Nickel-manganese bimetallic supported catalyst for catalyzing selective oxidative depolymerization of lignin, and preparation method and application thereof

Abstract

The present application relates to a kind of nickel manganese bimetallic supported catalyst for catalyzing selective oxidative depolymerization of lignin and its preparation method and application.Preparation method includes: by hydrothermal coprecipitation and calcination, prepare layered structure magnesium-aluminum bimetallic oxide carrier;Soluble nickel salt and manganese salt are uniformly mixed with the carrier, and nickel manganese active precursor is deposited on the surface of carrier by coprecipitation method under alkaline conditions;After secondary calcination, supported catalyst product is obtained.The catalyst utilizes the strong interaction between carrier and active component and the synergistic catalysis effect between nickel and manganese species, and can efficiently and selectively catalyze lignin in alkaline aqueous solution and oxygen atmosphere, and directionally convert into aromatic aldehyde and aromatic acid high-value chemicals.Compared with prior art, the catalyst in the present application has the advantages of high activity, mild reaction conditions for catalyzed lignin or lignin model compound, good selectivity and wide substrate universality.

Description

Technical Field

[0001] This invention relates to the field of high-value utilization of biomass, and in particular to a nickel-manganese bimetallic supported catalyst for selective oxidative depolymerization of lignin, its preparation method, and its application. Background Technology

[0002] With the increasing depletion of fossil resources and the proposal of carbon neutrality, the high-value utilization of renewable biomass resources has gradually become a research hotspot in the fields of energy, chemical engineering, and green catalysis. Lignin, as the most abundant aromatic renewable biomass resource in nature, is widely found in wood and agricultural waste. Its molecular structure is rich in phenylpropane units and various ether and carbon-carbon bonds, theoretically making it an important source for the preparation of aromatic chemicals and fine chemical raw materials. However, due to the complex structure, wide bond energy distribution, and poor reaction selectivity of lignin, its efficient and controllable conversion still faces significant challenges.

[0003] Currently, the conversion of lignin and its model compounds into aromatic compounds mainly relies on pathways such as pyrolysis, hydrocracking, and oxidative depolymerization. Among these, oxidative depolymerization, which can break key bonds such as β-O-4 under relatively mild conditions, is considered one of the effective strategies for the directional conversion of lignin into high-value-added aromatic compounds. However, over-oxidation is prone to occur during the oxidation reaction, leading to the further conversion of the target aromatic products into acids or CO2, thereby reducing the yield and selectivity. Therefore, high requirements are placed on the activity, selectivity, and stability of the catalyst.

[0004] In existing research, noble metal catalysts (such as Pd, Pt, Au, etc.) have shown high catalytic activity in the oxidative depolymerization reaction of lignin, but they are expensive, scarce, and have limited resistance to poisoning, making it difficult to meet the needs of industrial applications.

[0005] Patent application CN113649036A discloses a Ru-Ni / NbOPO4 bimetallic catalyst for the hydrogenation degradation of the lignin model compound benzylphenyl ether. This technology leverages the high hydrogenation activity of the noble metal Ru and the cost advantage of Ni, achieving a conversion rate of up to 99.9% for the model compound under a hydrogen atmosphere. However, this hydrogenation technology has a fundamental limitation: its reaction pathway tends to saturate the hydrogenation of aromatic rings, generating non-aromatic products such as cyclohexanes, making it difficult to directly and selectively obtain and retain aromatic ring structures such as aromatic aldehydes and aromatic acids, which have higher market value. Furthermore, this technology relies on the noble metal Ru, resulting in high costs, and the reaction typically requires high hydrogen pressure (1-2 MPa), placing high demands on equipment safety and posing certain risks for industrial scale-up. Therefore, developing efficient, stable, and low-cost non-noble metal catalyst systems has become an important research direction in this field.

[0006] Therefore, there is an urgent need to design a novel non-precious metal-based catalytic system that can achieve highly selective and directional conversion of lignin to specific aromatic aldehydes / acids under mild conditions without the need for precious metals, thereby providing core technological support for the industrial value-added utilization of lignin. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the existing technology by providing a nickel-manganese bimetallic supported catalyst for the selective oxidative depolymerization of lignin, its preparation method, and its application. In this invention, the catalyst is composed of Ni... x Mn y O z The preparation of MgAl-LDO has the advantages of high activity, mild reaction conditions for catalyzing lignin or lignin model compounds, good selectivity, and broad substrate versatility.

[0008] In the conceptualization process of this invention, it was considered that transition metal oxides have attracted widespread attention among non-noble metal catalysts due to their variable valence states and excellent redox properties. Among them, Ni-based catalysts possess strong electron transfer and substrate activation capabilities, effectively promoting the activation and cleavage of ether bonds in lignin or model compounds, playing a crucial role in the adsorption and initial conversion of organic matter; while Mn-based oxides, due to their rich valence state variations (Mn... 2+ / Mn 3+ / Mn 4+ Ni and Mn exhibit excellent oxygen migration capabilities, demonstrating significant advantages in oxygen or oxidant activation, reactive oxygen species generation, and selective oxidation processes. Synergistic regulation of Ni and Mn is expected to produce synergistic effects in substrate adsorption, bond breaking, and oxidation reaction pathway control, thereby improving the efficiency and selectivity of lignin oxidative depolymerization.

[0009] Furthermore, the catalyst support also significantly influences the dispersibility, stability, and reactivity of metal species. Layered bimetallic hydroxides and their calcined bimetallic oxides (such as MgAl bimetallic oxide) possess advantages such as large specific surface area, tunable structure, and moderate acid-base properties, making them excellent catalyst supports. However, current research on loading Ni and Mn bimetallic oxides onto the surface of MgAl bimetallic oxides for lignin oxidative depolymerization remains limited, particularly regarding the synergistic mechanism of metal species, the stability of the supported structure, and the control of reaction selectivity, leaving room for further optimization and improvement.

[0010] Therefore, this invention constructs a method for using Ni x Mn y O zA multifunctional catalytic system supported on a MgAl-LDO support is used to catalyze the oxidative depolymerization of lignin to prepare high-value-added aromatic chemicals, thereby promoting the high-value utilization of biomass resources and the development of green chemical processes.

