In2O3-TiO2 composite oxide catalyst as well as preparation method and application thereof

Abstract

The invention discloses an In2O3-TiO2 composite oxide catalyst as well as a preparation method and application thereof, TiO2 is taken as a carrier, In salt is loaded on TiO2 through an impregnation method, and then the In2O3-TiO2 catalyst is obtained through calcination and is used for catalyzing selective demethoxylation reaction of lignin phenolic compounds. According to the In2O3-TiO2 composite oxide catalyst disclosed by the invention, crystal defects and a strong adsorption effect of TiO2 are utilized, In2O3 without hydrogenation activity on a benzene ring is selected as a hydrogen activation center, an In2O3-TiO2 interface, an In-O-Ti structure and oxygen vacancies are formed, adsorption and activation of a Caryl-OCH3 group are promoted, hydrogenation of the benzene ring and breakage of a Carl-OH bond are inhibited, further methylation reaction is inhibited, and the catalytic activity of the catalyst is improved. And the catalyst has excellent selective demethoxylation activity.

Description

Technical Field

[0001] The present invention belongs to the field of catalyst development for renewable energy development, and particularly relates to an In2O3-TiO2 composite oxide catalyst, a preparation method thereof, and an application thereof in the selective demethoxylation of lignin phenols. Background Art

[0002] As the fourth largest energy source after coal, oil, and natural gas, biomass is known as a renewable zero-carbon energy source because its net carbon dioxide emissions are zero during the carbon cycle. Lignin, as one of the three important components of biomass, has a chemical structure that is a natural phenolic polymer formed by the random connection of phenylpropane structural units through C–C bonds and C–O bonds. The liquid oil formed after the depolymerization of lignin is mainly alkylphenols and guaiacol compounds, which are rich in aromatic ring structures on the earth and are considered ideal raw materials for replacing petrochemical phenols, alkylphenols, benzene, alkylbenzenes, and other bulk chemicals or fuels. Among them, phenol and alkylphenols are one of the most important aromatic chemicals in the chemical industry and are widely used in the synthesis of nonionic surfactants, agricultural chemicals, plastics, and pharmaceutical intermediates. However, due to the p–π conjugation formed between the oxygen of the methoxy group in guaiacol and the benzene ring, the competition between the cleavage of different C–O bonds and the hydrogenation reaction of the benzene ring, and the difference in the adsorption mode of the raw materials on the catalyst, the selectivity of demethoxylation is significantly reduced. In addition, most demethoxylation catalysts cause methylation side reactions of the target product due to the acidity of their carriers, making it difficult to obtain a single product. Therefore, constructing a catalyst that can efficiently remove methoxy groups while retaining the aromatic ring and phenolic hydroxyl groups is crucial for the selective deoxygenation of lignin-derived guaiacol.

[0003] Noble metals such as Pt, Pd, and Ru have high hydrogen activation ability and are prone to cause hydrogenation saturation of the aromatic ring; it is reported in Document 1 [ACS Catal. 2020, 10, 595] that after Pt is atomized, the hydrodeoxygenation activity of Pt1 / TiO2 is 1 / 40 of that of Pt cluster / TiO2, and the isolated Pt atoms have weak adsorption to m-cresol, inhibiting the cleavage of the C–O bond; it is reported in Document 2 [Angew. Chem. Int. Ed. 2024, e202404683] that Pt1 / TiO 2-xThe single-atom catalyst can convert 4-propylguaiacol into 4-propylphenol with a selectivity as high as 92.3%, but about 15% of the methylation products are detected at the same time; Patent 1 [CN 115894177 B] discloses that the atomically dispersed Ru-containing catalyst prepared by the impregnation-carbonization method catalyzes the selective demethoxylation reaction of guaiacol, and the selectivity of the product phenol is about 70%; Patent 2 [CN 113333006 A] discloses a highly dispersed Pd / MoC catalyst, its preparation method and its application in the selective hydrodeoxygenation of lignin derivatives to prepare alkylphenol compounds, and the highest yield of alkylphenol is 72.8%. Noble metals such as Au and Ag are located in Group IB of the periodic table. Due to their special d-band electron layer, they have a relatively large first ionization energy and are difficult to lose electrons. The interaction between metal particles and surface molecules is weak, resulting in weak hydrogen activation ability and difficulty in hydrogenating the benzene ring. Literature 3 [Green Chem. 2019, 21, 3081] reports that the Au / Nb2O5 catalyst can completely convert 4-propylguaiacol to obtain a mixed product of 4-propylphenol and 3-propylphenol with a selectivity of 84.2%. Literature 4 [J. Catal. 2019, 369, 396] reports that Ag / TiO2 can selectively demethoxylate guaiacol to phenol (selectivity is 67.1%). Among them, Ag serves as the dissociation center of H2, and the dissociated hydrogen overflows to the TiO2 surface, causing partial reduction to form oxygen vacancies, which become the subsequent demethoxylation active center of guaiacol. The above catalysts all use noble metal components, resulting in high catalyst costs. Patent 3 [CN 109503330 B] discloses a method for catalytically preparing phenol or alkylphenol by selective demethoxylation of lignin phenols using a bimetallic Co-Fe supported catalyst, which can significantly reduce the catalyst cost, but Co and Fe need to be reduced to the metallic state at a high temperature of 600 °C. Summary of the Invention

