A method for catalytic oxidative cleavage of aromatic ethers

Abstract

The application discloses a method for catalytic oxidative cleavage of aromatic ether substances. The method is that aromatic ether substances, metal-base composite catalysts and water medium are placed in an autoclave, and oxygen-containing gas is filled for hydrothermal reaction; the metal-base composite catalysts contain metal active components and base active components, wherein the metal active components are ruthenium, palladium, platinum, copper or cobalt, and the base active components are magnesium oxide, barium oxide or calcium oxide; the method can catalytically oxidize and cleave the aromatic ether substances into high-value-added small organic molecules such as phenols and carboxylic acids with high selectivity, and does not need to use organic solvent medium and add a large amount of inorganic base, and has the characteristics of simple process, high product added value and the like, and can produce important economic value and social benefits.

Description

Technical Field

[0001] This invention relates to a method for the catalytic oxidation and decomposition of aromatic ethers, and particularly to a method for the synergistic heterogeneous catalysis of aromatic ethers into low molecular weight phenols and carboxylic acids by a composite catalyst containing both metal active components and solid base active components, belonging to the field of catalysis technology. Background Technology

[0002] Lignin, as a biomass resource, is renewable. In recent years, the oxidative cleavage of lignin has attracted widespread attention due to its ability to form aromatic carboxylic acids, ketones, and quinones, which are used to produce oxygen-functionalized aromatic compounds for the production of fine chemicals. The core challenge of lignin oxidative cleavage lies in designing highly efficient catalysts capable of selectively breaking the high-energy C–C / C–O bonds in lignin to form specific aromatic alcohols, aldehydes, acids, and other special functionalized aromatic compounds that are difficult to produce. These aromatic compounds may be highly functionalized, and their traditional sources mainly involve several synthetic steps from petroleum feedstocks or require expensive initial synthetic raw materials.

[0003] Traditional lignin oxidative cracking reactions use stoichiometric amounts of hydrogen peroxide or nitric acid as oxidants, which presents separation and reactor corrosion problems. Chinese invention patent (application number CN202110755586.2) discloses a method for preparing three-dimensional nitrogen-doped graphene-supported cobalt nanoparticles (Co / 3DNG) catalysts using a hydrothermal-impregnation-pyrolysis method and their application in the oxidative conversion of lignin and its β-O-4 model compound. The catalyst exhibits good catalytic activity in the oxidative cracking of the β-O-4 model compound (2-phenoxy-1-phenylethanol) in methanol, with a β-O-4 model compound conversion rate and phenol yield of 97%. This patented technology can yield single phenolic compounds, but it requires the use of non-green organic solvents. Chinese invention patent (application number CN202010814102.2) proposes a method for highly selective catalytic oxidation of lignin to vanillic acid using a supported rhenium-based catalyst. The method uses an organic acid as a solvent and adds an oxidant. Under the action of the supported rhenium-based catalyst, lignin model compound monomers, lignin β-O-4 model compounds, or lignin raw materials are converted into small molecule compounds mainly composed of vanillic acid. However, this patented technology requires the use of organic acid solvents, which are expensive. Summary of the Invention

[0004] To achieve the above-mentioned technical objectives, the present invention aims to provide a method for the catalytic oxidative cracking of aromatic ethers. This method can selectively convert aromatic ethers into small organic molecules such as phenols and carboxylic acids with high added value through catalytic oxidative cracking. Moreover, it does not require the use of organic solvent media or the addition of large amounts of inorganic bases. It has the characteristics of simple process and high added value of products, and is expected to generate significant economic value and social benefits.

[0005] To achieve the above-mentioned technical objectives, the present invention provides a method for the catalytic oxidative cracking of aromatic ethers. The method involves placing the aromatic ethers, a metal-alkali composite catalyst, and an aqueous medium in a high-pressure reactor and introducing oxygen-containing gas to carry out a hydrothermal reaction. The metal-alkali composite catalyst contains both a metal active component and an alkali active component. The metal active component includes at least one of ruthenium, palladium, platinum, copper, and cobalt. The alkali active component includes at least one of magnesium oxide, barium oxide, and calcium oxide.