[0011] The objective of this invention can be achieved through the following technical solutions: The first aspect of this invention provides a method for preparing a nickel-manganese bimetallic supported catalyst for the selective oxidative depolymerization of lignin, comprising: A magnesium-aluminum bimetallic hydroxide precursor with a layered structure was prepared by hydrothermal coprecipitation. The precursor was then calcined to induce a topological transformation, thereby forming a magnesium-aluminum bimetallic oxide support. Soluble nickel salt and manganese salt are dissolved together in water at a preset molar ratio and mixed uniformly with the magnesium-aluminum bimetallic oxide carrier. Then, an alkaline precipitant is introduced into the mixture to allow nickel and manganese metal ions to be deposited in situ in the form of hydroxide or carbonate composites and firmly attached to the surface of the magnesium-aluminum bimetallic oxide carrier. Through a secondary calcination process, the deposits on the surface of the magnesium-aluminum bimetallic oxide support are transformed into dispersed nickel-manganese bimetallic oxide active components, thereby obtaining a nickel-manganese bimetallic supported catalyst product for selective oxidative depolymerization of lignin, in which the active components interact with the support.

[0012] Furthermore, the specific process of the hydrothermal coprecipitation method includes: Soluble magnesium salts and soluble aluminum salts in a molar ratio of 1.5:1 to 5:1 are dissolved in deionized water to form a homogeneous mixed salt solution. More preferably, Mg:Al = 3:1.

[0013] A mixed alkaline solution, prepared by mixing sodium hydroxide and sodium carbonate in a molar ratio of 1:9 to 9:1, is added dropwise to the mixed salt solution under continuous stirring until the pH value of the system is adjusted and maintained in the alkaline range of 9.0 to 14.0, so as to promote the full co-precipitation reaction of magnesium ions and aluminum ions and initially form a layered structure to obtain a mixed slurry.

[0014] Furthermore, the process for preparing the magnesium-aluminum bimetallic hydroxide precursor after completing the co-precipitation reaction includes: The mixed slurry is transferred to a closed high-pressure reactor and subjected to hydrothermal crystallization treatment at a temperature range of 120°C to 200°C for 12 to 30 hours. This process promotes the transformation of amorphous precipitates into magnesium-aluminum bimetallic hydroxides with good crystallinity and highly ordered lamellar structure. The hydrothermal product is then filtered, repeatedly washed until neutral, and dried at 80°C to 120°C to obtain magnesium-aluminum bimetallic hydroxide precursors.

[0015] Furthermore, in the process of calcining the precursor to induce its topological transformation, the calcination is carried out in an air atmosphere, heating the dried magnesium-aluminum bimetallic hydroxide precursor to a target temperature of 500°C to 900°C at a heating rate of 2°C to 10°C per minute, and maintaining this temperature at a constant temperature for 1 hour to 6 hours. This process removes interlayer water and hydroxyl groups, causing the precursor layers to collapse and reconstruct, transforming it into a magnesium-aluminum bimetallic oxide carrier.

[0016] Furthermore, in the nickel-manganese bimetallic supported catalyst product, the mass fraction of the active component of nickel-manganese bimetallic oxide is 5% to 50%, and the molar ratio of nickel to manganese is in the range of 1:10 to 10:1.

[0017] More preferably, in the nickel-manganese bimetallic supported catalyst product, the mass fraction of the nickel-manganese bimetallic oxide active component is 15% to 25%.

[0018] More preferably, the molar ratio of nickel to manganese is in the range of 1:2 to 2:1.

[0019] The second aspect of the present invention provides a nickel-manganese bimetallic supported catalyst for selective oxidative depolymerization of lignin prepared by the method described above. The nickel-manganese bimetallic supported catalyst uses a porous magnesium-aluminum bimetallic oxide derived from layered double hydroxides as a structural support, and nickel-manganese bimetallic oxide nanoparticles are anchored on its surface. In the nickel-manganese bimetallic oxide nanoparticles, nickel species serve as the main electron transfer and substrate activation center, while manganese species, through their variable valence states, act as oxygen activation and reactive oxygen transport centers. Through close interfacial contact and electronic synergy, nickel and manganese species form a multifunctional catalytic active site that can efficiently activate molecular oxygen and selectively attack carbon-oxygen and carbon-carbon bonds in the lignin matrix.

[0020] A third aspect of the present invention provides the application of the nickel-manganese bimetallic supported catalyst as described above in catalyzing the oxidative depolymerization of lignin or its model compounds to prepare high-value-added chemicals such as aromatic aldehydes and aromatic acids.

[0021] 8. The application of the nickel-manganese bimetallic supported catalyst according to claim 7 in catalyzing the oxidative depolymerization of lignin or its model compounds to prepare high-value-added aromatic aldehydes and aromatic acids, characterized in that the specific reaction process of the application includes: The nickel-manganese bimetallic supported catalyst product and lignin or its model compound substrate are added to a sodium hydroxide aqueous solution with a concentration of 0.5-5 mol / L at a mass ratio of 1:2 to 1:200 to form a reaction slurry. The reaction slurry is placed in a pressure-resistant reactor, oxygen or oxygen-containing gas is introduced into it, and the pressure of the reaction system is maintained at 0.1-1 MPa; The reaction system is heated to a reaction temperature of 80°C to 180°C and stirred for 1 to 6 hours under these conditions. The alkaline environment promotes the dissolution and dispersion of lignin, while the selective oxidation, bond breaking and transformation of the substrate are achieved based on the catalytic effect of the nickel-manganese bimetallic supported catalyst.

[0022] 9. The application of the nickel-manganese bimetallic supported catalyst according to claim 7 in catalyzing the oxidative depolymerization of lignin or its model compounds to prepare aromatic aldehydes and aromatic acids, characterized in that the lignin is selected from any one of herbaceous lignin, softwood lignin, and hardwood lignin; The model compound is 2-phenoxy-1-phenylethanol.

