Method for preparing syringyl products by hydrogenolysis of lignin catalyzed by nickel supported on molybdenum oxide modified zirconia

Abstract

The application discloses a method for preparing eugenol products by hydrogenolysis of lignin catalyzed by molybdenum oxide modified zirconium oxide supported nickel. The method uses lignin as raw material, adds a nickel-based catalyst and an alcohol solvent into the raw material, and then reacts under the condition that H2 pressure is 1-3 MPa, reaction temperature is 230-270 DEG C and reaction time is 2-6 h, so that the lignin is depolymerized to obtain eugenol products; the nickel-based catalyst is composed of a carrier ZrO2-xMoO3 and an active component nickel. The conversion rate of the lignin reaches 81.6%, the total yield of monophenol products can reach 15.4%, the yield of eugenol products reaches 7.5%, and the selectivity reaches 48.7%. The catalyst used in the application has low raw material cost, the preparation process is simple, and the lignin can be depolymerized under mild conditions to obtain eugenol products and other high value-added chemicals.

Description

Technical Field

[0001] This invention relates to catalytic hydrogenolysis of lignin, and in particular to a method for preparing high-value-added chemicals by catalytic hydrogenolysis of lignin using molybdenum oxide-modified zirconium oxide-supported nickel metal, which belongs to the field of high-value utilization of renewable biomass. Technical Background

[0002] With ever-increasing energy demand and unavoidable environmental problems, developing green, clean, and renewable energy sources can effectively alleviate these issues. Biomass is the only renewable carbon resource in nature and the world's fourth largest energy source, possessing immense potential to become the best alternative to fossil fuels.

[0003] Lignin, one of the three major components of biomass, is composed of CO, C-C bonds and three phenylpropane basic structural units. It possesses high energy density and holds promise as an excellent fuel for producing high-value-added products such as aromatics and phenolic chemicals. However, due to its complex and disordered internal cross-linked structure and chemical bonds, lignin is difficult to efficiently depolymerize to obtain the target products. Therefore, the industrial applications of lignin are currently very limited; most lignin is directly burned as fuel, and only 5% is used for low-value commercial applications.

[0004] Among existing lignin depolymerization strategies, catalytic hydrogenolysis has gained favor among researchers due to its high conversion rate of lignin and high product yield. The pore structure, acidity / basicity, and oxygen vacancies of the catalyst significantly affect its hydrogenolysis activity for lignin; therefore, designing a highly active catalyst is crucial for lignin catalytic hydrogenolysis systems. Supported non-precious metal catalysts are widely used lignin hydrogenolysis catalysts, possessing advantages such as wide availability, low cost, and strong CO bond breaking ability. Meanwhile, metal oxides, with their high stability and abundant acid-base sites, have attracted considerable attention as excellent supports.

[0005] Syringols mainly include: They are found in dried fish, natural smoked spices, etc., and can be used as raw materials for synthetic fragrances and flavorings, making them important industrial raw materials. Meanwhile, syringols are also intermediates in organic synthesis; demethoxylation can produce 4-propylguaiacol and 4-propylphenol, which are important intermediates in the production of daily chemical fragrances and flavorings; dealkylation yields 2,6-dimethoxyphenol, an important food additive and pharmaceutical intermediate.

[0006] In the existing technology, syringol products are mainly prepared by chemical synthesis methods such as selective methyl etherification or complete etherification of pyrogallol with bromomethane followed by selective demethylation. However, the gallic acid raw material used in this method is expensive and is prone to side reactions, resulting in complex products and low yield and selectivity of the target product.

[0007] Chinese invention patent CN113527065B discloses a method for preparing aviation fuel precursors by catalytic depolymerization of alkali lignin in an ethanol-water solvent using a Pd / C catalyst in synergistic alkaline catalyst. The method uses alkali lignin as raw material and an ethanol-water two-phase solvent as the reaction solvent. Pd / C and NaOH catalysts are added separately to carry out the depolymerization reaction, yielding the aviation fuel precursor. Under conditions of 5 wt.% Pd loading, a Pd / C to NaOH mass ratio of 1:5, a reaction pressure of 2 MPa, a reaction temperature of 260℃, and a reaction time of 4 h, the yield of monocyclic aromatic compounds can reach 37.5 wt.%. However, this technology uses precious metal catalysts with limited reserves and high costs; while activated carbon as a support provides a good specific surface area, it lacks sufficient acidic and basic sites; furthermore, the use of dual catalysts for lignin depolymerization makes the process relatively complex, which is not conducive to subsequent separation and quality improvement.

[0008] Chinese invention patent application CN116924891A discloses a method for preparing 2,6-dimethoxy-4-propylphenol by nickel-catalyzed hydrogenolysis of lignin supported by a cerium-zirconium composite metal oxide. This technique uses lignin as a raw material and a methanol / water binary solvent as the reaction medium, wherein the methanol content is 0.5-99.5% by mass. A nickel catalyst is added, and the reaction is carried out at an H2 pressure of 0.5-2.5 MPa and a temperature of 220-260℃ for 1-8 hours. This selectively converts lignin into a high-value-added monophenolic compound, and 2,6-dimethoxy-4-propylphenol is extracted. The nickel-based catalyst contains a Ce-based support. x Zr 1-x The catalyst consists of two components: O2 and active nickel, with a nickel loading of 5–25 wt.%; the catalyst support is Ce. x Zr 1-x The x in O2 is 0.2–0.8; the lignin conversion rate of this technology can reach 71.2–91.6%, and the yield of volatile products can reach 6.4–15.6%, of which the yield of syringol products is 1.9–5.7%. However, the cerium-zirconium composite metal oxide supported nickel catalyst used in this technology is difficult to effectively break the bonds between S units, resulting in poor selectivity for the products, especially for syringol products (S units), with a maximum selectivity of only 36.5%. At the same time, the methanol / water system used in this technology is difficult to guarantee the hydrothermal stability of the catalyst, and the catalyst is difficult to recycle multiple times. Summary of the Invention

[0009] The purpose of this invention is to provide an environmentally friendly, low-cost, and highly efficient hydrogenolysis catalyst for the selective catalytic conversion of lignin to prepare high-value-added chemicals such as syringin. By changing the amount of molybdenum oxide incorporated, the catalyst's acidity / basicity and pore structure are controlled, achieving efficient depolymerization of lignin. In this method, the lignin conversion rate can reach 68.9–79.2%, the total yield of monophenolic products can reach 7.6–15.4%, and the yield of syringin products can reach 3.6–7.5%, with a selectivity of 40.0%–52.6%. The high selectivity of the catalyst for these high-value-added chemicals not only helps reduce the occurrence of side reactions but also reduces the difficulty of separating the target products.

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

[0011] A method for preparing syringin derivatives by nickel-catalyzed hydrogenolysis of lignin using molybdenum oxide-modified zirconium oxide-supported catalyst is characterized by using lignin as a raw material, adding a nickel-based catalyst and an alcohol solvent to the raw material, and reacting at an H2 pressure of 1–3 MPa and a reaction temperature of 230–270 °C for 2–6 h to depolymerize the lignin and obtain syringin derivatives; wherein the nickel-based catalyst is composed of a support ZrO2-xMoO3 and an active component nickel, wherein the nickel loading is 5–20 wt.%; and in the support ZrO2-xMoO3, x represents the amount of molybdenum oxide incorporated, which is 5–20 mol%.

[0012] To further achieve the objectives of this invention, preferably, the preparation method of the nickel-based catalyst is as follows: nickel nitrate (Ni(NO3)2·6H2O) is fully dissolved in deionized water, and impregnated with a support ZrO2-xMoO3; after standing for 10-12 hours, it is dried and calcined in air to obtain a precursor; the precursor is reduced under an H2 atmosphere to obtain the nickel-based catalyst.

