A modified ni-mof-74 catalyst, its preparation method and application in lignin depolymerization

Abstract

A preparation method of modified Ni-MOF-74, pyrolyzing Ni-MOF-74 under the protection of hydrogen-nitrogen mixed gas at a temperature of 300-450 DEG C for 60-240 min. A lignin depolymerization method is also disclosed, using the modified Ni-MOF-74 as a catalyst for hydrogen reduction depolymerization reaction of biomass raw material containing lignin. The mass ratio of the modified Ni-MOF-74 to the biomass raw material is 5-25:100. The depolymerization reaction is carried out in a methanol solvent. The application uses MOF-74 as a precursor to improve the stability of the material by heat treatment, and at the same time, the defect structure of the material is regulated, a new catalyst suitable for preferential depolymerization of bagasse lignin is prepared, which not only retains the structural advantages of MOFs material, but also solves the stability defect of pure MOFs. In the depolymerization of bagasse, it shows better monomer yield and unique selectivity to ester monomers than industrial Ru / C. The lignin depolymerization method can realize nearly 48% total monomer yield under relatively mild conditions, and the catalytic efficiency and controllability of energy consumption are considered.

Description

Technical Field

[0001] This invention belongs to the field of biomass application technology, specifically a modified Ni-MOF-74 catalyst, its preparation method, and its application in lignin depolymerization. Background Technology

[0002] Bagasse is the world's largest agricultural processing byproduct, and the large amount of lignin produced in it (accounting for 20%–25%) has long been underutilized. Traditional papermaking processes primarily utilize cellulose, with the extracted lignin mostly used for energy recovery through combustion power generation; while emerging biomass refining processes continue this cellulose-first approach, similarly resulting in low lignin utilization efficiency. The unique chemical structure of lignin makes it a promising candidate for producing high-value-added fine chemicals through depolymerization. By efficiently and selectively breaking specific chemical bonds in lignin, highly selective extraction of target products can be achieved. Numerous methods exist for lignin depolymerization, with reductive depolymerization showing the greatest potential. Metal-organic frameworks (MOFs) are a class of novel porous crystalline materials formed by the self-assembly of metal ions or metal clusters (metal nodes) and organic ligands through coordination bonds. They possess unique advantages such as controllable pore structure, ultra-high specific surface area, abundant active sites, and structural designability, showing broad application prospects in the field of lignin reduction and depolymerization. However, MOF materials often suffer from poor thermal stability, poor solvent resistance, and easy ligand dissolution, which greatly limits the application of MOFs in the catalytic depolymerization of lignin. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a modified Ni-MOF-74 catalyst, its preparation method, and its application in lignin depolymerization.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A modified Ni-MOF-74, wherein the modified Ni-MOF-74 satisfies any one or more of the following (a), (b), (c), (d), or (f): (a) the X-ray powder diffraction pattern measured using Cu Kα radiation at λ = 1.5406 Å has diffraction peaks at 2θ values ​​of 2θ ≈ 44.5°±0.2°, 51.8°±0.2°, and 76.3°±0.2°, respectively, belonging to the (111), (200), and (220) crystal planes of standard face-centered cubic Ni0, and the peak signals are weakened compared to the characteristic peak signals of the original Ni-MOF-74 at 2θ = 6.8°±0.2° and 11.7°±0.2°; (b) in the Fourier transform infrared spectrum, in the range of 500–800 cm⁻¹… -1 The absorption band in the range belongs to Ni. 2+The Ni-O stretching vibration formed with the carboxyl oxygen of the ligand; the intensity of this peak is weakened compared to the original Ni-MOF-74, preferably weakened to below 60%; in the 1200-1600 cm⁻¹ range. -1 The absorption band in this region is attributed to CO stretching and C=C vibrations of the aromatic ring in the organic ligands; the intensity of this peak is reduced compared to the original Ni-MOF-74, preferably reduced to below 60%; in the 1600-1700 cm⁻¹ range... -1 The absorption band in the range is attributed to the C=O stretching vibration of the coordinating carboxyl group; the intensity of this peak is weakened compared to the original Ni-MOF-74, preferably reduced to below 60%; in the 2500-3500 cm⁻¹ range... -1 The absorption band in the range includes the OH and aromatic CH stretching vibrations of the DHTP ligand; the intensity of this peak is weakened compared to the original Ni-MOF-74, preferably weakened to below 60%; (c) the mass fraction of Ni element measured by inductively coupled plasma atomic emission spectrometry is 65.0–70.0 wt%; (d) a large number of uniformly distributed fine cracks and pores are observed on the surface of a single prism and at its junctions by scanning electron microscopy; (e) a large number of uniformly sized and higher-contrast nanoparticles are clearly observed on the surface and inside the framework by transmission electron microscopy, the nanoparticles being Ni element metal nanoparticles, or the corresponding energy dispersive X-ray spectroscopy surface scan showing that metallic Ni is anchored on the carbonized framework in a highly dispersed nanoscale state; (f) the BET specific surface area is 100–115 m². 2 / g, average pore size 6.5-7.5 nm, total pore volume 0.15-0.20 cm³. 3 / g. The above parameters of the modified Ni-MOF-74 can be controlled within a certain range according to the method of the present invention. Typical values ​​are as shown in the data obtained in the specific embodiments. Due to the acceptable fluctuations in the measurement and preparation process, the above parameters should be understood to include a range of reasonable error.

[0005] A method for preparing modified Ni-MOF-74 involves pyrolyzing Ni-MOF-74 under a protective atmosphere of hydrogen-nitrogen mixture at a temperature of 280-450 °C for 60-240 min, wherein the hydrogen-nitrogen mixture contains 3-8% hydrogen by volume and the remainder is nitrogen.

[0006] The modified Ni-MOF-74 is used as a catalyst in the depolymerization of lignin.

[0007] A method for depolymerizing lignin, using the modified Ni-MOF-74 described in claim 1 as a catalyst, to carry out a hydrogen reduction depolymerization reaction on extracted lignin or lignin-containing biomass raw materials.

[0008] The modified Ni-MOF-74 is added at a mass ratio of 5-25:100 to the biomass feedstock. The depolymerization reaction uses methanol as the solvent, and the amount of solvent added is calculated based on the mass of the biomass feedstock, at a ratio of 60-80 L of solvent per kilogram of biomass feedstock. The hydrogen pressure is 0.5-2 MPa. The temperature of the depolymerization reaction is 225-275℃. The time of the depolymerization reaction is 1-4 h. The biomass feedstock is sugarcane bagasse, eucalyptus, beech, fir, pine, or birch.

[0009] The lignin depolymerization method includes the following steps: (1) weighing biomass raw materials, catalysts and solvents according to proportions and mixing them evenly in a high-temperature and high-pressure reactor; (2) pressurizing the reactor to the depolymerization pressure using hydrogen and then depressurizing it to completely remove the air in the reactor, and then pressurizing the reactor to the depolymerization pressure using hydrogen; (3) heating the reactor to the depolymerization temperature to carry out the depolymerization reaction.

[0010] Compared with the prior art, the present invention has the following beneficial effects: This invention uses MOF-74 as a precursor and improves the material's stability through heat treatment while simultaneously controlling its defect structure to prepare a novel catalyst adapted for the preferential depolymerization of lignin in bagasse. This catalyst retains the structural advantages of MOFs while overcoming the stability defects of pure MOFs, providing a new approach for the efficient depolymerization of lignin. The XCNi-MOF-74 series catalysts exhibit superior monomer yields and unique selectivity for ester monomers compared to industrial Ru / C catalysts in the depolymerization of RCF in bagasse. Systematic optimization of reaction conditions shows that this catalytic system can achieve a total monomer yield of nearly 48% under relatively mild conditions, balancing catalytic efficiency and controllable energy consumption. Attached Figure Description

[0011] Figure 1 This is a schematic diagram illustrating the preparation of Ni-MOF-74 and XCNi-MOF-74 series catalysts.

[0012] Figure 2 Thermogravimetric analysis curves for Ni-MOF-74.

[0013] Figure 3 Thermogravimetric analysis curves of Ni-MOF-74 are shown.

[0014] Figure 4 Isothermal adsorption-desorption curves (a) and pore size distribution curves (b) of Ni-MOF-74 and XCNi-MOF-74 series catalysts are shown.

[0015] Figure 5 Ammonia temperature-programmed chemisorption-desorption curves for Ni-MOF-74 and XCNi-MOF-74 series catalysts.

[0016] Figure 6 The XRD patterns of Ni-MOF-74 and XCNi-MOF-74 series catalysts are shown.

[0017] Figure 7 The images show the scanning electron microscope (SEM) analysis results from Example 6. In the figures, (a) is the SEM image of Ni-MOF-74 at 300 nm; (b) is the SEM image of 300C Ni-MOF-74 at 500 nm; (c) is the SEM image of Ni-MOF-74 at 200 nm; (e) is the elemental plane distribution map of Ni-MOF-74; and (f) is the elemental plane distribution map of 300C Ni-MOF-74.

[0018] Figure 8 The figures show the TEM and HR-TEM analysis results from Example 7. In the figures, (a) is the TEM image of Ni-MOF-74; (b) is the TEM image of 300°C Ni-MOF-74; (c) is the TEM image of 550°C Ni-MOF-74; (d) is the energy dispersive spectroscopy (EDS) surface scan image of Ni-MOF-74; (e) is the EDS surface scan image of 300°C Ni-MOF-74; (f) is the EDS surface scan image of 550°C Ni-MOF-74; and (g) is the Ni content in 300°C Ni-MOF-74. 0 (111) crystal plane image; (h) Ni in 300CNi-MOF-74 0 (200) crystal plane image; (i) Ni-MOF-74 at 300C 0 (111) Image of the coexistence interface between the NiO(200) crystal plane and the NiO(200) crystal plane.

[0019] Figure 9 XPS full-spectrum spectra of Ni-MOF-74 and XCNi-MOF-74 series catalysts are shown in the figures. (a) XPS full-spectrum spectrum of Ni-MOF-74; (b) XPS full-spectrum spectrum of 300CNi-MOF-74; (c) XPS full-spectrum spectrum of 350CNi-MOF-74; (d) XPS full-spectrum spectrum of 400CNi-MOF-74; (e) XPS full-spectrum spectrum of 450CNi-MOF-74; (f) XPS full-spectrum spectrum of 500CNi-MOF-74; (g) XPS full-spectrum spectrum of 550CNi-MOF-74.

[0020] Figure 10 XPS Ni 2p spectra of Ni-MOF-74 and XCNi-MOF-74 series catalysts.

[0021] Figure 11 This is the standard operating curve for ICP-OES.

[0022] Figure 12 Fourier transform infrared spectra of Ni-MOF-74 and XCNi-MOF-74 series catalysts.

[0023] Figure 13 The standard curves for carbohydrates in the component tests are shown in the following figures: (a) cellobiose, (b) glucose, (c) xylose, and (d) arabinose.

[0024] Figure 14 GC-MS total flow chromatogram of the second filtrate obtained from depolymerization of bagasse using Ru / C and XCNi-MOF-74 series catalysts.

[0025] Figure 15 The structural formulas and abbreviations of eight monomers present in high concentrations in the second filtrate obtained from the depolymerization of bagasse using Ru / C and XCNi-MOF-74 series catalysts.

[0026] Figure 16 GPC results for the depolymerization products of bagasse using Ru / C and XCNi-MOF-74 series catalysts.

