N-co / cn nano catalyst and preparation method and application thereof
By preparing N-Co/CN nanocatalysts, using ZIF-67 as a precursor and treating it with N2 and NH3, the problems of high activity and low methanol selectivity in the methanation reaction of cobalt-based catalysts were solved, and an efficient and stable CO2 hydrogenation to methanol process was realized.
Patent Information
- Application Number
- CN202410406251.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-04-07
- Publication Date
- 2025-11-11
- Estimated Expiration
- 2044-04-07
AI Technical Summary
Existing cobalt-based catalysts exhibit high activity in the methanation reaction during CO2 hydrogenation, but low selectivity for methanol, and their preparation process is complex and their stability is not ideal.
Using ZIF-67 as a precursor, N-Co/CN nanocatalysts were prepared by N2 pyrolysis and NH3 treatment. The introduction of a small amount of N atoms modulates the electronic structure of Co, inhibits the methanation reaction, and improves methanol selectivity.
It improves the selectivity and stability of CO2 hydrogenation to methanol, simplifies the preparation process, reduces costs, and is suitable for large-scale production.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of catalyst technology, and in particular to an N-Co / CN nanocatalyst and its applications. Background Technology
[0002] Catalysts for CO2 hydrogenation to produce lower alcohols can be broadly classified into four categories: modified Fischer-Tropsch synthesis catalysts (using Fe or Co as the active component), Cu-based modified methanol synthesis catalysts, Rh-based noble metal catalysts, and Mo-based catalysts. Modified Fischer-Tropsch synthesis catalysts utilize abundant and inexpensive raw materials and possess excellent catalytic activity and stability. They can be used in various types of hydrogenation reactors, including hydrogenation units under high temperature, high pressure, and high oxygen conditions, as well as industrial applications with less stringent temperature requirements, and are considered one of the most promising catalytic systems.
[0003] Compared to iron-based catalysts, cobalt-based catalysts exhibit stronger hydrogenation capabilities, thus readily generating methane in the CO2 hydrogenation reaction with a selectivity typically exceeding 30%. This results in relatively lower selectivity for methanol. Therefore, the design focus for cobalt-based catalysts is to suppress the rate of methanation to improve their selectivity. This can be achieved through catalyst pretreatment, the addition of promoters, or utilizing strong metal-support interactions to inhibit the complete reduction of Co3O4 to metallic Co, thereby increasing the electron-deficient Co content. x + The number of sites can significantly inhibit the activity of the methanation reaction. Currently, the catalytic performance of CO2 hydrogenation to methanol catalysts has been extensively studied through appropriate pretreatment of the catalyst and the addition of alkali metal promoters. Lian et al. partially oxidized a Co / CN catalyst to reduce the content of metallic Co in the catalyst and the amount of H2 dissociation in the reaction gas. The methanol selectivity increased significantly from 12.5% to 39.8% with decreasing Co content, but the CO2 conversion rate decreased from 19.4% to 4.4%. This indicates that the catalyst pretreatment method reduced the catalyst hydrogenation efficiency and inhibited the activity of the methanation reaction, while improving the methanol selectivity. (Yun Lian et al., Journal of Catalysis (Gnanamani et al., 2019, 379: 46-51.) By incorporating an appropriate amount of K into the FeCo bimetallic catalyst, the strength of the Fe-H bond was reduced, leading to a decrease in the dissociation ability of H2. This, in turn, limited the ability of CO2 to directly hydrogenate to methane, while significantly increasing the selectivity for lower alcohols. ChemCatChemGnanamani et al. also studied the pretreatment conditions of the 1%Na / 20%Co-SiO2 catalyst and the effect of nano-doping on the activity and product selectivity of CO2 hydrogenation. They found that after reduction with CO, CoO and Co2C phases were generated. Na doping played a role in stabilizing the carbonized phases, reducing the selectivity of CH4 to 15.3%, while increasing the selectivity of alcohols to 73.2%. Applied Catalysis A: General (2015, 499: 39-46.) Although modifying the catalyst pretreatment method and adding alkali metal promoters can effectively suppress the activity of methanation and improve the selectivity of alcohols (such as methanol), changing the pretreatment method can easily damage the catalyst's own performance, and the alkali metal doping process is relatively complex, resulting in significant differences in the performance of the prepared catalysts. This leads to less than ideal stability of the catalysts prepared by this strategy, and they are prone to a significant decrease in activity during long-term cycling tests. Nitrogen (N) can effectively regulate the electronic structure of Co, thereby increasing the selectivity of CO2 hydrogenation to methanol, and has received considerable attention in recent years. For example, Wang et al. introduced N atoms into Co nanosheets, and the prepared Co4N nanosheets significantly improved the activity of CO2 hydrogenation to methanol. (Wang et al., 2015, 499: 39-46.) Nature Energy (2017, 2: 869-876.) However, the preparation process of Co4N nanosheets is complex and the conditions are relatively harsh, which is not conducive to the practical application of cobalt-based CO2 hydrogenation to methanol.
