A method for highly selective photocatalytic production of acetone from methane

Abstract

This invention relates to the field of new energy and discloses a highly selective photocatalytic method for producing acetone from methane. The method includes: placing a transparent substrate coated with a photocatalyst in a photocatalytic reactor, adding liquid water, introducing methane gas to purge air, sealing the photocatalytic reactor, and conducting a gas-solid two-phase photocatalytic reaction under light irradiation and heating at 50-100°C to generate a liquid oxygen-containing organic compound, primarily acetone. The photocatalyst is BiVO4, ZnO, or a modified photocatalyst based on morphology control, surface modification, semiconductor composite, or elemental doping of BiVO4 or ZnO. This invention uses methane and water as raw materials, reacting with a photocatalyst in a gas-solid two-phase reaction to produce a liquid oxygen-containing organic compound, primarily acetone, with high acetone yield and selectivity. This invention has advantages such as low requirements for the reaction environment, simple and environmentally friendly process, and low cost.

Description

Technical Field

[0001] This invention relates to the field of new energy, and more particularly to a method for the highly selective photocatalytic production of acetone from methane. Background Technology

[0002] In the current global energy structure and chemical production system, methane, as an abundant natural gas resource, possesses enormous application potential due to its high calorific value, low cost, and safety (non-toxicity). However, the primary method of methane utilization is direct combustion, which is not only inefficient in energy use but also produces large amounts of greenhouse gases such as carbon dioxide. Therefore, converting methane into chemicals with higher added value is crucial for promoting the long-term sustainable use of energy and environmental protection. Methane is chemically relatively stable, with an average dissociation energy of 440 kJ / mol for its CH bonds, making homolytic or heterolytic cleavage challenging. Traditional methane conversion methods, such as steam reforming and oxidative coupling, are often accompanied by high energy consumption, high emissions, and low efficiency, severely limiting the in-depth development and application of methane. Therefore, developing an efficient and environmentally friendly methane conversion technology is of great significance for promoting the optimization of the energy structure and the greening of chemical production.

[0003] Photocatalysis technology has attracted much attention due to its environmental friendliness and high energy conversion efficiency. It utilizes light energy to drive chemical reactions, exhibiting high efficiency, cleanliness, and renewability. In the field of methane conversion, photocatalysis technology has shown enormous application potential. Through photocatalysis, methane can be efficiently converted at lower temperatures and pressures, not only improving the utilization value of methane but also avoiding the harsh conditions of traditional catalytic reactions such as high temperature and high pressure. Currently, research on photocatalytic methane conversion mainly focuses on the production of C1 oxygen-containing compounds such as methanol and formaldehyde. With the development of the chemical industry, the demand for multi-carbon oxygen-containing compounds is constantly increasing, especially for high-value-added multi-carbon oxygen-containing organic chemicals such as acetone. As an important organic solvent and chemical raw material, acetone has wide applications in pharmaceuticals, coatings, plastics, and other fields. Therefore, developing a method for efficiently photocatalyzing the production of acetone from methane, providing a new source of raw materials for the chemical industry, and increasing the added value of natural gas not only has significant theoretical value but also urgent practical significance. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a highly selective photocatalytic method for the production of acetone from methane. This invention uses methane gas and water as raw materials, which undergo a gas-solid two-phase reaction with a photocatalyst to produce a liquid oxygen-containing organic compound, primarily acetone, with high acetone yield and selectivity.

[0005] The specific technical solution of this invention is as follows: a method for highly selective photocatalytic production of acetone from methane, comprising: placing a transparent substrate coated with a photocatalyst in a photocatalytic reactor, adding liquid water, introducing methane gas to purge air, sealing the photocatalytic reactor, and carrying out a gas-solid two-phase photocatalytic reaction under light irradiation and heating at 50-100℃ to generate a liquid oxygen-containing organic compound mainly composed of acetone; the photocatalyst is BiVO4, ZnO, or a modified photocatalyst after morphological control, surface modification, semiconductor composite, or elemental doping of BiVO4 and ZnO. In this invention, methane gas and water vapor are used as raw materials in a sealed photocatalytic reactor to undergo a gas-solid two-phase reaction with the photocatalyst to generate a liquid oxygen-containing organic compound mainly composed of acetone. The entire photocatalytic reaction process utilizes photogenerated holes generated by the photocatalyst under light irradiation to generate hydroxyl radicals from water as key active species. These hydroxyl radicals combine with methane molecules to generate methoxy radicals, which then continue to undergo free radical chain growth reactions with methane molecules to ultimately form a liquid oxygen-containing compound mainly composed of acetone. According to the method of the present invention, the highest yield of acetone can reach 27.9 μmol / g / h, with a selectivity of 91.8%.

