Rhenium-tungsten nano-alloy cluster catalyst and catalytic application of rhenium-tungsten nano-alloy cluster catalyst in preparation of phenolic compounds through lignin depolymerization

Abstract

The invention discloses a rhenium-tungsten nano-alloy cluster catalyst and catalytic application of the rhenium-tungsten nano-alloy cluster catalyst in preparation of phenolic compounds through lignin depolymerization. The catalyst is composed of a mesoporous Al2O3 carrier and a tungsten core-rhenium shell structure nano-alloy cluster loaded on the mesoporous Al2O3 carrier, diffusion and deposition growth behaviors of rhenium atoms at the junction of tungsten nano-cluster crystal faces (110) are simulated through molecular dynamics, and a high-activity site enriched structure is formed through regulation and control of factors such as temperature control. The preparation process comprises the steps of carrier pretreatment, active component loading, roasting and activation. When the rhenium-tungsten nano-alloy cluster is applied, lignin beta-O-4 bonds are preferentially broken through segmented temperature control, monophenol generation is promoted, MgO is combined for regulating and controlling the acid-base property to inhibit excessive hydrogenation, in the constructed rhenium-tungsten nano-alloy cluster, tungsten activates C-O bonds through the strong electron transfer capacity to promote directional breakage, and the problem that the depolymerization efficiency is low is solved; rhenium passes through a high-hydrogenation-activity stable intermediate, so that side reaction is avoided, and directional production of monophenol is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of nanocatalytic materials, in particular to a rhenium-tungsten nano alloy cluster catalyst and its catalytic application in the preparation of phenolic compounds by depolymerization of lignin. Background Art

[0002] Traditional lignin depolymerization technology faces difficult bottlenecks in industrial applications. For one thing, depolymerization efficiency has long remained low, with conversion rates generally below 40%. This stems from the fact that lignin, as a complex aromatic polymer, contains numerous stable chemical bonds in its molecular structure, particularly CO bonds (of which β-O-4 bonds account for the largest proportion, over 50% of the total) and CC bonds. These bonds have extremely high bond energies and strong chemical stability, making them difficult to effectively break. Existing catalysts, limited by their structural design, are unable to accurately identify and act on these specific chemical bonds, making selective cleavage difficult. Consequently, most lignin raw materials cannot be fully decomposed, resulting in inefficient resource utilization.

[0003] On the other hand, the system of depolymerization products is extremely complex, mainly composed of mixed phenolic compounds, including guaiacol, eugenol, p-ethylphenol and other components, and is also accompanied by by-products such as polycyclic aromatic hydrocarbons and cycloalkanes, making the subsequent separation and purification process lengthy and costly.

[0004] The core of the above two problems lies in the fact that when the chemical bonds in the lignin molecules are broken, the intermediates generated are highly chemically active. Without precise control, random reactions such as over-hydrogenation, rearrangement or polymerization are prone to occur, thereby generating a large number of non-target products. This not only reduces the yield of the target monophenolic compounds, but also greatly increases the difficulty and economic cost of product separation.

[0005] Bimetallic nanoclusters exhibit excellent catalytic properties due to unique electronic and geometric effects. Rhenium-tungsten alloys have been shown to exhibit high catalytic activity in a variety of reactions, such as the conversion of ethanol / glycerol to olefins and the synthesis of α-methylstyrene. However, existing bimetallic catalysts for lignin depolymerization suffer from significant structural limitations. Most preparation methods struggle to achieve an atomically ordered distribution of active components, resulting in insufficient exposure of active sites, weakened synergistic effects, and an inability to balance chemical bond cleavage efficiency with product orientation.

[0006] Therefore, it is necessary to provide a rhenium-tungsten nanoalloy cluster catalyst and its catalytic application in the depolymerization of lignin to prepare phenolic compounds to solve the above technical problems. Summary of the Invention

[0007] The purpose of the present invention is to provide a rhenium-tungsten nanoalloy cluster catalyst and its catalytic application in the depolymerization of lignin to prepare phenolic compounds, so as to utilize the electron transfer ability of tungsten to enhance the cleavage of β-O-4 bonds, thereby solving the problem of low depolymerization efficiency in traditional methods; and by leveraging the hydrogenation activity of rhenium and the directional nature of its core-shell structure, reduce the generation of by-products and solve the problem of product complexity.

[0008] To achieve the above object, the present invention provides the following technical solutions: In a first aspect, the present invention provides a rhenium-tungsten nanoalloy cluster catalyst, comprising a mesoporous Al2O3 carrier and a tungsten core-rhenium shell structured nanoalloy cluster supported thereon, wherein the atomic ratio of rhenium to tungsten is 1:3-1:5, and the catalyst is prepared by the following steps: Step 1: Grind and sieve the mesoporous Al2O3 carrier, wash it with deionized water, and dry it to obtain the pretreated mesoporous Al2O3 carrier for later use; Step 2: adding the tungsten core-rhenium shell structured nanoalloy clusters into anhydrous ethanol and ultrasonically dispersing them to form a uniform suspension; The pretreated mesoporous Al2O3 support is added to the suspension at a loading ratio of 5% to 10% of the total mass of rhenium and tungsten to the mass of the mesoporous Al2O3 support, and stirred to uniformly load the tungsten core-rhenium shell structured nanoalloy clusters in the suspension onto the surface of the support, and then ethanol in the system is evaporated to obtain a solid precursor loaded with tungsten core-rhenium shell structured nanoalloy clusters; The tungsten core-rhenium shell structure is formed by molecular dynamics simulation control: a BCCWulff structure tungsten nanocluster substrate (containing 6 crystal planes (100) and 12 crystal planes (110)) is constructed using the LAMMPS program, rhenium atoms are deposited at a rate of 1 atom / ns at 1600-2200K, and the diffusion of rhenium atoms at the interface of the crystal planes (110) is controlled (diffusion depth 0.5-2 atomic layers) so that the proportion of tungsten atoms in the core region is ≥80% and the proportion of rhenium atoms in the shell is ≥70%, ultimately forming an alloy cluster containing body-centered cubic, face-centered cubic and hexagonal close-packed lattices, wherein the proportion of active sites at the interface of the crystal planes (110) is ≥60%; Step 3: placing the solid precursor obtained in step 2 in a tube furnace, heating it to 280-320°C in an air atmosphere and maintaining the temperature to remove residual impurities to obtain a calcined product; Step 4: Switch the air atmosphere in the tube furnace to a hydrogen atmosphere, heat it to 420-480°C and keep it warm, then cool it down and introduce nitrogen protection to obtain an activated product; Step 5: Grind and sieve the activated product obtained in step 5 to obtain a rhenium-tungsten nanoalloy cluster catalyst.

[0009] Preferably, in step 1, the mesoporous Al2O3 carrier is ground and passed through a 200-300 mesh sieve, washed with deionized water 3-5 times, and dried at a temperature of 100-120°C for 10-14 hours; In step 2, the ultrasonic dispersion time is 20-40 minutes, the power is 250-350W, the frequency is 35-45kHz, the stirring rate is 250-350r / min, the stirring time is 2-4 hours, and the temperature for evaporating the ethanol is 70-90°C; In step 2, the lattice ratio of the tungsten core-rhenium shell structure is controlled by temperature: the body-centered cubic lattice ratio is ≥70% at a deposition temperature of 2200K, the hexagonal close-packed lattice ratio is ≥20% at 1800-2000K, and the lattice distortion rate is ≤5% after 1ns relaxation treatment.

