Preparation method of zif-67 derived cobalt manganese catalyst and application thereof in catalytic oxidation of benzene

Abstract

The application relates to a preparation method of a ZIF-67 derived cobalt-manganese catalyst and application of the ZIF-67 derived cobalt-manganese catalyst in catalytic oxidation of benzene, and belongs to the technical field of catalyst preparation. The preparation method is as follows: a ZIF-67 precursor is prepared; the ZIF-67 is dispersed in water to form a suspension, a potassium permanganate aqueous solution is added to carry out etching reaction, and a mixed system is obtained; the mixed system is transferred into a reaction kettle to carry out hydrothermal reaction, and black precipitates are obtained; the black precipitates are washed, dried, calcined, and ground to obtain the ZIF-67 derived cobalt-manganese catalyst. 140 The catalyst realizes 90% benzene conversion rate under the reaction conditions that the space velocity is up to 60000 mL / (g.h), the benzene concentration is 1000 ppm, the oxygen content is 20%, and the reaction temperature is about 210 DEG C.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalyst preparation, and particularly relates to a preparation method of a ZIF-67 derived cobalt-manganese catalyst and application of the catalyst in catalytic oxidation of benzene. BACKGROUND

[0002] Volatile organic compounds (VOCs) are one of the main hazardous substances causing acid rain, photochemical smog and global climate change, and pose a serious impact on the ecological environment and human health. As a typical aromatic VOC, benzene (C6H6) has high toxicity, carcinogenicity and mutagenicity due to its unique structure, and is difficult to handle, and has been a hot and difficult point in air governance. The removal methods of benzene mainly include adsorption, absorption, thermal combustion, biodegradation, low-temperature plasma, photocatalysis and catalytic oxidation, etc., among which the catalytic oxidation method has the advantages of high efficiency, less by-products and low cost, and is considered as one of the most effective VOCs removal methods. The core bottleneck of this technology is to develop a non-noble metal catalyst with high activity, excellent stability and low cost. In non-noble metal catalysts, metal organic framework (MOFs) derived catalysts provide an ideal precursor for constructing a high-efficiency multi-metal synergistic catalytic system due to their ability to flexibly control active components and unique pore structure.

[0003] In the MOFs system, ZIF-67 derived catalysts show considerable potential. The cobalt-based catalysts derived from ZIF-67 have the advantages of controllable structure, adjustable active components and good pore structure. In the performance research of ZIF-67@Co3O4 catalytic oxidation of VOCs published by Lei Juan et al., the catalysts prepared at different calcination temperatures from ZIF-67 as a precursor have the structural characteristics of MOFs derived catalysts, but the catalysts prepared by them have a benzene conversion rate of 90% at a space velocity of 20000 mL / (g·h) and a reaction temperature of 254℃-295℃, still facing the problems of poor benzene oxidation activity at low temperature and low space velocity. In order to improve the benzene oxidation activity at low temperature, different methods are usually used to introduce active components to prepare catalysts with different morphologies based on ZIF-67, and the existing methods include complexing agent assisted method, coprecipitation method, template method and sol-gel method, etc., but the above methods all have residual substances that are difficult to completely remove, and the catalysts prepared by the existing methods are difficult to achieve high space velocity, low reaction temperature and long-term stability at the same time to achieve a benzene conversion rate of 90%.

[0004] In order to break through the above bottleneck, it is urgent to improve the catalytic performance by introducing new active components and regulating the microstructure. SUMMARY

[0005] Invention purposes: The application provides a preparation method of ZIF-67 derived cobalt manganese catalyst and application thereof in catalytic oxidation of benzene, and aims to solve the problems that the existing preparation method of ZIF-67 catalyst is prone to residual substances, and it is difficult to achieve high space velocity, low reaction temperature and long-term stability when the ZIF-67 catalyst reaches 90% benzene conversion.

[0006] Technical means:

[0007] The first aspect of the application provides a preparation method of ZIF-67 derived cobalt manganese catalyst, comprising the following steps:

[0008] S1, preparing a ZIF-67 precursor;

[0009] S2, dispersing the ZIF-67 in water to form a suspension, and adding the ZIF-67 suspension into a potassium permanganate aqueous solution in equal volume to perform etching reaction, the mass concentration ratio of the ZIF-67 suspension to the potassium permanganate aqueous solution is 5:1-2, and a mixed system is obtained;

[0010] S3, transferring the mixed system into a reaction kettle to perform hydrothermal reaction, and obtaining a black precipitate;

[0011] S4, washing, drying and calcining the black precipitate, and grinding to obtain the ZIF-67 derived cobalt manganese catalyst.

[0012] Preferably, in the step S1, the method for preparing the ZIF-67 precursor is: under magnetic stirring, the cobalt nitrate hexahydrate aqueous solution is quickly poured into the 2-methylimidazole aqueous solution, the molar ratio of 2-methylimidazole to cobalt nitrate hexahydrate is 2-6:1, the stirring is continuously performed at room temperature for 2h-6h, the solid product is separated by centrifugation, and then washed with deionized water for 3-5 times, and dried in an oven at 60-90 DEG C for 10-14h to obtain a purple solid, and the ZIF-67 powder is obtained after grinding.

[0013] Preferably, in the step S2, the mass concentration ratio of the ZIF-67 suspension to the potassium permanganate aqueous solution is 5:2.

[0014] Preferably, in the step S3, the hydrothermal temperature is 100-160 DEG C, and the reaction time is 4-8h.

[0015] Preferably, the hydrothermal temperature is 120-140 DEG C.