[0027] Figure 17 The standard curves for GC-FID are for eight monomers: (a) PG, (b) PS, (c) EtG, (d) EtP, (e) POH-G, (f) POH-S, (g) G-ester, and (h) H-ester.

[0028] Figure 18 The yields of each monomer in the products obtained by depolymerizing bagasse using MeOH, Ru / C, Ni-MOF-74 and XCNi-MOF-74 series catalysts.

[0029] Figure 19 The yields of eight major monomers of bagasse depolymerization were obtained using the 300CNi-MOF-74 catalyst under different temperature conditions.

[0030] Figure 20 The yields of eight major monomers for depolymerization of bagasse using a 300CNi-MOF-74 catalyst under different hydrogen pressure conditions are shown.

[0031] Figure 21 The yields of eight major monomers depolymerized from bagasse using the 300CNi-MOF-74 catalyst at different reaction times are shown.

[0032] Figure 22 The yields of eight major monomers of bagasse depolymerization by 300CNi-MOF-74 under different catalyst addition amounts are shown.

[0033] Figure 23The yields of eight major monomers for depolymerization of bagasse using the 300CNi-MOF-74 catalyst under different solvent conditions are shown.

[0034] Figure 24 The GPC results for the depolymerization of bagasse products under optimal conditions using 300CNi-MOF-74 and Ru / C catalysts are presented.

[0035] Figure 25 The yields of eight major monomers depolymerized from bagasse by the 300CNi-MOF-74 catalyst at different cycle numbers are shown.

[0036] Figure 26 The 2D-HSQC results are shown for lignin from bagasse and crude lignin oil obtained from bagasse depolymerization catalyzed by 300CNi-MOF-74. In the figure, A is the fatty region of bagasse lignin; B is the fatty region of the depolymerized crude oil product -1; C is the structural formula of the corresponding region on NMR; D is the aromatic region of bagasse lignin; E is the aromatic region of the depolymerized crude oil product; and F is the fatty region of the depolymerized crude oil product -2.

[0037] Figure 27 The GC-MS total flow chromatogram shows the depolymerization products of lignin from different sources produced by the 300CNi-MOF-74 catalyst.

[0038] Figure 28 The yields of eight major monomers from different sources were obtained by using the 300CNi-MOF-74 catalyst to depolymerize lignin.

[0039] Figure 29 This is a possible reaction pathway diagram for the 300CNi-MOF-74 catalyst in the depolymerization of bagasse. Detailed Implementation

[0040] The technical solution of the present invention will be further illustrated below through embodiments.

[0041] Example 1 1.1 The preparation method of Ni-MOF-74 includes the following steps: (1.1.1) Mix NN, dimethylformamide (DMF), water (H2O), and ethanol (EtOH) in a volume ratio of 15:1:1 to 280 mL; (1.1.2) Add 3.36 g of nickel nitrate hexahydrate (Ni(NO3)•6H2O) and 0.672 g of 2,5-dihydroxyterephthalic acid (DHTA) to it and stir for 30 min until the solution is mixed evenly; (1.1.3) Placed in a hydrothermal synthesis reactor, reacted at 100 °C for 24 h, and then filtered to obtain the first solid. (1.1.4) The first solid obtained was washed repeatedly with DMF and soaked in DFM for 12 h. (1.1.5) Wash and soak in methanol for 24 hours, changing the methanol every 12 hours. (1.1.6) The second solid obtained by filtration through a 0.22 μm organic filter membrane is Ni-MOF-74. The second solid is dried in a vacuum drying oven for 24 h and stored for later use.

[0042] 1.2 The preparation method of XCNi-MOF-74 series catalysts includes the following steps: (1.2.1) Weigh 1g of Ni-MOF-74 and place it in a quartz boat. (1.2.2) Place the quartz boat in a tube furnace and purge for 30 min using a hydrogen-nitrogen mixture as a protective atmosphere. The hydrogen-nitrogen mixture consists of 5% hydrogen and 95% nitrogen by volume.

[0043] (1.2.3) Pyrolysis was performed at 300, 350, 450, 500, and 550 °C for 120 min, respectively, to obtain 300CNi-MOF-74, 350CNi-MOF-74, 450CNi-MOF-74, 500CNi-MOF-74, and 550CNi-MOF-74. The obtained samples were stored in desiccants for later use. The code XCNi-MOF-74 indicates that Ni-MOF-74 was pyrolyzed at X °C. 300CNi-MOF-74, 350CNi-MOF-74, 450CNi-MOF-74, 500CNi-MOF-74, and 550CNi-MOF-74 are collectively referred to as the XCNi-MOF-74 series catalysts.

[0044] Example 2: Thermogravimetric (TGA) Analysis of Ni-MOF-74 Thermal stability is a crucial prerequisite for the construction of MOF-derived catalytic systems, directly determining the structural evolution path of the precursor during heat treatment and the distribution of active sites in the final catalyst. Thermal stability analysis was performed using a STA 449 F3 simultaneous thermal analyzer (Germany). An appropriate amount of the Ni-MOF-74 sample prepared in section 1.1 of Example 1 was weighed into an alumina crucible. The heating rate was 10 °C / min, the measurement range was 20-800 °C, the protective gas was pure nitrogen, and the gas flow rate was 100 mL / min. The results are as follows: Figure 2 and Figure 3 As shown. By Figure 2 and Figure 3It can be seen that the weight loss of Ni-MOF-74 is mainly divided into two stages. The first stage of rapid weight loss occurs at around 120 °C, which corresponds to the residual solvent molecules involved in coordination in the Ni-MOF-74 channels. The second stage of rapid weight loss occurs at around 400 °C, which corresponds to the disintegration of the Ni-MOF-74 structure. Furthermore, the weight loss rate of Ni-MOF-74 does not increase significantly with further increases in temperature, indicating that Ni-MOF-74 is in a stable state after the second stage of rapid weight loss. Figure 2-3 The weight loss rate derivative plot can more intuitively show the weight loss stage of Ni-MOF-74 during the heating process. It is clear that there is a relatively slow weight loss stage between 200 and 350 °C; while the weight loss rate approaches 0 after 500 °C. To investigate the defect structures that may be generated during the decomposition of Ni-MOF-74, the temperature of its second rapid weight loss stage was further subdivided, with 400 °C as the relative median temperature. By precisely controlling the pyrolysis temperature of Ni-MOF-74, catalytically active structures with specific defect concentrations and Ni nanoparticle dispersions can be directionally generated during the framework decomposition process. Therefore, subsequent pyrolysis investigations used 300, 350, 400, 450, 500, and 550 °C as nodes. The XCNi-MOF-74 series catalysts were prepared sequentially in Section 1.2 of Example 1.

[0045] Example 3: Specific surface area, pore volume, and pore size of Ni-MOF-74 and XCNi-MOF-74 series catalysts In the catalytic process, the adsorption of active sites in the substrate and catalyst plays an important role in promoting the entire catalytic process. The larger the specific surface area and the more developed the pore structure of the catalyst, the more active sites can be exposed, and the effective contact area between the substrate and the active sites increases accordingly, thereby significantly improving catalytic efficiency and product selectivity.

[0046] (1) Sample pretreatment: Take an appropriate amount of the sample to be tested and put it into the sample tube, and accurately weigh the sample mass. Install the sample tube onto the standard degassing station manufactured by Micro Instruments, and perform the test under vacuum conditions (vacuum degree not less than 10). - The sample was heated to 120°C (2 Pa) and pretreated at this temperature for 8 hours to remove adsorbed impurity gases and moisture from the sample surface and pores. After pretreatment, the sample tube was cooled to room temperature under vacuum and backfilled with high-purity nitrogen for protection. The samples to be tested were Ni-MOF-74 and XCNi-MOF-74 series catalysts prepared in Example 1.

[0047] (2) Nitrogen adsorption-desorption test: The pretreated sample tubes were transferred to an ASAP 2460 four-station fully automated specific surface area and porosity analyzer manufactured by Micromeritics, USA. Using high-purity nitrogen as the adsorbate, the nitrogen adsorption and desorption amounts of the samples were measured at different relative pressures (P / P0) under liquid nitrogen temperature (77 K), and the isothermal adsorption-desorption curves were automatically recorded (e.g., Figure 4 (as shown in a).

[0048] (3) Specific surface area, total pore volume and pore size analysis: The following calculations were performed based on the isothermal adsorption-desorption curves: Total specific surface area: Adsorption branch data with relative pressure P / P0 in the range of 0.05 to 0.30 were selected, and linear fitting was performed using the BET (Brunauer-Emmett-Teller) multilayer adsorption theory to calculate the total specific surface area of ​​the material (as shown in Table 1). Total pore volume: The nitrogen adsorption amount at relative pressure P / P0≈ 0.99 was taken, and the total pore volume was calculated based on the molar volume of liquid nitrogen (as shown in Table 1), with units of cm³ / g. Average desorption pore size: The BJH (Barrett-Joyner-Halenda) model was used, based on the desorption branch of the isothermal adsorption-desorption curve, to calculate the pore size distribution, and the average desorption pore size (as shown in Table 1) (unit nm) was obtained from the cumulative pore volume and cumulative specific surface area. Pore ​​size distribution curve: Based on the pore size distribution data calculated using the BJH model, a pore size distribution curve is plotted with pore size (nm) on the x-axis and the change in pore volume per unit pore size interval (dV / dD) or cumulative pore volume on the y-axis. Figure 4 (as shown in b).

[0049] (4) Results Analysis As shown in Table 1, with increasing calcination temperature, Ni The specific surface area and pore structure parameters of the MOF-74 derived material are significantly reconstructed. The original Ni MOF-74 has a high specific surface area (220.34 cm³·g). - ¹) and a relatively small average pore size (4.45 nm), exhibiting a typical MOF porous framework dominated by small pores. When heated to 300-350 ℃, the specific surface area decreases rapidly, while the average pore size increases from 4.45 nm to 7.06-9.82 nm, and the total pore volume increases from 0.06 cm³·g. - ¹ Increased to 0.23 cm³·g -¹ indicates that the organic ligands begin to decompose and release gaseous byproducts, the pores widen and connect, accompanied by partial framework collapse, forming more mesopores / macropores. Further increasing the temperature to 400-500 ℃ reduces the average pore size of the sample to approximately 6-8 nm, while the specific surface area and pore volume are at approximately 115.33 cm³·g at 400 ℃. - ¹, 0.25 cm³·g - ¹) and 500 ℃ (84.28 cm³·g - ¹, 0.13 cm³·g - ¹) A certain degree of recovery occurred, which can be attributed to the competitive process between the continuous carbonization and densification of the MOF framework and the local sintering, pore wall shrinkage, and partial pore reopening caused by the formation of metal / oxide nanoparticles. At 550 °C, the specific surface area and total pore volume of the material both decreased significantly (18.30 cm³·g, respectively). - ¹ and 0.06 cm³·g - ¹), while the average pore size increased to 10.24 nm, indicating that the framework structure collapsed severely at high temperature, and the pores merged and the particles agglomerated, leaving only a small number of large pores, resulting in a high degree of degradation of the overall pore structure.

