Organic liquid efficient hydrogen storage and release catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of hydrogen storage catalysts, and relates to an organic liquid efficient hydrogen storage and release catalyst and a preparation method and application thereof.The organic liquid efficient hydrogen storage and release catalyst is a supported metal catalyst, and the supported metal catalyst comprises a carrier and a metal active component supported on the carrier; the carrier is a nitrogen-containing carbon source carrier with an ordered mesoporous structure; the metal active component is ruthenium element; according to the supported metal catalyst, an inorganic compound of Ru and a carrier containing a nitrogen carbon source form a coordinate bond, the dispersion uniformity and stability of noble metal on the carrier are improved, and meanwhile, a nitrogen-doped carbon carrier is introduced, so that the catalytic performance of the low-content noble metal catalyst on a liquid organic hydrogen carrier (LOHC) is greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of hydrogen storage catalyst technology, specifically relating to an organic liquid hydrogen storage catalyst, its preparation method, and its application. Background Technology

[0002] Hydrogen energy, as one of the most representative clean energy sources of the future, holds the promise of transitioning from fossil resources to carbon-neutral renewable energy. Key technologies for hydrogen energy mainly include large-scale hydrogen production, safe and efficient storage and transportation, utilization, and infrastructure. Among these, safe hydrogen storage and transportation are one of the most critical technologies. Among the various hydrogen storage technologies currently available, organic liquid hydrogen storage is considered one of the most promising technologies for large-scale hydrogen storage due to its advantages such as storage capacity, safe and reliable storage process, and ease of utilizing existing fuel oil storage facilities. Using liquid organic hydrogen carriers (LOHCs), such as aromatic compounds, existing fuel oil infrastructure can be used to efficiently store and transport hydrogen under environmental conditions, as shown in Equation 1. Using liquid aromatics as hydrogen storage carriers allows for stable storage of hydrogen in liquid compounds, and the hydrogenated liquid can be stored and transported under environmental conditions, enabling long-term, large-scale hydrogen storage. However, the kinetics of hydrogen storage and removal in LOHCs are slow, requiring catalysts to achieve efficient hydrogen storage / removal. Commonly used catalysts for LOHC hydrogen storage are mostly noble metal catalysts such as Pt, Pd, and Ru, with catalyst supports typically being materials such as Al2O3, carbon, and SiO2. Although these catalysts are highly effective in achieving efficient hydrogen storage, they are generally characterized by high cost.

[0003]

[0004] Equation 1. Schematic diagram of organic liquid hydrogen storage principle

[0005] To reduce costs, the main solutions currently being adopted include:

[0006] Improve the preparation process. Conventional catalyst preparation often employs the simplest impregnation method. However, this method struggles to uniformly load noble metal catalysts onto the support. In recent years, to address this issue, methods such as stepwise deposition, applying external magnetic or electric fields have been proposed to prevent metal particle aggregation and promote uniform distribution of metal particles on the support surface.

[0007] Reducing the amount of precious metals used presents two main problems. First, reducing the amount of precious metals makes it even more difficult to achieve uniform dispersion of the already challenging precious metal catalyst on the support. Second, the catalytic performance of the precious metal catalyst decreases as the amount of precious metals used decreases.

[0008] Non-precious metal catalysts are used. However, when non-precious metal catalysts are used in LOHC, they often exhibit catalytic performance that is far inferior to that of precious metal catalysts.

[0009] Improving the cycle performance of catalysts. Enhancing the cycle performance of precious metal catalysts often involves more complex material structure design, complex preparation processes, and precise control of process parameters.

[0010] Overall, the aforementioned solutions all have certain disadvantages in achieving the goal of cost reduction. Therefore, there is an urgent need for an efficient organic liquid hydrogen storage and release catalyst that can reduce the amount of precious metals used and has high catalytic performance. Summary of the Invention

[0011] To address the aforementioned technical problems, this invention provides a high-efficiency organic liquid hydrogen storage catalyst, its preparation method, and its application. This improves upon the uneven loading and high cost associated with impregnation methods for preparing organic liquid hydrogen storage catalysts, achieving the goal of high-efficiency hydrogen storage at lower temperatures. Addressing the issues of common impregnation methods for catalyst preparation, this invention provides an organic liquid hydrogen storage catalyst, its preparation method, and its application. By introducing a nitrogen-containing carbon source support to form a complex with the catalyst's supported metal and using it as the catalyst support, and simultaneously using a template agent to control the catalyst's crystal morphology and pore structure, a highly dispersed ruthenium-based catalyst with a unique hierarchically ordered porous structure and the synergistic effect of nitrogen doping is prepared, ultimately improving the catalyst's catalytic performance.

