A method for preparing a dual-core-shell structured low-temperature methane catalyst, its product, and its applications.

Abstract

This invention relates to the preparation of a dual-core-shell structured cryogenic methane catalyst, its products, and applications. The dual-core-shell structured cryogenic methane catalyst is Co / Co3O4-C@MFI, using ZIF-67 as the precursor of the active component. With the immobilization of MFI molecular sieves, it exhibits a high specific surface area and a unique core-shell structure, achieving a methane conversion rate of over 80% at low temperatures. The in-situ synthesized MFI semi-encapsulates the active component Co / Co3O4-C, increasing the catalyst's specific surface area and promoting the full exposure of active sites. The active component of this highly efficient catalyst consists of a Co / Co3O4 core-shell structure and an amorphous C framework structure. This unique hierarchical structural feature also endows the catalyst with abundant Co and Co3O4 active sites, promoting electron transfer between Co species.

Description

Technical Field

[0001] This invention relates to a method for preparing a dual-core-shell structured low-temperature methane catalyst Co / Co3O4-C@MFI, its products, and applications. The dual-core-shell structure increases the number of active sites and catalytic mass transfer efficiency, promoting the catalytic oxidation of methane, and is applicable to the field of VOC treatment. Background Technology

[0002] The accelerated pace of industrialization has exacerbated air pollution, particularly the production of toxic and carcinogenic VOCs. These VOCs not only damage the ozone layer but also react with other air pollutants to form photochemical smog, harming the environment and human health. Long-term exposure to this environment can cause irreversible damage. Catalytic combustion is currently one of the most effective methods for removing VOCs. It utilizes a catalyst at a specific temperature to catalytically oxidize and degrade pollutants, completely converting them into CO2 and H2O without secondary pollution. Compared to direct combustion, catalytic combustion, by adding a catalyst, effectively lowers the activation energy of the reaction, accelerates the reaction rate, and reduces the ignition temperature. The catalyst plays a crucial role in the catalytic combustion reaction. Supported noble metals such as Pt and Pd, and transition metal oxides such as Mn / Co are commonly used as catalysts for the complete oxidation of VOCs. Compared to the high cost of noble metals, transition metal oxides are more favored in the market. In particular, the low Co-O bond energy of Co3O4 catalysts maintains high catalytic activity. Single Co3O4 catalysts tend to aggregate at high temperatures, leading to a significant decrease in activity. Loading it onto a carrier with a high specific surface area can effectively prevent particle aggregation and promote increased activity.

[0003] On the other hand, the structural stability of catalysts is also a key issue in the field of catalytic combustion. The design of layered or core-shell structured catalysts can provide abundant active sites for the catalyst body, increasing the contact area between the catalyst and reactants. Furthermore, physical confinement is also a common and feasible solution to improve the structural stability of catalysts. Fixing a metal within a protective layer restricts nanoparticle growth and passivates surface active sites, achieving high-temperature resistance. Therefore, this patent application uses ZIF-67 as a sacrificial precursor and employs an in-situ synthesis method to confine the Co-based active component with a special morphology within a three-dimensional structure, limiting the growth of Co particles. It also fully utilizes the cavities of porous molecular sieves to enhance the transport efficiency of reactants and products, fully exposing the active component and improving its catalytic performance and high-temperature resistance. Summary of the Invention

[0004] To address the critical issues of cobalt-based catalysts agglomerating and exhibiting insufficient catalytic or deactivation activity at high temperatures, this invention proposes a method for preparing a dual-core-shell structure methane low-temperature catalyst, Co / Co3O4-C@MFI, by utilizing the confinement effect to highly disperse the active components within the carbon framework structure and achieving high-temperature resistance and deactivation resistance through the dual-core-shell mechanism.

[0005] Another objective of this invention is to provide a Co / Co3O4-C@MFI product, a methane low-temperature catalyst with a dual core-shell structure prepared by the above method.

[0006] Another object of the present invention is to provide an application of the above-mentioned product.

[0007] The objective of this invention is achieved through the following method: a method for preparing a dual-core-shell structured low-temperature methane catalyst, Co / Co3O4-C@MFI, using ZIF-67 as the precursor of the active component, exhibits a high specific surface area and a unique core-shell structure under the immobilization of MFI molecular sieves, achieving a methane conversion rate of over 80% at low temperatures, comprising the following steps:

[0008] (1) Under magnetic stirring, take ZIF-67 into a beaker and add a mixture of ethanol and water to disperse it. Then add 2-methylimidazole to it, wherein the mass ratio of ZIF-67 to 2-methylimidazole is 1:(4~6), and mix evenly.

