Preparation method and application of hierarchical porous nitrogen-doped carbon material with ruthenium monatomic and cluster sites

Abstract

The invention discloses a preparation method and application of a hierarchical porous nitrogen-doped carbon material with ruthenium single atoms and cluster sites. In the catalyst, ruthenium is loaded on a hierarchical porous nitrogen-doped carbon material in the form of nanoclusters consisting of dispersed single atoms and multiple atoms; the catalyst is prepared by a two-step alcohol reduction method, and the method comprises the following steps: preparing a hierarchical porous nitrogen-doped carbon material by adopting a blending carbonization method and taking a zeolite imidazole skeleton-8 as a template, fully mixing the hierarchical porous nitrogen-doped carbon material with a ruthenium chloride precursor in methanol, preparing a ruthenium monatomic catalyst through reflux condensation, centrifugation, washing and drying, and then dispersing the ruthenium monatomic catalyst in ethylene glycol to obtain the catalyst. Meanwhile, dispersing a ruthenium chloride precursor and polyvinylpyrrolidone in ethylene glycol, fully mixing the two solutions, and then carrying out reflux condensation, centrifugation, washing and drying to obtain the catalyst. The preparation process is simple, does not need further hydrogen reduction, and is green and environment-friendly; the catalyst is applied to the catalytic hydrogenation reaction of vanillin, and has high catalytic efficiency and good stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of noble metal catalysts, and particularly relates to a ruthenium-based catalyst supported on nitrogen-doped carbon, and more particularly to a preparation method and application of a hierarchical pore nitrogen-doped carbon material with both ruthenium single atoms and cluster sites. Background Art

[0002] Single-atom and cluster catalysts are a new type of catalysts, which are composed of dispersed metal atoms and nanocluster structures composed of multiple atoms. Compared with traditional single-atom or single-cluster catalysts, single-atom and cluster co-catalysts have more excellent catalytic performance and stability, and are widely used in the catalytic field.

[0003] The design of single-atom and cluster catalysts is an extremely important process, which determines the performance of the catalysts. Therefore, before designing single-atom and cluster catalysts, multiple factors need to be considered, mainly including: suitable carriers, the interaction between the metal and the carrier, the size and shape of the clusters, etc.

[0004] Currently, the commercial noble metal catalyst carriers on the market are mostly activated carbon. However, the activated carbon carrier lacks active metal site anchoring, resulting in a weak interaction between the metal active center and the carrier, making it difficult to disperse the noble metal and extremely easy to agglomerate during the preparation and use of the catalyst, thus leading to poor hydrogenation activity and stability of the catalyst. Therefore, developing noble metal catalysts with high activity and stability has very important industrial application value.

[0005] As a potential fine chemical product, vanillyl alcohol has important application value in the fields of food, daily chemicals, and medicine. However, the current mainstream preparation process has obvious drawbacks. The sodium borohydride reduction method has high costs and generates a large amount of difficult-to-treat borate waste, hindering the industrialization process; the synthesis route using guaiacol as the raw material is long, with many by-products and large pollution from some reagents, putting pressure on the environment. Therefore, exploring an efficient, low-cost, and environmentally friendly vanillyl alcohol synthesis process is crucial for promoting sustainable development.

[0006] Vanillin is a biomass-based green chemical raw material that has attracted much attention and has a considerable annual supply, making it a key raw material for development. The hydrogenation of vanillin to vanillyl alcohol has significant advantages, such as easy availability of raw materials, clear principles, high atom utilization rate, and the ability to produce high-value-added vanillyl alcohol, which has attracted much attention in both academic and industrial fields and promotes the green development of fine chemicals. Currently, the main problems for this reaction are still relatively low catalyst activity and poor stability. Summary of the Invention

[0007] The object of the present invention is to provide a preparation method and application of a hierarchical porous nitrogen-doped carbon material with both ruthenium single atoms and cluster sites, so as to overcome the problems of single type of metal active sites in existing hydrogenation catalysts for bio-oil model compounds, difficult dispersion and easy agglomeration of ruthenium in supported catalysts, as well as insufficient hydrogenation activity and poor stability of existing noble metal catalysts.