[0012] The technical solution provided by this invention is as follows:

[0013] A supported metal catalyst, comprising a support and a metal active component supported on the support, wherein the support is a nitrogen-containing carbon source support with an ordered mesoporous structure; and the metal active component is ruthenium.

[0014] Furthermore, the mass percentage of metal in the supported metal catalyst is 0.1% to 5%.

[0015] The present invention also provides a method for preparing the above-mentioned supported metal catalyst, comprising the following steps: dispersing an inorganic compound of Ru in an impregnation solution, ultrasonically vibrating it to obtain a Ru precursor solution, impregnating the Ru precursor solution in a support containing a nitrogen-containing carbon source with a template agent, stirring and drying it, then pyrolyzing it under a nitrogen atmosphere, followed by alkaline washing, reducing the dried product under a hydrogen-argon mixed atmosphere, cooling it to room temperature after the reduction is completed, and passing nitrogen gas through it to carry out a passivation reaction, and obtaining the supported metal catalyst after the passivation reaction.

[0016] A method for preparing an organic liquid hydrogen storage catalyst includes the following steps:

[0017] A certain amount of Ru inorganic compound was dispersed in 20 mL of impregnation solution and then impregnated in a carrier mixed solution containing a certain amount of template agent and nitrogen-containing carbon source. After thorough mixing for a period of time, the mixture was dried at a certain temperature. The dried product was ground for a period of time and then placed in a tube furnace. Under a nitrogen atmosphere, the temperature was gradually increased to a first predetermined temperature and held for a period of time for pyrolysis. After pyrolysis, the obtained product was dissolved in an alkaline solution of a certain concentration and stirred thoroughly for a period of time. After washing with water a certain number of times, the product was dried at a certain temperature. The dried product was ground and then placed in a reduction furnace. Under a 10% hydrogen-argon mixed atmosphere, the temperature was gradually increased to a second predetermined temperature and held for a period of time for catalyst reduction. Then, the temperature was gradually decreased to a third predetermined temperature, and the atmosphere was changed to a nitrogen atmosphere and held for a period of time for catalyst passivation, thus obtaining an organic liquid hydrogen storage catalyst.

[0018] Furthermore, the stirring speed is 100~500 r / min, and the stirring time is 8~12 h.

[0019] Furthermore, the drying temperature is 80~140℃, and the time is 8~12 h.

[0020] Furthermore, the passivation temperature is 20~40℃, the time is 4~12 h, the heating rate is 1℃ / min~2℃ / min, and the passivation atmosphere is N2.

[0021] Furthermore, the inorganic compound of Ru is one or more of dodecyltriruthenium, ruthenium chloride, and ruthenium nitrate; the template agent is one or more of SBA-15, SPAO-11, and γ-Al2O3; and the support for the nitrogen-containing carbon source is one or more of pyridine, 2'2-bipyridine, and 4'4-bipyridine.

[0022] Furthermore, the solvent of the impregnation solution is one or more of acetone, ethanol, N,N-dimethylformamide, tetrahydrofuran, and water; the alkaline washing solution is one or more of KOH, NaOH, and Ba(OH)2, with a concentration of 0.1~4 mol / L, and the alkaline washing time is 4~12 h.

[0023] Furthermore, the pyrolysis temperature is 400~800℃, the time is 1~4 h, and the heating rate is 2 ℃ / min~10 ℃ / min.

[0024] Furthermore, the reduction temperature of the catalyst is 200~400℃, the time is 1~4 h, the heating rate is 2 ℃ / min ~ 10 ℃ / min, and the reducing atmosphere is 10% H2 / Ar.

[0025] The present invention also provides the application of the above-mentioned supported metal catalyst as a hydrogen storage catalyst in the catalytic hydrogenation and dehydrogenation reaction of organic liquids.

[0026] Furthermore, the conditions for the hydrogenation reaction of the organic liquid are: reaction temperature 80 ~ 300℃, hydrogen pressure 0.1 ~ 10 MPa.

[0027] Furthermore, the organic liquid is one or more of N-propylcarbazole, N-ethylcarbazole, 1-methylindole, 1,2-dimethylindole, and naphthalene.

[0028] Beneficial effects

[0029] This invention, based on template-assisted pyrolysis, introduces a nitrogen-containing carbon source support to form coordination bonds between the inorganic Ru compound and the support, thereby improving the dispersion uniformity and stability of noble metals on the nitrogen-doped carbon support. While maintaining catalyst performance, it reduces the amount of noble metal used, achieving the goal of ensuring catalytic performance and reducing costs.

