Preparation method of niobium pentoxide loaded molybdenum disulfide catalyst and application of niobium pentoxide loaded molybdenum disulfide catalyst in lignin conversion

Abstract

The invention relates to a preparation method of a niobium pentoxide loaded molybdenum disulfide catalyst and application of the niobium pentoxide loaded molybdenum disulfide catalyst in lignin conversion. The preparation method comprises the following steps: dissolving ammonium molybdate heptahydrate and thiourea in distilled water, adding Nb2O5, and adjusting the pH value of the mixture to 0.8-1.1 by using hydrochloric acid; transferring the solution into a stainless steel autoclave for hydrothermal reaction; centrifugally separating to obtain a black precipitate, washing with water and absolute ethyl alcohol, and drying in vacuum overnight; and placing the obtained substance in a high-temperature and high-pressure reaction kettle, screwing the reaction kettle to seal the reaction kettle, discharging gas after introducing H2, discharging air in the device, pressurizing to 3-5 MPa, and reacting to obtain the catalyst Nb2O5-MoS2. The catalyst shows excellent activity of aromatic phenol and ether compound hydrodeoxygenation for aromatic hydrocarbon preparation. The invention provides the catalyst which is low in cost, simple and convenient to prepare and excellent in performance, after ten cycle experiments, the activity of the catalyst is still stable, and the indexes of the conversion rate and the yield are reduced by less than 5%.

Description

Technical Field

[0001] This invention belongs to the fields of industrial catalysis and bioenergy conversion technology, and particularly relates to a novel catalyst and preparation method for catalyzing the hydrodeoxygenation of lignin to produce aromatics. Specifically, it relates to a method for preparing a niobium pentoxide-supported molybdenum disulfide catalyst and its application in lignin conversion. Background Art

[0002] Biomass energy, derived from solar energy stored in the form of chemical energy, is the fourth largest energy source after coal, oil, and natural gas. It is currently the only sustainable, renewable source of organic carbon in nature and a key option for addressing the fossil energy crisis. Of the three components of biomass, lignin has a C / H ratio closest to that of petroleum and is the only renewable resource in nature containing aromatic ring structures. Lignin undergoes upstream processing to produce smaller molecular weight lignin-derived bio-oils, composed of compounds such as phenols, ethers, furans, and ketones. These derivatives have the potential to produce aromatic commodity chemicals and, due to their high carbon content, are also promising candidates for the production of high-energy-density fuels. However, excessive oxygen content is a significant challenge in their application. Hydrodeoxygenation (HDO) is a widely used and effective method for converting lignin-derived oxygenates into stable deoxygenated products. Through the HDO reaction, the long chains of lignin are broken down, yielding high-quality fuels such as aromatics and alkanes, as well as high-value-added fine chemicals such as phenols. However, because lignin is composed of randomly linked monomers with varying oxidation levels, its structural complexity and heterogeneity complicate its processing and utilization. In practical HDO research, specific lignin model compounds with typical CO bonds and aromatic structures (such as aromatic phenols and ether compounds) are often selected for investigation. Existing techniques for evaluating HDO performance often utilize micro-reactors (such as high-temperature and high-pressure reactors) to combine a predetermined amount of catalyst and substrate with hydrogen in a closed reaction system. After the reaction, the product composition and content are analyzed using gas chromatography.

[0003] By designing a suitable catalyst, it is expected to achieve the selective activation and cleavage of chemical bonds in lignin, thereby obtaining a certain or a certain type of specific target product with high selectivity and realizing directional catalytic conversion. MoS2-based catalysts are low in price and have good catalytic performance, and are favored by many researchers. However, in the HDO process, due to the selective cleavage of C Ar -OH groups are often accompanied by the generation of water. At the same time, HDO usually requires relatively high temperatures. Therefore, MoS2-based catalysts will undergo some inevitable changes, including sulfur loss, poisoning, sintering and coke deposition. These changes will significantly affect the HDO activity. Therefore, the problem of easy deactivation of MoS2-based catalysts needs to be solved urgently.