[0008] To achieve the above object, the present invention adopts the following technical solutions: A preparation method of a hierarchical porous nitrogen-doped carbon material with both ruthenium single atoms and cluster sites, which is applicable to the preparation of noble metal supported single atom and cluster catalysts and the catalytic hydrogenation application of bio-oil and its model compounds; it includes the following steps: 1) Mix the zeolitic imidazolate framework-8 material and polyethylene glycol in a mass ratio of 1:1.5, transfer them to a tubular furnace, use an inert gas as the carrier gas, then carry out heat treatment, and after completion, naturally cool to room temperature, and obtain a hierarchical porous nitrogen-doped carbon material through pickling, water washing and drying; 2) Disperse the hierarchical porous nitrogen-doped carbon material obtained in step 1) and the ruthenium precursor in methanol respectively, then fully mix the two solutions, transfer them to a three-necked flask, carry out condensation reflux, and after the reaction is completed, naturally cool to room temperature, and obtain a hierarchical porous nitrogen-doped carbon material with ruthenium single atom sites through washing and drying, which is called a ruthenium single atom catalyst; 3) Disperse the hierarchical porous nitrogen-doped carbon material with ruthenium single atom sites obtained in step 2) in ethylene glycol, and at the same time disperse the metal precursor and polyvinylpyrrolidone (PVP) in ethylene glycol, then fully mix the two solutions, transfer them to a three-necked flask, carry out condensation reflux, and after the reaction is completed, naturally cool to room temperature, and obtain a hierarchical porous nitrogen-doped carbon material with both ruthenium single atoms and cluster sites through washing and drying, which is called a ruthenium single atom and cluster catalyst.

[0009] Further, the inert gas in step 1) includes any one of nitrogen, argon, and helium.

[0010] Further, the pickling detergent in step 1) is concentrated hydrochloric acid with a concentration of 36-38 wt%.

[0011] Further, the flow rate of the carrier gas in step 1) is 80 mL / min.

[0012] Further, the heat treatment temperature in step 1) is 900 °C and the time is 2 h.

[0013] Further, the ruthenium precursors in steps 2) and 3) are both ruthenium trichloride.

[0014] Further, the dosage of the ruthenium precursor described in step 2) is added according to the proportion of metallic ruthenium in the dosage of the hierarchically porous nitrogen-doped carbon material, and the dosage of metallic ruthenium accounts for 0.2-1 wt% of the dosage of the hierarchically porous nitrogen-doped carbon material.

[0015] Further, the dosage of the ruthenium precursor described in step 3) is added according to the proportion of metallic ruthenium in the dosage of the ruthenium single-atom catalyst obtained in step 2), and the amount of metallic ruthenium accounts for 1-1.8 wt% of the dosage of the ruthenium single-atom catalyst.

[0016] Further, the total amount of metal ions used in steps 2) and 3) is 2 wt% of the dosage of the hierarchically porous nitrogen-doped carbon material.

[0017] Further, the washing in steps 2) and 3) is carried out using any one of methanol, ethanol, water, tetrahydrofuran, N,N-dimethylformamide, and acetone as the detergent.

[0018] Further, in the hierarchically porous nitrogen-doped carbon material with both ruthenium single atoms and cluster sites, the content of metallic ruthenium is 2 wt% of the total mass of the catalyst.

[0019] Application: Application of a hierarchically porous nitrogen-doped carbon material with both ruthenium single atoms and cluster sites as a catalyst in the hydrogenation of vanillin to vanillyl alcohol.

[0020] The present invention has the following beneficial effects: The present invention synthesizes a synergistic catalyst with both ruthenium single atoms and clusters by a two-step alcohol reduction method. On the one hand, through simple methanol reduction, ruthenium metal ions coordinate with nitrogen atoms in the hierarchically porous nitrogen-doped carbon material, and there is a strong interaction between the metal-nitrogen atoms, forming dispersed single-atom sites. On the other hand, the metal ion precursor is reduced to nanoclusters by the ethylene glycol reduction method and then introduced into the ruthenium single-atom catalyst to form nanocluster sites. The ratio between ruthenium single atoms and clusters is regulated by the two-step method, thereby preparing a synergistic catalyst with both ruthenium single-atom and cluster sites. Therefore, the catalyst prepared by the present invention has both ruthenium single-atom sites and cluster sites, with less noble metal usage, good dispersion, high atomic utilization rate, and excellent catalytic performance.