[0006] The key to the catalytic oxidative cracking method for aromatic ethers provided by this invention lies in two aspects: First, water can be used as a medium. Since the metal-alkali composite catalyst, water, and aromatic ethers are all immiscible, a heterogeneous catalytic reaction occurs. The small organic molecules, mainly phenols and carboxylic acids, generated by the catalytic oxidative cracking of aromatic ethers are soluble in water, thus promoting the smooth progress of the catalytic oxidative cracking of aromatic ethers. Second, a special metal-alkali composite catalyst is used, which simultaneously contains both metal and alkali active components. The synergistic catalytic effect between the metal and alkali catalytic active sites can greatly improve the conversion rate and selectivity of the catalytic oxidative cracking of aromatic ethers. Furthermore, it eliminates the need for adding alkaline substances such as sodium hydroxide or ammonia, or significantly reduces the amount of alkaline substances used, avoiding the generation of alkaline waste liquid and reducing production costs.

[0007] As a preferred embodiment, the aromatic ethers include at least one of 2-phenoxy-1-phenylethanol, diphenyl ether, benzyl ether, phenoxyethylbenzene, alkali lignin, organic soluble lignin, sulfate lignin, furfural residue, and sawdust. These aromatic ethers are all common compounds and contain stable C–C / C–O bonds with high bond dissociation energies.

[0008] As a preferred embodiment, the metal-alkali composite catalyst comprises an alkaline active component and a metal active component supported on a carbon material. The adjacent loading of the alkaline and metal active components in the metal-alkali composite catalyst shortens the effective distance between the alkaline sites and the metal active sites, significantly enhancing the synergistic catalytic effect between them. This reduces the amount of alkali required and achieves excellent catalytic performance without the need for external alkali addition.

[0009] As a preferred embodiment, in the metal-alkali composite catalyst, the loading of the alkali active component is 1–30 wt.%, and the loading of the metal active component is 1–10 wt%. If the loading of the alkali and metal active components is too low, the content of alkali and metal active sites will be relatively low, resulting in a decrease in the catalytic activity and selectivity of the metal-alkali composite catalyst. Conversely, if the loading of the alkali and metal active components is too high, some metal active sites will occupy alkali active sites, which will also cause a decrease in the catalytic activity of the metal-alkali composite catalyst. Furthermore, the specific surface area of ​​the carbon material support will also decrease, leading to a reduction in catalytic activity.

[0010] As a preferred embodiment, the mass ratio of the alkali active component to the metal active component in the metal-alkali composite catalyst is 1–3:2. The ratio of the alkali active component to the metal active component has a certain influence on the catalytic activity and catalytic selectivity of the metal-alkali composite catalyst and needs to be controlled within an appropriate range. If the alkali active component is loaded too much or too little on the carbon support, its catalytic activity will be reduced, and its catalytic selectivity will be affected. For example, if the alkali active component is relatively too little, the catalytic activity will decrease due to the insufficient number of alkali active sites; conversely, if the alkali active component is relatively too much, the probability of some metal active component depositing on the alkaline sites will increase, and the role of the alkali active component cannot be fully utilized, thus reducing the catalytic activity.

[0011] As a preferred embodiment, the amount of the metal-alkali composite catalyst is 5-80% of the mass of the aromatic ether substance; more preferably, it is 30%-60%. With the increase in the amount of the metal-alkali composite catalyst, the yield of small molecules of phenols and carboxylic acids from the cracking products increases accordingly due to the increase in both the base and metal active sites. However, excessive use of the metal-alkali composite catalyst will reduce its utilization rate and result in higher operating costs.

[0012] As a preferred embodiment, the hydrothermal reaction conditions are: oxygen pressure of 0.2–1 MPa, temperature of 80–200 °C, and time of 0.5–10 h. The hydrothermal reaction temperature is further preferably 100–180 °C, and most preferably 120–160 °C. During the hydrothermal reaction, oxygen pressure and temperature affect the conversion rate of aromatic ethers and side reactions. Therefore, oxygen pressure and temperature need to be controlled within appropriate ranges to ensure both a high conversion rate of aromatic ethers and highly selective conversion of aromatic ethers into small molecules such as phenols and carboxylic acids.

[0013] As a preferred embodiment, the amount of water medium used is 10 to 50 times the mass of the aromatic ether substance.

[0014] As a preferred embodiment, the carbon material is at least one of activated carbon, carbon nanotubes, graphene, and mesoporous carbon. Using carbon material as a carrier not only improves the stability of the metal active component and the alkali active component, but also disperses and loads the metal active component and the alkali active component, thus fully exposing more alkali sites and metal active sites.

[0015] As a preferred embodiment, the oxygen-containing gas is oxygen, or a combination of at least one of nitrogen, carbon dioxide, and ammonia with oxygen.

