Composite metal oxide monatomic catalyst, preparation method and application

Abstract

This invention discloses a composite metal oxide single-atom catalyst, its preparation method, and its applications. The transition metal Mo is dispersed as isolated atoms on the metal oxide with a loading of 0.2-10 wt%. This catalyst has multiple active centers, including transition metal single atoms and solid acid-base sites, and exhibits excellent catalytic activity, selectivity, and stability in heterogeneous catalysis. It shows great promise for industrial applications, especially in the catalytic decomposition of lignin.

Description

Technical Field

[0001] This invention belongs to the field of inorganic functional materials technology, and in particular, provides a composite metal oxide single-atom catalyst with transition metal single atoms and solid acid-base sites supported, its preparation method and application. Background Technology

[0002] In recent years, single-atom catalysts have attracted widespread attention in the field of heterogeneous catalysis due to their high atom utilization and excellent catalytic activity (Nat. Rev. Chem. 2018, 2, 65-81; Chem. Soc. Rev. 2019, 48, 5207-5241; Nat. Catal. 2019, 2, 590-602; Nat. Catal. 2018, 1, 63-72; Nat. Nanotechnol. 2018, 13, 702-707; Science 2016, 353, 150-154; Nature 2019, 565, 631-635). However, for some complex reactions, which often involve multiple reaction steps and require multiple catalytic sites to complete the entire transformation process, theoretically, a single atom site cannot efficiently catalyze all reaction steps simultaneously. Therefore, constructing multiple catalytic sites is an important strategy for optimizing the performance and developing applications of single-atom catalysts, such as the design of bimetallic or trimetallic central sites (Nat. Commun. 2019, 10, 4936; J. Am. Chem. Soc. 2019, 141, 17763-17770; Nat. Chem. 2019, 11, 222-228; J. Am. Chem. Soc. 2017, 139, 9795-9798). Solid acid / base catalysts have demonstrated excellent catalytic activity and selectivity in a variety of heterogeneous catalytic reactions (ACS Catal, 2019, 9, 3266-3277; Catal Rev Eng, 2018, 60, 337-436; Energy Convers. Manage, 2017, 141, 171-182; Appl Catal A, 2022, 633, 118525; ACS Catal, 2020, 10, 9555-9584). Selecting substrates rich in Brønsted or Lewis acid or base sites as supports for single-atom catalysts is an effective strategy for constructing multifunctional single-atom catalysts. Therefore, co-loading Brønsted or Lewis acid or base sites with metal single-atom sites on specific supports can leverage the synergistic advantages of solid acid or base sites and single-atom sites to design highly efficient heterogeneous catalysts. This is of great significance for the performance optimization and application development of single-atom catalysts. However, to date, there are few reports on the synergistic catalysis of solid acid / base sites and single-atom sites, and the lack of effective synthetic strategies is also one of the challenges to its development.

[0003] Lignin is the species with the highest content of aromatic polymers in lignocellulosic biomass, containing numerous phenylpropyl units linked by different types of C / C bonds. Due to the high proportion of aryl ether bonds in lignin (50-85%, depending on the plant species), CO pyrolysis depolymerization of lignin has attracted widespread attention in recent years, providing a promising method for extracting valuable chemicals from natural renewable resources. In recent decades, various efficient catalytic conversion methods for lignin depolymerization have been developed, including reductive, oxidative, and non-redox pyrolysis. However, due to the complex structure and multiple reaction pathways of lignin, developing efficient catalysts to drive the cleavage of CO (β-O-4) bonds to generate monophenolic compounds in high yields and with selectivity remains a significant challenge. Furthermore, among the many aromatic monomer products, those with C / C bonds... α =C β Side-chain monomer products (such as coniferyl / mustardyl methyl ether and coniferyl / mustardyl alcohol) are more valuable for development due to their greater versatility in functionalization. Therefore, developing a high-yield, highly selective inert atmosphere reaction system and an efficient catalyst is both urgent and a significant challenge. Summary of the Invention

[0004] This invention discloses a composite metal oxide single-atom catalyst, characterized in that it has a Mo1Al / MgO structure, wherein Mo is supported on Al and Mg oxide supports in a single-atom site state, and the Mo loading is 0.1-10 wt% based on the total weight of the catalyst, preferably 0.2-5 wt% Mo metal content.