[0004] Nb2O5 is an oxide with abundant acidic sites. In recent years, great progress has been made in the field of catalysis, and various types of catalytic reactions have been developed, including hydrogenation and dehydrogenation, dehydration and hydration. In the catalytic conversion application of lignin and its model compounds, the role of Nb2O5 is mainly the support in the supported metal catalyst, which can improve the catalyst performance in the following three aspects: 1) Promote the breaking of the CO bond. Nb2O5 can minimize the energy required for the breaking of the CO bond (Δ = 1.35eV). Once the CO bond breaks and aromatics are formed, their adsorption is weakened, and they are easily desorbed from the catalyst surface and quickly leave the reaction system. Therefore, Nb2O5 has excellent selectivity for aromatics. 2) Metal-support interaction. H2 is dissociated by the active metal to form H radicals and transfer to the surface of the Nb2O5 support, promoting the reduction of Nb2O5, thereby promoting the formation of oxygen-philic sites. At the same time, when the active metal is partially absorbed by NbO x The exposed metal sites provide dissociated hydrogen, while the oxygen-philic sites on Nb2O5 activate oxygen in phenolic compounds, promoting the HDO process. 3) Excellent water resistance. Nb2O5 possesses water-resistant Lewis acid sites, which can maintain a good structure without being destroyed in an aqueous environment. Water not only provides a catalytic reaction environment but also inhibits the occurrence of side reactions, improving the selectivity of the deoxygenated product.

[0005] This technology is based on a catalyst modification strategy and is dedicated to improving the cyclic stability of MoS2-based catalysts. A new sulfide catalyst of Nb2O5-loaded MoS2 was innovatively designed and synthesized, which improved the substrate conversion rate and aromatic hydrocarbon yield of the hydrodeoxygenation reaction of lignin model aromatic phenols and ether compounds. At the same time, the catalytic activity of the catalyst remained stable after multiple cycles (the conversion rate and yield indicators decreased by less than 5% after ten cycles), achieving the high activity and high stability of the MoS2-based catalyst in this reaction. Summary of the Invention

[0006] The present invention provides a preparation method of a Nb2O5-loaded MoS2-based catalyst and its application in catalyzing the hydrodeoxygenation of lignin model aromatic phenols and ether compounds to produce aromatic hydrocarbons.

[0007] The present invention aims to improve the substrate conversion rate, aromatic product yield and cycle stability of the hydrodeoxygenation reaction of lignin model aromatic phenols and ether compounds catalyzed by MoS2-based catalysts. Based on the MoS2-based catalyst modification strategy, a preparation method of Nb2O5-loaded MoS2-based catalysts is developed by precisely controlling the synergistic effect between the carrier and the active components, which achieves a significant improvement in conversion rate, yield and cycle stability.

[0008] In order to achieve the above objectives, the technical solution adopted by the present invention is:

[0009] A niobium pentoxide-supported molybdenum disulfide catalyst, represented by Nb2O5-MoS2.

[0010] The present invention provides a method for preparing a Nb2O5-loaded MoS2-based catalyst, comprising the following steps:

[0011] a) dissolving ammonium molybdate heptahydrate and thiourea in distilled water, adding Nb2O5, and adjusting the pH of the mixture to 0.8-1.1 with hydrochloric acid;

[0012] The solution was then transferred to a polytetrafluoroethylene-lined stainless steel autoclave for hydrothermal reaction. After the reaction was complete, the resulting black precipitate was separated by centrifugation, washed with water and anhydrous ethanol, and then dried under vacuum overnight.

[0013] b) placing the substance obtained in step a) in a high-temperature and high-pressure reactor, tightening the reactor to seal it, introducing H2 and then venting it. After the air in the device is discharged, the pressure is increased to 3-5 MPa to start the reaction to obtain the catalyst Nb2O5-MoS2.

[0014] In the step a), the mass feed ratio of sodium molybdate heptahydrate to thiourea is 1:4-5, and the Nb / Mo molar ratio is 0.11-0.33.

[0015] The hydrothermal reaction temperature in step a) is 160-200° C. and the reaction time is 12-24 hours.

[0016] In the step b), the reaction temperature is 280-300° C., and the reaction time is 3-5 hours.