[0016] The metal-alkali composite catalyst of the present invention is prepared by the following method:

[0017] (1) Dissolve at least one of magnesium salt, calcium salt and barium salt in water to obtain a metal solution. Add the metal solution dropwise to carbon material and stir thoroughly. Then dry and calcine to obtain a carbon-supported alkaline active ingredient.

[0018] (2) Dissolve at least one of ruthenium salt, palladium salt, platinum salt, copper salt and cobalt salt and an alkali in ethylene glycol and carry out reflux reaction I. Then add carbon-supported alkaline active ingredients and carry out reflux reaction II. The resulting solid product is vacuum dried to obtain the metal-alkali composite catalyst.

[0019] Preferably, the calcination conditions are: calcination at 300℃~500℃ for 4~10h.

[0020] Preferably, the conditions for reflux reaction I or reflux reaction II are: reflux at 130℃~150℃ for 2~4h.

[0021] Preferably, the alkali is a strong alkali such as sodium hydroxide or potassium hydroxide.

[0022] The metal-alkali composite catalyst of the present invention has both metal catalytic active sites and alkali catalytic active sites. The synergistic catalytic effect between the metal catalytic active sites and the alkali catalytic active sites can greatly improve the conversion rate and selectivity of catalytic oxidation and cracking of aromatic ethers. It can directly catalyze the efficient cracking of aromatic ether bonds without the need for additional alkali source.

[0023] Compared with existing technologies, the beneficial technical effects of the present invention are as follows:

[0024] This invention utilizes a composite catalyst that simultaneously possesses metal catalytic active sites and base active sites. Without requiring the addition of additional inorganic bases or significantly reducing the amount of base used, it can selectively convert aromatic ethers into high-value-added organic small molecules such as phenols and carboxylic acids through catalytic oxidative cracking. In particular, it can efficiently convert lignin into high-value-added organic small molecules such as aldehydes, phenols, and carboxylic acids. Furthermore, it eliminates the need for organic solvents, avoiding the generation of alkaline and organic wastewater, and reducing production costs. The invention features a simple process and high-value-added products, and is expected to generate significant economic and social benefits. Attached Figure Description

[0025] Figure 1 Ru-MgO 0.1 X-ray diffraction pattern of / C.

[0026] Figure 2 Ru-MgO 0.1 X-ray photoelectron spectra of / C and Ru / C.

[0027] Figure 3 Ru-MgO 0.1 Scanning electron microscope image of / C.

[0028] Figure 4 Ru / CS (carbon nanotubes) and Ru-MgO with different MgO doping amounts x Transmission electron microscopy image of / C.

[0029] Figure 5 Ru-MgO with different MgO doping amounts x Specific surface area (a) and pore size analysis spectrum (b) of / C.

[0030] Figure 6 Ru-MgO 0.1 / C cyclic usage curve. Detailed Implementation

[0031] The following specific embodiments are intended to further illustrate the content of the present invention, but are not intended to limit the scope of protection of the claims of the present invention.

[0032] Unless otherwise specified, all chemical reagents used in the following examples are conventional commercially available reagents.

[0033] The preparation of various catalysts in the following examples can be carried out in accordance with Example 4, with only the raw materials needing to be replaced.

[0034] Example 1 (Control Example)

[0035] 200 mg of 2-phenoxy-1-phenylethanol, 100 mg (5 wt% Ru / C, 5 wt% Pd / C, or 5 wt% Pt / C), and 10 mL of deionized water were placed in a 100 mL mechanically stirred stainless steel autoclave with a polytetrafluoroethylene liner. 0.5 MPa O2 was introduced into the autoclave, and the reaction was carried out at 120 °C and 500 rpm for 2 h. After the reaction was completed, the reaction solution was acidified with 5 mL of 0.1 M sulfuric acid and extracted three times with 25 mL of ethyl acetate to obtain small molecule aromatic phenols and aromatic acids. The conversion rate of 2-phenoxy-1-phenylethanol and the yield of each product were calculated using gas chromatography-mass spectrometry (GC-MS) and gas chromatography with the internal standard method. The reaction results are shown in Table 1.