[0013] Preferably, the ZrO2-xMoO3 support is prepared by: mixing zirconium oxychloride (ZrOCl2·8H2O) and ammonium molybdate tetrahydrate ((NH4)6Mo7O). 24 The solution of ZrO2-xMoO3 was obtained by fully dissolving 4H2O and hexadecyltrimethylammonium bromide (CTAB) in deionized water and controlling the pH to 9-10. The reaction was carried out with stirring, and the resulting solution was aged at 60-80℃ for 2-4 hours. The filtered solid was dried and calcined in air to obtain the support ZrO2-xMoO3.

[0014] Preferably, the calcination is carried out in a muffle furnace at a temperature of 500–600°C for 3–5 hours; 0.10–0.12 g of zirconium oxychloride, 0.004–0.014 g of ammonium molybdate tetrahydrate and 0.04–0.06 g of cetyltrimethylammonium bromide are added per milliliter of deionized water; the pH is controlled to be 9–10 by adding ammonia dropwise.

[0015] Preferably, the reduction under H2 atmosphere is carried out in a vertical tube furnace at a temperature of 400–600°C for a time of 4–6 hours.

[0016] Preferably, the calcination temperature is 500–600°C, and the calcination time is 3–5 hours.

[0017] Preferably, the mass ratio of lignin to nickel-based catalyst is 1:0.4 to 1:1.2; and the mass ratio of lignin to alcohol solvent is 1:10 to 1:20.

[0018] Preferably, the alcohol solvent is any one of methanol, isopropanol, and n-hexanol.

[0019] Preferably, the lignin is derived from any one of bagasse, corn stalks, poplar, and bamboo; and the syringol product is one or more of 4-propylsyringol, 4-allylsyringol, 4-ethylsyringol, and 4-methylsyringol.

[0020] Preferably, the lignin is extracted by the following method: lignin raw material and extractant are added to a reaction vessel and reacted at 100-120℃ for 2-6 hours, followed by filtration and separation; the obtained filtrate is added to deionized water and filtered to obtain a solid, which is then dried to obtain organosoluble lignin; the extractant is composed of concentrated sulfuric acid, anhydrous ethanol, and deionized water; wherein the mass concentration of concentrated sulfuric acid is 95-98%, and 3200-4000 mL of anhydrous ethanol and 800-1000 mL of deionized water are added to every 24 g of concentrated sulfuric acid; 120-150 mL of extractant is added to every 10.0 g of lignin raw material.

[0021] Compared with other lignin catalytic depolymerization technologies, this invention has the following characteristics:

[0022] (1) Starting from the problems of low lignin depolymerization conversion rate and low product yield, this invention finds that by rationally selecting reaction media and catalysts, the reaction media, catalysts and syringol products can be synergistically combined, so that the lignin conversion rate can reach 68.9-79.2%, the total yield of monophenol products can reach 7.6-15.4%, of which the yield of syringol products can reach 3.6-7.5%, and the selectivity is 40.0%-52.6%.

[0023] (2) The molybdenum oxide-modified zirconium oxide-supported nickel catalyst used in this invention exhibits excellent catalytic activity. The incorporation of molybdenum oxide transforms the zirconium oxide crystal phase into a more active tetragonal phase, while simultaneously adjusting the overall acidity and basicity of the catalyst, providing suitable acid-base sites and further enhancing its catalytic activity. Compared to the catalyst without molybdenum oxide modification, the molybdenum oxide-incorporated catalyst exhibits nearly twice the reactivity towards lignin. Because the incorporation of molybdenum oxide improves the acidity and basicity of the supported catalyst, it enables efficient cleavage of CO bonds in lignin, resulting in highly selective S and G unit products.

[0024] (3) The catalyst used in this invention has a hexadecyltrimethylammonium bromide solution added as a template agent during the preparation process to obtain a multi-level porous material with mesoporous structure and a small amount of micropores. This pore structure is conducive to the mass transfer of lignin macromolecules, thereby improving its reactivity.

[0025] (4) The catalyst used in this invention has low cost, simple preparation process and low environmental pollution. The reaction conditions for lignin depolymerization are mild. A high monophenol yield can be obtained at a reaction pressure of 1-3 MPa and a reaction temperature of 230-270℃, which is beneficial to reduce energy consumption and achieve lignin depolymerization under mild conditions.

[0026] (5) The catalyst used in this invention can efficiently catalyze the hydrogenolysis of lignin, while exhibiting high selectivity for S and G units. The high selectivity of the catalyst for such high-value-added chemicals not only helps to reduce the occurrence of side reactions, but also reduces the difficulty of separating the target product.

[0027] (6) The catalyst of the present invention has strong stability and its activity does not decrease significantly after being used 8 times, which is significantly better than existing similar catalysts. Attached Figure Description

[0028] Figure 1 The image shows the XRD pattern of the molybdenum oxide-modified zirconium oxide support ZrO2-10MoO3 in Example 1 of this invention.

[0029] Figure 2 This is the N2 physical adsorption-desorption isotherm of the ZrO2-10MoO3 support in Example 1 of the present invention.

[0030] Figure 3 This is a pore size distribution diagram of the ZrO2-10MoO3 support in Example 1 of the present invention.

[0031] Figure 4 This is a SEM image of the ZrO2-10MoO3 support in Example 1 of the present invention.

[0032] Figure 5The image shows the Mo 3d spectrum in the XPS spectrum of the ZrO2-10MoO3 support in Example 1 of this invention.

[0033] Figure 6 This is a CO2-TPD diagram of the ZrO2-10MoO3 support in Example 1 of the present invention.

[0034] Figure 7 This is the NH3-TPD diagram of the ZrO2-10MoO3 support in Example 1 of the present invention.

[0035] Figure 8 The image shows the XRD pattern of the molybdenum oxide-modified zirconium oxide-supported nickel catalyst 15Ni / ZrO2-10MoO3 in Example 1 of this invention.

[0036] Figure 9 This is the N2 physical adsorption-desorption isotherm of the 15Ni / ZrO2-10MoO3 catalyst in Example 1 of this invention.

[0037] Figure 10 This is a pore size distribution diagram of the 15Ni / ZrO2-10MoO3 catalyst in Example 1 of the present invention.

[0038] Figure 11 This is a SEM image of the 15Ni / ZrO2-10MoO3 catalyst in Example 1 of the present invention.

[0039] Figure 12 The XPS spectrum of the 15Ni / ZrO2-10MoO3 catalyst in Example 1 of this invention shows the Mo 3d pattern.

[0040] Figure 13 The image shows the Ni 2p spectrum in the XPS pattern of the 15Ni / ZrO2-10MoO3 catalyst in Example 1 of this invention.

[0041] Figure 14 The CO2-TPD diagrams are shown for the 15Ni / ZrO2-5MoO3, 15Ni / ZrO2-10MoO3, and 15Ni / ZrO2-20MoO3 catalysts in Examples 1-3 of this invention.

[0042] Figure 15 The NH3-TPD diagrams are shown for the 15Ni / ZrO2-5MoO3, 15Ni / ZrO2-10MoO3, and 15Ni / ZrO2-20MoO3 catalysts in Examples 1-3 of this invention.

[0043] Figure 16 The image shows the GC-MS-FID spectrum of the product obtained by catalyzing organosolubilizing lignin using 15Ni / ZrO2-10MoO3 in Example 6 of this invention. Detailed Implementation

[0044] To better understand the present invention, the invention will be further described below with reference to the accompanying drawings and embodiments, but the implementation of the present invention is not limited thereto.

[0045] The syringol products of the present invention are one or more of 4-propylsyringol, 4-allylsyringol, 4-ethylsyringol, and 4-methylsyringol.