[0030] This invention involves the co-pyrolysis of one or more of 2'2-bipyridine and 4'4-bipyridine with a metal precursor at high temperature in a tubular furnace reactor under a nitrogen atmosphere. By controlling different raw material ratios and pyrolysis reaction processes, the synergistic effect between molecules at high temperature is enhanced. This improves the dispersion of metal particles and the bonding between the support, while simultaneously producing nitrogen-doped carbon material as a catalyst support. Further, the obtained nitrogen-doped carbon material is subjected to alkaline washing and other treatments to obtain a carbon material support with a high specific surface area. The preparation method includes thoroughly mixing the raw materials in a specific ratio, heat-treating under an inert atmosphere at a temperature of 400-800℃ for a reaction time of 1-4 h, and a heating rate of 2℃ / min-10℃ / min. The product after the reaction contains a portion of residual template agent in addition to the desired catalyst. This residual template agent is removed by alkaline washing and water washing. The product is then subjected to catalyst reduction in a reduction reactor under a hydrogen-argon mixed atmosphere to alter the catalyst's activity and selectivity. The reduction method includes a reduction temperature of 200–400 °C, a pyrolysis reaction time of 1–4 h, and a reduction heating rate of 2 °C / min–10 °C / min under a hydrogen-argon mixed atmosphere. After the reduction process, the temperature is gradually reduced to the passivation set temperature, and then the atmosphere is changed to a nitrogen atmosphere and maintained for a period of time to passivate the catalyst, thereby improving its stability and preventing over-reaction, ultimately yielding the catalyst.

[0031] This invention utilizes one or more of Ru inorganic compounds, including dodecacarbonyltriruthenium and ruthenium chloride, as precursors for the supported metal. Ruthenium catalysts offer advantages such as high catalytic activity, good high-temperature stability, low poisoning tendency, acid and alkali resistance, and excellent catalytic selectivity. One or more of SBA-15, SPAO-11, and γ-Al₂O₃ are used as template agents for the catalyst. These template agents provide high surface area, tunable pore structure, good stability, and can optimize catalytic performance by adjusting the pore structure. By introducing one or more of pyridine, 2'2-bipyridine, and 4'4-bipyridine, the supported metal forms a complex with the template, thereby improving metal dispersion. Furthermore, pyrolysis converts the metal into nitrogen-doped carbon material as a catalyst support. Utilizing nitrogen-doped carbon material as a catalyst support exhibits unique advantages in catalytic performance, including improved catalytic activity, increased catalytic stability, and adjustment of conductivity and acid-base properties. Compared to traditional impregnation methods for catalyst preparation, this invention offers advantages such as low cost, low metal loading, high catalytic efficiency, and high stability. This method offers the ability to provide highly controllable catalyst structures and morphologies, thereby improving catalyst activity, stability, and selectivity. This makes it a promising approach for catalyst design and preparation, particularly advantageous in reactions requiring highly efficient catalysts and specific catalytic properties.

[0032] Compared to traditional organic liquid hydrogen storage systems, such as the N-ethylcarbazole (NECZ) system, the catalyst prepared in this invention exhibits significantly superior catalytic performance. The reaction product is predominantly dodecylhydro-ethylcarbazole (12H-NECZ), with a conversion rate as high as 99.99% and a selectivity of over 99% for 12H-NECZ. This technology promises to enable large-scale organic liquid hydrogen storage, and its hydrogenation process can be seen in Equation 2.

[0033]

[0034] Equation 2. Schematic diagram of NECZ hydrogenation. Attached Figure Description

[0035] Figure 1 Here is a SEM image of the Ru / NC catalyst prepared according to Example 1;

[0036] Figure 2 This is a TEM image of the Ru / NC catalyst prepared according to Example 1;

[0037] Figure 3 The image shows the XRD pattern of the Ru / NC catalyst prepared according to Example 1.

[0038] Figure 4 This is the NH3-TPD diagram of the Ru / NC catalyst prepared according to Example 1;

[0039] Figure 5 This is a GC-MS image of the product obtained by hydrogenating NECZ using the Ru / NC catalyst prepared in Example 1. Detailed Implementation

[0040] Example 1

[0041] Step 1: Measure 20 mL of water and 20 mL of ethanol into a 100 mL beaker, mix them, and heat to 80°C.

[0042] Step 2: Weigh 0.5 g of SBA-15 and dissolve it in the mixed solution from Step 1. Set the stirring temperature to 80℃, the stirring speed to 400 r / min, and the stirring time to 30 min.

[0043] Step 3: Weigh 468 mg of 2'2 bipyridine and slowly add it to the solution obtained in Step 2, maintaining the temperature and rotation speed unchanged for 30 min.