[0036] Example 2 (Control Example)

[0037] 200 mg of 2-phenoxy-1-phenylethanol, 100 mg (5 wt% Ru / C, 5 wt% Ru / CNTs, 5 wt% Pd / C, 5 wt% Pt / C, 5 wt% Cu / C, or 5 wt% Co / C), 60 mg of NaOH, and 10 ml of deionized water were placed in a 100 ml mechanically stirred stainless steel autoclave with a polytetrafluoroethylene liner. The autoclave was charged with 0.5 MPa O2, and the reaction was carried out at 120 °C and 500 rpm for 2 h. After the reaction was completed, the reaction solution was acidified with 5 ml of 0.1 M sulfuric acid and extracted three times with 25 ml of ethyl acetate to obtain small molecule aromatic phenols and aromatic acids. The conversion rate of 2-phenoxy-1-phenylethanol and the yield of each product were calculated using gas chromatography-mass spectrometry and gas chromatography with internal standard method. The reaction results are shown in Table 1.

[0038] Table 1. Results of combined catalytic oxidation of different metal catalysts with NaOH alkaline catalysts in Examples 1 and 2

[0039]

[0040]

[0041] a, b, and c: Results of the reaction without alkali catalysis in Example 1.

[0042] As shown in Table 1, without the addition of alkali, the main product is 2-phenoxy-1-acetophenone, the dehydrogenation product of 2-phenoxy-1-phenylethanol, rather than the ideal products of phenol and benzoic acid. However, with the addition of alkali, the main products are phenol and benzoic acid, the cracking products of 2-phenoxy-1-phenylethanol. This indicates that the alkali promotes the breaking of ether bonds, and Ru exhibits the highest conversion rate under alkaline conditions compared to other noble metals. Non-noble metal catalysts Cu and Co also show similar effects, but their selectivity for phenol and benzoic acid is inferior to that of Ru.

[0043] Example 3 (Control Example)

[0044] 200 mg of 2-phenoxy-1-phenylethanol, 100 mg (5 wt% Ru / C, 5 wt% Ru / CNTs, 5 wt% Pd / C, 5 wt% Pt / C, 5 wt% Cu / C, or 5 wt% Co / C), 60 mg of MgO, and 10 ml of deionized water were placed in a 100 ml mechanically stirred stainless steel autoclave with a polytetrafluoroethylene liner. The autoclave was charged with 0.5 MPa O2, and the reaction was carried out at 120 °C and 500 rpm for 2 h. After the reaction was completed, the reaction solution was acidified with 5 ml of 0.1 M sulfuric acid and extracted three times with 25 ml of ethyl acetate to obtain small molecule aromatic phenols and aromatic acids. The conversion rate of 2-phenoxy-1-phenylethanol and the yield of each product were calculated using gas chromatography-mass spectrometry and gas chromatography with internal standard method. The reaction results are shown in Table 2.

[0045] Table 2. Results of combined catalytic oxidation of different metal catalysts and magnesium oxide alkaline catalysts in Example 3.

[0046]

[0047]

[0048] As shown in Table 2, solid magnesium oxide plays the same role as NaOH in the aqueous phase 2-phenoxy-1-phenylethanol cracking reaction. Therefore, solid magnesium oxide can be used as the base source for this reaction. However, the amount of magnesium oxide added is relatively large, and the overall catalytic conversion rate of 2-phenoxy-1-phenylethanol is below 95%.

[0049] Example 4

[0050] (1) Dissolve 0.16 g Mg(NO3)2·6H2O in 1 g deionized water, add it dropwise to 500 mg activated carbon, stir thoroughly and dry. After drying, transfer the sample to a nitrogen atmosphere and calcine at 400 °C for 6 h to obtain carbon-supported alkaline oxide carrier MgO. 0.05 / C.

[0051] (2) Add (5wt% metal loading) RuCl3·3H2O and 0.012g NaOH to a three-necked flask containing 50ml ethylene glycol and dissolve and disperse for 30min. Place the flask in an oil bath at 140℃ for 500r and reflux for 3h. Then add the MgO obtained in step (1) to the flask. x Add 100 ml of deionized water to the catalyst and continue reflux at 140 °C for 3 hours. Filter and wash the catalyst, then vacuum dry it overnight at 80 °C.

[0052] By changing the amount of magnesium nitrate used in step (1) to 0.16, 0.32, 0.64, or 0.96 g, Ru-MgO was obtained. 0.05 / C、Ru-MgO0.1 / C、Ru-MgO 0.2 / C、Ru-MgO 0.3 / C catalyst available.

