Preparation method and application of lignin-based RuZn aerogel composite material

Abstract

The present application relates to a kind of lignin-based RuZn aerogel composite material preparation method and application.The present application is with sodium lignosulfonate as carbon source, by initiating polymerization, sol-gel forming and nitrogen atmosphere calcination etc., in situ build up high dispersity Ru-Zn bimetallic nanoparticles are loaded in the composite structure of carbon aerogel network.The material has aerogel porous structure, high specific surface area and metal synergistic activity, can be in the self-supply hydrogen system without additional hydrogen High-efficiency catalytic lignin directional depolymerization.Lignin-based RuZn aerogel composite material preparation process provided by the present application is simple, raw material is green and low price, structure is highly controllable, suitable for the efficient conversion of lignin and other biomass, provides new material selection and research direction for biomass catalytic conversion technology, has wide industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of organic / inorganic hybrid composite materials technology, specifically relating to a method for preparing and applying a lignin-based RuZn aerogel composite material, particularly its application in lignin depolymerization. Background Technology

[0002] Lignin is the most abundant renewable aromatic polymer in nature, accounting for 15%-30% of the weight of plant biomass. It is an important potential raw material for the production of chemicals such as phenol and aromatics, replacing fossil resources. With the deepening research on biomass energy and renewable resource utilization, lignin, as a large-scale byproduct generated in the papermaking industry and biomass refining process, has received widespread attention. Due to its complex structure, diverse functional groups, and rich aromatic rings, lignin is regarded as a natural aromatic polymer with high added value conversion potential, especially showing good prospects in catalytic depolymerization.

[0003] Efficient depolymerization of lignin is a crucial step in realizing its resource utilization, but current technology bottlenecks include insufficient catalytic activity, poor selectivity, complex products, and high energy consumption. In particular, traditional hydrodepolymerization systems generally rely on external hydrogen, which not only involves large equipment investments and high safety risks but also contradicts the development trend of green and low-carbon processes. Therefore, constructing a lignin depolymerization catalytic system that does not rely on external hydrogen and has self-supplying hydrogen capabilities has significant research and application value.

[0004] Meanwhile, aerogel materials, due to their high specific surface area, continuous pore structure, and excellent thermal stability, show broad application prospects in supported catalysts. Using lignin itself as a carbon source to construct functionalized aerogel materials not only enables in-situ utilization of waste resources but also endows the catalyst support with good hydrophilicity and porous structure, facilitating lignin molecule diffusion and product release. However, a novel catalyst system that can simultaneously achieve self-supplying hydrogen characteristics, high catalytic selectivity, and green sustainability is still lacking. Summary of the Invention

[0005] The main objective of this invention is to address the problems of poor dispersibility, easy agglomeration and deactivation, and dependence on external hydrogen in existing Ru-based catalysts. Simultaneously, it aims to improve the selectivity and structural stability of the catalyst for lignin depolymerization, thereby providing a highly efficient, green, and renewable method for preparing a lignin-based RuZn aerogel composite material. This material possesses self-hydrogen supply characteristics, enabling efficient catalytic depolymerization of lignin without the need for additional hydrogen introduction. This invention uses lignin as a carbon source and structure guide, utilizes acrylamide monomers and crosslinking agents to form a three-dimensional gel framework, and constructs a RuZn bimetallic composite aerogel structure in situ through high-temperature calcination under a nitrogen atmosphere. The resulting material exhibits high specific surface area, good pore structure, good metal dispersibility, and strong carrier stability, effectively improving the conversion rate and selectivity of lignin catalytic depolymerization.

[0006] To achieve the above objectives, the present invention is accomplished by the following means:

[0007] The first aspect of this invention provides a method for preparing a lignin-based RuZn aerogel composite material, comprising the following steps:

[0008] (1) Dissolve acrylamide in water, add crosslinking agent and lignin and mix well; then add zinc source and ruthenium source and stir well again;

[0009] (2) The initiator was quickly added and stirred evenly, and then heated and cured to obtain the precursor of lignin-derived carbon / RuZn aerogel composite material;

[0010] (3) The lignin-derived carbon / RuZn aerogel composite material precursor obtained in step (2) is placed in a tube furnace for high-temperature calcination to obtain the final product.

[0011] Preferably, the lignin in step (1) is selected from one or more of enzymatically hydrolyzed lignin, alkali lignin, and sodium lignin sulfonate; more preferably, the lignin is sodium lignin sulfonate.

[0012] Preferably, the mass ratio of lignin to acrylamide in step (1) is 0.1-1:1; more preferably, the mass ratio of lignin to acrylamide is 0.5-0.7:1.