[0005] In the catalyst, the Mg:Al ratio can be adjusted, and the molar ratio can vary between 5:1 and 1:2. In this embodiment of the invention, the ratio is 3:1.

[0006] In this catalyst, Mo serves as the active component and Al serves as the Lewis acid site, forming a dual-active-center catalyst. The " / " symbol in Mo1Al / MgO is only used to distinguish between the active component and the support; in this invention, both Mo and Al serve as active centers.

[0007] This invention also discloses a Mo-containing magnesium-aluminum layered hydroxide material, which is MoO4. 2- / MgAl-LDHs. This material is an intermediate for preparing a Mo1Al / MgO single-atom catalyst. The ratio of Mg to Al can be adjusted according to the product, with a molar ratio ranging from 5:1 to 1:2. This invention implements a Mg:Al ratio of 3:1.

[0008] This invention discloses a method for preparing the single-atom catalyst, comprising:

[0009] S1. Soluble molybdenum salt and soluble metallic Mg and Al salts are co-deposited under alkaline conditions to form layered bis(multi)metal hydroxides MoO4. 2- / MgAl-LDHs,

[0010] S2. Calcination and reduction in a reducing atmosphere yields the catalyst;

[0011] The soluble molybdenum salt is a molybdate selected from ammonium molybdate, sodium molybdate, potassium molybdate, magnesium molybdate, and thallium molybdate. The soluble magnesium and aluminum salts are soluble inorganic salts, organic salts, or complexes; for example, they can be selected from MgCl2, Mg(NO3)2, Mg3(PO4)2, Mg(CH3COO)2, AlCl3, Al(NO3)3, AlPO4, and Al(CH3COO)3. The alkaline conditions refer to adjusting the pH of the mixed solution during the co-deposition process using an alkali and controlling the pH value between 7 and 10. The alkali is a conventionally used alkaline compound for adjusting pH, such as KOH, NaOH, K2CO3, and Na2CO3.

[0012] After co-precipitation in step S1, the mixture can be allowed to mature for 2-24 hours as needed.

[0013] The reducing atmosphere in step S2 is preferably in the presence of hydrogen, and the calcination conditions are 100-600℃, 5%-100% hydrogen atmosphere, and calcination time is 1-6 hours.

[0014] This invention further discloses the use of the catalyst for the selective decomposition of lignin, the use of which includes using the catalyst to catalyze the decomposition of lignin feedstock to obtain a product with C α =C β Aromatic monomeric compounds with unsaturated side chains.

[0015] This invention also discloses a method for preparing C from lignin. α =C β A method for producing an aromatic monomer compound with unsaturated side chains includes reacting eucalyptus wood as a raw material in a pressurized nitrogen atmosphere under the catalysis of the aforementioned catalyst to obtain the product.

[0016] In the method, the reaction is carried out at a pressure of 0.1-10 MPa and a temperature of 20-300 °C.

[0017] Definitions or noun explanations:

[0018] The dispersion state, including single-atom site dispersion, single-atom state, single-atom distribution, single-atom morphology, and single-atom level dispersion states, as described in this invention refers to the isolated state in which active metal elements exhibit independent separation between metal atoms (ions), without direct metal-metal bonds connecting the active metal atoms. This state is characterized by atomic-level dispersion or single-atom site dispersion. Metals dispersed at single-atom sites may exist in an atomic state, an ionic state, or more likely, an intermediate state. In metal nanoparticles, the metal atoms within the same nanoparticle are bonded to each other and do not fall under the single-atom state or single-atom dispersion state defined in this invention. Similarly, for compound or mixture nanoparticles formed by metals and other elements (such as O, S, and other metals), although the metals are separated by other elements, and especially since these compound or mixture nanoparticles often easily transform into metallic nanoparticles (e.g., oxide nanoparticles undergo transformation upon reduction), they also do not fall under the single-atom site state or single-atom separation state defined in this invention. The single-atom site state of metals protected by this invention is theoretically completely independent of each other. However, random deviations in the control of preparation conditions between different batches may result in the presence of a small amount of agglomerated metal species in the product, such as clusters containing a small number of atoms or ions; it is also possible that some metals may exist in a nanoparticle state. In other words, the active metal in the catalyst of this invention may exist in a dispersed state at single atomic sites, while some may exist in a cluster state containing aggregated metal atoms, and / or some metals may exist in a nanoparticle state. The single atomic state protected in this application requires that the single atomic transition metal in the catalyst has a certain proportion in different existence forms such as transition metal single atoms, metal clusters, and transition metal nanoparticles, for example, higher than 10%, preferably higher than 20%, and particularly preferably higher than 50%. However, due to the limitations of current technical means, only relatively coarse statistical methods can be used. High-resolution spherical aberration electron microscopy can be used to randomly select a large number of different local regions in the catalyst test sample for analysis and characterization, and various forms of transition metal existence states can be randomly selected for statistical analysis, or X-ray absorption fine structure spectroscopy (EXAFS) can be used to analyze the catalyst sample to obtain the ratio of metal and other atomic bonding signals to metal-metal bonding signals, thereby determining the approximate proportion of single atomic states. It should be noted that, in essence, as long as a product uses the technology of this invention to obtain a catalyst product with even only a partial single-atom state, the product will exhibit improved performance. Therefore, as long as a product is prepared according to the method of this invention to obtain a catalyst with lignin decomposition activity, it should fall within the scope of protection of this application.

[0019] Complexes, also known as coordination compounds, include complexes formed by transition metals and ligands. Common ligands include halogens (fluorine, chlorine, bromine, iodine), nitro groups, nitroso groups, cyanide groups, ammonia, water molecules, or organic groups. Common complexes include chloride complexes, ammonia complexes, and cyanide complexes, such as chloroplatinic acid, chloroplatinate, and chloroplatinic acid hydrate. See *Handbook of Synthesis of Noble Metal Compounds and Complexes (Deluxe Edition)* (Yu Jianmin, 2009, Chemical Industry Press).

[0020] Beneficial effects:

[0021] This invention synthesizes layered bis(multi) metal hydroxides through a simple room-temperature co-deposition process without the need for templates and surfactants. These hydroxides are then reduced at high temperature with hydrogen to obtain a composite metal oxide single-atom catalyst material with both transition metal single atoms and solid acid-base sites supported. The method is simple, low-cost, and highly reproducible; it does not use any organic solvents or surfactants, making it very environmentally friendly. Furthermore, this catalyst exhibits excellent catalytic performance in the decomposition of lignin, showing great promise for industrial applications. Attached Figure Description

[0022] Figure 1 Transmission electron microscopy (TEM) image of the catalyst in Example 1.

[0023] Figure 2 X-ray diffraction (XRD) pattern of the catalyst in Example 1.

[0024] Figure 3 Example 1: Aberration-corrected high-angle annular dark-field scanning electron microscopy (AC-HAADF-STEM) of the catalyst.

[0025] Figure 4 Example 1 Catalytic performance diagram of the catalyst for lignin decomposition reaction.

[0026] Figure 5 Transmission electron microscopy (TEM) image of the catalyst in Example 2.

[0027] Figure 6 Transmission electron microscopy (TEM) image of the catalyst in Example 3.

[0028] Figure 7 Transmission electron microscopy (TEM) image of the catalyst in Example 4.

[0029] Figure 8 Transmission electron microscopy (TEM) image of Al / MgO in Comparative Example 1.

[0030] Figure 9 Transmission electron microscopy (TEM) image of Mo1 / MgO in Comparative Example 2.

[0031] Figure 10 X-ray diffraction (XRD) pattern of Mo1 / MgO in Comparative Example 2. Detailed Implementation

[0032] To enable those skilled in the art to better understand the technical solution of the present invention, the following describes in detail, with reference to embodiments and accompanying drawings, the composite metal oxide single-atom catalyst material with transition metal single atoms and solid acid-base sites co-supported by the present invention, its preparation method, and its heterogeneous catalytic application.