[0044] Step 4: Grind and crush RuCl3•3H2O, dissolve 261 mg of the treated RuCl3•3H2O in 5 mL of ethanol solution, and obtain the Ru precursor by ultrasonic vibration for 10 min.

[0045] Step 5: Adjust the rotation speed to 500 r / min, and slowly add the Ru precursor solution obtained in Step 4 to the solution obtained in Step 3. Maintain the temperature and rotation speed for a period of time, and then adjust the temperature and rotation speed appropriately according to the change in solution volume until the solution is completely evaporated. After evaporation, transfer it to a 100℃ oven for further drying for 24 h.

[0046] Step Six: Place the dried mixed raw materials in the isothermal zone of a tubular furnace reactor, introduce high-purity nitrogen gas at a flow rate of 50 mL / min, and raise the temperature from room temperature to 800℃ at a rate of 2℃ / min. Hold the mixture at 800℃ for 2 hours to carry out the pyrolysis reaction. After the reaction is complete, collect the product at the end of the tubular furnace reactor.

[0047] Step 7: Wash the product obtained in Step 6 with 2 mol / L NaOH aqueous solution, filter it, wash it with distilled water until neutral, and then dry it in a 100℃ oven.

[0048] Step 8: Place the product obtained in Step 7 in the isothermal zone of the reduction reactor, and introduce a hydrogen-argon mixture at a flow rate of 50 mL / min. Increase the temperature from room temperature to 400℃ at a rate of 2℃ / min, and hold at 400℃ for 2 h to carry out the reduction reaction. After the reaction is complete and the temperature drops to room temperature, change the gas path and introduce nitrogen at a flow rate of 50 mL / min. Increase the temperature from room temperature to 40℃ at a rate of 2℃ / min, and hold at 40℃ for 12 h to carry out the passivation reaction. The resulting product is the prepared catalyst.

[0049] This embodiment yielded a Ru / NC catalyst with a Ru to 2'2-bipyridine molar ratio of 1:3 (based on the initial weight of the raw materials). This catalyst was used to conduct a series of hydrogenation and dehydrogenation reactions with N-ethylcarbazole in a relatively conventional organic liquid hydrogen storage system. A reactor was used as the reaction vessel. A 2-hour hydrogenation experiment was conducted at a reaction temperature of 120°C, a hydrogen pressure of 4 MPaH2, and a substrate-to-catalyst mass ratio of 20:1. The conversion rate of N-ethylcarbazole in the reaction products was 100%, and the yield of 12H-ethylcarbazole was 99.9%. Specific results are shown in Table 1. A 2-hour dehydrogenation experiment was conducted at a reaction temperature of 200°C, a nitrogen pressure of 0.1 MPaH2, and a substrate-to-catalyst mass ratio of 20:1. The conversion rate of dodeca-hydroethylcarbazole in the reaction products was 100%, and the yield of N-ethylcarbazole was 79.2%. Specific results are shown in Table 2.

[0050] Table 1. Results of using the catalyst prepared in Example 1 for NECZ hydrogenation.

[0051]

[0052] Note: Selectivity refers to the selective conversion rate of 12H-NECZ; hydrogen pressure for hydrogenation reaction is 4 MPa; reaction time is 2 h; feed ratio is the mass ratio of catalyst to reactant.

[0053] Table 2 shows the results of using the catalyst prepared in Example 1 for 12H-NECZ dehydrogenation.

[0054]

[0055] Note: Selectivity refers to the selective conversion rate of NECZ; nitrogen pressure for dehydrogenation reaction is 0.1 MPa; reaction time is 2 h; feed ratio is the mass ratio of catalyst to reactant.