[0013] Preferably, the zinc source in step (1) is selected from one or more of zinc nitrate, zinc chloride, and zinc acetate; more preferably, the zinc source is selected from zinc nitrate hexahydrate.

[0014] Preferably, the mass ratio of zinc source to acrylamide in step (1) is 0.1-1:1; more preferably, the mass ratio of zinc source to acrylamide is 0.15-0.3:1.

[0015] Preferably, the ruthenium source in step (1) is selected from one or more of ruthenium chloride, ruthenium nitrate, and ruthenium acetate; more preferably, the ruthenium source is selected from ruthenium chloride hexahydrate.

[0016] Preferably, the amount of ruthenium source used in step (1) is 0.01-0.05% of the total mass; more preferably, the amount of ruthenium source used is 0.015-0.03% of the total mass.

[0017] Preferably, the crosslinking agent in step (1) is selected from N,N-methylenebisacrylamide.

[0018] Preferably, the amount of crosslinking agent used in step (1) is 0.3-0.7% of the molar mass of acrylamide; more preferably, the amount of crosslinking agent used is 0.4-0.6% of the molar mass of acrylamide.

[0019] Preferably, the initiator in step (2) is selected from ammonium persulfate.

[0020] Preferably, the amount of initiator used in step (2) is 0.5-1.5% of the molar mass of acrylamide; more preferably, the amount of initiator used is 0.8-1.2% of the molar mass of acrylamide.

[0021] Preferably, the temperature of the heating and curing reaction in step (2) is 50-70°C and the time is 10-60 min; more preferably, the temperature of the heating and curing reaction is 55-65°C and the time is 15-30 min.

[0022] Preferably, the heating rate of the high-temperature calcination in step (3) is 3-8℃ / min, the temperature is 500-700℃, and the time is 1-3h; more preferably, the heating rate of the high-temperature calcination is 4-6℃ / min, the temperature is 550-650℃, and the time is 1.5-2.5h.

[0023] Preferably, the high-temperature calcination in step (3) is carried out under a protective gas atmosphere.

[0024] Preferably, the protective gas is selected from one or more of ammonia, argon, and nitrogen; more preferably, the protective gas is selected from nitrogen.

[0025] A second aspect of the present invention provides a lignin-based RuZn aerogel composite material prepared according to the above preparation method.

[0026] The third aspect of this invention provides the application of the lignin-based RuZn aerogel composite material prepared according to the above preparation method in biomass catalytic conversion.

[0027] Preferably, the biomass is selected from lignin.

[0028] Preferably, the application is a thermocatalytic lignin depolymerization reaction to prepare a sustainable aviation fuel precursor.

[0029] Preferably, the temperature of the thermocatalytic lignin depolymerization reaction is 523-583K, the reaction system contains nitrogen gas at 0-1 MPa, the solvent in the reaction system is selected from ethanol, and the substrate is selected from lignin; more preferably, the substrate is selected from enzymatically hydrolyzed alkali lignin or other naturally sourced lignin.

[0030] Preferably, the mass ratio of lignin to lignin-based RuZn aerogel composite material is 10-20:1.

[0031] Ruthenium (Ru)-based catalysts exhibit outstanding performance in the hydrodepolymerization of lignin due to their excellent CO and C-C bond breaking capabilities. However, Ru monometallic catalysts still have shortcomings in terms of dispersibility, anti-sintering properties, and reaction selectivity. This invention reveals that by introducing zinc (Zn) to form a bimetallic system, not only can the electronic structure of ruthenium be modulated to improve its catalytic behavior, but it can also promote the excitation and transfer of in-situ hydrogen sources, thereby achieving self-hydrogenated lignin depolymerization under mild conditions. Therefore, developing a RuZn bimetallic composite aerogel material based on lignin for the self-hydrogenated catalytic depolymerization of lignin not only simplifies the process and reduces energy consumption but also aligns with the development needs of green chemical engineering, which is of great significance for promoting biomass refining technology and sustainable development.

[0032] Compared with existing technologies, the present invention has the following advantages:

[0033] (1) This invention uses lignin as a carbon source and structure directing agent to guide the formation of a three-dimensional aerogel framework structure, effectively controlling the pore distribution and specific surface area, while achieving high dispersion of metal particles; it uses acrylamide + N,N-methylenebisacrylamide + sodium lignin sulfonate to form a polyacrylamide cross-linked framework, which is then calcined under nitrogen to form a carbon aerogel support with a porous three-dimensional network. Compared with traditional carbon powder loading systems (such as AC, carbon cloth, CNTs, etc.), this structure provides higher pore volume and larger specific surface area, which is more conducive to substrate entry and product diffusion. It effectively solves the problem of metal particle agglomeration during calcination and improves the exposure of active sites.