[0023] 10. The application of the nickel-manganese bimetallic supported catalyst according to claim 7 in the catalytic oxidation and depolymerization of lignin or its model compounds to prepare high-value-added aromatic aldehydes and aromatic acids, characterized in that the nickel-manganese bimetallic oxide active component on the surface of the nickel-manganese bimetallic supported catalyst first activates the adsorbed oxygen molecules to generate active oxygen species such as superoxide or peroxide. At the same time, the nickel active sites activate and weaken the key chemical bonds in the lignin substrate through electronic interactions. Then, the active oxygen species migrate under the variable valence state cycle driven by the manganese center and selectively attack the activated chemical bond sites, achieving highly selective cleavage of carbon-oxygen bonds or carbon-carbon bonds and oxidation to generate the corresponding aldehyde or carboxyl groups. Finally, high-value aromatic compounds such as vanillin, benzaldehyde, and vanillic acid are obtained in high yield. Moreover, the catalyst can still maintain the stability of its layered support structure and the dispersion state of the active components after multiple cycles of repeated use, showing excellent recycling performance.

[0024] Compared with the prior art, the present invention has the following beneficial effects: (1) Layered bimetallic hydroxides and their calcined bimetallic oxides (such as MgAl-LDO) have advantages such as large specific surface area, adjustable structure and moderate acid-base properties, and can be used as excellent catalyst supports.

[0025] The catalyst system of this invention relies on a MgAl-LDO support and Ni x Mn y O z Synergistic effects among active components. Specifically, MgAl-LDO, with its large specific surface area, exposes abundant active sites, which is beneficial for achieving high dispersion and fine particle size of the active metal, enhancing the carrier-metal interaction, and thus effectively inhibiting metal sintering and agglomeration. In Ni... x Mn y O zNi-based catalysts possess strong electron transfer and substrate activation capabilities, effectively promoting the activation and cleavage of ether bonds in lignin or model compounds, playing a crucial role in the adsorption and initial conversion of organic matter; while Mn-based oxides, due to their rich valence state variations (Mn... 2+ / Mn 3+ / Mn 4+ This catalyst exhibits excellent oxygen migration capabilities and demonstrates significant advantages in oxygen or oxidant activation, reactive oxygen species generation, and selective oxidation processes. Under certain conditions, it can efficiently catalyze the selective cleavage of the CO / CC bonds in lignin, yielding aromatic compounds such as vanillin, vanillic acid, syringaldehyde, and p-hydroxybenzaldehyde with high selectivity and high yield.

[0026] This characteristic also reduces energy consumption during operation and makes the pressure resistance requirements of the equipment more lenient, thereby helping to control production costs and improve the safety of the operation process, thus providing conditions for its practical application in industrial plants.

[0027] (2) The catalyst of this invention is readily available from readily available raw materials, has a simple synthesis process with high yield, and is safe, convenient, environmentally friendly, and easy to recycle. Under certain conditions, this catalyst can depolymerize lignin to prepare high-value-added aromatic compounds, exhibiting high activity, high conversion rate, and high selectivity. Under optimal reaction conditions, the total monomer yield of the lignin oxidative depolymerization reaction reaches approximately 20%, and the yield of the lignin model compound oxidative depolymerization reaction reaches approximately 90%, demonstrating excellent catalytic effect and good industrial application value.

[0028] (3) The catalyst of the present invention exhibits excellent catalytic activity, substrate adaptability and cycle stability, and has good industrial application potential in the field of lignin high-value conversion. Attached Figure Description

[0029] Figure 1 For Ni x Mn y O z Schematic diagram of the preparation process and morphology of the supported MgAl-LDO catalyst; Figure 2 and 5 For Ni x Mn y O z Reactivity diagram of the supported MgAl-LDO catalyst for the depolymerization of 2-phenoxy-1-phenylethanol into aromatic compounds; Figure 3 Ni prepared x Mn y O z XRD patterns before and after use of the supported MgAl-LDO catalyst; Figure 4 For Ni x Mn y O z Reactivity diagram of the depolymerization of real lignin into aromatic compounds by the supported MgAl-LDO catalyst. Detailed Implementation

[0030] Overall, this invention discloses a Ni / Mn bimetallic oxide catalyst supported on a layered MgAl bimetallic oxide surface, its preparation method, and its application. This catalyst uses a layered MgAl bimetallic oxide (MgAl-LDO) as a support, with Ni / Mn bimetallic oxides (Ni...) supported on its surface. x Mn y O z The active component forms a highly efficient catalytic system rich in Ni active sites. Under relatively mild conditions, this catalyst can efficiently catalyze the selective cleavage of C–O / C–C bonds in lignin or its model compounds, yielding aromatic aldehydes and acids such as vanillin, benzaldehyde, and vanillic acid with high selectivity and high yield. Compared with traditional processes, the catalyst of this invention has advantages such as simple preparation process, readily available raw materials, and environmental friendliness, and exhibits excellent catalytic activity, broad substrate adaptability, and good cycling stability, showing significant industrial application potential in the field of high-value conversion of lignin.

[0031] One of the technical solutions of the present invention is to provide a method for preparing a Ni and Mn bimetallic oxide catalyst supported on the surface of a layered MgAl bimetallic oxide, comprising the following steps: S1: Dissolve Mg and Al salts in deionized water, then add a certain amount of a mixed solution of NaOH and Na₂CO₃ to adjust the pH to alkalinity. After stirring for a period of time, transfer the mixed solution to a sealed reaction vessel and heat. The resulting precipitate is washed and dried to obtain MgAl-LDH.

[0032] S2: Calcine MgAl-LDH to obtain MgAl-LDO.

[0033] S3: Dissolve Ni and Mn salts in a certain amount of deionized water, add MgAl-LDO and stir until homogeneous. Then, add a mixed solution of NaOH and Na2CO3 dropwise to adjust the pH to alkaline. Wash and dry the precipitate to obtain Ni(OH)2, Mn(OH)2, NiCO3 and MnCO3-supported MgAl-LDO.

[0034] S4: MgAl-LDO supported on Ni(OH)2, Mn(OH)2, NiCO3, and MnCO3 is calcined to obtain Ni, Mn bimetallic oxide supported MgAl-LDO (Ni... x Mn y O z / MgAl-LDO).

[0035] x, y, and z are all variables. The molar ratio of x to y can be continuously adjusted between 1:10 and 10:1, while z corresponds to the number of oxygen atoms in the formed nickel-manganese bimetallic oxide phase, which is usually in the range of 2 to 6. The actual value is determined by the preparation process parameters.