[0056] In the hydrogenation reaction of Ru / NC with N-ethylcarbazole, Example 1 obtained the best product yield at 120°C. Figure 5The diagram shows the product distribution at the end of hydrogenation, with all products concentrated in 12H-NECZ. In the dehydrogenation reaction of Ru / NC with 12H-NECZ, Example 1 obtained the best product yield at 200°C, with 78.2% of the product being NECZ, which meets the standards for hydrogen storage catalysts for the NECZ system. Figure 1 and Figure 2 The XRD and TEM images of the catalyst show that the catalyst prepared in this invention has a large specific surface area and a high number of active sites, enabling it to provide more reaction sites in the N-ethylcarbazole hydrogen storage process, thereby improving the catalytic efficiency for organic liquid hydrogen storage. Secondly, its high dispersibility and finely tunable surface properties allow it to provide high selectivity in hydrogenation and dehydrogenation processes with low metal content, reducing side reactions and ensuring efficient reaction. For N-ethylcarbazole hydrogenation, Ru / NC preferentially and selectively hydrogenates N-ethylcarbazole molecules, ensuring a high yield of the target product. For dodecylhydro-ethylcarbazole dehydrogenation, Ru / NC preferentially and selectively completely dehydrogenates dodecylhydro-ethylcarbazole molecules, ensuring a high yield of the target product N-ethylcarbazole. Furthermore, Ru / NC exhibits good thermal and chemical stability in the reaction, maintaining activity at high temperatures and under complex reaction environments, and has a long lifespan. Finally, nitrogen-doped carbon as a support provides stable support and prevents ruthenium aggregation. Nitrogen-doped carbon supports not only possess excellent thermal stability and electronic conductivity, but also facilitate the dispersion of ruthenium particles, thereby enhancing catalytic activity. In summary, the catalyst prepared in this invention exhibits advantages including high catalytic activity, high selectivity, excellent catalytic stability, high hydrogen dissociation efficiency, and the supporting effect of nitrogen-doped carbon supports, making Ru / NC a promising candidate for applications in N-ethylcarbazole hydrogen storage and other hydrogen storage reactions.

[0057] Comparative Example 1

[0058] Except that the mass of 2'2 bipyridine in step three of Example 1 and RuCl3•3H2O in step four is 1.728 g : 0.272 g, the same preparation method as in Example 1 is used.

[0059] In this embodiment, a 5 wt% Ru / NC catalyst (based on the initial weight of the carbon precursor) was obtained. A series of hydrogenation and dehydrogenation experiments were conducted using this catalyst with N-ethylcarbazole, a commonly used organic liquid hydrogen storage system. A reactor was used as the reaction vessel. Hydrogenation experiments were conducted for 2 h at a reaction temperature of 125°C, a hydrogen pressure of 4 MPaH2, and a substrate-to-catalyst mass ratio of 20:1. The conversion rate of N-ethylcarbazole was 100%, and the yield of 12H-ethylcarbazole was 97.8%. Specific results are shown in Table 3. Dehydrogenation experiments were conducted for 2 h at a reaction temperature of 220°C, a nitrogen pressure of 0.1 MPaH2, and a substrate-to-catalyst mass ratio of 20:1. The conversion rate of dodecahydro-ethylcarbazole in the reaction products was 100%, and the yield of N-ethylcarbazole was 77.8%. Specific results are shown in Table 4.

[0060] Table 3 shows the results of using the catalyst prepared in Comparative Example 1 for NECZ hydrogenation.

[0061]

[0062] Note: Selectivity refers to the selective conversion rate of 12H-NECZ; hydrogen pressure for hydrogenation reaction is 4 MPa; reaction time is 2 h; feed ratio is the mass ratio of catalyst to reactant.

[0063] Table 4 shows the results of using the catalyst prepared in Comparative Example 1 for 12H-NECZ dehydrogenation.

[0064]

[0065] Note: Selectivity refers to the selective conversion rate of NECZ; nitrogen pressure for dehydrogenation reaction is 0.1 MPa; reaction time is 2 h; feed ratio is the mass ratio of catalyst to reactant.

[0066] In this series of embodiments, the catalytic performance of the catalyst prepared under the reaction conditions of Example 1 is relatively weakened. Compared to Example 1, the ruthenium content in this series of embodiments is reduced, which to some extent results in an excessively low supported metal content and an insufficient number of active sites on the catalyst surface. This makes it difficult for reactant molecules to find enough active sites for adsorption and reaction, leading to a significant reduction in catalytic activity. This may result in reduced catalyst selectivity, increased susceptibility to side reactions in the reaction system, and the generation of more byproducts. Therefore, compared to the catalytic performance of Example 1, the catalytic performance of this series of embodiments is reduced, which may lead to increased costs in industrial production. Therefore, controlling the appropriate supported metal content is one of the necessary conditions for preparing a high-performance catalyst.

[0067] Comparative Example 2

[0068] Except for replacing the 2'2 bipyridine in step three of Example 1 with coconut shell carbon, the same preparation method as in Example 1 was used.

[0069] This comparative example obtained Ru / C based on coconut shell carbon as a support. Using this catalyst, a series of hydrogenation experiments were conducted with N-ethylcarbazole in the currently more conventional organic liquid hydrogen storage system. A reaction vessel was used as the reaction vessel, and the hydrogenation experiments were carried out under the reaction conditions of 120℃, hydrogen pressure of 4 MPaH2, and substrate to catalyst mass ratio of 20:1. The conversion rate of N-ethylcarbazole was 32.3%, and the yield of 12H-ethylcarbazole was 13.2%.