[0046] The alcohol-based solvent medium of this invention, due to its inherent hydroxyl groups, is an excellent hydrogen donor and also promotes hydrogen exchange between the solvent and H2, which is beneficial for the breaking of CO bonds in lignin. More importantly, the nickel-based catalyst used in this invention consists of a ZrO2-xMoO3 support and a nickel active component, wherein the nickel loading is 5-20 wt.%; in the ZrO2-xMoO3 support, x represents the molybdenum oxide incorporation, which is 5-20 mol%. The 5-20 wt.% nickel loading means that Ni accounts for 5-20% of the total catalyst mass, with the remainder being 80-95 wt.% from the support; the molybdenum oxide incorporation x in the ZrO2-xMoO3 support is the ratio of the molar amount of Mo to the total molar amount of Mo and Zr. The strong synergistic effect between the acidic and basic sites of the ZrO2 support enhances the transfer of H atoms, while MoO3 and Ni provide stronger acidity and basicity, respectively, and have excellent ability to break the bonds between syringin groups (S units). The target product of this invention, syringol, involves two ortho-methoxy groups of the syringol group, which weaken the bond energy of the β-O-4 linkage between S units, making it easier to break. Therefore, the method of preparing syringol products by nickel-catalyzed hydrogenolysis of lignin using molybdenum oxide-modified zirconium oxide-supported molybdenum oxide in this invention uses lignin as a raw material. After adding a nickel-based catalyst and an alcohol solvent to the raw material, the process conditions are controlled at H2 pressure of 1-3 MPa and reaction temperature of 230-270°C for 2-6 hours to depolymerize lignin and obtain syringol products.

[0047] Preferably, the alcohol solvent can be any one of methanol, isopropanol, and n-hexanol; the lignin can be derived from any one of bagasse, corn stalks, poplar wood, and bamboo; the mass ratio of lignin to nickel-based catalyst is 1:0.4 to 1:1.2; and the mass ratio of lignin to alcohol solvent is 1:10 to 1:20.

[0048] The preparation of the nickel-based catalyst of the present invention can refer to the preparation of similar catalysts. A preferred preparation method is as follows: nickel nitrate (Ni(NO3)2·6H2O) is fully dissolved in deionized water, and impregnated with a support ZrO2-xMoO3; after standing for 10-12 hours, it is dried and calcined in air to obtain a precursor; the precursor is reduced under a H2 atmosphere to obtain the nickel-based catalyst. The preparation method of the support ZrO2-xMoO3 is as follows: zirconium oxychloride (ZrOCl2·8H2O) and ammonium molybdate tetrahydrate ((NH4)6Mo7O) are mixed. 24 Zirconium oxychloride (·4H₂O) and hexadecyltrimethylammonium bromide (CTAB) are fully dissolved in deionized water, with the pH controlled at 9–10. The reaction is carried out under stirring, and the resulting solution is aged at 60–80°C for 2–4 hours. The filtered solid is dried and calcined in air to obtain the support ZrO₂-xMoO₃. In this method, calcination is carried out in a muffle furnace. The calcination temperature, calcination time, and the amounts of zirconium oxychloride, ammonium molybdate tetrahydrate, and hexadecyltrimethylammonium bromide added can be determined experimentally by those skilled in the art based on the purpose of the invention.

[0049] The lignin extraction method of this invention is basically the same as that disclosed in the prior art. Specifically, the lignin raw material and the extraction solution are added to a reaction vessel and reacted at 100-120°C for 2-6 hours, followed by filtration and separation. The obtained filtrate is added to deionized water and filtered to obtain a solid, which is then dried to obtain organosoluble lignin. The extraction solution is composed of concentrated sulfuric acid, anhydrous ethanol, and deionized water. The mass concentration of the concentrated sulfuric acid is 95-98%, and 3200-4000 mL of anhydrous ethanol and 800-1000 mL of deionized water are added to every 24 g of concentrated sulfuric acid. 120-150 mL of the extraction solution is added to every 10.0 g of lignin raw material.

[0050] Example 1: Preparation of 15Ni / ZrO2-10MoO3 catalyst

[0051] The preparation of the molybdenum oxide-modified zirconium oxide-supported nickel catalyst 15Ni / ZrO2-10MoO3 was achieved through a two-step method:

[0052] (1) Preparation of ZrO2-10MoO3 support: 11.60 g (36 mmol) of zirconium oxychloride solid (ZrOCl2·8H2O) and 0.71 g (4 mmol) of ammonium molybdate tetrahydrate solid ((NH4)6Mo7O) were weighed respectively. 24 Dissolve 4H₂O in 100 mL of deionized water and add 50 mL of 0.1 mol L⁻¹. -1A solution of hexadecyltrimethylammonium bromide (CTAB) was stirred at room temperature for 30 min. An appropriate amount of 25 wt.% ammonia water was weighed and slowly added dropwise to the above mixture, with continuous stirring and the pH of the solution controlled at 10. After the addition was complete, the resulting white emulsion was aged at 80 °C for 3 h. After the emulsion cooled to room temperature, it was filtered and washed with deionized water until neutral. The filter cake was then dried in a 120 °C oven for 12 h. The dried solid was ground into a uniform white powder and calcined in a muffle furnace at 550 °C for 4 h. The resulting pale yellow solid was the ZrO2-10MoO3 support.

[0053] The prepared ZrO2-10MoO3 support was characterized by X-ray diffraction to investigate its crystal structure. The results are as follows: Figure 1 As shown, distinct characteristic diffraction peaks were observed at 2θ values ​​of 30.3°, 34.9°, 50.2°, 60.0°, 62.6°, 73.7°, 81.7°, and 84.3°, belonging to tetragonal zirconium oxide (t-ZrO2). Tetragonal zirconium oxide exhibits higher catalytic activity than monoclinic zirconium oxide (m-ZrO2). Due to the relatively low content and uniform dispersion of molybdenum oxide in the support, no molybdenum oxide-related diffraction peaks were observed in the figure.

[0054] The prepared ZrO2-10MoO3 support was characterized by N2 physical adsorption-desorption to investigate its pore structure. The results are as follows: Figure 2 and Figure 3 As shown. By Figure 2 It can be seen that the adsorption isotherm of the ZrO2-10MoO3 support is a typical type IV isotherm, and a distinct H4 type hysteresis loop can be observed in the moderate relative pressure range (P / P0 = 0.4–1.0), indicating the presence of a mesoporous structure in the support. Combined with... Figure 3 The pore size distribution diagram shows that the main pore structure of the carrier is mesopores of 2–11 nm, and it also contains a small number of micropores of 1–2 nm.

[0055] The prepared ZrO2-10MoO3 support was characterized by SEM to investigate its surface morphology. The results are as follows: Figure 4 As shown, the surface morphology of the carrier is clearly observed to be an accumulation of spherical clusters.

[0056] The prepared ZrO2-10MoO3 support was characterized by XPS to investigate the presence of Mo on its surface. Figure 5 This is the 3d spectrum of Mo. After peak separation, the characteristic peaks at 231.4 and 234.4 eV correspond to Mo, respectively. 5+ 3D 5 / 2 and Mo 5+ 3D 3 / 2The characteristic peaks at 232.7 and 235.8 eV correspond to Mo, respectively. 6+ 3D 5 / 2 and Mo 6+ 3D 3 / 2 Orbit. The fitted peak areas indicate that the Mo element in the support mainly exists in the +6 valence state. 6+ and Mo 5+ The percentages were 96.1% and 3.9%, respectively.

[0057] The prepared ZrO2-10MoO3 support was characterized by CO2-TPD to investigate its basicity, and the results are as follows: Figure 6 As shown, two CO2 desorption peaks can be observed in the low-temperature region (0–200℃) and the medium-high temperature region (200–400℃), corresponding to the weak-base site and the medium-strong-base site of the support, respectively, indicating that there are a large number of weak-base sites and medium-strong-base sites in the support.