[0010] Preferably, in step 3, the heating rate under air atmosphere is 4-6°C / min, and the holding time is 1.5-2.5 hours; In step 4, the flow rate of hydrogen atmosphere is 40-60 mL / min, the heating rate is 1-3°C / min, and the holding time is 2-4 hours; In the activated catalyst, rhenium atoms are enriched at the (110) steps of the crystal plane, and their synergistic effect with tungsten atoms reduces the CO bond energy by 30%-40%.

[0011] Preferably, the activated product in step 5 is ground and passed through an 80-120 mesh sieve; The proportion of (110) atoms in the catalyst to the total number of cluster atoms is ≥50%, and the ratio of rhenium to Re is 4+ Mainly (accounting for 60%-70%), tungsten is W 6+ The two enhance the catalytic activity through the synergistic effect of d orbital electron transfer and hydrogen proton supply.

[0012] In a second aspect, the present invention provides a catalytic application of a rhenium-tungsten nanoalloy cluster catalyst in the depolymerization of lignin to prepare phenolic compounds, comprising the following steps: Step 1: Grind the lignin raw material into a particle size of 50-100 μm by ball milling, and sieve it for later use; Step 2: Mix the lignin treated in step 1 with the catalyst in a mass ratio of 10:1, add a methanol-water mixed solvent to the mixed system, wherein the volume ratio of methanol to water is 3:1, and introduce 0.1%-0.5% of MgO powder by weight of the catalyst. Stir until the lignin, catalyst and MgO are uniformly dispersed in the solvent, and adjust the pH of the system to 3-4 with dilute sulfuric acid; The MgO neutralizes some strong acid sites on the catalyst surface, namely the highly active acid sites at the center of the crystal plane (100), thereby reducing the probability of excessive hydrogenation of monophenol products at the active center, thereby inhibiting the deep conversion of monophenols into non-target products.

[0013] Specifically, on one hand, MgO and W exposed on the catalyst surface 6+ Weak interactions between the sites reduce the adsorption energy of monophenolic products at strong acidic sites from -5.2 eV to -3.8 eV, shortening the residence time of monophenolic molecules at the active center. Furthermore, the alkalinity of MgO buffers pH fluctuations in the system, preventing side reactions such as hydrogenation of monophenolic aromatic rings (e.g., conversion of guaiacol to cyclohexanol) or dehydration of phenolic hydroxyl groups caused by localized excessive acidity. This site-selective neutralization and regulation reduces the probability of over-hydrogenation of monophenolic products at the active center by over 40%, inhibiting their deep conversion to non-target products such as cycloalkanes and polycyclic aromatic hydrocarbons at the molecular level and significantly improving the targeted retention rate of target products.

[0014] Step 3: Transfer the mixed system obtained in step 2 to a high-pressure reactor, seal it, and introduce H2 to replace the air in the reactor, maintaining the H2 pressure at 2-3 MPa. Use a segmented temperature control method during the reaction: The reaction is first heated to 210-230°C for 1.5-2.5 hours to preferentially break the β-O-4 bonds in the lignin molecules. This is due to the high adsorption capacity of the active sites at the interface of the catalyst crystal face (110) and the activation of the CO bond by the tungsten atom's d orbital electron transfer. The reaction is then heated to 230-250°C for 1.5-2.5 hours to promote the formation of monophenolic compounds. This is achieved by rhenium atoms providing hydrogen protons that combine with the broken oxygen atoms to form hydroxyl groups, thus stabilizing the monophenol intermediates. The entire reaction process is carried out at a stirring rate of 500-800 rpm. By controlling the temperature and time of the two-stage reaction, excessive hydrogenation of the monophenolic products can be reduced. Specifically, the first heating stage (210-230℃, 1.5-2.5h): This temperature range precisely matches the adsorption energy of the active site at the interface of the catalyst crystal plane (110) and the rupture energy barrier of the β-O-4 bond (about 360kJ / mol). The electron-rich microregion at the interface of the crystal plane (110) has a low atomic coordination number (6-8), which has a strong coordination adsorption ability (adsorption energy -4.5eV) for the oxygen atom of the β-O-4 bond in the lignin molecule, and can selectively wrap the two benzene ring units connected by the CO bond through the steric effect; at the same time, the tungsten atom (W 6+) transfers electrons from the 5d orbital of the oxygen atom to the 2p orbital of the oxygen atom, extending the C-O bond length from 1.43 Å to 1.51 Å and reducing the bond energy by 30%-40%. Homolysis preferentially occurs in an H2 atmosphere, generating an intermediate containing a phenoxy radical. This stage, through the synergistic effect of spatially selective adsorption and electron transfer activation, increases the cleavage efficiency of β-O-4 bonds by over 50% compared to conventional catalysts, inhibiting C-C bond cleavage by 70%, achieving a targeted decomposition of the lignin skeleton.

[0015] The second stage (230-250℃, 1.5-2.5h): After the temperature is raised to this range, the rhenium atoms (Re 4+ ) interacts electronically with the σ bond of H2, resulting in efficient dissociation via a hydrogen overflow mechanism. and generate active hydrogen protons (H + ), which reacts with the phenoxy radicals generated in the first stage (containing ) rapidly bind (with a reaction barrier of only 12 kJ / mol) to form a stable phenolic hydroxyl group (-OH), locking the active intermediate into a monophenol structure. Simultaneously, the rhenium atoms at the (110) crystal plane interface bind to the benzene ring through π-π stacking, further inhibiting the polymerization or rearrangement of the intermediate. This stage, through the dual effects of hydrogen proton donation and steric stabilization, increases the selectivity of monophenolic products to over 80%, with the targeted formation of target products such as guaiacol and eugenol accounting for 60%-70%.

[0016] Step 4: After the reaction is completed, the mixed system in the high-pressure reactor is cooled to room temperature and the residual pressure in the reactor is released. The catalyst is recovered from the mixed liquid after the reaction by centrifugation, and the methanol-water mixed solvent is removed from the remaining reaction liquid by reduced pressure distillation. The obtained crude product is purified by silica gel column chromatography, and the target fraction containing the monophenol compound is collected and dried to obtain the monophenol compound.

[0017] Preferably, in step 1, the lignin raw material is herbaceous plant straw or woody plant sawdust, which is ball-milled for 2-4 hours using zirconium oxide grinding balls at a ball-to-material ratio of 10:1, and screened through a 150-300 mesh standard sieve; in step 2, the stirring is magnetic stirring at 300-500 rpm for 30-60 minutes; and the concentration of dilute sulfuric acid is 0.1-0.5 mol / L.

[0018] Preferably, in step 3, the H2 purity is 99.99%, and the heating rate is 5-10°C / min. The generated monophenol intermediates contain at least guaiacol, eugenol, and p-ethylphenol. The catalyst selectively adsorbs β-O-4 structural units through active sites at the interface of the crystal face (110), inhibiting excessive C-C bond cleavage and achieving a monophenol selectivity of ≥80%.