[0021] The nitrogen atoms in the ZIF-8-derived nitrogen-rich doped carbon material have 5 valence electrons, can form strong covalent bonds with the metal active centers, serve as sites for anchoring active metals, and promote the dispersion of metals in the carrier. In addition, through polyethylene glycol modification, a hierarchically porous nitrogen-doped carbon material with micro-mesopores is constructed, which promotes the diffusion of reactants or hydrogen in the catalyst. The hierarchically porous nitrogen-doped carbon material has pore structures of different sizes, a relatively high specific surface area, and good thermal stability, which can effectively improve the hydrogenation activity of the catalyst. Description of the Drawings

[0022] Figure 1 Nitrogen adsorption - desorption isotherm and pore size distribution diagram of the sample prepared in Example 2.

[0023] Figure 2 XRD spectrum of the sample prepared in Example 2.

[0024] Figure 3 Spherical aberration - corrected scanning transmission electron microscope image and EDS mapping image of the sample prepared in Example 2.

[0025] Figure 4 XPS spectrum of the sample prepared in Example 2.

[0026] Figure 5 Spherical aberration - corrected scanning transmission electron microscope image of the sample prepared in Comparative Example 1.

[0027] Figure 6 Spherical aberration - corrected scanning transmission electron microscope image of the sample prepared in Comparative Example 2. Detailed implementation mode

[0028] A preparation method and application of a hierarchical pore nitrogen - doped carbon material with both ruthenium single atoms and cluster sites, which includes the following steps: 1) Mix the zeolitic imidazolate framework - 8 material and polyethylene glycol in a mass ratio of 1:1.5, and transfer it to a tubular furnace. Use an inert gas as the carrier gas with a flow rate of 80 mL / min, then perform heat treatment at 900 °C for 2 h. After that, cool it naturally to room temperature, and carry out pickling, washing, and drying to obtain a hierarchical pore nitrogen - doped carbon material; 2) Disperse the hierarchical pore nitrogen - doped carbon material obtained in step 1) and the ruthenium precursor in methanol respectively. Then, fully mix the two solutions, transfer them to a three - necked flask, and carry out condensation reflux for 18 h. After the reaction is completed, cool it naturally to room temperature, and carry out washing and drying to obtain a hierarchical pore nitrogen - doped carbon material with ruthenium single - atom sites, called ruthenium single - atom catalyst; 3) Disperse the hierarchical pore nitrogen - doped carbon material with ruthenium single - atom sites obtained in step 2) in ethylene glycol. At the same time, disperse the ruthenium precursor and polyvinylpyrrolidone in ethylene glycol. Then, fully mix the two solutions, transfer them to a three - necked flask, and carry out condensation reflux for 3 h. After the reaction is completed, cool it naturally to room temperature, and carry out washing and drying to obtain a hierarchical pore nitrogen - doped carbon material with both ruthenium single atoms and cluster sites, called ruthenium single - atom and cluster catalyst.

[0029] Among them, the inert gas in step 1) includes any one of nitrogen, argon, and helium. The detergent for pickling is concentrated hydrochloric acid.

[0030] The ruthenium precursor in steps 2) and 3) is ruthenium trichloride.

[0031] The amount of the ruthenium precursor in step 2) is added according to the ratio of the metal ruthenium to the amount of the hierarchical pore nitrogen-doped carbon material, and the amount of the metal ruthenium accounts for 0.2-1wt% of the amount of the hierarchical pore nitrogen-doped carbon material.

