A porous polymer-derived nitrogen-doped carbon supported bimetallic catalyst, and a preparation method and application thereof

Abstract

The present application belongs to the field of lignin depolymerization, and discloses a porous polymer-derived nitrogen-doped carbon-supported bimetallic catalyst, a preparation method and application thereof. In the present application, resorcinol, polyether, formaldehyde, 1,6-hexanediamine and 1,3,5-trimethylbenzene are mixed to obtain a porous polymer; then, chloropalladic acid solution and X metal salt solution are added to obtain a porous polymer-derived nitrogen-doped carbon-supported bimetallic catalyst, denoted as X / Pd-C; wherein X is Co or Cu; the loading amount of palladium is 1wt%-3wt%; and the loading amount of X metal is 0.5wt%-2wt%. The porous polymer-derived nitrogen-doped carbon-supported bimetallic catalyst of the present application has high conversion rate, high yield of phenolic acid monomer and good cyclic stability in lignin depolymerization.

Description

Technical Field

[0001] This invention belongs to the field of lignin depolymerization, and specifically relates to a nitrogen-doped carbon-supported bimetallic catalyst derived from a porous polymer, its preparation method, and its application. Background Technology

[0002] With societal development, the dwindling supply of fossil fuels is insufficient to meet human energy demands, making the search for alternatives urgent. Among numerous new energy sources, biomass energy is widely available and renewable, representing a high-quality sustainable energy source. Its use in the production of biofuels and chemicals can serve as a substitute for petroleum-derived products, reducing the consumption of fossil fuels. Lignin is the most abundant source of aromatic compounds in nature, giving it a significant advantage in the production of renewable aromatic products (ChemSusChem 2020, 13, 4181-4198). Therefore, the development and utilization of lignin has attracted widespread attention.

[0003] Lignin has a complex structure, primarily consisting of a three-dimensional amorphous polymer formed by three phenylpropane units—syringylphenylpropane (S), guaiacylphenylpropane (G), and p-hydroxyphenylpropane (H)—linked by C-C and CO bonds. This structural complexity significantly complicates its polymerization process. Various methods exist for lignin depolymerization, including acid catalysis, base catalysis, oxidation, and hydrogenolysis (Chem. Rev. 2015, 115, 11559-11624). Among these, hydrogenolysis offers advantages such as low oxygen content in the converted product, high conversion yield, and low coking rate, making it considered the most promising method for lignin depolymerization. In hydrogenolysis, the catalyst is indispensable, crucial for improving monomer yield, increasing product selectivity, and promoting lignin depolymerization. Therefore, finding an efficient and stable catalyst is of great significance for lignin depolymerization.

[0004] Li et al. (ACS Sustainable Chem. Eng. 2020, 8, 15685-15695) used La 3+ In studies on the depolymerization of lignin using doped Ni / MgO catalysts, results showed that compared with undoped catalysts, the yield of volatile products was significantly increased on La-doped Ni / MgO catalysts, while biochar formation was significantly inhibited. Hu et al. (Energy Fuels 2020, 34, 9754-9762) used a bimetallic catalyst, Ni... 50 Pd 50 / SBA-15 was used to depolymerize natural birch lignin. The results showed that the bimetallic catalyst exhibited higher catalytic activity than the monometallic catalyst under the same conditions, with a monophenol yield of 37.2 wt% obtained at 245 °C. Zeng et al. (Fuel Processing Technology 213(2021)106713) prepared a bimetallic catalyst Fe-Pd / HZSM-5 by impregnation for the hydrogenolysis of lignin. The study showed that the presence of Fe promoted the dispersion of Pd, and there was a synergistic effect between the bimetals. This catalyst had good catalytic activity for the hydrogenolysis of lignin. Therefore, the preparation of bimetallic catalysts by introducing a second metal is beneficial to the dispersion of the metal, and the synergistic effect between the metals provides a strategy for the efficient depolymerization of lignin.