[0019] Preferably, in step three, the lignin conversion rate is 65%-75%, and the selectivity of monophenolic compounds is ≥80%; among the monophenolic compounds, guaiacol accounts for 30%-40% and eugenol accounts for 25%-35%.

[0020] Preferably, the speed of centrifugation in step 4 is 8000-10000 rpm, and the time is 10-15 min; the vacuum degree of reduced pressure distillation is 0.08-0.1 MPa, the temperature is 60-80°C, a rotary evaporator is used, and the speed is 50-100 rpm; the silica gel particle size used for silica gel column chromatography is 100-200 mesh, the chromatography column diameter-to-height ratio is 1:8-1:12, and the eluent is petroleum ether-ethyl acetate, with a volume ratio of 5:1; drying is vacuum drying at 40-60°C for 12-24 hours to obtain a monophenol compound with a purity of ≥95%.

[0021] Preferably, the catalytic application of the rhenium-tungsten nanoalloy cluster catalyst also includes a catalyst regeneration step: the catalyst recovered by centrifugation is first ultrasonically washed with anhydrous ethanol 5-10 times its mass at a power of 300W for 30 minutes, then soaked in a 0.05mol / L H2SO4 solution for 1 hour to dissolve the residue, and finally washed with deionized water until neutral; after drying at 120°C for 2-4 hours, it is secondary activated at 400°C in a H2 atmosphere for 2 hours to restore Re 4+ and W 6+ active valence state.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention leverages the synergistic catalytic mechanism of rhenium-tungsten nanoalloy clusters. The strong electron transfer ability of tungsten can precisely act on the CO bonds in lignin, especially the β-O-4 bonds. Through d-orbital electron transfer, the chemical bond energy is weakened, achieving directional breakage of stable chemical bonds. This fundamentally solves the problem of traditional methods that are difficult to decompose due to high bond energy, and significantly improves the overall depolymerization efficiency of lignin.

[0023] 2. The present invention utilizes the high hydrogenation activity of rhenium to specifically stabilize the intermediates after CO bond rupture. By providing hydrogen protons to combine with oxygen atoms to form hydroxyl groups, random reactions or excessive hydrogenation of the intermediates are avoided, thereby guiding the reaction toward the formation of monophenolic compounds. This addresses the defects of traditional methods such as complex products and lack of directionality, and reduces subsequent separation costs.

[0024] 3. The atomic-level regulation based on molecular dynamics simulation of the present invention can control the diffusion depth and distribution density of rhenium atoms, avoid the ineffective wrapping of rare metal rhenium, and maximize its proportion in the catalytic reaction; by regulating the formed tungsten core-rhenium shell structure, the active component rhenium is enriched at the junction of the crystal plane (110), thereby improving the exposure efficiency of the active sites; at the same time, the directional regulation of the lattice structure (synergistic effects such as body-centered cubic and hexagonal close packing) reduces distortion, improves atomic economy while ensuring catalytic performance, reduces resource waste, enhances the structural stability of the catalyst, extends its service life, and reduces the replacement frequency and cost in industrial applications.

[0025] 4. In the catalytic application process of the rhenium-tungsten nano alloy cluster catalyst provided by the present invention in the depolymerization of lignin to prepare phenolic compounds, the highly active acid sites at the center of the catalyst crystal face (100) are neutralized by MgO and the surface W 6+ The sites form weak interactions, reducing the adsorption energy of monophenolic products at strong acid sites and shortening their retention time at the active center. Furthermore, the alkalinity of MgO buffers pH fluctuations in the system, preventing side reactions such as hydrogenation of monophenol aromatic rings or dehydration of phenolic hydroxyl groups caused by localized excessive acidity. This reduces the probability of over-hydrogenation by over 40% and significantly improves the targeted retention rate of the target product.

[0026] 5. In the catalytic application of the rhenium-tungsten nanoalloy cluster catalyst provided by the present invention in the depolymerization of lignin to produce phenolic compounds, a staged temperature control mechanism is employed. In the first stage (210-230°C), the high adsorption capacity of the active sites at the interface of the catalyst crystal face (110) and the electron transfer effect of the tungsten atoms are utilized to efficiently break the lignin β-O-4 bond. The breaking efficiency is increased by more than 50% compared to conventional catalysts, and the inhibition rate of C-C bond breaking reaches 70%. In the second stage (230-250°C), the rhenium atoms provide hydrogen protons to stabilize the monophenol intermediates, and the π-π stacking effect is combined to inhibit polymerization or rearrangement, thereby increasing the monophenol selectivity to more than 80%, and the targeted production of the target product accounts for 60%-70%. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of BCC Wulff and FCC Wulff structures, where Figure 1 a is the BCC Wulff structure, with the crystal planes (110) and (100) marked; Figure 1 b is the FCC Wulff structure, with the crystal planes (111) and (100) marked; Figure 2 is the exchange process of rhenium atoms and tungsten atoms at specific positions and the corresponding energy barrier curve, where Figure 2 a- Figure 2 f is the atomic exchange process at different positions (blue is rhenium atom, red is tungsten atom); Figure 3 for Figure 2 Energy barrier curve of the exchange process (the horizontal axis is the number of images, the vertical axis is energy); Figure 4 is the diffusion diagram of rhenium atoms on tungsten nanoclusters at the initial stage of deposition, where Figure 4 a is the sharp angle formed by the adsorption of rhenium atoms and tungsten atoms on the crystal plane (100); Figure 4 b is the exchange of rhenium atoms with the surface atoms of tungsten nanoclusters; Figure 4 c is the adsorption of rhenium atoms and tungsten atoms on the crystal plane (110); Figure 5 Schematic diagram of vacancy formation and migration mechanism, where Figure 5 a is the initial state where tungsten atoms are adsorbed on the (100) four-fold coordination site and rhenium atoms exist on the step; Figure 5 b- Figure 5 e is the process of tungsten atom transition to form vacancies and long chain transition (blue is rhenium atom, red is tungsten atom, and white is tungsten atom to be observed); Figure 6 Schematic diagram of the migration mechanism of tungsten atoms under different conditions, where Figure 6 a- Figure 6 d is a schematic diagram of four different conditions (with or without adsorbed atoms and rhenium atoms); Figure 7 for Figure 6 Corresponding energy barrier curve (the horizontal axis is the number of images, the vertical axis is energy); Figure 8 Surface diffusion diagram of rhenium-tungsten nanoclusters of different sizes (rhenium-tungsten ratio 1:1, temperature 2000K), Figure 8 a is a cross-sectional view with a total atomic number of 118; Figure 8 b is a cross-sectional view with a total atomic number of 678; Figure 8 c is a cross-sectional view with a total atomic number of 2042; Figure 9 The number of atoms of each lattice type changes with the number of deposited Re atoms. Figure 9 a is the change of the number of BCC lattice atoms with the number of deposited rhenium atoms; Figure 9 b is the change of the number of FCC lattice atoms with the number of deposited rhenium atoms; Figure 9 c is the change of the number of HCP lattice atoms with the number of deposited rhenium atoms; Figure 9 d is the change curve of the number of atoms of tungsten and rhenium in the FCC lattice; Figure 10 A line graph showing the conversion rate of lignin in the catalytic application of Examples 1-3 of the present invention and Comparative Examples 1-3 in the preparation of phenolic compounds by depolymerization of lignin; Figure 11A line graph showing the selectivity of monophenols in the catalytic applications of Examples 1-3 of the present invention and Comparative Examples 1-3 in preparing phenolic compounds by depolymerization of lignin; Figure 12 It is a line graph of the β-O-4 bond cleavage efficiency (relative value) of the catalytic application of Examples 1-3 of the present invention and Comparative Examples 1-3 in the preparation of phenolic compounds by depolymerization of lignin. DETAILED DESCRIPTION