[0070] In this comparative example, under the same reaction conditions, its catalytic performance was significantly weaker than that of Example 1. Due to the change in the catalyst support from nitrogen-doped carbon to coconut shell carbon, the number of defect sites and active sites on the catalyst surface decreased to some extent, reducing the specific surface area and adsorption capacity of the carbon material. These characteristics are detrimental to the dispersion of the metal active component, thus reducing the overall performance of the catalyst. Furthermore, nitrogen-doped carbon supports can enhance the interaction between the metal and the support through electron transfer between N atoms and the metal active component, thereby improving the stability and dispersibility of the catalyst, a function not possessed by coconut shell carbon. In addition, compared to coconut shell carbon, nitrogen-doped carbon supports can directly participate in the reaction as a catalyst. The nitrogen-containing groups on their surface can generate active sites for reactions such as redox, catalytic hydrogenation, and catalytic reforming, which is beneficial for improving catalytic selectivity and activity. Therefore, compared to Comparative Example 2, Example 1, by introducing 2'2-bipyridine as a nitrogen-doped carbon support with a nitrogen-containing carbon source, significantly improved the catalytic performance in the organic liquid hydrogen storage process.

[0071] Comparative Example 3

[0072] Except for omitting the use of SBA-15 in step two of Example 1, the same preparation method as in Example 1 was used.

[0073] This embodiment yielded a Ru / NC catalyst with a Ru to 2'2-bipyridine molar ratio of 1:3 (based on the initial weight of the raw materials). This catalyst was used to conduct a series of hydrogenation and dehydrogenation reactions with N-ethylcarbazole in a relatively conventional organic liquid hydrogen storage system. A reactor was used as the reaction vessel, and a hydrogenation experiment was conducted for 2 hours at a reaction temperature of 120°C, a hydrogen pressure of 4 MPaH2, and a substrate to catalyst mass ratio of 20:1. The conversion rate of N-ethylcarbazole in the reaction products was 78.9%, and the yield of 12H-ethylcarbazole was 56.1%. Specific results are shown in Table 5. Furthermore, the metal dispersion and specific surface area of ​​the catalysts prepared in Example 1 and Comparative Example 3 were compared, and specific results are shown in Tables 6 and 7.

[0074] Table 5 shows the results of using the catalyst prepared in Comparative Example 3 for NECZ hydrogenation.

[0075]

[0076] Note: Selectivity refers to the selective conversion rate of 12H-NECZ; hydrogen pressure for hydrogenation reaction is 4 MPa; reaction time is 2 h; feed ratio is the mass ratio of catalyst to reactant.

[0077] Table 6 Comparison of metal dispersion in the catalysts prepared in Example 1 and Comparative Example 3

[0078]

[0079] Note: The metal dispersion was tested using CO-pulse assay; the test methods and quantities used for both catalysts were the same.

[0080] Table 7 Comparison of specific surface area between the catalysts prepared in Example 1 and Comparative Example 3

[0081]

[0082] Note: The test methods and test quantities used for the two catalysts were the same in the specific surface area test.

[0083] In this series of examples, the catalytic performance of Comparative Example 3 was significantly weakened compared to the catalyst prepared in Example 1. Compared to Example 1, Comparative Example 3 exhibited reduced metal dispersion and a smaller specific surface area. This, to some extent, caused the aggregated loading of metal particles and uneven distribution of active centers. Simultaneously, the number of available active sites on the catalyst surface decreased, making it difficult for reactant molecules to be fully adsorbed and react, thus resulting in a significant reduction in catalytic activity. Furthermore, insufficient metal dispersion and a small specific surface area may also lead to decreased catalyst selectivity, making the reaction system more prone to side reactions and generating more byproducts. Therefore, compared to the catalytic performance of Example 1, the catalytic performance of Comparative Example 3 was reduced, which could lead to reduced raw material utilization and increased costs in industrial production. Therefore, regulating and optimizing metal dispersion and specific surface area is one of the necessary conditions for preparing high-performance catalysts.

[0084] Comparative Example 4

[0085] Except for replacing 2'2 bipyridine with 4'4 bipyridine in step three of Example 1, the same preparation method as in Example 1 was used.

[0086] In this embodiment, a Ru / NC catalyst with a Ru to 4'4 bipyridine molar ratio of 1:3 (based on the initial weight of the raw materials) was obtained. This catalyst was used to conduct a series of hydrogenation reactions with N-ethylcarbazole in a relatively conventional organic liquid hydrogen storage system. A reaction vessel was used as the reaction vessel, and hydrogenation experiments were carried out under the following conditions: reaction temperature 120°C, hydrogen pressure 4 MPaH2, and substrate to catalyst mass ratio 20:1. The conversion rate of N-ethylcarbazole in the reaction products was 86.5%, and the yield of 12H-ethylcarbazole was 65.2%. Specific results are shown in Table 8.