[0033] LDH: Layered Double Hydroxide is a collective term for hydrotalcite (HT) and hydrotalcite-like compounds (HTLCs). A series of supramolecular materials assembled by intercalation of these compounds are called hydrotalcite-like intercalated materials (LDHs).

[0034] NPs: Nanoparticles;

[0035] TEM: Transmission electron microscopy;

[0036] AC-HAADF-STEM: High-angle annular dark-field scanning transmission electron microscope with spherical aberration correction;

[0037] XRD: X-ray diffraction pattern;

[0038] mmol: millimole;

[0039] min: minutes;

[0040] ml: milliliters;

[0041] rpm: revolutions per minute;

[0042] GC-MS: Gas chromatography-mass spectrometry;

[0043] Example 1

[0044] a. Dissolve 16 mmol Mg(NO3)2·6H2O and 5.33 mmol Al(NO3)3·9H2O in 20 ml of deionized water to form solution A.

[0045] b. Dissolve 34.15 mmol NaOH and 0.05 mmol Na2MoO4 in 20 ml of deionized water to form solution B.

[0046] c. Place the cleaned magnetic rotor into a beaker containing 40 ml of deionized water (solution C), place the beaker on a magnetic stirrer, and turn on the stirring speed to 600 rpm.

[0047] d. Add solutions A and B dropwise to solution C while adjusting the pH of the solution to 8.5 using a pH indicator.

[0048] e. After stirring the above mixture for another 12 hours, collect the white precipitate and wash it six times alternately with ethanol and water by high-speed centrifugation. After drying at 60°C for 4 hours and grinding, obtain adsorbed MoO4. 2- Magnesium aluminum layered hydroxide material (MoO4) 2- / MgAl-LDHs). f. The obtained MoO4 2- / MgAl-LDHs were transferred to a tube furnace and heated at 2 °C for 1 minute under a 5% H2 / N2 atmosphere. -1 The heating rate was increased to 300 °C for 3 h to obtain a composite metal oxide single-atom catalyst with molybdenum single atoms and Lewis acid (Al) and base (Mg) sites co-supported.

[0049] See its transmission electron microscope (TEM) image. Figure 1 See X-ray diffraction (XRD) pattern. Figure 2 See the aberration-corrected high-angle annular dark-field scanning transmission electron microscope (AC-HAADF-STEM) image. Figure 3 For its catalytic performance in the lignin decomposition reaction, please refer to [link / reference]. Figure 4 .

[0050] Example 2

[0051] a. Dissolve 16 mmol Mg(NO3)2·6H2O, 5.33 mmol Al(NO3)3·9H2O and 0.05 mmol Na2MoO4 in 20 ml of deionized water to form solution A.

[0052] b. Dissolve 34.15 mmol NaOH in 20 ml of deionized water to form solution B.

[0053] c. Place the cleaned magnetic rotor into a beaker containing 40ml of deionized water (solution C), place the beaker on a magnetic stirrer, and turn on the stirring speed to 600rpm.

[0054] d. Add solutions A and B dropwise to solution C while adjusting the pH of the solution to 8.5 using a pH indicator.

[0055] e. After stirring the above mixture for another 12 hours, collect the white precipitate and wash it six times alternately with ethanol and water by high-speed centrifugation. After drying at 60°C for 4 hours and grinding, obtain adsorbed MoO4. 2- Magnesium aluminum layered hydroxide material (MoO4)2- / MgAl-LDHs).

[0056] f. The obtained MoO4 2- / MgAl-LDHs were transferred to a tube furnace and heated at 2 °C for 1 minute under a 5% H2 / N2 atmosphere. -1 The heating rate was increased to 300 °C for 3 h to obtain a composite metal oxide single-atom catalyst with molybdenum single atoms and Lewis acid (Al) and base (Mg) sites co-supported.