[0058] The prepared ZrO2-10MoO3 support was characterized by NH3-TPD to investigate its acidity, and the results are as follows: Figure 7 As shown in the figure, the NH3 desorption peaks A and B in the temperature range of 0–200℃ belong to weak acid sites, the NH3 desorption peaks C and D in the temperature range of 200–400℃ belong to medium-strong acid sites, and the desorption peak E above 400℃ belongs to strong acid sites.

[0059] (2) Preparation of 15Ni / ZrO2-10MoO3 catalyst: 0.87g of Ni(NO3)2·6H2O solid was weighed and dissolved in deionized water. The solution was added dropwise to a petri dish containing 1.00g of support, and stirred continuously until the mixture became viscous. The mixture was then allowed to stand at room temperature for 12h. The mixture was then dried in an oven at 120℃. After drying, the sample was ground into powder and placed in a muffle furnace, where it was calcined at 550℃ for 4h to obtain the catalyst precursor. The obtained precursor was reduced in a vertical tube furnace at 550℃ with an H2 flow rate of 10mL / min. -1 The 15Ni / ZrO2-10MoO3 catalyst can be obtained by reduction for 4 hours.

[0060] The prepared 15Ni / ZrO2-10MoO3 catalyst was characterized by X-ray diffraction to investigate its crystal structure. The results are as follows: Figure 8As shown, the catalyst is still mainly composed of tetragonal zirconium oxide (t-ZrO2), corresponding to diffraction peaks at 2θ of 30.3°, 34.9°, 50.2°, 60.0°, 62.6°, 73.7°, 81.7°, and 84.3°. Meanwhile, two newly observed characteristic diffraction peaks were observed at 2θ of 44.5° and 51.8°, corresponding to the (111) and (200) crystal planes of elemental Ni, respectively, proving that Ni was successfully supported on the catalyst carrier.

[0061] The prepared 15Ni / ZrO2-10MoO3 catalyst was characterized by N2 physical adsorption-desorption to investigate its pore structure. The results are as follows: Figure 9 and Figure 10 As shown. By Figure 9 It can be seen that the adsorption isotherm of the catalyst is also a typical type IV isotherm. Compared to the support, the catalyst exhibits an H4-type hysteresis loop at a higher relative pressure. According to capillary condensation theory, this indicates a reduction in the catalyst's pore size, which is attributed to the partial blockage of the pore structure caused by the loading of metallic Ni. Meanwhile, Figure 10 The pore size distribution diagram also shows that the pore volume of the catalyst is lower than that of the support.

[0062] The prepared 15Ni / ZrO2-10MoO3 catalyst was characterized by SEM to investigate its surface morphology. The results are as follows: Figure 11 As shown, a series of spherical particles, corresponding to the loaded Ni metal particles, can be clearly observed forming on the surface of the support.

[0063] The prepared 15Ni / ZrO2-10MoO3 catalyst was characterized by XPS to investigate the presence of Mo and Ni elements on its surface. The results are as follows: Figure 12 and 13 As shown. Figure 12 The 3d spectrum of Mo in the 15Ni / ZrO2-10MoO3 catalyst is shown. Unlike the support, the Mo element in the catalyst is in the form of Mo2O3. 6+ Mo 5+ Mo 4+ The three forms exist, accounting for 49.1%, 26.3%, and 24.6% respectively, indicating that MoO3 is also partially reduced during NiO reduction. Figure 13 The Ni 2p spectrum of the catalyst shows two characteristic peaks observed at 853.1 and 870.2 eV, corresponding to Ni, respectively. 0 2p 3 / 2 and Ni 0 2p 1 / 2 The characteristic peaks at 854.6 and 872.2 eV are attributed to Ni, respectively. 2+ 2p 3 / 2 and Ni 2+ 2p1 / 2 Compared to the standard characteristic peaks, the binding energies of the Ni orbitals are all shifted to higher levels, indicating electron transfer between Ni and the support, further proving the existence of metal-support interaction (MSI). Furthermore, based on the fitted peak areas, the binding energies of Ni can be obtained... 0 with Ni 2+ The ratio is approximately 7:3, indicating that most Ni species exist in the form of metallic elemental form, while the catalyst transfer and storage processes will cause the surface elemental Ni to be oxidized into Ni. 2+ .

[0064] The prepared catalyst was characterized by CO2-TPD to investigate its basicity, and the results are as follows: Figure 14 As shown, similar to the support, two CO2 desorption peaks can be observed in the low-temperature region (0-200℃) of the catalyst, corresponding to weak base sites. However, after loading with metallic Ni, new CO2 desorption peaks C and D appear in the catalyst, indicating that metallic Ni can provide medium-strong base and strong base sites. Among these, CO2 reacts with the coordinatingly unsaturated oxygen anion O. 2- The combination of bidentate carbonates provides strong base sites, and the presence of oxygen anions also signifies the formation of oxygen vacancies, indicating the presence of numerous oxygen vacancies in the catalyst. The basicity of the catalyst initially increases and then decreases with increasing MoO3 content, reaching its maximum when the MoO3 content is 10%.

[0065] The prepared catalyst was characterized by NH3-TPD to investigate its acidity, and the results are as follows: Figure 15 As shown, the loading of metallic Ni leads to a decrease in the number of weak acid sites on the catalyst, while the number of moderately strong acid sites increases slightly. Similar to the CO2-TPD characterization results, the acidity of the catalyst increases and then decreases with increasing MoO3 content. The amount of MoO3 incorporation mainly affects the number of moderately strong acid sites on the catalyst; when the MoO3 incorporation is 10%, both the number of moderately strong acid sites and the total number of acid sites reach their maximum values. Combined with CO2-TPD characterization, it can be found that the 15Ni / ZrO2-10MoO3 catalyst has optimal acid-base properties, which is beneficial to the depolymerization of lignin.

[0066] Example 2: Preparation of 15Ni / ZrO2-5MoO3 catalyst

[0067] The preparation of the molybdenum oxide-modified zirconium oxide-supported nickel catalyst 15Ni / ZrO2-5MoO3 was achieved through a two-step method:

[0068] (1) Preparation of ZrO2-5MoO3 support: 12.24 g (38 mmol) of zirconium oxychloride solid (ZrOCl2·8H2O) and 0.35 g (2 mmol) of ammonium molybdate tetrahydrate solid ((NH4)6Mo7O3) were weighed respectively. 24Dissolve 4H₂O in 100 mL of deionized water and add 50 mL of 0.1 mol L⁻¹. -1 A solution of hexadecyltrimethylammonium bromide (CTAB) was stirred at room temperature for 30 min. An appropriate amount of 25 wt.% ammonia water was weighed and slowly added dropwise to the above mixture, with continuous stirring and the pH of the solution controlled at 10. After the addition was complete, the resulting white emulsion was aged at 80℃ for 3 h. After the emulsion cooled to room temperature, it was filtered and washed with deionized water until neutral. The filter cake was then dried in an oven at 120℃ for 12 h. The dried solid was ground into a uniform white powder and calcined in a muffle furnace at 550℃ for 4 h. The resulting pale yellow solid was the ZrO2-5MoO3 support.

[0069] (2) Preparation of 15Ni / ZrO2-5MoO3 catalyst: 0.87g of Ni(NO3)2·6H2O solid was weighed and dissolved in deionized water. The solution was added dropwise to a petri dish containing 1.00g of support, and stirred continuously until the mixture became viscous. The mixture was then allowed to stand at room temperature for 12h. After drying, the sample was ground into powder and placed in a muffle furnace, where it was calcined at 550℃ for 4h to obtain the catalyst precursor. The obtained precursor was reduced in a vertical tube furnace at 550℃ with an H2 flow rate of 10mL / min. -1 The 15Ni / ZrO2-5MoO3 catalyst can be obtained by reduction for 4 hours.