[0087] Table 8 shows the results of using the catalyst prepared in Comparative Example 4 for NECZ hydrogenation.

[0088]

[0089] Note: Selectivity refers to the selective conversion rate of 12H-NECZ; hydrogen pressure for hydrogenation reaction is 4 MPa; reaction time is 2 h; feed ratio is the mass ratio of catalyst to reactant.

[0090] In this comparative example, under the same reaction conditions, its catalytic performance was significantly weaker than that of Example 1. Due to the change in the catalyst support, from the previous 2'2 bipyridine material to 4'4 bipyridine, their molecular structures and coordination modes differ, which to some extent caused differences in the formation of complexes between the catalyst support and the metal active component. Structurally, 2'2 bipyridine has two pyridine rings connected by adjacent carbon atoms (at the 2-position). Given this connection, the distance between the two pyridine rings is relatively short, resulting in a more compact and stable ligand during coordination. Furthermore, the pyridine rings in 2'2 bipyridine provide electron density through their nitrogen atoms, resulting in a complex with high electron density, thus contributing to the stability of ruthenium's redox properties. In contrast, 4'4 bipyridine has two pyridine rings connected by carbon atoms at the para (4-position). Due to the greater distance between the two pyridine rings at the para position, the entire molecule exhibits a more extended structure. Given the looser structure of 4'4 bipyridine, it exhibits a different geometry when coordinating with ruthenium. Its larger dimensional space allows the complex to form different coordination modes, often exhibiting a relatively loose six-coordinate structure, which may slightly reduce the stability of the complex. Therefore, Example 1, using 2'2 bipyridine as the support, showed better catalytic performance than Comparative Example 4, using 4'4 bipyridine as the support, under the same reaction conditions.

[0091] Comparative Example 5

[0092] Except that the NaOH aqueous solution in step seven of Example 1 is replaced with deionized water, the same preparation method as in Example 1 is used.

[0093] This embodiment yielded a Ru / NC catalyst with a Ru to 2'2-bipyridine molar ratio of 1:3 (based on the initial weight of the raw materials). This catalyst was used to conduct a series of hydrogenation and dehydrogenation reactions with N-ethylcarbazole in a relatively conventional organic liquid hydrogen storage system. A reactor was used as the reaction vessel, and a hydrogenation experiment was conducted for 2 h at a reaction temperature of 120°C, a hydrogen pressure of 4 MPaH2, and a substrate to catalyst mass ratio of 20:1. The conversion rate of N-ethylcarbazole in the reaction products was 65.4%, and the yield of 12H-ethylcarbazole was 56.14%. Specific results are shown in Table 9.

[0094] Table 9 shows the results of using the catalyst prepared in Comparative Example 5 for NECZ hydrogenation.

[0095]

[0096] Note: Selectivity refers to the selective conversion rate of 12H-NECZ; hydrogen pressure for hydrogenation reaction is 4 MPa; reaction time is 2 h; feed ratio is the mass ratio of catalyst to reactant.

[0097] In this comparative example, under the same reaction conditions, its catalytic performance was significantly weaker than that of Example 1. The core reason is that the template agent SBA-15 was not removed by alkaline washing during the preparation of Comparative Example 5. Its silicon-based framework occupies the original mesoporous channels and covers the surface of the supported active components. This, to some extent, causes pore blockage of the catalyst and insufficient exposure of active sites, making it difficult for reactant molecules to diffuse to the active centers and complete adsorption and reaction, thus leading to a significant reduction in catalytic activity. Furthermore, the obstructed mass transfer in the pores and the altered microenvironment of the active centers may lead to a decrease in catalyst selectivity, making the reaction system more prone to side reactions and generating more byproducts. Therefore, compared to the catalytic performance of Example 1, the catalytic performance of Comparative Example 5 is lower. Therefore, thoroughly removing the template agent during the preparation of catalysts using template agents is one of the necessary conditions for obtaining catalysts with superior performance.

[0098] Comparing the reaction results of each example, it is clear that Example 1, which uses 2'2 bipyridine as a support and a Ru / NC catalyst with a molar ratio of 1:3 (based on the initial weight of the raw materials), has the best catalytic performance. The specific results are shown in Table 10.

[0099] Table 10 Results of using various catalysts in NECZ hydrogenation

[0100]

[0101] Note: The hydrogen pressure for the hydrogenation reaction is 4 MPa; the feed ratio is the mass ratio of catalyst to reactant.