[0006] Preferably, the photocatalyst is BiVO4, ZnO, Zn / BiVO4, BiVO4 / Bi2S3 with a heterojunction structure, or Pd-supported BiVO4, or m / t-BiVO4 with a heterojunction structure.

[0007] More preferably, the Zn doping amount in the Zn / BiVO4 is 1-9 mol%, and even more preferably 2-4 mol%. Appropriate Zn doping introduces an impurity energy level into the band gap of the semiconductor. This impurity energy level can reduce the photon energy required to excite the photocatalyst, broaden the absorption range of visible light, and enable even lower-energy photons to excite the photocatalyst, thereby improving photon utilization and enhancing the activity of the photocatalytic reaction. Conversely, the introduction of excessive metal ions can become recombination centers for photogenerated electron-hole pairs, promoting carrier recombination and hindering subsequent photocatalytic reactions.

[0008] Preferably, the preparation method of the Zn-doped modified BiVO4 is as follows: dissolve bismuth salt in nitric acid solution, dissolve ammonium metavanadate in sodium hydroxide solution, add the obtained ammonium metavanadate solution to the obtained bismuth salt solution, add zinc nitrate and stir, adjust the pH to 8.5-9.5; carry out hydrothermal reaction at 150-200℃; cool, centrifuge, wash, and dry to obtain Zn-doped modified BiVO4.

[0009] Preferably, the ratio of the amount of photocatalyst added to the light window area of ​​the photocatalytic reactor is 0.1-2.0 mg / cm². 2 More preferably 0.4-1.0 mg / cm³ 2 .

[0010] Preferably, the temperature of the gas-solid two-phase photocatalytic reaction is 85-95℃, and the time is 1-100 hours.

[0011] Higher reaction temperatures can effectively increase the basic potential energy of the reaction, lower the activation barrier of the reaction substrate, and increase the effective collision probability of free radicals, thereby increasing the reaction rate of the reactants. This allows C1 species to effectively increase their carbon number, promoting the formation of the final reactant acetone.

[0012] Preferably, the light source for the gas-solid two-phase photocatalytic reaction is a xenon lamp or a mercury lamp, with a light intensity of 10-500 mW / cm². -2 .

[0013] Preferably, the initial pressure of the system during the reaction is 0.10-0.50 MPa, and more preferably 0.10-0.25 MPa.

[0014] Preferably, the ratio of the volume of liquid water to the volume of the photocatalytic reactor is 0.01-0.1:1, and more preferably 0.02-0.03:1.

[0015] Preferably, the photocatalytic reactor is a sealed container made of glass or metal, with a quartz light window on the top or side for the intake of light source.

[0016] Preferably, the method for preparing the transparent substrate coated with the photocatalyst is as follows: the photocatalyst is dispersed in ethanol, ultrasonically treated, the resulting catalyst slurry is spread evenly on the transparent substrate, dried, and the transparent substrate coated with the photocatalyst is placed under the light window of the photocatalytic reactor.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] (1) This invention achieves the preparation of acetone by photocatalysis of methane at lower temperatures and pressures with high selectivity. It is a novel preparation method that paves a practical and promising path for the in-depth development and application of methane.

[0019] (2) In the process of preparing acetone oxygenated compounds in this invention, the yield efficiency of acetone can reach up to 27.9 μmol / g / h and the selectivity can reach 91.8%.

[0020] (3) The reaction of this invention uses only methane and water as raw materials, which are widely available. Moreover, the entire reaction process does not require the addition of any harmful auxiliary agents or auxiliaries, ensuring that the reaction process is green and environmentally friendly. At the same time, since the reaction conditions are mild and do not require high temperature and high pressure, the safety risks are effectively reduced, making the entire reaction process safer and more reliable, and more conducive to practical applications. Attached Figure Description

[0021] Figure 1 XRD patterns for different materials;

[0022] Figure 2 The graph shows the photocatalytic methane oxidation coupling performance of BiVO4 with Zn doping.