[0036] In some specific implementations, step S1 may include: The anions of the Mg salt and Al salt are selected from any one of nitrate, sulfate, acetate, and chloride ions; The molar ratio of the Mg salt to the Al salt is 3:1; The sealed reactor is heated to a temperature of 120-200℃ for 12-30 hours. The ratio of NaOH to Na2CO3 is 1:5-5:1; the pH value is adjusted to 10-14.

[0037] In some specific implementations, steps S2 and S4 may include: The calcination temperature is 500-900 ℃, and the time is 1-6 h.

[0038] In some specific implementations, step S3 may include: The anions of the Ni and Mn salts are selected from any one of nitrate, acetate, sulfate, and chloride ions; The molar ratio of Ni salt to Mn salt is 1:10-10:1; the prepared Ni x Mn y O z The mass ratio of MgAl-LDO to MgAl-LDO is 0:1-1:1; The ratio of NaOH to Na2CO3 is 1:9-9:1 to adjust the pH value to 8-13; The second technical solution of the present invention is to provide a Ni and Mn bimetallic oxide catalyst supported on the surface of a layered MgAl bimetallic oxide, which is obtained by the preparation method described in one of the above technical solutions.

[0039] The third technical solution of the present invention is to provide an application of the Ni and Mn bimetallic oxide catalyst supported on the surface of the layered MgAl bimetallic oxide as described in the second technical solution above in the catalytic depolymerization of lignin or lignin model compounds to prepare aromatic compounds.

[0040] In some specific embodiments, the method for preparing aromatic compounds by catalyzing the depolymerization of lignin or lignin model compounds by supporting Ni and Mn bimetallic oxide catalysts on the surface of layered MgAl bimetallic oxides is as follows: A Ni / Mn bimetallic oxide catalyst loaded on the surface of a layered MgAl bimetallic oxide, along with lignin or a lignin model compound substrate, is added to an aqueous sodium hydroxide solution. The mixture is then heated in a reactor, oxygen is introduced, and the reaction is carried out under pressure to obtain an aromatic compound.

[0041] In some specific embodiments, the lignin is selected from any one of herbaceous lignin, softwood lignin, and hardwood lignin; The lignin model compound is 2-phenoxy-1-phenylethanol; Lignin from plants, for example, corn stalks; Softwood lignin, exemplified by: dawn redwood; Hardwood lignin, exemplified by oak.

[0042] In some specific embodiments, the mass ratio of Ni, Mn bimetallic oxide catalyst and lignin substrate supported on the surface of the layered MgAl bimetallic oxide is 1:2-1:200. The concentration of the sodium hydroxide aqueous solution is 0.5-5 mol / L.

[0043] In some specific embodiments, the pressure of the pressurized and heated reaction is 0.1-1 MPa, the temperature is 80-180℃, and the time is 1-6 h.

[0044] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Any preparation methods, materials, structures, or composition ratios not explicitly described in this technical solution are considered common technical features disclosed in the prior art or existing commercial products.

[0045] Unless otherwise specified, percentages in this invention can be considered as mass percentages.

[0046] Example 1 This embodiment provides a 20% NiMn2O4-supported MgAl-LDO catalyst and its preparation method, including the following steps: (1) The metal salts Al(NO3)3·9H2O and MgCl2·6H2O were mixed and dissolved in deionized water at a molar ratio of 1:3. A mixed solution of NaOH and Na2CO3 at a ratio of 2:1 was slowly added to the mixed solution to adjust the pH to 14. The mixture was heated at 180 °C for 12 h in a sealed autoclave. The precipitate was washed with water and centrifuged, and the pH was adjusted to neutral. The solid was dried at 100 °C overnight. After grinding, the solid was calcined at 700 °C for 3 h at a heating rate of 5 °C / min to obtain the desired MgAl-LDO.

[0047] (2) Add 3 g MgAl-LDO, 2.497 mmol (0.7262 g) Ni(NO3)2·6H2O and 4.994 mmol (0.9884 g) MnCl2·4H2O to a 250 mL round-bottom flask, and then add 180 mL of deionized water to dissolve them. Slowly add a mixed solution of NaOH and Na2CO3 in a 1:9 ratio to the round-bottom flask, adjust the pH to 12, and age for 2 h. Wash the solid with deionized water 4 to 5 times, adjust the pH to neutral, and then dry the solid in an oven at 80 ℃ for 12 h. The dried solid was then calcined in a muffle furnace at 700 °C for 1 h with a heating rate of 5 °C / min, ultimately yielding a 20% NiMn2O4-supported MgAl-LDO catalyst (denoted as 20% NiMn2O4 / MgAl-LDO, where the mass ratio of NiMn2O4 to MgAl-LDO is 1:5, i.e., the mass percentage of NiMn2O4 is 20%). Figure 1 This is a schematic diagram showing the preparation and morphology of the NixMnyOz-supported MgAl-LDO catalyst, where a and b show Ni x Mn y O z The MgAl-LDO loading retains a layered structure and contains abundant porous structures. The mapping diagram in cf shows that metallic nickel and manganese are uniformly distributed on the MgAl-LDO.

[0048] Test Example 1 The 20% NiMn2O4-supported MgAl-LDO catalyst prepared in Example 1 was used for lignin catalysis, comprising the following steps: (1) Add 20% NiMn2O4 / MgAl-LDO catalyst (0.02 g), lignin molding compound 2-phenoxy-1-phenylethanol (0.04 g) and solvent 1 mol / L NaOH (50 mL) into the micro reactor and tighten the reactor nut; (2) Control the oxygen pressure in the oxygen cylinder through the pressure reducing valve and adjust the pressure inside the reactor to not exceed 0.88 MPa; (3) Set the temperature of the micro reactor to 160 °C and the time to 3 h. After the reaction is completed, cool it to room temperature, and treat the sample by acidification, filtration and volume adjustment. Finally, calculate the conversion rate and reaction yield of the aromatic chemicals by liquid chromatography.

[0049] Specifically, the conversion rate reached 92.72%; The product yields were as follows: benzaldehyde 31.24%, benzoic acid 12.38%, acetophenone 5.47%, o-hydroxybenzaldehyde 7.15%, p-hydroxybenzaldehyde 23.37%, o-hydroxybenzoic acid 8.6%, p-hydroxybenzoic acid 1.77%, phenylethylene glycol 1.7%, acetophenone acid 1.03%, phenol 41.75%, p-benzoquinone 50.95%, etc. Figure 2 As shown.