[0034] (2) This invention introduces a bimetallic component of Ru and Zn, while lignin provides surface activity, exhibiting dual functionality. This improves carbon source utilization and metal dispersion, helping to uniformly disperse metal salts. During calcination, a lignin-derived carbon / RuZn aerogel composite material is formed in situ. The synergistic effect between Ru and Zn enhances the electronic structure regulation capability, improves the breaking efficiency of C–O bonds and some C–C bonds in lignin, and further improves the selectivity of product distribution and catalytic activity. The porous carbon framework formed during high-temperature carbonization serves as a stable support, not only improving the thermal stability and cycle performance of the catalyst but also endowing the catalytic system with a good reaction interface and mass transfer channels.

[0035] (3) This invention constructs a self-supplying hydrogen reaction system under conditions without external hydrogen. Hydrogen is supplied in situ through intermediates (such as alcohols, acids, and phenols) generated during lignin pyrolysis, eliminating the need for external high-pressure hydrogen and significantly improving the safety and green sustainability of the reaction system. Simultaneously, the one-step in-situ gelation + calcination method significantly simplifies the preparation process, resulting in a simple and highly reproducible process. The resulting composite material has a stable structure, is easy to prepare, uses inexpensive raw materials, and can be prepared on a large scale. It is suitable for the high-value conversion of biomass such as lignin, and exhibits excellent catalytic performance and broad industrial application prospects, particularly in the catalytic depolymerization of lignin to prepare aromatic platform compounds under hydrogen-free conditions. Attached Figure Description

[0036] Figure 1 The X-ray diffraction patterns are those of the lignin-based RuZn aerogel composite materials prepared in Example 1 and Comparative Examples 1-3.

[0037] Figure 2 The image shows a scanning electron microscope (SEM) image of the lignin-based RuZn aerogel composite material prepared in Example 1.

[0038] Figure 3 Scanning electron microscope image of the lignin-based Ru aerogel composite material prepared for Comparative Example 1.

[0039] Figure 4 Scanning electron microscope image of the lignin-based Zn aerogel composite material prepared for Comparative Example 2.

[0040] Figure 5 The image shows a scanning electron microscope (SEM) image of the lignin-based aerogel composite material prepared in Comparative Example 3.

[0041] Figure 6 Atomic force microscopy (AFM) morphology images of Example 1 and Comparative Examples 1-3: (a) Comparative Example 3, (b) Comparative Example 2, (c) Comparative Example 1, (d) Example 1.

[0042] Figure 7Atomic force microscopy (AFM) 3D topographic images of Example 1 and Comparative Examples 1-3: (a) Comparative Example 3, (b) Comparative Example 2, (c) Comparative Example 1, (d) Example 1.

[0043] Figure 8 The roughness is shown in the atomic force microscope morphology images of Example 1 and Comparative Examples 1-3.

[0044] Figure 9 The nitrogen adsorption-desorption isotherms and pore size distribution diagrams are for samples of Example 1 and Comparative Examples 1-3.

[0045] Figure 10 The image shows the structural characterization of the RuZn aerogel composite material in Example 1 using transmission electron microscopy.

[0046] Figure 11 This is a transmission electron microscope combined with elemental energy dispersive spectroscopy (EDS) mapping of the lignin-based RuZn aerogel composite material in Example 1.

[0047] Figure 12 The yield of lignin depolymerization products was determined for samples 1 and 1-3 of the comparative examples.

[0048] Figure 13 The image shows the lignin depolymerization product spectrum obtained by GC-MS analysis in Example 1. Detailed Implementation

[0049] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0050] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0051] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. In the embodiments and comparative examples of this invention, sodium lignin sulfonate is used as an example of lignin. It should be understood that lignin is only used as a raw material to provide a carbon source, and its specific type has no significant impact on the properties of the finished catalyst. When other types of lignin, such as alkali lignin, enzymatically hydrolyzed lignin, or sulfite-processed lignin, are used for catalyst preparation, the resulting catalyst structure is not significantly different from that of sodium lignin sulfonate, and therefore will not be listed individually here.

[0052] Example 1

[0053] A lignin-based RuZn aerogel composite material is prepared by the following steps:

[0054] (1) Dissolve 1.5g of acrylamide in 5mL of water, add 0.5% N,N-methylenebisacrylamide by molar mass of acrylamide and stir to dissolve, then add 1.0g of sodium lignosulfonate; after all dissolves, add 1mmol of zinc nitrate hexahydrate and 0.02% ruthenium chloride hexahydrate by total mass and stir to dissolve again.

