Research on inhibition of excessive oxidation in methane photocatalytic conversion process by heteropoly acid
By preparing Ag-PW12/TiO2 photocatalysts, the problems of low yield and over-oxidation in the conversion of methane into high-value-added chemicals were solved, achieving photocatalytic conversion with high selectivity and high yield.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-19
- Publication Date
- 2026-04-07
AI Technical Summary
In existing technologies, the yield of methane converted into high-value-added chemicals under mild conditions is low and it is prone to over-oxidation, resulting in poor selectivity.
Ag-PW12/TiO2 photocatalysts were prepared by combining Keggin-type heteropolyacids and AgNO3 with mesoporous TiO2. By modifying TiO2 to expose more active sites and utilizing the electron-rich sites of polyoxometalates, the separation of photogenerated carriers was promoted, thereby improving catalytic performance.
A highly selective conversion of methane into liquid C1 oxygen-containing compounds was achieved under mild conditions, with significantly improved yield and selectivity.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of photocatalytic methane conversion technology, specifically relating to a method for preparing a photocatalyst composed of Keggin-type heteropolyacid, AgNO3 and mesoporous TiO2 and its performance study. Technical Background
[0002] Methane (CH4), a major component of natural gas, is an important fuel and industrial feedstock. Traditional methane conversion processes mainly rely on indirect routes such as methane reforming and Fischer-Tropsch synthesis, which typically require high temperatures and pressures and involve significant energy consumption. In contrast, directly converting CH4 into high-value-added chemicals under mild conditions has become a promising process route. However, the CH bond energy of the methane molecule is as high as 439 kJ / mol, and its polarizability is relatively low, making it difficult to activate. Furthermore, the target products are generally more reactive than methane, easily over-oxidized to carbon dioxide, which severely reduces the selectivity of the target products. Therefore, the selective oxidation of methane into high-value-added chemicals under mild conditions is highly attractive but also faces considerable challenges. In this study, TiO2 was modified with heteropolyacids and silver species to promote the separation of photogenerated carriers, thereby improving the performance of photocatalytic CH4 conversion under mild conditions. The photocatalytic oxidation of methane in a composite photocatalyst was investigated using oxygen as the oxidant. Ultimately, high yields and high selectivity of liquid C1 oxygen-containing compounds were achieved on the TWA-1.0 catalyst, providing new insights into the design of efficient photocatalysts. Summary of the Invention
[0003] The purpose of this invention is to provide a method for preparing a composite photocatalyst of Keggin-type heteropolyacid, AgNO3 and mesoporous TiO2, which solves the problems of low yield and over-oxidation of the photocatalytic direct conversion of methane into liquid C1 oxygen-containing compounds.
[0004] The objective of this invention can be achieved through the following technical solutions:
[0005] The chemical formula for this photocatalyst is Ag-PW. 12 / TiO2. Its preparation process includes the following steps:
[0006] S1: Based on the literature [Stoichiometric methane conversion to ethane using photochemical looping at ambient temperature[J]. Nature Energy, 2020(5), 511–519], we prepared heteropolyacid and silver-modified TiO2 catalysts using an improved one-step impregnation-calcination method. During the impregnation process, a certain amount of TiO2 and PW were first weighed... 12 AgNO3 (with only the mass percentage of AgNO3 to TiO2 varying between 0.5%, 1.0%, 1.5%, and 2.5%) was added to 50 ml of water, ultrasonically dispersed, stirred for 12 hours, and the sample was washed with deionized water, filtered, and collected.
[0007] S2: Then the obtained material is dried at 100°C for 12 hours.
[0008] S3: Next, the obtained material was heated to 300 °C in a muffle furnace at a heating rate of 2 °C / min, and maintained at 300 °C for 3 hours. After cooling to room temperature, the sample was collected.
[0009] The innovation of this invention lies in:
[0010] (1) The mesoporous TiO2 photocatalyst in this invention can expose more active sites.
[0011] (2) The present invention further improves the electronic storage performance of composite materials by using polyoxometalates as electron-rich sites.
[0012] (3) The preparation method is to combine with mesoporous TiO2 nanoparticles, in which the heteropolyacids and silver species are highly dispersed, promoting the separation of photogenerated carriers. The catalyst has a mesoporous structure, providing a large surface area and abundant adsorption sites. The photocatalyst synthesis method is simple, and at the same time, it achieves high yield and high selectivity of liquid C1 oxygen-containing compounds, which is conducive to its application in the photocatalytic reaction of methane to liquid C1 oxygen-containing compounds. Attached Figure Description
[0013] Figure 1 These are the XRD patterns of the photocatalysts in Implementation Example 1 and Comparative Example 1 of the present invention.