[0050] Table 1. Specific surface area, pore volume, and pore size of Ni-MOF-74 and XCNi-MOF-74

[0051] Depend on Figure 4 (a) Figure 4 (b) It can be seen that Ni Both MOF-74 and XCNi-MOF-74 series catalysts exhibited typical N2 adsorption-desorption isotherm characteristics of the transition from Type I to Type IV at 77 K: In the low relative pressure range (P / P0 < 0.1), the adsorption capacity of each sample increased slowly with pressure, indicating that a certain number of micropores were still retained in the material; while in the medium-to-high relative pressure range (P / P0 > 0.4), the adsorption capacity increased significantly, accompanied by the appearance of hysteresis loops, indicating that a relatively rich mesoporous structure was gradually formed and developed inside the material with calcination. Compared with the original Ni-MOF-74, the adsorption capacity of the calcined XCNi-MOF-74 series catalyst samples was significantly improved throughout the entire pressure range, with the highest adsorption capacity observed at 400-550 °C when P / P0→1, corresponding to the larger total pore volume measured in Table 1 (up to 0.25 cm³·g). - ¹), further confirming that the framework reconstruction and gas evolution process during pyrolysis promotes the widening and interconnection of the original micropores, forming a large number of mesopores / macropores.

[0052] Example 4: Temperature-programmed chemisorption analysis of ammonia in Ni-MOF-74 and XCNi-MOF-74 series catalysts After completing BET measurements to obtain the specific surface area, pore size distribution, and pore volume of the catalyst, ammonia adsorption was used as a bridge to further investigate the description of the catalyst's acidic properties. Ammonia, as a weak base molecule, can adsorb onto acidic sites on the catalyst surface, especially Brønsted acid sites and Lewis acid sites of varying strengths. This makes ammonia adsorption one of the most intuitive tools for revealing the acidity of the catalyst. Through temperature-programmed chemical adsorption-desorption (TPD-NH3), the total density and distribution of acidic sites, as well as the strength distribution differentiated by desorption peak temperature, can be quantitatively obtained. Combined with desorption information from temperature gradients, the relationship between the thermal stability of acidic sites and catalytic activity can be evaluated, further revealing the distribution pattern of acidic centers and their preference for specific reaction pathways.

[0053] Weigh 100 mg of sample (the sample being the Ni-MOF-74 and XCNi-MOF-74 series catalysts prepared in Example 1), place it in the quartz reaction tube of a chemisorption analyzer, and pre-treat it by heating from room temperature to 120 °C at a programmed rate of 10 °C / min. Purge with a He gas stream (30-50 mL / min) for 1 h, cool to 50 °C, and then purge with a 10% NH3 / He mixture (30-50 mL / min) for 1 h until saturation. Switch to a He gas stream (30-50 mL / min) and purge for 1 h to remove weakly physically adsorbed NH3. Finally, desorb at 250 °C under a He atmosphere at a heating rate of 10 °C / min. Detect the desorbed gas using a TCD. The results are as follows: Figure 5 As shown. By Figure 5 As can be seen, compared with samples pyrolyzed at other temperatures, 300CNi-MOF74 exhibits the best adsorption characteristics: the signal steadily increases within 0-20 min and tends to a higher stable value, indicating a high density of accessible acidic sites and more favorable diffusion of NH3 into the pores. The precursor state at this temperature can retain or generate a suitable ratio of Brønsted and Lewis acidic sites without excessive removal of hydration / hydroxyl groups, thus maintaining a high density of acidic centers and accessibility of active sites. Simultaneously, the pore distribution at this temperature is uniform and relatively intact, making it easier for NH3 to diffuse into the pores and bind to the acidic sites.

[0054] In contrast, the Ni-MOF-74 samples exhibited rapid but unstable adsorption behavior, while samples treated at 350-550℃ showed a decreasing trend in adsorption capacity. Treatment at 350-550℃ may have excessively removed hydroxyl groups, reduced the number of Brønsted sites, or triggered partial structural reorganization and minor changes in pore size / volume, leading to narrowing of adsorbable acidic sites or pore channels, and a decrease in the overall adsorption capacity of NH3. Furthermore, excessively high temperatures may cause localized aggregation or increased particle size, thereby reducing the specific surface area and the exposure of active sites, further weakening the adsorption capacity. Overall, heat treatment at 300℃ maintained structural integrity while achieving the optimal combination of acidic sites and pore accessibility.

[0055] Example 5: X-ray diffraction (XRD) analysis of Ni-MOF-74 and XCNi-MOF-74 series catalysts. The crystal structure of the samples (Ni-MOF-74 and XCNi-MOF-74 series catalysts prepared in Example 1) was determined using a Bruker D8 advanced diffractometer. Appropriate amounts of sample powder were placed in the sample cell and repeatedly compacted with coverslips until a smooth surface was formed, then placed inside the instrument. The instrument used a copper target, with an operating voltage of 40 kV, a current of 30 mA, a scanning range of 3° ≤ 2θ ≤ 80°, a step size of 0.02°, and a scanning speed of 10° / min. The results are shown below. Figure 6 As shown.

[0056] Depend on Figure 6 As can be seen, Ni-MOF-74 was successfully prepared in Example 1. The diffraction peaks at 6.7° and 11.8° correspond to its (110) and (300) crystal planes, respectively, indicating that the obtained Ni-MOF74 has good crystallinity and an ordered pore structure. With the increase of calcination temperature, the characteristic MOF diffraction peaks in these low-angle regions gradually weaken and eventually disappear, indicating that the organic ligand framework is gradually decomposed and the original MOF framework structure is destroyed. In addition, new diffraction peaks that appear and gradually increase in the high-angle regions 2θ ≈ 44.5°, 51.8° and 76.3° can be attributed to standard face-centered cubic metal Ni. 0 The (111), (200), and (220) crystal planes indicate that during pyrolysis, the Ni elements inside Ni-MOF-74 are reduced and rearranged into metallic Ni nanocrystals. As the calcination temperature increases from 300 °C to 550 °C, these Ni... 0 The increasing intensity of the diffraction peaks and the gradually narrowing full width at half maximum (FWHM) indicate that Ni... 0 The grain size continued to grow and the degree of crystallinity increased, while no obvious diffraction peaks of other impurity phases were observed, indicating that metallic Ni was the main crystalline phase in the obtained product.

[0057] Example 6 Scanning electron microscopy (SEM) analysis of Ni-MOF-74 and 300CNi-MOF-74 To further reveal the microstructure and elemental distribution characteristics, this embodiment performed SEM and EDS characterization on Ni-MOF-74 and 300CNi-MOF-74, which has better specific surface area.

[0058] A small amount of sample / bulk / thin film sample (Ni-MOF-74 and 300CNi-MOF-74 prepared in Example 1) was directly adhered to the conductive adhesive and sputtered with gold for 45 seconds using a Quorum SC7620 sputtering system at 10 mA. Subsequently, the sample morphology and energy dispersive spectroscopy (EDS) mapping were performed using a ZEISS Sigma 300 scanning electron microscope. The accelerating voltage for morphology imaging was 3 kV, and for EDS mapping, it was 15 kV. An SE2 secondary electron detector was used. The results are as follows: Figure 7 As shown.

[0059] Depend on Figure 7 a and Figure 7 As can be seen from c, the original Ni-MOF-74 consists of petal-shaped secondary aggregates formed by the radial stacking of regular prismatic crystals. The particles have clear outlines and relatively smooth crystal faces, exhibiting high crystallinity. Figure 7 As can be seen, C, O, and Ni are uniformly distributed throughout the entire particle size distribution, with no obvious enrichment or depletion regions. This indicates that the prepared Ni-MOF-74 has a uniform composition and complete structure, which is consistent with the XRD analysis results and further proves the successful synthesis of the material.

[0060] Depend on Figure 7 b and Figure 7 As can be seen, after pyrolysis at 300 °C, the 300C Ni-MOF-74 as a whole still maintains a similar macroscopic petal-like aggregate morphology to Ni-MOF-74, indicating that the MOF framework was well preserved under intermediate-temperature pyrolysis conditions. However, it can be observed that a large number of uniformly distributed fine cracks and pores appear on the surface of individual prisms and at their interfaces, indicating that the framework structure has begun to undergo gradual decomposition and rearrangement. These newly formed cracks and pores are beneficial in two ways: firstly, they facilitate the construction of a connected hierarchical pore network within the particles, shortening the diffusion path of reactants / products and improving mass transfer performance; secondly, they may also locally generate unsaturated coordination or structural defects, providing more potential active sites for subsequent catalytic reactions. Figure 7As can be seen, C, O, and Ni are still uniformly distributed in 300°C Ni-MOF-74, and no obvious Ni-rich agglomeration region was observed. This indicates that the metal elements can maintain good spatial dispersion at this temperature, which lays the foundation for obtaining stable and highly dispersed Ni active centers.

[0061] Example 7: Transmission Electron Microscopy (TEM) and High-Resolution Transmission Electron Microscopy (HR-TEM) Analysis TEM characterization primarily reflects the overall morphology and elemental plane distribution information at the submicron scale, which is insufficient to reveal the true particle size, crystal structure, and interfacial features between Ni and the carbon-based framework. To further understand the fine structural evolution of Ni-MOF-74 during pyrolysis and the crystallographic properties of Ni in samples with different heat treatments at the nanoscale and even atomic scale, this embodiment selects representative Ni-MOF-74, 300C Ni-MOF-74, and 550C Ni-MOF-74 samples for TEM and HR-TEM characterization.

[0062] The TEM and HR-TEM analysis methods are as follows: Samples (Ni-MOF-74, 300CNi-MOF-74, and 550CNi-MOF-74 prepared in Example 1) were taken and dispersed in an ethanol solution. Ultrasonic treatment was used to ensure uniform dispersion. A few drops of the dispersed liquid were added dropwise to a copper grid and allowed to air dry. High-resolution imaging, diffraction, and energy dispersive spectroscopy (EDS) were performed on the samples using a FEI Talos F200X (USA), accelerating voltage 200kV, and OXFORD-Xplore spectrometer to obtain morphological and compositional information. The results are as follows: Figure 8 As shown.

[0063] like Figure 8 As shown in (a), the original Ni-MOF-74 appears as regular sheet-like / block-like particles under TEM, with clear outlines and relatively uniform internal contrast. No obvious dark nanoparticle distribution is observed, indicating that Ni is uniformly immobilized within the MOF framework constructed by the organic ligands. The corresponding elemental distribution diagram (e.g.) Figure 8 In (d), the three elements C, O and Ni are highly uniformly distributed throughout the entire particle range, consistent with the aforementioned SEM-EDS results, further proving that the obtained Ni-MOF-74 has a complete structure and uniform composition.

[0064] TEM images of 300CNi-MOF-74 after pyrolysis at 300 ℃ (e.g.) Figure 8As shown in (b), a large number of uniformly sized, high-contrast nanoparticles are clearly observed on the surface and inside the sample framework, indicating that some Ni elements were reduced and precipitated during pyrolysis to form metal nanoparticles. The corresponding EDS surface scan results (e.g.) Figure 8 As shown in (e), C, O, and Ni are still uniformly distributed within the particles, with no obvious large-particle agglomeration regions of Ni enrichment, indicating that at this temperature, metallic Ni is anchored on the carbide framework in a highly dispersed nanoscale state. HR-TEM image ( Figure 8 (g), (h), and (i) further revealed the structural features of these nanoparticles at the crystallographic scale. Figure 8 Regular and clear lattice fringes can be distinguished in (g) and (h), with interplanar spacings of approximately 2.04 Å and 1.76 Å, respectively, which can be attributed to metallic Ni. 0 The (111) and (200) crystal planes; while Figure 8 In (i), Ni with a spacing of 2.04 Å was simultaneously observed. 0 The (111) crystal plane and the 2.08 Å NiO(200) crystal plane coexist closely in a local region, indicating that the outer layer of some Ni nanoparticles has undergone slight oxidation, and Ni has formed at 300 °C. 0 The heterostructure of / NiO was observed. The results above are consistent with those in the XRD patterns.