[0005] The most commonly used catalysts for lignin hydrogenolysis are metal-supported carriers such as activated carbon, alumina, and silica. However, traditional catalyst supports suffer from low product yield and selectivity, carbon buildup, and uneven metal dispersion. Therefore, finding an efficient catalyst support for supporting metal-catalyzed lignin depolymerization is crucial. In recent years, the development of nitrogen-doped carbon materials has provided new ideas for the design of lignin depolymerization catalysts. Nitrogen atoms on nitrogen-doped carbon supports provide anchoring sites for metal nanoparticles, enhancing the interaction between the metal and the support and improving metal dispersion. In addition, the emergence of bimetallic catalysts has also provided a new strategy for lignin depolymerization; the synergistic effect between the two metals can help improve catalytic activity. Summary of the Invention

[0006] In order to overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for preparing a porous polymer-derived nitrogen-doped carbon-supported bimetallic catalyst.

[0007] Another object of the present invention is to provide a nitrogen-doped carbon-supported bimetallic catalyst derived from a porous polymer prepared by the above method.

[0008] The catalyst of this invention is a nitrogen-doped carbon-supported bimetallic catalyst derived from a nitrogen-containing polymer, polybenzoxazine. This nitrogen-doped carbon material facilitates the loading of metal particles. The introduction of a second metal on top of Pd results in a synergistic effect between the two metals, which is beneficial for improving catalytic performance. Furthermore, the introduction of the second metal reduces the loading of the noble metal Pd, thus helping to lower the cost of the catalyst.

[0009] Another object of the present invention is to provide the application of the above-mentioned porous polymer-derived nitrogen-doped carbon-supported bimetallic catalyst in the depolymerization of lignin.

[0010] The objective of this invention is achieved through the following solution:

[0011] A method for preparing a porous polymer-derived nitrogen-doped carbon-supported bimetallic catalyst includes the following steps:

[0012] (1) Add resorcinol (C6H6O2), polyether (F127), formaldehyde, and 1,6-hexanediamine (C6H) 16 N2)1,3,5-trimethylbenzene (TMB) was added to water and mixed evenly. The mixture was heated to react, centrifuged, and dried to obtain a porous polymer, namely TMB-modified polybenzoxazine.

[0013] (2) Disperse the porous polymer in water, add chloropalladium acid (H2PdCl4) solution and X metal salt solution, stir, centrifuge, dry and calcine to obtain a nitrogen-doped carbon-supported bimetallic catalyst derived from the porous polymer, denoted as X / Pd-C; where X is Co or Cu.

[0014] The molar ratio of resorcinol (C6H6O2), polyether (F127), formaldehyde, 1,6-hexanediamine and 1,3,5-trimethylbenzene (TMB) in step (1) is 1-1.5:0.004-0.006:2-3:0.25-0.375:0.3-1.26.

[0015] The mass ratio of resorcinol to water in step (1) is 0.1648 g: 300-320 mL; the water is deionized water.

[0016] The ambient temperature for uniform mixing in step (1) is 20-30℃, preferably 25℃; the mixing time is 80-100min, preferably 80min.

[0017] The heating reaction in step (1) is carried out at 75-85°C for 18-30 hours.

[0018] After centrifugation in step (1), the centrifuge is washed with water and ethanol. The centrifugation speed is 11,000 to 13,000 rpm, preferably 12,000 rpm, and the time is 5 to 7 minutes.

[0019] The drying temperature in step (1) is 50-60℃ and the time is 18-24h.

[0020] In step (2), the mass-to-volume ratio of the porous polymer to water is 0.1–0.15 g: 2–3 mL; the dispersion is ultrasonic dispersion, and the ultrasonic dispersion time is 15–20 min.

[0021] The concentration of the chloropalladium acid solution (H2PdCl4) in step (2) is 0.01-0.03 mol / L, preferably 0.02-0.03 mol / L; the concentration of the X metal salt solution is 0.005 mol / L-0.02 mol / L.

[0022] The amount of chloropalladium acid solution used in step (2) satisfies the following: the palladium loading in the nitrogen-doped carbon-supported bimetallic catalyst derived from the porous polymer is 1 wt% to 3 wt%, preferably 1 wt%;

[0023] The amount of X metal salt solution used in step (2) satisfies the following condition: the loading amount of X metal in the nitrogen-doped carbon-supported bimetallic catalyst derived from porous polymer is 0.5wt% to 2wt%.