[0014] Figure 2 This is Ag-PW in Implementation Example 1 of the present invention. 12 SEM image of TiO2 (TWA-1.0) photocatalyst.
[0015] Figure 3This is a comparison chart of the yield and selectivity of liquid C1 oxygenated compounds produced by photocatalytic methane oxidation in Implementation Example 1 and Comparative Example 1 of the present invention.
[0016] Figure 4 It is the Ag-PW implementation of Case 1, Case 2, and Case 3. 12 Comparison of the yield and selectivity of photocatalytic methane oxidation to liquid C1 oxygenated compounds using TiO2 (TWA-1.0) and photocatalysts supported only by heteropolyacids and AgNO3, respectively.
[0017] Figure 5 Implementation Case 4, Implementation Case 1, Implementation Case 5, and Implementation Case 6 use Ag-PW with different AgNO3:TiO2 mass percentages. 12 / Comparison of yield and selectivity of liquid C1 oxygenated compounds produced by TiO2 photocatalytic methane oxidation. Detailed Implementation
[0018] The present invention will be described in detail below with reference to specific implementation examples. These examples are used to illustrate the invention but are not intended to limit its scope.
[0019] Implementation Case 1:
[0020] S1: Based on the literature [Stoichiometric methane conversion to ethane using photochemical looping at ambient temperature[J]. Nature Energy, 2020(5), 511–519], we prepared heteropolyacid and silver-modified TiO2 catalysts using an improved one-step impregnation-calcination method. In the impregnation process, a certain amount of TiO2 and PW were first weighed... 12 AgNO3 (AgNO3 to TiO2 mass percentage is 1.0%) was added to 50 ml of water, ultrasonically dispersed, stirred for 12 hours, washed with deionized water, filtered, and the sample was collected; S2: The obtained material was then dried at 100 °C for 12 hours; S3: Next, the obtained material was heated to 300 °C in a muffle furnace at a heating rate of 2 °C / min and maintained at 300 °C for 3 hours. After cooling to room temperature, Ag-PW was obtained. 12 / TiO2 (TWA-1.0). 5 mg of catalyst was dispersed in 50 mL of deionized water, and the mixture was purged with a methane-to-oxygen ratio of 29:1 at a total pressure of 3 MPa. A 300 W xenon lamp was used as the light source, and the reaction was carried out at room temperature for 1 h. The yield of the liquid C1 oxygen-containing compound was 10.53 mmol g. -1 h -1The selectivity rate was 98.22%.
[0021] Comparison Case 1:
[0022] Commercially available TiO2 nanoparticles with mesoporous structure were used. 5 mg of the catalyst was dispersed in 50 mL of deionized water. The mixture was charged with methane at a methane-to-oxygen ratio of 29:1 at a total pressure of 3 MPa. The light source was a 300 W xenon lamp, and the reaction was carried out at room temperature for 1 h. The yield of the liquid Cl-containing oxygen-containing compound was 0.88 mmol g. -1 h -1 The selectivity rate was 81.11%.
[0023] Implementation Case 2:
[0024] S1: During the impregnation process, a certain amount of TiO2 and PW are first weighed out. 12 Add it to 50 ml of water, sonicate to disperse, stir for 12 hours, wash with deionized water, filter and collect the sample; S2: Then dry the obtained material at 100 °C for 12 hours; S3: Next, heat the obtained material in a muffle furnace to 300 °C at a heating rate of 2 °C / min, maintain at 300 °C for 3 hours, and then cool to room temperature to obtain PW. 12 / TiO2. 5 mg of catalyst was dispersed in 50 mL of deionized water, and the mixture was purged with a methane-to-oxygen ratio of 29:1 at a total pressure of 3 MPa. A 300 W xenon lamp was used as the light source, and the reaction was carried out at room temperature for 1 hour under irradiation. The yield of liquid C1 oxygen-containing compounds was 5.87 mmol g. -1 h -1 The selectivity rate was 98.36%.
[0025] Implementation Case 3:
[0026] S1: During the impregnation process, a certain amount of TiO2 and AgNO3 were weighed and added to 50 ml of water. After ultrasonic dispersion, the mixture was stirred for 12 hours, washed with deionized water, filtered, and the sample was collected. S2: The obtained material was then dried at 100 °C for 12 hours. S3: Next, the obtained material was heated to 300 °C in a muffle furnace at a heating rate of 2 °C / min and maintained at 300 °C for 3 hours. After cooling to room temperature, Ag / TiO2 was obtained. 5 mg of the catalyst was dispersed in 50 mL of deionized water, filled with a methane-to-oxygen ratio of 29:1, with a total pressure of 3 MPa, using a 300 W xenon lamp as the light source, and reacted at room temperature for 1 hour under irradiation. The yield of liquid C1 oxygen-containing compounds was 3.42 mmol g. -1 h -1 The selectivity rate was 94.22%.
