A MOFs derived porous carbon-based composite catalyst and a preparation method and application thereof

Abstract

The application discloses a MOFs derived porous carbon-based composite catalyst and a preparation method and application thereof. The catalyst is an Fe / Zn-NC catalyst rich in Fe / Zn active sites, and a hierarchical porous nitrogen-doped carbon derived from MOFs is used as a carrier. Fe and Zn bimetal are uniformly dispersed, and the surface has oxygen vacancies and doped sites such as graphite N and pyridine N. The key active phase is Fe / Zn synergistic active sites. The preparation method comprises the following steps: mixing iron nitrate, zinc nitrate and an organic ligand, then performing one-step solvothermal reaction, and then performing high-temperature calcination under an inert atmosphere to obtain the catalyst. The catalyst has high CO2 conversion rate, high CH4 selectivity, low by-products, excellent stability and strong working condition adaptability when used for a CO2 hydrogenation reaction to prepare CH4. The preparation process is simple, can be scaled up, and can be adapted to industrial reactors such as fixed beds and fluidized beds, and is suitable for scenes such as electricity-to-gas technology, industrial CO2 resource utilization and green CH4 synthesis.

Description

Technical Field

[0001] This invention belongs to the field of catalytic materials technology, specifically relating to a MOFs-derived porous carbon-based composite catalyst, its preparation method, and its application. Background Technology

[0002] Against the backdrop of advancing the "dual carbon" goals and reducing global greenhouse gas emissions, CO2 resource utilization has become an important direction for green and low-carbon development. Among them, the electro-gas technology for producing CH4 from CO2 hydrogenation can realize green energy storage and targeted CO2 conversion, which has both important industrial application value and environmental benefits.

[0003] Currently, CO2 methanation catalysis technology mainly faces the following technical bottlenecks: Traditional catalysts often use Ni, Ru, etc. as active components, which are prone to particle sintering and deactivation under high-temperature reaction conditions, making it difficult to balance CH4 selectivity and catalytic stability. Single-metal active site catalysts cannot simultaneously and efficiently achieve CO2 adsorption and enrichment, H2 dissociation and activation, and deep hydrogenation of reaction intermediates, resulting in low CH4 space-time yield, poor adaptability to operating conditions, and high content of by-products (such as CO, CH3OH, C2-C3 hydrocarbons), which seriously affects product purity. Most metal-organic framework (MOF) derived carbon-based catalysts have cumbersome preparation processes, poor dispersion of active components, and are difficult to scale up. They also lack precision in controlling the bimetallic active phase, failing to fully utilize the synergistic effect between the bimetal and the support, and suffer from low utilization of active sites and insufficient mass transfer efficiency.

[0004] While existing MOF-derived porous carbon catalysts possess the advantage of high specific surface area, they still have significant shortcomings in the synergistic design of Fe / Zn bimetallic doping, the directional construction of key active phases, and the synergistic regulation of oxygen vacancies and nitrogen doping sites. Currently, no Fe / Zn-based CO2 methanation catalyst has been developed that simultaneously achieves high activity, high selectivity, low byproducts, high stability, and scalable production. In particular, breakthroughs have not yet been achieved in regulating performance stability under different reaction conditions (temperature, pressure, C-H ratio) and in further optimizing catalytic performance through doping modification. Furthermore, existing bimetallic MOF-derived catalysts have significant limitations in product distribution control, making it difficult to effectively suppress byproduct formation, further affecting catalytic efficiency and product purity.

[0005] Therefore, developing a Fe / Zn-NC catalyst with simple preparation process, well-defined active sites, synergistic high efficiency of two components, low by-product content, and strong adaptability to operating conditions is a key breakthrough for promoting the industrial application of CO2 hydrogenation to CH4 technology. Summary of the Invention

[0006] The purpose of this invention is to provide a MOFs-derived porous carbon-based composite catalyst, its preparation method, and its application. This method is simple, scalable, and the prepared Fe / Zn-NC catalyst features a well-developed hierarchical pore structure, uniform dispersion of Fe / Zn active components, and abundant oxygen vacancies and nitrogen doping sites. It can efficiently achieve the CO2 hydrogenation to CH4 reaction, maintaining high CO2 conversion, high CH4 selectivity, low byproduct content, and excellent catalytic stability, and can be flexibly adapted to different reaction conditions. Furthermore, this invention can also be achieved through K… + Doping further optimizes catalyst performance, improves CH4 space-time yield, and reduces industrial application costs, making it suitable for applications such as power-to-gas technology, industrial CO2 resource utilization, and green CH4 synthesis.