[0017] The application of the Nb2O5-loaded MoS2 catalyst in lignin conversion of the present invention comprises the following steps:

[0018] a) The reaction substrate, catalyst, internal standard substance and reaction solvent are fully mixed and added to the reaction kettle, which is sealed and the air in the kettle is replaced with hydrogen, and then the pressure in the kettle is filled with hydrogen to the target pressure of 3 to 5 MPa;

[0019] b) heating the reactor to 280-300°C and starting stirring for 3-5 hours;

[0020] c) After the reaction, stirring was stopped and the temperature was lowered to room temperature. The pressure was then released and the kettle was opened to separate the liquid product and the catalyst. The liquid product was qualitatively and quantitatively analyzed by mass spectrometry-gas chromatography to calculate the substrate conversion rate and the yield of the aromatic product.

[0021] The reaction substrate used is one of lignin model aromatic phenol compounds such as p-cresol, o-cresol, m-cresol, phenol, guaiacol, and 2-ethylphenol, and one of lignin model ether compounds such as anisole and diphenyl ether; the reaction solvent is one of n-pentane, n-hexane, and n-heptane.

[0022] The mass ratio of the catalyst to the substrate is 1:0.4-1.

[0023] The significant advantages of the present invention are:

[0024] 1. The Nb2O5-loaded MoS2 catalyst of the present invention is prepared using conventional cheap chemicals as raw materials, which is low in cost and has a simple and easy preparation process, and consumes less time, materials and energy.

[0025] 2. The doping of Nb2O5 increases the surface area of ​​the catalyst and the number of stacking layers of MoS2, providing more active sites and more strong acid sites, which promotes the breaking of the CO bond of phenolic substances, showing excellent activity in the hydrodeoxygenation of aromatic phenols and ether compounds to produce aromatic hydrocarbons, and achieving a significant increase in the conversion rate of the phenolic and ether compounds and the yield of single aromatic hydrocarbon products.

[0026] 3. The catalyst described in the present invention has excellent cyclic stability. Compared with the problem of easy deactivation of MoS2-based catalysts in the prior art, the catalyst described in this technology still maintains a high activity after ten cycle experiments, and the yield of aromatic products has hardly decreased. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The XRD pattern of the sample described in Example 2 DETAILED DESCRIPTION

[0028] In order to make the contents of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0029] Example 1

[0030] a) Dissolve 0.68 g of ammonium molybdate heptahydrate and 2.72 g of thiourea in distilled water, add 0.0574 g of Nb2O5, and adjust the pH of the mixture to 0.8 with hydrochloric acid. The solution is then transferred to a Teflon-lined stainless steel autoclave and reacted at 160°C for 12 hours. After the hydrothermal reaction, the resulting black precipitate is separated by centrifugation, washed with water and anhydrous ethanol, and then dried under vacuum overnight.

[0031] b) Place the sample in a high-temperature, high-pressure reactor, tighten the reactor to seal it, connect the apparatus, introduce H2, and then vent the air. After exhausting the air from the apparatus, pressurize the apparatus to a preset initial pressure of 3 MPa. Set the reaction temperature to 280°C and the reaction time to 3 hours. The pretreated catalyst is designated Nb2O5-MoS2-1.

[0032] Example 2

[0033] a) Dissolve 0.68 g of ammonium molybdate heptahydrate and 3.06 g of thiourea in distilled water, add 0.0731 g of Nb2O5, and adjust the pH of the mixture to 0.9 with hydrochloric acid. The solution is then transferred to a Teflon-lined stainless steel autoclave and reacted at 170°C for 16 hours. After the hydrothermal reaction, the resulting black precipitate is centrifuged, washed with water and anhydrous ethanol, and then vacuum-dried overnight.

[0034] b) Place the sample in a high-temperature, high-pressure reactor, tighten the reactor to seal it, connect the device, introduce H2, and then release the air. After the air in the device is exhausted, pressurize to the preset initial pressure value of 3MPa, set the reaction temperature to 300℃, and the reaction time to 3h. The pretreated catalyst is recorded as Nb2O5-MoS2-2, and the XRD spectrum of the corresponding sample is as follows: Figure 1 As shown, the catalyst exhibits typical Nb2O5 diffraction peaks at 2θ = 22.6°, 28.3°, 28.9°, 36.5°, 46.1°, and 50.9°, corresponding to the characteristic crystal planes (001), (180), (200), (181), (002), and (380), respectively. For the MoS2 component, two crystal phases, 1T and 2H, appear. The characteristic peaks at 2θ = 9.3° and 18.2° correspond to the (002) and (004) crystal planes of 1T-MoS2, while the characteristic peaks at 2θ = 32.7°, 39.5°, and 58.3° correspond to the (100), (103), and (110) crystal planes of 2H-MoS2, respectively.