[0057] See its TEM image. Figure 5 The XRD patterns, AC-HAADF-STEM images, and catalytic performance for lignin decomposition were basically the same as in Example 1.

[0058] Example 3

[0059] a. Dissolve 16 mmol Mg(NO3)2·6H2O and 5.33 mmol Al(NO3)3·9H2O in 20 ml of deionized water to form solution A.

[0060] b. Dissolve 34.15 mmol NaOH and 0.02 mmol Na2MoO4 in 20 ml of deionized water to form solution B.

[0061] c. Place the cleaned magnetic rotor into a beaker containing 40 ml of deionized water (solution C), place the beaker on a magnetic stirrer, and turn on the stirring speed to 600 rpm.

[0062] d. Add solutions A and B dropwise to solution C while adjusting the pH of the solution to 8.5 using a pH indicator.

[0063] e. After stirring the above mixture for another 12 hours, collect the white precipitate and wash it six times alternately with ethanol and water by high-speed centrifugation. After drying at 60°C for 4 hours and grinding, obtain adsorbed MoO4. 2- Magnesium aluminum layered hydroxide material (MoO4) 2- / MgAl-LDHs).

[0064] f. The obtained MoO4 2- / MgAl-LDHs were transferred to a tube furnace and heated at 2 °C for 1 minute under a 5% H2 / N2 atmosphere. -1 The heating rate was increased to 300 °C for 3 h to obtain a composite metal oxide single-atom catalyst with molybdenum single atoms and Lewis acid (Al) and base (Mg) sites co-supported.

[0065] See its TEM image. Figure 6The XRD pattern is basically the same as that in Example 1.

[0066] Example 4

[0067] a. Dissolve 16 mmol Mg(NO3)2·6H2O and 5.33 mmol Al(NO3)3·9H2O in 20 ml of deionized water to form solution A.

[0068] b. Dissolve 34.15 mmol NaOH and 0.02 mmol Na2RuCl5 in 20 ml of deionized water to form solution B.

[0069] c. Place the cleaned magnetic rotor into a beaker containing 40 ml of deionized water (solution C), place the beaker on a magnetic stirrer, and turn on the stirring speed to 600 rpm.

[0070] d. Add solutions A and B dropwise to solution C while adjusting the pH of the solution to 8.5 using a pH indicator.

[0071] e. After stirring the above mixture for another 12 hours, collect the white precipitate and wash it six times alternately with ethanol and water by high-speed centrifugation. After drying at 60°C for 4 hours and grinding, obtain adsorbed RuCl5. 2- Magnesium aluminum layered hydroxide material (RuCl5) 2- / MgAl-LDHs).

[0072] f. The obtained RuCl5 2- / MgAl-LDHs were transferred to a tube furnace and heated at 2 °C for 1 min under a 5% H2 / N2 atmosphere. -1 The heating rate was increased to 200 °C for 3 h to obtain a composite metal oxide single-atom catalyst with Ru single atoms and Lewis acid (Al) and base (Mg) sites co-supported.

[0073] See its TEM image. Figure 7 .

[0074] Example 5

[0075] To evaluate cycle stability, the catalyst was collected, washed by centrifugation, and dried for cycle testing. The test method is described in the test application method below.

[0076] Comparative Example 1

[0077] Preparation of Al / MgO

[0078] a. Dissolve 16 mmol Mg(NO3)2·6H2O and 5.33 mmol Al(NO3)3·9H2O in 20 ml of deionized water to form solution A.

[0079] b. Dissolve 34.15 mmol NaOH in 20 ml of deionized water to form solution B.

[0080] c. Place the cleaned magnetic rotor into a beaker containing 40 ml of deionized water (solution C), place the beaker on a magnetic stirrer, and turn on the stirring speed to 600 rpm.

[0081] d. Add solutions A and B dropwise to solution C while adjusting the pH of the solution to 8.5 using a pH indicator.

[0082] e. After stirring the above mixture for another 12 hours, collect the brown precipitate and wash it six times alternately with ethanol and water by high-speed centrifugation. After drying at 60°C for 4 hours and grinding, magnesium aluminum layered hydroxide material (MgAl-LDHs) is obtained.

