A tungsten oxide catalyst, a method for preparing the same, and a method for oxidizing lignin

Abstract

The application provides a tungsten oxide catalyst and a preparation method thereof, and a method for oxidizing lignin, wherein the preparation method of the tungsten oxide catalyst comprises the following steps: preparing a tungsten-containing substance into a tungsten oxide precursor; and calcining the tungsten oxide precursor in an oxygen-containing atmosphere at 200-400 DEG C for 2-6 hours to obtain a tungsten oxide catalyst containing lattice oxygen; and the catalyst can efficiently and selectively break a beta-1 bond of lignin in a photocatalytic oxidation reaction of lignin, so that high-value aromatic compounds are generated, and efficient utilization of lignin is realized.

Description

Technical Field

[0001] This application relates to the field of tungsten oxide catalyst technology, and in particular to a tungsten oxide catalyst and its preparation method, and a method for oxidizing lignin. Background Technology

[0002] Currently, the utilization efficiency of lignin resources is extremely low. Most lignin is directly burned as low-value fuel in the pulp and paper industry, which not only wastes resources but also causes serious environmental problems. Therefore, research on how to prepare lignin into high-value chemicals is of great scientific significance and application value for promoting the green and low-carbon transformation of the chemical industry. Summary of the Invention

[0003] In view of this, the purpose of this application is to propose a tungsten oxide catalyst and its preparation method, as well as a method for oxidizing lignin, in order to solve the problem of low utilization rate of lignin.

[0004] To achieve the above objectives, this application provides a method for preparing a tungsten oxide catalyst, comprising: Tungsten-containing materials are prepared into tungsten oxide precursors; The tungsten oxide precursor was calcined at 200-400°C in an oxygen-containing atmosphere for 2-6 hours to obtain a tungsten oxide catalyst containing lattice oxygen.

[0005] Optionally, the step of preparing the tungsten-containing material into a tungsten oxide precursor includes: Na2WO4 2H2O is dissolved in water, citric acid and glucose are added in sequence and stirred until no precipitate is formed, then HCl solution is added and stirred to obtain a mixed solution; The mixed solution was reacted at a temperature of 80-140℃ for 12-36 hours, and after cooling to room temperature, a solid product was obtained. The solid product was washed and dried to obtain the tungsten oxide precursor.

[0006] Optionally, the step of preparing the tungsten-containing material into a tungsten oxide precursor includes: Tungsten powder was dissolved in H2O2 solution to obtain a precursor sol; Stir the precursor sol, add anhydrous ethanol, and continue stirring at a temperature of 50-100°C to obtain a wet gel. The wet gel was dried and ground to obtain the tungsten oxide precursor.

[0007] Optionally, the step of preparing the tungsten-containing material into a tungsten oxide precursor includes: Tungsten powder was dissolved in H2O2 solution and stirred to obtain a precursor solution; The precursor solution was placed in a temperature environment of 50-100℃ to obtain tungstic acid peroxide powder. The tungstic peroxide powder is dissolved in water, and a surfactant is added. The mixture is stirred at 50-100°C for 2-10 hours to obtain the tungsten oxide precursor.

[0008] Based on the same inventive concept, this disclosure also provides a tungsten oxide catalyst, which is prepared by any of the above-described preparation methods.

[0009] Based on the same inventive concept, this disclosure also provides a method for oxidizing lignin, comprising: Lignin and the above-mentioned tungsten oxide catalyst were placed in a solvent and reacted for 0.5-24 hours under 5-30W blue LED illumination in an oxygen-containing atmosphere to oxidize the β-1 bonds of lignin.

[0010] Optionally, the mass ratio of the tungsten oxide catalyst to the lignin is 1:(1~10).

[0011] Optionally, the solvent includes one or more of ethyl acetate, dichloromethane, ethanol, acetonitrile, and tetrahydrofuran.

[0012] Optionally, the mass ratio of the tungsten oxide catalyst to the lignin is 1:1.

[0013] Optionally, the oxygen-containing atmosphere includes an oxygen atmosphere and an air atmosphere.