[0035] Example 3

[0036] a) Dissolve 0.68 g of ammonium molybdate heptahydrate and 3.40 g of thiourea in distilled water, add 0.104 g of Nb2O5, and adjust the pH of the mixture to 1.0 with hydrochloric acid. The solution is then transferred to a Teflon-lined stainless steel autoclave and reacted at 180°C for 20 h. After the hydrothermal reaction, the resulting black precipitate is separated by centrifugation, washed with water and anhydrous ethanol, and then dried in vacuo overnight.

[0037] b) Place the sample in a high-temperature, high-pressure reactor, tighten the reactor to seal it, connect the apparatus, introduce H2, and then vent the air. After exhausting the air from the apparatus, pressurize the apparatus to a preset initial pressure of 4 MPa. Set the reaction temperature to 300°C and the reaction time to 4 hours. The pretreated catalyst is designated Nb2O5-MoS2-3.

[0038] Example 4

[0039] a) Dissolve 0.68 g of ammonium molybdate heptahydrate and 3.40 g of thiourea in distilled water, add 0.172 g of Nb2O5, and adjust the pH of the mixture to 1.1 with hydrochloric acid. The solution is then transferred to a Teflon-lined stainless steel autoclave and reacted at 200°C for 24 hours. After the hydrothermal reaction, the resulting black precipitate is separated by centrifugation, washed with water and anhydrous ethanol, and then vacuum-dried overnight.

[0040] b) Place the sample in a high-temperature, high-pressure reactor, tighten the reactor to seal it, connect the apparatus, introduce H2, and then vent the air. After exhausting the air from the apparatus, pressurize the apparatus to a preset initial pressure of 5 MPa. Set the reaction temperature to 300°C and the reaction time to 5 hours. The pretreated catalyst is designated Nb2O5-MoS2-4.

[0041] Example 5

[0042] p-Cresol Hydrodeoxygenation

[0043] a) adding 54 mg of the Nb2O5-MoS2-1 catalyst obtained according to Example 1 and 10 mL of an n-pentane solution containing 0.125 mol / L p-cresol and 0.125 mol / L n-dodecane to a high-temperature and high-pressure reactor;

[0044] b) The air in the autoclave was replaced with hydrogen three times, and then hydrogen was added to the autoclave until the initial pressure was 3 MPa. The temperature was raised to 300°C, the stirring rate was 1000 rpm, and the reaction time was 3 h.

[0045] c) After the reaction, stirring was stopped and the temperature was lowered to room temperature. The pressure was then released and the kettle was opened to separate the liquid product and the catalyst. The liquid product was qualitatively and quantitatively analyzed by mass spectrometry-gas chromatography to calculate the substrate conversion rate and the yield of the aromatic product.

[0046] The reaction results are shown in Table 1.

[0047] Table 1. Conversion results of p-cresol catalyzed by Nb2O5-MoS2-1

[0048]

[0049] Example 6

[0050] p-Cresol Hydrodeoxygenation

[0051] The implementation scheme is basically the same as Example 5, except that the catalyst described in Example 2 is selected and n-hexane is selected as the reaction solvent. The reaction results are shown in Table 2.

[0052] Table 2. Conversion results of p-cresol catalyzed by Nb2O5-MoS2-2

[0053]

[0054] Example 7

[0055] p-Cresol Hydrodeoxygenation

[0056] The implementation scheme is basically the same as Example 5, except that the catalyst described in Example 3 is selected and n-heptane is selected as the reaction solvent. The reaction results are shown in Table 3.

[0057] Table 3. Conversion results of p-cresol catalyzed by Nb2O5-MoS2-3

[0058]

[0059] Example 8

[0060] p-Cresol Hydrodeoxygenation

[0061] The implementation scheme is basically the same as Example 5, except that the catalyst described in Example 4 is selected and n-hexane is selected as the reaction solvent. The reaction results are shown in Table 4.