[0070] Example 3: Preparation of 15Ni / ZrO2-20MoO3 catalyst

[0071] The preparation of the molybdenum oxide-modified zirconium oxide-supported nickel catalyst 15Ni / ZrO2-20MoO3 was achieved through a two-step method:

[0072] (1) Preparation of ZrO2-15MoO3 support: 10.31 g (32 mmol) of zirconium oxychloride solid (ZrOCl2·8H2O) and 1.41 g (6 mmol) of ammonium molybdate tetrahydrate solid ((NH4)6Mo7O) were weighed respectively. 24 Dissolve 4H₂O in 100 mL of deionized water and add 50 mL of 0.1 mol L⁻¹. -1A solution of hexadecyltrimethylammonium bromide (CTAB) was stirred at room temperature for 30 min. An appropriate amount of 25 wt.% ammonia water was weighed and slowly added dropwise to the above mixture, with continuous stirring and the pH of the solution controlled at 10. After the addition was complete, the resulting white emulsion was aged at 80 °C for 3 h. After the emulsion cooled to room temperature, it was filtered and washed with deionized water until neutral. The filter cake was then dried in an oven at 120 °C for 12 h. The dried solid was ground into a uniform white powder and calcined in a muffle furnace at 550 °C for 4 h. The resulting pale yellow solid was the ZrO2-20MoO3 support.

[0073] (2) Preparation of 15Ni / ZrO2-20MoO3 catalyst: 0.87g of Ni(NO3)2·6H2O solid was weighed and dissolved in deionized water. The solution was added dropwise to a petri dish containing 1.00g of support, and stirred continuously until the mixture became viscous. The mixture was then allowed to stand at room temperature for 12h. After drying, the sample was ground into powder and placed in a muffle furnace, where it was calcined at 550℃ for 4h to obtain the catalyst precursor. The obtained precursor was reduced in a vertical tube furnace at 550℃ with an H2 flow rate of 10mL / min. -1 The 15Ni / ZrO2-20MoO3 catalyst can be obtained by reduction for 4 hours.

[0074] Example 4: Preparation of 5Ni / ZrO2-10MoO3 catalyst

[0075] The preparation of the molybdenum oxide-modified zirconium oxide-supported nickel catalyst 10Ni / ZrO2-10MoO3 was achieved through a two-step method:

[0076] (1) Preparation of ZrO2-10MoO3 support: 11.60 g (36 mmol) of zirconium oxychloride solid (ZrOCl2·8H2O) and 0.71 g (4 mmol) of ammonium molybdate tetrahydrate solid ((NH4)6Mo7O) were weighed respectively. 24 Dissolve 4H₂O in 100 mL of deionized water and add 50 mL of 0.1 mol L⁻¹. -1 A solution of hexadecyltrimethylammonium bromide (CTAB) was stirred at room temperature for 30 min. An appropriate amount of 25 wt.% ammonia water was weighed and slowly added dropwise to the above mixture, with continuous stirring and the pH of the solution controlled at 10. After the addition was complete, the resulting white emulsion was aged at 80 °C for 3 h. After the emulsion cooled to room temperature, it was filtered and washed with deionized water until neutral. The filter cake was then dried in a 120 °C oven for 12 h. The dried solid was ground into a uniform white powder and calcined in a muffle furnace at 550 °C for 4 h. The resulting pale yellow solid was the ZrO2-10MoO3 support.

[0077] (2) Preparation of 5Ni / ZrO2-10MoO3 catalyst: 0.26 g of Ni(NO3)2·6H2O solid was weighed and dissolved in deionized water. The solution was added dropwise to a petri dish containing 1.00 g of support, and stirred continuously until the mixture became viscous. The mixture was then allowed to stand at room temperature for 12 h. The mixture was then dried in an oven at 120 °C. After drying, the sample was ground into powder and placed in a muffle furnace, where it was calcined at 550 °C for 4 h to obtain the catalyst precursor. The obtained precursor was reduced in a vertical tube furnace at 550 °C with an H2 flow rate of 10 mL / min. -1 The 5Ni / ZrO2-10MoO3 catalyst can be obtained by reduction for 4 hours.

[0078] Example 5: Preparation of 20Ni / ZrO2-10MoO3 catalyst

[0079] The preparation of the molybdenum oxide-modified zirconium oxide-supported nickel catalyst 20Ni / ZrO2-10MoO3 was achieved through a two-step method:

[0080] (1) Preparation of ZrO2-10MoO3 support: 11.60 g (36 mmol) of zirconium oxychloride solid (ZrOCl2·8H2O) and 0.71 g (4 mmol) of ammonium molybdate tetrahydrate solid ((NH4)6Mo7O) were weighed respectively. 24 Dissolve 4H₂O in 100 mL of deionized water and add 50 mL of 0.1 mol L⁻¹. -1 A solution of hexadecyltrimethylammonium bromide (CTAB) was stirred at room temperature for 30 min. An appropriate amount of 25 wt.% ammonia water was weighed and slowly added dropwise to the above mixture, with continuous stirring and the pH of the solution controlled at 10. After the addition was complete, the resulting white emulsion was aged at 80 °C for 3 h. After the emulsion cooled to room temperature, it was filtered and washed with deionized water until neutral. The filter cake was then dried in a 120 °C oven for 12 h. The dried solid was ground into a uniform white powder and calcined in a muffle furnace at 550 °C for 4 h. The resulting pale yellow solid was the ZrO2-10MoO3 support.

[0081] (2) Preparation of 20Ni / ZrO2-10MoO3 catalyst: 2.48 g of Ni(NO3)2·6H2O solid was weighed and dissolved in deionized water. The solution was added dropwise to a petri dish containing 1.00 g of support, and stirred continuously until the mixture became viscous. The mixture was then allowed to stand at room temperature for 12 h. Subsequently, the mixture was dried in an oven at 120 °C. After drying, the sample was ground into powder and placed in a muffle furnace, where it was calcined at 550 °C for 4 h to obtain the catalyst precursor. The obtained precursor was reduced in a vertical tube furnace at 550 °C with an H2 flow rate of 10 mL / min. -1The 20Ni / ZrO2-10MoO3 catalyst can be obtained by reduction for 4 hours.

[0082] Example 6: Lignin depolymerization catalyzed by 15Ni / ZrO2-10MoO3

[0083] (1) Extraction of lignin: Weigh 10.0g of sugarcane bagasse raw material and 120mL of extract, add them to a 250mL hydrothermal reactor, and react in an oven at 110℃ for 4h. After cooling to room temperature, filter and wash with ethanol, collect the filtrate and washings, add 500mL of deionized water to precipitate lignin. After filtering through a 0.22μm filter membrane, air dry in a fume hood, and grind into powder to obtain organosoluble sugarcane bagasse lignin. The extract consists of 24g of 98% concentrated sulfuric acid, 3200mL of anhydrous ethanol, and 800mL of deionized water.

[0084] (2) Catalytic depolymerization of lignin: 100 mg of the organosoluble bagasse lignin extracted in step (1), 100 mg of 15Ni / ZrO2-10MoO3 catalyst, and 20 mL of isopropanol were weighed into a 50 mL reactor. The reactor was sealed, and the air inside was replaced three times with high-purity hydrogen. Hydrogen was then introduced at 2.0 MPa, and the reaction was carried out at 250 °C for 4 h. After the reaction was completed and cooled to room temperature, the reaction solution was taken out and dimethyl phthalate (DMT) was added as an internal standard. 1 mL of the reaction solution was analyzed by GC-MS-FID. The reaction solution was filtered to obtain a filtrate, and deionized water was added to 200 mL. The solution was allowed to stand for about 24 h to precipitate unreacted lignin. After filtration and drying, regenerated lignin was obtained.

