A method for photocatalytic selective oxidation of alkanes to the corresponding monohydric alcohol

Abstract

The application provides a method for photocatalytic selective oxidation of alkane to prepare corresponding monohydric alcohol. The method comprises a reaction solvent system used by the method and a heterogeneous catalyst used by the method. The reaction solvent system is perfluoroalkane or a two-phase system composed of perfluoroalkane and other solvents. The heterogeneous catalyst used is a supported molybdenum catalyst. The method provided by the application has the characteristics of mild reaction condition, high efficiency and high product selectivity, and has good practicability and application prospect.

Description

Technical Field

[0001] This invention relates to a method for the selective oxidation of alkanes to corresponding monohydric alcohols via photocatalysis. Background Technology

[0002] Alkanes are both a clean energy source and an important chemical raw material. Monohydric alcohols are important chemical products and platform compounds. Selective oxidation of alkanes can produce corresponding monohydric alcohols; for example, the oxidation of methane to methanol. The oxidation of methane to methanol has many advantages, including low energy consumption, low investment, and low greenhouse gas emissions. However, current methane-to-methanol production mainly uses an indirect conversion method, where methane is first converted to syngas via steam reforming or carbon dioxide reforming, and then the syngas is converted to methanol. The methane reforming to syngas is a strongly endothermic reaction, carried out at high temperatures (800-1000℃). The process route for producing methanol from methane via syngas is relatively long, the reaction is carried out under high temperature and pressure, resulting in high energy consumption and equipment investment, leading to high production costs.

[0003] Photocatalytic oxidation of methane to methanol can occur at room temperature, offering the advantage of mild reaction conditions. Current research on photocatalytic methane oxidation to methanol using oxygen as the oxidant generally uses water as the solvent. This is because methane is insoluble in water, while methanol is miscible with water in any proportion. Furthermore, methanol is more reactive than methane, making it more readily oxidized to carbon dioxide under the same reaction conditions.

[0004] Ye Jinhua et al. studied the photocatalytic oxidation of methane to methanol in water using TiO2 with different crystal facets as catalysts, and found that TiO2 with the 001 crystal facet can efficiently catalyze the oxidation of methane to methanol. Tang Junwang et al. found that Au-Cu bimetallic modified ZnO can efficiently oxidize methane to methanol, peroxymethanol, and formaldehyde in aqueous solution, with selective oxidation product yields as high as 11225 μmol·g. -1 ·h -1 .

[0005] Currently, the oxidation of alkanes to their corresponding monohydric alcohols still faces challenges such as high reaction temperatures and low selectivity for the target product. This invention provides a method for the photocatalytic oxidation of alkanes to their corresponding monohydric alcohols using a supported molybdenum-based catalyst in a two-phase system consisting of perfluoroalkanes or perfluoroalkanes and other solvents. Summary of the Invention

[0006] The purpose of this invention is to provide a method for the selective oxidation of alkanes to the corresponding monohydric alcohols via photocatalysis. To achieve the above objective, the technical solution adopted by this invention is as follows: Specifically, a supported molybdenum catalyst and a solvent are added to a container, and after the container is sealed, alkanes and oxygen are introduced. The reaction is carried out under ultraviolet light for 0.1-100 hours, and then the reaction system is cooled to room temperature, where a monohydric alcohol compound is generated on the upper layer of perfluoroalkanes.

[0007] According to a specific embodiment of the present invention, the solvent system is a solvent containing perfluoroalkane;

[0008] Specifically, it refers to: perfluoroalkanes, or two-phase systems composed of perfluoroalkanes and other solvents that are immiscible with perfluoroalkanes;

[0009] In the solvent system, the volume ratio of perfluoroalkanes and other solvents immiscible with perfluoroalkanes varies from 0.01 to 100, preferably from 0.2 to 5, and more preferably from 0.5 to 2.

[0010] According to a specific embodiment of the present invention, the perfluoroalkane includes one or more of the following: perfluoropentane, perfluorohexane, perfluorocyclohexane, perfluoromethylcyclohexane, perfluoroheptane, perfluorooctane, perfluorononane, perfluorodecane, perfluoroundecane, perfluorododecane, perfluorotridecane, perfluorotetradecane, perfluoropentadecane, perfluorohexadecane, perfluoroheptadecane, perfluorooctadecane, perfluorononadecane, perfluoroeicosane, perfluoronaphthane, perfluoroadamantane, perfluoro-1,3-dimethylcyclohexane, perfluoro(methylcyclopentane), perfluoro-2-methylpentane, and perfluoro-1,2-dimethylcyclobutane.