[0062] Table 4. Conversion results of p-cresol catalyzed by Nb2O5-MoS2-4

[0063]

[0064] Example 9

[0065] p-Cresol Hydrodeoxygenation

[0066] The implementation scheme is basically the same as Example 6, except that the reaction temperature is adjusted from 300°C to 280°C. The reaction results are shown in Table 5.

[0067] Table 5. Conversion results of p-cresol catalyzed by Nb2O5-MoS2-2

[0068]

[0069] Example 10

[0070] p-Cresol Hydrodeoxygenation

[0071] The implementation scheme is basically the same as Example 6, except that the initial hydrogen pressure is adjusted from 3 MPa to 4 MPa or 5 MPa. The reaction results are shown in Table 6.

[0072] Table 6. Conversion results of p-cresol catalyzed by Nb2O5-MoS2-2

[0073]

[0074] Example 11

[0075] p-Cresol Hydrodeoxygenation

[0076] The implementation scheme is basically the same as Example 6, except that the reaction time is adjusted from 3 h to 4 h or 5 h. The reaction results are shown in Table 7.

[0077] Table 7. Conversion results of p-cresol catalyzed by Nb2O5-MoS2-2

[0078]

[0079] Example 12

[0080] p-Cresol Hydrodeoxygenation

[0081] The implementation scheme is basically the same as Example 6, except that the amount of catalyst used is adjusted from 54 mg to 67.5, 81 and 108 mg. The reaction results are shown in Table 8.

[0082] Table 8. Conversion results of p-cresol catalyzed by Nb2O5-MoS2-2

[0083]

[0084]

[0085] Example 13

[0086] Cyclic stability test of catalyst for p-cresol hydrodeoxygenation reaction

[0087] The catalyst from Example 6 was filtered, separated, washed multiple times with n-hexane and ethanol, and vacuum-dried to obtain a Nb2O5-MoS2-2 catalyst after one cycle. This catalyst was then used in the hydrodeoxygenation of p-cresol under the same operating conditions as in Example 6. This operation was repeated 10 times, and the activity data for each of the 10 cycles were measured. The reaction results are shown in Table 9.

[0088] Table 9. Stability test results of Nb2O5-MoS2-2 catalytic conversion of p-cresol

[0089]

[0090] The results in Table 9 show that the catalytic activity of the catalyst remains stable after multiple cycles, and the substrate conversion rate and product yield indicators decrease by less than 5%, indicating that the catalyst has good cyclic stability.

[0091] Example 14

[0092] Hydrodeoxygenation of different aromatic phenols and ethers

[0093] The implementation scheme is basically the same as Example 6, except that the reaction substrate is replaced with 0.125 mol / L o-cresol, m-cresol, phenol, guaiacol, 2-ethylphenol, anisole, and diphenyl ether, the reaction temperature is 300° C., and the reaction results are shown in Table 10.

[0094] Table 10. Conversion results of different lignins catalyzed by Nb2O5-MoS2-2

[0095]

[0096]

[0097] The results in Table 10 show that the catalyst has high catalytic activity for the hydrodeoxygenation of various aromatic phenols and ether compounds to aromatic hydrocarbons.

[0098] In summary, the present invention focuses on the preparation of a niobium pentoxide-loaded molybdenum disulfide catalyst and its application in lignin conversion. In terms of application effect, it shows significant advantages. From the catalytic performance point of view, it has high conversion rate and high aromatic hydrocarbon yield for a variety of lignins such as o-cresol, m-cresol, phenol, etc. In terms of cyclic stability, after ten cycle experiments, the catalyst activity remained stable, and the conversion rate and yield indicators decreased by less than 5%, which solved the problem of poor cyclic stability of traditional MoS2-based catalysts. Overall, the invention provides a low-cost, easy-to-prepare and excellent performance catalyst, which provides a more efficient and stable way to convert aromatic phenols and ether compounds into aromatic hydrocarbons, and has broad application prospects.