[0007] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows: a MOFs-derived porous carbon-based composite catalyst, wherein the catalyst is a Fe / Zn-NC catalyst rich in Fe / Zn synergistic active sites, wherein the catalyst uses MOFs-derived hierarchical porous nitrogen-doped carbon as a support, and Fe and Zn bimetals are uniformly dispersed on the surface and inside the support; the catalyst surface has oxygen vacancies and contains graphite N and pyridine N nitrogen doping sites; the key active phase is the Fe / Zn synergistic active site.

[0008] Preferably, the MOFs are ZIFs.

[0009] Furthermore, the catalyst also contains potassium ion doping.

[0010] To achieve the above-mentioned objectives, this invention also provides a method for preparing the above-mentioned MOFs-derived porous carbon-based composite catalyst, comprising the following steps: (1) Raw material ratio and mixing: Iron nitrate, zinc nitrate and organic ligands are dissolved in organic solvents respectively, mixed and stirred to form a uniform Fe / Zn-MOFs seed system solution; (2) Solvothermal reaction: The Fe / Zn-MOFs seed system solution is transferred to a high-pressure reactor for a one-step solvothermal reaction to generate Fe / Zn bimetallic doped MOFs precursor in situ; (3) Calcination treatment: The obtained MOF precursor was pyrolyzed and calcined under an inert atmosphere to obtain Fe / Zn-NC catalyst.

[0011] Preferably, in step (1), the organic ligand is an imidazole ligand; the molar ratio between iron nitrate, zinc nitrate and the organic ligand is 1:(0.1-1):(12-40); wherein the concentration of Fe in the Fe / Zn-MOFs seed system solution is 0.5wt% ~ 5wt%; potassium salt is also added in the raw material mixing stage of step (1) to prepare K +Doped Fe / Zn-NC catalyst.

[0012] Preferably, in step (2), the solvothermal reaction temperature is 80-200℃ and the reaction time is 6-48 h.

[0013] Preferably, in step (3), the roasting temperature is 800-1000℃ and the roasting time is 60-240 min.

[0014] To achieve the above-mentioned objectives, this invention also provides the application of the above-mentioned MOFs-derived porous carbon-based composite catalyst in the hydrogenation of CO2 to CH4.

[0015] Preferably, the reaction conditions for the application are: a reaction temperature of 300-500°C. o C. Reaction pressure 1.5-2.5 MPa, C-H ratio 1 / 3-1 / 5.

[0016] Preferably, the application is adapted to a fixed-bed reactor or a fluidized-bed reactor.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The Fe / Zn synergistic active phase of the present invention achieves CO2 adsorption, activation and hydrogenation in a high efficiency, and can stably achieve a CO2 conversion rate of more than 82.47%, a CH4 selectivity of more than 80.02%, and a CH4 yield of more than 30.97%, which is significantly better than Cu / Zn-NC and other comparative catalysts. At the same time, it effectively inhibits the formation of by-products such as CO, CH3OH, and C2C3, and the product purity is high.

[0018] (2) The present invention maintains stable catalytic performance within a reaction temperature range of 300-500 ℃, a reaction pressure of 1.5-2.5 MPa, and a carbon-hydrogen ratio of 1 / 3-1 / 5; the calcination temperature is 800-1000 ℃. o C is adjustable; add 10 mmol K. + The CO2 conversion rate can be increased to 84.01%, which can be flexibly adapted to different industrial conditions.

[0019] (3) In this invention, the hierarchical porous structure and Fe / Zn support work together to effectively suppress the sintering deactivation of active components. The catalyst has no obvious activity decay during long-term operation and can maintain stable CO2 conversion rate and CH4 selectivity under different operating conditions, thus solving the problem of easy deactivation of traditional catalysts at high temperatures.

[0020] (4) This invention uses a one-step solvothermal method for preparation, which has a short process, simple operation, readily available raw materials, and flexible adjustment of metal ratio and calcination temperature. It does not require complex equipment and is suitable for industrial-scale production. It can be prepared by K + Doping further optimizes performance and reduces application costs.