[0085] Gas chromatography-mass spectrometry (GC-MS) was used (HP-INNOWAX column: 30m × 0.25mm × 0.25μm, column flow rate 2mL·min). -1 The split ratio is 4:1. The heating program is as follows: hold at 50℃ for 1 minute, then increase by 10℃ per minute. -1 The product was qualitatively analyzed and quantitatively calculated by heating at a rate of 280℃ and holding for 15 min. The GC-FID results of the product are as follows: Figure 16 As shown in Table 1.

[0086] Calculations show that under the action of the 15Ni / ZrO2-10MoO3 catalyst, the conversion rate of lignin reaches 78.0%, the total yield of monophenols is 15.4%, of which the yield of syringol products is 7.5%, and the selectivity is 48.7%. Among all products, S and G units produce the most products, with a total selectivity of 76.6%, indicating that the catalyst system has good reactivity for S and G structural units.

[0087] Table 1. Classification and Yield of Volatile Products

[0088]

[0089]

[0090] Example 7: Lignin depolymerization catalyzed by 15Ni / ZrO2-5MoO3

[0091] The difference between this embodiment and embodiment 6 is that:

[0092] 100 mg of organosoluble sugarcane bagasse lignin, 100 mg of 15Ni / ZrO2-5MoO3 catalyst, and 20 mL of isopropanol were weighed sequentially into a 50 mL reaction vessel. The reaction vessel was sealed, and the air inside was replaced three times with high-purity hydrogen. Hydrogen gas was then introduced at 2.0 MPa, and the reaction was carried out at 250 °C for 4 h. After the reaction was completed and cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. 1 mL of the reaction solution was analyzed by GC-MS-FID.

[0093] The calculation results show that the conversion rate of lignin is 74.2%, the total yield of monophenol products is 12.6%, of which the yield of syringol products is 6.1%, and the selectivity of this product is 48.4%.

[0094] Example 8: Lignin depolymerization catalyzed by 15Ni / ZrO2-20MoO3

[0095] The difference between this embodiment and embodiment 6 is that:

[0096] 100 mg of organosoluble sugarcane bagasse lignin, 100 mg of 15Ni / ZrO2-20MoO3 catalyst, and 20 mL of isopropanol were weighed sequentially into a 50 mL reaction vessel. The reaction vessel was sealed, and the air inside was replaced three times with high-purity hydrogen. Hydrogen gas was then introduced at 2.0 MPa, and the reaction was carried out at 250 °C for 4 h. After the reaction was completed and cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (dimethyl phthalate) was added as an internal standard. One mL of the reaction solution was analyzed by GC-MS-FID.

[0097] The calculation results show that the conversion rate of lignin is 73.7%, the total yield of monophenol products is 11.1%, of which the yield of syringol products is 5.4%, and the selectivity of this product is 48.6%.

[0098] Example 9: Lignin depolymerization catalyzed by 5Ni / ZrO2-10MoO3

[0099] The difference between this embodiment and embodiment 6 is that:

[0100] 100 mg of organosoluble sugarcane bagasse lignin, 100 mg of 10Ni / ZrO2-10MoO3 catalyst, and 20 mL of isopropanol were weighed sequentially into a 50 mL reaction vessel. The reaction vessel was sealed, and the air inside was replaced three times with high-purity hydrogen. The vessel was then purged with 2.0 MPa of hydrogen and reacted at 250 °C for 4 h. After the reaction was completed and cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. One mL of the reaction solution was analyzed by GC-MS-FID.

[0101] The calculation results show that the conversion rate of lignin is 78.5%, the total yield of monophenol products is 10.2%, of which the yield of syringol products is 4.1%, and the selectivity of this product is 40.2%.

[0102] Example 10: Lignin depolymerization catalyzed by 20Ni / ZrO2-10MoO3

[0103] 100 mg of organosoluble sugarcane bagasse lignin, 100 mg of 20Ni / ZrO2-10MoO3 catalyst, and 20 mL of isopropanol were weighed sequentially into a 50 mL reaction vessel. The reaction vessel was sealed, and the air inside was replaced three times with high-purity hydrogen. Hydrogen gas was then introduced at 2.0 MPa, and the reaction was carried out at 250 °C for 4 h. After the reaction was completed and cooled to room temperature, the reaction solution was removed, and dimethyl phthalate (DMT) was added as an internal standard. One mL of the reaction solution was analyzed by GC-MS-FID.

[0104] The calculation results show that the conversion rate of lignin is 73.4%, the total yield of monophenol products is 10.5%, of which the yield of syringol products is 4.2%, and the selectivity of this product is 40.0%.

[0105] Example 11: Lignin depolymerization catalyzed by 15Ni / ZrO2-10MoO3

[0106] The difference between this embodiment and embodiment 6 is that:

[0107] 100 mg of organosoluble sugarcane bagasse lignin, 40 mg of 15Ni / ZrO2-10MoO3 catalyst, and 20 mL of isopropanol were weighed sequentially into a 50 mL reaction vessel. The reaction vessel was sealed, and the air inside was replaced three times with high-purity hydrogen. Finally, 2.0 MPa of hydrogen was introduced, and the reaction was carried out at 250 °C for 4 h. After the reaction was completed and cooled to room temperature, the reaction solution was taken out, and dimethyl phthalate (dimethyl phthalate) was added as an internal standard. 1 mL of the reaction solution was analyzed by GC-MS-FID.

[0108] The calculation results show that the conversion rate of lignin is 77.8%, the total yield of monophenol products is 8.2%, of which the yield of syringol products is 3.9%, and the selectivity of this product is 47.6%.

[0109] Example 12: Lignin depolymerization catalyzed by 15Ni / ZrO2-10MoO3

[0110] The difference between this embodiment and embodiment 6 is that:

[0111] 100 mg of organosoluble sugarcane bagasse lignin, 60 mg of 15Ni / ZrO2-10MoO3 catalyst, and 20 mL of isopropanol were weighed sequentially into a 50 mL reaction vessel. The reaction vessel was sealed, and the air inside was replaced three times with high-purity hydrogen. Finally, 2.0 MPa of hydrogen was introduced, and the reaction was carried out at 250 °C for 4 h. After the reaction was completed and cooled to room temperature, the reaction solution was taken out, and dimethyl phthalate (DMT) was added as an internal standard. 1 mL of the reaction solution was analyzed by GC-MS-FID.

[0112] The calculation results show that the conversion rate of lignin is 76.9%, the total yield of monophenol products is 9.8%, of which the yield of syringol products is 4.1%, and the selectivity of this product is 41.8%.

[0113] Example 13: Lignin depolymerization catalyzed by 15Ni / ZrO2-10MoO3

[0114] The difference between this embodiment and embodiment 6 is that:

[0115] 100 mg of organosoluble sugarcane bagasse lignin, 100 mg of 15Ni / ZrO2-10MoO3 catalyst, and 20 mL of isopropanol were weighed sequentially into a 50 mL reaction vessel. The reaction vessel was sealed, and the air inside was replaced three times with high-purity hydrogen. Finally, 1.0 MPa of hydrogen was introduced, and the reaction was carried out at 250 °C for 4 h. After the reaction was completed and cooled to room temperature, the reaction solution was taken out, and dimethyl phthalate (dimethyl phthalate) was added as an internal standard. 1 mL of the reaction solution was analyzed by GC-MS-FID.

[0116] The calculation results show that the conversion rate of lignin is 75.2%, the total yield of monophenol products is 13.3%, of which the yield of syringol products is 5.8%, and the selectivity of this product is 43.6%.

[0117] Example 14: Lignin depolymerization catalyzed by 15Ni / ZrO2-10MoO3

[0118] The difference between this embodiment and embodiment 6 is that:

[0119] 100 mg of organosoluble sugarcane bagasse lignin, 100 mg of 15Ni / ZrO2-10MoO3 catalyst, and 20 mL of isopropanol were weighed sequentially into a 50 mL reaction vessel. The reaction vessel was sealed, and the air inside was replaced three times with high-purity hydrogen. Finally, hydrogen gas was introduced at 2.5 MPa, and the reaction was carried out at 250 °C for 4 h. After the reaction was completed and cooled to room temperature, the reaction solution was taken out, and dimethyl phthalate (dimethyl phthalate) was added as an internal standard. 1 mL of the reaction solution was analyzed by GC-MS-FID.