[0055] (2) Quickly add 1% of acrylamide by molar mass of ammonium persulfate and stir. After dissolving, drop the mixed solution evenly into the mold and place it in a 60℃ oven to cure into a gel for 20 min to obtain the precursor of lignin-derived carbon / RuZn aerogel composite material.

[0056] (3) The lignin-derived carbon / RuZn aerogel composite material precursor obtained in step (2) is placed in a tube furnace and calcined at 600°C for 2 hours under a nitrogen atmosphere at a rate of 5°C / min.

[0057] Comparative Example 1

[0058] A lignin-based Ru aerogel composite material, the preparation method of which includes the following steps:

[0059] (1) Dissolve 1.5g of acrylamide in 5mL of water, add 0.5% N,N-methylenebisacrylamide by molar mass of acrylamide and stir to dissolve, then add 1.0g of sodium lignosulfonate; after it is completely dissolved, add 0.02% ruthenium chloride hexahydrate by total mass and stir to dissolve again.

[0060] (2) Quickly add 1% of acrylamide by molar mass of ammonium persulfate and stir. After dissolving, drop the mixed solution evenly into the mold and place it in a 60℃ oven to cure into a gel for 20 min to obtain the precursor of lignin-derived carbon / RuZn aerogel composite material.

[0061] (3) The lignin-derived carbon / RuZn aerogel composite material precursor obtained in step (2) is placed in a tube furnace and calcined at 600℃ for 2 hours under a nitrogen atmosphere at a rate of 5℃ / min.

[0062] Comparative Example 2

[0063] A lignin-based Zn aerogel composite material is prepared by the following steps:

[0064] (1) Dissolve 1.5g of acrylamide in 5mL of water, add 0.5% N,N-methylenebisacrylamide by molar mass of acrylamide and stir to dissolve, then add 1.0g of sodium lignosulfonate; after it is completely dissolved, add 1mmol of zinc nitrate hexahydrate and stir to dissolve again.

[0065] (2) Quickly add 1% of acrylamide by molar mass of ammonium persulfate and stir. After dissolving, drop the mixed solution evenly into the mold and place it in a 60℃ oven to cure into a gel for 20 min to obtain the precursor of lignin-derived carbon / RuZn aerogel composite material.

[0066] (3) The lignin-derived carbon / RuZn aerogel composite material precursor obtained in step (2) is placed in a tube furnace and calcined at 600℃ for 2 hours under a nitrogen atmosphere at a rate of 5℃ / min.

[0067] Comparative Example 3

[0068] A lignin-based aerogel composite material, the preparation method of which includes the following steps:

[0069] (1) Dissolve 1.5g of acrylamide in 5mL of water, add 0.5% N,N-methylenebisacrylamide by molar mass of acrylamide and stir to dissolve, then add 1.0g of sodium lignosulfonate.

[0070] (2) Quickly add 1% of acrylamide by molar mass of ammonium persulfate and stir. After dissolving, drop the mixed solution evenly into the mold and place it in a 60℃ oven to cure into a gel for 20 min to obtain the precursor of lignin-derived carbon / RuZn aerogel composite material.

[0071] (3) The lignin-derived carbon / RuZn aerogel composite material precursor obtained in step (2) is placed in a tube furnace and calcined at 600℃ for 2 hours under a nitrogen atmosphere at a rate of 5℃ / min.

[0072] Verification Example 1

[0073] The crystal structure of the prepared aerogel composite material was determined using a Rigaku D / Max-2400 X-ray powder diffractometer according to the test method (10°~80°, 10° / min). The microstructure of the prepared aerogel composite material was observed using a Hitachi SU8220 field emission scanning electron microscope. The specific surface area and pore structure of the prepared aerogel composite material were tested using a Micron ASAP 2460 physical adsorption analyzer. The lattice size and elemental distribution of the prepared aerogel composite material were observed using a Thermo Fisher Talos F200s transmission electron microscope.

[0074] Figure 1X-ray diffraction (XRD) patterns of the aerogel composites prepared in Example 1 and Comparative Examples 1-3 are shown. The figures display the diffraction peak distribution in the range of 10°–80° for the samples of Example 1 and Comparative Examples 1-3, characterizing their crystal structure composition. The crystallinity of the samples gradually increased with adjusting conditions. Multiple sharp diffraction peaks were clearly observed in Example 1, corresponding to the appearance of a highly crystalline phase. Referring to the PDF card standard, the standard diffraction peak positions of ZnO (PDF#36-1451) and RuO2 (PDF#28-0713) are marked in the figures. Comparative Example 1 shows a high degree of metal species dispersion or is in an amorphous state; Comparative Example 2 shows weak crystalline peaks, indicating the formation of some ZnO nanocrystals; Comparative Example 3 exhibits relatively broad and gentle diffraction peaks, indicating that the material is mainly an amorphous carbon structure; Example 1 clearly shows multiple characteristic peaks consistent with the standard diffraction peaks of ZnO and RuO2, indicating the formation of a relatively obvious metal oxide crystal structure under these conditions. These XRD patterns confirm the significant influence of calcination on metal phase formation and the degree of material crystallinity.