[0016] Preferably, in the step S4, the calcination temperature is 350-500 DEG C, and the calcination time is 2-4h.

[0017] Preferably, the pore volume of the prepared ZIF-67 derived cobalt manganese catalyst can reach 0.59cm 3 / g, and the pore size can reach 16.2nm.

[0018] The application further provides application of the ZIF-67 derived cobalt-manganese catalyst prepared by the preparation method of the ZIF-67 derived cobalt-manganese catalyst in catalyzing oxidation of benzene.

[0019] The application further provides application of the ZIF-67 derived cobalt-manganese catalyst prepared by the preparation method of the ZIF-67 derived cobalt-manganese catalyst in catalyzing oxidation of benzene. Beneficial effects

[0020] The application controls the hydrothermal parameters and the mass ratio of cobalt and manganese sources, adjusts the pore structure of the catalyst, and optimizes the surface active components, so that the high space velocity and low temperature catalytic oxidation activity of the ZIF-67 derived catalyst is improved. Under the optimized hydrothermal conditions, the potassium permanganate oxidation etching promotes the Co 2+ Oxidation and reduction reaction with permanganate, one-step construction of cobalt-manganese synergistic active center; and by optimizing the etching amount of potassium permanganate, the pore structure of the material can be precisely controlled, and a more optimal mesoporous structure, larger pore volume and pore diameter can significantly reduce the mass transfer resistance, so that the reactant molecules can more easily contact the active sites, thereby improving the reaction efficiency.

[0021] The application adopts potassium permanganate as the etchant, which has obvious advantages compared with traditional complexing agent assisted method, coprecipitation method, template method and sol-gel method, especially in the aspect of "cleanliness". The potassium permanganate realizes etching of ZIF-67 through oxidation reaction, and the conversion product thereof is completely inorganic (such as manganese ions), and will not leave any harmful impurities in the catalyst system. In contrast, the traditional methods often have the problem of residual pollutants - for example, the complexing agent assisted method may leave residual complexing agent, and the template method may leave residual template, which will occupy the active sites of the catalyst, interfere with the electronic structure thereof or induce side reactions, resulting in a decrease in catalytic activity or even deactivation. The potassium permanganate etching process adopted in the application is complete, and the conversion product has good compatibility with the catalytic system, and will not have a negative impact on the subsequent reaction. In this way, the purity of the catalyst is maximized, and the long-term stability and service life thereof are significantly improved. Therefore, the "non-harmful residue" characteristic of the potassium permanganate as the etchant is the core advantage of the potassium permanganate compared with the traditional methods, and the problem of performance degradation of the catalyst caused by residual impurities is successfully solved.

[0022] The low-temperature catalytic activity of the application is excellent. The Co-Mn8-T 140The catalyst has excellent low-temperature activity in the catalytic oxidation reaction of benzene. Under the reaction conditions that the space velocity is up to 60,000 mL / (g.h), the benzene concentration is 1,000 ppm, and the oxygen content is 20%, the catalyst can achieve 90% benzene conversion at a reaction temperature of about 210 DEG C. The excellent low-temperature activity indicates that the catalyst can catalyze the oxidation of benzene efficiently under the condition of lower energy consumption, and has significant application potential and economic benefits.

[0023] The preparation process of the application is simple and easy to operate, and the conditions are mild and controllable. The application uses ZIF-67 as a precursor, and the synthesis can be obtained by simple mixing and stirring under room temperature conditions without complex equipment or harsh conditions. The subsequent etching step is simple to operate, and the calcination process belongs to the conventional range. The whole process flow is clear, the raw materials are easy to obtain, and only involves conventional stirring, centrifugation, hydrothermal and calcination operation, which significantly reduces the preparation difficulty, equipment requirement and production cost. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The XRD graph of the catalyst prepared for example 1 and comparative example 1 of the application;

[0025] Figure 2 The EPR graph of the catalyst prepared for example 1 and comparative example 1 of the application;

[0026] Figure 3 The SEM graph of the catalyst prepared for example 1 of the application;

[0027] Figure 4 The SEM graph of the catalyst prepared for comparative example 1 of the application;

[0028] Figure 5 The N2 adsorption-desorption curve graph of the catalyst prepared for example 1 and comparative example 1 of the application;

[0029] Figure 6 The long-term stability and cycle test graph of example 1 of the application. DETAILED DESCRIPTION

[0030] The beneficial effects of the application are proved by the following examples.

[0031] In order to better explain the application, the following will be described in detail in combination with the drawings and specific embodiments.

[0032] The application provides a preparation method of a ZIF-67 derived cobalt-manganese catalyst and application of the catalyst in catalytic oxidation of benzene. The application etches ZIF-67 by using a strong oxidant potassium permanganate, and the reduction product of KMnO4 is Mn 2+ , which has lower toxicity and no harmful residue, and is more in line with the requirements of green chemistry.

[0033] The reaction equation is as follows:

[0034] Co 2+ +MnO4 − +8 H + →Co 3+ +Mn 2+ +4 H2O

[0035] Potassium permanganate is a strong oxidizing agent (standard electrode potential: +1.51V, acidic conditions), which can selectively oxidize Co in ZIF-67 2+ to higher valence Co 3+ , and after the calcination process, active species such as Co3O4 are formed, which improves the activity of the catalytic oxidation reaction. Through oxidation etching, the surface morphology of ZIF-67 (such as forming a porous structure) can be controlled, and the specific surface area and active site exposure are increased.