[0032] The amount of the ruthenium precursor in step 3) is added according to the ratio of metallic ruthenium to the amount of the ruthenium single atom catalyst, and the amount of metallic ruthenium accounts for 1-1.8 wt % of the amount of the ruthenium single atom catalyst.

[0033] The total amount of metal ions in steps 2) and 3) is 2 wt % of the amount of the hierarchical porous nitrogen-doped carbon material.

[0034] The washing in steps 2) and 3) uses any one of methanol, ethanol, water and acetone as a washing agent.

[0035] Application: A hierarchical porous nitrogen-doped carbon material with both ruthenium single atom and cluster sites is used as a catalyst in the hydrogenation of vanillin to produce vanillyl alcohol.

[0036] In order to make the contents of the present invention easier to understand, the technical solution of the present invention is further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0037] Example 1 10 g of zeolite imidazole framework-8 material was thoroughly mixed with 15 g of polyethylene glycol and stirred vigorously for 30 min. The mixture was then transferred to the center of a tubular furnace with nitrogen as the carrier gas at a flow rate of 80 mL / min. The temperature of the tubular furnace was set to 900 °C and maintained for 2 h. The tubular furnace was then cooled to room temperature, the sample was taken out, washed with concentrated hydrochloric acid (concentration 36 wt%) for 48 h, and then washed with water until the solution was neutral. The sample was then transferred to an oven and dried at 80 °C for 12 h to obtain a hierarchical pore nitrogen-doped carbon material.

[0038] Take 1.2 g of the above-obtained hierarchical porous nitrogen-doped carbon material and 0.012 g of ruthenium trichloride and disperse them in 100 mL of methanol respectively. The two solutions are fully mixed and then transferred to a three-necked flask. They are condensed and refluxed at 65 °C for 18 h. After the reaction is completed, they are naturally cooled to room temperature. After washing with methanol, they are dried at 80 °C for 12 h to obtain a hierarchical porous nitrogen-doped carbon-supported ruthenium single atom catalyst.

[0039] Take 0.6 g of the above-mentioned hierarchical pore nitrogen-doped carbon-supported ruthenium single-atom catalyst and disperse it in 50 mL of ethylene glycol. At the same time, disperse 0.024 g of ruthenium(III) chloride and 0.4 g of polyvinylpyrrolidone in 50 mL of ethylene glycol. Then, mix the two solutions thoroughly, transfer them to a three-necked flask, and carry out reflux condensation at 198 °C for 3 h. After the reaction is completed, cool it naturally to room temperature, wash it with ethanol, and dry it at 80 °C for 12 h to obtain a hierarchical pore nitrogen-doped carbon-supported ruthenium single-atom and cluster catalyst, denoted as Ru 1+NPs / HPNC-1. The Ru content in the catalyst accounts for 2% of the total mass of the catalyst.

[0040] Example 2 Mix 10 g of zeolitic imidazolate framework-8 material with 15 g of polyethylene glycol thoroughly and stir vigorously for 30 min. Then, transfer the mixture to the center of a tubular furnace and use nitrogen with a flow rate of 80 mL / min as the carrier gas. Set the temperature of the tubular furnace to 900 °C and keep it for 2 h. Then, cool the tubular furnace to room temperature, take out the sample, wash it with concentrated hydrochloric acid (concentration 36 wt%) for 48 h, and then wash it with water until the solution is neutral. Then, transfer the sample to an oven and dry it at 80 °C for 12 h to obtain a hierarchical pore nitrogen-doped carbon material.

[0041] Take 1.2 g of the above-mentioned hierarchical pore nitrogen-doped carbon material and 0.018 g of ruthenium(III) chloride and disperse them in 100 mL of methanol respectively. Mix the two solutions thoroughly, then transfer them to a three-necked flask, and carry out reflux condensation at 65 °C for 18 h. After the reaction is completed, cool it naturally to room temperature, wash it with methanol, and dry it at 80 °C for 12 h to obtain a hierarchical pore nitrogen-doped carbon-supported ruthenium single-atom catalyst.