[0004] In view of this, the present invention provides an efficient and convenient method for preparing N-doped Co-based CO2 hydrogenation to methanol catalyst. The method uses the cobalt metal-organic framework compound ZIF-67 as a precursor, and introduces a small amount of N into Co nanoparticles through N2 pyrolysis and NH3 reprocessing to prepare an N-Co / CN catalyst, thereby improving the selectivity and stability of the cobalt-based catalyst in the CO2 hydrogenation reaction. Summary of the Invention
[0005] In view of the above problems, this invention proposes an N-Co / CN nanocatalyst, its preparation method, and its application. The technical solution adopted to achieve the purpose of this invention is as follows:
[0006] The method for preparing N-Co / CN nanoparticles proposed in this invention includes the following steps:
[0007] (1) Cobalt nitrate was dissolved in methanol to prepare solution A, and 2-methylimidazole was dissolved in methanol to prepare solution B. Solution A and solution B were then mixed and stirred evenly. After centrifugation, washing and drying, ZIF-67 was obtained as a precursor of Co.
[0008] (2) The ZIF-67 obtained in (1) was placed in a quartz tube and pyrolyzed with nitrogen to obtain Co / CN nanoparticles, which were used as precursors for the catalyst.
[0009] (3) The catalyst precursor Co / CN nanoparticles obtained in (2) were placed in a quartz tube and ammonia gas was introduced and heated twice to obtain N-Co / CN nanoparticles.
[0010] Preferably, in step (1), the molar volume ratio of cobalt nitrate and methanol in solution A is 1 mol: 1000 mL; the molar volume ratio of 2-methylimidazole and methanol in solution B is 1 mol: 7000 mL; the stirring time is controlled at 6~12 h; the centrifugation speed is 7000 rpm / min; the temperature is 60 ℃; and the drying time is controlled at 6~12 h.
[0011] Preferably, in step (2), the nitrogen flow rate is 40 mL / min; the nitrogen pressure is 0.1 MPa; the heating rate is 5 ℃ / min; the temperature is controlled at 400~700 ℃; and the holding time is 2 h.
[0012] Preferably, in step (3), the ammonia gas flow rate is 100 mL / min; the ammonia gas pressure is 0.1 MPa; the heating rate for the first heating is 5 ℃ / min, the temperature is 300 ℃, and the holding time is 10 min; the heating rate for the second heating is 1 ℃ / min, the temperature is controlled at 350~600 ℃, and the holding time is 4 h.
[0013] As can be seen from the above technical solution, the present invention has the following beneficial effects:
[0014] (1) The catalyst provided by this invention can effectively improve the activity of catalytic CO2 hydrogenation to methanol (higher than commercial CuZnAl catalyst), realize the efficient conversion and high added value of CO2, and is conducive to the realization of the "dual carbon" goal.