[0065] TEM image of 550CNi-MOF-74 after further heating to 550℃ ( Figure 8 (c) shows that the overall particle structure is more compact, and the size of the dark nanoparticles attached to the surface is significantly increased and local agglomeration occurs, indicating that Ni under high temperature conditions... 0 The nanoparticles continued to grow and sintered. (EDS elemental distribution map) Figure 8 In (f), the Ni and O signals overlap to some extent in the outer region of the particles, suggesting that during high-temperature treatment and subsequent air exposure, the surface Ni element is further oxidized to form NiO. This phenomenon is consistent with the Ni signal in the XRD pattern of 550C Ni-MOF-74. 0 The trend of continued enhancement of characteristic peaks and the appearance of weak NiO diffraction signals in the high-angle region is consistent with this, indicating that high-temperature pyrolysis is beneficial to Ni grain growth and increased crystallinity, and also promotes the growth of some surface Ni. 0 Oxidation.

[0066] It should be noted that although higher-temperature pyrolysis is beneficial to improving the crystallinity of Ni to some extent, the high-temperature-induced Ostwald ripening process promotes sintering and agglomeration of Ni nanoparticles, leading to significant grain growth and a substantial loss of specific surface area, thereby weakening the accessibility of active sites. (TEM results...) Figure 8As can be seen from (b) and (c), the Ni nanoparticles in 300CNi-MOF-74 are small in size and highly dispersed, while the dark particles in 550CNi-MOF-74 are significantly larger and agglomerated. HR-TEM and XRD together show that the particle size of the internal metal and metal oxide crystals is significantly increased. At the same time, nitrogen adsorption-desorption tests show that the BET specific surface area and pore volume of 550CNi-MOF-74 are significantly reduced, indicating partial collapse of the framework structure and pore blockage.

[0067] Based on the above structural characterization results, it can be inferred that in 550CNi-MOF-74, although Ni 0 / NiO has high crystallinity, but the reduced effective exposure of active sites due to over-sintering and the increased mass transfer resistance in the pores together limit its catalytic performance: the former reduces the amount of reactants and Ni 0 The contact probability of the NiO heterostructure, which in turn limits the effective transfer of substrate molecules to the active interface, results in the synergistic effect of the two leading to a significantly lower catalytic efficiency of 550CNi-MOF-74 compared to the low-temperature pyrolysis sample.

[0068] Example 8: X-ray photoelectron spectroscopy (XPS) of Ni-MOF-74 and XCNi-MOF-74 series catalysts The XPS analysis method is as follows: Take an appropriate amount of sample (the sample is the Ni-MOF-74 and XCNi-MOF-74 series catalysts prepared in Example 1), compress it into a tablet, attach it to the sample tray, and place the sample into the sample chamber of the Thermo Scientific K-Alpha XPS instrument. The pressure in the sample chamber should be better than 5 x 10⁻⁶. -7 At mbar, the sample was sent into the analysis chamber with a spot size of 400 μm, an operating voltage of 12 kV, and a filament current of 6 mA. The full-spectrum scan pass energy was 150 eV with a step size of 1 eV. The results are as follows: Figure 9 As shown; the narrow-spectrum scan pass energy is 50 eV, the step size is 0.1 eV, and the results are as follows. Figure 10 As shown.

[0069] like Figure 9 As shown, all samples exhibited distinct C1s, O1s, and Ni2p characteristic peaks only around 284.8 eV, 531 eV, and 855 eV, with no other impurity element-related peaks detected. This indicates that the prepared sample surface is mainly composed of C, O, and Ni elements, and the sample purity is high. The full spectrum of the original Ni-MOF-74 (…) Figure 9In sample a), the C1s and O1s peaks are relatively high, while the Ni 2p peak is relatively weak, indicating that the surface is still dominated by organic ligands and coordinated oxygen, with Ni mostly embedded within the MOF framework. This is consistent with the observation that no independent metal particles were observed in SEM / TEM. As the pyrolysis temperature increases from 300 ℃ to 550 ℃, the C1s peak in each sample spectrum gradually strengthens, while the O1s peak relatively weakens, reflecting that decarboxylation and dehydroxylation reactions may occur during the carbonization process, leading to a gradual enrichment of carbon on the surface and a reduction in oxygen-containing functional groups. This aligns with the trend of decreasing specific surface area and the evolution of the pore structure from ordered MOF to a dense carbon-based framework observed in the BET results. Simultaneously, the relative intensity of the Ni 2p peak in the pyrolysis samples is significantly higher than that of the original Ni-MOF-74, indicating that Ni gradually migrates to the surface and is exposed during pyrolysis. 3 / 2 With 2p 1 / 2 All regions can be decomposed into a main peak and distinct satellite peaks, indicating that the sample surface is dominated by coordinated or oxidized Ni elements. Peak fitting can be used to determine the Ni 2p... 3 / 2 The main peak decomposes into Ni 2+ with Ni 0 Two types of components, one located at approximately 855-856 eV and the other at the corresponding 2p. 1 / 2 The peak in the region is attributed to Ni. 2+ The peak in the low binding energy region of approximately 852-853 eV can be attributed to metallic Ni. 0 For undylated Ni-MOF-74, only strong Ni spectral density was observed in its Ni 2p spectrum. 2+ Peaks and characteristic satellite peaks, almost entirely free of Ni 0 This indicates that at this point, the Ni element is completely coordinated as Ni. 2+ The form exists within the MOF skeleton. This differs from the fact that only MOFs appear in XRD. The presence of characteristic diffraction peaks (74) and the absence of independent metal nanoparticles in TEM results confirm that the original sample is pure Ni-MOF-74 with a regular and ordered framework. As the pyrolysis temperature increases to 300-450 ℃, Ni ions gradually appear and strengthen on the low binding energy side of the Ni 2p spectra of each sample. 0 Peak, and Ni 2+ The relative decrease in intensity of the peak and its satellite peaks indicates that some coordinated Ni 2+ It is reduced to metallic Ni nanoparticles and precipitated onto the carbon framework surface. This trend is consistent with Ni in XRD. 0The diffraction peaks (2θ≈44.5°, 51.8°) gradually increased with temperature, and the large number of uniformly dispersed Ni nanoparticles and the clear Ni0(111) / (200) crystal plane fringes in the TEM / HRTEM were highly consistent. It is noteworthy that in the 300C Ni-MOF-74 and 400C Ni-MOF-74 samples, Ni... 0 with Ni 2+ The relatively similar area contributions of the two types of peaks indicate that a certain amount of metallic Ni is simultaneously enriched on the inner surface of this temperature range. 0 with Ni 2+ It is beneficial to construct Ni 0 / NiO heterostructure interface. Combined with the aforementioned TEM results, Ni was observed at the outer edge of some nanoparticles. 0 The phenomenon of (111) closely coexisting with the NiO(200) crystal plane suggests that a considerable amount of well-dispersed NiO crystals formed on the surface of the medium-temperature pyrolysis sample. 0 / NiO interface sites, these interfaces are generally considered excellent active centers for many hydrogenation reactions. When the pyrolysis temperature is further increased to 500-550 °C, the Ni in the spectrum... 0 The composition continues to be enhanced, as seen in the Ni-MOF-74 XRD spectrum at 550°C. 0 The diffraction peaks are most intense, with only weak NiO peaks remaining. However, it should be emphasized that although XPS shows that the Ni on the 550CNi-MOF-74 surface is... 0 The highest content was observed at this point, but combined TEM and BET results showed that the Ni nanoparticles had already undergone significant growth and aggregation, with a more compact framework structure. This resulted in a significant decrease in specific surface area and pore volume, and exposed Ni on the surface. 0 The NiO interface length also decreases accordingly. While high-temperature pyrolysis increases the crystallinity of Ni and the surface metal ratio, it sacrifices the dispersion of nanoparticles and the openness of the pore structure, thereby reducing the accessibility and effective utilization of Ni in the catalytic process.

[0070] Example 9: Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-OES) Analysis of Ni-MOF-74 and XCNi-MOF-74 Series Catalysts After completing XPS characterization and clarifying the valence state composition and evolution of Ni on the surface of each sample, the nickel content of each catalyst was determined to further quantify the actual Ni content in samples with different heat treatments and to combine it with the surface chemical state for structure-performance correlation analysis. By establishing a series of standard solutions and plotting a standard working curve for Ni, the test results of the sample solutions were quantitatively converted to obtain the actual Ni loading and retention rate in each catalyst, providing reliable basic data support for subsequent catalytic performance attribution.

[0071] Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-OES) Analysis: The elemental content in the sample was determined using an Agilent Technologies 7800 inductively coupled plasma mass spectrometer (ICP-MS). Approximately 50-100 mg of sample was weighed precisely using a 0.0001 g electronic balance and placed in a polytetrafluoroethylene crucible that had been pre-soaked in dilute nitric acid, thoroughly washed with pure water, and dried. A suitable acid system was selected based on the sample type for digestion. After digestion, the sample was allowed to cool naturally, yielding approximately 5 mL of digest. The cooled digest was quantitatively transferred to a graduated volumetric flask or centrifuge tube. The crucible was rinsed 3-5 times with pure water, and the rinsings were added to the same volumetric flask. The volume was then adjusted to 10 mL for samples less than 50 mg and to 25 mL for samples of 50-100 mg. The mixture was thoroughly mixed to obtain the analytical solution.

[0072] Purchased single-element or multi-element standard solutions were used to prepare a series of standard working solutions at concentration gradients of 0.5, 1, 3, 5, and 10 mg / L to plot a standard curve. Volumetric flasks and pipettes used for preparing the standard solutions were pre-soaked in dilute nitric acid and rinsed with pure water to reduce background and matrix interference. For ICP-MS analysis, the standard curve was first established by measuring the concentration gradient of the standard solutions, and then the test solution was tested. Simultaneously, a reagent blank sample (without the sample, but following the same steps as the sample) was prepared for background correction and blank subtraction. A series of standard Ni solutions were used to plot the ICP-OES standard working curve, as shown below. Figure 11 As shown. The obtained calibration curve shows a good linear relationship (y=2714.19x+3.45, R). 2 =0.99991), indicating that the instrument response is highly linearly correlated with the Ni concentration within the selected concentration range, which can provide a reliable basis for the quantitative calculation of Ni content in subsequent samples.

[0073] according to Figure 11The Ni mass fractions in each sample, calculated from the standard curves shown, are as follows: Ni-MOF74 30.1%, 300°C Ni-MOF74 67.8%, 350°C Ni-MOF74 87.2%, 400°C Ni-MOF74 86.3%, 450°C Ni-MOF74 82.9%, 500°C Ni-MOF74 98.2%, and 550°C Ni-MOF74 96.2%. It can be seen that the original Ni-MOF-74 contains approximately 30.1 wt%, indicating that before pyrolysis, the sample is still dominated by a MOF framework containing a relatively large amount of organic ligands and porous structures, with Ni accounting for only about one-third of the total mass. As the pyrolysis temperature increased from 300 °C to 500 °C, the Ni content in the sample gradually increased from 67.8 wt% to 98.2 wt%, showing a continuous upward trend, and remained at a high level of 96.2 wt% at 550 °C. This result indicates that during pyrolysis, the organic framework continuously carbonizes, accompanied by weight loss processes such as decarboxylation and dehydroxylation. A large number of light elements (C, O, H) are released as gases (CO2, H2O), significantly increasing the mass fraction of Ni in the residual solid. Simultaneously, Ni-based species showed minimal loss throughout the temperature range, exhibiting good retention and thermal stability.

