Platinum-oxygen vacancy double-site synergistic molybdenum-doped tungsten oxide photocatalyst as well as preparation method and application thereof

Abstract

The invention provides a platinum-oxygen vacancy double-site synergistic molybdenum-doped tungsten oxide photocatalyst as well as a preparation method and application thereof, and belongs to the technical field of photocatalytic oxidation. In the photocatalyst, platinum is in atomic-scale dispersion, molybdenum doping is utilized to reduce an energy barrier formed by photoinduced oxygen vacancies in the material, and platinum-oxygen vacancy active sites are accurately constructed through a photochemical deposition strategy. According to the photocatalyst, oxygen is used as an oxidizing agent under the light-heat synergistic catalysis condition, the excellent methane conversion performance is achieved, the reaction condition is mild, and the catalysis process is environmentally friendly. In addition, by innovatively designing platinum-oxygen vacancy active sites, high catalytic activity is achieved with a small platinum loading amount, then the cost of the catalyst is reduced, the methane conversion rate is greatly increased through mild heat assistance, and industrial application value is achieved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalytic oxidation, and relates to a platinum-oxygen vacancy double-site synergistic molybdenum-doped tungsten oxide photocatalyst as well as a preparation method and application thereof. BACKGROUND

[0002] Methane (CH4) is one of the important fossil energies as the main component of natural gas, shale gas and associated gas. Due to its abundant reserves and low cost, methane is also a potential greenhouse gas. Therefore, the efficient conversion of methane into high-value chemicals under low energy consumption has become a focus of the academic community. In recent years, significant progress has been made in the directional conversion of methane into C1 platform chemicals (methanol, formaldehyde, formic acid, etc.). Among them, formic acid, as a key industrial platform molecule, has important significance in the livestock industry, textile industry, pharmaceutical industry and energy field. However, the C-H bond in methane molecule has a very high bond energy (about 439 kJ·mol -1 ) and strong chemical inertness; in addition, the direct one-step synthesis of formic acid from methane involves a complex multi-step reaction path and multiple intermediates, making it still a great challenge to achieve the efficient and high-selectivity conversion of methane to formic acid under mild conditions.

[0003] Achieving the photocatalytic selective oxidation of methane in an aqueous environment is an extremely attractive strategy. The advantage of this method is that it can activate water molecules or oxygen under mild conditions using light energy to produce reactive oxygen species, thereby realizing the effective activation of methane and providing a new idea for the conversion of methane under mild conditions.

[0004] The Chinese invention patent "Method for preparing formic acid by photocatalytic conversion of methane" (CN115745775A) discloses a method for realizing the photocatalytic oxidation of methane to prepare formic acid at room temperature. The method uses a palladium-loaded tungsten trioxide carrier as a photocatalyst, controls the content of the palladium active component, and uses inexpensive oxygen as an oxidant by controlling the preparation process parameters, thereby achieving a high formic acid yield, but the formic acid product selectivity is low, only 62%.

[0005] Xiong Yujie et al. (J. Am. Chem. Soc. 2025, 147, 2444-2454) improved the platinum-loaded tungsten oxide photocatalyst by using sulfuric acid solution as the reaction medium to promote the proton-coupled electron transfer process. The reaction system can achieve a formic acid yield of 177 μmol and a formic acid liquid product selectivity as high as 84%, however, the reaction requires more than 12 hours of reaction time to achieve high formic acid selectivity, which will inevitably lead to the peroxidation of formic acid to carbon dioxide, and the production cost is very high, so it cannot be applied on a large scale. SUMMARY

[0006] In view of the above deficiencies of the prior art, the present application provides a high-activity and low-cost molybdenum-doped tungsten oxide photocatalyst with platinum-oxygen vacancy dual sites and a preparation method and application thereof, which can achieve high yield and high formic acid selectivity in the one-step reaction of converting methane into formic acid, has mild reaction conditions, a green and environmentally-friendly catalytic process, and industrial application value.

[0007] The present application is realized by the following technical solutions:

[0008] The molybdenum-doped tungsten oxide photocatalyst with platinum-oxygen vacancy dual sites is in a nano-block structure and has a particle size of 50-80 nanometers. In the molybdenum-doped tungsten oxide photocatalyst, platinum is atomically dispersed on the surface of the molybdenum-doped tungsten oxide photocatalyst and selectively deposited around the photo-generated oxygen vacancies formed by the adjacent molybdenum, thereby forming platinum-oxygen vacancy active sites.