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0029] In the present invention, crystal plane (100), crystal plane (110), and crystal plane (111) are all defined based on the crystallographic Miller indices, which are used to characterize the planes of atomic arrangement with different orientations in a crystal: Crystal plane (100): Miller indices are (h, k, l) = (1, 0, 0), which refers to the atomic plane parallel to the y-axis and z-axis of the crystal coordinate system and intersecting only with the x-axis; Crystal plane (110): Miller indices are (h, k, l) = (1, 1, 0), which refers to the atomic plane parallel to the z-axis of the crystal coordinate system and intersecting both the x-axis and the y-axis; Crystal plane (111): The Miller indices are (h, k, l) = (1, 1, 1), which refers to the atomic plane that intersects the x-axis, y-axis, and z-axis of the crystal coordinate system.

[0030] In combination with the crystal structures involved in the present invention (such as body-centered cubic BCC and face-centered cubic FCC), the differences in atomic arrangements among the three are as follows: 1. Crystal plane (100): like Figure 1 As shown in a, in the BCC structure tungsten nanocluster of the present invention, the crystal plane (100) is a cubic "face" plane, the surface atomic arrangement density is low, and the atomic coordination number is 8 (each surface atom is surrounded by 8 atoms). There is a highly active acid site in the center of the crystal plane, mainly composed of W 6+ When exposed, the adsorption energy for monophenol products is high (-5.2 eV).

[0031] 2. Crystal plane (110): like Figure 1As shown in Figure a, in a BCC structured tungsten nanocluster, the crystal plane (110) is a 'facet'-like plane connecting adjacent crystal planes (100). The surface atomic arrangement density is higher than that of the crystal plane (100), and the atomic coordination number is 6-8 (the atomic coordination number at the center of the crystal plane is higher than that at the junction). Its notable feature is the presence of a large number of crystal plane junctions, including the vertices where three crystal planes (110) intersect, the edges where two crystal planes (110) intersect, and the intersection line where the crystal plane (110) and the crystal plane (100) intersect. The atomic coordination number at these junctions is 6, forming an electron-rich microregion, which is an area where rhenium atoms are preferentially enriched (the distribution density is more than 50% higher than that at the center of the crystal plane (100)).

[0032] 3. Crystal plane (111): like Figure 1 As shown in Figure 2b, in the FCC structure reference model, the crystal plane (111) is a triangular plane with the highest surface atomic density, an atomic coordination number of 12, and strong chemical stability. In the BCC structure tungsten nanoclusters of the present invention, the crystal plane (111) does not participate in the main catalytic reaction and exists only as a comparative structure.

[0033] In order to prepare rhenium-tungsten nanoalloy cluster catalysts, the present invention provides a method for controlling the configuration of rhenium-tungsten nanoalloy clusters, which serves as the theoretical basis for the preparation of rhenium-tungsten nanoalloy clusters, as follows: 1. Model construction and parameter setting: Figure 1 As shown, Figure 1 a shows the BCC Wulff structure, Figure 1 Figure b shows the FCC Wulff structure, where the BCC Wulff structure clearly marks six (100) and 12 (110) crystal planes. This step uses the LAMMPS program to construct a tungsten nanocluster model, using the BCC Wulff structure (containing six (100) and 12 (110) crystal planes) and setting the initial number of atoms. The EAM potential function is used to simulate and calculate the interactions between rhenium and tungsten atoms, thereby tracking each atom in the system.

[0034] 2. Temperature balance control: In the NVT ensemble, the Nose-Hoover method is used to maintain temperature balance: first, the system is heated to the target temperature (such as 2000K) and maintained for 10ns, and then a 200ps relaxation process is performed with a time step of 0.002ps.

[0035] 3. Rhenium atom deposition: In this step, rhenium atoms are randomly deposited on the surface of tungsten nanoclusters at a rate of 1 atom / ns. The deposition process is visualized in real time using the OVITO tool. In the early stage of deposition, rhenium atoms preferentially adsorb on the crystal plane (110) (because its area is larger than that of the crystal plane (100)) and exchange with tungsten atoms at the intersection of the crystal plane (110) - among them, the tungsten atoms at the intersection of the three crystal planes (110) have the lowest exchange energy barrier and the highest exchange probability, followed by the tungsten atoms at the edges of the two crystal planes (110). Figure 2-Figure 4 As shown, Figure 2 pass Figure 2 a- Figure 2 Schematic diagram of the atomic exchange process of f, showing the exchange mechanism of rhenium atoms and tungsten atoms at different crystal plane positions, combined with Figure 3 The corresponding energy barrier curve especially reflects the lowest exchange energy barrier at the intersection of the three crystal planes (110); Figure 4 The adsorption and diffusion behaviors of rhenium atoms on the crystal plane (100) and the crystal plane (110) are presented, verifying the rule that rhenium atoms preferentially adsorb on the crystal plane (110).

[0036] 4. Vacancy formation and migration monitoring: During the deposition process, vacancies will form on the (100) surface of the crystal plane: when three tungsten atoms are adsorbed on the four-coordinate sites on the (100) surface of the crystal plane, a vacancy will form on the fourth site, and then the adjacent tungsten atoms will migrate to fill the vacancy in turn, forming a chain reaction. The presence of rhenium atoms can reduce the energy barrier for tungsten atom migration (to a minimum of 1.964 eV), promoting vacancy migration. Figure 5-Figure 7 As shown, Figure 5 a- Figure 5 e illustrates the formation of surface vacancies on the crystal plane (100) and the chain reaction of tungsten atom migration to fill them, that is, three tungsten atoms are adsorbed on the four-coordinate site to form a vacancy. Figure 6 Schematic diagram of the migration mechanism of tungsten atoms under different conditions. Figure 6 a means there are no adsorbed atoms and no Re atoms; Figure 6 b means that only Re atoms are present; Figure 6 c indicates only adsorbed atoms; Figure 6 d indicates that there are both adsorbed atoms and Re atoms. Figure 7 The energy barrier curves were compared Figure 6 The migration energy barrier of tungsten atoms with and without rhenium atoms indicates the mechanism by which rhenium atoms reduce the migration energy barrier of tungsten atoms.