[0024] The X metal salt mentioned in step (2) is at least one of copper chloride, copper nitrate, cobalt chloride, and cobalt nitrate.

[0025] The stirring temperature in step (2) is room temperature; the stirring time is 2 to 4 hours.

[0026] The drying temperature in step (2) is 50-60°C, and the drying time is 24-36 hours.

[0027] The calcination temperature in step (2) is 450-550℃, the heating rate is 3-5℃ / min, and the time is 2-4h; the calcination is carried out in a nitrogen or inert gas atmosphere, and the flow rate of the nitrogen or inert gas atmosphere is 30-50mL / min.

[0028] The above preparation method yields a porous polymer-derived nitrogen-doped carbon-supported bimetallic catalyst.

[0029] Application of the above-mentioned porous polymer-derived nitrogen-doped carbon-supported bimetallic catalyst in lignin depolymerization.

[0030] The application includes the following steps:

[0031] The nitrogen-doped carbon-supported bimetallic catalyst derived from the above porous polymer, lignin, and solvent were placed in a high-pressure reactor and reacted for 1 to 9 hours at a hydrogen pressure of 0–3.5 MPa and a temperature of 250–290 °C. Solid-liquid separation was then performed to obtain the lignin depolymerization product.

[0032] The mass-volume ratio of the porous polymer-derived nitrogen-doped carbon-supported bimetallic catalyst, lignin, and solvent is 0.1–0.2 g: 0.2–0.4 g: 35–45 mL, more preferably 0.1 g: 0.2 g: 35 mL.

[0033] The solvent is a mixed solution of ethanol and isopropanol, with a volume ratio of ethanol to isopropanol of 1:1 to 4:3.

[0034] Before the reaction, the reactor was purged with nitrogen 3 to 4 times. After the reaction, the reactor was placed in cold water and rapidly cooled to room temperature.

[0035] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0036] This invention utilizes the porous polymer polybenzoxazine as a support, and loads Pd, Co, and Cu using a simple impregnation method, followed by calcination to prepare a nitrogen-doped carbon-supported bimetallic catalyst derived from the porous polymer. Polybenzoxazine is a nitrogen-containing polymer; its use as a support facilitates the anchoring of metal nanoparticles. This invention introduces Co and Cu as second metals to modify Pd, promoting electron transfer in Pd. The synergistic effect between the two metals significantly improves catalytic performance, thereby promoting the depolymerization of lignin. When this porous polymer-derived nitrogen-doped carbon-supported bimetallic catalyst is used for lignin depolymerization, it exhibits superior catalytic performance. At 280℃, 2.5 MPa H2, and a loading of 1 wt% for both Pd and Co, the conversion rate of lignin in a mixed solution of ethanol and isopropanol reaches 93.65% after 5 hours of reaction, with a high phenolic acid monomer yield of 36.38%, and a yield of 22.13% for the single product 4-hydroxy-3,5-dimethoxyphenylacetic acid, exhibiting a selectivity of 60.8%. After four cycles of catalyst recycling, the monomer yield remained at 33.73%, demonstrating excellent recycling performance. This indicates that the porous polymer-derived nitrogen-doped carbon-supported bimetallic catalyst of this invention exhibits superior catalytic performance in lignin depolymerization. Attached Figure Description

[0037] Figure 1 The images are SEM and TEM images of the catalysts obtained in Comparative Example 1 and Example 2. The SEM images are: (a) Pd-C, (b) 1Co / Pd-C; and (c)-(g) 1Co / Pd-C. The TEM images are: (c) TEM image, (d) HAADF-STEM image, and (e)-(g) elemental distribution diagrams of C, N, and O.

[0038] Figure 2 The images show the GC-MS diagrams of the products obtained after catalytic depolymerization of lignin in Comparative Example 1 and Example 2, where (a) are the products obtained after catalytic depolymerization of lignin using catalysts Pd-C and 1Co / Pd-C, respectively; and (b) are the peak positions of the single product 4-hydroxy-3,5-dimethoxyphenylacetic acid.

[0039] Figure 3 XPS plots of the catalysts obtained in Comparative Example 1 and Example 2, including (a) Pd 3d, (b) Co 2P of 1Co / Pd-C, (c) Pd 3d of Pd-C, and (d) comparison of Pd 3d binding energies in 1Co / Pd-C and Pd-C catalysts.