[0004] In the existing catalytic selective demethoxylation reaction of lignin phenols, there are often problems such as high catalyst cost, complex preparation, hydrogenation of the benzene ring in the product, and complete deoxygenation products. The purpose of the present invention is to provide an In2O3-TiO2 composite oxide catalyst, its preparation method and its application in the selective demethoxylation of lignin phenols. Utilizing the crystal defects and strong adsorption of TiO2, In2O3, which has no hydrogenation activity for the benzene ring, is selected as the hydrogen activation center to form an In2O3-TiO2 interface, an In-O-Ti structure and oxygen vacancies, promoting the adsorption and activation of the C aryl –OCH3 group and inhibiting benzene ring hydrogenation and the cleavage of the C aryl –OH bond, and inhibiting further methylation reactions, with excellent selective demethoxylation activity.

[0005] In order to achieve the above technical objectives, the technical solution of the present invention is as follows:

[0006] A preparation method of an In2O3-TiO2 composite oxide catalyst uses TiO2 as a carrier. An In salt is loaded onto TiO2 by an impregnation method and then calcined to obtain the In2O3-TiO2 catalyst. The TiO2 is obtained by using tetrabutyl titanate as a raw material, through hydrolysis, washing, drying, and calcination.

[0007] Further, the In salt is selected from one or more of indium nitrate, indium sulfate, indium phosphate, indium acetate, indium chloride, indium bromide, indium iodide, indium phosphide, and indium acetylacetonate.

[0008] Further, the content of In in the In2O3-TiO2 catalyst is 3-30 wt%, preferably 10-20 wt%.

[0009] Further, the solvent used in the impregnation method is one or more of water, methanol, ethanol, and acetone.

[0010] Further, the calcination temperature is 400-700 °C and the time is 1-24 h.

[0011] Further, after calcination, it is further treated by hydrogen reduction. The temperature of hydrogen reduction is not higher than 400 °C and the time is not higher than 24 h. In the present invention, low-temperature hydrogen reduction treatment after calcination will neither reduce In2O3 to metallic In, but also better form oxygen vacancies, further enhancing its selective demethoxylation activity.

[0012] The present invention also provides an In2O3-TiO2 composite oxide catalyst prepared by the above preparation method.

[0013] The present invention also provides the application of the above In2O3-TiO2 composite oxide catalyst, which is used for catalyzing the selective demethoxylation reaction of lignin phenolic compounds.