[0015] (2) The catalyst provided by the present invention is a highly active non-precious metal catalyst for CO2 hydrogenation, and the raw materials required for its preparation are inexpensive and abundant.
[0016] (3) The catalyst preparation process provided by the present invention is simple, easy to scale up, and conducive to the practical application of cobalt-based catalysts. Attached Figure Description
[0017] Figure 1 This is a transmission electron microscope image of the N-Co / CN nanoparticles obtained in Example 1 of the present invention.
[0018] Figure 2 The image shows the X-ray diffraction pattern of the N-Co / CN and Co / CN nanoparticles obtained in Example 1 of this invention.
[0019] Figure 3 The infrared spectrum of the N-Co / CN and Co / CN nanoparticles obtained in Example 1 of this invention is shown.
[0020] Figure 4 This is a comparison of the product yields of the N-Co / CN nanoparticles obtained in Example 1 of this invention, Co nanoparticles, and the product yields of the CO2 hydrogenation reaction catalyzed by the commercial Cu / ZnO / Al2O3 catalyst.
[0021] Figure 5 This is a comparison of the activation energies of N-Co / CN nanoparticles obtained in Example 1 of the present invention with those of Co nanoparticles and commercial Cu / ZnO / Al2O3 catalyst in the catalytic hydrogenation reaction of CO2.
[0022] Figure 6 The image shows a TOF bar chart of the N-Co / CN nanoparticles obtained in Example 1 of this invention catalyzing the CO2 hydrogenation reaction at different temperatures.
[0023] Figure 7 This is a five-cycle test diagram of the CO2 hydrogenation reaction catalyzed by N-Co / CN nanoparticles obtained in Example 1 of the present invention.
[0024] Figure 8 The X-ray diffraction pattern of the N-Co / CN nanoparticles obtained in Example 2 of this invention is shown.
[0025] Figure 9 This is a comparison of the yield of products from the CO2 hydrogenation reaction catalyzed by N-Co / CN nanoparticles obtained in Example 2 of the present invention.
[0026] Figure 10 The X-ray diffraction pattern of the N-Co / CN nanoparticles obtained in Example 3 of this invention is shown.
[0027] Figure 11 This is a comparison of the yield of products from the CO2 hydrogenation reaction catalyzed by N-Co / CN nanoparticles obtained in Example 3 of the present invention. Detailed Implementation
[0028] To better understand the present invention, the following description, in conjunction with embodiments, further illustrates the present invention. However, the scope of protection claimed by the present invention is not limited to the scope shown in the embodiments.
[0029] The technical solution of the present invention will now be described in detail through specific embodiments.
[0030] Example 1 (Preparation and application of N-Co / CN catalyst)
[0031] Catalyst preparation:
[0032] (1) Preparation of ZIF-67: 2.91 g of cobalt nitrate hexahydrate was added to 10 mL of methanol and sonicated for 15 min to prepare mixture A; 3.28 g of 2-methylimidazole was weighed and added to 70 mL of methanol and sonicated for 15 min to prepare solution B; solution A was poured into solution B and stirred for 12 h. Then, the mixture was centrifuged and washed three times to obtain a purple solid. The purple solid obtained by centrifugation was dried at 60 ℃ for 12 h to obtain ZIF-67.
[0033] (2) Pyrolysis of ZIF-67: 500 mg ZIF-67 was placed in a quartz tube and nitrogen gas was introduced for heat treatment. Under the atmosphere of nitrogen gas flow rate of 40 mL / min, the gas pressure was maintained at 0.1 MPa and nitrogen gas was purged for 10 min. The temperature was increased to 600 ℃ at a heating rate of 5 ℃ / min and held for 2 h. Then, the temperature was naturally cooled to room temperature under the nitrogen atmosphere to obtain Co / CN nanoparticles.