[0042] Take 0.6 g of the above-mentioned hierarchical pore nitrogen-doped carbon-supported ruthenium single-atom catalyst and disperse it in 50 mL of ethylene glycol. At the same time, disperse 0.021 g of ruthenium(III) chloride and 0.4 g of polyvinylpyrrolidone in 50 mL of ethylene glycol. Then, mix the two solutions thoroughly, transfer them to a three-necked flask, and carry out reflux condensation at 198 °C for 3 h. After the reaction is completed, cool it naturally to room temperature, wash it with ethanol, and dry it at 80 °C for 12 h to obtain a hierarchical pore nitrogen-doped carbon-supported ruthenium single-atom and cluster catalyst, denoted as Ru 1+NPs / HPNC-2. The Ru content in the catalyst accounts for 2% of the total mass of the catalyst.

[0043] Example 3 Mix 10 g of zeolitic imidazolate framework-8 material with 15 g of polyethylene glycol thoroughly and stir vigorously for 30 min. Then transfer the mixture to the center of a tubular furnace, using nitrogen with a flow rate of 80 mL / min as the carrier gas. Set the temperature of the tubular furnace to 900 °C and hold for 2 h. After that, cool the tubular furnace to room temperature, take out the sample, wash it with concentrated hydrochloric acid (concentration 36 wt%) for 48 h, and then wash it with water until the solution is neutral. Then transfer the sample to an oven and dry it at 80 °C for 12 h to obtain a hierarchically porous nitrogen-doped carbon material.

[0044] Take 1.2 g of the obtained hierarchically porous nitrogen-doped carbon material and 0.024 g of ruthenium(III) chloride, disperse them separately in 100 mL of methanol, mix the two solutions thoroughly, then transfer them to a three-necked flask, and reflux at 65 °C for 18 h. After the reaction ends, cool it naturally to room temperature, wash it with methanol, and dry it at 80 °C for 12 h to obtain a hierarchically porous nitrogen-doped carbon-supported ruthenium single-atom catalyst.

[0045] Take 0.6 g of the obtained hierarchically porous nitrogen-doped carbon-supported ruthenium single-atom catalyst and disperse it in 50 mL of ethylene glycol. At the same time, disperse 0.018 g of ruthenium(III) chloride and 0.4 g of polyvinylpyrrolidone in 50 mL of ethylene glycol. Then mix the two solutions thoroughly, transfer them to a three-necked flask, and reflux at 198 °C for 3 h. After the reaction ends, cool it naturally to room temperature, wash it with ethanol, and dry it at 80 °C for 12 h to obtain a hierarchically porous nitrogen-doped carbon-supported ruthenium single-atom and cluster catalyst, denoted as Ru 1+NPs / HPNC-3. The Ru content in the catalyst accounts for 2% of the total mass of the catalyst.

[0046] 1. Perform nitrogen physical adsorption-desorption characterization on the sample prepared in Example 2, and the results are as Figure 1 shown. As Figure 1 can be seen, the nitrogen adsorption-desorption isotherm of the Ru 1+NPs / HPNC-2 catalyst is a typical type-IV isotherm, and there is an obvious adsorption hysteresis loop. The type of the hysteresis loop is H4, which often appears in micro-mesoporous materials. The pore size distribution diagram also proves that the material has both micropores and mesopores.

[0047] 2. Perform XRD analysis on the sample prepared in Example 2, and the results are as Figure 2 shown. As Figure 2 can be seen, for the Ru 1+NPs / HPNC-2 catalyst prepared in the present invention, there is no obvious diffraction peak of crystalline Ru at 2θ = 44.6 °, indicating that the supported Ru has good dispersion.

[0048] 3. Perform aberration-corrected scanning transmission electron microscopy analysis on the sample prepared in Example 2, and the results are asFigure 3 As shown. From Figure 3 It can be seen that Ru single atoms on the hierarchically porous nitrogen-doped carbon material are distributed around Ru clusters. The cluster size is about 2 nm, and no Ru nano-metal particles are observed, which is consistent with the XRD results. The EDX mapping image shows that C, N, and Ru elements are uniformly dispersed.