[0036] The present application adopts a high space velocity of 60000 mL / (g·h), which is much higher than the low space velocity of less than 30000 mL / (g·h) in conventional industrial catalytic processes. The low space velocity in existing industrial catalysis leads to a large reactor volume, high equipment investment, and long material residence time, which easily causes side reactions. For example, in the benzene oxidation process, the long residence time will lead to an increase in by-products such as CO, and a significant decrease in degradation rate. Through the high active site density and reasonable mesoporous structure of the catalyst, high mass transfer efficiency is achieved, the reaction of benzene is completed in a short residence time in the catalyst bed, the industrial processing capacity is significantly improved, and the side reactions are effectively inhibited.

[0037] The present application has a low reaction temperature of 210℃, which is much lower than the high temperature of more than 300℃ in conventional industrial catalysis. The high temperature in the prior art leads to high energy consumption, short catalyst life, and high safety risk. Through the synergistic effect of Co-Mn bimetallic sites, high activity at low temperature is achieved. Under the synergistic effect of high space velocity and low temperature, the contradiction between high space velocity and low temperature in existing industrial catalysis is overcome, that is, high temperature is needed to make up for the insufficient conversion rate, and low temperature is needed to ensure the reaction time. The comprehensive advantages of high processing capacity, low energy consumption, and long life are achieved, effectively solving the pain points of the prior art of "low efficiency or high cost", and meeting the needs of industrial catalysis for high efficiency, economy, and safety.

[0038] The present application provides a preparation method of a ZIF-67 derived cobalt-manganese catalyst, comprising the following steps:

[0039] (1) ZIF-67 precursor preparation: under magnetic stirring, rapidly pour the cobalt nitrate hexahydrate aqueous solution into the 2-methylimidazole aqueous solution, the molar ratio of 2-methylimidazole to cobalt nitrate hexahydrate is 2-6:1, continuously stir at room temperature for 10h-14h, and then dry to obtain a purple solid. After grinding, ZIF-67 powder is obtained.

[0040] (2) Etching: A ZIF-67 suspension was prepared using deionized water. An equal volume of the ZIF-67 suspension was added to a potassium permanganate aqueous solution for etching. The mass concentration ratio of the ZIF-67 suspension to the potassium permanganate aqueous solution was 5:1–2, resulting in a mixed system. After stirring at room temperature for 1 hour, the mixture was transferred to a reactor lined with 100 mL of polytetrafluoroethylene and reacted at 100–140 °C for 4–8 hours under hydrothermal conditions. After cooling, the solid was separated by centrifugation, washed 3–5 times with deionized water, and dried at 60–90 °C for 10–14 hours to obtain the etched black powder.

[0041] (3) Calcination: The black powder is placed in a crucible and then placed in a muffle furnace. The temperature is increased to 350℃~500℃ at 2℃ / min and calcined for 2h~4h. After natural cooling, it is ground to obtain the catalyst Co-Mn. x -T y Take the mass ratio of potassium permanganate and ZIF-67 as x:20, where y is the hydrothermal temperature.

[0042] The catalyst Co-Mn prepared by the above method x -T y Through scanning electron microscope images, such as Figure 3 As shown, they all exhibit a loose, spherical morphology; the N2 adsorption-desorption curves, as shown... Figure 5 As shown, all exhibit typical Type IV isotherms (IUPAC classification) and H3 hysteresis loops, indicating that the materials possess typical mesoporous structure characteristics. Given the similarity in morphology and pore structure among catalysts prepared under different parameters, to clarify the influence mechanism of hydrothermal parameters and the mass ratio of cobalt and manganese sources on the pore structure regulation and surface active components of the catalysts, the following examples and comparative examples are compared using a single-factor substitution method.

[0043] Example 1: Catalyst Co-Mn8-T 140 Preparation and application

[0044] (1) Preparation of ZIF-67 precursor: 16 mmol of 2-methylimidazole was dissolved in 30 mL of deionized water and labeled as solution A; 4 mmol of cobalt nitrate hexahydrate was dissolved in 30 mL of deionized water and labeled as solution B. Solution B was quickly poured into solution A under magnetic stirring and stirred continuously at room temperature for 4 h. After centrifugation to separate the solid product, it was washed three times with deionized water and dried in an oven at 80 °C for 12 h to obtain a purple solid, which was then ground to obtain ZIF-67 powder.

[0045] (2) Etching: 1.0 g of the above ZIF-67 powder was dispersed in 30 mL of deionized water, denoted as suspension C; 0.4 g of potassium permanganate was dissolved in 30 mL of deionized water, denoted as solution D. Solution D was added to suspension C, stirred at room temperature for 1 h, and then transferred to a reaction kettle containing 100 mL of a polytetrafluoroethylene liner, and reacted at 140 °C under hydrothermal conditions for 6 h. After cooling, the solid was separated by centrifugation, washed with deionized water 3 times, and dried at 80 °C for 12 h to obtain black powder after etching.

[0046] (3) Calcination: the black powder was loaded into a 50 mL crucible and placed in a muffle furnace, heated to 450 °C at a rate of 2 °C / min, and calcined for 2 h. After natural cooling, grinding was performed to obtain the catalyst Co-Mn8-T x -T y , the mass ratio of potassium permanganate and ZIF-67 was x:20, y was the hydrothermal temperature, thus obtaining the catalyst Co-Mn8-T 140 .