[0074] Example 10: Fourier transform infrared spectroscopy (FT-IR) determination of Ni-MOF-74 and XCNi-MOF-74 series catalysts. To gain a deeper understanding of the molecular structure evolution of Ni-MOF-74 during pyrolysis, Fourier transform infrared (FTIR) spectroscopy analysis was performed on Ni-MOF-74 and XCNi-MOF-74 series catalysts. The method was as follows: An appropriate amount of dried sample to constant weight (the sample being the Ni-MOF-74 and XCNi-MOF-74 series catalysts prepared in Example 1) was placed in an agate mortar, and KBr was added at a ratio of 1:100. The mixture was thoroughly ground and homogeneous, then pressed into a transparent tablet using a tablet press and placed in an infrared spectroscopy chamber. The scanning range was 600–4000 cm⁻¹. -1 The number of scans was 32, and the resolution was 4 cm. -1 The result is as follows Figure 12 As shown.

[0075] Depend on Figure 12 The structural changes of the sample at different heat treatment temperatures can be visually observed. The original Ni-MOF-74 at 500-800 cm⁻¹ - ¹ Region has multiple absorption peaks, corresponding to Ni² +The Ni-O stretching vibration formed with the carboxyl oxygen of the DHTP ligand can be used as a criterion for judging the integrity of the MOF framework. These peaks gradually weaken as the pyrolysis temperature increases from 300 °C to 550 °C, and almost disappear in the sample at 550 °C, indicating that the ordered MOF framework has completely collapsed. This result is in perfect agreement with the XRD test results. (1200-1600 cm⁻¹) - The absorption band in region ¹ corresponds to the CO stretching and C=C vibration of the aromatic ring in the organic ligands. The original MOF exhibits a clear and strong peak in this region. These peaks begin to weaken significantly after 400 °C, indicating that the ligand side chains begin to detach and undergo initial decomposition. At higher temperatures, these peaks decay to baseline, reflecting a significant loss of organic components. ICP-OES data also demonstrate that the Ni content increases with decreasing organic components. (1600-1700 cm⁻¹) - The C=O stretching vibration of the coordinated carboxyl groups in the ¹ region is a sensitive indicator for determining the coordination state of Ni-OC. The pristine Ni-MOF-74 exhibits a strong and sharp absorption peak in this region, indicating the presence of a large number of uniformly coordinated carboxyl groups. This is consistent with the Ni² region observed in XPS. + The spectral results are consistent. As the temperature increases, this characteristic peak gradually weakens and even disappears, which is consistent with the Ni² peak in XPS. + The weakening trend of the peak also matches this. 2500-3500 cm - The broad absorption band of ¹ contains the OH and aromatic CH stretching vibrations of the DHTP ligand. This broad peak gradually narrows and weakens with increasing temperature, reflecting the dehydroxylation reaction and the carbonization process of the aromatic ring.

[0076] Based on the FT-IR spectral analysis, the pyrolysis process of Ni-MOF-74 first involves the desorption of the adsorbed solvent, followed by the large-scale decomposition of the organic ligands. Simultaneously, the Ni-O coordination bonds break, and Ni elements precipitate from the MOF framework and are reduced to metallic Ni nanoparticles. At 500-550 °C, the organic ligands completely decompose, the MOF framework collapses completely, and carbon atoms rearrange to form a porous carbon matrix containing larger and partially sintered Ni nanoparticles. 0 And NiO nanoparticles. This mechanism is completely consistent with the results of BET pore structure evolution, XRD phase transformation, and nanoparticle precipitation and growth under TEM. The intermediate-temperature pyrolysis products show differences in Ni content, specific surface area, pore structure, and Ni... 0 An ideal balance was achieved between the NiO and NiO interface densities, providing the necessary structural basis for subsequent catalytic reactions.

[0077] Example 11: Component Analysis of Sugarcane Bagasse and Different Biomass Bagasse was supplied by Dongtang Company, located in Nanning, China. The bagasse was washed in running tap water and dried in an oven at 60°C for 48 hours. It was then pulverized using a planetary ball mill, passed through a 200-mesh sieve, and dried in a vacuum drying oven for 24 hours. The powder was then stored in resealable bags in desiccants for later use. The eucalyptus, beech, fir, pine, and birch wood materials were purchased, ball-milled, passed through a 200-mesh sieve, and dried in a vacuum drying oven for 24 hours. The powder was then stored in resealable bags in desiccants for later use.

[0078] To measure the relative contents of cellulose, hemicellulose, lignin, and ash in sugarcane bagasse and various woody raw materials, a modified method developed by the National Renewable Energy Laboratory (NREL) was used. Approximately 300 mg (octane-dry weight) of pre-crushed biomass sample was accurately weighed and placed in a pressure-resistant glass tube. 3.00 mL of 72% (w / w) sulfuric acid was added, and the mixture was reacted intermittently with stirring in a 30 °C water bath for 60 min. Then, 84.0 mL of deionized water was added to dilute the acid concentration to approximately 4%. 10.00 mL of the sugar solution standard was transferred to another pressure-resistant tube. All pressure-resistant tubes were placed in an autoclave and kept at 121 °C for 60 min. The caps were opened after the temperature cooled to room temperature. The solution was then filtered using a constant-weight sand core funnel. The filtrate was used to analyze the carbohydrate content (cellulose, hemicellulose) and acid-soluble lignin (ASL%). The residue was used to analyze acid-insoluble lignin (AIL%) and ash (AIR%).

[0079] Method for determining cellulose and hemicellulose content: Take 10 mL of acid hydrolysate, add approximately 0.5 g of calcium carbonate to neutralize the sample to pH 5-6, allowing the sample to precipitate, and pour off the supernatant. The pH of the settled liquid is approximately 7. Filter the liquid through a 0.22 μm filter and place it into a 2 mL injection bottle to prepare the sample for high-performance liquid chromatography (HPLC) analysis. Use an Animex HPX-87H column equipped with an appropriate guard column to analyze the carbohydrate standard and sample by HPLC. HPLC conditions: Injection volume: 20 μL; Mobile phase: ultrapure water; Flow rate: 0.6 mL / min. Monosaccharide content was determined by HPLC. After conversion based on recovery efficiency, glucose content was multiplied by a factor of 0.9, and the sum of xylose and arabinose contents was multiplied by a factor of 0.88.

[0080] Method for determining acid-soluble lignin content (ASL%): Using 4% sulfuric acid solution as a blank, measure the absorbance of the filtered filtrate at a wavelength of 240 nm using a UV-Vis spectrophotometer. If necessary, dilute the sample to bring the absorbance within a suitable range and record the dilution. Measure the UV absorbance value of the filtrate. The formula for calculating the acid-soluble lignin content is shown in Equation 3-1.

[0081] (3-1) Where: A: OD value; V: filtrate volume, 87 mL; D: dilution factor; : Absorption rate of lignin at 240 nm (L / gcm); ODW: Sample mass.

[0082] Methods for determining acid-insoluble lignin (AIL%) and ash (AIR%) content: Place the empty crucible back into the muffle furnace at 575°C until a constant weight is achieved. Transfer directly to a desiccator and cool for 30 min, recording the weight W1. Rinse the solid residue from the sand core funnel with at least 50 mL of deionized water, then dry the crucible and acid-insoluble residue at 105°C until a constant weight is achieved. Remove the sample from the oven and cool in the desiccator, recording the weight of the crucible and dried residue as W2. Place the crucible and residue in a muffle furnace and heat to 575°C at a rate of 20°C / min, holding for 240 min. Transfer the crucible directly from the furnace to a desiccator and cool for 30 min, weighing the crucible and ash, recording the weight W3. The formula for calculating the acid-insoluble lignin content is shown in Equation 3-2, and the formula for calculating the ash content is shown in Equation 3-3.

[0083] (3-2) (3-3) Method for determining total lignin content: Total lignin content is the sum of acid-soluble lignin content and acid-insoluble lignin content, as shown in Formula 3-4.

[0084] (3-4) The composition of biomass from different sources varies significantly. The specific distribution of its main components (cellulose, hemicellulose, lignin) and ash is shown in Table 2. Table 2. Components of different types of biomass

[0085] Example 12: Method for depolymerization of sugarcane bagasse and analytical detection method for depolymerization products 12.1 A method for depolymerizing sugarcane bagasse, comprising the following steps: (1) weighing biomass, catalyst and solvent and mixing them evenly in a 50mL high-temperature and high-pressure reactor; (2) pressurizing the reactor to the depolymerization pressure with hydrogen and then depressurizing it three times to completely remove the air in the reactor, and then pressurizing the reactor to the depolymerization pressure with hydrogen; (3) heating the reactor to the depolymerization temperature to carry out the depolymerization reaction. (4) After the reactor is cooled to room temperature and depressurized, open the lid and transfer all the reaction mixture in the reactor to a sand filter. Filter the mixture under vacuum using a 0.45 μm organic filter membrane and wash the filter cake three times with solvent. Discard the filter cake and collect the first filtrate for later use. (5) Rotate the first filtrate at 60 °C until all the solvent evaporates. The residue obtained is crude lignin oil. (6) Add 10 mL of chromatographic grade MeOH to the crude lignin oil and sonicate it to fully dissolve the crude lignin oil in MeOH. Then add anhydrous sodium sulfate to remove water. After filtration through a 0.22 μm organic filter membrane, collect the second filtrate. In steps (1)-(3), maintain a stirring speed of 800 rpm. The hydrogen gas is high-purity hydrogen gas with a purity of not less than 99.99% by volume. The remaining reaction conditions and parameters are tested in sequence as shown in Table 3, and then analyzed according to the corresponding methods in Table 4.

[0086] Table 3 Reaction conditions and parameters in each example

[0087] The different depolymerization temperatures described in Example 16(1) are 175, 200, 225, 250, 275, and 300 °C.

[0088] The different depolymerization pressures described in Example 16(2) are 0, 0.5, 1, 1.5, 2, 2.5, and 3 MPa.

[0089] The different depolymerization times described in Example 16(3) are 0.5, 1, 2, 4 and 8 h respectively.

[0090] The different catalyst addition amounts described in Example 16(4) were 2.5, 5, 10, 20, 30, and 40 wt%.

[0091] The different solvents described in Example 16(5) are methanol (MeOH), ethanol, isopropanol, and 1,4-dioxane.

[0092] The different biomass mentioned in Example 20 are eucalyptus, beech, cedar, pine, and birch.