[0050] Test Example 2 The 20% NiMn2O4-supported MgAl-LDO catalyst prepared in Example 1 was used for lignin catalysis, comprising the following steps: (1) Add 20% NiMn2O4 / MgAl-LDO catalyst (0.05 g), lignin molding compound 2-phenoxy-1-phenylethanol (0.2 g) and solvent 1.25 mol / L NaOH (50 mL) into the micro reactor and tighten the reactor nut; (2) Control the oxygen pressure in the oxygen cylinder through the pressure reducing valve and adjust the pressure inside the reactor to not exceed 0.66 MPa; (3) Set the temperature of the micro reactor to 140 °C and the time to 3 h. After the reaction is completed, cool it to room temperature, and treat the sample by acidification, filtration and volume adjustment. Finally, calculate the conversion rate and reaction yield of the aromatic chemicals by liquid chromatography.

[0051] Specifically, the conversion rate reached 52.91%; The product yields were as follows: benzaldehyde 15.68%, benzoic acid 8.67%, acetophenone 2.78%, o-hydroxybenzaldehyde 6.31%, p-hydroxybenzaldehyde 11.33%, o-hydroxybenzoic acid 4.08%, p-hydroxybenzoic acid 1.16%, phenylethylene glycol 0.38%, acetophenone acid 2.47%, phenol 37.28%, p-benzoquinone 15.62%, etc. Figure 2 As shown.

[0052] (4) Stability test of 20% NiMn2O4 / MgAl-LDO catalyst The 20% NiMn2O4 / MgAl-LDO catalyst after the reaction in Test Example 2 was filtered and dried. The 20% NiMn2O4 / MgAl-LDO catalyst from Example 1 and the 20% NiMn2O4 / MgAl-LDO catalyst after the reaction in Test Example 2 were subjected to X-ray diffraction (XRD) tests. Figure 3 The results showed that the diffraction peak intensity of the 20% NiMn2O4 / MgAl-LDO catalyst was slightly reduced after the reaction, indicating that its structure was not significantly damaged and it still has excellent utilization value.

[0053] Test Example 3 The 20% NiMn2O4-supported MgAl-LDO catalyst prepared in Example 1 was used for lignin catalysis, comprising the following steps: (1) Add 20% NiMn2O4 / MgAl-LDO catalyst (1.0 g), corn stalks containing lignin (3.0 g), and 1.5 mol / L NaOH solvent (50 mL) to the micro reactor and tighten the reactor nut; (2) Control the oxygen pressure in the oxygen cylinder through the pressure reducing valve and adjust the pressure inside the reactor to not exceed 1.21 MPa; (3) Set the temperature of the micro reactor to 180 °C and the time to 3 h. After the reaction is completed, cool it to room temperature, and treat the sample by acidification, filtration and volume adjustment. Finally, calculate the conversion rate and reaction yield of the aromatic chemicals by liquid chromatography.

[0054] The product yields were as follows: vanillin 0.83%, vanillic acid 2.14%, vanillin ethyl ketone 0.18%, ferulic acid 0.1%, guaiacol 2.44%, syringic acid 0.13%, eugenol 0.52%, p-hydroxybenzoic acid 0.06%, p-hydroxybenzaldehyde 0.13%, p-coumaric acid 0.73%, etc. Figure 4 As shown.

[0055] Example 2 This embodiment provides a 15% Ni1Mn1O 2.3 Supported MgAl-LDO catalyst and its preparation method include the following steps: (1) The metal salts Al(NO3)3·9H2O and MgCl2·6H2O were mixed and dissolved in deionized water at a molar ratio of 1:3. A mixed solution of NaOH and Na2CO3 at a ratio of 2:1 was slowly added to the mixed solution to adjust the pH to 14. The mixture was heated at 180 °C for 12 h in a sealed autoclave. The precipitate was washed with water and centrifuged, and the pH was adjusted to neutral. The solid was dried at 100 °C overnight. After grinding, the solid was calcined at 700 °C for 3 h at a heating rate of 5 °C / min to obtain the desired MgAl-LDO.

[0056] (2) Add 3 g MgAl-LDO, 2.8091 mmol (0.8175 g) Ni(NO3)2·6H2O and 2.8091 mmol (0.5565 g) MnCl2·4H2O to a 250 mL round-bottom flask, and then add 180 mL of deionized water to dissolve them. Slowly add a mixed solution of NaOH and Na2CO3 in a 3:7 ratio to the round-bottom flask, adjust the pH to 10, and age for 2 h. Wash the solid with deionized water 4 to 5 times, adjust the pH to neutral, and then dry the solid in an oven at 80 ℃ for 12 h. Then calcine the dried solid in a muffle furnace at 500 ℃ for 1 h with a heating rate of 5 ℃ / min to finally obtain 15% Ni1Mn1O. 2.3 Supported MgAl-LDO catalyst (denoted as 15% Ni1Mn1O) 2.3 / MgAl-LDO, Ni1Mn1O 2.3 The mass ratio of Ni1Mn1O to MgAl-LDO is 3:20. 2.3 The quality percentage is 15%.

[0057] Test Example 4 The 15% Ni1Mn1O prepared in Example 1 2.3 The supported MgAl-LDO catalyst is used for lignin catalysis, comprising the following steps: (1) Add 15% Ni1Mn1O catalyst 2.3 MgAl-LDO (0.15 g), lignin-modified 2-phenoxy-1-phenylethanol (0.4 g), and solvent 1.5 mol / L NaOH (50 mL) were added to the micro reactor, and the reactor nut was tightened. (2) Control the oxygen pressure in the oxygen cylinder through the pressure reducing valve and adjust the pressure inside the reactor to not exceed 1.21 MPa; (3) Set the temperature of the micro reactor to 180 °C and the time to 3 h. After the reaction is completed, cool it to room temperature, and treat the sample by acidification, filtration and volume adjustment. Finally, calculate the conversion rate and reaction yield of the aromatic chemicals by liquid chromatography.