[0023] Figure 3 Gas chromatograms before and after 3 hours of photocatalytic methane oxidative coupling reaction with 3% Zn / BiVO4.

[0024] Figure 4 The graph shows the photocatalytic methane oxidation coupling performance of 3% Zn / BiVO4 at different reaction temperatures.

[0025] Figure 5 The NMR spectrum of the liquid after 10 hours of photocatalytic methane oxidative coupling reaction with 3% Zn / BiVO4. Detailed Implementation

[0026] The present invention will be further described below with reference to embodiments.

[0027] The products of the photocatalytic reaction in this invention were detected by GC-FID gas chromatography. The gas chromatography packed column used was a capillary column, and the carrier gas was argon. The amounts of acetone, ethanol, and methanol generated were determined using the external standard method.

[0028] Example 1

[0029] Example 1 uses BiVO4 as a photocatalyst to illustrate the catalytic preparation effect of the present invention.

[0030] The synthesis of BiVO4 was as follows: 1.455 g of bismuth nitrate pentahydrate was dissolved in 15 mL of 2 mol / L nitric acid solution, and 0.351 g of ammonium metavanadate was dissolved in 15 mL of 2 mol / L sodium hydroxide solution. The ammonium metavanadate solution was slowly added to the bismuth nitrate solution, and after stirring for 30 minutes, the pH was adjusted to 9 with 2 mol / L sodium hydroxide solution. The yellow solution was transferred to a 50 mL hydrothermal reactor and heated to 180 °C for 10 hours. After cooling to room temperature, the product was collected by centrifugation, washed three times each with deionized water and ethanol, and then dried overnight in a 60 °C oven. The XRD pattern of the synthesized BiVO4 material is shown below. Figure 1 As shown, its diffraction pattern perfectly matches the monoclinic BiVO4 of standard card No. 14-0688.

[0031] 5 mg BiVO4 was dispersed in 1 mL of anhydrous ethanol and sonicated for 30 minutes. The resulting solution was then coated onto a 4 cm diameter circular glass substrate. The substrate was placed in a 60 °C oven until completely dry, and then placed in a 50 mL glass reactor. 1 mL of deionized water was added, followed by the introduction of pure methane gas. After the air was purged, the exhaust port was closed, and methane was continued to be introduced until the pressure reached 0.1 MPa. The gas inlet was then closed, and the reaction apparatus was heated to 90 °C using a heating device. The reaction was carried out under xenon lamp irradiation for 3 hours, after which the reactor was cooled.

[0032] After cooling completely to room temperature, the liquid was collected and its components were analyzed by gas chromatography. The overall yield efficiency was 3.13 μmol / g / h for acetone, 1.80 μmol / g / h for ethanol, and 0.80 μmol / g / h for methanol, with a selectivity of 54.6% for acetone.

[0033] Example 2

[0034] Example 2 uses ZnO as a photocatalyst to illustrate the catalytic preparation effect of the present invention.

[0035] The synthesis of ZnO was as follows: 0.892 g of zinc nitrate hexahydrate was dissolved in 30 mL of deionized water, stirred for 30 minutes, and then the pH was adjusted to 9 with 2 mol / L sodium hydroxide solution. The solution was transferred to a 50 mL hydrothermal reactor and heated to 180 °C for 10 hours. After cooling to room temperature, the product was collected by centrifugation, washed three times each with deionized water and ethanol, and then dried overnight in a 60 °C oven. The XRD pattern of the synthesized ZnO material is shown below. Figure 1 As shown, its diffraction pattern perfectly matches the ZnO species in standard card No. 36-1415.

[0036] 5 mg of ZnO was dispersed in 1 mL of anhydrous ethanol and sonicated for 30 minutes. The resulting solution was then coated onto a circular glass substrate with a diameter of 4 cm. The substrate was placed in a 60 °C oven until completely dry, and then placed in a 50 mL glass reactor. 1 mL of deionized water was added, followed by the introduction of pure methane gas. After the air was purged, the exhaust port was closed, and methane was continued to be introduced until the pressure reached 0.1 MPa. The gas inlet was then closed, and the reaction apparatus was heated to 90 °C using a heating device. The reaction was carried out under xenon lamp irradiation for 3 hours, after which the reactor was cooled.

[0037] After cooling completely to room temperature, the liquid was collected and its components were analyzed by gas chromatography. The overall yield efficiency was 2.83 μmol / g / h for acetone, 0.84 μmol / g / h for ethanol, and 0.44 μmol / g / h for methanol, with a selectivity of 68.9% for acetone.