[0009] (2) Add tetraethyl orthosilicate and surfactant to (1), wherein the mass ratio of tetraethyl orthosilicate to surfactant is 1:(0.2~1), to obtain a mixed solution;

[0010] (3) After stirring for 10 minutes, press n Si :n 碱性模板剂 The molar ratio is (8~20):1. Add alkaline template agent to the mixed solution, ultrasonically disperse for 30 min, then transfer to a hydrothermal reactor for hydrothermal reaction.

[0011] (4) After the hydrothermal reactor cools to room temperature, centrifuge and wash the precipitate, and then dry it at 80°C;

[0012] (5) The dried product from (4) is placed in an atmosphere of N2 or H2. 2 / Ar, roasted at high temperature;

[0013] (6) The product from (5) is further calcined in air, and the calcination temperature and time are controlled to obtain the Co / Co3O4-C@MFI catalyst with a double core-shell structure.

[0014] Preferably, in step (3), the alkaline template agent is any one of tetrapropylammonium hydroxide, ammonia, or hydrazine hydrate. Si :n 碱性模板剂 The molar ratio is (10~20):1; the hydrothermal reaction temperature and time are 80~120℃ and 12~24h, respectively.

[0015] Preferably, in step (5), the calcination atmosphere is N2 or H2 / Ar, and the calcination time and temperature are 600~800℃ and 2~4h, respectively.

[0016] Preferably, in step (6), the air atmosphere calcination temperature and time are 300~450℃ and 2~4h, respectively.

[0017] This invention provides a dual-core-shell structured low-temperature methane catalyst Co / Co3O4-C@MFI, which is prepared according to any of the methods described above.

[0018] This invention provides the application of a dual-core-shell structured low-temperature methane catalyst, Co / Co3O4-C@MFI, in methane conversion, achieving a methane conversion rate of over 80% at low temperatures.

[0019] The catalytic experiment of the dual-core-shell structure methane low-temperature catalyst Co / Co3O4-C@MFI was carried out in a combustion tube. 0.1 g of catalyst was added to the combustion tube, methane and air were introduced, the flow rate was adjusted, the temperature was programmed to 410 °C, and the methane was detected by gas chromatography. The conversion rate was calculated based on the peak area.

[0020] In-situ synthesized MIF semi-encapsulated active component Co / Co3O4-C enhances the catalyst's specific surface area and promotes full exposure of active sites. This highly efficient catalyst's active component consists of a Co / Co3O4 core-shell structure and an amorphous C framework structure. This unique hierarchical structure endows the catalyst with abundant Co and Co3O4 active sites, promoting electron transfer between Co species. Furthermore, the core-shell structure effectively increases the contact area between methane and the catalyst. Combined with the porous MIF shell and the cavities between the active component, this enhances the transport efficiency of reactants and products, promoting methane conversion. This also provides new insights for the design and application of highly efficient and stable heterogeneous low-temperature catalysts.

[0021] The present invention has the following advantages:

[0022] (1) The present invention proposes a method for preparing and applying a dual-core-shell structured low-temperature methane catalyst Co / Co3O4-C@MFI. ZIF-67 is used as a sacrificial precursor and is in-situ combined with a molecular sieve. The catalyst undergoes reduction heat treatment at high temperature and passivation in an air atmosphere to obtain the dual-core-shell catalyst. This fully utilizes its large surface area, promotes the full exposure of active sites, and allows for the controllable degradation of surface active components by adjusting the calcination temperature.

[0023] (2) The dual-shell structure proposed in this invention makes full use of the confinement effect to retain the large specific surface area of ​​the ZIF dodecahedral framework structure and encapsulates the active components in the carbon shell and molecular sieve shell. This hierarchical structure effectively disperses the active components of the catalyst, while accelerating electron transport and increasing the mass transfer efficiency between methane and the catalyst, thus realizing low-temperature catalysis of methane.

[0024] (3) The preparation method of Co / Co3O4-C@MFI proposed in this invention is not only controllable, but also has rich pore structure and good stability. More importantly, it can effectively avoid the agglomeration of active components of the catalyst at high temperature, fully expose the active sites, and greatly improve the surface catalytic reaction rate. It has guiding significance for the development of high-activity and high-stability low-temperature catalysts. Detailed Implementation

[0025] The present invention will be further illustrated by the examples.