[0009] Further, the mass percentage of molybdenum in the molybdenum-doped tungsten oxide photocatalyst is 0.125-1 wt%, and preferably the mass percentage is 0.25-0.5 wt%. When the molybdenum doping ratio is within this range, the yield and selectivity of the target product are higher. If the doping ratio is too low, the oxygen vacancy active sites are insufficient, resulting in a low yield of the product. Too many oxygen vacancy defects as electron and hole recombination sites will reduce the utilization efficiency of the photo-generated carriers by the catalyst.

[0010] Further, in the molybdenum-doped tungsten oxide photocatalyst with platinum-oxygen vacancy dual sites, the mass percentage of platinum is 0.03-0.3 wt%, and preferably the mass percentage is 0.1-0.2%. When the platinum loading ratio is within this range, the yield and selectivity of the target product are higher. If the loading mass is too low, the platinum promoter active sites are insufficient, resulting in a low yield of the product. If the loading mass is too high, platinum is easily detached from the oxygen vacancy and agglomerated into nanoparticles, which reduces the adsorption and regulation ability of the oxygen vacancy to the active intermediates, and thus reduces the selectivity of the product.

[0011] A preparation method of a molybdenum-doped tungsten oxide photocatalyst with platinum-oxygen vacancy dual sites, comprising the following steps:

[0012] Step 1. At room temperature, dissolve molybdate and tungstate in deionized water, and the concentrations of molybdate and tungstate in the mixed solution are 0.025-0.2 mg / mL and 5-15 mg / mL, respectively. Add a 37 wt% hydrochloric acid solution to the mixed solution and stir uniformly. The volume ratio of the mixed solution to the hydrochloric acid solution is 200-100:1.

[0013] Step 2. Add anhydrous citric acid to the solution to make the concentration 4-5 mg / mL. Then add a 30 wt% hydrogen peroxide solution to the mixed solution, and the volume ratio of the mixed solution to the hydrogen peroxide solution is 50-30:1. After stirring for 10-20 minutes, transfer the solution to a high-pressure reaction kettle lined with Teflon.o C for 5-8 hours, after cooling, the product was filtered and washed thoroughly with deionized water and dried at 60-90 o C overnight to obtain the molybdenum-doped tungsten oxide precursor.

[0014] Step 3, the obtained molybdenum-doped tungsten oxide precursor was placed in a muffle furnace at 450-600 o C for 2 hours to obtain the molybdenum-doped tungsten oxide powder.

[0015] Step 4, the molybdenum-doped tungsten oxide and the platinum salt were added to deionized water to form a suspension, wherein the concentrations of the molybdenum-doped tungsten oxide and the platinum salt were 2-5 mg / mL and 0.0016-0.01 mg / mL respectively, the suspension was transferred to a quartz reactor and then methanol was added, the volume ratio of the suspension to the methanol was 19-5:1, the reactor was replaced with an argon atmosphere, and then the reactor was exposed to a xenon lamp, the light intensity was 180 mW·cm -2 After irradiation for 0.5-2 hours, the powder was collected by centrifugation, washed with deionized water, and dried at 60-80 o C overnight to obtain the molybdenum-doped tungsten oxide photocatalyst with platinum-oxygen vacancy active sites.

[0016] Further, in step 1, the molybdate is one or more of ammonium molybdate, sodium molybdate, and potassium molybdate, and the tungstate is one or more of ammonium tungstate, sodium tungstate, and potassium tungstate.

[0017] Further, in step 4, the platinum salt is one or more of chloroplatinic acid, ammonium chloroplatinate, potassium chloroplatinate, and sodium chloroplatinate.

[0018] The application of a platinum-oxygen vacancy dual-site synergistic molybdenum-doped tungsten oxide photocatalyst in the preparation of formic acid from methane, the specific steps are as follows:

[0019] The platinum-oxygen vacancy dual-site synergistic molybdenum-doped tungsten oxide photocatalyst was ultrasonically dispersed in deionized water at a solid-liquid ratio of (5-20) mg:180 mL, the pH was adjusted to 1.5-2.3 by concentrated sulfuric acid, and then transferred to a high-pressure reactor with a light-transmitting window at the top, oxygen and methane were introduced, and the reactor was continuously stirred in the dark and heated to a reaction temperature of 45-80 o C, and then reacted under light irradiation at a wavelength of 365 nm to obtain a liquid-phase product mainly composed of formic acid; wherein the reaction temperature is preferably 60 o C, the air in the reactor was replaced with oxygen, and the final oxygen partial pressure in the reactor was 0.2-0.6 MPa, and the methane raw material gas partial pressure was 2.4-2.8 MPa; if the methane pressure is too small, the target product and selectivity are low; if the pressure is too large, gas-phase product CO2 is easily generated; the reaction time is 0.5-2 hours, and if the reaction time is too long, gas-phase product carbon dioxide is easily generated.