[0049] 4. The sample prepared in Example 2 was subjected to XPS analysis, and the results are as Figure 4 shown. From Figure 4 It can be seen that the full XPS spectrum shows characteristic peaks of C, N, and Ru elements, which is consistent with the EDX mapping results. In addition, the fine spectrum of the Ru3p orbital shows that two characteristic peaks with binding energies of 462.3 eV and 484.5 eV correspond to Ru 0 's Ru3p 1 / 2 and Ru3p 3 / 2 . Two characteristic peaks with binding energies of 464.4 eV and 487.5 eV correspond to Ru δ⁺ 's Ru3p 1 / 2 and Ru3p 3 / 2 . The positively charged Ru δ⁺ may be due to the coordination effect between heteroatom N and Ru, which promotes the dispersion of Ru.

[0050] Comparative Example 1 10 g of zeolitic imidazolate framework-8 material was thoroughly mixed with 15 g of polyethylene glycol and stirred vigorously for 30 min. Then, the mixture was transferred to the center of a tubular furnace with nitrogen as the carrier gas at a flow rate of 80 mL / min. The temperature of the tubular furnace was set at 900 °C and maintained for 2 h. After that, the tubular furnace was cooled to room temperature, and the sample was taken out. It was washed with concentrated hydrochloric acid (concentration 36 wt%) for 48 h, and then washed with water until the solution was neutral. Then, the sample was transferred to an oven and dried at 80 °C for 12 h to obtain a hierarchically porous nitrogen-doped carbon material.

[0051] 1.2 g of the obtained hierarchically porous nitrogen-doped carbon material and 0.03 g of ruthenium chloride were respectively dispersed in 100 mL of methanol. The two solutions were thoroughly mixed and then transferred to a three-necked flask. The mixture was refluxed under condensation at 65 °C for 18 h. After the reaction ended, it was naturally cooled to room temperature, washed with methanol, and dried at 80 °C for 12 h to obtain a hierarchically porous nitrogen-doped carbon-supported ruthenium single-atom catalyst, denoted as Ru 1 / HPNC. The Ru content in the catalyst accounts for 1% of the total mass of the catalyst.

[0052] Comparative Example 2 Mix 10 g of zeolitic imidazolate framework-8 material with 15 g of polyethylene glycol thoroughly, and stir vigorously for 30 min. Then transfer the mixture to the center of a tubular furnace, using nitrogen with a flow rate of 80 mL / min as the carrier gas. Set the temperature of the tubular furnace to 900 °C and hold for 2 h. Then cool the tubular furnace to room temperature, take out the sample, wash it with concentrated hydrochloric acid (concentration 36 wt%) for 48 h, and then wash it with water until the solution is neutral. Then transfer the sample to an oven and dry it at 80 °C for 12 h to obtain a hierarchically porous nitrogen-doped carbon material.

[0053] Take 0.6 g of the obtained hierarchically porous nitrogen-doped carbon material and disperse it in 50 mL of ethylene glycol. At the same time, disperse 0.03 g of ruthenium chloride and 0.4 g of polyvinylpyrrolidone in 50 mL of ethylene glycol. Then mix the two solutions thoroughly, transfer them to a three-necked flask, and carry out condensation reflux at 198 °C for 3 h. After the reaction is completed, cool it naturally to room temperature, wash it with ethanol, and dry it at 80 °C for 12 h to obtain a hierarchically porous nitrogen-doped carbon-supported ruthenium nanocluster catalyst, denoted as Ru NPs / HPNC. The Ru content in the catalyst accounts for 2% of the total mass of the catalyst.

[0054] Comparative Example 3 Take 0.6 g of commercial activated carbon material and disperse it in 50 ml of deionized water. At the same time, disperse 0.03 g of ruthenium chloride in 50 ml of deionized water. Then mix the two solutions thoroughly, stir vigorously for 4 h, and then remove the water by rotary evaporation. Place the remaining powder in a tubular furnace, using a carrier gas of 10% hydrogen / 90% nitrogen by volume concentration, and carry out reduction treatment at 500 °C for 3 h to obtain an activated carbon-supported ruthenium cluster catalyst, denoted as Ru / AC. The Ru content in the catalyst accounts for 2% of the total mass of the catalyst.