[0053] (3) Add 200 mg of 2-phenoxy-1-phenylethanol and 100 mg of Ru-MgO x 10 ml of deionized water and 10 ml of acetone were placed in a 100 ml mechanically stirred stainless steel autoclave with a polytetrafluoroethylene liner. The autoclave was charged with 0.5 MPa O2, and the reaction was carried out at 120 °C and 500 rpm for 2 h. After the reaction was completed, the reaction solution was acidified with 5 ml of 0.1 M sulfuric acid and extracted three times with 25 ml of ethyl acetate to obtain small molecule aromatic phenols and aromatic acids. The conversion rate of 2-phenoxy-1-phenylethanol and the yield of each product were calculated using gas chromatography-mass spectrometry and gas chromatography with internal standard method. The reaction results are shown in Table 3.

[0054] Table 3. Results of oxidation of 2-phenoxy-1-phenylethanol by Ru-based catalysts with different magnesium oxide contents.

[0055]

[0056]

[0057] As shown in Table 3, a conversion rate of 97.63% and the pyrolysis products benzoic acid and phenol can be obtained when the MgO loading is 5 wt%. The conversion rate is relatively high when the MgO loading is 10 wt%. The conversion rate tends to decrease with the increase of MgO addition.

[0058] Ru-MgO 0.1 / C Perform the cyclic experiment according to step (3), and the results are as follows Figure 6 As shown.

[0059] Example 5

[0060] The catalyst Ru-MgO prepared in steps (1) to (2) of Example 4 was used. 0.1 / C. Add 500mg of poplar sawdust and 100mg of Ru-MgO. 0.1C, 200 mg NaOH (the addition of a small amount of NaOH helps lignin dissolve from the primary biomass; the current technology uses 1-2 M alkali) and 10 ml deionized water were placed in a 100 ml mechanically stirred stainless steel autoclave with a polytetrafluoroethylene liner. 0.5 MPa O2 was introduced into the autoclave, and the pressure was maintained at 2 MPa using N2. The reaction was carried out at 160 °C and 600 rpm for 2 hours. After the reaction, the reaction solution was acidified with 5 ml of 0.1 M sulfuric acid and extracted three times with 25 ml of ethyl acetate to obtain small molecule aromatic phenols and aromatic acids. The conversion rate of lignin and the selectivity of each product were calculated using gas chromatography-mass spectrometry and gas chromatography with the internal standard method. The lignin content of poplar sawdust was determined to be 29 wt.% by organic solvent extraction. See Table 4 for details.

[0061] Table 4. Results of aqueous phase catalytic oxidation of poplar wood chips

[0062]

[0063] Table 4 shows that the addition of Ru-MgO 0.1 After using the / C catalyst, the yield of small lignin molecules in poplar wood chips increased from 2.87 wt.% to 7.85 wt.%, and the selectivity of small aromatic acid molecules also increased.

[0064] Example 6

[0065] The catalyst Ru-MgO prepared in steps (1) to (2) of Example 4 was used. 0.1 / C. Add 500mg of pine sawdust and 100mg of Ru-MgO 0.1 200 mg NaOH and 10 ml deionized water were placed in a 100 ml mechanically stirred stainless steel autoclave with a polytetrafluoroethylene liner. 0.5 MPa O2 was introduced into the autoclave, and the pressure was maintained at 2 MPa using N2. The reaction was carried out at 160 °C and 600 rpm for 2 hours. After the reaction, the reaction solution was acidified with 5 ml of 0.1 M sulfuric acid and extracted three times with 25 ml of ethyl acetate to obtain small molecule aromatic phenols and aromatic acids. The conversion rate of lignin and the selectivity of each product were calculated using gas chromatography-mass spectrometry and gas chromatography with the internal standard method. The lignin content of pine sawdust was determined to be 25 wt.% by organic solvent extraction. See Table 5 for details.

[0066] Table 5. Results of aqueous phase catalytic oxidation reaction of pine sawdust

[0067]

[0068] Similarly, as shown in Table 5, after adding Ru-MgO0.1 / C catalyst, the yield of lignin small molecules in pine sawdust increased from 1.28 wt.% to 6.74 wt.%, and the selectivity of aromatic acid small molecules also increased.

[0069] Figure 1 Ru-MgO prepared in Example 4 0.1 The XRD pattern of / C shows that no diffraction peaks of MgO were observed, indicating that MgO is uniformly dispersed on the carbon support and has a small particle size. Similarly, no diffraction peaks of Ru were observed, indicating that ruthenium metal is uniformly dispersed on the carbon support and has a small particle size. For details, please refer to TEM and particle size analysis.