[0020] The mechanism of the present application is that:

[0021] The platinum-oxygen vacancy double-site synergistic molybdenum-doped tungsten oxide photocatalyst provided by the present application has platinum-oxygen vacancy active sites, platinum as an electron acceptor promotes the activation of oxygen, produces active oxygen substances (hydroxyl and superoxide radicals), and the oxygen vacancy as a hole acceptor enhances the adsorption capacity of active intermediates such as methyl and methoxy, realizes high yield and high formic acid selectivity in the one-step reaction of methane conversion to formic acid through the synergistic effect of platinum and oxygen vacancy, and heat-assisted regulation of the reaction path of methane-methanol-formaldehyde-formic acid.

[0022] Compared with the prior art, the present application has at least the following beneficial effects:

[0023] The present application designs and constructs a molybdenum-doped tungsten oxide photocatalyst loaded with a platinum assistant catalyst, reduces the energy barrier of the formation of photo-induced oxygen vacancies in the material by molybdenum doping, and precisely constructs platinum-oxygen vacancy active sites through a photochemical deposition strategy. Under the condition of light-heat synergistic catalysis, oxygen is used as an oxidant, and under the synergistic action of light and photocatalyst, methane is efficiently catalytically converted into formic acid, and the production rate of formic acid is as high as 69.26 mmol·g -1 ·h -1 The selectivity is as high as 80.21%, and the reaction conditions are mild, and the catalytic process is green and environmentally friendly. In addition, the present application innovatively designs platinum-oxygen vacancy active sites to realize high catalytic activity with less platinum loading, thereby reducing the cost of the catalyst, and greatly improving the methane conversion rate through mild heat assistance, which has industrial application value. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The preparation method principle of the present application is shown.

[0025] Figure 2 The nuclear magnetic resonance hydrogen spectrum (H-NMR) of the products obtained by testing the methane conversion of the Pt-MoWO3 photocatalyst prepared in Example 1 is shown. 1

[0026] Figure 3 The structure characterization comparison chart of the Pt-MoWO3, Pt-WO3, MoWO3 and WO3 photocatalysts prepared in Example 1, Comparative Example 1, Comparative Example 2 and Comparative Example 3 is shown, wherein a is the X-ray diffraction spectrum comparison chart (XRD), b is the X-ray photoelectron spectroscopy (XPS) Mo3d spectrum comparison chart, and c is the X-ray photoelectron spectroscopy (XPS) Pt4f spectrum comparison chart.

[0027] Figure 4 ​Morphology images of the Pt-MoW03photocatalyst prepared in Example 1, wherein a is a transmission electron microscope image (TEM), b is a high-angle annular dark-field scanning transmission electron microscope image (HAADF-STEM), c is an energy dispersive spectroscopy image (EDS), d is a tungsten element distribution image, e is an oxygen element distribution image, f is a molybdenum element distribution image, and g is a platinum element distribution image.

[0028] Figure 5 Morphology images of the Pt-MoW03, Pt-W03and W03photocatalysts prepared in Example 1, Comparative Example 1 and Comparative Example 3, wherein a is a transmission electron microscope image of the Pt-MoW03photocatalyst obtained in Example 1, b is a transmission electron microscope image of the Pt-W03photocatalyst obtained in Comparative Example 1, and c is a transmission electron microscope image of the W03photocatalyst obtained in Comparative Example 3.

[0029] Figure 6 X-ray diffraction images of the Pt-MoW03photocatalyst obtained in Example 2 before and after the reaction. DETAILED DESCRIPTION

[0030] In order to further understand the implementation method of the present application, the technical solutions in the examples of the present application are described clearly and completely. Meanwhile, the examples described below are only a part of the present application, not all. The following description is only for further illustrating the advantages and features of the present application, not for limiting the claims of the present application. Other examples obtained by the ordinary skilled in the art without creative labor are within the scope of protection of the present application.