[0058] Specifically, the conversion rate reached 95.39%; The product yields were as follows: benzaldehyde 19.83%, benzoic acid 20.11%, acetophenone 4.16%, o-hydroxybenzaldehyde 1.36%, p-hydroxybenzaldehyde 18.99%, o-hydroxybenzoic acid 12.61%, p-hydroxybenzoic acid 1.15%, phenylethylene glycol 1.23%, acetophenone acid 1.13%, phenol 13.01%, p-benzoquinone 4.14%, etc. Figure 2 As shown.

[0059] Test Example 5 The 15% Ni1Mn1O prepared in Example 1 2.3 The supported MgAl-LDO catalyst is used for lignin catalysis, comprising the following steps: (1) Add 15% Ni1Mn1O catalyst 2.3 MgAl-LDO (0.3 g), lignin-modified 2-phenoxy-1-phenylethanol (1.0 g), and solvent 0.75 mol / L NaOH (50 mL) were added to the micro reactor, and the reactor nut was tightened. (2) Control the oxygen pressure in the oxygen cylinder through the pressure reducing valve and adjust the pressure inside the reactor to not exceed 0.96 MPa; (3) Set the temperature of the micro reactor to 150 °C and the time to 3 h. After the reaction is completed, cool it to room temperature, and treat the sample by acidification, filtration and volume adjustment. Finally, calculate the conversion rate and reaction yield of the aromatic chemicals by liquid chromatography.

[0060] Specifically, the conversion rate reached 73.95%; The product yields were as follows: benzaldehyde 20.77%, benzoic acid 12.71%, acetophenone 1.82%, o-hydroxybenzaldehyde 6.55%, p-hydroxybenzaldehyde 15.79%, o-hydroxybenzoic acid 4.73%, p-hydroxybenzoic acid 1.34%, ethylene glycol 0.79%, acetophenone acid 4.28%, etc. Figure 2 As shown.

[0061] Test Example 6 The 15% Ni1Mn1O prepared in Example 1 2.3 The supported MgAl-LDO catalyst is used for lignin catalysis, comprising the following steps: (1) Add 15% Ni1Mn1O catalyst 2.3 MgAl-LDO (1.0 g), pine lignin metasequoia (3.0 g) and solvent 0.75 mol / L NaOH (50 mL) were added to the micro reactor and the reactor nut was tightened. (2) Control the oxygen pressure in the oxygen cylinder through the pressure reducing valve and adjust the pressure inside the reactor to not exceed 0.76 MPa; (3) Set the temperature of the micro reactor to 130 °C and the time to 3 h. After the reaction is completed, cool it to room temperature, and treat the sample by acidification, filtration and volume adjustment. Finally, calculate the conversion rate and reaction yield of the aromatic chemicals by liquid chromatography.

[0062] The product yields were as follows: vanillin 12.25%, vanillic acid 2.35%, vanillin ethyl ketone 0.89%, ferulic acid 0.19%, guaiacol 3.29%, syringic acid 0.05%, eugenol 0.92%, p-hydroxybenzoic acid 1.19%, p-hydroxybenzaldehyde 0%, p-coumaric acid 0.15%, etc. Figure 4 As shown.

[0063] Example 3 This embodiment provides a 25% Ni2Mn1O 3.3 Supported MgAl-LDO catalyst and its preparation method include the following steps: (1) The metal salts Al(NO3)3·9H2O and MgCl2·6H2O were mixed and dissolved in deionized water at a molar ratio of 1:3. A mixed solution of NaOH and Na2CO3 at a ratio of 2:1 was slowly added to the mixed solution to adjust the pH to 14. The mixture was heated at 180 °C for 12 h in a sealed autoclave. The precipitate was washed with water and centrifuged, and the pH was adjusted to neutral. The solid was dried at 100 °C overnight. After grinding, the solid was calcined at 700 °C for 3 h at a heating rate of 5 °C / min to obtain the desired MgAl-LDO.

[0064] (2) Add 3 g MgAl-LDO, 6.2425 mmol (1.8162 g) Ni(NO3)2·6H2O and 3.1212 mmol (0.6187 g) MnCl2·4H2O to a 250 mL round-bottom flask, and then add 180 mL of deionized water to dissolve them. Slowly add a mixed solution of NaOH and Na2CO3 in a 2:3 ratio to the round-bottom flask, adjust the pH to 10, and age for 2 h. Wash the solid with deionized water 4 to 5 times, adjust the pH to neutral, and then dry the solid in an oven at 80 ℃ for 12 h. Then calcine the dried solid in a muffle furnace at 600 ℃ for 2 h with a heating rate of 5 ℃ / min to finally obtain 25% Ni2Mn1O. 3.3 Supported MgAl-LDO catalyst (denoted as 25% Ni2Mn1O) 3.3 / MgAl-LDO, Ni2Mn1O 3.3 The mass ratio of Ni2Mn1O to MgAl-LDO is 1:4. 3.3 The quality percentage is 25%. Test Example 7 The 25% Ni2Mn1O prepared in Example 3 3.3 The supported MgAl-LDO catalyst is used for lignin catalysis, comprising the following steps: (1) Add 15% Ni1Mn1O catalyst 2.3MgAl-LDO (0.03 g), lignin-modified 2-phenoxy-1-phenylethanol (0.5 g), and solvent 0.5 mol / L NaOH (50 mL) were added to the micro reactor, and the reactor nut was tightened. (2) Control the oxygen pressure in the oxygen cylinder through the pressure reducing valve and adjust the pressure inside the reactor to not exceed 0.76 MPa; (3) Set the temperature of the micro reactor to 160 °C and the time to 3 h. After the reaction is completed, cool it to room temperature, and treat the sample by acidification, filtration and volume adjustment. Finally, calculate the conversion rate and reaction yield of the aromatic chemicals by liquid chromatography.

[0065] Specifically, the conversion rate reached 66.59%; The product yields were as follows: benzaldehyde 17.73%, benzoic acid 12.333%, acetophenone 2.9%, o-hydroxybenzaldehyde 5.37%, p-hydroxybenzaldehyde 10.68%, o-hydroxybenzoic acid 2.34%, p-hydroxybenzoic acid 1.64%, phenylethylene glycol 1.01%, acetophenone acid 2.89%; phenol: 33.01%, p-benzoquinone: 23.9%, etc. Figure 2 As shown.