[0040] Figure 4 This is a graph showing the total yield of monophenols obtained after cycling the catalyst of Example 2 under the conditions of Example 1. Detailed Implementation

[0041] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0042] Unless otherwise specified, all reagents used in the examples are commercially available.

[0043] Polyether F127: purchased from Sigma-Aldrich, with a relative molecular mass of 12600 g / mol;

[0044] Formaldehyde solution: purchased from Guangzhou Chemical Reagent Factory, concentration 37wt%.

[0045] In the examples, the liquid phase products of lignin depolymerization were determined by gas chromatography-mass spectrometry (GC-MS). The calculation method for GC-MS detection used the internal standard method, with n-dodecane as the internal standard. The nitrogen-doped carbon-supported bimetallic catalyst derived from the porous polymer was characterized by ultra-high resolution field emission electron microscopy (SU8220), field emission transmission electron microscopy (JEM2100F), and X-ray photoelectron spectroscopy (ThermoFisher Nexsa).

[0046] In the examples and comparative examples, the yield of aromatic acids / phenols in the depolymerization products was calculated using the formula: Y = mass of target product / mass of added lignin × 100%; the conversion rate of lignin was calculated using the formula: X = (mass of added lignin - mass of remaining lignin) / mass of added lignin × 100%; the selectivity of 4-hydroxy-3,5-dimethoxyphenylacetic acid was calculated using the formula: S = mass of 4-hydroxy-3,5-dimethoxyphenylacetic acid / mass of phenolic acid monomer × 100%.

[0047] Example 1

[0048] At 25°C, 0.1648 g resorcinol, 0.0751 g polyether F127, 220 μL formaldehyde, 750 μL of 58 mg / mL 1,6-hexanediamine aqueous solution, and 175 μL TMB were sequentially added to 300 mL of water. After stirring and dissolving for 80 min, the mixture was reacted at 80°C for 24 h. After the reaction was completed, the mixture was centrifuged at 12000 rpm for 7 min, washed three times with deionized water and once with ethanol, and dried in a forced-air drying oven at 50°C for 18 h to obtain a porous polymer, namely TMB-modified polybenzoxazine.

[0049] Weigh 0.1 g of porous polymer, add 3 mL of deionized water, and ultrasonically disperse for 20 min. Weigh 0.0027 g of CuCl2·2H2O, dissolve it in 2 mL of deionized water, and add it to the ultrasonically dispersed porous polymer. Then add 316 μL of 0.03 mol / L H2PdCl4 aqueous solution, stir and impregnate at room temperature for 2 h, centrifuge, and dry in a 50℃ forced-air drying oven for 24 h. Calcination is carried out under a nitrogen atmosphere (temperature program: increase to 400℃ at 3℃ / min, hold for 1 h, then increase to 500℃ at 5℃ / min, hold for 2 h) to obtain a nitrogen-doped carbon-supported bimetallic catalyst derived from the porous polymer with 1 wt% Pd and 1 wt% Cu loading, denoted as 1Cu / Pd-C.

[0050] Example 2

[0051] This embodiment is the same as Example 1 except for the following conditions: the added metal salt X is 0.0041g CoCl2·6H2O, and the resulting catalyst with a Pd loading of 1wt% and a Co loading of 1wt% is denoted as 1Co / Pd-C.

[0052] Example 3

[0053] This embodiment is the same as Example 2 except for the following conditions: 0.002g CoCl2·6H2O is added to obtain a catalyst with a Pd loading of 1wt% and a Co loading of 0.5wt%, which is denoted as 0.5Co / Pd-C.

[0054] Example 4

[0055] This embodiment is the same as Example 2 except for the following conditions: 0.0061g of CoCl2·6H2O is added to obtain a catalyst with a Pd loading of 1wt% and a Co loading of 1.5wt%, which is denoted as 1.5Co / Pd-C.

[0056] Comparative Example 1

[0057] This comparative example is the same as Example 1 except that: no second metal is loaded, that is, no copper chloride solution is added, and the resulting catalyst with a Pd loading of 1 wt% is denoted as Pd-C.