[0011] According to a specific embodiment of the present invention, the other solvents that are immiscible with perfluoroalkanes include one or more of water, alcohols, and organic acids.

[0012] According to a specific embodiment of the present invention, the alcohol includes one or more of monohydric alcohols, dihydric alcohols, and trihydric alcohols;

[0013] According to a specific embodiment of the present invention, the monohydric alcohol includes one or more of methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, heptanol, and undecaneol.

[0014] The diols mentioned include one or more of ethylene glycol, propylene glycol, butanediol, pentanediol, and hexanediol;

[0015] The triols include one or more of trimethylolpropane and glycerol;

[0016] The acids mentioned include one or more of the following: formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, heptanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, and eicosanoic acid.

[0017] According to a specific embodiment of the present invention, the molybdenum loading in the supported molybdenum catalyst is between 0.01% and 25% of the catalyst mass, preferably 0.1% to 5%, and more preferably 0.1% to 1%.

[0018] According to a specific embodiment of the present invention, the support for the supported molybdenum catalyst is one or more of alumina, silicon oxide, cerium oxide, zirconium oxide, magnesium oxide, zinc oxide, and tungsten oxide; preferably, the support includes one or two of silicon oxide and alumina.

[0019] According to a specific embodiment of the present invention, the supported molybdenum catalyst further includes an electronic additive, which includes one or more of copper, silver, gold, platinum, palladium, rhodium, ruthenium, and iridium. The loading of the electronic additive is between 0.01% and 10% of the catalyst mass, preferably 0.1% to 3%, and more preferably 0.3% to 2%.

[0020] According to a specific embodiment of the present invention, the alkane includes one or more of methane, ethane, propane, isopropane, butane, dimethylpropane, pentane, hexane, and cyclohexane.

[0021] According to a specific embodiment of the present invention, the ultraviolet light wavelength is 200-400nm, preferably 280-400nm, and more preferably 320-400nm.

[0022] According to a specific embodiment of the present invention, the reaction time is preferably 1-20 h, more preferably 2-12 h. The reaction temperature is 0-100℃, preferably 40-100℃, more preferably 60-80℃.

[0023] The present invention will be described in detail below through specific embodiments, but these embodiments do not constitute a limitation on the content of the present invention.

[0024] The method provided by this invention has the characteristics of mild reaction conditions, high efficiency, and high product selectivity, and has good practicality and application prospects. Detailed Implementation

[0025] Example 1

[0026] Preparation of molybdenum-supported catalysts with different electronic additives:

[0027] Taking the preparation of a molybdenum-supported catalyst CuMoOx / Al2O3 with copper as the electronic additive and alumina as the support as an example: Copper nitrate and ammonium molybdate were dissolved in water, and alumina was impregnated in equal volumes. After drying at 110℃ for 12 h, the catalysts were calcined at 500℃ for 4 h in air atmosphere to obtain CuMoOx / Al2O3 catalysts with molybdenum loadings of 0.3, 0.6, and 1.2 wt% and corresponding copper loadings of 0.2, 0.4, and 0.8 wt% (x represents the number of oxygen atoms coordinated with copper and molybdenum). By replacing the electronic additive and support with other metals and supports (MgO, SnO2, WO3, Y2O3, CeO2, or ZnO), catalysts such as CuMoOx / SiO2, AuMoOx / SiO2, and AuMoOx / Al2O3 can be synthesized.

[0028] The preparation process of other catalysts used in the following examples is the same as above, except that the types of supports and / or electronic additives used are different.

[0029] Example 2

[0030] CuMoOx / Al2O3 photocatalyst for methane oxidation to methanol:

[0031] 0.01 g of CuMoOx / Al2O3 (molybdenum loading of 0.3 wt% and copper loading of 0.2 wt%) prepared in Example 1 was added to 2.5 mL of perfluorooctane (perfluorooctane apparatus in a reaction vessel, the same below). After sealing the reaction vessel, 1 bar of air and 38 bar of 5% CH4 / Ar (CH4 and Ar mixture with a volume content of 5% CH4, the same below) were introduced into the reaction vessel. After irradiation with 100 W 365 nm LED light for 2 h, samples were taken, and gas phase and liquid phase products were quantitatively analyzed by gas chromatography to calculate the raw material conversion rate and the selectivity of various products.