[0047] Activity test: 0.1 g of the catalyst Co-Mn8-T 140 was loaded into the reactor of a tube furnace, and a mixed gas of 1000 ppm benzene and 20% O2 was introduced, with N2 as the balance gas, and the space velocity was 60000 mL / (g·h), and the detection was performed by a Fourier transform infrared spectrometer. It can be seen from Table 1 that when the reaction temperature is about 210 °C, the benzene conversion rate is 90%.

[0048] Preparation and application of catalyst Co-Mn8-T 100 .

[0049] (1) Preparation of ZIF-67 precursor: 16 mmol of 2-methylimidazole was dissolved in 30 mL of deionized water, and denoted as solution A; 4 mmol of cobalt nitrate hexahydrate was dissolved in 30 mL of deionized water, and denoted as solution B. Solution B was quickly poured into solution A under magnetic stirring, and the stirring was continued at room temperature for 4 h. After centrifugation of the solid product, it was washed with deionized water 3 times, and dried in an oven at 80 °C for 12 h to obtain a purple solid, which was ground to obtain ZIF-67 powder.

[0050] (2) Etching: 1.0 g of the above ZIF-67 powder was dispersed in 30 mL of deionized water, denoted as suspension C; 0.4 g of potassium permanganate was dissolved in 30 mL of deionized water, denoted as solution D. Solution D was added to suspension C, stirred at room temperature for 1 h, and then transferred to a reaction kettle containing 100 mL of a polytetrafluoroethylene liner, and reacted at 100 °C under hydrothermal conditions for 6 h. After cooling, the solid was separated by centrifugation, washed with deionized water 3 times, and dried at 80 °C for 12 h to obtain black powder after etching.

[0051] (3) Calcination: the black powder was loaded into a 50 mL crucible and placed in a muffle furnace, heated to 450℃ at a rate of 2℃ / min for 2h, and then ground after natural cooling to obtain the catalyst Co-Mn8-T 100 .

[0052] Activity test: 0.1 g of the catalyst Co-Mn8-T 100 was loaded into the reactor of a tube furnace, and a mixed gas of 1000 ppm benzene and 20% O2 was introduced, with N2 as the balance gas, at a space velocity of 60000 mL / (g·h), and then detected by a Fourier transform infrared spectrometer. As can be seen from Table 1, when the reaction temperature is about 223℃, the benzene conversion rate is 90%.

[0053] Example 3: Preparation of the catalyst Co-Mn8-T 120

[0054] (1) Preparation of ZIF-67 precursor: 16 mmol of 2-methylimidazole was dissolved in 30 mL of deionized water, and was denoted as solution A; 4 mmol of cobalt nitrate hexahydrate was dissolved in 30 mL of deionized water, and was denoted as solution B. Solution B was quickly poured into solution A under magnetic stirring, and stirring was continued at room temperature for 4h. After centrifugal separation of the solid product, it was washed with deionized water for 3 times, and was dried in an oven at 80℃ for 12h to obtain a purple solid, which was ground to obtain ZIF-67 powder.

[0055] (2) Etching: 1.0 g of the above ZIF-67 powder was dispersed in 30 mL of deionized water, and was denoted as suspension C; 0.4 g of potassium permanganate was dissolved in 30 mL of deionized water, and was denoted as solution D. Solution D was added to suspension C, which was stirred at room temperature for 1h, and then was transferred to a reaction kettle containing a 100 mL polytetrafluoroethylene liner, and was reacted under hydrothermal conditions at 120℃ for 6h. After cooling, the solid was centrifugally separated, washed with deionized water for 3 times, and dried at 80℃ for 12h to obtain black powder after etching.

[0056] (3) Calcination: the black powder was loaded into a 50 mL crucible and placed in a muffle furnace, heated to 450℃ at a rate of 2℃ / min for 2h, and then ground after natural cooling to obtain the catalyst Co-Mn8-T 120 .

[0057] 0.1 g of the catalyst Co-Mn8-T 120 was loaded into the reactor of a tube furnace, and a mixed gas of 1000 ppm benzene and 20% O2 was introduced, with N2 as the balance gas, at a space velocity of 60000 mL / (g·h), and then detected by a Fourier transform infrared spectrometer. As can be seen from Table 1, when the reaction temperature is about 217℃, the benzene conversion rate is 90%.

[0058] Example 4: Preparation of the catalyst Co-Mn8-T 160 ​Preparation of the catalyst Co-Mn8-T

[0059] (1) Preparation of ZIF-67 precursor: 16 mmol of 2-methylimidazole was dissolved in 30 mL of deionized water, and was recorded as solution A; 4 mmol of cobalt nitrate hexahydrate was dissolved in 30 mL of deionized water, and was recorded as solution B. Solution B was quickly poured into solution A under magnetic stirring, and stirring was continued at room temperature for 4 h. After centrifugal separation of the solid product, it was washed with deionized water for 3 times, and was dried in an oven at 80°C for 12 h to obtain a purple solid, which was ground to obtain ZIF-67 powder.

[0060] (2) Etching: 1.0 g of the above ZIF-67 powder was dispersed in 30 mL of deionized water, and was recorded as suspension C; 0.4 g of potassium permanganate was dissolved in 30 mL of deionized water, and was recorded as solution D. Solution D was added to suspension C, and after stirring at room temperature for 1 h, it was transferred to a reaction kettle containing 100 mL of polytetrafluoroethylene liner, and was reacted under hydrothermal conditions at 160°C for 6 h. After cooling, the solid was centrifugally separated, washed with deionized water for 3 times, and dried at 80°C for 12 h to obtain black powder after etching.