[0055] Performance Evaluation of the Catalyst in Example 4 Samples: Examples 1-3, Comparative Examples 1-3 Method: Place 50 mg of the catalyst in a high-pressure reactor, and sequentially add 3 mmol of vanillin and 20 mL of isopropanol; after installing the reactor, replace the air with hydrogen three times to evacuate most of the air in the reactor; introduce hydrogen to keep the hydrogen pressure in the reactor at 2 MPa; adjust the temperature to 100 °C, start stirring at 500 rpm, and continue the reaction for 10 min. After the reaction, cool the reactor to room temperature, remove the reaction solution and place it in a centrifuge tube, and add dodecane as an internal standard. Remove the catalyst through a 0.45 μm filter head, and quantitatively analyze the obtained clear liquid by gas chromatography (Shimadzu 2014C). After separation using an HP-5 capillary column, the product is detected by an FID detector, and the conversion rate is calculated by the internal standard method, and the TOF value is calculated through a formula. The TOF value can reflect the intrinsic activity of the catalyst. In addition, the TOF value needs to be calculated at a relatively low conversion rate. The formulas for the conversion rate and TOF value are as follows: The results obtained are shown in Table 1.

[0056] Table 1 Intrinsic activities of different catalysts in Examples 1-3 and Comparative Examples 1-3 As can be seen from the results in Table 1, compared with the comparative samples Ru 1 / HPNC, Ru NPs / HPNC, and Ru / AC, the catalysts prepared according to the method of the present invention all exhibit excellent intrinsic activity (TOF value), and the reason for the excellent performance is closely related to the ruthenium structure on the catalyst.

[0057] For general single-atom catalysts and single-cluster catalysts, such as Ru 1 / HPNC and Ru NPs / HPNC, due to the single type of active sites, the activity of the catalyst is insufficient. Figure 5 And Figure 6 are the aberration-corrected scanning transmission electron microscopy images of Ru 1 / HPNC and Ru NPs / HPNC, respectively, showing a single type of active sites, simple ruthenium single atoms or ruthenium clusters. Conversely, as described above, the aberration-corrected scanning transmission electron microscopy image of the Ru 1+NPs / HPNC-2 sample prepared by the present invention shows that both ruthenium single atoms and clusters coexist on the hierarchical pore nitrogen-doped carbon material. This structural difference is the main reason for the excellent performance of the catalyst of the present invention.

[0058] Catalyst recovery experiment in Example 5 The stability of Ru 1+NPs / HPNC-2 prepared in Example 2 is as follows: Method: First, collect the reaction solution after the catalyst completes the performance test, and then use centrifugation to separate the catalyst from the reaction solution. After that, wash and dry the separated catalyst, and then place 50 mg of the recovered catalyst in a high-pressure reactor. Then, add 1 mmol of vanillin and 20 mL of isopropanol in sequence; after installing the reactor, displace it with hydrogen three times to evacuate most of the air in the reactor; introduce hydrogen to keep the hydrogen pressure in the reactor at 2 MPa; adjust the temperature to heat to 100 °C, turn on the stirrer to 500 rpm, and keep the reaction time for 3 h. After the reaction, cool the reactor to room temperature, remove the reaction solution and place it in a centrifuge tube, and add dodecane as an internal standard. Remove the catalyst through a 0.45 μm filter head, and perform quantitative analysis on the obtained clear liquid by gas chromatography (Shimadzu 2014C). After separation using an HP-5 capillary column, the product is detected by an FID detector, and the vanillin conversion rate and yield (vanillyl alcohol) are calculated by the internal standard method. The formula for calculating the yield is as follows: This operation was repeated 4 times, and the experimental results are shown in Table 2.

[0059] Table 2 Experimental results of the recovery of the catalyst in Example 2 It can be seen from the recovery experimental results in Table 2 that the Ru 1+NPs / HPNC-2 catalyst is easy to separate and recover, and the catalyst still has good catalytic performance after being used 4 times, and the conversion rate of vanillin remains above 98%. Therefore, the ruthenium single-atom and cluster catalyst Ru 1+NPs / HPNC-2 prepared in the present invention has good recyclability and cycle stability.