[0014] The beneficial effects of the present invention are as follows:

[0015] For the In2O3-TiO2 composite oxide catalyst of the present invention, by utilizing the crystal defects and strong adsorption of TiO2, and selecting In2O3, which has no hydrogenation activity for the benzene ring, as the hydrogen activation center, an In2O3-TiO2 interface, an In-O-Ti structure, and oxygen vacancies are formed. Among them, the oxygen vacancies on TiO2 promote the adsorption and activation of the C aryl –OCH3 group, and the oxygen vacancies on In2O3 promote the dissociation of hydrogen and inhibit the planar adsorption of guaiacol-like compounds and the cleavage of the C aryl –OH bond, and inhibit further methylation reactions, having excellent selective demethoxylation activity. Description of the Drawings

[0016] Figure 1 Scanning transmission electron microscope image of the In2O3-TiO2 catalyst prepared in Example 1;

[0017] As Figure 1 shown, the lattice fringes of In2O3 and TiO2 are intertwined, forming an In2O3-TiO2 interface and an In-O-Ti structure.

[0018] Figure 2 XRD patterns of the In2O3-TiO2 catalyst prepared in Example 1 and the In2O3 catalyst prepared in Comparative Example 2.

[0019] As Figure 2 shown, after adding TiO2 to In2O3, the characteristic diffraction peaks of In2O3 are significantly weakened, mainly because of the dispersion effect of TiO2 and the formation of the In-O-Ti structure that prevents the growth of In2O3 particles.

[0020] Figure 3 Comparison diagram of oxygen vacancies of the In2O3-TiO2 catalyst prepared in Example 1 before and after hydrogen reduction. Before reduction in the figure is In2O3-TiO2-No, and after reduction is In2O3-TiO2-300.

[0021] As Figure 3 shown, after hydrogen reduction treatment at 300 °C, the number of oxygen vacancies increases. Detailed implementation manners

[0022] The present invention will be further described in detail below with reference to specific embodiments, but the present invention is not limited thereto.

[0023] The reagents used in the examples are all of analytical grade, and the water is deionized water.

[0024] Example 1

[0025] Preparation of TiO2: 20 ml of tetrabutyl titanate was dissolved in 150 ml of deionized water, and hydrolysis reaction was carried out with vigorous stirring for 1 h, followed by suction filtration and washing, then drying at 60 °C in vacuum for 10 h, and then calcining at 500 °C for 4 h to obtain a TiO2 support.

[0026] Prepared according to an In loading of 10 wt%, 0.262 g of indium nitrate was dissolved in 20 mL of deionized water, then the above TiO2 support was added, and stirred vigorously for 1 h. After evaporation to dryness at 140 °C, it was continued to be dried at 60 °C in vacuum for 10 h, then calcined at 500 °C for 4 h, and finally reduced with hydrogen at 300 °C for 2 h to obtain an In2O3-TiO2 catalyst.

[0027] Take 0.1 g of the above catalyst, 1.2 g of 4-propylguaiacol and 15.0 g of n-dodecane and add them into a high-pressure reactor. Use the displacement method to remove the air in the reactor. Then, after adjusting the hydrogen pressure to 3.0 MPa, raise the temperature to 300 °C and continue the reaction for 10 h. The conversion rate reaches 99.1%, and the selectivity of propylphenol reaches 95.5%.

[0028] Example 2

[0029] Same as Example 1, the difference is that after calcination, no hydrogen reduction treatment is carried out and it is directly used in the reaction process. Under the same reaction conditions, the conversion rate of 4-propylguaiacol is 96.2%, and the selectivity of propylphenol is 92.5%.

[0030] Example 3

[0031] Prepare according to an In loading of 3 wt%. Dissolve indium sulfate in 20 mL of methanol, then add the TiO2 support prepared in Example 1, stir vigorously for 1 h, evaporate to dryness at 100 °C and then continue to dry in vacuum at 60 °C for 10 h. Then calcine it at 400 °C for 4 h, and finally reduce it with hydrogen at 400 °C for 2 h to obtain the In2O3-TiO2 catalyst.

[0032] Take 0.1 g of the above catalyst, 1.2 g of 4-propylguaiacol and 15.0 g of n-dodecane and add them into a high-pressure reactor. Use the displacement method to remove the air in the reactor. Then, after adjusting the hydrogen pressure to 3.0 MPa, raise the temperature to 300 °C and continue the reaction for 10 h. The conversion rate reaches 95.5%, and the selectivity of propylphenol is 80.7%.