[0093] 12.2 Analytical and detection methods for depolymerization products 12.2.1 Gas Chromatography-Mass Spectrometry (GC-MS) Detection Method: 1.5 mL of the second filtrate was injected into a 2 mL brown screw-top vial. The main monomer components in the depolymerization products were structurally identified and characterized using a gas chromatograph-mass spectrometer (GC-MS). The chromatographic column used was an Agilent HP-5 column (Agilent 19091S-433UI HP-5MS Ultra Inert, 30 m × 0.25 mm, 0.25 µm). The conditions were as follows: inlet temperature 250 ℃, column oven temperature maintained at 70 ℃ for 3 min, then increased to 320 ℃ at a rate of 6 ℃ / min and held for 5 min; injection volume 1 μL, split ratio 20:1, split flow rate 10 mL / min; MS ion source temperature 230 ℃, MS quadrupole temperature 150 ℃. The structure of each chromatographic peak was confirmed by comparison with a mass spectrometry library. The relative content (area percentage) of each identified monomer was calculated using the peak area normalization method to characterize the monomer composition and distribution of the depolymerization products. Since different compounds exhibit varying responses in mass spectrometry, the results obtained by this method are semi-quantitative and are primarily used to compare the trends in product distribution under different catalytic systems.

[0094] 12.2.2 Gel Chromatography (GPC) Method: Tetrahydrofuran (THF) was used as the mobile phase. Preparation method: Take an appropriate amount of analytical grade THF and filter it twice through a 0.22 μm polyamide organic filter membrane to remove impurities. Degas the filtered THF using ultrasonic degassing for 30 min to remove air bubbles and avoid interference with the test. Accurately weigh the lignin crude oil sample to be tested, and use the degassed THF as a solvent to prepare a sample solution with a concentration of 1 mg / mL. Stir thoroughly until completely dissolved. Filter using a 0.22 μm polyamide organic filter membrane to remove insoluble impurities. Transfer the clear sample solution to a labeled injection bottle for later use. After the GPC instrument self-test is completed, connect the mobile phase. The chromatographic column used is a Shodex GPC KF-401 HQ, and the column oven temperature is set to 40℃. After the column temperature stabilizes, adjust the mobile phase flow rate until stable. Once the baseline is stable, begin the injection test. The automatic injection mode was used, with an injection volume of 90 μL and a single analysis time of 25 min. After the test of a single sample was completed, the column was rinsed with the mobile phase to avoid residue. All samples were tested in sequence and the parameters were recorded.

[0095] 12.2.3 Quantitative Method Using Gas Chromatography-Flame Ionization Detector (GC-FID) (1) Method for plotting the GC-FID standard curve for each individual: The following eight monomers were identified as having relatively high content by GC-MS: 4-propyl-2-methoxyphenol (PG), 4-propyl-2,6-dimethoxyphenol (PS), 4-ethylphenol (EtP), 4-ethyl-2-methoxyphenol (EtG), methyl 3-(4-hydroxyphenyl)propionate (H-ester), methyl 3-(4-hydroxy-3-methoxyphenyl)propionate (G-ester), 3-(4-hydroxy-3-methoxyphenyl)-1-propanol (POH-G), and 4-(3-hydroxypropyl)-2,6-dimethoxyphenol (POH-S). The relative content of each monomer component in the depolymerization product was semi-quantitatively estimated using the GC-MS peak area normalization method to determine the upper limit of yield for each monomer. Based on this, each monomer standard was accurately weighed and prepared into a high-concentration mixed standard stock solution using chromatographic grade methanol as the solvent. Subsequently, the mixed standard stock solution was serially diluted with chromatographic grade methanol to obtain a series of mixed standard working solutions of different concentrations. The above series of standard working solutions were injected into GC-FID for analysis, and the peak areas of each monomer at different concentrations were recorded to establish a quantitative relationship between the concentration of each monomer and the corresponding peak area. Linear regression fitting was performed on the obtained data points to obtain the standard curves for each monomer, as shown below. Figure 17 As shown, the linear equations are as follows: 4-propyl-2-methoxyphenol (a): y = 0.0015x + 0.008(R) 2 =0.9976), 4-propyl-2,6-dimethoxyphenol (b): y=0.0024x+0.034(R 2 =0.9981), 4-Ethylphenol (c): y=0.0014x+0.008(R) 2 =0.9992), 4-Ethyl-2-methoxyphenol (d): y=0.0018x-0.0075(R 2 =0.9993), Methyl 3-(4-hydroxyphenyl)propionate (e): y=0.0029x+0.0831(R 2 =0.9987), Methyl 3-(4-hydroxy-3-methoxyphenyl)propionate (f): y=0.0032x+0.1216(R 2 =0.9969), 3-(4-hydroxy-3-methoxyphenyl)-1-propanol (g): y=0.0016x+0.0217(R) 2 =0.9992), 4-(3-hydroxypropyl)-2,6-dimethoxyphenol (h): y=0.0020x+0.00348(R) 2=0.9987). The GC-FID conditions were as follows: The column used was an Agilent HP-5 column (Agilent 19091J-436 UI HP-5, 60 m × 0.25 mm, 0.25 µm), and the conditions were: the inlet temperature was 250 ℃, the column oven was held at 70 ℃ for 3 min and then increased to 250 ℃ at a rate of 6 ℃ / min and held for 3 min; the injection volume was 1 μL, the split ratio was 20:1, and the split flow rate was 10 mL / min; the FID detector temperature was 200 ℃, and the hydrogen and air flow rates were 30 mL / min and 300 mL / min, respectively.

[0096] (2) Detection of the second filtrate The second filtrate obtained from each depolymerization reaction was analyzed under the same GC-FID conditions as those used to establish the standard curve. (3) Substitute the peak area obtained from the test into the equation of the standard curve to obtain the specific yield of different monomers.

[0097] 12.2.4 Nuclear Magnetic Resonance Spectroscopy (NMR) Detection Method: 2D HSQC NMR can identify different types of linkages and aromatic units at the molecular level. 40 mg of lignin or crude lignin oil was added to 0.75 mL of DMSO-d6 or CDCl-d6, vortexed to ensure complete dissolution, and then injected into an NMR tube for analysis in an NMR spectrometer. Experimental conditions were as follows: HSQCETGPSI as the experimental pulse, NS=64, D1=0.5, T1=512.

[0098] Table 4. Detection and analysis methods for depolymerization products obtained in each embodiment.

[0099] Example 13 Structure of monomer products obtained from depolymerization of bagasse using Ru / C and XCNi-MOF-74 series catalysts The depolymerization reaction was carried out according to the method and conditions described in section 12.1 of Example 12, and the detection was performed according to the method described in section 12.2.1 of Example 12, resulting in a GC-MS total flow plot as shown below. Figure 14 As shown, the structural formulas of the eight monomers with higher content in the second filtrate are as follows: Figure 15 As shown. By Figure 14 and Figure 15As can be seen, the main monomer depolymerization products can be classified into eight types, divided into three categories, based on the different para-hydroxyl groups: alkyl groups (PG, PS, EtG, EtP), alcohols (POH-G, POH-S), and esters (G-ester, H-ester), corresponding to different reaction pathways or degrees of reaction. In general, the products of bagasse depolymerization are mainly derivatives of lignin monomers (H, G, S). Subsequent experiments will further investigate... Figure 14 and Figure 15 The monomers listed in the document are quantified to determine their yield and selectivity.

[0100] Example 14 Molecular weight distribution of monomer products obtained from depolymerization of bagasse using Ru / C and XCNi-MOF-74 series catalysts The depolymerization reaction was carried out according to the method and conditions described in section 12.1 of Example 12, and the results were detected according to the method described in section 12.2.2 of Example 12. Figure 16 As shown, compared to Ru / C, the elution peak of the product obtained by depolymerizing bagasse using the XCNi-MOF-74 series catalysts shifted significantly forward, indicating a higher relative molecular weight. The main peak positions of the various samples from the XCNi-MOF-74 series catalysts were close, indicating that the heat treatment temperature had a limited effect on the average molecular weight; however, the peak shapes differed, with samples treated at medium temperatures showing a more concentrated molecular weight distribution, while samples treated at lower or higher temperatures showed a relatively wider distribution, indicating that the heat treatment temperature had a significant impact on the molecular weight distribution.

[0101] Example 15: Yields of various monomers in the products obtained from the depolymerization of bagasse using MeOH, Ru / C, Ni-MOF-74, and XCNi-MOF-74 series catalysts. The depolymerization reaction was carried out according to the method and conditions described in section 12.1 of Example 12, and the detection was performed according to the method described in section 12.2.3 of Example 12. The GC-FID measurement results are as follows: Figure 18 As shown. By Figure 18 It is evident that the yields of all monomers in the depolymerization product of bagasse using the XCNi-MOF-74 series catalysts are significantly improved. The total yield of all monomers generally increases and then decreases with increasing pyrolysis temperature. The total yield of all monomers in the product obtained by depolymerizing bagasse using the 300°C Ni-MOF-74 catalyst reaches the highest level of 44.65%. The total yields of all monomers in the control group (MeOH with only solvent) and the unpyrolyzed Ni-MOF-74 catalyst are relatively low, at 8.73% and 8.68%, respectively, indicating that the XCNi-MOF-74 series catalysts significantly improve the depolymerization of lignin. These results are consistent with the characterization results in the aforementioned examples, indicating that the pyrolysis process significantly affects the physicochemical properties of the catalyst, thereby improving its catalytic effect. Figure 18The distribution of different monomer products was also shown, indicating that the XCNi-MOF-74 series catalysts exhibit high selectivity for formate esters during the depolymerization of sugarcane bagasse, especially the 300CNi-MOF-74 catalyst, which shows a selectivity of up to 37.41% for H-ester. Furthermore, comparative experiments were conducted under the same conditions using Ru / C catalysts, which are widely used in industry. Regarding product distribution, the Ru / C catalyst produced a homogeneous monomer composition and failed to effectively improve the yield of specific lignin derivatives. In contrast, the XCNi-MOF-74 series catalysts showed superior selectivity for high-value-added compounds such as G-ester and H-ester. This demonstrates that high-yield and highly selective depolymerization in sugarcane bagasse can be achieved under appropriate pyrolysis temperatures. In conclusion, the XCNi-MOF-74 series catalysts can improve the depolymerization efficiency of lignin in sugarcane bagasse and influence the product distribution. The 300CNi-MOF-74 catalyst showed significant improvements in both product yield and selectivity, so it was used for subsequent condition optimization experiments.

[0102] Example 16 Optimization of reaction conditions for depolymerization of bagasse catalyzed by 300CNi-MOF-74 The depolymerization reaction was carried out according to the method and conditions described in section 12.1 of Example 12, and the results were tested according to the method described in section 12.2.3 of Example 12. The effects of key parameters such as depolymerization temperature, depolymerization pressure, depolymerization time, catalyst addition amount and solvent type on monomer yield and average molecular weight were systematically investigated.

[0103] (1) Optimization of depolymerization temperature Depend on Figure 19 It is evident that the monomer yield of bagasse lignin gradually increases with increasing depolymerization temperature, rising from 7.62% at 175℃ to 45.26% at 250℃. This indicates that temperature significantly affects the depolymerization of lignin structure, promoting its degradation. However, as the temperature continues to rise, the monomer yield of bagasse lignin no longer increases significantly and may even decrease to some extent. This may suggest that excessively high temperatures could lead to condensation of some products, thus affecting the final selectivity and yield. The continuous increase in temperature not only promotes the depolymerization rate of lignin but may also affect the reverse reaction rate and the occurrence of side reactions. In summary, depolymerization temperature has a significant impact on lignin depolymerization efficiency and product distribution. From 175℃ to 250℃, the monomer yield gradually increases with increasing temperature; subsequently, from 275℃ to 300℃, the product yield is less affected by temperature, indicating the importance of appropriate depolymerization temperature in the lignin depolymerization process. In practical applications, considering the high requirements of temperature on energy consumption and equipment performance, the depolymerization temperature of 250 ℃, which has a high cost-performance ratio, is preferred.