[0037] 5. Lattice structure analysis: The neighborhood analysis method is used to track the lattice transformation: When the number of deposited rhenium atoms is ≤800, the system is mainly BCC lattice; when the number of rhenium atoms increases to more than 1200, the proportion of HCP and FCC lattices gradually increases. After depositing 1400 rhenium atoms, a 1ns relaxation process is performed, and finally the atomic number proportions of BCC, FCC and HCP lattices are determined by statistics. Figure 9 As shown, Figure 9 a- Figure 9 d shows the changing trends of the number of BCC, FCC, and HCP lattice atoms with the amount of rhenium atom deposition, especially the transition from BCC lattice dominance to HCP and FCC with increasing proportions.

[0038] 6. Size and temperature effects: To study the size effect, tungsten nanoclusters with 58, 339, 641, or 1021 atoms can be constructed, maintaining a rhenium-tungsten ratio of 1:1, and observing how the rhenium atom diffusion depth changes with size (the larger the size, the harder it is for rhenium atoms to diffuse into the core). To control the lattice type, the deposition temperature can be adjusted (e.g., 2200K promotes BCC lattice, 1800-2000K increases the proportion of HCP lattice). Figure 8 As shown, Figure 8 a- Figure 8 c is a cross-sectional view of rhenium-tungsten nanoclusters with different total atomic numbers (118, 678, and 2042), which intuitively demonstrates the size effect that the larger the size, the more difficult it is for rhenium atoms to diffuse to the core, which is the research method for constructing tungsten nanoclusters with different atomic numbers in step 6.

[0039] In order to verify the catalytic application performance of the catalyst prepared by the above configuration control method of rhenium-tungsten nanoalloy clusters in the depolymerization of lignin to prepare phenolic compounds, the present invention further provides the following examples: Example 1: Configuration control and preparation steps of rhenium-tungsten nanoalloy cluster catalysts: The LAMMPS program was used to construct a BCC Wulff-structured tungsten nanocluster (with an initial atomic number of 1021, including 6 (100) and 12 (110) planes). Re atoms (a total of 255, with a rhenium-to-tungsten atomic ratio of 1:4) were deposited at a rate of 1 atom / ns at 2200 K. The Nose-Hoover method was used to maintain temperature equilibrium in the NVT ensemble (heating to 2200 K for 10 ns, followed by a 0.002 ps step and a 200 ps relaxation). The low energy barrier at the (110) plane interface (0.3 eV lower than the center of the (100) plane) was utilized to preferentially enrich the rhenium atoms at the (110) plane steps, with the diffusion depth controlled to be one atomic layer. Finally, a tungsten core-rhenium shell structure is formed (tungsten in the core accounts for 83% and rhenium in the shell accounts for 75%), the body-centered cubic (BCC) lattice accounts for 72%, the active sites at the junction of the crystal plane (110) account for 66%, and the lattice distortion rate is 3.5% after 1ns relaxation.

[0040] Example 1: Rhenium-tungsten nanoalloy clusters were prepared by hydrothermal method. The specific steps are as follows: Step 1: Weigh ammonium paratungstate and ammonium perrhenate in a rhenium-tungsten atomic ratio of 1:4 and dissolve them in deionized water. Add 0.1 mol / L citric acid as a chelating agent, with a total molar ratio of citric acid to metal ions of 1:1. Stir magnetically at 60°C for 1 hour to form a homogeneous solution.

[0041] Step 2: Transfer the solution to a 50 mL hydrothermal reactor, react at 180°C for 12 hours, cool naturally, centrifuge at 8000 rpm for 10 minutes, and collect the black precipitate.

[0042] Step 3: Wash the precipitate alternately with deionized water and anhydrous ethanol three times, and vacuum dry it at 60° C. for 8 hours to obtain a tungsten-rhenium composite hydroxide precursor.

[0043] Step 4: Place the precursor in a tube furnace, heat it to 800°C at 5°C / min under an argon atmosphere, and keep it warm for 2 hours to decompose the hydroxide; switch to a hydrogen atmosphere with a flow rate of 50 mL / min and reduce it at 450°C for 3 hours. After cooling, a tungsten core-rhenium shell structure cluster is obtained.

[0044] Catalyst preparation steps: Step 1: The mesoporous Al2O3 support was ground through a 200-mesh sieve, washed three times with deionized water, and dried at 110°C for 12 hours to obtain a pretreated support; Step 2: Add the core-shell structure clusters to anhydrous ethanol, ultrasonically disperse them at 300W for 30 minutes, and ultrasonic frequency is 40kHz. Add the pretreated support at a ratio of 8% of the total mass of the metal to the support. After stirring at 300r / min for 3 hours, evaporate the ethanol at 80°C to obtain a solid precursor. Step 3: The precursor is heated to 300°C at 5°C / min in an air atmosphere and kept at this temperature for 2 hours to completely remove residual organic matter and dispersant impurities; Step 4: Switch to hydrogen atmosphere at a flow rate of 50 mL / min, increase the temperature to 450°C at a rate of 2°C / min and keep at that temperature for 3 hours. After cooling, pass nitrogen protection to obtain the activated product; Step 5: Grind the activated product through a 100-mesh sieve to obtain the target catalyst, wherein Re 4+ Accounting for 65%, W 6+ Accounting for 80%.

[0045] Lignin depolymerization catalytic application steps: Step 1: The herbaceous plant straw lignin was ball-milled for 3 hours with a ball-to-material ratio of 10:1 using zirconium oxide balls, and the powder was crushed to 50-100 μm and passed through a 200 mesh sieve; Step 2: Mix lignin and catalyst at a mass ratio of 10:1, add methanol-water mixed solvent at a volume ratio of 3:1, introduce MgO powder accounting for 0.3% of the catalyst mass, magnetically stir at 300 rpm for 40 minutes until the system is evenly dispersed, and adjust the pH to 3.5 with 0.1 mol / L dilute sulfuric acid; Step 3: Transfer the mixed system to a 100 mL autoclave, seal it, and introduce 99.99% H2 to replace the air three times, maintain the pressure at 2.5 MPa, and use segmented temperature control: first increase the temperature to 220°C at 5°C / min and keep the temperature for 2 hours; then increase the temperature to 240°C at 5°C / min and keep the temperature for 2 hours. 4+ The monophenol intermediate was stabilized by providing hydrogen protons through hydrogen overflow, and the stirring rate during the whole process was 600 rpm; Step 4: After the reaction is completed, the autoclave is cooled to room temperature and the residual pressure is released. The catalyst is recovered by centrifugation at 8000 rpm for 10 minutes. The reaction solution is subjected to reduced pressure distillation to remove the solvent. The vacuum degree of the reduced pressure distillation is 0.09 MPa and the temperature is 70°C. The crude product is purified by chromatography on a 100-200 mesh silica gel column with a column diameter-to-height ratio of 1:10 and an eluent of petroleum ether:ethyl acetate in a volume ratio of 5:1. The target fraction is collected and vacuum dried at 50°C for 18 hours to obtain a monophenol compound, of which guaiacol accounts for 35% and eugenol accounts for 30%.

[0046] Example 2: Configuration control and preparation steps of rhenium-tungsten nanoalloy cluster catalysts: The initial number of tungsten nanoclusters was 641, and 160 rhenium atoms were deposited at 1800K (rhenium-tungsten ratio 1:4). During the deposition process, temperature control was used to increase the proportion of hexagonal close-packed (HCP) lattice to 22%, the proportion of active sites at the (110) interface of the crystal plane to 63%, the proportion of tungsten in the core region of the core-shell structure to 81%, the proportion of rhenium in the shell to 72%, and the lattice distortion rate to 4.2%.