[0032] Conversion rate [mol%] = (A0 - A) / A0 × 100%

[0033] Selectivity [mol%] = B / (A0-A) × 100%

[0034] In the formula, A0 is the amount of methane added before the reaction [mol], A is the amount of methane after the reaction [mol], and B is the amount of methanol produced during the reaction [mol].

[0035] After the reaction, the methanol conversion rate was 0.34%, the methanol selectivity was 18%, and the carbon dioxide selectivity was 82%.

[0036] Example 3

[0037] Comparison of the performance of supported molybdenum catalysts (0.3 wt% molybdenum loading and 0.2 wt% copper loading) on ​​the methane oxidation reaction:

[0038] Except for the catalyst, the other reaction conditions were the same as in Example 2. The reaction results are shown in Table 1.

[0039] Table 1 CuMoO X Comparison of the catalytic performance of Support catalysts for methane oxidation

[0040]

[0041]

[0042] Example 4

[0043] Comparison of the performance of supported molybdenum catalysts with different electronic additives (molybdenum loading of 0.3 wt%, gold, silver or copper loading of 0.2 wt%, and alumina support) in the catalytic reaction of methane oxidation:

[0044] Except for the catalyst, the other reaction conditions were the same as in Example 2. The reaction results are shown in Table 2.

[0045] Table 2 metal-MoO X Comparison of the catalytic performance of Al2O3 catalysts for methane oxidation

[0046]

[0047] Example 5

[0048] Supported molybdenum catalysts CuMoO in different solvents X Comparison of the performance of Al2O3 (0.3wt% molybdenum loading, 0.2wt% gold, silver or copper loading, alumina support) in catalyzing methane oxidation:

[0049] Except for the different solvent, the reaction conditions were the same as in Example 2. The reaction results are shown in Table 3.

[0050] Table 3 CuMoO X Comparison of the catalytic performance of Al2O3 catalysts for methane oxidation

[0051]

[0052]

[0053] Example 6

[0054] Comparison of the performance of a supported molybdenum catalyst in the methane oxidation reaction of a two-phase system consisting of water and perfluorooctane (2.5 mL):

[0055] Except for the different solvent, the reaction conditions were the same as in Example 2. The reaction results are shown in Table 4.

[0056] Table 4 CuMoO X Comparison of the catalytic performance of Al2O3 catalysts for methane oxidation

[0057]

[0058] Example 7

[0059] Comparison of the performance of supported molybdenum catalysts in the methane oxidation reaction in two-phase solvent systems composed of other organic solvents (alcohols, acids) and perfluorooctane (2.5 mL):

[0060] Except for the different solvent, the reaction conditions were the same as in Example 2. The reaction results are shown in Table 5.

[0061] Table 5 CuMoO X Comparison of the catalytic performance of Al2O3 catalysts for methane oxidation

[0062]

[0063]

[0064] Example 8

[0065] Comparison of the performance of supported molybdenum catalysts in catalyzing different alkane oxidation reactions:

[0066] Except for the different alkane reactants, the reaction conditions were the same as in Example 2. The reaction results are shown in Table 6.

[0067] Table 6 CuMoO X Comparison of the catalytic performance of Al2O3 catalysts for methane oxidation

[0068]

[0069] Example 9

[0070] Comparison of the performance of supported molybdenum catalysts in catalyzing different alkane oxidation reactions:

[0071] Except for the catalyst, the reaction conditions were the same as in Example 2. The reaction results are shown in Table 7.

[0072] Table 7 CuMoO X Comparison of the catalytic performance of Al2O3 catalysts for methane oxidation

[0073]

[0074] Example 10

[0075] Supported molybdenum supported catalyst CuMoO X Comparison of the catalytic performance of Al2O3 (0.3wt% molybdenum loading, 0.2wt% copper loading, alumina support) in different alkane oxidation reactions:

[0076] Except for the reaction time, the reaction conditions were the same as in Example 2. The reaction results are shown in Table 8.

[0077] Table 8 CuMoO X Comparison of the catalytic performance of Al2O3 catalysts for methane oxidation

[0078]

[0079] Example 11

[0080] Supported molybdenum supported catalyst CuMoO X Comparison of the catalytic performance of Al2O3 (0.3wt% molybdenum loading, 0.2wt% copper loading, alumina support) in different alkane oxidation reactions:

[0081] Except for the different ultraviolet light wavelength, the reaction conditions were the same as in Example 2. The reaction results are shown in Table 9.