[0014] As can be seen from the above, the method for preparing a tungsten oxide catalyst provided in this application includes: preparing a tungsten-containing material into a tungsten oxide precursor; calcining the tungsten oxide precursor at 200-400℃ in an oxygen-containing atmosphere for 2-6 hours to obtain a tungsten oxide catalyst containing lattice oxygen. The precursor preparation step in this application lays the foundation for the formation of lattice oxygen in the catalyst. Whether prepared by hydrothermal method, sol-gel method, or template method, the tungsten oxide precursor possesses high purity and uniform tungsten species distribution, providing structural assurance for the directional generation of lattice oxygen during subsequent calcination. The calcination temperature range of 200-400℃ promotes the dehydration and crystallization of the tungsten oxide precursor, forming a stable tungsten oxide crystal structure, while avoiding lattice oxygen loss or excessive oxygen vacancy generation due to high temperatures. The 2-6 hour duration ensures sufficient crystallization, allowing lattice oxygen to be uniformly distributed in the catalyst lattice, avoiding insufficient active sites due to incomplete calcination. The choice of an oxygen-containing atmosphere (such as air or oxygen) is crucial for the formation of lattice oxygen. During calcination, an oxygen-containing atmosphere provides sufficient oxygen for the construction of the tungsten oxide crystal structure, suppressing the excessive generation of oxygen vacancy defects, thereby directionally preparing tungsten oxide catalysts rich in lattice oxygen. The resulting catalyst has the advantages of high lattice oxygen content, sufficient exposure of active sites, and structural stability. In the photocatalytic oxidation of lignin, it can efficiently and selectively break the β-1 bond of lignin through the synergistic effect of the Mars-van Krevelen (MvK) mechanism and the Norrish type I reaction, thereby generating high-value aromatic compounds and achieving efficient utilization of lignin, which is conducive to promoting the development of a green, low-carbon, and circular economy. Furthermore, this preparation method is simple, with easily controllable parameters, mild calcination conditions (no need for high temperature and high pressure), and is compatible with various precursor preparation routes. The raw material cost is controllable, providing reliable technical support for the large-scale production and industrial application of the catalyst. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in this application or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram illustrating the oxidation of lignin by a tungsten oxide catalyst, as shown in the embodiments of this application. Figure 2 This is a schematic diagram illustrating the oxidation of 1,2-diphenylethanol by a tungsten oxide catalyst, as shown in the embodiments of this application. Figure 3 This is a schematic diagram illustrating the oxidation of industrial lignin by a tungsten oxide catalyst, as shown in the embodiments of this application. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with specific embodiments and the accompanying drawings.

[0018] It should be noted that, unless otherwise defined, the technical or scientific terms used in the embodiments of this application should have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms "first," "second," and similar terms used in the embodiments of this application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are only used to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0019] As mentioned in the background, lignin, as the only abundant renewable aromatic compound source in nature, occupies a core position in biomass resources, with considerable resource reserves and production scale. Data shows that lignin accounts for approximately 30% of terrestrial carbon reserves and is a key component in maintaining the terrestrial ecological carbon cycle. Furthermore, relying on industries such as pulp and paper making and agricultural and forestry waste processing, its global annual production reaches as high as 50 million tons, providing a sufficient raw material base for large-scale resource utilization, making it a green chemical raw material with great development potential.

[0020] However, the current state of lignin resource utilization is severely mismatched with its abundant reserves, with overall utilization efficiency at an extremely low level. Statistics show that less than 5% of the lignin produced globally is successfully converted into high-value chemicals, realizing resource value-added; more than 95% of lignin is directly incinerated as low-value fuel in the pulp and paper industry. This extensive disposal model not only causes a huge waste of valuable renewable aromatic resources, but also releases pollutants such as dust and harmful gases during incineration, leading to a series of serious environmental problems such as air and soil pollution, which contradicts the concept of green development.

[0021] Addressing the core technological bottlenecks of low lignin resource utilization and secondary pollution caused by traditional treatment methods, research on the directional depolymerization of lignin to prepare high-value chemicals is both urgent and significant. This research approach can fundamentally change the crude incineration disposal mode of lignin, reduce pollutant emissions, and avoid the environmental risks brought about by traditional treatment methods. At the same time, it can transform low-value lignin into high-value-added chemical products, significantly improving the comprehensive utilization efficiency of biomass resources.

[0022] The following is in conjunction with the appendix Figure 1-3 The embodiments of this application will be described in detail below.

[0023] The reagents and medicines used in the embodiments of this application are all conventional commercially available products.

[0024] A method for preparing a tungsten oxide catalyst, comprising: Tungsten-containing materials are prepared into tungsten oxide precursors; The tungsten oxide precursor was calcined at 200-400°C in an oxygen-containing atmosphere for 2-6 hours to obtain a tungsten oxide catalyst containing lattice oxygen.

[0025] Specifically, the tungsten oxide precursor is calcined in a muffle furnace at a heating rate of 2-10 °C / min in an air atmosphere at 200-400 °C for 2-6 h to obtain a tungsten oxide catalyst containing lattice oxygen.