[0075] Figure 2 The image shows a scanning electron microscope (SEM) image of the lignin-based RuZn aerogel composite material prepared in Example 1, illustrating its microstructure and lamellar stacking. The image reveals a typical three-dimensional lamellar aerogel structure with a rough surface exhibiting rich undulations and textures. Significant pores exist between the lamellar layers, providing excellent channels for reactant transport and product diffusion. The left image shows a large number of uniformly distributed nano-sized particles on the material surface, and rod-like structures within the gel structure are visible, presumably representing RuZn metal / metal oxide components. These particles are well-dispersed and show no obvious agglomeration, indicating that the metal can be stably anchored on the carbon support during high-temperature calcination. The right image reflects the porous stacking structure between the carbon lamellar layers, which helps to improve the specific surface area and gas diffusion efficiency. These morphological characterization results demonstrate that the preparation process employed in Example 1 successfully constructed a RuZn aerogel composite material with good structural integrity and uniform metal distribution, providing a stable and efficient catalytic platform for subsequent lignin self-hydrogen-donating catalytic depolymerization.

[0076] Figure 3The scanning electron microscope (SEM) images of the lignin-based Ru aerogel composite material prepared in Comparative Example 1 show the microstructure of the lignin-derived Ru-based composite material without the introduction of zinc metal. As can be observed from the images, the structure of this material is more loosely structured than that of Example 1, exhibiting a coexistence of particle agglomeration and lamellar fracture. The interlayer structure is not obvious, and the distribution of metal particles is relatively uneven. The left image shows blocky or clustered particle accumulation on the material surface, lacking a continuous and uniform lamellar structure. Larger metal or carbon fragments are also visible, indicating that the lack of Zn element to stabilize and guide the structure leads to a certain degree of Ru particle agglomeration during calcination. The right image shows the overall material packing morphology, with no obvious pore structure between particles and severe agglomeration in local areas, which is detrimental to the diffusion of reactants and the exposure of active sites. These images illustrate that, without the addition of a zinc source, the prepared lignin-based Ru material is prone to metal agglomeration and structural inhomogeneity during carbonization and calcination, resulting in incomplete development of the aerogel framework structure, which may affect its catalytic activity and stability. In contrast, the RuZn synergistic system in Example 1 is more conducive to constructing uniform sheet structures and dispersing metal nanoparticles.

[0077] Figure 4 The images show scanning electron microscope (SEM) images of the lignin-based Zn aerogel composite material prepared in Comparative Example 2, used to observe the microstructure morphology of the material under the condition of introducing only Zn. The images show that the material exhibits a relatively uniform lamellar structure with a large number of nanoscale particles attached to the surface. However, the structural stability and electrical conductivity are slightly insufficient in the absence of Ru. The left image shows dense white granular material on the material surface, presumably ZnO nanoparticles, uniformly attached to the surface of lignin-derived carbon sheets. The lamellars are tightly connected but slightly curled, indicating that the addition of Zn promotes crystal nucleation and lamellar network construction. The right image shows the uniform distribution morphology of a large area of ​​the material surface, with nanoparticles dispersed in a dotted pattern and widely distributed, but lacking a clear three-dimensional porous structure. Compared with the condition of introducing Ru, its lamellar support and porosity are slightly weaker. The results of Comparative Example 2 show that under the condition of introducing only Zn without Ru, the material can form a lamellar structure and effectively generate ZnO particles, but it is inferior to the RuZn synergistic system (Example 1) in terms of structural integrity and metal distribution synergy. Its metal particles are relatively uniformly distributed, but the types of catalytic active sites are relatively limited, which may restrict its performance in complex catalytic reactions.