[0026] Example 1:

[0027] A dual-core-shell structured methane cryogenic catalyst, wherein the dual-core-shell structured methane cryogenic catalyst is Co / Co3O4-C@MFI, using ZIF-67 as the precursor of the active component, exhibits high specific surface area and a unique core-shell structure under the immobilization of MFI molecular sieve, achieving a methane conversion rate of over 80% at low temperatures, and is prepared according to the following steps:

[0028] (1) Under magnetic stirring, take ZIF-67 into a beaker and add a mixture of ethanol and water to disperse it. Then add 2-methylimidazole to it according to the mass ratio of ZIF-67 to 2-methylimidazole of 1:4 and mix evenly.

[0029] (2) Add tetraethyl orthosilicate and surfactant to (1) at a mass ratio of 1:1 to obtain a mixed solution;

[0030] (3) After stirring for 10 minutes, press n Si :n 碱性模板剂 The molar ratio of the two components was 8:1. The alkaline template agent tetrapropylammonium hydroxide was added to the mixed solution, and after ultrasonic dispersion for 30 min, it was transferred to a hydrothermal reactor and hydrothermally reacted at 120 °C for 24 h.

[0031] (4) After the hydrothermal reactor cools to room temperature, centrifuge and wash the precipitate, and then dry it at 80°C;

[0032] (5) The dried product from (4) was calcined at 600 °C for 2 h under an H2 / Ar atmosphere;

[0033] (6) The product in (5) is further calcined in air at 350°C for 2 hours to obtain the Co / Co3O4-C@MFI catalyst with a dual core-shell structure.

[0034] The prepared catalyst achieved a methane conversion rate of 80.77% at 210℃.

[0035] Example 2:

[0036] A dual-core-shell structured low-temperature methane catalyst, prepared according to steps similar to those in Example 1, is as follows:

[0037] (1) Under magnetic stirring, take ZIF-67 into a beaker and add a mixture of ethanol and water to disperse it. Then add 2-methylimidazole to it according to the mass ratio of ZIF-67 to 2-methylimidazole of 1:5 and mix evenly.

[0038] (2) Add tetraethyl orthosilicate and surfactant to (1) at a mass ratio of 1:0.5 to obtain a mixed solution;

[0039] (3) After stirring for 10 minutes, press n Si :n 碱性模板剂 The molar ratio of the two components was 10:1. The alkaline template agent tetrapropylammonium hydroxide was added to the mixed solution, and after ultrasonic dispersion for 30 min, it was transferred to a hydrothermal reactor and hydrothermally reacted at 120 °C for 24 h.

[0040] (4) After the hydrothermal reactor cools to room temperature, centrifuge and wash the precipitate, and then dry it at 80°C;

[0041] (5) The dried product from (4) was calcined at 800°C for 2 hours under an H2 / Ar atmosphere;

[0042] (6) The product in (5) is further calcined in air at 300°C for 2 hours to obtain the Co / Co3O4-C@MFI catalyst with a double core-shell structure.

[0043] The prepared catalyst achieved a methane conversion rate of 84.62% at 210 °C.

[0044] Example 3:

[0045] A dual-core-shell structured low-temperature methane catalyst, prepared according to steps similar to those in Example 1, is as follows:

[0046] (1) Under magnetic stirring, take ZIF-67 into a beaker and add a mixture of ethanol and water to disperse it. Then add 2-methylimidazole to it according to the mass ratio of ZIF-67 to 2-methylimidazole of 1:6 and mix evenly.

[0047] (2) Add tetraethyl orthosilicate and surfactant to (1) at a mass ratio of 1:1 to obtain a mixed solution;

[0048] (3) After stirring for 10 minutes, press n Si :n 碱性模板剂 The molar ratio of the two components was 20:1. Alkaline template agent hydrazine hydrate was added to the mixed solution, and after ultrasonic dispersion for 30 min, it was transferred to a hydrothermal reactor and hydrothermally reacted at 110 °C for 24 h.

[0049] (4) After the hydrothermal reactor cools to room temperature, centrifuge and wash the precipitate, and then dry it at 80°C;

[0050] (5) The dried product from (4) was calcined at 700 °C for 4 h in an H2 / Ar atmosphere;

[0051] (6) The product in (5) is further calcined in air at 450°C for 2 hours to obtain the core-shell structured Co / Co3O4-C@MFI catalyst.