[0026] In this embodiment, the precursor preparation step lays the foundation for the formation of lattice oxygen in the catalyst. Whether prepared by hydrothermal method, sol-gel method, or template method, the tungsten oxide precursor possesses high purity and uniform tungsten species distribution, providing structural assurance for the directional generation of lattice oxygen during subsequent calcination. A calcination temperature range of 200-400℃ promotes dehydration and crystallization of the tungsten oxide precursor, forming a stable tungsten oxide crystal structure, while avoiding lattice oxygen loss or excessive oxygen vacancy generation due to high temperatures. A calcination time of 2-6 hours ensures sufficient crystallization, resulting in uniform distribution of lattice oxygen within the catalyst lattice, preventing insufficient active sites due to incomplete calcination. The selection of an oxygen-containing atmosphere (such as air or oxygen) is crucial for lattice oxygen formation. During calcination, an oxygen-containing atmosphere provides a sufficient oxygen source for the construction of the tungsten oxide crystal structure, suppressing excessive oxygen vacancy defects, thereby directionally preparing a tungsten oxide catalyst rich in lattice oxygen. The resulting catalyst possesses advantages such as high lattice oxygen content, sufficient exposure of active sites, and structural stability. In the subsequent photocatalytic oxidation of lignin, it can efficiently and selectively break the β-1 bonds of lignin through the synergistic effect of the Mars-van Krevelen (MvK) mechanism and the Norrish type I reaction, thereby generating high-value aromatic compounds and achieving efficient utilization of lignin, which is conducive to promoting the development of a green, low-carbon, and circular economy. Furthermore, this preparation method is simple, with easily controllable parameters, mild calcination conditions (no need for high temperature and high pressure), and is compatible with various precursor preparation routes. The raw material cost is controllable, providing reliable technical support for the large-scale production and industrial application of the catalyst.

[0027] In some embodiments, the oxide precursor is prepared using a hydrothermal method.

[0028] The process of preparing a tungsten oxide precursor from a tungsten-containing material includes: Na2WO4 2H2O is dissolved in water, citric acid and glucose are added in sequence and stirred until no precipitate is formed, then HCl solution is added and stirred to obtain a mixed solution; The mixed solution was reacted at a temperature of 80-140℃ for 12-36 hours, and after cooling to room temperature, a solid product was obtained. The solid product was washed and dried to obtain the tungsten oxide precursor.

[0029] Specifically, Na2WO4 2H₂O was dissolved in deionized water and stirred until dissolved. Citric acid and glucose were added sequentially, and the mixture was stirred vigorously until no precipitate was formed. Then, a certain amount of HCl solution was added dropwise, and the mixture was stirred for 20-60 minutes to obtain a mixed solution. The mixed solution was then transferred to a stainless steel reactor lined with polytetrafluoroethylene and reacted at 80-140°C for 12-36 hours. After cooling to room temperature, a solid product was obtained. The product was washed three times with water and ethanol alternately and dried in a vacuum oven at 50-80°C for 6-12 hours to obtain the tungsten oxide precursor.

[0030] In this embodiment, Na2WO4 is used. Using tungsten-containing raw material Na2WO4, the process of preparing tungsten oxide precursor through composite modification and hydrothermal reaction has several outstanding advantages. Firstly, the raw material Na2WO4... 2H₂O is widely available and inexpensive. The synergistic effect of citric acid and glucose can effectively regulate the morphology and structure of the precursor. Citric acid can form a stable complex with tungsten ions, inhibiting particle aggregation, while glucose plays a dispersing and structure-guiding role in subsequent reactions. The two are stirred together until no precipitate is found, ensuring the homogeneity of the reaction system and laying the foundation for the formation of a high-quality precursor. The addition of HCl solution can precisely adjust the pH of the system, optimize the hydrolysis and polymerization process of tungsten, and further improve the structural regularity of the precursor. Secondly, the hydrothermal reaction temperature of 80-140℃ and the reaction time of 12-36h are reasonably matched, which can ensure that the reaction proceeds fully, promote the formation of a stable crystalline structure of tungsten, and avoid excessive particle growth and structural defects caused by excessive temperature or time. After the reaction, washing and drying can effectively remove unreacted impurity ions and residual organic matter, resulting in a high-purity and well-dispersed tungsten oxide precursor. After calcination in an oxygen-containing atmosphere at 200-400℃, the precursor can form a tungsten oxide catalyst with abundant lattice oxygen content and fully exposed active sites. In the photocatalytic oxidation of lignin, it can efficiently and selectively break β-1 bonds, exhibiting excellent catalytic activity and selectivity. Moreover, the preparation process is mild, the parameters are easy to control, and no complex equipment is required, providing a feasible path for the large-scale preparation and industrial application of the catalyst.

[0031] In some embodiments, the tungsten oxide precursor is prepared using a sol-gel method.

[0032] The process of preparing a tungsten oxide precursor from a tungsten-containing material includes: Tungsten powder was dissolved in H2O2 solution to obtain a precursor sol; Stir the precursor sol, add anhydrous ethanol, and continue stirring at a temperature of 50-100°C to obtain a wet gel. The wet gel was dried and ground to obtain the tungsten oxide precursor.

[0033] Specifically, tungsten powder is dissolved in a 30% H2O2 solution to obtain a precursor sol, which is then stirred vigorously for 12-36 hours. Anhydrous ethanol is added, and stirring is continued at 50-100°C for 1-6 hours. The wet gel is dried in an oven at 80-120°C for 12-24 hours. The dried gel is then ground using an agate mortar to obtain the tungsten oxide precursor.