[0078] Figure 5Scanning electron microscopy (SEM) images of the lignin-based aerogel composite material prepared in Comparative Example 3 show the microstructure of the lignin-based self-assembled carbon aerogel material without the introduction of any metal components. The images reveal a regular stacking of rod-like or needle-like structures, exhibiting a highly ordered overall structure. However, it clearly lacks a typical lamellar three-dimensional network, and no particulate metal distribution was observed, indicating that it is a pure carbon aerogel product without metal. The left image shows a large number of elongated strip-like structures arranged interlaced, possibly spontaneously formed by the polymer matrix during gelation. Lacking a metal-guided skeletal support, the overall structure is relatively fragile. The right image shows a large-area, regular rod-like network stacking morphology. Although structurally ordered, the surface is flat, active sites are scarce, and pores are few, which is unfavorable for catalytic loading and reactant transport. Image analysis indicates that without the addition of metal components, the material mainly forms a metal-free carbon gel structure, exhibiting some self-assembly capability, but its overall specific surface area, pore structure, and surface activity are lower than other metal-containing examples. Compared with other groups, this material lacks metal dispersion sites and synergistic effects, which may limit its activity in lignin-catalyzed depolymerization reactions.

[0079] Figure 6 Atomic force microscopy (AFM) morphology tests were performed on Examples 1 and Comparative Examples 1-3. The results showed that different metal components significantly affected the surface uniformity and microstructure of the materials. The composite material prepared in Example 1 had the smoothest surface, with a continuous and uniform lamellar structure, and no obvious agglomeration or folding, indicating that the synergistic effect of the bimetallic compounds helps to construct a stable and ordered aerogel framework structure. The surface of the Comparative Example 1 sample showed obvious undulations, with local folds and collapses, and a relatively loose structure. Comparative Example 2 exhibited better lamellar arrangement and particle uniformity, but slightly lower smoothness. The surface of the Comparative Example 3 sample was rough and irregular, lacking effective guiding and shaping effects. These AFM results further validated the key role of the synergistic guiding effect of Ru and Zn bimetals in regulating the microstructure of materials, providing structural assurance for the efficient exposure and stable construction of active sites on the catalyst surface.

[0080] Figure 7The images show the 3D structural diagrams obtained from AFM morphology testing of Examples 1 and Comparative Examples 1-3. AFM morphology analysis of the materials obtained in Examples 1 and Comparative Examples 1-3 reveals that different metal components significantly regulate the microstructure of the material surface. The material obtained in Example 1 exhibits high surface smoothness, uniform particle distribution, and continuous lamellar structure, forming an ordered nanoscale three-dimensional composite structure. The sample of Comparative Example 1 (containing only Ru) shows severe surface undulations with numerous high-peak protrusions, indicating significant particle agglomeration and poor structural uniformity. The sample of Comparative Example 2 (containing only Zn) is covered with a large number of dense micro / nano particles, significantly increasing roughness. Although the overall distribution is relatively uniform, it lacks lamellar support structures. The sample of Comparative Example 3 (containing no metal) exhibits a striped surface morphology with low structural regularity and lacks effective structural guidance. Comprehensive analysis indicates that the synergistic effect of Ru and Zn can effectively guide the formation of lamellar structures and promote the uniform distribution of nanoparticles, thereby significantly improving the structural integrity and microscopic order of the material surface, providing an excellent structural basis for subsequent catalytic performance.

[0081] like Figure 8 As shown, surface roughness statistics were performed on the AFM test samples of Example 1 and Comparative Examples 1-3. The results show that different metal components have a significant impact on the micro-roughness of the material surface. Comparative Example 2 (containing only Zn) has the highest surface roughness, reaching 68.23 nm, indicating that under the condition of no Ru participation, Zn particles form a large number of randomly distributed nanoprotrusions in the carbon framework, resulting in severe surface undulations. The roughness of Comparative Example 1 is 28.83 nm, slightly lower than that of Comparative Example 2, which is presumably due to the uneven distribution and easy aggregation of Ru on the surface, forming some local high protrusions. The surface of Comparative Example 3 is the smoothest, with a roughness of only 21.47 nm, but it lacks the support of active particles, and the overall structure is not dense and functional. The roughness of Example 1 is 25.08 nm, which is between that of Comparative Example 1 and Comparative Example 3, showing a good synergy between structural uniformity and particle distribution, with moderate protrusions, and combining smoothness and nano-functional structure characteristics.