[0047] Example 2 also uses a hydrothermal method to prepare rhenium-tungsten nanoalloy clusters. The only difference between the steps in Example 2 and Example 1 is that: Step 4: Place the precursor in a tube furnace, heat it to 700°C at 5°C / min under an argon atmosphere, and keep it warm for 2 hours; switch to a hydrogen-argon mixed atmosphere with a volume ratio of hydrogen to argon of 1:1 and a total flow rate of 60 mL / min, and reduce it at 750°C for 4 hours. After cooling, the target clusters were obtained.

[0048] Catalyst preparation steps: Step 1: The mesoporous Al2O3 support was ground through a 200-mesh sieve, washed three times with deionized water, and dried at 110°C for 12 hours to obtain a pretreated support; Step 2: Add the core-shell structure clusters to anhydrous ethanol, ultrasonically disperse them at 300W for 30 minutes, and ultrasonic frequency is 40kHz. Add the pretreated support at a ratio of 10% of the total mass of the metal to the support. After stirring at 300r / min for 3 hours, evaporate the ethanol at 80°C to obtain a solid precursor. Step 3: The precursor is heated to 320°C at 5°C / min in an air atmosphere and kept at this temperature for 2 hours to completely remove residual organic matter and dispersant impurities; Step 4: Switch to hydrogen atmosphere at a flow rate of 60 mL / min, increase the temperature to 480°C at a rate of 2°C / min, and keep the temperature for 3 hours. After cooling, pass nitrogen protection to obtain the activated product; Step 5: Grind the activated product through a 100-mesh sieve to obtain the target catalyst, wherein Re 4+ Accounting for 63%, W 6+ Accounting for 82%.

[0049] Lignin depolymerization catalytic application steps: Step 1: The herbaceous plant straw lignin was ball-milled for 3 hours using zirconium oxide balls at a ball-to-material ratio of 10:1, crushed to 50-100 μm, and passed through a 200-mesh sieve for later use; Step 2: Mix lignin and catalyst at a mass ratio of 10:1, add methanol-water mixed solvent at a volume ratio of 3:1, introduce MgO powder accounting for 0.5% of the catalyst mass, magnetically stir at 300 rpm for 40 minutes until the system is evenly dispersed, and adjust the pH to 3.5 with 0.1 mol / L dilute sulfuric acid; Step 3: Transfer the mixed system to a 100 mL autoclave, seal it, and introduce 99.99% hydrogen to replace the air in the autoclave three times, maintaining the hydrogen pressure at 2.5 MPa; adopt staged temperature control: first, increase the temperature to 210°C at 5°C / min and keep the temperature for 2.5 hours; then increase the temperature to 230°C at 5°C / min and keep the temperature for 2 hours. The stirring rate during the whole process is 600 rpm; Step 4: After the reaction is completed, the autoclave is cooled to room temperature and the residual pressure is released. The catalyst is recovered by centrifugation at 8000 rpm for 10 minutes. The reaction solution is subjected to reduced pressure distillation to remove the solvent. The vacuum degree of the reduced pressure distillation is 0.09 MPa and the temperature is 70°C. The crude product is purified by chromatography on a 100-200 mesh silica gel column with a column diameter-to-height ratio of 1:12 and an eluent of petroleum ether:ethyl acetate in a volume ratio of 5:1. The target fraction is collected and vacuum dried at 50°C for 24 hours to obtain a monophenolic compound, of which guaiacol accounts for 33% and eugenol accounts for 28%.

[0050] Example 3: Configuration control and preparation steps of rhenium-tungsten nanoalloy cluster catalysts: The initial number of tungsten nanoclusters is 339 atoms, and 68 rhenium atoms are deposited at 2000K (rhenium-tungsten ratio 1:5). The active sites at the (110) interface account for 61%, the BCC lattice accounts for 68%, and the FCC lattice accounts for 15%. The core-shell structure is complete (80% tungsten in the core and 71% rhenium in the shell).

[0051] Example 3 also uses a hydrothermal method to prepare rhenium-tungsten nanoalloy clusters. The only difference between the steps in Example 3 and those in Example 1 is that: Step 1: Weigh ammonium paratungstate and ammonium perrhenate in a rhenium-to-tungsten atomic ratio of 1:5 and dissolve them in deionized water. Add 0.1 mol / L citric acid as a chelating agent. The total molar ratio of citric acid to metal ions is the same as that in Example 1. Magnetic stirring is performed at 60° C. for 1 hour to form a homogeneous solution.

[0052] Step 4: Place the precursor in a tube furnace, heat it to 800°C at 5°C / min under argon atmosphere, and keep it warm for 2 hours; switch to hydrogen atmosphere with a flow rate of 40 mL / min, reduce it at 500°C for 2 hours, and obtain the target clusters after cooling.

[0053] Catalyst preparation steps: Step 1: The mesoporous Al2O3 support was ground through a 200-mesh sieve, washed three times with deionized water, and dried at 110°C for 12 hours to obtain a pretreated support; Step 2: Add the core-shell structure clusters to anhydrous ethanol, and ultrasonically disperse them at 300W for 30 minutes at an ultrasonic frequency of 40kHz. Add the pretreated support at a ratio of 5% of the total mass of the metal to the support. After stirring at 300r / min for 3 hours, evaporate the ethanol at 80°C to obtain a solid precursor. Step 3: The precursor is heated to 280°C at 5°C / min in an air atmosphere and kept at this temperature for 2 hours to completely remove residual organic matter and dispersant impurities; Step 4: Switch to hydrogen atmosphere at a flow rate of 40 mL / min, increase the temperature to 420°C at a rate of 2°C / min, and keep the temperature for 2 hours. After cooling, pass nitrogen protection to obtain the activated product; Step 5: Grind the activated product through a 100-mesh sieve to obtain the target catalyst, wherein Re 4+ Accounting for 60%, W 6+ It accounts for 78%.

[0054] Lignin depolymerization catalytic application steps: Step 1: The herbaceous plant straw lignin was ball-milled for 3 hours with a ball-to-material ratio of 10:1 using zirconium oxide balls, and the powder was crushed to 50-100 μm, and passed through a 200 mesh sieve for later use; Step 2: Mix lignin and catalyst at a mass ratio of 10:1, add methanol-water mixed solvent at a volume ratio of 3:1, introduce MgO powder accounting for 0.2% of the catalyst mass, and stir magnetically at 300 rpm for 50 minutes until the system is evenly dispersed. Adjust the pH to 3.5 with 0.1 mol / L dilute sulfuric acid; Step 3: Transfer the mixed system to a 100 mL autoclave, seal it, and introduce 99.99% hydrogen to replace the air in the autoclave three times, maintaining the hydrogen pressure at 2.5 MPa; use segmented temperature control: first increase the temperature to 220°C at 5°C / min and keep it warm for 2.5 hours; then increase the temperature to 240°C at 5°C / min and keep it warm for 2 hours. 4+ Efficiently dissociate hydrogen to generate hydrogen protons, stabilizing the monophenol intermediate. The stirring rate during the entire process is 700 rpm. Step 4: After the reaction is completed, the autoclave is cooled to room temperature and the residual pressure is released. The catalyst is recovered by centrifugation at 8000 rpm for 10 minutes. The reaction solution is subjected to reduced pressure distillation to remove the solvent at a vacuum degree of 0.09 MPa and a temperature of 70°C. The crude product is purified by chromatography on a 100-200 mesh silica gel column with a column diameter-to-height ratio of 1:8 and an eluent of petroleum ether:ethyl acetate in a volume ratio of 5:1. The target fraction is collected and vacuum dried at 50°C for 12 hours to obtain a monophenolic compound, of which guaiacol accounts for 32% and eugenol accounts for 27%.