[0034] In this embodiment, tungsten powder is used as the starting tungsten-containing raw material. A sol-gel process involving sol preparation, gelation, and drying / grinding is employed to prepare tungsten oxide precursors, offering advantages in both process mildness and structural control, resulting in significant effects. First, the tungsten powder undergoes an oxidation-dissolution reaction in H2O2 solution, forming a uniform and stable precursor sol. H2O2 not only efficiently dissolves the tungsten powder but also inhibits impurity formation, laying the foundation for high purity of the precursor. Continuous stirring ensures complete dissolution of the tungsten powder, avoiding structural defects caused by uneven local concentrations and ensuring good uniformity of the sol system. Second, the addition of anhydrous ethanol to the sol allows ethanol to act as a co-solvent, adjusting the system's viscosity and surface tension, and promoting cross-linking polymerization between sol molecules. Continued stirring at a mild temperature of 50-100°C accelerates solvent evaporation and gelation, forming a dense, uniformly networked wet gel. This temperature range ensures sufficient gelation while avoiding particle agglomeration or functional group decomposition caused by high temperatures. Simultaneously, stirring further optimizes the regularity of the gel network. Finally, after drying to remove residual solvent and grinding, a tungsten oxide precursor with fine particles and excellent dispersibility was obtained. Its microstructure showed no obvious agglomeration and was uniformly distributed. This precursor, after subsequent calcination in an oxygen-containing atmosphere at 200-400℃, forms a tungsten oxide catalyst with abundant lattice oxygen active sites and a large specific surface area. In the photocatalytic oxidation of lignin, it can fully contact the substrate, efficiently activate lattice oxygen to participate in the reaction, and achieve selective cleavage of the β-1 bond in lignin. Furthermore, this preparation process does not require high-pressure equipment or complex modifiers, is simple to operate, has easily controllable parameters, and uses widely available and cost-effective tungsten powder, balancing catalytic performance with industrial production potential.

[0035] In some embodiments, the tungsten oxide precursor is prepared using a template method.

[0036] The process of preparing a tungsten oxide precursor from a tungsten-containing material includes: Tungsten powder was dissolved in H2O2 solution and stirred to obtain a precursor solution; The precursor solution was placed in a temperature environment of 50-100℃ to obtain tungstic acid peroxide powder. The tungstic peroxide powder is dissolved in water, and a surfactant is added. The mixture is stirred at 50-100°C for 2-10 hours to obtain the tungsten oxide precursor.

[0037] Specifically, tungsten powder is dissolved in a 30% (w / w) H₂O₂ solution, followed by vigorous stirring for 12-36 hours. After stirring is stopped, the mixture is slowly dried in an oven at 50-100°C to obtain tungstic acid peroxide powder. The tungstic acid peroxide powder is then dissolved in deionized water, and a surfactant (hexadecyltrimethylammonium bromide) is added. The mixture is stirred and reacted at 50-100°C for 2-10 hours to obtain the tungsten oxide precursor.

[0038] In this embodiment, tungsten powder is used as the tungsten-containing raw material. A stepwise process of peroxidation dissolution, pyrolysis to powder, and template modification is employed to prepare tungsten oxide precursor, resulting in significant effects and advantages. First, the tungsten powder is fully dissolved in H2O2 solution and undergoes an oxidation reaction to generate a stable tungsten oxide precursor solution. H2O2 acts as an oxidant, effectively preventing the formation of insoluble impurities and ensuring the purity of the precursor. Subsequently, a temperature environment of 50-100℃ allows for the mild pyrolysis of the precursor solution, gradually removing the solvent and forming a structurally uniform tungstic acid peroxide powder. This temperature range ensures sufficient pyrolysis while avoiding powder agglomeration or structural collapse caused by high temperatures. The key lies in the introduction of surfactants and the subsequent stirring reaction at 50-100℃ for 2-10 hours. Surfactants act as template guides for tungstic acid peroxide powder through adsorption and assembly, controlling the microstructure of the precursor (e.g., forming porous structures or particles of specific sizes) and increasing the potential exposed area of ​​active sites. Simultaneously, the stirring process further promotes the full interaction between the surfactant and tungsten species, optimizing the dispersion and structural regularity of the precursor. The resulting tungsten oxide precursor exhibits high purity, controllable morphology, and good dispersibility. After calcination in an oxygen-containing atmosphere at 200-400℃, it forms a tungsten oxide catalyst with abundant lattice oxygen active sites and a stable structure. In the photocatalytic oxidation of lignin, it can efficiently and selectively break β-1 bonds and shows good compatibility with different types of lignin (including industrial hardwood lignin). Furthermore, this preparation process uses readily available raw materials, operates under mild reaction conditions, and allows for easy parameter control, eliminating the need for complex equipment such as high-pressure systems, thus providing reliable support for the large-scale production and practical application of the catalyst.

[0039] Based on the same inventive concept, this disclosure provides a tungsten oxide catalyst prepared by any of the above-described preparation methods, and has the beneficial effects of the corresponding method embodiments, which will not be repeated here.

[0040] Based on the same inventive concept, this disclosure provides a method for oxidizing lignin, comprising: Lignin and the above-mentioned tungsten oxide catalyst were placed in a solvent and reacted for 0.5-24 hours under 5-30W blue LED illumination in an oxygen-containing atmosphere to oxidize the β-1 bonds of lignin.