[0070] Figure 2 Ru-MgO prepared in Example 4 0.1 The X-ray photoelectron spectroscopy of the Ru 3p orbital in Ru / C, compared with Ru / C, shows that MgO loading affects the electronic states of Ru, resulting in Ru-MgO. 0.1 The binding energy of Ru in / C shifts to higher energies by 1.37 eV.

[0071] Figure 3 Ru-MgO prepared in Example 4 0.1 Scanning electron microscope image of / C. Ru-MgO 0.1 / C scanning electron microscopy images show that the carbon support loaded with MgO has abundant pores on its surface, indicating that loading 10wt% MgO does not cause significant changes to the overall structure of the carbon support, but only occupies some of the pores and reduces its specific surface area.

[0072] Figure 4 Transmission electron microscopy, particle size analysis, and Ru-MgO analysis of various carbon-based Ru catalysts. 0.1 / C elemental mapping, where a is the Ru / CS TEM image and particle size analysis, b is the Ru / CS HRTEM image, c is the Ru / CNTs TEM image and particle size analysis, and d is the Ru-MgO elemental mapping. 0.1 / C TEM images and particle size analysis, e~h are Ru-MgO 0.1 / C elemental mapping diagram (Mg is yellow, O is blue, Ru is green). From transmission electron microscopy images a-d and elemental distribution diagrams e-h, it can be seen that Ru is uniformly distributed on each support, and the Ru nanoparticles have a particle size of about 1 nm. MgO is uniformly distributed on the carbon support, and no MgO crystal particles were observed in image d.

[0073] Figure 5 The diagrams show the specific surface area and pore size distribution of Ru catalysts on activated carbon with different MgO doping amounts. As can be seen from the diagrams, the specific surface area gradually decreases with increasing MgO content, indicating that MgO occupies the pore structure of the carbon support. Similarly, the pore size distribution shows that pores smaller than 5 nm gradually decrease with increasing MgO content.

[0074] Figure 6 Ru-MgO 0.1The cyclic curve of the / C catalyst shows that the catalyst still has a high conversion rate and selectivity for aromatic alcohols / acids after 5 cycles, indicating that the catalyst has good stability.

Claims

1. A method for the catalytic oxidative cracking of aromatic ethers, characterized in that: Aromatic ethers, metal-alkali composite catalysts, and water media are placed in an autoclave and oxygen-containing gas is introduced to carry out a hydrothermal reaction. The metal-alkali composite catalyst contains both metal active components and alkali active components; The active metal component includes at least one of ruthenium, palladium, platinum, copper, and cobalt; The alkaline active ingredient includes at least one of magnesium oxide, calcium oxide and barium oxide; The aromatic ethers include at least one of 2-phenoxy-1-phenylethanol, diphenyl ether, benzyl ether, phenoxyethylbenzene, alkali lignin, organic soluble lignin, sulfate lignin, furfural residue, and sawdust.

2. The method for catalytic oxidative cracking of aromatic ethers according to claim 1, characterized in that: The metal-alkali composite catalyst is composed of alkali active components and metal active components supported on carbon materials.

3. The method for catalytic oxidative cracking of aromatic ethers according to claim 2, characterized in that: In the metal-alkali composite catalyst, the loading of alkali active component is 1~30wt%, and the loading of metal active component is 1~10wt%.

4. A method for catalytic oxidative cracking of aromatic ethers according to claim 2 or 3, characterized in that: The mass ratio of the alkali active component to the metal active component in the metal-alkali composite catalyst is 1~3:

2.

5. The method for catalytic oxidative cracking of aromatic ethers according to claim 2, characterized in that: The carbon material is at least one of activated carbon, carbon nanotubes, graphene, and mesoporous carbon.

6. A method for catalytic oxidative cracking of aromatic ethers according to claim 1, 2, 3 or 5, characterized in that: The amount of the metal-alkali composite catalyst used is 5-80% of the mass of the aromatic ether substance.

7. A method for catalytic oxidative cracking of aromatic ethers according to claim 1, 2 or 3, characterized in that: The conditions for the hydrothermal reaction are: oxygen pressure of 0.2~1MPa, temperature of 80~200℃, and time of 0.5~10 h.

8. The method for catalytic oxidative cracking of aromatic ethers according to claim 1, characterized in that: The amount of water medium used is 10 to 50 times the mass of the aromatic ether substance.

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