[0082] Figure 9 The nitrogen adsorption-desorption isotherms for samples of Example 1 and Comparative Examples 1-3 are shown below. Figure 9 a) and the corresponding aperture distribution curve ( Figure 9(b) The results showed that the introduction of different metal components significantly affected the specific surface area and pore structure distribution of the materials. Example 1 exhibited a typical type IV isotherm with a significant hysteresis loop and high adsorption capacity, indicating that it possesses a well-developed mesoporous-macroporous structure. Its pore size distribution curve showed obvious distribution peaks in the 2–10 nm and 50–100 nm ranges, indicating that it has a hierarchical pore structure, which is beneficial to reactant mass transfer and product release. Comparative Example 1 showed a relatively low overall adsorption curve with almost no significant hysteresis, and the pore size was concentrated below 10 nm, indicating that its pore structure was simple, mainly micropores, and the specific surface area was low. Comparative Example 2 showed a relatively slow-rising adsorption curve with a slight increase in the high-pressure region, but the overall adsorption capacity was still low. Its pore size distribution was relatively dispersed between 2 and 50 nm, indicating that its pore structure was relatively disordered. Comparative Example 3 showed the lowest adsorption capacity and lacked the typical hysteresis characteristics of porous materials, indicating that its overall porosity was the lowest, mainly a dense carbon structure, with almost no mesoporous or macroporous distribution. Analysis of specific surface area and pore structure revealed that the synergistic introduction of Ru and Zn significantly improved the specific surface area and hierarchical pore development of the material. The material prepared in Example 1 exhibited the optimal pore structure, characterized by high adsorption capacity, hierarchical pore size distribution, and good hysteresis loop characteristics, which is beneficial for improving molecular diffusion efficiency and reaction site exposure in the catalytic reaction. In contrast, although Comparative Examples 1 and 2 introduced single metals, their pore development was weaker due to the lack of structural synergistic regulation. Comparative Example 3, without metal guidance, formed a dense carbon structure with the lowest porosity and specific surface area. These results are consistent with the aforementioned XRD, SEM, and AFM analyses, further verifying the crucial role of the Ru-Zn bimetallic compound in constructing the ideal microstructure of the catalytic material.

[0083] Figure 10The structural characterization results of the RuZn aerogel composite material obtained in Example 1 were presented using high-resolution transmission electron microscopy. Images a and d show the distribution characteristics of ZnO and RuO2 nanocrystals. The right side of Figures b, c, e, and f shows the corresponding interplanar spacing measurement curves, further confirming the crystal structure of the metal oxides in the material. Figure a is a low-magnification TEM image, observing a large-area lamellar structure loaded with nanoparticles; Figure b is a high-resolution lattice image, showing obvious parallel lattice fringes, which were confirmed by Fourier transform to be the (1 1 0) crystal plane of ZnO; Figure d shows the Ru component distributed in the form of bulk nanocrystals on the carbon support surface; the high-resolution image shows a clear lattice, and the corresponding crystal plane in the FFT image is RuO2 (310); the interplanar spacing analysis result is 0.142 nm, consistent with the RuO2 reference value. Transmission electron microscopy and high-resolution crystal plane analysis results show that in the lignin-based RuZn aerogel composite material prepared in Example 1, Ru and Zn elements are stably embedded in the carbon framework in the form of RuO2 and ZnO nanocrystals, respectively, and have clear crystal orientation characteristics. ZnO mainly exposes the (1 1 0) crystal plane, and RuO2 mainly exposes the (3 10) crystal plane, indicating that the metal precursor is effectively transformed into a stable crystalline phase structure during calcination. The lattice spacing measurements are 0.162 nm (ZnO) and 0.142 nm (RuO2), respectively, which are highly consistent with the standard data, further proving that the bimetallic components are uniformly dispersed in the carbon support and form a highly crystalline structure, which helps to improve the electron conduction efficiency and structural stability in the catalytic reaction. This verifies the high orderliness of the material's microstructure and the effectiveness of the bimetallic synergistic effect.

[0084] Through transmission electron microscopy combined with elemental energy dispersive spectroscopy (EDS) Figure 11Compositional and structural analyses were performed on the lignin-based RuZn aerogel composite material prepared in Example 1. The results showed that the distribution of each element was highly consistent, with Ru, Zn, C, O, and N elements uniformly distributed throughout the material, and no obvious agglomeration or elemental segregation was observed. Specifically, Zn was mainly concentrated in the lamellar structure region, corresponding to the ZnO crystal plane structure observed in the HRTEM image; while Ru was uniformly dispersed on the surface of the carbon-based framework, indicating a nanoscale distribution that provides abundant catalytic active sites. Furthermore, the continuous distribution of O and C elements in the framework confirmed that the lignin carbon source successfully participated in the construction of the aerogel framework, and that the introduction of an acrylamide network template assisted in the formation of a porous lamellar structure. The presence of N elements may originate from the reaction residues of the initiator and crosslinking agent, and also contributes to enhancing the electronic conductivity of the material. The above mapping results, along with TEM lattice fringe analysis, AFM three-dimensional morphology images, and BET test results, collectively validated the excellent performance of the composite material in terms of structural uniformity, nanoscale dispersion, and synergistic elemental construction, providing structural assurance and an active basis for its efficient catalytic reactions such as lignin depolymerization.