[0083] f. The prepared MgAl-LDHs were transferred to a tube furnace and heated at 2 °C for 2 min under a 5% H2 / N2 atmosphere. -1 The heating rate was increased to 300℃ for 3 h to obtain the Al / MgO composite oxide catalyst material.

[0084] See its TEM image. Figure 8 The XRD pattern is basically the same as that in Example 1.

[0085] Comparative Example 2

[0086] Preparation of Mo / MgO

[0087] a. Dissolve 21.33 mmol Mg(NO3)2·6H2O in 20 ml of deionized water to form solution A.

[0088] b. Dissolve 34.15 mmol NaOH and 0.05 mmol Na2MoO4 in 20 ml of deionized water to form solution B.

[0089] c. Place the cleaned magnetic rotor into a beaker containing 40 ml of deionized water (solution C), place the beaker on a magnetic stirrer, and turn on the stirring speed to 600 rpm.

[0090] d. Add solutions A and B dropwise to solution C while adjusting the pH of the solution to 8.5 using a pH indicator.

[0091] e. After stirring the above mixture for another 12 hours, collect the white precipitate and wash it six times alternately with ethanol and water by high-speed centrifugation. After drying at 60°C for 4 hours and grinding, obtain adsorbed MoO4. 2- Magnesium hydroxide material (MoO4) 2- / Mg(OH)2).

[0092] f. The obtained MoO4 2- The Mg(OH)₂ was transferred to a tube furnace and heated at 2 °C for 1 minute under a 5% H₂ / N₂ atmosphere. -1 The heating rate was increased to 300 °C for 3 h to obtain a composite metal oxide single-atom catalyst with molybdenum single atoms and Lewis base (Mg) sites co-supported.

[0093] See its TEM image. Figure 9 See XRD pattern Figure 10 .

[0094] Structural test data and interpretation

[0095] Figure 1 The results show that Mo1Al / MgO has a nanosheet-like morphology. Figure 8 The image shows a TEM image of Al / MgO. It indicates that both have similar morphologies, suggesting that the loading of single metal atoms has little effect on the material's morphology.

[0096] Figure 2 This indicates that the XRD pattern of Mo1Al / MgO conforms to the standard peaks of MgO. And from... Figure 3 Numerous isolated bright spots, which are Mo atoms, can be observed. This indicates that isolated Mo atoms are uniformly embedded on the surface of the Al / MgO nanocrystals.

[0097] Figure 4 The activity test information of the catalyst of the present invention (Example 1) is shown, indicating that Mo1Al / MgO exhibits excellent catalytic performance. Under the reaction conditions of 200℃ and 8h, the monomer yield reached nearly 46% of the theoretical yield, and the selectivity reached 92%. These results are far superior to comparative samples such as Al / MgO and Mo / MgO. To further evaluate its cycling stability, the reaction was performed for 5 cycles (200℃, 8h), and it was found that the monomer yield and selectivity did not decrease significantly. This result indicates that the Mo1Al / MgO catalyst has excellent structural stability.

[0098] Figure 6 Showing Embodiment 3 compared to Embodiments 1 and 2 ( Figure 1 and 5 The obtained Mo1Al / MgO materials exhibit similar morphologies, indicating that the Mo loading has little effect on the material morphology. Figure 7The Ru1Al / MgO and Mo1Al / MgO intermetallic compounds have similar morphologies, indicating that the loading of different metal single atoms has little effect on the morphology of the materials.