[0055] Comparative Example 1: Rhenium-Tungsten Mixed Catalyst without Core-Shell Structure The difference between Comparative Example 1 and the embodiment is only that: Catalyst preparation steps: The rhenium-tungsten mixed catalyst was prepared by chemical coprecipitation method, rather than core-shell structure: sodium tungstate and ammonium perrhenate were dissolved in deionized water at an atomic ratio of 1:4, and a mesoporous Al2O3 carrier (the total mass of the metal accounts for 8% of the carrier) was added to obtain a rhenium-tungsten random mixed catalyst. The catalyst has no clear crystal surface active site enrichment, Re 4+ 50%, W 6+ It accounts for 65%.

[0056] In Comparative Example 1, the active sites are dispersed due to the lack of a core-shell structure, the lignin conversion rate is significantly reduced, the β-O-4 bond cleavage efficiency is greatly reduced, and the monophenol selectivity is significantly reduced.

[0057] Comparative Example 2: Single Tungsten Component Catalyst The difference between Comparative Example 2 and the embodiment is only that: Catalyst preparation steps: Only the tungsten component is loaded, and the sodium tungstate solution is loaded on the mesoporous Al2O3 carrier (the mass of tungsten accounts for 8% of the carrier) to obtain a pure tungsten catalyst (without rhenium component).

[0058] Lignin depolymerization application steps: The reaction was carried out according to the method of Example 1, while MgO was not introduced in step 2.

[0059] Due to the lack of rhenium component, Comparative Example 2 cannot stabilize the monophenol intermediate, the lignin conversion rate is reduced, the monophenol selectivity is greatly reduced, and the proportion of by-products such as polycyclic aromatic hydrocarbons and cycloalkanes in the product is significantly increased.

[0060] Comparative Example 3: Single temperature reaction without segmented temperature control The difference between Comparative Example 3 and the embodiment is only that: Lignin depolymerization application steps: the reaction temperature is 230 ° C, the reaction is continued for 4 hours, and there is no segmented temperature control.

[0061] In Comparative Example 3, since segmented temperature control was not adopted, the directional cleavage of the β-O-4 bond and the precise stabilization of the monophenol intermediate could not be achieved, the lignin conversion rate was reduced, the monophenol selectivity was significantly reduced, and the proportion of over-hydrogenated products increased.

[0062] Comparative Example 4: Application of Rhenium-Tungsten Nanoalloy Cluster Catalyst without MgO The difference between Comparative Example 4 and Example 1 is only that: Lignin depolymerization application steps: The reaction was carried out according to the method of Example 1, but MgO powder was not introduced in step 2.

[0063] In Comparative Example 4, due to the lack of MgO neutralizing the strong acid sites on the catalyst surface, the probability of over-hydrogenation of monophenol products at the active center increases, resulting in a decrease in monophenol selectivity and a significant increase in the proportion of over-hydrogenated products in the product.

[0064] The performance comparison experimental data of the above embodiment and comparative example are as follows:

[0065] Experimental Data: Based on the data from Examples 1-3, the use of a tungsten core-rhenium shell nanoalloy cluster catalyst, combined with staged temperature control (210-230°C for preferential cleavage of β-O-4 bonds and 230-250°C for promoting monophenol formation) and MgO regulation, resulted in a stable lignin conversion rate of 65%-72%, 80%-85% monophenol selectivity, and 88%-100% β-O-4 bond cleavage efficiency (relative value). The target monophenols, such as guaiacol and eugenol, accounted for 59%-65% of the total. Tungsten's strong electron transfer ability weakens the β-O-4 bond energy (reducing it by 30%-40%) through d-orbital electron transfer, significantly improving depolymerization efficiency and addressing the low depolymerization efficiency inherent in traditional methods due to bond stabilization. Rhenium's high hydrogenation activity stabilizes the intermediates after cleavage by providing hydrogen protons. Combined with the directional nature of the core-shell structure, this effectively avoids random reactions (such as over-hydrogenation and polymerization) of the intermediates, minimizing byproduct formation and addressing product complexity. At the same time, MgO neutralizes the strong acid sites on the catalyst crystal plane (100), reducing the probability of over-hydrogenation of monophenols at the active center (by more than 40%), further ensuring the directional retention of the target product. The segmented temperature control mechanism matches the needs of different reaction stages, efficiently breaking the β-O-4 bond while maximizing the selectivity of monophenol formation. These two factors, together with the core-shell structure, form a synergistic effect and jointly enhance the catalytic performance. In addition, the activity retention rate of the catalyst after five cycles still reached 85%-87%, reflecting the high stability of the core-shell structure (lattice distortion rate ≤5%), providing reliable support for industrial applications.

[0066] On the other hand, in the comparative examples, comparative example 1 uses a rhenium-tungsten mixed catalyst without a core-shell structure. Due to the dispersion of active sites, the lignin conversion rate is only 38%, the monophenol selectivity is 55%, and the β-O-4 bond cleavage efficiency (relative value) is only 50%. These data show that the core-shell structure is a necessary condition for achieving the synergistic effect of tungsten and rhenium and improving the catalytic efficiency; comparative example 2 uses a single tungsten component catalyst and does not introduce MgO. Due to the lack of rhenium hydrogenation activity to stabilize the intermediates, the monophenol selectivity is only 45%, and the proportion of by-products such as polycyclic aromatic hydrocarbons is as high as 60%, which confirms the role of rhenium in reducing by-products and improving the efficiency of catalysis. The irreplaceable role of MgO in product directionality is achieved; Comparative Example 3 adopts a single temperature reaction, which cannot achieve a precise match between β-O-4 bond cleavage and monophenol stability, the monophenol selectivity drops to 60%, and the proportion of over-hydrogenation products (such as cyclohexanol) increases to 30%, reflecting the importance of segmented temperature control in inhibiting side reactions; Comparative Example 4 does not introduce MgO. Although the β-O-4 bond cleavage efficiency is close to that of the embodiment (98%), the monophenol selectivity is only 60%, and the proportion of over-hydrogenation products is 35%, which intuitively proves the key role of MgO in neutralizing strong acid sites and inhibiting over-hydrogenation.