[0104] (2) Depolymerization pressure optimization analysis Depend on Figure 20 It is evident that the monomer yield of lignin generally shows a gradual upward trend as the depolymerization pressure increases from 0 to 3 MPa. The highest monomer yield, reaching 47.56%, was achieved at 2 MPa, representing a 36.18% increase compared to the depolymerization monomer yield at 0 MPa. Appropriate depolymerization pressure can enhance the collision probability between reactants, thereby accelerating the reaction rate. Hydrogen, as a source of reducing atmosphere, can effectively promote lignin decomposition and improve the selectivity of specific products. However, except for the depolymerization experiment without hydrogen pressure, where the monomer yield was below 40%, the monomer yields at other hydrogen pressures all reached relatively high levels. Nevertheless, at 3 MPa, although the overall yield remained high, the yield of some monomers decreased. This may be because the high-pressure environment promoted the conversion mechanism of gaseous or liquid reactions, causing some products to be further reduced or converted, thus affecting the final product distribution. In conclusion, depolymerization pressure has a significant impact on monomer yield and product distribution during the depolymerization process of bagasse lignin. Increasing the depolymerization pressure appropriately can effectively improve the yield, with the highest monomer yield achieved at 2 MPa. Therefore, a depolymerization pressure of 2 MPa is preferred.

[0105] (3) Optimization of de-aggregation time Depend on Figure 21 It is evident that the monomer yield of lignin gradually increases with the extension of depolymerization time, rising from 24.96% at 0.5 h to 48.06% at 2 h. Further extension of depolymerization time has a smaller impact on monomer yield thereafter. This trend indicates that appropriately extending the depolymerization time helps to more thoroughly depolymerize lignin. In shorter depolymerization times, lignin may not be fully depolymerized, resulting in a lower overall product yield. As time increases, the reaction proceeds more thoroughly, and the product yield gradually increases. However, excessively long depolymerization times, compared to 4 hours, slow down this gradual increase and may even lead to the conversion or degradation of some high-value products. In summary, depolymerization time has a significant impact on lignin depolymerization efficiency and product distribution. By appropriately extending the depolymerization time, the monomer yield gradually increases; therefore, a depolymerization time of 2 h is preferred.

[0106] (4) Optimization of catalyst addition amount Depend on Figure 22As can be seen, the monomer yield of lignin generally increases with the increase of catalyst addition. At a 20.0% addition, the yield reached 47.94%, the highest among all experimental conditions. Lower additions of 2.5% and 5.0% catalyst showed lower monomer yields, at 30.59% and 38.29%, respectively. This trend indicates that appropriately increasing the catalyst addition can effectively improve the efficiency of lignin depolymerization. At 30% and 40% additions, although the total monomer yield remained high, the yields of some specific products decreased. This phenomenon may indicate that excessive catalyst addition can lead to saturation of catalytic active sites, thus affecting the selectivity of the reaction process. Appropriate catalyst addition can ensure sufficient catalytic active sites, improving reaction efficiency and conversion. However, excessive addition may lead to mutual interference between catalysts or intermolecular competition of reactants, thereby affecting the selectivity for specific products. Since the effective contact area and concentration of the catalyst change, its mechanism of action in the depolymerization process also changes accordingly; therefore, controlling the addition amount is crucial. In summary, the catalyst dosage has a significant impact on the depolymerization yield and product distribution of bagasse lignin. Appropriately increasing the catalyst dosage can significantly improve monomer yield and product selectivity. However, excessive dosage can lead to decreased reaction efficiency and a reduction in high-value products. Therefore, a catalyst dosage of 20% is preferred.

[0107] (5) Optimization of reaction solvent Depend on Figure 23 It is evident that methanol yielded the highest monomer yield of lignin, reaching 47.89%, when used as the solvent. This result indicates that methanol excels in promoting lignin depolymerization, providing optimal conditions for lignin conversion, which is strongly related to methanol's superior hydrogen-donating capacity. Other solvents, such as ethanol, isopropanol, and 1,4-dioxane, yielded relatively lower yields, at 15.85%, 10.69%, and 11.33%, respectively. The polarity and chemical properties of the solvent directly affect the interaction between reactants. The higher polarity of methanol may help increase the solubility of lignin, thereby enhancing its reactivity and effectively promoting the depolymerization reaction. Other solvents, such as 1,4-dioxane, although relatively stable, may not provide adequate hydrogen donation for the reaction or may not have good contact and dispersion with the reactants, limiting the occurrence of the reaction. In summary, the type of solvent has a significant impact on the monomer yield and selectivity of the target product in the depolymerization of bagasse lignin. Methanol as a solvent shows a clear advantage in improving the efficiency of lignin depolymerization. Therefore, methanol is preferred as a solvent, which can maximize the performance of the catalyst within a limited range.

[0108] Example 17 Molecular weight distribution of depolymerization products obtained under preferred depolymerization conditions Under optimized conditions, catalytic depolymerization of bagasse was carried out using a 300CNi-MOF-74 catalyst and an industrial Ru / C catalyst, respectively. Subsequently, GPC was used to analyze the molecular weight of the depolymerization products obtained from both catalysts and the lignin extracted from bagasse using the wood-grinding method. The results are as follows: Figure 24 As shown. By Figure 24 As can be seen, the wood-grinding method for extracting lignin from bagasse exhibits a broad elution curve, centered at a relatively short retention time (5–10 min), indicating a high average molecular weight and significant molecular weight polydispersity, characteristic of the heterogeneous and highly cross-linked structure of natural lignin. In the product obtained by Ru / C catalytic depolymerization, the high molecular weight component is largely suppressed, and the molecular weight distribution shifts significantly to longer retention times (14–18 min), indicating effective fragmentation of the lignin macromolecular skeleton. However, the presence of multiple peaks suggests the continued existence of oligomers, indicating partial depolymerization under these conditions. In contrast, the product obtained by 300CNi-MOF-74 catalytic depolymerization shows a further shift towards the lower molecular weight region (16–19 min), accompanied by a significantly narrower distribution. The near-complete disappearance of high molecular weight substances highlights the superior depolymerization efficiency of 300CNi-MOF-74, which can be attributed to its strong hydrogenolytic activity and its ability to stabilize lignin fragments, thereby inhibiting the recondensation reaction.

[0109] Example 18: Reusability of 300CNi-MOF-74 Catalyst To systematically evaluate the reusability and structural stability of the 300CNi-MOF-74 catalyst under actual reaction conditions, multiple rounds of cyclic catalytic experiments were conducted. The depolymerization reaction conditions were identical in each round, and the specific parameters are shown in Table 3. After each round of reaction, the catalyst was rapidly recovered from the reaction mixture using magnetic separation technology. After thorough washing and drying, it was added to the next round of reaction. Simultaneously, the obtained crude lignin oil was subjected to GPC analysis according to the method described in Section 12.2.2 of Example 12. By comparing the yields of aromatic monomer products generated from lignin depolymerization in each round of reaction, the changing trend of catalyst activity can be visually reflected. The results are as follows: Figure 25 As shown. By Figure 25As can be seen, 300CNi-MOF-74 exhibited good catalytic stability in the first two cycles. The total yield of aromatic monomers fluctuated only slightly, around 5.7%, indicating that the catalyst did not experience significant activity degradation or structural damage during this stage. However, starting from the third cycle, the product yield showed a more significant decrease. By the fourth cycle, the total yield had decreased by 19.47% compared to the initial use, indicating that the catalyst activity had been partially lost. To verify whether the catalyst deactivation was reversible and to explore its regeneration potential, the catalyst recovered after the fourth cycle was subjected to re-pyrolysis treatment (300 °C, 2 h) to remove surface-adsorbed organic residues and impurities. The treated catalyst was reused for the catalytic reaction. The results showed that the total yield of aromatic monomers was significantly improved compared to before regeneration, recovering to a level lower than that of the fresh catalyst. In summary, 300CNi-MOF-74 demonstrates good recyclability potential in the lignin depolymerization reaction. Its activity decline is mainly caused by physical covering and surface contamination, rather than irreversible structural damage. Effective regeneration can be achieved through simple calcination. Therefore, in practical applications, a periodic regeneration strategy is needed to maintain the high activity and long-term stability of the catalyst.

[0110] Example 19 Structural changes of lignin in sugarcane bagasse before and after catalytic depolymerization under 300CNi-MOF-74 catalysis To understand the structural changes of lignin in bagasse after catalytic depolymerization using 300CNi-MOF-74 catalyst, lignin was first extracted from bagasse using the wood-grinding method. Then, the bagasse was catalytically depolymerized using 300CNi-MOF-74 to obtain crude lignin oil (the depolymerization reaction steps are described in Example 12, and the conditions are shown in Table 3). Following the method described in section 12.2.4 of Example 12, the lignin and crude lignin oil obtained in this example were subjected to 2D HSQC nuclear magnetic resonance detection. The results are as follows: Figure 26 As shown. By Figure 26 It can be seen that the oxygen-containing side chain regions (δC / δH 50.0-100.0 / 3.0-6.0) of sugarcane bagasse correspond to the C of the α-O-4 substructure (A). α / H α (δC / δH 57.8-65.1 / 3.1-3.9) and C β / H β (δC / δH 81.8-87.7 / 3.9-4.5) correlation. Furthermore, as shown in the figure, units corresponding to H, G, and S, as well as FA and [other elements], can be detected in the bagasse sample. pThe δC / δH (100.0-135.0 / 6.0-8.0) signals of the CA unit highly match the composition of lignin in sugarcane bagasse, a herbaceous plant, indicating that the extraction of lignin from sugarcane bagasse largely preserves the original structure of lignin without any loss of related structures, which can be compared with lignin depolymerization products. The obtained lignin oil showed some aromatic correlations in the NMR spectrum of the oil fraction. Several new CH-related signals are attributed to methyl groups (δC / δH 51.0 / 3.6) attached to phenolic methyl esters derived from natural lignin, and ethyl and propyl groups of phenolic monomers in the δC / δH (10.0-50.0 / 0.5-3.0) region. Furthermore, the figure shows aromatic rings in phenolic compounds (such as phenol, guaiacol, and eugenol derivatives), which are generated from the reductive depolymerization of lignin subunits in sugarcane bagasse. This demonstrates that the original multi-benzene ring bonded structure in lignin is broken down into various monomeric structures after depolymerization, further verifying the good performance of the 300CNi-MOF-74 catalyst in depolymerizing lignin from sugarcane bagasse. Furthermore, the chemical shift signals at δC / δH (58.3-78.8 / 2.8-3.7) are related to the methyl functional groups of the methylated sugar derivatives formed during the liquefaction reaction. It can be seen that the high-temperature depolymerization process also depolymerizes cellulose and hemicellulose to varying degrees, producing sugars, which is related to… Figure 14 and Figure 15 The chromatogram results corroborate each other.

[0111] Example 20: Performance of 300CNi-MOF-74 catalyst in the depolymerization of lignin from different sources As demonstrated in Examples 13-19, the XCNi-MOF-74 series catalysts, especially 300CNi-MOF-74, exhibit excellent depolymerization effects on bagasse, a herbaceous biomass. Compared to commonly used Ru / C catalysts in industry, the effect is significantly improved, with monomer yield increasing by 21.27%, mostly due to the increase in H-ester and G-ester esters. However, in nature, a significant amount of biomass exists in the form of woody materials and their byproducts.