[0099] The present invention discloses a preparation method of a niobium pentoxide-supported molybdenum disulfide catalyst and its application in catalyzing the hydrodeoxygenation of lignin to produce aromatic hydrocarbons. A niobium pentoxide-supported molybdenum disulfide catalyst is represented by Nb2O5-MoS2. The catalyst is prepared using conventional inexpensive chemicals as raw materials, has low cost, and the preparation process is simple and easy, and consumes less time, materials, and energy. The doping of Nb2O5 in the catalyst increases the surface area of ​​the catalyst and increases the number of stacking layers of MoS2, providing more active sites and more strong acid sites, thereby promoting the breaking of the CO bond of phenolic substances and showing excellent activity in the hydrodeoxygenation of aromatic phenols and ether compounds to produce aromatic hydrocarbons. The catalyst of the present invention has excellent cyclic stability, maintains a high activity after ten cycle experiments, and the yield of aromatic hydrocarbon products remains almost unchanged. Compared with the prior art, the catalytic activity and stability of the catalyst under mild conditions are significantly improved.

[0100] The technical solutions disclosed and proposed by the present invention can be implemented by those skilled in the art by drawing on the content of this document and appropriately changing the conditions, routes, and other aspects. Although the methods and preparation techniques of the present invention have been described through preferred embodiments, it is obvious that those skilled in the art can modify or recombine the methods and technical routes described herein without departing from the content, spirit, and scope of the present invention to achieve the ultimate preparation technology. It is particularly important to point out that all similar substitutions and modifications that are obvious to those skilled in the art are considered to be included in the spirit, scope, and content of the present invention.

Claims

1. A method for preparing a niobium pentoxide-supported molybdenum disulfide catalyst, characterized in that: The steps include: a) dissolving ammonium molybdate heptahydrate and thiourea in distilled water, adding Nb2O5, and adjusting the pH of the mixture to 0.8-1.1 with hydrochloric acid; then transferring the solution to a polytetrafluoroethylene-lined stainless steel autoclave for a hydrothermal reaction; after completion of the reaction, separating the resulting black precipitate by centrifugation, washing with water and anhydrous ethanol, and drying under vacuum overnight; b) placing the substance obtained in step a) in a high-temperature and high-pressure reactor, tightening the reactor to seal it, introducing H2 and then venting it. After the air in the device is discharged, the pressure is increased to 3-5 MPa to start the reaction to obtain the catalyst Nb2O5-MoS2.

2. The preparation method according to claim 1, wherein In step a), the mass feed ratio of sodium molybdate heptahydrate to thiourea is 1:4-5, and the Nb / Mo molar ratio is 0.11-0.

33.

3. The preparation method according to claim 1, wherein In step a), the hydrothermal reaction temperature is 160-200° C. and the reaction time is 12-24 hours.

4. The preparation method according to claim 1, wherein In step b), the reaction temperature is 280-300° C., and the reaction time is 3-5 hours.

5. Use of the Nb2O5-loaded MoS2 catalyst prepared by the method of claim 1 in the conversion of lignin model compounds.

6. Use of the Nb2O5-supported MoS2 catalyst prepared by the method of claim 5 in the conversion of lignin model compounds, characterized in that: The steps include: a) The reaction substrate, catalyst, internal standard substance and reaction solvent are fully mixed and added to the reaction kettle, which is sealed and the air in the kettle is replaced with hydrogen, and then the pressure in the kettle is filled with hydrogen to the target pressure of 3 to 5 MPa; b) heating the reactor to 280-300°C and starting stirring for 3-5 hours; c) After the reaction, stirring was stopped and the temperature was lowered to room temperature. The pressure was then released and the kettle was opened to separate the liquid product and the catalyst. The liquid product was qualitatively and quantitatively analyzed by mass spectrometry-gas chromatography to calculate the substrate conversion rate and the yield of the aromatic product.

7. The use according to claim 6, characterized in that: The reaction substrate is one of the lignin model aromatic phenol compounds of p-cresol, o-cresol, m-cresol, phenol, guaiacol and 2-ethylphenol and the lignin model ether compounds of anisole and diphenyl ether.

8. The use according to claim 6, characterized in that: The reaction solvent is selected from one of n-pentane, n-hexane and n-heptane.

9. The use according to claim 6, characterized in that: The mass ratio of the catalyst to the substrate is 1:0.4-1.

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