[0061] (3) Calcination: the black powder was loaded into a 50 mL crucible, and was placed in a muffle furnace, and was heated to 450°C at a rate of 2°C / min, and was calcined for 2 h. After natural cooling, it was ground to obtain the catalyst Co-Mn8-T 160 .

[0062] Activity test: 0.1 g of the catalyst Co-Mn8-T 160 was loaded into the reactor of a tube furnace, and a mixed gas of 1000 ppm benzene and 20% O2 was introduced, N2 was the balance gas, the space velocity was 60000 mL / (g·h), and it was detected by a Fourier transform infrared spectrometer. It can be seen from Table 1 that when the reaction temperature is about 225°C, the benzene conversion rate is 90%.

[0063] Preparation of the catalyst Co-Mn4-T 140

[0064] (1) Preparation of ZIF-67 precursor: 16 mmol of 2-methylimidazole was dissolved in 30 mL of deionized water, and was recorded as solution A; 4 mmol of cobalt nitrate hexahydrate was dissolved in 30 mL of deionized water, and was recorded as solution B. Solution B was quickly poured into solution A under magnetic stirring, and stirring was continued at room temperature for 4 h. After centrifugal separation of the solid product, it was washed with deionized water for 3 times, and was dried in an oven at 80°C for 12 h to obtain a purple solid, which was ground to obtain ZIF-67 powder.

[0065] ​(2) Etching: 1.0 g of the above ZIF-67 powder was dispersed in 30 mL of deionized water, denoted as suspension C; 0.2 g of potassium permanganate was dissolved in 30 mL of deionized water, denoted as solution D. Solution D was added to suspension C, stirred at room temperature for 1 h, and then transferred to a reaction kettle containing 100 mL of a polytetrafluoroethylene liner, and reacted under hydrothermal conditions at 140 °C for 6 h. After cooling, the solid was separated by centrifugation, washed with deionized water 3 times, and dried at 80 °C for 12 h to obtain a black powder after etching.

[0066] (3) Calcination: the black powder was loaded into a 50 mL crucible and placed in a muffle furnace, heated to 450 °C at a rate of 2 °C / min, and calcined for 2 h. After natural cooling, grinding was performed to obtain the catalyst Co-Mn4-T 140 .

[0067] Activity test: 0.1 g of the catalyst Co-Mn4-T 140 was loaded into the reactor of a tube furnace, a mixed gas of 1000 ppm benzene and 20% O2 was introduced, N2 was the balance gas, the space velocity was 60000 mL / (g·h), and detection was performed by a Fourier transform infrared spectrometer. As can be seen from Table 1, when the reaction temperature is about 218 °C, the benzene conversion rate is 90%.

[0068] Comparative Example 1: Preparation and application of catalyst Co3O4

[0069] (1) Preparation of ZIF-67 precursor: 16 mmol of 2-methylimidazole was dissolved in 30 mL of deionized water, and denoted as solution A; 4 mmol of cobalt nitrate hexahydrate was dissolved in 30 mL of deionized water, and denoted as solution B. Solution B was quickly poured into solution A under magnetic stirring, and stirring was continued at room temperature for 4 h. After centrifugation of the solid product, washing with deionized water 3 times, and drying in an oven at 80 °C for 12 h, a purple solid was obtained, and grinding was performed to obtain ZIF-67 powder.

[0070] (2) Calcination: the ZIF-67 powder was loaded into a 50 mL crucible and placed in a muffle furnace, heated to 450 °C at a rate of 2 °C / min, and calcined for 2 h. After natural cooling, grinding was performed to obtain the catalyst Co3O4.

[0071] Activity test: 0.1 g of the catalyst Co3O4 was loaded into the reactor of a tube furnace, a mixed gas of 1000 ppm benzene and 20% O2 was introduced, N2 was the balance gas, the space velocity was 60000 mL / (g·h), and detection was performed by a Fourier transform infrared spectrometer. As can be seen from Table 1, when the reaction temperature is about 258 °C, the benzene conversion rate is 90%.

[0072] Comparative Example 2: Preparation and application of catalyst Co-Mn8-RT

[0073] (1) ZIF-67 precursor preparation: 1 mmol of 2-methylimidazole was dissolved in 30 mL of deionized water, and was recorded as solution A; 4 mmol of cobalt nitrate hexahydrate was dissolved in 30 mL of deionized water, and was recorded as solution B. Solution B was quickly poured into solution A under magnetic stirring, and stirring was continued at room temperature for 4 h. After centrifugal separation of the solid product, it was washed with deionized water for 3 times, and was dried in an oven at 80°C for 12 h to obtain a purple solid, which was ground to obtain ZIF-67 powder.

[0074] (2) Etching: 1.0 g of the above ZIF-67 powder was dispersed in 30 mL of deionized water, and was recorded as suspension C; 0.4 g of potassium permanganate was dissolved in 30 mL of deionized water, and was recorded as solution D. Solution D was added to suspension C, and after stirring at room temperature for 6 h, the solid was centrifugally separated, washed with deionized water for 3 times, and dried at 80°C for 12 h to obtain black powder after etching.

[0075] (3) The black powder was loaded into a 50 mL crucible, and was placed in a muffle furnace, and was heated to 450°C at a rate of 2°C / min, and was calcined for 2 h, and was ground after natural cooling, and was obtained at RT. The catalyst Co-Mn8-RT was obtained by stirring.