[0027] Example 4
[0028] Take 5 mg of Ag-PW with a mass percentage of 0.5% AgNO3:TiO2. 12 TiO2 (TWA-0.5) photocatalyst was dispersed in 50 mL of deionized water, with a methane-to-oxygen ratio of 29:1, a total pressure of 3 MPa, and a 300 W xenon lamp as the light source. The reaction was carried out at room temperature for 1 hour under irradiation. The yield of liquid C1 oxygen-containing compounds was 8.89 mmol g. -1 h -1 The selectivity rate was 98.09%.
[0029] Implementation Case 5
[0030] Take 5 mg of Ag-PW with a mass percentage of 1.5% AgNO3:TiO2. 12 TiO2 (TWA-1.5) photocatalyst was dispersed in 50 mL of deionized water, with a methane-to-oxygen ratio of 29:1, a total pressure of 3 MPa, and a 300 W xenon lamp as the light source. The reaction was carried out at room temperature for 1 hour under irradiation. The yield of liquid C1 oxygen-containing compounds was 9.39 mmol g. -1 h -1 The selectivity rate was 98.16%.
[0031] Implementation Case 6
[0032] Take 5 mg of Ag-PW with a mass percentage of 2.5% AgNO3:TiO2. 12 TiO2 (TWA-2.5) photocatalyst was dispersed in 50 mL of deionized water, with a methane-to-oxygen ratio of 29:1, a total pressure of 3 MPa, and a 300 W xenon lamp as the light source. The reaction was carried out at room temperature for 1 hour under irradiation. The yield of liquid C1 oxygen-containing compounds was 7.56 mmol g. -1 h -1 The selectivity rate was 97.62%.
Claims
1. A photocatalyst composed of a Keggin-type heteropolyacid, AgNO3, and mesoporous TiO2, characterized in that, Its chemical formula is: Ag-PW 12 / TiO2, where PW 12 The components are commercial Keggin-type heteropolyacids and TiO2, which are commercial TiO2 nanoparticles with mesoporous structures (hereinafter collectively referred to as TiO2).
2. The preparation method of the above-mentioned Keggin-type heteropolyacid, AgNO3 and mesoporous TiO2 composite photocatalyst is characterized in that, Includes the following steps: S1: Based on the literature [Stoichiometric methane conversion to ethane using photochemical looping at ambient temperature[J]. Nature Energy, 2020(5), 511–519], we prepared heteropolyacid and silver-modified TiO2 catalysts using an improved one-step impregnation-calcination method. During the impregnation process, a certain amount of TiO2 and PW were first weighed... 12 And AgNO3 (only the mass percentage of AgNO3 and TiO2 was varied between 0.5%, 1.0%, 1.5%, and 2.5%), added to 50 ml of water, ultrasonically dispersed, stirred for 12 hours, washed with deionized water, filtered and collected the sample; S2: Then the obtained material is dried at 100°C for 12 hours; S3: The material prepared in S2 is placed in a muffle furnace and heated to 300 °C at a heating rate of 2 °C / min, and maintained at 300 °C for 3 hours to obtain TWA-X, where X represents the mass percentage values of AgNO3 and TiO2 (0.5, 1.0, 1.5, 2.5).
3. The method for preparing a photocatalyst composed of Keggin-type heteropolyacid, AgNO3, and mesoporous TiO2 nanoparticles according to claim 2, characterized in that, During the S1 process, the mass percentages of AgNO3 and TiO2 varied between 0.5%, 1.0%, 1.5%, and 2.5%.
4. The application of the above-mentioned photocatalyst composed of Keggin-type heteropolyacid, AgNO3, and mesoporous TiO2 is characterized in that, The specific steps for photocatalytic oxidation of methane to produce liquid C1 oxygen-containing compounds are as follows: 5 mg of catalyst was dispersed in 50 mL of deionized water. Oxygen was selected as the oxidant. The ratio of methane to oxygen was 29:
1. The total pressure was 3 MPa. The light source was a 300 W xenon lamp. The reaction temperature was room temperature. The reaction was carried out for 1 hour under the light source irradiation. The product content was then measured.