[0060] The above are only the preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims

1. A method for preparing a hierarchical porous nitrogen-doped carbon material having both ruthenium single atom and cluster sites, characterized in that: The steps include: 1) Mixing zeolite imidazole framework-8 material and polyethylene glycol in a mass ratio of 1:1.5, transferring the mixture to a tube furnace, using an inert gas as a carrier gas, and then subjecting the mixture to heat treatment. After the heat treatment, the mixture is naturally cooled to room temperature, and then acid-washed, water-washed, and dried to obtain a hierarchical porous nitrogen-doped carbon material. 2) The hierarchical porous nitrogen-doped carbon material obtained in step 1) and the ruthenium precursor are dispersed in methanol respectively, and then the two solutions are fully mixed, transferred to a three-necked flask, condensed and refluxed, and naturally cooled to room temperature after the reaction is completed, and washed and dried to obtain a hierarchical porous nitrogen-doped carbon material with a ruthenium single atom site; 3) The hierarchical porous nitrogen-doped carbon material with ruthenium single atom sites obtained in step 2) is dispersed in ethylene glycol, and the ruthenium precursor and polyvinyl pyrrolidone are dispersed in ethylene glycol at the same time. The two solutions are then fully mixed and transferred to a three-necked flask, condensed and refluxed. After the reaction is completed, it is naturally cooled to room temperature, washed and dried to obtain a hierarchical porous nitrogen-doped carbon material with both ruthenium single atom and cluster sites.

2. The method for preparing a hierarchical porous nitrogen-doped carbon material having both ruthenium single atom and cluster sites according to claim 1, characterized in that: The inert gas in step 1) includes any one of nitrogen, argon and helium; the flow rate of the carrier gas is 80 mL / min.

3. The method for preparing a hierarchical porous nitrogen-doped carbon material having both ruthenium single atom and cluster sites according to claim 1, characterized in that: The heat treatment temperature in step 1) is 900°C and the time is 2 h.

4. The method for preparing a hierarchical porous nitrogen-doped carbon material having both ruthenium single atom and cluster sites according to claim 1, characterized in that: Step 1) The pickling detergent is concentrated hydrochloric acid with a concentration of 36-38wt%.

5. The method for preparing a hierarchical porous nitrogen-doped carbon material having both ruthenium single atom and cluster sites according to claim 1, characterized in that: The ruthenium precursors in steps 2) and 3) are both ruthenium trichloride.

6. The method for preparing a hierarchical porous nitrogen-doped carbon material having both ruthenium single atom and cluster sites according to claim 1, characterized in that: In step 2), the amount of ruthenium precursor added is 0.2-1 wt% of the amount of hierarchical porous nitrogen-doped carbon material.

7. The method for preparing a hierarchical porous nitrogen-doped carbon material having both ruthenium single atom and cluster sites according to claim 1, characterized in that: In step 3), the amount of ruthenium precursor added is such that the metallic ruthenium contained in the precursor accounts for 1-1.8 wt % of the amount of the hierarchical porous nitrogen-doped carbon material having a ruthenium single atom site.

8. The method for preparing a hierarchical porous nitrogen-doped carbon material having both ruthenium single atom and cluster sites according to claim 1, characterized in that: The washing in steps 2) and 3) uses any one of methanol, ethanol, water and acetone as a washing agent.

9. A hierarchical porous nitrogen-doped carbon material having both ruthenium single atom and cluster sites, obtained by the preparation method according to any one of claims 1 to 8, characterized in that: In the hierarchical porous nitrogen-doped carbon material having both ruthenium single atom and cluster sites, metallic ruthenium accounts for 2 wt%.

10. Use of the hierarchical porous nitrogen-doped carbon material having both ruthenium single atom and cluster sites according to claim 9 as a catalyst in catalyzing the hydrogenation of vanillin to produce vanillyl alcohol.

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