[0076] Activity test: 0.1 g of the catalyst Co-Mn8-T 140 was loaded into the reactor of a tube furnace, and a mixed gas of 1000 ppm benzene and 20% O2 was introduced, N2 was the balance gas, the space velocity was 60000 mL / (g·h), and the detection was performed by a Fourier transform infrared spectrometer. It can be seen from Table 1 that when the reaction temperature is about 227°C, the benzene conversion rate is 90%.

[0077] Preparation of the catalyst Co-Mn8-T 180 of Comparative Example 3

[0078] (1) ZIF-67 precursor preparation: 1 mmol of 2-methylimidazole was dissolved in 30 mL of deionized water, and was recorded as solution A; 4 mmol of cobalt nitrate hexahydrate was dissolved in 30 mL of deionized water, and was recorded as solution B. Solution B was quickly poured into solution A under magnetic stirring, and stirring was continued at room temperature for 4 h. After centrifugal separation of the solid product, it was washed with deionized water for 3 times, and was dried in an oven at 80°C for 12 h to obtain a purple solid, which was ground to obtain ZIF-67 powder.

[0079] (2) Etching: 1.0 g of the above ZIF-67 powder was dispersed in 30 mL of deionized water, denoted as suspension C; 0.4 g of potassium permanganate was dissolved in 30 mL of deionized water, denoted as solution D. Solution D was added to suspension C, stirred at room temperature for 1 h, and then transferred to a reaction kettle containing 100 mL of a polytetrafluoroethylene liner, and reacted at 180 °C under hydrothermal conditions for 6 h. After cooling, the solid was separated by centrifugation, washed with deionized water for 3 times, and dried at 80 °C for 12 h to obtain black powder after etching.

[0080] (3) Calcination: the black powder was loaded into a 50 mL crucible and placed in a muffle furnace, heated to 450 °C at a rate of 2 °C / min, and calcined for 2 h. After natural cooling, grinding was performed to obtain the catalyst Co-Mn8-T 180 .

[0081] Activity test: 0.1 g of the catalyst Co-Mn8-T 180 was loaded into the reactor of a tube furnace, and a mixed gas of 1000 ppm benzene and 20% O2 was introduced, with N2 as the balance gas, and the space velocity was 60000 mL / (g·h). The reaction was detected by a Fourier transform infrared spectrometer. As can be seen from Table 1, when the reaction temperature is about 237 °C, the benzene conversion rate is 90%.

[0082] Preparation of Comparative Example 4: Catalyst Co-Mn1-T 140

[0083] (1) Preparation of ZIF-67 precursor: 16 mmol of 2-methylimidazole was dissolved in 30 mL of deionized water, and denoted as solution A; 4 mmol of cobalt nitrate hexahydrate was dissolved in 30 mL of deionized water, and denoted as solution B. Solution B was quickly poured into solution A under magnetic stirring, and the stirring was continued at room temperature for 4 h. After centrifugation of the solid product, washing with deionized water for 3 times, and drying at 80 °C in an oven for 12 h, a purple solid was obtained, and grinding was performed to obtain ZIF-67 powder.

[0084] (2) Etching: 1.0 g of the above ZIF-67 powder was dispersed in 30 mL of deionized water, denoted as suspension C; 0.05 g of potassium permanganate was dissolved in 30 mL of deionized water, denoted as solution D. Solution D was added to suspension C, stirred at room temperature for 1 h, and then transferred to a reaction kettle containing 100 mL of a polytetrafluoroethylene liner, and reacted at 140 °C under hydrothermal conditions for 6 h. After cooling, the solid was separated by centrifugation, washed with deionized water for 3 times, and dried at 80 °C for 12 h to obtain black powder after etching.

[0085] (3) Calcination: the black powder was loaded into a 50 mL crucible and placed in a muffle furnace, heated to 450 °C at a rate of 2 °C / min, and calcined for 2 h. After natural cooling, grinding was performed to obtain the catalyst Co-Mn1-T 140 . ​

[0086] Activity test: 0.1 g of catalyst Co-Mn1-T 140 was loaded into the reactor of a tube furnace, mixed gas of 1000 ppm benzene, 20% O2was passed, N2was the balance gas, the space velocity was 60000 mL / (g h), and it was detected by a Fourier transform infrared spectrometer. It can be obtained from Table 1 that when the reaction temperature is about 230℃, the benzene conversion rate is 90%.

[0087] Comparative example 5: preparation of catalyst Co-Mn2-T 140

[0088] (1) Preparation of ZIF-67 precursor: 16 mmol of 2-methylimidazole was dissolved in 30 mL of deionized water, and was recorded as solution A; 4 mmol of cobalt nitrate hexahydrate was dissolved in 30 mL of deionized water, and was recorded as solution B. Solution B was quickly poured into solution A under magnetic stirring, and stirring was continued at room temperature for 4 h. After centrifugal separation of the solid product, it was washed with deionized water for 3 times, and was dried in an oven at 80℃ for 12 h to obtain a purple solid, which was ground to obtain ZIF-67 powder.

[0089] (2) Etching: 1.0 g of the above ZIF-67 powder was dispersed in 30 mL of deionized water, and was recorded as suspension C; 0.1 g of potassium permanganate was dissolved in 30 mL of deionized water, and was recorded as solution D. Solution D was added to suspension C, and after stirring at room temperature for 1 h, it was transferred to a reaction kettle containing 100 mL of a polytetrafluoroethylene liner, and was reacted under hydrothermal conditions at 140℃ for 6 h. After cooling, the solid was centrifugally separated, washed with deionized water for 3 times, and dried at 80℃ for 12 h to obtain black powder after etching.