[0041] In this embodiment, as Figure 1As shown, the tungsten oxide catalyst prepared by the aforementioned method is rich in lattice oxygen active sites. Under the activation of 5-30W blue LED light, it can precisely target the β-1 bond of lignin and achieve highly efficient selective cleavage through the synergistic effect of the Mars-van Krevelen (MvK) mechanism and the Norrish type I reaction, with a CC bond cleavage selectivity exceeding 90%. Specifically, the lattice oxygen in the catalyst is first activated and oxidizes the lignin substrate through the MvK mechanism. The consumed lattice oxygen can be replenished by the oxygen-containing atmosphere in the reaction system to ensure the continuous catalytic cycle. After the intermediate activated and oxidized by lattice oxygen is desorbed, it will further undergo the Norrish type I reaction, which promotes the homolytic cleavage of the CC bond corresponding to the β-1 bond, generating benzoyl and benzyl alcohol radicals. The two radicals are then converted into aromatic aldehydes through redox reactions, and the aromatic aldehydes are further oxidized to generate aromatic acids. Meanwhile, the lattice oxygen catalytic system exhibits excellent cycling stability, with no significant activity decay after 10 cycles. It also demonstrates good universality for various β-1 lignin model compounds and hardwood industrial lignin, providing stable and reliable technical support for the directional depolymerization of lignin to prepare high-value chemicals.

[0042] The reaction conditions in this embodiment are mild and environmentally friendly. Blue LED light, as a clean energy source, can initiate the catalytic reaction without high temperature and pressure, avoiding the high energy consumption and high pollution problems of traditional processes. The reaction time of 0.5-24 hours ensures the full breaking of lignin β-1 bonds while meeting the time cost requirements of industrial production. Simultaneously, the oxygen-containing atmosphere (air or oxygen) not only ensures the continuous replenishment of lattice oxygen, maintaining the catalyst's sustained activity, but also promotes the appropriate conversion of the target product, aromatic aldehydes, to aromatic acids, increasing the product's added value. This method requires no addition of precious metals or toxic reagents, the catalyst has high activity and selectivity, good stability, and is recyclable. It also has a wide range of substrate applicability and yields high-value aromatic aldehydes and aromatic acids. This method achieves the resource utilization of biomass resources and reduces environmental pollution from lignin incineration at the source, providing a feasible path for the green and low-carbon transformation of the chemical industry. It has both significant scientific value and broad industrial application prospects.

[0043] In some embodiments, the mass ratio of the tungsten oxide catalyst to the lignin is 1:(1~10).

[0044] In this embodiment, when the mass ratio of tungsten oxide catalyst to lignin is controlled within the range of 1:(1~10), an optimal balance between catalytic activity and raw material utilization can be achieved. While an excessively high mass ratio (excess catalyst) may increase the reaction rate, it also increases production costs, and excess catalyst can easily create a separation burden. Conversely, an excessively low mass ratio (insufficient catalyst) leads to an insufficient number of active sites, incomplete cleavage of lignin β-1 bonds, and a low conversion rate. This suitable ratio range balances reaction efficiency, cost control, and practicality, providing flexible parameter selection for industrial scale-up.

[0045] In some embodiments, the solvent includes one or more of ethyl acetate, dichloromethane, ethanol, acetonitrile, and tetrahydrofuran.

[0046] In this embodiment, one or more of ethyl acetate, dichloromethane, ethanol, acetonitrile, and tetrahydrofuran are selected as solvents to adapt to different reaction scenarios and substrate characteristics. Dichloromethane, when used as a solvent, exhibits good solubility for both lignin model compounds and industrial lignin, promoting sufficient contact between the catalyst and substrate and optimizing β-1 bond breaking selectivity and conversion. Solvents such as ethyl acetate and tetrahydrofuran can be flexibly selected based on the solubility requirements of the reaction system, environmental requirements, or separation difficulty. For example, ethanol, as a green solvent, is more suitable for scenarios with high environmental requirements. Mixed solvents can optimize solubility and catalytic environment by adjusting the proportions. This solvent selection scheme improves the versatility of the method, allowing for flexible adjustments based on actual production needs and reducing the difficulty of process adaptation.

[0047] In some embodiments, the mass ratio of the tungsten oxide catalyst to the lignin is 1:1.

[0048] In this embodiment, an optimal balance between catalytic activity and economic cost is achieved when the mass ratio of tungsten oxide catalyst to lignin is 1:1. At this ratio, the number of lattice oxygen active sites provided by the catalyst is highly matched with the molar amount of β-1 bonds in lignin, maximizing the catalytic effect and resulting in a high conversion rate of lignin β-1 bond breaking and a high yield of the target product. Compared to other ratios, a 1:1 mass ratio achieves efficient depolymerization without requiring additional catalyst, reducing raw material costs. It also avoids incomplete reaction due to insufficient catalyst, balancing production efficiency and economy, making it a preferred ratio parameter for industrial production.