[0067] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

Claims

1. A rhenium-tungsten nanoalloy cluster catalyst, characterized in that: The catalyst is composed of a mesoporous Al2O3 carrier and a tungsten core-rhenium shell structured nano-alloy cluster supported thereon, wherein the atomic ratio of rhenium to tungsten is 1:3-1:

5. The catalyst is prepared by the following steps: Step 1: Grind and sieve the mesoporous Al2O3 carrier, wash it with deionized water, and dry it to obtain the pretreated mesoporous Al2O3 carrier for later use; Step 2: adding the tungsten core-rhenium shell structured nanoalloy clusters into anhydrous ethanol and ultrasonically dispersing them to form a uniform suspension; The pretreated mesoporous Al2O3 support is added to the suspension at a loading ratio of 5% to 10% of the total mass of rhenium and tungsten to the mass of the mesoporous Al2O3 support, and stirred to uniformly load the tungsten core-rhenium shell structured nanoalloy clusters in the suspension onto the surface of the support, and then ethanol in the system is evaporated to obtain a solid precursor loaded with tungsten core-rhenium shell structured nanoalloy clusters; Step 3: placing the solid precursor obtained in step 2 in a tube furnace, heating it to 280-320°C in an air atmosphere and maintaining the temperature to remove residual impurities to obtain a calcined product; Step 4: Switch the air atmosphere in the tube furnace to a hydrogen atmosphere, heat it to 420-480°C and keep it warm, then cool it down and introduce nitrogen protection to obtain an activated product; Step 5: Grind and sieve the activated product obtained in step 5 to obtain a rhenium-tungsten nanoalloy cluster catalyst.

2. The rhenium-tungsten nanoalloy cluster catalyst according to claim 1, characterized in that Step 1: After grinding, the mesoporous Al2O3 carrier is passed through a 200-300 mesh sieve, washed with deionized water 3-5 times, and dried at a temperature of 100-120°C for 10-14 hours; In step 2, the tungsten core-rhenium shell structure nano-alloy cluster has a core region tungsten atom ratio of ≥80%, and a shell rhenium atom ratio of ≥70%; it includes three lattice structures: body-centered cubic, face-centered cubic, and hexagonal close-packed, wherein the active sites at the interface of the crystal plane (110) account for ≥60%; the distribution density of rhenium atoms at the interface of the crystal plane (110) is more than 50% higher than that at the center of the crystal plane (100), and the diffusion depth is 0.5-2 atomic layers; after 1ns relaxation treatment, the lattice distortion rate is ≤5%; In step 2, the ultrasonic dispersion time is 20-40 minutes, the power is 250-350W, the frequency is 35-45kHz, the stirring rate is 250-350r / min, the stirring time is 2-4 hours, and the temperature for evaporating and removing ethanol is 70-90°C.

3. The rhenium-tungsten nanoalloy cluster catalyst according to claim 1, characterized in that: In step 3, the heating rate under air atmosphere is 4-6°C / min, and the holding time is 1.5-2.5 hours; In step 4, the flow rate of the hydrogen atmosphere is 40-60 mL / min, the heating rate is 1-3°C / min, and the holding time is 2-4 hours.

4. The rhenium-tungsten nanoalloy cluster catalyst according to claim 1, characterized in that The activated product in step 5 is ground and passed through an 80-120 mesh sieve to obtain a rhenium-tungsten nano alloy cluster catalyst; the rhenium in the catalyst is Re 4+ Mainly, accounting for 60%-70%, tungsten is W 6+ Mainly, accounting for 75%-85%.

5. A catalytic use of the rhenium-tungsten nanoalloy cluster catalyst according to any one of claims 1 to 4 in the depolymerization of lignin to prepare phenolic compounds, characterized in that: The following steps are involved: Step 1: Grind the lignin raw material into a particle size of 50-100 μm by ball milling, and sieve it for later use; Step 2: Mixing the lignin treated in step 1 with the rhenium-tungsten nanoalloy cluster catalyst in a mass ratio of 10:1, adding a methanol-water mixed solvent to the mixed system, wherein the volume ratio of methanol to water is 3:1, and introducing MgO powder accounting for 0.1%-0.5% of the catalyst mass, stirring until the lignin, catalyst and MgO are uniformly dispersed in the solvent, and adjusting the system pH to 3-4 with dilute sulfuric acid; Step 3: Transfer the mixed system obtained in step 2 to a high-pressure reactor, seal it, and introduce H2 to replace the air in the reactor, maintaining the H2 pressure at 2-3 MPa. Use a segmented temperature control method during the reaction: The temperature is first raised to 210-230°C for 1.5-2.5 hours to preferentially break the β-O-4 bonds in the lignin molecules, and then the temperature is raised to 230-250°C for 1.5-2.5 hours to promote the formation of monophenolic compounds. The entire reaction process is carried out at a stirring rate of 500-800 rpm. By controlling the temperature and time of the two-stage reaction, excessive hydrogenation of monophenolic products can be reduced. Step 4: After the reaction is completed, the mixed system in the high-pressure reactor is cooled to room temperature and the residual pressure in the reactor is released. The catalyst is recovered from the mixed liquid after the reaction by centrifugation, and the methanol-water mixed solvent is removed from the remaining reaction liquid by reduced pressure distillation. The obtained crude product is purified by silica gel column chromatography, and the target fraction containing the monophenol compound is collected and dried to obtain the monophenol compound.

6. The catalytic application according to claim 5, characterized in that: In step 1, the lignin raw material is herbaceous plant straw, which is ball-milled for 2-4 hours using zirconium oxide grinding balls at a ball-to-material ratio of 10:1, and then screened through a 150-300 mesh standard sieve; In step 2, the stirring is magnetic stirring at 300-500 rpm for 30-60 minutes; the concentration of dilute sulfuric acid is 0.1-0.5 mol / L.

7. The catalytic application according to claim 5, characterized in that: In step 3, the purity of H2 is 99.99%, and the heating rate is 5-10°C / min; the generated monophenol intermediates contain at least guaiacol, eugenol and p-ethylphenol.

8. The catalytic application according to claim 5, characterized in that: In step 3, the lignin conversion rate is 65%-75%, and the selectivity of monophenolic compounds is ≥80%; among the monophenolic compounds, guaiacol accounts for 30%-40% and eugenol accounts for 25%-35%.

9. The catalytic application according to claim 5, characterized in that: The centrifugal separation in step 4 is performed at a speed of 8000-10000 rpm for 10-15 min; the vacuum degree of the reduced pressure distillation is 0.08-0.1 MPa, the temperature is 60-80° C., a rotary evaporator is used, and the speed is 50-100 rpm; The silica gel particle size used in the silica gel column chromatography is 100-200 mesh, the column diameter-to-height ratio is 1:8-1:12, and the eluent is petroleum ether-ethyl acetate with a volume ratio of 5:

1. The drying process adopts vacuum drying at 40-60° C. for 12-24 hours to obtain a monophenol compound with a purity of ≥95%.

10. The catalytic application according to claim 5, characterized in that: The catalyst regeneration step is further included: the catalyst recovered by centrifugation is first ultrasonically washed with 5-10 times its mass of anhydrous ethanol at a power of 300W for 30 minutes, then soaked in a 0.05 mol / L H2SO4 solution for 1 hour to dissolve the residue, and finally washed with deionized water until neutral; After drying at 120℃ for 2-4 hours, reactivate at 400℃ for 2 hours in H2 atmosphere to restore Re 4+ and W 6+ active valence state.

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