[0090] (3) Calcination: the black powder was loaded into a 50 mL crucible, and was placed in a muffle furnace, and was calcined at 2℃ / min to 450℃ for 2 h. After natural cooling, it was ground to obtain catalyst Co-Mn2-T 140 .

[0091] Activity test: 0.1 g of catalyst Co-Mn2-T 140 was loaded into the reactor of a tube furnace, mixed gas of 1000 ppm benzene, 20% O2was passed, N2was the balance gas, the space velocity was 60000 mL / (g h), and it was detected by a Fourier transform infrared spectrometer. It can be obtained from Table 1 that when the reaction temperature is about 228℃, the benzene conversion rate is 90%.

[0092] Comparative example 6: preparation of catalyst Co-Mn 16 -T 140

[0093] ​​(1) ZIF-67 precursor preparation: 16 mmol of 2-methylimidazole was dissolved in 30 mL of deionized water, and was recorded as solution A; 4 mmol of cobalt nitrate hexahydrate was dissolved in 30 mL of deionized water, and was recorded as solution B. Solution B was quickly poured into solution A under magnetic stirring, and stirring was continued at room temperature for 4 h. After centrifugal separation of the solid product, it was washed with deionized water for 3 times, and was dried in an oven at 80°C for 12 h to obtain a purple solid, which was ground to obtain ZIF-67 powder.

[0094] (2) Etching: 1.0 g of the above ZIF-67 powder was dispersed in 30 mL of deionized water, and was recorded as suspension C; 0.8 g of potassium permanganate was dissolved in 30 mL of deionized water, and was recorded as solution D. Solution D was added to suspension C, and after stirring at room temperature for 1 h, it was transferred to a reaction kettle containing 100 mL of a polytetrafluoroethylene liner, and was reacted under hydrothermal conditions at 140°C for 6 h. After cooling, the solid was centrifugally separated, washed with deionized water for 3 times, and dried at 80°C for 12 h to obtain black powder after etching.

[0095] (3) Calcination: the black powder was loaded into a 50 mL crucible, and was placed in a muffle furnace, and was heated to 450°C at a rate of 2°C / min, and was calcined for 2 h. After natural cooling, it was ground to obtain catalyst Co-Mn 16 -T 140 .

[0096] Activity test: 0.1 g of catalyst Co-Mn 16 -T 140 was loaded into the reactor of a tube furnace, and a mixed gas of 1000 ppm benzene and 20% O2 was introduced, N2 was the balance gas, the space velocity was 60000 mL / (g·h), and it was detected by a Fourier transform infrared spectrometer. As can be seen from Table 1, when the reaction temperature was 300°C, the conversion rate of the catalyst Co-Mn 16 -T 140 to benzene still did not reach 90%.

[0097] Table 1: Summary of catalysts of examples and comparative examples

[0098]

[0099] According to the data in Table 1, by comparing Example 1 and Comparative Example 1 alone, it can be seen that without the process of hydrothermal oxidation etching by potassium permanganate, the catalyst is obtained by directly calcining ZIF-67, and the catalytic effect is poor. It shows that the addition of new active metal component Mn can effectively improve the catalytic activity of the catalyst, and the synergistic effect of the Mn-Co bimetallic active center is beneficial to the catalytic oxidation of benzene at low temperature.

[0100] Taking Example 1 as an example, Figure 1The XRD test results of Example 1 and Comparative Example 1 are shown. Both Example 1 and Comparative Example 1 belong to spinel Co3O4. Although the catalyst Co-Mn8-T 140 underwent potassium permanganate hydrothermal etching and subsequent high-temperature calcination, the crystal structure of the ZIF-67 pyrolysis product did not change. This indicates that the etching process preserved the ZIF-67-derived Co3O4 spinel framework, and the cubic crystal structure was not damaged, providing a stable structural basis for catalytic reactions. In addition, the crystallinity of the catalyst Co-Mn8-T 140 decreased significantly, indicating that KMnO4 hydrothermal etching reduced the crystallinity of Co3O4, resulting in more amorphous phases, which are beneficial to the generation of more abundant oxygen vacancies, as shown in Figure 2 , the catalyst Co-Mn8-T 140 has more significant EPR symmetrical signals, which also confirms the presence of more abundant oxygen vacancies, thereby improving catalytic activity; at the same time, the peak position is significantly red-shifted with KMnO4 etching, which is due to the change in the unit cell caused by the introduction of Mn into the crystal structure of Co3O4.

[0101] Figure 3 and Figure 4 are scanning electron microscope images of Example 1 and Comparative Example 1, respectively. Compared with the dense spherical morphology of Co3O4 in Figure 4 , Figure 3 the catalyst Co-Mn8-T 140 has a more regular loose spherical morphology, thus having a more developed pore structure, and the regular loose spherical structure is beneficial to reducing the gas diffusion resistance, accelerating the transmission of benzene molecules to the internal active sites and the desorption of products through the interconnected pores, effectively inhibiting mass transfer limitations.

[0102] Figure 5 shows the N2 adsorption-desorption curves of Example 1 and Comparative Example 1, both of which exhibit typical type IV isotherms (IUPAC classification) and H3 hysteresis loops, indicating that the materials have typical mesoporous structure characteristics. The catalyst Co-Mn8-T 140 catalyst exhibits more significant hysteresis than Co3O4, which also indicates that the catalyst Co-Mn8-T 140 forms a more abundant pore structure during the etching process. And the catalyst Co-Mn8-T 140 has a larger pore volume and pore size, which are 0.59 cm 3 / g and 16.2 nm, respectively. Larger pore volume and pore size can significantly improve the mass transfer efficiency of reactants, thereby improving reaction activity.