[0066] Test Example 8 The 25% Ni2Mn1O prepared in Example 3 3.3 The supported MgAl-LDO catalyst is used for lignin catalysis, comprising the following steps: (1) Add 15% Ni1Mn1O catalyst 2.3 MgAl-LDO (1.0 g), hardwood lignin oak (3.0 g), and solvent 1.0 mol / L NaOH (50 mL) were added to the micro reactor, and the reactor nut was tightened. (2) Control the oxygen pressure in the oxygen cylinder through the pressure reducing valve and adjust the pressure inside the reactor to not exceed 0.66 MPa; (3) Set the temperature of the micro reactor to 150 °C and the time to 3 h. After the reaction is completed, cool it to room temperature, and treat the sample by acidification, filtration and volume adjustment. Finally, calculate the conversion rate and reaction yield of the aromatic chemicals by liquid chromatography.

[0067] The product yields were as follows: vanillin 4.06%, vanillic acid 0.84%, vanillin ethyl ketone 0.71%, ferulic acid 0.09%, guaiacol 2.91%, syringic acid 0.47%, syringaldehyde 7.4%, p-hydroxybenzoic acid 0.21%, p-hydroxybenzaldehyde 0.06%, p-coumaric acid 0.08%, etc. Figure 4 As shown.

[0068] Comparative Example 1 Compared with Example 1, most of the results are the same, except that the addition of Ni salt in step (2) is omitted and the amount of Mn salt added is 0.7522 g (3.801 mmol), and 20% Mn3O4 / MgAl-LDO is prepared.

[0069] The prepared 20% Mn3O4 / MgAl-LDO was subjected to the following tests: (1) Add 20% Mn3O4 / MgAl-LDO catalyst (0.025 g), lignin analog 2-phenoxy-1-phenylethanol (0.05 g) and solvent 1 mol / L NaOH (50 mL) into the micro reactor and tighten the reactor nut; (2) Control the oxygen pressure in the oxygen cylinder through the pressure reducing valve and adjust the pressure inside the reactor to not exceed 0.66 MPa; (3) Set the temperature of the micro reactor to 150 °C and the time to 3 h. After the reaction is completed, cool it to room temperature, and treat the sample by acidification, filtration and volume adjustment. Finally, calculate the conversion rate and reaction yield of the aromatic chemicals by liquid chromatography.

[0070] Specifically, the conversion rate reached 64.88%; The product yields were as follows: benzaldehyde 13.05%, benzoic acid 8.9%, acetophenone 2.92%, o-hydroxybenzaldehyde 5.98%, p-hydroxybenzaldehyde 14.01%, o-hydroxybenzoic acid 4.85%, p-hydroxybenzoic acid 1.98%, phenylethylene glycol 1.26%, acetophenone acid 3.68%, phenol 43.99%, p-benzoquinone 10.88%, etc. Figure 5 As shown.

[0071] Comparative Example 2 Compared with Example 1, most of the results are the same, except that the addition of Mn salt in step (2) is omitted and the amount of Ni salt added is 2.3354g (8.032mmol) to prepare 20% NiO / MgAl-LDO.

[0072] The prepared 20% NiO / MgAl-LDO was subjected to the following tests: (1) Add 20% NiO / MgAl-LDO catalyst (0.025 g), lignin analog 2-phenoxy-1-phenylethanol (0.05 g) and solvent 1 mol / L NaOH (50 mL) to the micro reactor and tighten the reactor nut; (2) Control the oxygen pressure in the oxygen cylinder through the pressure reducing valve and adjust the pressure inside the reactor to not exceed 0.66 MPa; (3) Set the temperature of the micro reactor to 150 °C and the time to 3 h. After the reaction is completed, cool it to room temperature, and treat the sample by acidification, filtration and volume adjustment. Finally, calculate the conversion rate and reaction yield of the aromatic chemicals by liquid chromatography.

[0073] Specifically, the conversion rate reached 87.35%; The product yields were as follows: benzaldehyde 19.37%, benzoic acid 22.03%, acetophenone 3.55%, o-hydroxybenzaldehyde 3.46%, p-hydroxybenzaldehyde 10.01%, o-hydroxybenzoic acid 4.45%, p-hydroxybenzoic acid 1.33%, phenylethylene glycol 1.24%, acetophenone acid 0.98%, phenol 20.96%, p-benzoquinone 3.39%, etc. Figure 5 As shown.

[0074] Comparative Example 3 Compared with Example 1, most of the results are the same, except that the addition of Ni salt and Mn salt in step (2) is omitted to prepare MgAl-LDO.

[0075] The prepared MgAl-LDO was subjected to the following tests: (1) Add the catalyst MgAl-LDO (0.025 g), the lignin analog 2-phenoxy-1-phenylethanol (0.05 g) and the solvent 1 mol / L NaOH (50 mL) into the micro reactor and tighten the reactor nut; (2) Control the oxygen pressure in the oxygen cylinder through the pressure reducing valve and adjust the pressure inside the reactor to not exceed 0.66 MPa; (3) Set the temperature of the micro reactor to 150 °C and the time to 3 h. After the reaction is completed, cool it to room temperature, and treat the sample by acidification, filtration and volume adjustment. Finally, calculate the conversion rate and reaction yield of the aromatic chemicals by liquid chromatography.

[0076] Specifically, the conversion rate reached 47.24%; The product yields were as follows: benzaldehyde 12.29%, benzoic acid 5.52%, acetophenone 1.77%, o-hydroxybenzaldehyde 2.35%, p-hydroxybenzaldehyde 8.12%, o-hydroxybenzoic acid 3.22%, p-hydroxybenzoic acid 2.36%, phenylethylene glycol 1.18%, acetophenone acid 0.39%; phenol 27.48%, p-benzoquinone 13.17%, etc. Figure 5 As shown.