[0082] Table 9 CuMoO X Comparison of the catalytic performance of Al2O3 catalysts for methane oxidation

[0083]

[0084] Example 12

[0085] Supported molybdenum supported catalyst CuMoO X Comparison of the catalytic performance of Al2O3 (0.3wt% molybdenum loading, 0.2wt% copper loading, alumina support) in different alkane oxidation reactions:

[0086] Except for the reaction temperature, the reaction conditions were the same as in Example 2. The reaction results are shown in Table 10.

[0087] Table 10 CuMoO X Comparison of the catalytic performance of Al2O3 catalysts for methane oxidation

[0088]

[0089]

[0090] As shown in Table 1-10, supported molybdenum-based catalysts can efficiently oxidize methane to methanol.

Claims

1. A method for the selective oxidation of alkanes to corresponding monohydric alcohols via photocatalysis, characterized in that: Specifically, a supported molybdenum catalyst and solvent are added to a container, which is then sealed and filled with alkanes and oxygen. The reaction is carried out under ultraviolet light for 0.1-100 hours, and the reaction system is cooled to room temperature. A monohydric alcohol compound is generated on the upper layer of perfluoroalkane.

2. The method according to claim 1, characterized in that: The solvent system is a solvent containing perfluoroalkane; Specifically, it refers to: perfluoroalkanes, or two-phase systems composed of perfluoroalkanes and other solvents that are immiscible with perfluoroalkanes; In the solvent system, the volume ratio of perfluoroalkanes and other solvents immiscible with perfluoroalkanes varies from 0.01 to 100, preferably from 0.2 to 5, and more preferably from 0.5 to 2.

3. The method according to claim 2, characterized in that: The perfluoroalkane includes one or more of the following: perfluoropentane, perfluorohexane, perfluorocyclohexane, perfluoromethylcyclohexane, perfluoroheptane, perfluorooctane, perfluorononane, perfluorodecane, perfluoroundecane, perfluorododecane, perfluorotridecane, perfluorotetradecane, perfluoropentadecane, perfluorohexadecane, perfluoroheptadecane, perfluoroheptadecane, perfluorooctadecane, perfluorononadecane, perfluoroeicosane, perfluoronaphthane, perfluoroadamantane, perfluoro-1,3-dimethylcyclohexane, perfluoro(methylcyclopentane), perfluoro-2-methylpentane, and perfluoro-1,2-dimethylcyclobutane.

4. The method according to claim 2, characterized in that: Other solvents that are immiscible with perfluoroalkanes include one or more of water, alcohols, and organic acids.

5. The method according to claim 4, characterized in that: The alcohols mentioned include one or more of monohydric alcohols, dihydric alcohols, and trihydric alcohols; The monohydric alcohol includes one or more of methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, heptanol, and undecaneol; The diols mentioned include one or more of ethylene glycol, propylene glycol, butanediol, pentanediol, and hexanediol; The triols include one or more of trimethylolpropane and glycerol; The organic acids mentioned include one or more of the following: formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, heptanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, and eicosanoic acid.

6. The method according to claim 1, characterized in that: The molybdenum loading in the supported molybdenum catalyst is between 0.01% and 25% of the catalyst mass, preferably 0.1% to 5%, and more preferably 0.1% to 1%.

7. The method according to claim 1 or 6, characterized in that: The support for the supported molybdenum catalyst is one or more of alumina, silicon oxide, cerium oxide, zirconium oxide, magnesium oxide, zinc oxide, and tungsten oxide; preferably, the support includes one or two of silicon oxide and alumina.

8. The method according to claim 1 or 6, characterized in that: The supported molybdenum catalyst also includes electronic additives, which include one or more of copper, silver, gold, platinum, palladium, rhodium, ruthenium, and iridium. The loading of the electronic additives is between 0.01% and 10% of the catalyst mass, preferably 0.1% to 3%, and more preferably 0.3% to 2%.

9. The method according to claim 1, characterized in that: The alkane includes one or more of the following: methane, ethane, propane, isopropane, butane, dimethylpropane, pentane, hexane, and cyclohexane.

10. The method according to claim 1, characterized in that: The ultraviolet light wavelength is 200-400nm, preferably 280-400nm, and more preferably 320-400nm; The reaction time is preferably 1-20h, more preferably 2-12h; the reaction temperature is 0-100℃, preferably 40-100℃, more preferably 60-80℃.

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