[0058] Comparative Example 2

[0059] This comparative example is the same as Example 1 except for the following conditions: the added X metal salt is 0.0049g FeCl3·6H2O, and the resulting catalyst with a Pd loading of 1wt% and a Fe loading of 1wt% is denoted as 1Fe / Pd-C.

[0060] Comparative Example 3

[0061] This comparative example is the same as Example 1 except for the following conditions: the added X metal salt is 0.0041g NiCl2·6H2O, and the resulting catalyst with a Pd loading of 1wt% and a Ni loading of 1wt% is denoted as 1Ni / Pd-C.

[0062] Comparative Example 4

[0063] This comparative example is the same as Example 2 except that: no palladium is loaded, that is, no H2PdCl4 aqueous solution is added, and the resulting catalyst with a Co loading of 1wt% is denoted as 1Co-C.

[0064] Application Example 1: Application of the catalysts obtained in Examples 1-4 and Comparative Examples 1-4 in lignin depolymerization

[0065] Add 0.2 g lignin, 0.1 g catalyst (1Fe / Pd-C, 1Co / Pd-C, 1Ni / Pd-C, 1Cu / Pd-C, Pd-C, 0.5Co / Pd-C, 1.5Co / Pd-C, 1Co-C), and 35 mL solvent (V 乙醇 V 异丙醇 =4:3) was added to a high-pressure reactor, and 1 MPa of N2 was introduced to replace the air in the reactor. This process was repeated 3 times. After the pressure was reduced to atmospheric pressure, 2.5 MPa of H2 was introduced. After checking that the reactor was airtight with a hydrogen detector, the temperature was raised to 280℃ and the reaction was carried out for 5 hours. After the reaction was completed, the reactor was placed in cold water for rapid cooling. The gas was released in a fume hood, and the solid and liquid phases were separated by filtration. 5 mL of the filtrate was diluted with ethyl acetate, and the test solution was prepared using the internal standard method. Then, GC-MS analysis was performed. The yield of phenolic acid, the selectivity and yield of single products, and the conversion rate of lignin in the liquid product are shown in Tables 1 and 2.

[0066] Table 1. Effects of different metals on lignin depolymerization

[0067]

[0068] Table 2 Effect of different Co loading on lignin depolymerization

[0069]

[0070] Table 1 shows the different catalytic performances of the monometallic and bimetallic catalysts. Compared with Comparative Example 1, the addition of Fe and Ni in Comparative Examples 2 and 3 significantly increased the phenolic acid monomer yield due to the synergistic effect of the bimetallic catalysts, increasing from 22.41 wt% in the monometallic catalyst to 29.14 wt% (Fe / Pd) and 33.69 wt% (Ni / Pd). However, the selectivity of Fe and Ni for the single product 4-hydroxy-3,5-dimethoxyphenylacetic acid decreased compared to the monometallic catalyst. This is because the bimetallic catalysts generated more other monomeric products under synergistic effects, leading to a decrease in the selectivity of 4-hydroxy-3,5-dimethoxyphenylacetic acid as the phenolic acid monomer yield increased. Compared with Comparative Examples 1-3, the addition of Cu and Co in Examples 1 and 2 not only promoted the increase in phenolic acid yield and the selectivity of the single product 4-hydroxy-3,5-dimethoxyphenylacetic acid, but also promoted the increase in lignin conversion. Among them, Co / Pd showed the best bimetallic synergistic effect.

[0071] Application Example 2: Effect of Different Hydrogen Contents on Lignin Depolymerization

[0072] 0.2 g lignin, 0.1 g catalyst (1Co / Pd-C prepared in Example 2), and 35 mL solvent (V 乙醇 V 异丙醇 =4:3) was added to a high-pressure reactor, and 1 MPa of N2 was introduced to replace the air in the reactor. This process was repeated 3 times. After venting to atmospheric pressure, 0.5, 1.5, 2.5, and 3.5 MPa of H2 were introduced respectively. After checking the airtightness of the reactor with a hydrogen detector, the temperature was raised to 280℃ and the reaction was carried out for 5 hours. After the reaction was completed, the reactor was placed in cold water for rapid cooling. The gas was released in a fume hood, and the solid and liquid phases were separated by filtration. 5 ml of the filtrate was diluted with ethyl acetate, and the test solution was prepared using the internal standard method. Then, GC-MS analysis was performed. The yield of phenolic acid, the selectivity and yield of single products, and the conversion rate of lignin of the obtained liquid products are shown in Table 3.