[0033] Example 4

[0034] Prepare according to an In loading of 5 wt%. Dissolve indium chloride in 20 mL of acetone, then add the TiO2 support prepared in Example 1, stir vigorously for 1 h, evaporate to dryness at 100 °C and then continue to dry in vacuum at 60 °C for 10 h. Then calcine it at 600 °C for 4 h, and finally reduce it with hydrogen at 300 °C for 5 h to obtain the In2O3-TiO2 catalyst.

[0035] Take 0.1 g of the above catalyst, 1.2 g of 4-propylguaiacol and 15.0 g of n-dodecane and add them into a high-pressure reactor. Use the displacement method to remove the air in the reactor. Then, after adjusting the hydrogen pressure to 3.0 MPa, raise the temperature to 300 °C and continue the reaction for 10 h. The conversion rate reaches 98.0%, and the selectivity of propylphenol is 83.7%.

[0036] Example 5

[0037] Prepared with an In loading of 7.5 wt%, indium iodide was dissolved in 20 mL of water, and then the TiO₂ support prepared in Example 1 was added. After vigorously stirring for 1 h, it was evaporated to dryness at 140 °C and then dried at 60 °C under vacuum for 10 h. Then it was calcined at 600 °C for 24 h, and finally reduced with hydrogen at 300 °C for 5 h to obtain the In₂O₃-TiO₂ catalyst.

[0038] 0.1 g of the above catalyst, 1.2 g of 4-propylguaiacol, and 15.0 g of n-dodecane were added to a high-pressure reactor. The air in the reactor was removed by the displacement method. Then, after adjusting the hydrogen pressure to 3.0 MPa, the temperature was raised to 300 °C and the reaction was continued for 10 h. The conversion rate reached 97.2%, and the selectivity for propylphenol was 86.3%.

[0039] Example 6

[0040] Prepared with an In loading of 12.5 wt%, indium acetylacetonate was dissolved in 20 mL of acetone, and then the TiO₂ support prepared in Example 1 was added. After vigorously stirring for 1 h, it was evaporated to dryness at 100 °C and then dried at 60 °C under vacuum for 10 h. Then it was calcined at 500 °C for 5 h, and finally reduced with hydrogen at 200 °C for 5 h to obtain the In₂O₃-TiO₂ catalyst.

[0041] 0.1 g of the above catalyst, 1.2 g of 4-propylguaiacol, and 15.0 g of n-dodecane were added to a high-pressure reactor. The air in the reactor was removed by the displacement method. Then, after adjusting the hydrogen pressure to 3.0 MPa, the temperature was raised to 300 °C and the reaction was continued for 10 h. The conversion rate reached 96.8%, and the selectivity for propylphenol was 93.2%.

[0042] Example 7

[0043] Prepared with an In loading of 15 wt%, indium acetate was dissolved in 20 mL of water, and then the TiO₂ support prepared in Example 1 was added. After vigorously stirring for 1 h, it was evaporated to dryness at 100 °C and then dried at 60 °C under vacuum for 10 h. Then it was calcined at 500 °C for 4 h, and finally reduced with hydrogen at 100 °C for 24 h to obtain the In₂O₃-TiO₂ catalyst.

[0044] 0.1 g of the above catalyst, 1.2 g of 4-propylguaiacol, and 15.0 g of n-dodecane were added to a high-pressure reactor. The air in the reactor was removed by the displacement method. Then, after adjusting the hydrogen pressure to 3.0 MPa, the temperature was raised to 300 °C and the reaction was continued for 10 h. The conversion rate reached 95.9%, and the selectivity for propylphenol was 93.6%.

[0045] Example 8

[0046] Prepared with an In loading of 20 wt%, indium phosphate was dissolved in 20 mL of ethanol, and then the TiO2 support prepared in Example 1 was added. After vigorous stirring for 1 h, it was evaporated to dryness at 100 °C and then dried under vacuum at 60 °C for 10 h. Then it was calcined at 700 °C for 4 h to obtain the In2O3-TiO2 catalyst.