[0038] Example 3

[0039] Example 3 uses m / t-BiVO4 with a heterogeneous structure as a photocatalyst to illustrate the catalytic preparation effect of the present invention.

[0040] The synthesis of m / t-BiVO4 is as follows: 1.455 g of bismuth nitrate pentahydrate was dissolved in 15 mL of 2 mol / L nitric acid solution, and 0.351 g of ammonium metavanadate was dissolved in 15 mL of 2 mol / L sodium hydroxide solution. The ammonium metavanadate solution was slowly added to the bismuth nitrate solution, and after stirring for 30 minutes, the pH was adjusted to 12 with 2 mol / L sodium hydroxide solution. The yellow solution was transferred to a 50 mL hydrothermal reactor and heated to 180 °C for 10 hours. After cooling to room temperature, the product was collected by centrifugation, washed three times each with deionized water and ethanol, and then dried overnight in a 60 °C oven. The XRD pattern of the synthesized BiVO4 material is shown below. Figure 1 As shown, its diffraction pattern perfectly matches the monoclinic BiVO4 of standard card No. 14-0688 and the cubic BiVO4 of standard card No. 14-0133, indicating that the BiVO4 heterojunction material was successfully prepared.

[0041] 5 mg m / t-BiVO4 was dispersed in 1 mL of anhydrous ethanol and sonicated for 30 minutes. The resulting solution was then coated onto a 4 cm diameter circular glass substrate. The substrate was dried completely in a 60 °C oven and then placed in a 50 mL glass reactor. 1 mL of deionized water was added, followed by the introduction of pure methane gas. After the air was purged, the exhaust port was closed, and methane was continued to be introduced until the pressure reached 0.1 MPa. The inlet was then closed, and the reactor was heated to 90 °C using a heating device. The reaction was carried out under xenon lamp irradiation for 3 hours, after which the reactor was cooled.

[0042] After completely cooling to room temperature, the liquid was collected and its components were analyzed by gas chromatography. The overall yield efficiency was 8.75 μmol / g / h for acetone, 4.28 μmol / g / h for ethanol, and 1.50 μmol / g / h for methanol, with a selectivity of 60.2% for acetone.

[0043] Example 4

[0044] Example 4 uses BiVO4 / Bi2S3 material with a heterojunction structure as a photocatalyst to illustrate the catalytic preparation effect of the present invention.

[0045] The synthesis of BiVO4 / Bi2S3 was as follows: 0.2 g BiVO4 and 0.029 g sulfur were added to 20 mL oleic acid and sonicated for 20 minutes. 1.5 mL oleylamine was then rapidly added, and the mixture was heated in an oil bath at 180 °C for 60 minutes. After cooling to room temperature, the product was collected by centrifugation and washed several times with n-hexane. The solid was placed in a vacuum oven and dried overnight at 70 °C.

[0046] 5 mg of BiVO4 / Bi2S3 was dispersed in 1 mL of anhydrous ethanol and sonicated for 30 minutes. The resulting mixture was then coated onto a 4 cm diameter circular glass substrate. The substrate was dried completely in a 60 °C oven and then placed in a 50 mL glass reactor. 1 mL of deionized water was added, followed by the introduction of pure methane gas. After the air was purged, the exhaust port was closed, and methane was continued to be introduced until the pressure reached 0.1 MPa. The gas inlet was then closed, and the reaction apparatus was heated to 90 °C. The reaction was carried out under xenon lamp irradiation for 3 hours, after which the reactor was cooled.

[0047] After cooling completely to room temperature, the liquid was collected and its components were analyzed by gas chromatography. The overall yield efficiency was 8.79 μmol / g / h for acetone, 2.28 μmol / g / h for ethanol, and 0.65 μmol / g / h for methanol, with a selectivity of 76.0% for acetone.

[0048] Example 5

[0049] Example 5 uses Pd-supported BiVO4 material as a photocatalyst to illustrate the catalytic preparation effect of the present invention.

[0050] The synthesis of Pd-supported BiVO4 is as follows: 2 mg of Pd nanoparticles with a diameter of 10 nm were dispersed in 20 mL of ethanol, sonicated for 30 minutes, and then 0.2 g of solid BiVO4 was added. The mixture was heated and stirred at 50 °C until completely dry.