[0052] The prepared catalyst achieved a methane conversion rate of 73.08% at 210 °C.

[0053] Example 4:

[0054] A dual-core-shell structured low-temperature methane catalyst, prepared according to steps similar to those in Example 1, is as follows:

[0055] (1) Under magnetic stirring, ZIF-67 was placed in a beaker and dispersed in a mixed solvent of ethanol and water. Then, 2-methylimidazole was added to it at a mass ratio of ZIF-67 to 2-methylimidazole of 1:5. The mixture was then homogeneous.

[0056] (2) Add tetraethyl orthosilicate and surfactant to (1) at a mass ratio of 1:0.2 to obtain a mixed solution;

[0057] (3) After stirring for 10 minutes, press n Si :n 碱性模板剂 The molar ratio of the two components was 10:1. Alkaline template agent ammonia was added to the mixed solution, and after ultrasonic dispersion for 30 min, it was transferred to a hydrothermal reactor and hydrothermally reacted at 80 °C for 20 h.

[0058] (4) After the hydrothermal reactor cools to room temperature, centrifuge and wash the precipitate, and then dry it at 80°C;

[0059] (5) The dried product from (4) was calcined at 600 °C for 2 hours in an atmosphere of N2.

[0060] (6) The product in (5) is further calcined in air at 400°C for 2 hours. By controlling the calcination temperature and time, the Co / Co3O4-C@MFI catalyst with a double core-shell structure can be obtained.

[0061] The prepared catalyst achieved a methane conversion rate of 65.38% at 210 °C.

Claims

1. A method for preparing a low-temperature methane catalyst with a dual-core-shell structure, characterized in that, The dual-core-shell structured methane cryogenic catalyst is Co / Co3O4-C@MFI, using ZIF-67 as the precursor of the active component. With the immobilization of MFI molecular sieves, it exhibits a high specific surface area and a unique core-shell structure, achieving a methane conversion rate of over 80% at low temperatures. The catalyst includes the following steps: (1) Under magnetic stirring, take ZIF-67 into a beaker and add a mixture of ethanol and water to disperse it. Then add 2-methylimidazole to it, wherein the mass ratio of ZIF-67 to 2-methylimidazole is 1:(4~6), and mix evenly. (2) Add tetraethyl orthosilicate and surfactant to (1), wherein the mass ratio of tetraethyl orthosilicate to surfactant is 1:(0.2~1), to obtain a mixed solution; (3) After stirring for 10 minutes, press n Si :n 碱性模板剂 The molar ratio is (8~20):

1. Add alkaline template agent to the mixed solution, ultrasonically disperse for 30 min, then transfer to a hydrothermal reactor for hydrothermal reaction. (4) After the hydrothermal reactor cools to room temperature, centrifuge and wash the precipitate, and then dry it at 80°C; (5) The dried product from (4) is calcined at high temperature in an atmosphere of N2 or H2 / Ar; (6) The product in (5) is further calcined in air, and the calcination temperature and time are controlled to obtain the core-shell structured Co / Co3O4-C@MFI catalyst; In step (3), the alkaline template agent is any one of tetrapropylammonium hydroxide, ammonia or hydrazine hydrate; the hydrothermal reaction temperature and time are 80~120℃ and 12~24h, respectively; In step (5), the high-temperature calcination is calcination at 600~800℃ for 2~4 hours.

2. The method for preparing the dual-core-shell structured methane low-temperature catalyst according to claim 1, characterized in that, In step (6), the air atmosphere calcination is carried out at 300~450℃ for 2~4 hours.

3. The method for preparing a dual-core-shell structured methane low-temperature catalyst according to any one of claims 1 to 2, characterized in that, Prepare according to the following steps: (1) Under magnetic stirring, take ZIF-67 into a beaker and add a mixture of ethanol and water to disperse it. Then add 2-methylimidazole to it according to the mass ratio of ZIF-67 to 2-methylimidazole of 1:4 and mix evenly. (2) Add tetraethyl orthosilicate and surfactant to (1) at a mass ratio of 1:1 to obtain a mixed solution; (3) After stirring for 10 minutes, press n Si :n 碱性模板剂 The molar ratio of the two components was 8:

1. The alkaline template agent tetrapropylammonium hydroxide was added to the mixed solution, and after ultrasonic dispersion for 30 min, it was transferred to a hydrothermal reactor and hydrothermally reacted at 120 °C for 24 h. (4) After the hydrothermal reactor cools to room temperature, centrifuge and wash the precipitate, and then dry it at 80°C; (5) The dried product from (4) was calcined at 600 °C for 2 h under an H2 / Ar atmosphere; (6) The product in (5) is further calcined in air at 350°C for 2 hours to obtain the core-shell structured Co / Co3O4-C@MFI catalyst.