[0049] In some embodiments, the oxygen-containing atmosphere includes an oxygen atmosphere and an air atmosphere.

[0050] In this embodiment, the oxygen-containing atmosphere can be either an oxygen atmosphere or an air atmosphere, providing a flexible oxygen source solution for the reaction. An oxygen atmosphere, with its higher oxygen concentration, can quickly replenish the lattice oxygen consumed in the catalyst, accelerating the catalytic cycle and optimizing the conversion rate and selectivity of lignin β-1 bond breaking, making it suitable for scenarios with high conversion efficiency requirements. An air atmosphere, on the other hand, eliminates the need for additional oxygen preparation, resulting in lower costs and simpler operation. Although its conversion efficiency is slightly lower than that of an oxygen atmosphere, it meets the needs of large-scale production where cost control is more critical. Both atmospheres can support the lattice oxygen cycle, avoiding the problem of rapid catalyst activity decay in an oxygen-free atmosphere, and achieving flexible adaptation to different production needs.

[0051] The above embodiments will be described in detail below with reference to specific examples.

[0052] As can be seen from the above embodiments, tungsten oxide precursors can be prepared by hydrothermal method, sol-gel method, and template method, respectively. The tungsten oxide precursors prepared by the above hydrothermal method, sol-gel method, and template method are calcined in a muffle furnace at a heating rate of 2-10℃ / min in an air atmosphere at 200-400℃ for 2-6 hours to obtain tungsten oxide catalysts containing lattice oxygen, denoted as HO, respectively. L -WO3, SO L -WO3 and MO L -WO3. Correspondingly, tungsten oxide precursors prepared by the above-mentioned hydrothermal method, sol-gel method, and template method, when calcined at 200-400℃ in an argon atmosphere for 2-6 hours, yielded tungsten oxide catalysts containing vacant oxygen, denoted as HO respectively. V- WO3, SO V -WO3 and MO V -WO3.

[0053] Example 1 A method for oxidizing lignin, comprising: Lignin and tungsten oxide catalyst were placed in a solvent and reacted for 0.5-24 hours under 5-30W blue LED illumination in an oxygen-containing atmosphere to oxidize the β-1 bonds of lignin.

[0054] Specifically, 0.1 mmol (20 mg) of 1,2-diphenylethanol (1a) and 10 mg of tungsten oxide catalyst (HO) were added. L WO3 was placed in 2 mL of DCM (dichloromethane) as solvent and reacted for 1 hour under 15 W blue LED light in air atmosphere to oxidize the β-1 bond of lignin to obtain the depolymerization products benzaldehyde (2a) and benzoic acid (3a).

[0055] Example 2 The difference between Example 2 and Example 1 is that the tungsten oxide catalyst is HO.v -WO3, the remaining steps are the same as in Example 1.

[0056] Example 3 The difference between Example 3 and Example 1 is that the tungsten oxide catalyst is SO. L -WO3, the remaining steps are the same as in Example 1.

[0057] Example 4 The difference between Example 4 and Example 1 is that the tungsten oxide catalyst is SO. v -WO3, the remaining steps are the same as in Example 1.

[0058] Example 5 The difference between Example 5 and Example 1 is that the tungsten oxide catalyst is MO. L -WO3, the remaining steps are the same as in Example 1.

[0059] Example 6 The difference between Example 6 and Example 1 is that the tungsten oxide catalyst is MO. v -WO3, the remaining steps are the same as in Example 1.

[0060] Example 7 The difference between Example 7 and Example 1 is that 15 W LED light is not used and the reaction time is 2 hours. The remaining steps are the same as in Example 1.

[0061] Example 8 The difference between Example 8 and Example 1 is that no catalyst is used and the reaction time is 2 hours, while the remaining steps are the same as in Example 1.

[0062] Example 9 The difference between Example 9 and Example 1 is that the tungsten oxide catalyst is HO. v -WO3, with a weight of 20mg, the air atmosphere was replaced with a nitrogen atmosphere, the reaction time was 2 hours, and the remaining steps were the same as in Example 1.

[0063] Example 10 The difference between Example 10 and Example 1 is that HO L The weight of the WO3 tungsten oxide catalyst was 20 mg, the air atmosphere was replaced with a nitrogen atmosphere, the reaction time was 2 hours, and the remaining steps were the same as in Example 1.

[0064] Example 11 The difference between Example 11 and Example 1 is that the tungsten oxide catalyst is HO. v -WO3, with a weight of 20mg, and a reaction time of 2 hours, with the remaining steps being the same as in Example 1.

[0065] Example 12 The difference between Example 12 and Example 1 is that HO L The weight of the WO3 catalyst was 20 mg, the reaction time was 2 hours, and the remaining steps were the same as in Example 1. Example 13 The difference between Example 13 and Example 1 is that HO L - The weight of the WO3 tungsten oxide catalyst was 20 mg, the air atmosphere was replaced with an oxygen atmosphere, the reaction time was 2 hours, and the remaining steps were the same as in Example 1.