[0034] (3) Co / CN ammonia treatment: 100 mg of Co / CN nanoparticles were placed in a quartz tube and the pressure was maintained at 0.1 MPa under an ammonia gas flow rate of 100 mL / min. The ammonia gas was purged at 30 °C for 10 min, then the temperature was increased to 300 °C at 5 °C / min and held for 10 min. The temperature was then increased to 500 °C at a rate of 1 °C / min and held for 4 h. Finally, the temperature was naturally cooled to room temperature under an ammonia atmosphere to obtain N-Co / CN nanoparticles.
[0035] Catalyst activity evaluation:
[0036] 80 mg of the N-Co / CN nanoparticles obtained in this example were added to a 50 mL high-pressure reactor, followed by 2 mL of DMF and a magnetic stir bar. After assembling the reactor, it was purged with nitrogen five times, and then 0.5 MPa CO2 gas and 1.5 MPa H2 gas were introduced. The temperature was raised to 180 °C and held for 6 h, maintaining a stirring speed of 600 rpm during the reaction. The catalytic activity of the Co / CN nanoparticles and the commercial Cu / ZnO / Al2O3 catalyst for CO2 hydrogenation was evaluated according to the above steps for comparison.
[0037] The N-Co / CN obtained in this embodiment was observed using a high-resolution transmission electron microscope, such as... Figure 1 As shown, after treatment with N2 and NH3, the catalyst still exhibits a rhombic dodecahedral structure (the initial structure of ZIF-67), but it shows distortion and shrinkage, which is caused by the decomposition of some substances during the heat treatment process.
[0038] Figure 2The X-ray diffraction patterns of N-Co / CN and Co / CN obtained in Example 1 of this invention are shown in the figure. It can be seen from the figure that the crystal phases of the N-Co / CN and Co / CN nanoparticles are basically consistent, but there is a slight shift, which may be caused by the introduction of N.
[0039] Figure 3 The image shows the infrared spectrum of the N-Co / CN and Co / CN nanoparticles obtained in Example 1 of this invention. As can be seen from the image, the spectral peak of the N-Co / CN nanoparticles shows a blue shift at a wavelength of 668 cm⁻¹, indicating the introduction of N.
[0040] The results of the catalyst activity test are as follows Figure 4 , Figure 5 As shown, the methanol yields of N-Co / CN nanoparticles, Co / CN nanoparticles, and the commercial Cu / ZnO / Al2O3 catalyst were 14.1, 1.4, and 4.4 mmol, respectively, with activation energies of 93.7, 106.6, and 102.0 kJ / mol, respectively. -1 N-Co / CN nanoparticles exhibited the highest catalytic activity and the lowest activation energy among these three catalysts.
[0041] The N-Co / CN nanoparticles obtained in this embodiment were subjected to catalytic CO2 hydrogenation reaction at different temperatures, and the results are as follows: Figure 6 As shown, the catalytic performance of N-Co / CN nanoparticles increases with the increase of CO2 hydrogenation reaction temperature, reaching the optimal reaction temperature at 210℃.
[0042] The N-Co / CN nanoparticles obtained in this embodiment were subjected to five cycles of catalytic CO2 hydrogenation reaction, and the results are as follows: Figure 7 As shown, the catalytic activity of N-Co / CN nanoparticles did not significantly reduce the methanol yield, and they maintained high reactivity after multiple reactions, providing the possibility for catalyst recovery and reuse.
[0043] Example 2 (Different pyrolysis temperatures)
[0044] The nitrogen treatment temperature of ZIF-67 in Example 1 was adjusted from 600 ℃ to 400 ℃, 500 ℃, 600 ℃ and 700 ℃, and the remaining steps were the same as in Example 1.
[0045] Figure 8The image shows the XRD pattern of the N-Co / CN nanoparticles obtained in Example 2. As can be seen from the image, different nitrogen treatment temperatures have no significant effect on the crystal phase of the sample. Careful comparison reveals that the XRD diffraction peak width of the N-Co / CN nanoparticles is largest at a pyrolysis temperature of 600 °C, indicating that its grain size is the smallest. The smaller the grain size per unit mass of active component, the larger the surface area provided, the higher the surface free energy, and the higher the catalyst activity. This indicates that this is the optimal pyrolysis temperature.