[0073] Table 3. Effects of different hydrogen contents on lignin depolymerization

[0074]

[0075] like Figure 1 As shown in (a) and (b), the morphology of the nitrogen-doped carbon-supported monometallic Pd catalyst is unchanged compared with that of the nitrogen-doped carbon-supported bimetallic Co / Pd catalyst; both are regular spherical structures. Figure 1 (c) is a transmission electron microscope image. At this magnification, the metal can be seen to be uniformly dispersed, and the HAADF-STEM image (d) also clearly shows that the metal is uniformly dispersed on the support.

[0076] Figure 2(a) shows the gas chromatography-mass spectrometry (GC-MS) chromatograms of the liquid products obtained after lignin depolymerization catalyzed by nitrogen-doped carbon-supported monometallic Pd (Comparative Example 1) and bimetallic Co / Pd (Example 2), respectively. Calculations showed that the bimetallic catalyst yielded a higher yield of the depolymerized product than the monometallic catalyst. The yield of phenolic acid monomers obtained after catalytic conversion by the monometallic Pd-C catalyst was 22.41 wt%, while the yield of phenolic acid monomers obtained by the bimetallic catalyst Co / Pd-C was 36.38 wt%, indicating that the catalytic performance of the bimetallic catalyst was significantly better than that of the monometallic catalyst. Figure 2 Image (b) is the GC-MS peak position diagram of the pure substance 4-hydroxy-3,5-dimethoxyphenylacetic acid. Figure 2 As shown in (a), the main product in the depolymerization product is 4-hydroxy-3,5-dimethoxyphenylacetic acid.

[0077] Yield calculation: Figure 2 Substance 1 in (a) is the internal standard n-dodecane, and the internal standard method is used for calculation. Except for 1, which is the internal standard, all other substances marked in the figure are phenolic acid monomers. The phenolic acid yield mentioned above is the total yield of peaks 2-12. The internal standard method is calculated as: m1 / m2 = K(A1 / A2).

[0078] m1: Mass of the target product; m2: Mass of the internal standard; K: Proportionality constant; A1: Peak area of ​​the target product; A2: Peak area of ​​the internal standard.

[0079] Figure 3 XPS plots of the catalysts obtained in Comparative Example 1 and Example 2 are shown, where (a) is Pd 3d in 1Co / Pd-C, (b) is Co 2P in 1Co / Pd-C, (c) is Pd 3d in Pd-C, and (d) is a comparison of the Pd 3d binding energies in the 1Co / Pd-C and Pd-C catalysts. Through comparison... Figure 3 In the study (d), it was found that the electron binding energy of the Pd 3d peak decreased by 0.18 eV after Co doping in the bimetallic catalyst, which was due to electron transfer between Pd and Co.

[0080] The catalyst obtained in Example 2 was used to depolymerize lignin according to the method in Application Example 1. The catalyst was then separated by filtration, and the remaining lignin was washed away with tetrahydrofuran. After drying, the lignin depolymerization experiment was repeated under the conditions of Application Example 1, and this cycle was repeated. The results are as follows... Figure 4As shown, the phenolic acid yield was 36.38% after the first use of the catalyst; 35.73% after the first cycle (i.e., the second use of the catalyst); 35.63% after the second cycle (the third use of the catalyst); 34.57% after the third cycle (the fourth use of the catalyst); and remained at 33.73% after the fourth cycle (the fifth use of the catalyst). This demonstrates that the catalyst exhibits excellent cycle stability.