[0051] 5 mg of Pd-loaded BiVO4 was dispersed in 1 mL of anhydrous ethanol and sonicated for 30 minutes. The resulting solution was then coated onto a 4 cm diameter circular glass substrate. The substrate was dried completely in a 60 °C oven and then placed in a 50 mL glass reactor. 1 mL of deionized water was added, followed by the introduction of pure methane gas. After the air was purged, the exhaust port was closed, and methane was continued to be introduced until the pressure reached 0.1 MPa. The gas inlet was then closed, and the reactor was heated to 90 °C using a heating device. The reaction was carried out under xenon lamp irradiation for 3 hours, after which the reactor was cooled.

[0052] After cooling completely to room temperature, the liquid was collected and its components were analyzed by gas chromatography. The overall yield efficiency was 9.71 μmol / g / h for acetone, 4.20 μmol / g / h for ethanol, and 3.45 μmol / g / h for methanol, with a selectivity of 55.9% for acetone.

[0053] Example 6

[0054] Example 6 uses 1 mol% Zn-doped BiVO4 as a photocatalyst to illustrate the catalytic preparation effect of the present invention.

[0055] The synthesis of 1 mol% Zn-doped BiVO4 was as follows: 1.455 g of bismuth nitrate pentahydrate was dissolved in 15 mL of 2 mol / L nitric acid solution, and 0.351 g of ammonium metavanadate was dissolved in 15 mL of 2 mol / L sodium hydroxide solution. The ammonium metavanadate solution was slowly added to the bismuth nitrate solution, and after complete addition, 8.9 mg of zinc nitrate hexahydrate solid was added. After stirring for 30 minutes, the pH was adjusted to 9 with 2 mol / L sodium hydroxide solution. The yellow solution was transferred to a 50 mL hydrothermal reactor and heated to 180 °C for 10 hours. After cooling to room temperature, the product was collected by centrifugation, washed three times with deionized water and ethanol respectively, and then dried overnight in a 60 °C oven.

[0056] 5 mg of 1 mol% Zn / BiVO4 was dispersed in 1 mL of anhydrous ethanol and sonicated for 30 minutes. The resulting solution was then coated onto a 4 cm diameter circular glass substrate. The substrate was placed in a 60 °C oven until completely dry, and then placed in a 50 mL glass reactor. 1 mL of deionized water was added, followed by the introduction of pure methane gas. After the air was purged, the exhaust port was closed, and methane was continued to be introduced until the pressure reached 0.1 MPa. The inlet was then closed, and the reaction apparatus was heated to 90 °C using a heating device. The reaction was carried out under xenon lamp irradiation for 3 hours, after which the reactor was cooled.

[0057] After cooling completely to room temperature, the liquid was collected and its components were analyzed by gas chromatography. The overall yield efficiency was 23.11 μmol / g / h for acetone, 2.36 μmol / g / h for ethanol, and 0.61 μmol / g / h for methanol, with a selectivity of 88.6% for acetone.

[0058] Performance Comparison

[0059] A comparison of Examples 1-6 shows that pure-phase BiVO4 (Example 1) and ZnO (Example 2) as photocatalysts have the ability to oxidize methane to acetone, but their reactivity and selectivity are low, possibly due to inherent defects in the photocatalysts themselves, which prevent effective separation of charge carriers. Reasonable modification, such as constructing heterojunctions (Example 3) or heterogeneous junctions (Example 4), loading noble metals (Example 5), or doping with heterogeneous elements (Example 6), can effectively promote the separation of photogenerated charge carriers, effectively expand the light absorption range, and thus improve the yield of photocatalytic methane oxidative coupling to acetone.

[0060] Example 7

[0061] The preparation steps of 3% Zn / BiVO4 in Example 7 are the same as those in Example 3, except that the amount of zinc nitrate hexahydrate solid added is changed to 26.7 mg.

[0062] 5 mg of 3% Zn / BiVO4 was dispersed in 1 mL of anhydrous ethanol and sonicated for 30 minutes. The resulting solution was then coated onto a 4 cm diameter circular glass substrate. The substrate was dried completely in a 60 °C oven and then placed in a 50 mL glass reactor. 1 mL of deionized water was added, followed by the introduction of pure methane gas. After the air was purged, the exhaust port was closed, and methane was continued to be introduced until the pressure reached 0.1 MPa. The inlet was then closed, and the reactor was heated to 90 °C using a heating device. The reaction was carried out under xenon lamp irradiation for 3 hours, after which the reactor was cooled.