[0046] Figure 9 The figure compares the yields of products from the CO2 hydrogenation reaction catalyzed by N-Co / CN nanoparticles obtained in Example 2. As can be seen from the figure, the methanol yield is highest at a pyrolysis temperature of 600 °C, further indicating that this is the optimal pyrolysis temperature.
[0047] Example 3 (Different ammonia treatment temperatures)
[0048] The ammonia treatment temperature of Co / CN in Example 1 was changed from 500 ℃ to 350 ℃, 400 ℃, 450 ℃, 550 ℃ and 600 ℃, and the remaining steps were the same as in Example 1.
[0049] Figure 10 The image shows the XRD pattern of the N-Co / CN nanoparticles obtained in Example 3. As can be seen from the image, different ammonia treatment temperatures have no significant effect on the crystal phase of the sample. Careful comparison reveals that the N-Co / CN nanoparticles exhibit the largest half-peak width (WHM) of the XRD diffraction peak at an ammonia treatment temperature of 500 °C, indicating the smallest grain size. Smaller grains per unit mass of active component provide a larger surface area, higher surface free energy, and higher catalyst activity, suggesting that this is the optimal ammonia treatment temperature.
[0050] Figure 11 The figure shows a comparison of the yields of products from the CO2 hydrogenation reaction catalyzed by N-Co / CN nanoparticles obtained in Example 3. As can be seen from the figure, the methanol yield was highest when the ammonia treatment temperature was 500 °C, further indicating that this is the optimal ammonia treatment temperature.
[0051] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A method for preparing an N-Co / CN nanocatalyst, characterized in that, Includes the following steps: (1) Cobalt nitrate was dissolved in methanol to prepare solution A, and 2-methylimidazole was dissolved in methanol to prepare solution B. Solution A and solution B were then mixed and stirred evenly. After centrifugation, washing and drying, ZIF-67 was obtained as a precursor of Co. (2) The ZIF-67 obtained in step (1) was placed in a quartz tube and pyrolyzed by nitrogen gas to obtain Co / CN nanoparticles, which were used as precursors for the catalyst. (3) The catalyst precursor Co / CN nanoparticles obtained in step (2) were placed in a quartz tube, ammonia gas was introduced, and N-Co / CN nanoparticles were obtained after two heating treatments; In step (1), the molar volume ratio of cobalt nitrate to methanol in solution A is 1 mol: 1000 mL; the molar volume ratio of 2-methylimidazole to methanol in solution B is 1 mol: 7000 mL; the stirring time is controlled at 6~12 h; the centrifugation speed is 7000 rpm / min; the drying temperature is 60 ℃; and the drying time is controlled at 6~12 h. In step (3), the ammonia gas flow rate is 100 mL / min; the ammonia gas pressure is 0.1 MPa. In step (3), the heating rate for the first heating is 5 ℃ / min, the temperature is 300 ℃, and the holding time is 10 min; In step (3), the heating rate for the second heating is 1 ℃ / min, the temperature is controlled at 350~600 ℃, and the holding time is 4h.
2. The method for preparing an N-Co / CN nanocatalyst according to claim 1, characterized in that: In step (2), the nitrogen flow rate is 40 mL / min and the nitrogen pressure is 0.1 MPa.
3. The method for preparing an N-Co / CN nanocatalyst according to claim 1, characterized in that: The specific pyrolysis conditions in step (2) are: heating rate of 5 ℃ / min; temperature controlled at 400~700 ℃; and holding time of 2 h.
4. The N-Co / CN nanocatalyst prepared by the method according to any one of claims 1-3.
5. The application of the catalyst as described in claim 4 in the hydrogenation to methanol.
Citation Information
Patent Citations
Catalyst for preparing ethanol through carbon dioxide hydrogenation and performing in-situ alcoholysis on waste PET (Polyethylene Terephthalate)
CN117816170A