[0047] Take 0.1 g of the above catalyst, 1.2 g of 4-propylguaiacol, and 15.0 g of n-dodecane and add them to a high-pressure reactor. The air in the reactor was removed by the displacement method. Then, after adjusting the hydrogen pressure to 3.0 MPa, the temperature was raised to 300 °C and the reaction was continued for 10 h. The conversion rate reached 96.7%, and the selectivity of propylphenol was 92.8%.

[0048] Comparative Example 1

[0049] Same as Example 1, except that the catalyst was TiO2. Under the same reaction conditions, the conversion rate of 4-propylguaiacol was 96.0%, and the selectivity of alkylphenol was 47.0%.

[0050] Comparative Example 2

[0051] Same as Example 1, except that the catalyst was In2O3 (In2O3 was prepared by directly calcining and decomposing indium nitrate at 500 °C). Under the same reaction conditions, the conversion rate of 4-propylguaiacol was 78.5%, and the selectivity of propylphenol was 16.2%.

[0052] Comparative Example 3

[0053] Same as Example 1, except that the hydrogen reduction temperature was 600 °C. Under the same reaction conditions, the conversion rate of 4-propylguaiacol was 87.2%, and the selectivity of propylphenol was 65.2%.

[0054] Comparative Example 4

[0055] Same as Example 1, except that the support used was commercially purchased TiO2 (purchased from Macklin). Under the same reaction conditions, the conversion rate of 4-propylguaiacol was 79.6%, and the selectivity of propylphenol was 53.4%.

[0056] Comparative Example 5

[0057] Same as Example 1, except that the catalyst was In2O3-ZrO2, and the support used was commercially purchased ZrO2 (purchased from Macklin). Under the same reaction conditions, the conversion rate of 4-propylguaiacol was 89.0%, and the selectivity of propylphenol was 25.1%.

[0058] Comparative Example 6

[0059] Same as Example 1, except that the catalyst is In2O3-ZnO. The carrier is commercially purchased ZnO (purchased from Macklin). Under the same reaction conditions, the conversion rate of 4-propylguaiacol is 65.5%, and the selectivity of propylphenol is 9.0%.

[0060] Comparative Example 7

[0061] Same as Example 1, except that the catalyst is CuO-TiO2. Specifically, indium nitrate is replaced with copper nitrate. Under the same reaction conditions, the conversion rate of 4-propylguaiacol is 85.4%, and the selectivity of propylphenol is 56.8%.

Claims

1. A preparation method of an In2O3-TiO2 composite oxide catalyst, characterized in that: Using TiO2 as a carrier, an In salt is loaded onto TiO2 by an impregnation method, and then an In2O3-TiO2 catalyst is obtained through calcination; the TiO2 is obtained by using tetrabutyl titanate as a raw material, through hydrolysis, washing, drying, and calcination.

2. The preparation method according to claim 1, characterized in that: The In salt is selected from one or more of indium nitrate, indium sulfate, indium phosphate, indium acetate, indium chloride, indium bromide, indium iodide, indium phosphide, and indium acetylacetonate.

3. The preparation method according to claim 1, characterized in that: The content of In in the In2O3-TiO2 catalyst is 3-30 wt%.

4. The preparation method according to claim 3, characterized in that: The content of In in the In2O3-TiO2 catalyst is 10-20 wt%.

5. The preparation method according to claim 1, characterized in that: The solvent used in the impregnation method is one or more of water, methanol, ethanol, and acetone.

6. The preparation method according to claim 1, characterized in that: The calcination temperature is 400-700 °C, and the time is 1-24 h.

7. The preparation method according to any one of claims 1-6, characterized in that: After calcination, further hydrogen reduction treatment is carried out. The temperature of hydrogen reduction is not higher than 400 °C, and the time is not higher than 24 h.

8. The In2O3-TiO2 composite oxide catalyst prepared by the preparation method according to any one of claims 1-7.

9. Use of the In2O3-TiO2 composite oxide catalyst according to claim 8, characterized in that: It is used for catalyzing the selective demethoxylation reaction of lignin phenolic compounds.

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