[0063] After cooling completely to room temperature, the liquid was collected and its components were analyzed by gas chromatography. The overall yield efficiency was 27.95 μmol / g / h for acetone, 0.45 μmol / g / h for ethanol, and 0.92 μmol / g / h for methanol, with a selectivity of 91.8% for acetone.

[0064] Example 8

[0065] The preparation steps of 5% Zn / BiVO4 in Example 8 are the same as those in Example 3, except that the amount of zinc nitrate hexahydrate solid added is changed to 44.5 mg.

[0066] 5 mg of 5% Zn / BiVO4 was dispersed in 1 mL of anhydrous ethanol and sonicated for 30 minutes. The resulting solution was then coated onto a 4 cm diameter circular glass substrate. The substrate was dried completely in a 60 °C oven and then placed in a 50 mL glass reactor. 1 mL of deionized water was added, followed by the introduction of pure methane gas. After the air was purged, the exhaust port was closed, and methane was continued to be introduced until the pressure reached 0.1 MPa. The inlet was then closed, and the reactor was heated to 90 °C using a heating device. The reaction was carried out under xenon lamp irradiation for 3 hours, after which the reactor was cooled.

[0067] After cooling completely to room temperature, the liquid was collected and its components were analyzed by gas chromatography. The overall yield efficiency was 17.95 μmol / g / h for acetone, 1.64 μmol / g / h for ethanol, and 0.34 μmol / g / h for methanol, with a selectivity of 89.8% for acetone.

[0068] Example 9

[0069] The preparation steps of 7% Zn / BiVO4 in Example 9 are the same as those in Example 3, except that the amount of zinc nitrate hexahydrate solid added is changed to 62.3 mg.

[0070] 5 mg of 7% Zn / BiVO4 was dispersed in 1 mL of anhydrous ethanol and sonicated for 30 minutes. The resulting solution was then coated onto a 4 cm diameter circular glass substrate. The substrate was dried completely in a 60 °C oven and then placed in a 50 mL glass reactor. 1 mL of deionized water was added, followed by the introduction of pure methane gas. After the air was purged, the exhaust port was closed, and methane was continued to be introduced until the pressure reached 0.1 MPa. The inlet was then closed, and the reactor was heated to 90 °C using a heating device. The reaction was carried out under xenon lamp irradiation for 3 hours, after which the reactor was cooled.

[0071] After completely cooling to room temperature, the liquid was collected and its components were analyzed by gas chromatography. The overall yield efficiency was 15.56 μmol / g / h for acetone, 1.94 μmol / g / h for ethanol, and 0.34 μmol / g / h for methanol, with a selectivity of 87.2% for acetone.

[0072] Example 10

[0073] The preparation steps of 9% Zn / BiVO4 in Example 10 are the same as in Example 3, except that the amount of zinc nitrate hexahydrate solid added is changed to 80.1 mg.

[0074] 5 mg of 9% Zn / BiVO4 was dispersed in 1 mL of anhydrous ethanol and sonicated for 30 minutes. The resulting solution was then coated onto a 4 cm diameter circular glass substrate. The substrate was placed in a 60 °C oven until completely dry, and then placed in a 50 mL glass reactor. 1 mL of deionized water was added, followed by the introduction of pure methane gas. After the air was purged, the exhaust port was closed, and methane was continued to be introduced until the pressure reached 0.1 MPa. The gas inlet was then closed, and the reaction apparatus was heated to 90 °C using a heating device. The reaction was carried out under xenon lamp irradiation for 3 hours, after which the reactor was cooled.

[0075] After cooling completely to room temperature, the liquid was collected and its components were analyzed by gas chromatography. The overall yield efficiency was 13.58 μmol / g / h for acetone, 1.62 μmol / g / h for ethanol, and 0.32 μmol / g / h for methanol, with a selectivity of 87.4% for acetone.

[0076] Performance Comparison

[0077] As can be seen from the comparison of Examples 1, 6-10, doping with metal elements can improve the inherent defects of the initial photocatalyst. The results of different Zn doping modifications are as follows... Figure 2 As shown, the material with a Zn doping content of 3 mol% exhibits the best catalytic performance. The gas phase spectrum after the reaction of 3 mol% Zn / BiVO4 as a catalyst is shown in the figure below. Figure 3As shown, it can be inferred that Zn doping introduces an impurity energy level, lowers the excitation energy, broadens the light absorption range, and suppresses the recombination of photogenerated electron-hole pairs, thus providing favorable conditions for the subsequent conversion of methane to acetone.