[0085] Figure 12 The product yields and compositions of Examples 1 and Comparative Examples 1-3 during the lignin depolymerization process are presented. The results show that the RuZn aerogel composites prepared under different synthesis conditions exhibit significant differences in their catalytic performance in lignin depolymerization. Example 1 showed the highest total yield (19.19%), with phenolic products as the main component, along with a certain proportion of alcohols and other molecular products, indicating that this catalyst has superior selective aromatic skeleton fragmentation ability and higher catalytic activity. In contrast, the product yields of Comparative Examples 1-3 were 9.05%, 8.50%, and 8.02%, respectively, significantly lower than that of Example 1. While the main products were still phenols, the proportions of alcohols and other byproducts increased slightly, indicating that the catalyst's structural stability and active site distribution were not as good as the composite material prepared in Example 1. Based on previous characterization results from AFM, BET, and TEM, the uniform porous structure, low surface roughness, and good synergistic distribution of Ru and Zn formed in Example 1 provided more active sites and electron transfer channels, thereby significantly improving the directional depolymerization efficiency and product selectivity of lignin. The above results further demonstrate the effectiveness and innovation of the structural design of the catalyst of this invention in improving the high-value conversion of lignin.

[0086] Figure 13The GC-MS analysis of the lignin depolymerization product spectrum, primarily corresponding to the reaction system of Example 1, is presented. Several peaks in the spectrum are labeled as known aromatic monomer compounds, such as phenol, o-methylphenol, p-hydroxybenzyl alcohol, eugenol, vanillin, and isosyringic acid. These products exhibit typical lignin structural fragments, indicating that the RuZn aerogel composite material used can effectively break C–O and C–C bonds during depolymerization, particularly demonstrating excellent performance in the cleavage of the β-O-4 bond on the phenylpropane unit. The products are predominantly phenolic compounds, further confirming the previously stated quantitative analysis result that phenols constitute the largest proportion. Notably, some products, such as isosyringic acid and vanillic acid, possess multifunctional groups, indicating that the reaction not only involved aromatic ring-preserving depolymerization but also partial oxidation, which may be attributed to the oxidative activity of the Ru component in the catalyst. Combining the GC spectrum, product types, and characterization data, it is evident that the catalyst of this invention possesses high depolymerization efficiency and product selectivity, demonstrating broad application potential in achieving directional high-value conversion of lignin.

[0087] The above detailed embodiments provide a specific description of the analytical methods involved in this invention. It should be noted that the above description is only intended to help those skilled in the art better understand the methods and ideas of this invention, and is not intended to limit the scope of the invention. Without departing from the principles of this invention, those skilled in the art can make appropriate adjustments or modifications to this invention, and such adjustments and modifications should also fall within the protection scope of this invention.

Claims

1. A method for preparing a lignin-based RuZn aerogel composite material, characterized in that, Includes the following steps: (1) Dissolve acrylamide in water, add crosslinking agent and lignin and mix evenly; then add zinc source and ruthenium source and stir evenly again; the crosslinking agent is selected from N,N-methylenebisacrylamide; (2) The initiator is quickly added and stirred evenly, and then the heating and curing reaction is carried out to obtain the lignin-based RuZn aerogel composite material precursor; the initiator is selected from ammonium persulfate; the heating and curing reaction temperature is 50-70℃; (3) The lignin-based RuZn aerogel composite material precursor obtained in step (2) is placed in a tube furnace and calcined at high temperature under a protective gas atmosphere to obtain the lignin-based RuZn aerogel composite material; the heating rate of the high-temperature calcination is 3-8℃ / min, the temperature is 500-700℃, and the time is 1-3h.

2. The preparation method according to claim 1, characterized in that, The lignin mentioned in step (1) is selected from one or more of enzymatically hydrolyzed lignin, alkali lignin, and sodium lignin sulfonate.

3. The preparation method according to claim 1, characterized in that, The zinc source mentioned in step (1) is selected from one or more of zinc nitrate, zinc chloride, and zinc acetate.

4. The preparation method according to claim 1, characterized in that, The ruthenium source mentioned in step (1) is selected from one or more of ruthenium chloride, ruthenium nitrate, and ruthenium acetate.

5. The preparation method according to claim 1, characterized in that, The heating and curing reaction time in step (2) is 10-60 min.

6. The lignin-based RuZn aerogel composite material prepared by the preparation method according to any one of claims 1-5.

7. The application of the lignin-based RuZn aerogel composite material according to claim 6 in the thermocatalytic depolymerization of lignin under conditions without external hydrogen supply.

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