube furnace and calcined at 3℃ / min to 400℃ for 3 hours to obtain the Cu / Co / B-MFI-E bimetallic molecular sieve catalyst.

[0083] The impregnation solution prepared in this comparative example does not use ammonia water, and the experimental results show that a toluene removal rate of over 90% can be achieved at a reaction temperature of 260 °C.

[0084] Comparative Example 2

[0085] 0.073 g of Ni(NO3)2·6H2O was weighed and dissolved in 10 mL of anhydrous ethanol, and stirred until dissolved. 0.3 g of the ZIF-67 / B-MFI-E precursor prepared above was weighed and dispersed in the above impregnation solution, and impregnated with magnetic stirring at room temperature for 2 hours. After impregnation, the mixture was centrifuged, washed twice with deionized water, and dried in an oven at 80℃ for 12 hours. The dried solid was transferred to a tube furnace and calcined at 3℃ / min to 400℃ for 3 hours to obtain the Ni / Co / B-MFI-E bimetallic molecular sieve catalyst.

[0086] The impregnation solution prepared in this comparative example does not use ammonia water, and the experimental results show that a toluene removal rate of over 90% can be achieved at a reaction temperature of 275 °C.

[0087] Comparative Example 3

[0088] 0.072 g of Mn(NO3)2·6H2O was weighed and dissolved in 10 mL of anhydrous ethanol, and stirred until dissolved. 0.3 g of the ZIF-67 / B-MFI-E precursor prepared above was weighed and dispersed in the above impregnation solution, and impregnated with magnetic stirring at room temperature for 2 hours. After impregnation, the mixture was centrifuged, washed twice with deionized water, and dried in an oven at 80 ℃ for 12 hours. The dried solid was transferred to a tube furnace and calcined at 3 ℃ / min to 400 ℃ for 3 hours to obtain the Mn / Co / B-MFI-E bimetallic molecular sieve catalyst.

[0089] The impregnation solution prepared in this comparative example does not use ammonia water, and the experimental results show that a toluene removal rate of over 90% can be achieved at a reaction temperature of 280 °C.

[0090] Comparative Examples 1-3 show that the catalysts obtained by the protective impregnation method have better catalytic activity and better dispersibility than those obtained by the simple impregnation method.

Claims

1. A bimetallic molecular sieve catalyst for the oxidation of toluene, characterized in that, The bimetallic molecular sieve catalyst uses an alkaline-etched modified hierarchical porous MFI-E molecular sieve as a support, and is loaded with active components of Co and a second metal. Co is dispersed on the support in the form of Co3O4 nanoparticles, with a loading of 4.0-10.0 wt%. The second metal forms a close bimetallic interface with Co, with a loading of 3.0-10.0 wt%.

2. The bimetallic molecular sieve catalyst according to claim 1, characterized in that, The second metal is Cu, Ni, or Mn.

3. The bimetallic molecular sieve catalyst according to claim 1, characterized in that, The support is a B-MFI-E molecular sieve, a Si-MFI-E molecular sieve, or an Al-MFI-E molecular sieve; the mesopore volume of the alkali-etched modified hierarchical B-MFI-E molecular sieve is 0.50 cm³. 3 / g, with an external specific surface area of ​​173 m² 2 / g.

4. A method for preparing a bimetallic molecular sieve catalyst for toluene oxidation, characterized in that, A second metal species was introduced using a "protective impregnation method," and after heat treatment, an M / Co / MFI-E supported bimetallic molecular sieve catalyst was obtained. Includes the following steps: (1) Preparation of impregnation solution: Dissolve the second metal salt in anhydrous ethanol, stir and add ammonia water dropwise to adjust the pH of the solution to neutral, and prepare the metal ammonia complex impregnation solution; (2) Preparation of catalyst: The prepared ZIF-67 / MFI-E precursor was dispersed in a metal ammonia complex impregnation solution, stirred and impregnated, and calcined to obtain a bimetallic molecular sieve catalyst.

5. The preparation method according to claim 1, characterized in that, In step (1), the metal ammonia complex impregnation solution is a metal ammonia complex impregnation solution with a second metal concentration of 0.015-0.05 mol / L; the second metal salt is a copper salt, nickel salt or manganese salt.

6. The preparation method according to claim 1, characterized in that, In step (2), the stirring and soaking time is 2-12 hours.

7. The preparation method according to claim 1, characterized in that, In step (2), the calcination temperature is 350-500 ℃, the calcination time is 2-4 hours, and the heating rate is 1-5 ℃ / min.

8. An application of a bimetallic molecular sieve catalyst obtained by the above preparation method in the oxidation of toluene, characterized in that, At a reaction temperature of 200-300℃ and a space velocity of 30,000-90,000 mL·g -1 ·h -1 The experiment was conducted under the conditions of toluene concentration of 500-2000 ppm, O2 concentration of 10-25 vol%, and N2 balance gas.

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