[0078] Example 11

[0079] Examples 11-14 use 3% Zn / BiVO4 as a photocatalyst to illustrate the catalytic effect of the present invention at different temperatures. The preparation steps of 3% Zn / BiVO4 are the same as in Example 7.

[0080] 5 mg of 3% Zn / BiVO4 was dispersed in 1 mL of anhydrous ethanol and sonicated for 30 minutes. The resulting solution was then coated onto a 4 cm diameter circular glass substrate. The substrate was dried completely in a 60 °C oven and then placed in a 50 mL glass reactor. 1 mL of deionized water was added, followed by the introduction of pure methane gas. After the air was purged, the exhaust port was closed, and methane was continued to be introduced until the pressure reached 0.1 MPa. The inlet was then closed, and the reactor was heated to 50 °C using a heating device. The reaction was carried out under xenon lamp irradiation for 3 hours, after which the reactor was cooled.

[0081] After cooling completely to room temperature, the liquid was collected and its components were analyzed by gas chromatography. The overall yield efficiency was 6.60 μmol / g / h for acetone, 5.77 μmol / g / h for ethanol, and 2.77 μmol / g / h for methanol, with a selectivity of 43.5% for acetone.

[0082] Example 12

[0083] 5 mg of 3% Zn / BiVO4 was dispersed in 1 mL of anhydrous ethanol and sonicated for 30 minutes. The resulting solution was then coated onto a 4 cm diameter circular glass substrate. The substrate was placed in a 60 °C oven until completely dry, and then placed in a 50 mL glass reactor. 1 mL of deionized water was added, followed by the introduction of pure methane gas. After the air was purged, the exhaust port was closed, and methane was continued to be introduced until the pressure reached 0.1 MPa. The gas inlet was then closed, and the reaction apparatus was heated to 60 °C using a heating device. The reaction was carried out under xenon lamp irradiation for 3 hours, after which the reactor was cooled.

[0084] After completely cooling to room temperature, the liquid was collected and its components were analyzed by gas chromatography. The overall yield efficiency was 10.750 μmol / g / h for acetone, 4.28 μmol / g / h for ethanol, and 2.78 μmol / g / h for methanol, with a selectivity of 62.1% for acetone.

[0085] Example 13

[0086] 5 mg of 3% Zn / BiVO4 was dispersed in 1 mL of anhydrous ethanol and sonicated for 30 minutes. The resulting solution was then coated onto a 4 cm diameter circular glass substrate. The substrate was dried completely in a 60 °C oven and then placed in a 50 mL glass reactor. 1 mL of deionized water was added, followed by the introduction of pure methane gas. After the air was purged, the exhaust port was closed, and methane was continued to be introduced until the pressure reached 0.1 MPa. The inlet was then closed, and the reactor was heated to 70 °C. The reaction was carried out under xenon lamp irradiation for 3 hours, after which the reactor was cooled. After complete cooling to room temperature, the liquid was analyzed by gas chromatography. The overall yield efficiency was 14.16 μmol / g / h for acetone, 2.58 μmol / g / h for ethanol, and 1.58 μmol / g / h for methanol. The selectivity for acetone was 77.3%.

[0087] Example 14

[0088] 5 mg of 3% Zn / BiVO4 was dispersed in 1 mL of anhydrous ethanol and sonicated for 30 minutes. The resulting solution was then coated onto a 4 cm diameter circular glass substrate. The substrate was dried completely in a 60 °C oven and then placed in a 50 mL glass reactor. 1 mL of deionized water was added, followed by the introduction of pure methane gas. After the air was purged, the exhaust port was closed, and methane was continued to be introduced until the pressure reached 0.1 MPa. The inlet was then closed, and the reactor was heated to 80 °C. The reaction was carried out under xenon lamp irradiation for 3 hours, after which the reactor was cooled. After complete cooling to room temperature, the liquid was analyzed by gas chromatography. The overall yield efficiencies were 20.31 μmol / g / h for acetone, 2.24 μmol / g / h for ethanol, and 1.24 μmol / g / h for methanol. The selectivity for acetone was 85.4%.