[0102] Comparative Example 6

[0103] Except for other organic liquids used as reaction substrates in the hydrogen storage performance investigation experiments that replaced NECZ in Example 1, the experimental methods used to verify the hydrogen storage performance of the catalyst prepared in Example 1 on NECZ were used to verify the hydrogen storage effect of the catalyst prepared in Example 1 on other organic liquids.

[0104] First, using naphthalene as the reaction substrate, the hydrogen storage performance of the catalyst prepared in Example 1 for naphthalene was investigated. A series of hydrogenation reactions were carried out using a reaction vessel, and the specific results are shown in Table 11.

[0105] Table 11 Results of using the catalyst prepared in Example 1 for naphthalene hydrogenation

[0106]

[0107] Note: Selectivity refers to the selective conversion rate of decahydronaphthalene; hydrogen pressure for hydrogenation reaction is 4 MPa; reaction time is 2 h; feed ratio is the mass ratio of catalyst to reactant.

[0108] Finally, using 1,2-dimethylindole (1,2-DMID) as the reaction substrate, the hydrogen storage performance of the catalyst prepared in Example 1 for 1,2-DMID was investigated. A series of hydrogenation reactions were carried out using a reaction vessel, and the specific results are shown in Table 12.

[0109] Table 12 Results of hydrogenation of 1,2-dimethylindole using the catalyst prepared in Example 1.

[0110]

[0111] Note: Selectivity is the selective conversion rate of 8H-1,2-DMID; hydrogen pressure for hydrogenation reaction is 4 MPa; reaction time is 2 h; feed ratio is the mass ratio of catalyst to reactant.

[0112] Therefore, the catalyst prepared by the method in Example 1 not only exhibits significant efficacy for the NECZ hydrogen storage system, but also demonstrates highly efficient catalytic performance for other organic liquid hydrogen storage systems such as naphthalene and 1,2-DMID. This suggests a certain potential to promote the future realization of large-scale organic liquid hydrogen storage.

Claims

1. A supported metal catalyst, characterized in that, The supported metal catalyst includes a support and a metal active component supported on the support. The support is a nitrogen-containing carbon source support with an ordered mesoporous structure. The metal active component is ruthenium.

2. The supported metal catalyst according to claim 1, characterized in that, The supported metal catalyst contains 0.1% to 5% metal by mass.

3. The method for preparing the supported metal catalyst according to claim 1 or 2, characterized in that, Includes the following steps: After dispersing the inorganic compound of Ru in an impregnation solution, the Ru precursor solution was obtained by ultrasonic vibration. The Ru precursor solution was then impregnated in a support containing a nitrogen-containing carbon source with a template agent, stirred, dried, and then pyrolyzed under a nitrogen atmosphere. After alkaline washing, the dried product was subjected to catalyst reduction under a hydrogen-argon mixed atmosphere. After reduction, the temperature was lowered to room temperature, and nitrogen was introduced to carry out a passivation reaction. After the passivation reaction, a supported metal catalyst was obtained.

4. The preparation method according to claim 3, characterized in that, The inorganic compound of Ru is one or more of dodecacarbonyltriruthenium, ruthenium chloride, and ruthenium nitrate; the template agent is one or more of SBA-15, SPAO-11, and γ-Al2O3; and the nitrogen-containing carbon source support is one or more of pyridine, 2'2-bipyridine, and 4'4-bipyridine.

5. The preparation method according to claim 3, characterized in that, The solvent of the impregnation solution is one or more of acetone, ethanol, N,N-dimethylformamide, tetrahydrofuran, and water; the alkaline washing solution is one or more of KOH, NaOH, and Ba(OH)2, with a concentration of 0.1~4 mol / L, and the alkaline washing time is 4~12h.

6. The preparation method according to claim 3, characterized in that, The pyrolysis temperature is 400~800℃, the time is 1~4 h, and the heating rate is 2 ℃ / min ~ 10 ℃ / min.

7. The preparation method according to claim 3, characterized in that, The catalyst is reduced at a temperature of 200-400℃ for 1-4 h, with a heating rate of 2℃ / min to 10℃ / min, and the reducing atmosphere is 10% H2 / Ar.

8. The application of the supported metal catalyst according to claim 1 or 2 as a hydrogen storage catalyst in the catalytic hydrogenation and dehydrogenation reaction of organic liquids.

9. The application according to claim 8, characterized in that, The conditions for the hydrogenation reaction of the organic liquid are: reaction temperature 80 ~ 300℃, hydrogen pressure 0.1 ~ 10 MPa.

10. The application according to claim 8, characterized in that, The organic liquid is one or more of N-propylcarbazole, N-ethylcarbazole, 1-methylindole, 1,2-dimethylindole, and naphthalene.

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