[0112] To further verify the applicability of 300CNi-MOF-74 to lignin in woody biomass, 300CNi-MOF-74 was used as a representative catalyst. Depolymerization experiments were conducted on eucalyptus, beech, fir, pine, and birch trees according to the methods and conditions described in section 12.1 of Example 12, and the results were analyzed according to the methods described in sections 12.2.1 and 12.2.3 of Example 12. The results are as follows: Figure 27 and Figure 28 As shown. According to Figure 27It is evident that the depolymerization products of woody materials using the 300CNi-MOF-74 catalyst lack esters compared to those from bagasse depolymerization. Instead, they contain relatively higher levels of PS and PG. While the overall monomer yield is somewhat lower than that from bagasse, the significantly higher lignin content in woody materials compared to herbaceous bagasse results in a smaller difference in yield and considerable potential for improvement. Focusing on product yield and distribution, the depolymerization products from woody materials mainly fall into two categories, also reflected in the different groups at the para-position of the hydroxyl group: alkyl groups and alcohols. Figure 28 It is evident that the 300CNi-MOF-74 catalyst achieved depolymerization yields of over 15% for hardwoods, with the highest efficiency (25.13%) for eucalyptus, followed by beech (23.91%), and the lowest (17.58%) for birch. The depolymerization yields for softwoods were lower than those for hardwoods. The distribution of depolymerization products for pine (11.86%) and fir (12.03%) differed somewhat from that of hardwoods. In hardwoods, the depolymerization products contained a higher proportion of POH-S and PS related to S structural units, and a lower proportion of POH-G and PG related to G structural units. Conversely, in softwoods, the depolymerization products showed a higher proportion of POH-G and PG related to G structural units. This is related to the different proportions of different structural units in different lignins, indicating that 300CNi-MOF-74 also has a significant effect on the depolymerization of lignin in woody materials.

[0113] Example 21 Possible reaction pathways of 300CNi-MOF-74 catalyst in bagasse depolymerization Based on the above product bar chart and Figure 26 The two-dimensional NMR spectrum shows that the main products of the 300CNi-MOF-74 catalyst in the depolymerization of bagasse are two esters and two monomers, propanol. Figure 26 It can be seen that FA and [other compounds] are present in the original lignin. p Comparing the two CA structures with the structures of H-ester and G-ester in the depolymerization products, it is clear that these two products originate from FA and... p CA are two lignin substructures. The four products, PS, PG, POH-S, and POH-G, may originate from... Figure 26 The A structure in lignin is one of the main structures present in lignin. The difference between the four products PS, PG, POH-S, and POH-G lies in the presence or absence of the propyl-terminal hydroxyl group, which is related to the substructure of lignin and the degree of reduction during reductive depolymerization. Therefore, based on previous research, a possible reaction pathway for sugarcane bagasse lignin in a 300CNi-MOF-74 catalyst methanol system is proposed. Figure 29 As shown, for FA and in the methanol system pIn the lignin environment, methanol and hydrogen in the system dissociate into active H under the action of a 300CNi-MOF-74 catalyst. ● These active H ● It adheres to the catalyst surface, thus providing reducing power in the reaction to break the ester bonds between lignin and hemicellulose, while methanol dissociates into active H+. ● The subsequent production of methoxy radicals and FA and p The esters present in the CA and H structures undergo transesterification, followed by further hydrogenation to generate G-ester or H-ester. These two structures are abundant in bagasse, corresponding to the product distribution of bagasse depolymerization mentioned above. The most abundant monomer structures in bagasse depolymerized biomass oil are G-ester and H-ester. The reaction pathways for PS, PG, POH-S, and POH-G can be inferred to involve the reduction and breaking of the β-O-4 bond in the lignin structure to obtain an enol structure. The enol structure is generally unstable and undergoes tautomerization to a ketone structure, followed by dehydration to generate an enone structure. Subsequently, the active H-ester structure dissociates under a catalyst. ● Under the action of [unclear], the C=C and C=O in the ketone are successively reduced to finally obtain saturated fatty alcohol side chains, namely POH-S and POH-G. Based on this structure, further [unclear] ● Under the reducing action, dehydration further generates PS and PG. Furthermore, in the above processes for FA and pCA, there should be a possibility of incomplete C=C reduction after transesterification. Figure 15 The presence of US-H-ester products can be observed, which is likely due to insufficient reducing power of metallic Ni in the catalyst.

[0114] Example 22 The modified Ni-MOF-74 is prepared by pyrolyzing Ni-MOF-74 under a protective atmosphere of hydrogen-nitrogen mixture. The pyrolysis temperature is selected from 280, 290, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, 400, 410, 420, 430, 440 or 450 °C, and the pyrolysis time is selected from 60, 80, 100, 120, 140, 160, 180, 200, 220 or 240 min. The volume percentage of hydrogen in the hydrogen-nitrogen mixture is selected from 3, 4, 5, 6, 7 or 8%, with the balance being nitrogen.

[0115] Example 23 A method for depolymerizing lignin includes the following steps: (1) weighing sugarcane bagasse, catalyst, and methanol solvent according to a ratio and mixing them evenly in a high-temperature and high-pressure reactor; (2) pressurizing the reactor to the depolymerization pressure using hydrogen gas and then depressurizing it to completely remove air from the reactor, and then pressurizing the reactor to the depolymerization pressure using hydrogen gas again; (3) heating the reactor to the depolymerization temperature to carry out the depolymerization reaction. The mass ratio of the modified Ni-MOF-74 added to the sugarcane bagasse is selected from 5:100, 8:100, 10:100, 12:100, 15:100, 18:100, 20:100, 22:100, or 25:100. The amount of methanol solvent added is calculated according to the ratio of 60, 65, 70, 75, or 80 L of methanol solvent per kilogram of sugarcane bagasse. The pressure of the hydrogen gas is selected from 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, 2.0, or 2.2 MPa. The temperature of the depolymerization reaction is selected from 225, 230, 235, 240, 245, 250, 255, 260, 265, 270, or 275 °C. The time of the depolymerization reaction is selected from 1, 2, 3, or 4 hours.

[0116] Example 24 A method for depolymerizing lignin includes the following steps: 100 kg of sugarcane bagasse, 20 kg of 300CNi-MOF-74, and 6000 L of methanol are placed in a high-temperature and high-pressure reactor and mixed evenly; the reactor is pressurized to 1.8 MPa with hydrogen and then depressurized to completely remove air from the reactor; the reactor is then pressurized to 1.8 MPa with hydrogen; the temperature is raised to 260 °C, and the depolymerization reaction is carried out for 3 h.

[0117] Example 25 The modified Ni-MOF-74 has BET specific surface areas of 100, 102, 104, 106, 108, 110, 112, and 115 m². 2 / g, with average pore sizes of 6.5, 6.8, 7.0, 7.2, and 7.5 nm, and total pore volumes of 0.15, 0.16, 0.17, 0.18, 0.19, and 0.20 cm³. 3 / g. The mass fractions of Ni, determined by inductively coupled plasma atomic emission spectrometry, were 65.0, 66.0, 67.0, 68.0, 69.0, and 70.0 wt%.

Claims

1. A modified Ni-MOF-74, characterized in that, The modified Ni-MOF-74 satisfies any one or more of the following (a), (b), (c), (d), or (f): (a) The X-ray powder diffraction pattern measured by Cu Kα radiation λ = 1.5406 Å has diffraction peaks at 2θ values ​​of 2θ ≈ 44.5°±0.2°, 51.8°±0.2° and 76.3°±0.2°, which are attributed to the (111), (200) and (220) crystal planes of standard face-centered cubic metal Ni0, respectively. The peak signals are weakened compared to the characteristic peaks of the original Ni-MOF-74 at 2θ=6.8°±0.2° and 11.7°±0.2°. (b) In the Fourier transform infrared spectrum, In 500-800 cm -1 The absorption band in the range belongs to Ni. 2+ The Ni-O stretching vibration formed with the carboxyl oxygen of the ligand; the intensity of this peak is reduced to less than 60% compared to the original Ni-MOF-74; At 1200-1600 cm -1 The absorption band in the region is attributed to CO stretching and C=C vibration of the aromatic ring in the organic ligand; the intensity of this peak is reduced to less than 60% compared to the original Ni-MOF-74. At 1600-1700 cm -1 The absorption band in the region is attributed to the stretching vibration of the coordinated carboxyl group C=O; the intensity of this peak is reduced to less than 60% compared to the original Ni-MOF-74. At 2500-3500 cm -1 The absorption band in the region includes the OH and aromatic CH stretching vibrations of the DHTP ligand; the intensity of this peak is reduced to less than 60% compared to the original Ni-MOF-74. (c) The mass fraction of Ni, as determined by inductively coupled plasma atomic emission spectrometry, was 65.0–70.0 wt%; (d) Scanning electron microscopy revealed a large number of uniformly distributed fine cracks and pores on the surface of a single prism and at its junctions; (e) A large number of uniform nanoparticles with higher contrast can be clearly observed on the surface and inside the framework by transmission electron microscopy. The nanoparticles are Ni element metal nanoparticles, or the corresponding energy dispersive X-ray spectroscopy surface scan shows that metal Ni is anchored on the carbonized framework in a highly dispersed nano state. (f) The specific surface area of ​​BET is 100–115 m². 2 / g, average pore size 6.5-7.5 nm, total pore volume 0.15-0.20 cm³. 3 / g.

2. A method for preparing modified Ni-MOF-74, characterized in that, Ni-MOF-74 was pyrolyzed for 60-240 min under a protective atmosphere of hydrogen-nitrogen mixture at a temperature of 280-450 °C. The hydrogen-nitrogen mixture contains 3-8% hydrogen by volume, with the remainder being nitrogen.

3. The application of the modified Ni-MOF-74 as a catalyst in lignin depolymerization as described in claim 2.

4. A method for depolymerizing lignin, characterized in that, Using the modified Ni-MOF-74 prepared according to claim 1 or claim 2 as a catalyst, lignin or lignin-containing biomass raw materials are subjected to hydrogen reduction depolymerization reaction.

5. The lignin depolymerization method as described in claim 4, characterized in that, The amount of modified Ni-MOF-74 added is in a mass ratio of 5-25:100 to the lignin or biomass raw material.

6. The lignin depolymerization method as described in claim 4, characterized in that, The depolymerization reaction is carried out using methanol as the solvent. The amount of solvent to be added is calculated based on the mass of the biomass raw material, at a ratio of 60-80 L of solvent per kilogram of biomass raw material.

7. The lignin depolymerization method as described in claim 4, characterized in that, The pressure of the hydrogen gas is 0.5-2.2 MPa.

8. The lignin depolymerization method as described in claim 4, characterized in that, The depolymerization reaction is carried out at a temperature of 225-275℃ for 1-4 hours.

9. The lignin depolymerization method as described in claim 4, characterized in that, The biomass raw materials are sugarcane bagasse, eucalyptus, beech, fir, pine, or birch.

10. The lignin depolymerization method as described in claim 4, characterized in that, Includes the following steps: (1) Weigh the biomass raw materials, catalyst and solvent according to the proportion and put them into a high temperature and high pressure reactor and mix them evenly; (2) Pressurize the reactor with hydrogen to the depolymerization pressure and then depressurize to completely remove the air from the reactor. Then pressurize the reactor with hydrogen to the depolymerization pressure. (3) Heat the temperature to the depolymerization temperature to carry out the depolymerization reaction.

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