[0066] Example 14 The difference between Example 14 and Example 1 is that HO L The WO3 tungsten oxide catalyst weighed 20 mg, the air atmosphere was replaced with an oxygen atmosphere, the solvent was EtOH (ethanol), the reaction time was 2 hours, and the remaining steps were the same as in Example 1.

[0067] Example 15 The difference between Example 15 and Example 1 is that HO L - The WO3 tungsten oxide catalyst weighed 20 mg, the air atmosphere was replaced with an oxygen atmosphere, the solvent was THF (tetrahydrofuran), the reaction time was 2 hours, and the remaining steps were the same as in Example 1.

[0068] Example 16 The difference between Example 16 and Example 1 is that HO L - The WO3 tungsten oxide catalyst weighed 20 mg, the air atmosphere was replaced with an oxygen atmosphere, the solvent was EA (ethyl acetate), the reaction time was 2 hours, and the remaining steps were the same as in Example 1.

[0069] Example 17 The difference between Example 17 and Example 1 is that the tungsten oxide catalyst used is HO after 10 cycles. L -WO3 catalyst, with a weight of 20mg, the air atmosphere was replaced with an oxygen atmosphere, the reaction time was 2 hours, and the remaining steps were the same as in Example 1.

[0070] Qualitative and quantitative analyses were performed on the depolymerization products generated in Examples 1-17.

[0071] The depolymerization products were qualitatively and quantitatively analyzed by high performance liquid chromatography (HPLC, Agilent 1260 Infinity type: C18 column, 75 mm long, 4.6 mm inner diameter, 45℃), with naphthalene as an internal standard.

[0072] Using an acetonitrile-water system as the mobile phase (flow rate 0.80 mL / min), the specific conversion rate data can be calculated using the following formula:

[0073] Where R(1a) and R(naphthalene) represent the peak areas of the corresponding compounds in the high performance liquid chromatography after the reaction, and S(1a) and S(naphthalene) are the peak areas of the corresponding compounds in the high performance liquid chromatography of the standard sample.

[0074] The yields of depolymerization products 2a and 3a were calculated using the following formula:

[0075] Where R(2a-3a) and R(naphthalene) represent the peak areas of the corresponding compounds in the high performance liquid chromatography after the reaction, and S(2a–3a) and S(naphthalene) are the peak areas of the corresponding compounds in the high performance liquid chromatography of the standard sample.

[0076] 1,2-Diphenylethanol products such as Figure 2 As shown.

[0077] The yields of the products generated in Examples 1-17 are shown in the table below: Table 1 Yields of products generated in Examples 1-17

[0078] As shown in the table above, when the raw material is lignin β-1 model compound 1a, the reaction conditions are: 0.1 mmol 1a, 2 mL dichloromethane, 20 mg H₂O L -WO3 catalyst (lignin to catalyst mass ratio 1:1), 15 W LED illumination, reaction time 2 hours, oxygen atmosphere, substrate conversion was highest (conversion rate >99.9%), benzaldehyde yield was 63.8%, benzoic acid yield was 29.1%, achieving 94% C–C bond breaking selectivity. Based on the results of Examples 1 to 6, it can be seen that O3 rich in lattice oxygen... L The catalytic activity of -WO3 catalyst is superior to that of Ov-WO3 catalyst with more oxygen vacancies, indicating that lattice oxygen plays an important role in the selective cleavage of C-C bonds in the catalytic oxidation. Furthermore, HO prepared via a hydrothermal method... L -WO3 catalysts exhibit superior activity compared to SO3 catalysts prepared via sol-gel and template methods. L -WO3 and MO L -WO3. Based on the results of Examples 12 and 13, it can be seen that under an oxygen atmosphere, HO... L The catalytic activity of the WO3 catalyst is superior to that in an air atmosphere, indicating that oxygen can be continuously replenished for H2O. LThe lattice oxygen consumed in the WO3 catalyst, and the excessive oxidation leading to the oxidation of aromatic aldehydes to aromatic acids, indicate that the catalytic mechanism conforms to the MvK mechanism and the Norrish type I reaction mechanism. As shown in the results of Example 17, this lattice oxygen catalytic system exhibits excellent cycling stability, with no significant activity degradation after 10 cycles.

[0079] After optimizing the reaction conditions using lignin β–1 model compounds, HO was carried out. L Research on the depolymerization of real lignin by WO3 catalyst.

[0080] Example 18 like Figure 3 As shown, 50 mg of industrial lignin and 30 mg of tungsten oxide catalyst (HO) were added. L β-WO3 was placed in 4 mL of DCM solvent and reacted for 24 hours under 15 W blue LED light and oxygen atmosphere to oxidize the β-1 bond of lignin and obtain depolymerization products M1, M2, M3 and M4.

[0081] Example 19 The difference between Example 19 and Example 18 is that the substrate used is 50 mg of hardwood industrial lignin, while the other steps are the same as in Example 18.