[0099] Application Testing – Lignin Degradation Test Experiment:

[0100] 300 mg of extract-free eucalyptus powder and 100 mg of catalyst were added to a PTFE-lined high-pressure reactor (Anhui Komi Machinery Technology Co., Ltd.), along with 20 mL of methanol. The reactor was placed in a heating device connected to a temperature control chamber. The reaction temperature was measured using thermocouples through the thermocouple sheath. The reactor was purged five times with N2 to remove air and pressurized to 10 bar with N2 at room temperature. It was then heated to the desired temperature (180, 200, 220 °C) and continuously stirred at this temperature for a specific reaction time. When the reaction was complete, the reactor was removed from the heating device and allowed to cool naturally to room temperature. The reaction mixture was filtered through a 0.22-micron PTFE syringe filter. The filtrate was evaporated under vacuum, and the residue was then redissolved in 15 mL of ethyl acetate. Take 1 mL of solvent, along with 0.1 mL of N-(trimethylsilyl)trifluoroacetamide, 0.1 mL of pyridine, and 0.1 mL of internal standard solution (1.5 mg / mL 4,4'-ethylidene bisphenol dissolved in dioxane) and transfer them to a 2 mL vial. Incubate the vial in a sand bath at 50 °C for 1 hour. After silanization, characterize the sample by GC-MS. Comparative test results are shown in Table 1.

[0101] Table 1 Comparison of the catalytic decomposition performance of eucalyptus lignin

[0102]

[0103] Note Relevant monomer (product) structures and numbering:

[0104]

[0105] The data above show that, compared to Al / MgO and Mo / MgO catalysts, the Mo1Al / MgO catalyst exhibits higher activity and unsaturated monomer selectivity for this reaction. Therefore, it can be inferred that the coexistence of Al Lewis acid sites and Mo single-atom centers in this catalytic system is crucial for the efficient decomposition of lignin.

[0106] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A composite metal oxide single-atom catalyst, characterized in that, It has a Mo1Al / MgO structure, wherein Mo is supported on Al and Mg oxide supports in a single-atom site state, the Mo loading is 0.1-10 wt% based on the total weight of the catalyst, and the Mg:Al molar ratio of the catalyst is in the range of 5:1-1:

2.

2. The catalyst according to claim 1, characterized in that, The Mo metal content is 0.2-5 wt%.

3. The catalyst as described in claim 1, wherein, The catalyst has a Mg:Al molar ratio in the range of 3:

1.

4. A method for preparing the catalyst according to any one of claims 1-3, comprising: S1. Soluble molybdenum salt and soluble metallic Mg and Al salts are co-deposited under alkaline conditions to form a layered polymetallic hydroxide MoO4. 2- / MgAl-LDHs; S2. Calcination and reduction in a reducing atmosphere yields the catalyst; Among them, the soluble molybdenum salt is a molybdate, selected from ammonium molybdate, sodium molybdate, potassium molybdate or magnesium molybdate, and the soluble magnesium salt and aluminum salt are soluble inorganic salts, organic salts or complexes.

5. The method as described in claim 4, characterized in that, Magnesium salts are selected from MgCl2, Mg(NO3)2, Mg3(PO4)2 or Mg(CH3COO)2; aluminum salts are selected from AlCl3, Al(NO3)3, AlPO4 or Al(CH3COO)3.

6. The preparation method according to claim 4, wherein the alkaline condition refers to adjusting and controlling the pH value between 7 and 10 using an alkali, wherein the alkali is a conventional alkaline compound used to adjust the pH value.

7. The preparation method according to claim 4, wherein, After co-precipitation in step S1, allow it to mature for 2-24 hours.

8. The preparation method according to claim 4, wherein, The reduction atmosphere in step S2 is carried out in the presence of hydrogen, and the calcination conditions are 100-600℃, 5%-100% hydrogen atmosphere, and calcination time is 1-6 hours.

9. Use of the catalyst according to any one of claims 1-3 for the selective catalytic decomposition of lignin, the use comprising using the catalyst to catalytically decompose lignin feedstock to obtain a product having C α =C β Aromatic monomeric compounds with unsaturated side chains.

10. A method for preparing C from lignin α =C β A method for producing an aromatic monomer compound with unsaturated side chains includes reacting eucalyptus wood as a raw material in a pressurized nitrogen atmosphere under the catalysis of a catalyst as described in any one of claims 1-3 or a catalyst prepared by any one of claims 4-8 to obtain the product.

11. The method of claim 10, wherein, The reaction is carried out at a pressure of 0.1-10 MPa and a temperature of 20-300℃.

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