[0120] The calculation results show that the conversion rate of lignin is 73.6%, the total yield of monophenol products is 12.3%, of which the yield of syringol products is 5.9%, and the selectivity of this product is 48.0%.

[0121] Example 15: Lignin depolymerization catalyzed by 15Ni / ZrO2-10MoO3

[0122] The difference between this embodiment and embodiment 6 is that:

[0123] 100 mg of organosoluble sugarcane bagasse lignin, 100 mg of 15Ni / ZrO2-10MoO3 catalyst, and 20 mL of isopropanol were weighed sequentially into a 50 mL reaction vessel. The reaction vessel was sealed, and the air inside was replaced three times with high-purity hydrogen. Finally, 2.0 MPa of hydrogen was introduced, and the reaction was carried out at 240 °C for 4 h. After the reaction was completed and cooled to room temperature, the reaction solution was taken out, and dimethyl phthalate (dimethyl phthalate) was added as an internal standard. 1 mL of the reaction solution was analyzed by GC-MS-FID.

[0124] The calculation results show that the conversion rate of lignin is 72.6%, the total yield of monophenol products is 9.6%, of which the yield of syringol products is 4.6%, and the selectivity of this product is 47.9%.

[0125] Example 16: Lignin depolymerization catalyzed by 15Ni / ZrO2-10MoO3

[0126] The difference between this embodiment and embodiment 6 is that:

[0127] 100 mg of organosoluble sugarcane bagasse lignin, 100 mg of 15Ni / ZrO2-10MoO3 catalyst, and 20 mL of isopropanol were weighed sequentially into a 50 mL reaction vessel. The reaction vessel was sealed, and the air inside was replaced three times with high-purity hydrogen. Finally, 2.0 MPa of hydrogen was introduced, and the reaction was carried out at 260 °C for 4 h. After the reaction was completed and cooled to room temperature, the reaction solution was taken out, and dimethyl phthalate (DMT) was added as an internal standard. 1 mL of the reaction solution was analyzed by GC-MS-FID.

[0128] The calculation results show that the conversion rate of lignin is 77.7%, the total yield of monophenol products is 11.6%, of which the yield of syringol products is 5.2%, and the selectivity of this product is 44.8%.

[0129] Example 17: Lignin depolymerization catalyzed by 15Ni / ZrO2-10MoO3

[0130] The difference between this embodiment and embodiment 6 is that:

[0131] 100 mg of organosoluble bagasse lignin, 100 mg of 15Ni / ZrO2-10MoO3 catalyst, and 20 mL of isopropanol were weighed sequentially into a 50 mL reaction vessel. The reaction vessel was sealed, and the air inside was replaced three times with high-purity hydrogen. Finally, 2.0 MPa of hydrogen was introduced, and the reaction was carried out at 250 °C for 2 h. After the reaction was completed and cooled to room temperature, the reaction solution was taken out, and dimethyl phthalate (DMT) was added as an internal standard. 1 mL of the reaction solution was analyzed by GC-MS-FID.

[0132] The calculation results show that the conversion rate of lignin is 75.1%, the total yield of monophenol products is 8.7%, of which the yield of syringol products is 3.6%, and the selectivity of this product is 41.4%.

[0133] Example 18: Lignin depolymerization catalyzed by 15Ni / ZrO2-10MoO3

[0134] The difference between this embodiment and embodiment 6 is that:

[0135] 100 mg of organosoluble sugarcane bagasse lignin, 100 mg of 15Ni / ZrO2-10MoO3 catalyst, and 20 mL of isopropanol were weighed sequentially into a 50 mL reaction vessel. The reaction vessel was sealed, and the air inside was replaced three times with high-purity hydrogen. Finally, 2.0 MPa of hydrogen was introduced, and the reaction was carried out at 250 °C for 5 h. After the reaction was completed and cooled to room temperature, the reaction solution was taken out, and dimethyl phthalate (dimethyl phthalate) was added as an internal standard. 1 mL of the reaction solution was analyzed by GC-MS-FID.

[0136] The calculation results show that the conversion rate of lignin is 77.4%, the total yield of monophenol products is 12.3%, of which the yield of syringol products is 6.5%, and the selectivity of this product is 52.8%.

[0137] Example 19: Lignin depolymerization catalyzed by 15Ni / ZrO2-10MoO3

[0138] The difference between this embodiment and embodiment 6 is that:

[0139] 100 mg of organosoluble sugarcane bagasse lignin, 100 mg of 15Ni / ZrO2-10MoO3 catalyst, and 20 mL of methanol were weighed sequentially into a 50 mL reaction vessel. The reaction vessel was sealed, and the air inside was replaced three times with high-purity hydrogen. Finally, 2.0 MPa of hydrogen was introduced, and the reaction was carried out at 250 °C for 4 h. After the reaction was completed and cooled to room temperature, the reaction solution was taken out, and dimethyl phthalate (DMT) was added as an internal standard. 1 mL of the reaction solution was analyzed by GC-MS-FID.

[0140] The calculation results show that the conversion rate of lignin is 72.3%, the total yield of monophenol products is 7.6%, of which the yield of syringol products is 4.0%, and the selectivity of this product is 52.6%.

[0141] Example 20: Lignin depolymerization catalyzed by 15Ni / ZrO2-10MoO3

[0142] The difference between this embodiment and embodiment 6 is that:

[0143] 100 mg of organosoluble sugarcane bagasse lignin, 100 mg of 15Ni / ZrO2-10MoO3 catalyst, and 20 mL of n-hexanol were weighed sequentially into a 50 mL reaction vessel. The reaction vessel was sealed, and the air inside was replaced three times with high-purity hydrogen. Finally, 2.0 MPa of hydrogen was introduced, and the reaction was carried out at 250 °C for 4 h. After the reaction was completed and cooled to room temperature, the reaction solution was taken out, and dimethyl phthalate (dimethyl phthalate) was added as an internal standard. 1 mL of the reaction solution was analyzed by GC-MS-FID.

[0144] The calculation results show that the conversion rate of lignin is 71.9%, the total yield of monophenol products is 8.5%, of which the yield of syringol products is 4.2%, and the selectivity of this product is 49.4%.

[0145] Example 21: Lignin depolymerization catalyzed by 15Ni / ZrO2-10MoO3

[0146] The difference between this embodiment and embodiment 6 is that:

[0147] (1) Extraction of lignin: Weigh 10.0g of corn stalk raw material and 120mL of extract, add them to a 250mL hydrothermal reactor, and react in an oven at 110℃ for 4h. After cooling to room temperature, filter and wash with ethanol, collect the filtrate and washings, add 500mL of deionized water to precipitate lignin. After filtering through a 0.22μm filter membrane, air dry in a fume hood, and grind into powder to obtain organosoluble corn stalk lignin. The extract consists of 24g of 98% concentrated sulfuric acid, 3200mL of anhydrous ethanol, and 800mL of deionized water.

[0148] (2) Catalytic depolymerization of lignin: 100 mg of the organosoluble corn straw lignin extracted in step (1), 100 mg of 15Ni / ZrO2-10MoO3 catalyst, and 20 mL of isopropanol were weighed into a 50 mL reactor. The reactor was sealed, and the air inside was replaced three times with high-purity hydrogen. Hydrogen gas was then introduced at 2.0 MPa, and the reaction was carried out at 250 °C for 4 h. After the reaction was completed and cooled to room temperature, the reaction solution was taken out and dimethyl phthalate (DMT) was added as an internal standard. 1 mL of the reaction solution was analyzed by GC-MS-FID. The reaction solution was filtered to obtain a filtrate, and deionized water was added to 200 mL. The solution was allowed to stand for about 24 h to precipitate unreacted lignin. After filtration and drying, regenerated lignin was obtained.