4. The method for preparing the dual-core-shell structured methane low-temperature catalyst according to any one of claims 1 to 2, characterized in that, Prepare according to the following steps: (1) Under magnetic stirring, take ZIF-67 into a beaker and add a mixture of ethanol and water to disperse it. Then add 2-methylimidazole to it according to the mass ratio of ZIF-67 to 2-methylimidazole of 1:5 and mix evenly. (2) Add tetraethyl orthosilicate and surfactant to (1) at a mass ratio of 1:0.5 to obtain a mixed solution; (3) After stirring for 10 minutes, press n Si :n 碱性模板剂 The molar ratio of the two components was 10:

1. The alkaline template agent tetrapropylammonium hydroxide was added to the mixed solution, and after ultrasonic dispersion for 30 min, it was transferred to a hydrothermal reactor and hydrothermally reacted at 120 °C for 24 h. (4) After the hydrothermal reactor cools to room temperature, centrifuge and wash the precipitate, and then dry it at 80°C; (5) The dried product from (4) was calcined at 800°C for 2 hours under an H2 / Ar atmosphere; (6) The product in (5) is further calcined in air at 300°C for 2 hours to obtain the Co / Co3O4-C@MFI catalyst with a double core-shell structure.

5. The method for preparing a dual-core-shell structured methane low-temperature catalyst according to any one of claims 1 to 2, characterized in that, Prepare according to the following steps: (1) Under magnetic stirring, take ZIF-67 into a beaker and add a mixture of ethanol and water to disperse it. Then add 2-methylimidazole to it according to the mass ratio of ZIF-67 to 2-methylimidazole of 1:6 and mix evenly. (2) Add tetraethyl orthosilicate and surfactant to (1) at a mass ratio of 1:1 to obtain a mixed solution; (3) After stirring for 10 minutes, press n Si :n 碱性模板剂 The molar ratio of the two components was 20:

1. Alkaline template agent hydrazine hydrate was added to the mixed solution, and after ultrasonic dispersion for 30 min, it was transferred to a hydrothermal reactor and hydrothermally reacted at 110 °C for 24 h. (4) After the hydrothermal reactor cools to room temperature, centrifuge and wash the precipitate, and then dry it at 80°C; (5) The dried product from (4) was calcined at 700 °C for 4 h in an H2 / Ar atmosphere; (6) The product in (5) is further calcined in air at 450°C for 2 hours to obtain the core-shell structured Co / Co3O4-C@MFI catalyst.

6. The method for preparing a dual-core-shell structured methane low-temperature catalyst according to any one of claims 1 to 2, characterized in that, Prepare according to the following steps: (1) Under magnetic stirring, ZIF-67 was placed in a beaker and dispersed in a mixed solvent of ethanol and water. Then, 2-methylimidazole was added to it at a mass ratio of ZIF-67 to 2-methylimidazole of 1:

5. The mixture was then homogeneous. (2) Add tetraethyl orthosilicate and surfactant to (1) at a mass ratio of 1:0.2 to obtain a mixed solution; (3) After stirring for 10 minutes, press n Si :n 碱性模板剂 The molar ratio of the two components was 10:

1. Alkaline template agent ammonia was added to the mixed solution, and after ultrasonic dispersion for 30 min, it was transferred to a hydrothermal reactor and hydrothermally reacted at 80 °C for 20 h. (4) After the hydrothermal reactor cools to room temperature, centrifuge and wash the precipitate, and then dry it at 80°C; (5) The dried product from (4) was calcined at 600 °C for 2 hours in an atmosphere of N2. (6) The product from (5) was further calcined in air at 400°C for 2 hours. The calcination temperature and time were controlled to obtain a Co / Co3O4-C@MFI catalyst with a double core-shell structure.

7. A dual-core-shell structured low-temperature methane catalyst Co / Co3O4-C@MFI, characterized in that... Prepared by the method according to any one of claims 1-6.

8. The application of the dual-core-shell structured methane low-temperature catalyst Co / Co3O4-C@MFI according to claim 7 in methane conversion, achieving a methane conversion rate of over 80% at low temperatures.