[0103] Figure 6 shows the performance of Example 1 in the cycle and stability experiments. In the reactor of the tube furnace, 0.1 g of catalyst Co-Mn8-T 140, the mixed gas of 1000 ppm benzene and 20% O2, N2 as the balance gas, and the space velocity was 60000 mL / (g·h). The experiment was first carried out at 240℃, at which the benzene conversion rate reached 100%; then the temperature was reduced to 180℃, and the benzene conversion rate was reduced to about 13%. When the temperature was increased to 240℃ again, the benzene conversion rate returned to 100%. This cycle process was repeated stably for 5 times within 25 hours. In particular, after the 5th cycle, the temperature was kept at 240℃, and the benzene conversion rate remained at 100% for 20 hours, further proving the long-term stability and service life of the catalyst.

[0104] According to the data in Table 1, by comparing Examples 1 to 4, and Comparative Examples 2 (RT) and 3 (180℃), it can be seen that as the hydrothermal temperature increases, the reaction temperature shows a trend of first decreasing and then increasing, and the optimal hydrothermal temperature is 120-140℃. When the space velocity is 60000 mL / (g·h) and the reaction temperature is about lower than 220℃, the benzene conversion rate is 90%. Especially when the hydrothermal temperature is 140℃, the space velocity is 60000 mL / (g·h), and the reaction temperature is 210℃, the benzene conversion rate is 90%. By comparing Example 1 and Comparative Example 2 (RT) alone, it can be seen that compared with the catalyst obtained by etching at room temperature for 6h under the hydrothermal condition of 140℃, the catalytic effect of the catalyst obtained by etching at room temperature is poorer than that of Example 1, which indicates that under the hydrothermal condition, the potassium permanganate oxidation etching can more promote the Co 2+ The better redox reaction with permanganate ion and the better one-step construction of cobalt-manganese synergistic active center prove that the hydrothermal etching is better than the room temperature etching.

[0105] According to the data in Table 1, by comparing Examples 1 and 5, and Comparative Examples 4 to 6, it can be seen that when the mass ratio of manganese-cobalt source is 4-8:20, the space velocity is 60000 mL / (g·h), and the reaction temperature is about lower than 220℃, the benzene conversion rate is 90%. Especially when the mass ratio of manganese-cobalt source is 8:20, the space velocity is 60000 mL / (g·h), and the reaction temperature is 210℃, the benzene conversion rate is 90%.

[0106] In summary, under the conditions of a hydrothermal temperature of 140℃, a hydrothermal reaction time of 6h, and a mass ratio of potassium permanganate to ZIF-67 of 8:20, the prepared Co-Mn8-T 140 The catalyst exhibits the best benzene catalytic oxidation activity. Under the conditions of a reaction temperature of 210℃, a space velocity of 60000 mL / (g·h), and a benzene concentration of 1000 ppm, the benzene removal rate can reach 90%.

[0107] The present application utilizes the preparation method of hydrothermal etching of ZIF-67 by potassium permanganate to precisely control the Co-Mn8-T 140The catalyst porous mass transfer channel is constructed in one step, Co-Mn synergistic active centers are constructed, and the low-temperature catalytic activity of the catalyst is effectively improved.

[0108] The above merely describes preferred embodiments of the present application, and the protection scope of the present application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made by those skilled in the art without departing from the technical concept of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a ZIF-67-derived cobalt-manganese catalyst and its application in the catalytic oxidation of benzene, characterized in that... The preparation method of the ZIF-67 derived cobalt-manganese catalyst includes the following steps: S1. Preparation of ZIF-67 precursor; S2. Disperse ZIF-67 in water to form a suspension. Add an equal volume of ZIF-67 suspension to potassium permanganate aqueous solution to carry out an etching reaction. The mass concentration ratio of ZIF-67 suspension to potassium permanganate aqueous solution is 5:1 to 2 to obtain a mixed system. S3. The mixture is transferred to a reactor for hydrothermal reaction at a temperature of 100℃ to 160℃ for 4 to 8 hours to obtain a black precipitate. S4. The black precipitate is washed, dried, calcined, and ground to obtain the ZIF-67 derived cobalt-manganese catalyst.

2. The application according to claim 1, characterized in that, In step S1, the method for preparing the ZIF-67 precursor is as follows: Under magnetic stirring, an aqueous solution of cobalt nitrate hexahydrate is rapidly poured into an aqueous solution of 2-methylimidazole, with a molar ratio of 2-methylimidazole to cobalt nitrate hexahydrate of 2-6:

1. The mixture is stirred continuously at room temperature for 2-6 hours. After centrifugation to separate the solid product, it is washed 3-5 times with deionized water and dried in an oven at 60-90°C for 10-14 hours to obtain a purple solid. After grinding, ZIF-67 powder is obtained.

3. The application according to claim 1, characterized in that, In step S2, the mass concentration ratio of ZIF-67 suspension to potassium permanganate aqueous solution is 5:

2.

4. The application according to claim 1, characterized in that, The hydrothermal temperature is 120℃~140℃.

5. The application according to claim 1, characterized in that, In step S4, the calcination temperature is 350℃~500℃, and the calcination time is 2h~4h.

6. The application according to claim 1, characterized in that, The ZIF-67 derived cobalt-manganese catalyst achieved a pore volume of up to 0.59 cm³. 3 / g, with a pore size of up to 16.2nm.

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