[0149] The calculation results show that the conversion rate of lignin is 73.3%, the total yield of monophenol products is 9.1%, of which the yield of syringol products is 4.6%, and the selectivity of this product is 50.5%.

[0150] As can be seen from the above embodiments, the present invention achieves selective hydrogenolysis of lignin using a molybdenum oxide-modified zirconium oxide-supported nickel catalytic system. Under the conditions of H2 pressure of 1–3 MPa, reaction temperature of 230–270 °C, and reaction time of 2–6 h, the conversion rate of lignin is 68.9–79.2%, the total yield of monophenolic products is 5.9–15.4%, and the yield of syringol is 3.8–7.5%. The molybdenum oxide-modified zirconium oxide-supported nickel catalyst used in this invention has low cost, simple preparation process, and low environmental pollution, which is beneficial to reducing energy consumption and achieving lignin depolymerization under mild conditions.

[0151] Example 22: Catalyst Recyclability

[0152] Taking the reuse of the 15Ni / ZrO2-10MoO3 catalyst as an example, the reuse process is as follows: after the reaction, the catalyst is filtered and separated, then dried in an oven at 120℃ for 12 hours, calcined at 550℃ for 4 hours, and then reduced at 550℃ for 4 hours under H2 atmosphere. The resulting catalyst solid is then subjected to a recycling experiment according to the steps in Example 6. The test results show that after the catalyst is recycled 8 times, the activity does not decrease significantly, the lignin conversion rate is 76.2%, the yield of volatile products is 15.1%, and the yield of syringol products is 7.2%.

[0153] As can be seen from the above embodiments, the molybdenum oxide-modified zirconium oxide-supported nickel catalytic system of the present invention, combined with an alcohol solvent, achieves selective catalytic depolymerization of lignin to prepare syringin products. Under the conditions of a nickel loading of 5-20 wt.%, a molybdenum oxide doping of 5-20 mol%, an H2 pressure of 1-3 MPa, a reaction temperature of 230-270 °C, and a reaction time of 2-6 h, the conversion rate of lignin can reach 68.9-79.2%, the total yield of monophenolic products can reach 7.6-15.4%, of which the yield of syringin products can reach 3.6-7.5%, and the selectivity of syringin products can reach 40.0-52.6%. Syringin products are high-value-added chemicals, widely used in the production of food additives and pharmaceutical intermediates. Therefore, high selectivity for these products can improve the economic efficiency and overall utilization value of lignin. Compared to the method for preparing 2,6-dimethoxy-4-propylphenol by lignin hydrogenolysis supported by nickel and disclosed in Chinese invention patent application CN116924891A, the molybdenum oxide-modified zirconium oxide-supported nickel catalyst of this invention exhibits a synergistic effect of acidic and basic sites, which can significantly improve the selectivity for syringol products. Furthermore, it should be noted that existing catalysts for obtaining syringol products through lignin degradation generally lack both good acidity and basicity, resulting in low selectivity for syringol products. This invention effectively solves this problem by using a molybdenum oxide-modified zirconium oxide-supported nickel catalyst in conjunction with an alcohol solvent medium. Moreover, the catalyst of this invention exhibits strong stability, with no significant decrease in activity after eight cycles.

[0154] The catalyst used in this invention has low cost, simple preparation process and little environmental pollution. Its high selectivity for high-value-added chemicals such as syringol products not only helps to reduce the occurrence of side reactions, but also reduces the difficulty of separating the target product.

[0155] The implementation of the present invention is not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing syringol products by nickel-catalyzed hydrogenolysis of lignin using molybdenum oxide-modified zirconium oxide-supported molybdenum oxide, characterized in that, Using lignin as a raw material, a nickel-based catalyst and an alcohol solvent are added to the raw material, and the reaction is carried out at an H2 pressure of 1-3 MPa and a reaction temperature of 230-270℃ for 2-6 h to depolymerize the lignin and obtain syringol products; the nickel-based catalyst is supported by ZrO2- x Composed of MoO3 and active component nickel, wherein the nickel loading is 5~20 wt.%; support ZrO2- x MoO3 x The amount of molybdenum oxide incorporated is 5-20 mol%; the carrier ZrO2- x The preparation method of MoO3 is as follows: zirconium oxychloride, ammonium molybdate tetrahydrate, and hexadecyltrimethylammonium bromide are fully dissolved in deionized water solution, and the pH is controlled at 9-10; the reaction is carried out under stirring, and the resulting solution is aged at 60-80℃ for 2-4 h; the filtered solid is dried and calcined in air to obtain the carrier ZrO2-. x MoO3; The lignin is derived from any one of bagasse, corn stalks, poplar, and bamboo; the syringol products are 4-propylsyringol, 4-allylsyringol, 4-ethylsyringol, and 4-methylsyringol. The lignin is extracted by the following method: lignin raw material and extract are added to a reaction vessel and reacted at 100-120℃ for 2-6 h, followed by filtration and separation; the obtained filtrate is added to deionized water and filtered to obtain a solid, which is then dried to obtain organosoluble lignin; the extract is composed of concentrated sulfuric acid, anhydrous ethanol and deionized water; wherein the mass concentration of concentrated sulfuric acid is 95-98%, and 3200-4000 mL of anhydrous ethanol and 800-1000 mL of deionized water are added to every 24 g of concentrated sulfuric acid; 120-150 mL of extract is added to every 10.0 g of lignin raw material.

2. The method for preparing syringol products by molybdenum oxide-modified zirconium oxide-supported nickel-catalyzed hydrogenolysis of lignin according to claim 1, characterized in that, The preparation method of the nickel-based catalyst is as follows: nickel nitrate is fully dissolved in deionized water, and ZrO2- is added as a support. x MoO3 impregnation; after standing for 10-12 h, drying and calcination in air to obtain a precursor; reduction of the precursor under H2 atmosphere to obtain a nickel-based catalyst.

3. The method for preparing syringol products by molybdenum oxide-modified zirconium oxide-supported nickel-catalyzed hydrogenolysis of lignin according to claim 1, characterized in that, The calcination is carried out in a muffle furnace at a temperature of 500-600℃ for 3-5 hours. 0.10-0.12 g of zirconium oxychloride, 0.004-0.014 g of ammonium molybdate tetrahydrate, and 0.04-0.06 g of hexadecyltrimethylammonium bromide are added per milliliter of deionized water. The pH is controlled to be 9-10 by adding ammonia dropwise.

4. The method for preparing syringol products by molybdenum oxide-modified zirconium oxide-supported nickel-catalyzed hydrogenolysis of lignin according to claim 2, characterized in that, The reduction under H2 atmosphere is carried out in a vertical tube furnace at a temperature of 400~600℃ for 4~6 hours.

5. The method for preparing syringol products by molybdenum oxide-modified zirconium oxide-supported nickel-catalyzed hydrogenolysis of lignin according to claim 2, characterized in that, The calcination temperature is 500~600℃, and the calcination time is 3~5 h.

6. The method for preparing syringol products by molybdenum oxide-modified zirconium oxide-supported nickel-catalyzed hydrogenolysis of lignin according to claim 1, characterized in that, The mass ratio of lignin to nickel-based catalyst is 1:0.4 to 1:1.2; the mass ratio of lignin to alcohol solvent is 1:10 to 1:

20.

7. The method for preparing syringol products by molybdenum oxide-modified zirconium oxide-supported nickel-catalyzed hydrogenolysis of lignin according to claim 1, characterized in that, The alcohol solvent is any one of methanol, isopropanol, and n-hexanol.

Images