[0021] (5) This invention can be adapted to conventional reactors such as fixed beds and fluidized beds. The reaction conditions are mild and no complex pretreatment is required. It is suitable for various scenarios such as power-to-gas technology, industrial CO2 resource utilization, and green CH4 synthesis. It is in line with the development trend of CCUS technology towards high efficiency, large scale and low by-products. Attached Figure Description

[0022] Figure 1 The figures (a) and (b) show a comparison of CO2 conversion, CH4 selectivity, and yield of Fe / Zn-NC and Cu / Zn-NC catalysts in the embodiments of the present invention; Figure 2 A comparison of the content of byproducts (CO, CH3OH, C2-C3) of Fe / Zn-NC catalysts at different C / H ratios (1 / 3-1 / 5) (a) and a comparison of CO2 conversion, CH4 selectivity and yield (b). Figure 3 A comparison of CO2 conversion, CH4 selectivity, and yield of Fe / Zn-NC catalyst at different reaction temperatures (a) and a comparison of the content of by-products (CO, CH3OH, C2-C3) (b). Figure 4 A comparison of CO2 conversion, CH4 selectivity, and yield of Fe / Zn-NC catalyst under different pressures (a) and a comparison of the content of by-products (CO, CH3OH, C2-C3) (b). Figure 5 As a Fe / Zn-NC catalyst, 10 mmol K + Comparison of CO2 conversion, CH4 selectivity, and yield of Fe / Zn-NC catalysts; comparison of by-products (a) and by-product (CO, CH3OH, C2-C3) content (b). Figure 6 Fe / Zn-NC catalysts at different calcination temperatures (800-1000 °C) o Comparison of CO2 conversion rate, CH4 selectivity, and yield at different reaction temperatures (a) and (b) of byproduct (CO, CH3OH, C2-C3) content at different reaction temperatures; Figure 7 This is a SEM image of the Fe / Zn-NC catalyst. Detailed Implementation

[0023] To better understand the present invention, the present invention will be further described below with reference to the embodiments and accompanying drawings, but the scope of protection of the present invention is not limited to the scope shown in the embodiments.

[0024] Example 1

[0025] A method for preparing a MOF-derived porous carbon-based composite catalyst (Fe / Zn-NC) includes the following steps: (1) Raw material ratio and mixing: Iron nitrate, zinc nitrate and 2-methylimidazole are dissolved in an ethanol / water mixed solvent and stirred thoroughly for 30-60 minutes to form a homogeneous Fe / Zn-MOFs seed system solution; wherein, the molar ratio of iron nitrate, zinc nitrate and 2-methylimidazole is 1:0.5:25, and the concentration of Fe in the Fe / Zn-MOFs seed system solution is 2.5 wt%; (2) Solvent-thermal reaction: The Fe / Zn-MOFs seed crystal system solution was transferred to a high-pressure reactor and reacted at 180°C. o A one-step solvothermal reaction was carried out under C conditions for 24 h to generate Fe / Zn bimetallic doped MOF precursors in situ. (3) Calcination treatment: The obtained MOF precursor was placed in an inert atmosphere and calcined at 800 °C. o After high-temperature calcination at C for 3 h, the target Fe / Zn-NC catalyst was obtained through self-sacrificial template carbonization and in-situ conversion of Fe and Zn metal components.

[0026] The Fe / Zn-NC catalyst prepared in this embodiment was applied to the hydrogenation of CO2 to CH4. The specific application process was as follows: the Fe / Zn-NC catalyst was uniformly packed into a fixed-bed reactor and heated at a temperature of 400°C. o C. The CO2 hydrogenation to CH4 reaction is carried out under the process conditions of pressure 2.0 MPa and carbon-hydrogen ratio (1 / 4).

[0027] Test results are as follows Figure 1 As shown: CO2 conversion rate reached 30.96%, CH4 selectivity reached 82.47%, and CH4 yield reached 25.53%; the byproduct CO content was 6.80%, CH3OH content was 0.72%, and C2-C3 content was 10.01%, all at relatively low levels. The catalytic performance was significantly better than the blank group and the Cu / Zn-NC catalyst (Cu / Zn-NC had a CO2 conversion rate of 16.09%, CH4 selectivity of 5.96%, and CH4 yield of 0.96%; the byproduct CO content was as high as 92.15%, and the CH3OH content was 5.9%). Figure 7 As shown, the catalyst surface exhibits obvious Fe / Zn synergistic active phase characteristics, with uniform dispersion of Fe and Zn metal species, complete hierarchical pore structure, high specific surface area, excellent mass transfer efficiency, and active site utilization rate of over 90%, demonstrating excellent catalytic performance.