[0082] Example 20 The difference between Example 20 and Example 18 is that the substrate used was 50 mg of hardwood industrial lignin, and the solvent used was Acetone:CH3OH = 9:1. All other steps were the same as in Example 18.

[0083] Example 21 The difference between Example 21 and Example 18 is that the substrate used is 50 mg of hardwood industrial lignin, and the solvent used is CH3CN (acetonitrile). All other steps are the same as in Example 18.

[0084] Example 22 The difference between Example 22 and Example 18 is that the substrate used is 50 mg of hardwood industrial lignin, and the intensity of the blue LED is 30 W. The remaining steps are the same as in Example 18.

[0085] HO L The photocatalytic depolymerization process of industrial lignin using WO3 catalyst is as follows: Figure 3 As shown.

[0086] The yields of the products generated in Examples 18-22 are shown in the table below: Table 2 Yields of products generated in Examples 18-22

[0087] The experimental data from Examples 18-22 in the table clearly show that under different solvent systems (DCM, Acetone:CH3OH=9:1, CH3CN) and different lignin substrate conditions, HO L The WO3 catalyst effectively catalyzed the depolymerization of lignin to generate four high-value aromatic monomers, M1, M2, M3, and M4, with detectable total aromatic monomer yields (Total M) in all cases, demonstrating its good applicability for the photocatalytic depolymerization of lignin. Furthermore, industrial lignin raw materials typically contain trace amounts of sulfur impurities; however, in this experiment, regardless of whether softwood or hardwood industrial lignin was used as the substrate, HO... L -WO3 catalysts all exhibited stable catalytic activity and generated the target aromatic products, without any significant decrease in catalytic activity. In summary, these results fully demonstrate that HO... L -WO3 catalyst can effectively convert industrial lignin into high-value aromatic compounds, exhibiting excellent catalytic activity and stability, as well as significant sulfur resistance, providing reliable technical support for the efficient resource utilization of industrial lignin.

[0088] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of this application is limited to these examples; under the concept of this application, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of different aspects of the embodiments of this application as described above, which are not provided in detail for the sake of brevity.

[0089] Although this application has been described in conjunction with specific embodiments thereof, many substitutions, modifications, and variations of these embodiments will be apparent to those skilled in the art from the foregoing description. The embodiments of this application are intended to cover all such substitutions, modifications, and variations falling within the broad scope of the claims of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the embodiments of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a tungsten oxide catalyst, characterized in that, include: Tungsten-containing materials are prepared into tungsten oxide precursors; The tungsten oxide precursor was calcined at 200-400°C in an oxygen-containing atmosphere for 2-6 hours to obtain a tungsten oxide catalyst containing lattice oxygen.

2. The preparation method according to claim 1, characterized in that, The process of preparing a tungsten oxide precursor from a tungsten-containing material includes: Na2WO4 2H2O is dissolved in water, citric acid and glucose are added in sequence and stirred until no precipitate is formed, then HCl solution is added and stirred to obtain a mixed solution; The mixed solution was reacted at a temperature of 80-140℃ for 12-36 hours, and after cooling to room temperature, a solid product was obtained. The solid product was washed and dried to obtain the tungsten oxide precursor.

3. The preparation method according to claim 1, characterized in that, The process of preparing a tungsten oxide precursor from a tungsten-containing material includes: Tungsten powder was dissolved in H2O2 solution to obtain a precursor sol; Stir the precursor sol, add anhydrous ethanol, and continue stirring at a temperature of 50-100°C to obtain a wet gel. The wet gel was dried and ground to obtain the tungsten oxide precursor.

4. The preparation method according to claim 1, characterized in that, The process of preparing a tungsten oxide precursor from a tungsten-containing material includes: Tungsten powder was dissolved in H2O2 solution and stirred to obtain a precursor solution; The precursor solution was placed in a temperature environment of 50-100℃ to obtain tungstic acid peroxide powder. The tungstic peroxide powder is dissolved in water, and a surfactant is added. The mixture is stirred at 50-100°C for 2-10 hours to obtain the tungsten oxide precursor.

5. A tungsten oxide catalyst, characterized in that, It is prepared by the preparation method according to any one of claims 1-4.

6. A method for oxidizing lignin, characterized in that, include: Lignin and the tungsten oxide catalyst of claim 5 are placed in a solvent and reacted for 0.5-24 hours under 5-30W blue LED illumination in an oxygen-containing atmosphere to oxidize the β-1 bonds of lignin.

7. The method according to claim 6, characterized in that, The mass ratio of the tungsten oxide catalyst to the lignin is 1:(1~10).

8. The method according to claim 6, characterized in that, The solvent includes one or more of ethyl acetate, dichloromethane, ethanol, acetonitrile, and tetrahydrofuran.

9. The method according to claim 7, characterized in that, The mass ratio of the tungsten oxide catalyst to the lignin is 1:

1.

10. The method according to claim 6, characterized in that, The oxygen-containing atmosphere includes both oxygen atmosphere and air atmosphere.

Images