[0081] As shown in Comparative Examples 1-3 and Examples 1-2 above, the catalytic performance of the porous polymer-derived nitrogen-doped carbon-supported bimetallic catalysts Co / Pd and Cu / Pd is superior to that of supported single-metal Pd, indicating that the synergistic effect between the bimetals is beneficial to promoting the depolymerization of lignin, and the best depolymerization effect is observed when the second metal is Co. The results of Comparative Examples 1, 4, and Examples 2-4 show that the catalytic performance of single-metal Pd or single-metal Co is inferior to that of bimetallic Co / Pd. In summary, the modified polybenzoxazine-derived nitrogen-doped carbon-supported bimetallic Co / Pd catalyst exhibits a synergistic effect between the bimetals, promoting the depolymerization of lignin and demonstrating superior depolymerization effect, with a monomer yield of 36.38%, a yield of the single product 4-hydroxy-3,5-dimethoxyphenylacetic acid of 22.13%, and a selectivity of 60.83%.

[0082] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. The application of a porous polymer-derived nitrogen-doped carbon-supported bimetallic catalyst in the depolymerization of lignin, characterized in that, The method for preparing the catalyst includes the following steps: (1) Resorcinol, polyether, formaldehyde, 1,6-hexanediamine and 1,3,5-trimethylbenzene were added to water in sequence and mixed evenly. The mixture was heated to react, centrifuged and dried to obtain a porous polymer. (2) The porous polymer is dispersed in water, and chloropalladium acid solution and X metal salt solution are added. The mixture is stirred, centrifuged, dried and calcined to obtain a nitrogen-doped carbon-supported bimetallic catalyst derived from the porous polymer, denoted as X / Pd-C; where X is Co or Cu. The molar ratio of resorcinol, polyether, formaldehyde, 1,6-hexanediamine and 1,3,5-trimethylbenzene in step (1) is 1~1.5:0.004~0.006:2~3:0.25~0.375:0.3~1.26; The concentration of the chloropalladium acid solution in step (2) is 0.01~0.03 mol / L; the concentration of the X metal salt solution is 0.005 mol / L~0.02 mol / L; The metal salt X mentioned in step (2) is at least one of copper chloride, copper nitrate, cobalt chloride, and cobalt nitrate; The amount of chloropalladium acid solution used in step (2) satisfies the following condition: the palladium loading in the nitrogen-doped carbon-supported bimetallic catalyst derived from the porous polymer is 1 wt%; The amount of metal salt solution used in step (2) satisfies the following: the loading of metal X in the nitrogen-doped carbon-supported bimetallic catalyst derived from porous polymer is 0.5wt%~2wt%; The calcination temperature in step (2) is 450~550℃, the heating rate is 3~5℃ / min, and the time is 2~4h; the calcination is carried out in a nitrogen or inert gas atmosphere, and the flow rate of the nitrogen or inert gas atmosphere is 30~50mL / min. The application includes the following steps: The above-mentioned porous polymer-derived nitrogen-doped carbon-supported bimetallic catalyst, lignin and solvent were placed in a high-pressure reactor and reacted for 1 to 9 hours at a hydrogen pressure of 0 to 3.5 MPa and a temperature of 250 to 290 °C. Solid-liquid separation was performed to obtain the lignin depolymerization product. The mass-to-volume ratio of the porous polymer-derived nitrogen-doped carbon-supported bimetallic catalyst, lignin, and solvent is 0.1–0.2 g : 0.2–0.4 g : 35–45 mL.

2. The application according to claim 1, characterized in that: In step (1), the mass ratio of resorcinol to water is 0.1648 g: 300~320 mL; the water is deionized water.

3. The application according to claim 1, characterized in that: The ambient temperature for uniform mixing in step (1) is 20~30℃; the mixing time is 80~100min. The heating reaction in step (1) is carried out at 75~85℃ for 18~30h; The drying temperature in step (1) is 50-60℃ and the time is 18-24h.

4. The application according to claim 1, characterized in that: The ambient temperature for uniform mixing in step (1) is 25°C; the mixing time is 80 min.

5. The application according to claim 1, characterized in that: In step (2), the mass-to-volume ratio of the porous polymer to water is 0.1-0.15 g: 2-3 mL; the dispersion is ultrasonic dispersion, and the ultrasonic dispersion time is 15-20 min.

6. The application according to claim 1, characterized in that: The stirring temperature in step (2) is room temperature; the stirring time is 2~4 hours. The drying temperature in step (2) is 50-60℃ and the drying time is 24-36h.

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