[0028] Blank group MOF-derived porous carbon was used as the catalyst, without Fe / Zn bimetallic doping. In the catalyst preparation process, ferric nitrate was not added in step (1), and the calcination temperature in step (3) was set at 1000 °C. o At temperatures above 400°C, Zn can be distilled off to obtain the product; all other steps and process parameters remain consistent with Example 1. CH4 is produced under the same CO2 hydrogenation process conditions as in Example 1 (reaction temperature 400°C). o C. Performance tests were conducted at a reaction pressure of 2.0 MPa and a carbon-to-hydrogen ratio of 1 / 3.

[0029] Test results: CO2 conversion rate was low (below 20%), CH4 selectivity was poor (below 60%), byproduct (CO, CH3OH) content was high, there were no obvious Fe and Zn synergistic active phase characteristics on the catalyst surface, catalytic efficiency and operational stability were poor, mass transfer efficiency was low, and active site utilization was insufficient.

[0030] control group The preparation method of Cu / Zn-NC is the same as that of Fe / Zn-NC, except that "copper nitrate" is used instead of "ferric nitrate" in step (1).

[0031] Example 2

[0032] In this embodiment, only the roasting temperature in step (3) is changed to 900°C. o C. Other steps and process conditions remain consistent with Example 1. Under the same CO2 hydrogenation to CH4 process conditions as in Example 1 (reaction temperature 400°C), [the process continues]. o C. Performance tests were conducted at a reaction pressure of 2.0 MPa and a carbon-to-hydrogen ratio of 1 / 4.

[0033] Example 3

[0034] In this embodiment, only the roasting temperature in step (3) is changed to 1000. o C. Other steps and process conditions remain consistent with Example 1. Under the same CO2 hydrogenation to CH4 process conditions as in Example 1 (reaction temperature 400°C), [the process continues]. o C. Performance tests were conducted at a reaction pressure of 2.0 MPa and a carbon-to-hydrogen ratio of 1 / 4.

[0035] Examples 1-3 demonstrate the effects of different calcination temperatures on CO2 conversion, CH4 selectivity, yield, and byproduct content. The results are as follows: Figure 6 As shown: in the range of 800-1000 o Within the calcination range of C, the CO2 conversion rate is between 5% and 30.97%, the CH4 selectivity is stable at around 82.47%, and the calcination temperature is 900°C. o At temperature C, the byproduct content is lowest, and the overall performance of the catalyst is optimal.

[0036] The Fe / Zn-NC catalyst prepared in Example 1 was tested under different operating conditions: Operating condition adjustment: The Fe / Zn-NC catalyst prepared in Example 1 was applied to the CO2 hydrogenation to CH4 process, and the reaction temperature was adjusted accordingly (300°C). o C, 400 o C, 500 o C) CO2 hydrogenation to CH4 reaction was carried out under different operating conditions, including reaction pressure (1.5 MPa, 2.0 MPa, 2.5 MPa) and carbon-hydrogen ratio (1 / 3, 1 / 4, 1 / 5). Under each operating condition, the CO2 conversion rate, CH4 selectivity, CH4 yield and by-product content were measured to systematically evaluate the catalyst's adaptability to the operating conditions. Test results: (1) Temperature conditions ( Figure 3 ): 300-500 o Within the temperature range of 400°C, the CO2 conversion rate ranged from 0.51% to 42.42%, the CH4 selectivity ranged from 0% to 82.47%, and the CO content as a byproduct ranged from 0.03% to 34.57%. Overall, the trend was that with increasing temperature, the CO2 conversion rate increased, but the CO content as a byproduct slightly increased. o The catalyst exhibits optimal overall performance at time C; (2) Pressure conditions ( Figure 4 Within the range of 1.5-2.5 MPa, the catalysts maintained stable catalytic performance. As the pressure increased, the CO2 conversion rate and CH4 selectivity decreased slightly, and the by-product content decreased slightly and increased slightly. The catalysts exhibited the best overall performance at 2.0 MPa. (3) Carbon-hydrogen ratio conditions ( Figure 2 Within the range of 1 / 3 to 1 / 5, the CO2 conversion rate is between 25.15% and 30.97%, and the CH4 selectivity is between 77.73% and 82.47%. The catalyst exhibits optimal overall performance when the carbon-to-hydrogen ratio is 1 / 4. These results fully demonstrate that the Fe / Zn-NC catalyst of this invention possesses excellent adaptability to operating conditions, and its catalytic performance can be optimized by adjusting operating parameters according to actual industrial needs.