[0089] Performance Comparison

[0090] As can be seen from Examples 4 and 8-12, the results at different reaction temperatures (50-90℃) are as follows: Figure 4 As shown, at lower temperatures, the reactivity decreases, the selectivity of acetone is also lower, and the produced methanol and ethanol contents are higher. With increasing temperature, the ethanol content gradually decreases, while the acetone content increases, with the optimal catalytic performance observed at 90℃. At lower temperatures, the proportion of activated methane molecules is low, preventing continuous reaction to acetone. As the temperature gradually increases, the existence time of activated methane molecules prolongs, increasing the probability of continuous reaction and thus increasing the yield and selectivity of acetone.

[0091] Example 15

[0092] 5 mg of 3% Zn / BiVO4 was dispersed in 1 mL of anhydrous ethanol and sonicated for 30 minutes. The resulting solution was then coated onto a 4 cm diameter circular glass substrate. The substrate was placed in a 60 °C oven until completely dry, and then placed in a 50 mL glass reactor. 1 mL of deionized water was added, followed by the introduction of pure methane gas. After the air was purged, the exhaust port was closed, and methane was continued to be introduced until the pressure reached 0.1 MPa. The gas inlet was then closed, and the reaction apparatus was heated to 80 °C using a heating device. The reaction was carried out under xenon lamp irradiation for 10 hours, after which the reactor was cooled.

[0093] After cooling completely to room temperature, the liquid was collected and its components were analyzed by gas chromatography. The overall yield efficiency was 25.56 μmol / g / h for acetone, 0.71 μmol / g / h for ethanol, and 1.13 μmol / g / h for methanol, with a selectivity of 93.3% for acetone.

[0094] like Figure 5 The NMR spectrum of the liquid after the reaction is shown. Based on the elution position of H, it can be attributed to acetone, ethanol, and methanol, respectively, without the formation of other species.

[0095] Comparing Example 7 and Example 15, it can be seen that as the reaction time increases, the production efficiency of acetone, ethanol and methanol does not fluctuate significantly, and the production selectivity of acetone increases slightly, indicating the continuous stability of the reaction. It can achieve the goal of continuously and efficiently producing acetone and has the potential for large-scale industrialization.

[0096] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0097] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for highly selective photocatalytic production of acetone from methane, characterized in that: A transparent substrate coated with a photocatalyst is placed in a photocatalytic reactor, liquid water is added, methane gas is introduced to purge the air, and the photocatalytic reactor is sealed. Under light irradiation and heating at 50-100℃, a gas-solid two-phase photocatalytic reaction is carried out to generate a liquid oxygen-containing organic compound mainly composed of acetone. The photocatalyst is BiVO4, ZnO, Zn / BiVO4, BiVO4 / Bi2S3 with a heterojunction structure, or Pd-supported BiVO4, or m / t-BiVO4 with a heterojunction structure.

2. The method according to claim 1, characterized in that: The Zn doping amount in the Zn / BiVO4 is 1-9 mol.

3. The method according to claim 2, characterized in that: The Zn doping amount in the Zn / BiVO4 is 2-4 mol.

4. The method according to any one of claims 1-3, characterized in that: The ratio of the amount of photocatalyst added to the light window area of ​​the photocatalytic reactor is 0.1-2.0 mg / cm². 2 .

5. The method according to claim 1, characterized in that: The temperature of the gas-solid two-phase photocatalytic reaction is 85-95℃, and the time is 1-100 hours; The light source for the gas-solid two-phase photocatalytic reaction is a xenon lamp or a mercury lamp, with a light intensity of 10-500 mW / cm². -2 .

6. The method according to claim 1 or 5, characterized in that: The initial pressure of the system during the reaction is 0.10-0.50 MPa.

7. The method according to claim 1, characterized in that: The ratio of the volume of the liquid water to the volume of the photocatalytic reactor is 0.01-0.1:

1.

8. The method according to claim 1, characterized in that: The photocatalytic reactor is a sealed container made of glass or metal, with a quartz light window on the top or side for the intake of light source.

9. The method according to claim 1, characterized in that: The method for preparing the transparent substrate coated with the photocatalyst is as follows: the photocatalyst is dispersed in ethanol, ultrasonically treated, the resulting catalyst slurry is spread evenly on the transparent substrate, dried, and the transparent substrate coated with the photocatalyst is placed under the light window of the photocatalytic reactor.

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