[0077] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a nickel-manganese bimetallic supported catalyst for the selective oxidative depolymerization of lignin, characterized in that, include: A magnesium-aluminum bimetallic hydroxide precursor with a layered structure was prepared by hydrothermal coprecipitation. The precursor was then calcined to induce a topological transformation, thereby forming a magnesium-aluminum bimetallic oxide support. Soluble nickel salt and manganese salt are dissolved together in water at a preset molar ratio and mixed uniformly with the magnesium-aluminum bimetallic oxide carrier. Then, an alkaline precipitant is introduced into the mixture to allow nickel and manganese metal ions to be deposited in situ in the form of hydroxide or carbonate composites and firmly attached to the surface of the magnesium-aluminum bimetallic oxide carrier. Through a secondary calcination process, the deposits on the surface of the magnesium-aluminum bimetallic oxide support are transformed into dispersed nickel-manganese bimetallic oxide active components, thereby obtaining a nickel-manganese bimetallic supported catalyst product for selective oxidative depolymerization of lignin, in which the active components interact with the support.

2. The method for preparing a nickel-manganese bimetallic supported catalyst for the selective oxidative depolymerization of lignin according to claim 1, characterized in that, The specific process of the hydrothermal coprecipitation method includes: Soluble magnesium salts and soluble aluminum salts in a molar ratio of 1.5:1 to 5:1 are dissolved in deionized water to form a homogeneous mixed salt solution. A mixed alkaline solution, prepared by mixing sodium hydroxide and sodium carbonate in a molar ratio of 1:9 to 9:1, is added dropwise to the mixed salt solution under continuous stirring until the pH value of the system is adjusted and maintained in the alkaline range of 9.0 to 14.0, so as to promote the full co-precipitation reaction of magnesium ions and aluminum ions and initially form a layered structure to obtain a mixed slurry.

3. The method for preparing a nickel-manganese bimetallic supported catalyst for the selective oxidative depolymerization of lignin according to claim 2, characterized in that, The process for preparing the magnesium-aluminum bimetallic hydroxide precursor after completing the co-precipitation reaction includes: The mixed slurry is transferred to a closed high-pressure reactor and subjected to hydrothermal crystallization treatment at a temperature range of 120°C to 200°C for 12 to 30 hours. This process promotes the transformation of amorphous precipitates into magnesium-aluminum bimetallic hydroxides with good crystallinity and highly ordered lamellar structure. The hydrothermal product is then filtered, repeatedly washed until neutral, and dried at 80°C to 120°C to obtain magnesium-aluminum bimetallic hydroxide precursors.

4. The method for preparing a nickel-manganese bimetallic supported catalyst for the selective oxidative depolymerization of lignin according to claim 1, characterized in that, In the process of calcining the precursor to induce its topological transformation, the calcination is carried out in an air atmosphere, heating the dried magnesium-aluminum bimetallic hydroxide precursor to a target temperature of 500°C to 900°C at a heating rate of 2°C to 10°C per minute, and maintaining this temperature at a constant temperature for 1 hour to 6 hours. This process removes interlayer water and hydroxyl groups, causing the precursor layers to collapse and reconstruct, transforming it into a magnesium-aluminum bimetallic oxide carrier.

5. The method for preparing a nickel-manganese bimetallic supported catalyst for the selective oxidative depolymerization of lignin according to claim 1, characterized in that, In nickel-manganese bimetallic supported catalyst products, the mass fraction of the active component of nickel-manganese bimetallic oxide is 5% to 50%, and the molar ratio of nickel to manganese is in the range of 1:10 to 10:

1.

6. A nickel-manganese bimetallic supported catalyst for the selective oxidative depolymerization of lignin, prepared by the method according to any one of claims 1 to 5, characterized in that, The nickel-manganese bimetallic supported catalyst uses a porous magnesium-aluminum bimetallic oxide derived from layered double hydroxides as a structural support, and nickel-manganese bimetallic oxide nanoparticles are anchored on its surface. In the nickel-manganese bimetallic oxide nanoparticles, nickel species serve as the main electron transfer and substrate activation center, while manganese species, through their variable valence states, serve as the oxygen activation and reactive oxygen transport center. The nickel and manganese species, through close interfacial contact and electronic synergy, constitute a multifunctional catalytic active site that can efficiently activate molecular oxygen and selectively attack carbon-oxygen and carbon-carbon bonds in the lignin matrix.

7. The application of the nickel-manganese bimetallic supported catalyst as described in claim 6 in catalyzing the oxidative depolymerization of lignin or its model compounds to prepare high-value-added aromatic aldehydes and aromatic acids.

8. The application of the nickel-manganese bimetallic supported catalyst according to claim 7 in catalyzing the oxidative depolymerization of lignin or its model compounds to prepare high-value-added aromatic aldehydes and aromatic acids, characterized in that, The specific reaction process of the application includes: The nickel-manganese bimetallic supported catalyst product and lignin or its model compound substrate are added to a sodium hydroxide aqueous solution with a concentration of 0.5-5 mol / L at a mass ratio of 1:2 to 1:200 to form a reaction slurry. The reaction slurry is placed in a pressure-resistant reactor, oxygen or oxygen-containing gas is introduced into it, and the pressure of the reaction system is maintained at 0.1-1 MPa; The reaction system is heated to a reaction temperature of 80°C to 180°C and stirred for 1 to 6 hours under these conditions. The alkaline environment promotes the dissolution and dispersion of lignin, while the selective oxidation, bond breaking and transformation of the substrate are achieved based on the catalytic effect of the nickel-manganese bimetallic supported catalyst.

9. The application of the nickel-manganese bimetallic supported catalyst according to claim 7 in catalyzing the oxidative depolymerization of lignin or its model compounds to prepare high-value-added aromatic aldehydes and aromatic acids, characterized in that, The lignin is selected from any one of herbaceous lignin, softwood lignin, and hardwood lignin; The model compound is 2-phenoxy-1-phenylethanol.

10. The application of the nickel-manganese bimetallic supported catalyst according to claim 7 in catalyzing the oxidative depolymerization of lignin or its model compounds to prepare high-value-added aromatic aldehydes and aromatic acids, characterized in that, The nickel-manganese bimetallic oxide active component on the surface of the nickel-manganese bimetallic supported catalyst first activates the adsorbed oxygen molecules to generate reactive oxygen species such as superoxide or peroxide. At the same time, the nickel active sites activate and weaken the key chemical bonds in the lignin substrate through electronic interactions. Then, driven by the variable valence state cycle of the manganese center, the reactive oxygen species migrate and selectively attack the activated chemical bond sites, achieving highly selective breaking of carbon-oxygen bonds or carbon-carbon bonds and oxidation to generate the corresponding aldehyde or carboxyl groups.

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