[0037] Example 4

[0038] K + Preparation and performance optimization testing of Fe / Zn-NC doped catalysts 1. Preparation method: Following the raw material ratio and process parameters of Example 1, 10 mmol of potassium salt (KNO3) was added during the raw material mixing stage to prepare 10 mmol of K + The preparation steps for the doped Fe / Zn-NC catalyst are completely consistent with those in Example 1.

[0039] 2. Performance Testing: K +Fe / Zn-NC catalysts and undoped K + The Fe / Zn-NC catalyst, under the same process conditions (temperature 400), o C) CO2 hydrogenation to CH4 reaction was carried out under pressure of 2.0 MPa and carbon-hydrogen ratio of 1 / 4. The catalytic performance of the two reactions was compared.

[0040] Test results are as follows Figure 5 As shown: K + After doping, the CO2 conversion rate of the Fe / Zn-NC catalyst decreased to 13.08%, while the CH4 selectivity remained stable at 84.01%, and the CH4 yield slightly increased. The byproduct CO content decreased to 0.05%, the CH3OH content decreased to 0.55%, and the C2-C3 content increased to 15.39%, demonstrating a significant byproduct suppression effect. Simultaneously, the catalyst stability was further improved, with activity decay of less than 2% after long-term operation. These results demonstrate that by using K... + Doping can effectively optimize the product selectivity and operational stability of Fe / Zn-NC catalysts, significantly suppress the formation of by-products, and is suitable for industrial applications with high requirements for product purity.

Claims

1. A MOF-derived porous carbon-based composite catalyst, characterized in that, The catalyst is a Fe / Zn-NC catalyst rich in Fe / Zn synergistic active sites. The catalyst uses MOFs-derived hierarchical porous nitrogen-doped carbon as a support, and Fe and Zn bimetals are uniformly dispersed on the surface and inside the support. The catalyst surface has oxygen vacancies and contains graphite N and pyridine N nitrogen doping sites. The key active phase is the Fe / Zn synergistic active site.

2. The MOFs-derived porous carbon-based composite catalyst according to claim 1, characterized in that, The MOFs mentioned are ZIFs series.

3. The MOFs-derived porous carbon-based composite catalyst according to claim 1, characterized in that, The catalyst also contains potassium ion doping.

4. A method for preparing a MOFs-derived porous carbon-based composite catalyst as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Raw material ratio and mixing: Iron nitrate, zinc nitrate and organic ligands are dissolved in organic solvents respectively, mixed and stirred to form a uniform Fe / Zn-MOFs seed system solution; (2) Solvothermal reaction: The Fe / Zn-MOFs seed system solution is transferred to a high-pressure reactor for a one-step solvothermal reaction to generate Fe / Zn bimetallic doped MOFs precursor in situ; (3) Calcination treatment: The obtained MOF precursor was pyrolyzed and calcined under an inert atmosphere to obtain Fe / Zn-NC catalyst.

5. The method for preparing a MOFs-derived porous carbon-based composite catalyst according to claim 4, characterized in that, In step (1), the organic ligand is an imidazole ligand; the molar ratio between the iron nitrate, zinc nitrate and the organic ligand is 1:(0.1-1):(12-40); wherein the concentration of Fe in the Fe / Zn-MOFs seed system solution is 0.5 wt% ~ 5 wt%; a potassium salt is further added in the raw material mixing stage of step (1) to prepare K + Doped Fe / Zn-NC catalysts.

6. The method for preparing a MOFs-derived porous carbon-based composite catalyst according to claim 4, characterized in that, In step (2), the solvothermal reaction temperature is 80-200°C. o C, the reaction time is 8-48 h.

7. The method for preparing a MOFs-derived porous carbon-based composite catalyst according to claim 4, characterized in that, In step (3), the roasting temperature is 800-1000℃. o C, roasting time 60-240 min.

8. The application of the MOFs-derived porous carbon-based composite catalyst according to any one of claims 1-3 or the MOFs-derived porous carbon-based composite catalyst prepared by the preparation method according to any one of claims 4-7 in the hydrogenation of CO2 to CH4.

9. The application according to claim 8, characterized in that, The reaction conditions for the application are: reaction temperature 300-500°C. o C. Reaction pressure 1.5-2.5 MPa, C-H ratio 1 / 3-1 / 5.

10. The application according to claim 8, characterized in that, The application is compatible with fixed-bed reactors or fluidized-bed reactors.

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