[0031] Example 1

[0032] The present embodiment provides a preparation method of a molybdenum-doped tungsten trioxide photocatalyst with platinum-oxygen vacancy active sites, which is realized by the following steps, wherein the light-induced platinum-oxygen vacancy active site construction process is as shown in Figure 1 .

[0033] (1) 0.01 g of ammonium molybdate and 1.0 g of ammonium tungstate were dissolved in 95 mL of deionized water, and 0.7 mL of hydrochloric acid solution (37 wt%) was added under stirring; 0.4 g of anhydrous citric acid and 2 mL of hydrogen peroxide solution (30 wt%) were added to the solution, and after stirring for 15 minutes, the system was transferred to a Teflon-lined high-pressure reaction kettle, heated at 160 o C for 5 hours, and after cooling, the product was filtered and washed with deionized water, and dried at 80 o C overnight to obtain a molybdenum-doped tungsten trioxide precursor.

[0034] (2) The dried molybdenum-doped tungsten trioxide precursor was ground uniformly, and then heated in a muffle furnace at 500 oAfter annealing at C for 2 hours, molybdenum-doped tungsten oxide powder was obtained.

[0035] (3) The suspension obtained by dispersing 100 mg of molybdenum-doped tungsten oxide powder and 0.1 mg of chloroplatinic acid in 27 mL of deionized water was transferred to a quartz photoreactor, and 3 mL of methanol was added to replace the atmosphere with argon gas. The solution was then irradiated with a 300 W xenon lamp at a light intensity of 180 mW·cm. -2 After sedimentation for 2 hours, the product was collected by centrifugation and washed with deionized water for 80 hours. o Drying at C overnight yields a molybdenum-doped tungsten oxide photocatalyst (Pt-MoWO3) with platinum-oxygen vacancy active sites.

[0036] The XRD pattern of the Pt-MoWO3 photocatalyst prepared in this embodiment is as follows: Figure 3 As shown in Figure a, it matches well with the standard card for monoclinic tungsten oxide (JCPDS No. 43-1035), and the crystal structure remains stable after molybdenum doping and photodeposition. Figure 3 The presence of XPS peaks for molybdenum and platinum species in b and c indicates successful molybdenum doping and successful platinum loading.

[0037] TEM images of the Pt-MoWO3 photocatalyst prepared in this embodiment are shown below. Figure 4 As shown in Figure a, the interplanar spacing is consistent with that of monoclinic tungsten oxide (002); the HAADF-STEM image is shown below. Figure 4 As shown in Figure b, the bright spots in the yellow circles are platinum single atoms, indicating that platinum is atomically dispersed on the surface of the Pt-MoWO3 photocatalyst; the EDS spectrum is shown below. Figure 4 As shown in c, d, e, f, and g, this indicates that the elements are evenly distributed.

[0038] The photocatalyst prepared in this embodiment was subjected to a photothermal catalytic methane conversion test. The test method was as follows: 10 mg of the prepared Pt-MoWO3 photocatalyst was dispersed in 180 mL of deionized water under continuous stirring at 700 rpm. After adjusting the pH to 2.0 with concentrated sulfuric acid, the mixture was transferred to a high-pressure reactor with a light-transmitting window at the top. After replacing the air in the high-pressure reactor with oxygen, 0.4 MPa oxygen and 2.6 MPa methane were introduced, and the temperature was raised to 60°C under continuous stirring in the dark. o After C, irradiate with a 100W LED lamp (365nm) for 1 hour.

[0039] Example 2:

[0040] This embodiment provides a method for preparing a molybdenum-doped tungsten oxide photocatalyst with platinum-oxygen vacancy active sites, which is carried out according to the following steps:

[0041] (1) 0.025 g of sodium molybdate and 0.5 g of sodium tungstate were dissolved in 95 mL of deionized water, 0.5 mL of hydrochloric acid solution (37 wt%) was added under stirring, and 0.48 g of anhydrous citric acid and 3 mL of hydrogen peroxide solution (30%) were added to the solution. After stirring for 10 minutes, the system was transferred to a Teflon-lined high-pressure reaction kettle, heated at 180 o C for 6 hours, and after cooling, the product was filtered and washed with deionized water, and dried overnight at 60 o C to obtain a molybdenum-doped tungsten oxide precursor.

[0042] (2) After the dried powder was ground uniformly, it was annealed in a muffle furnace at 600 o C for 2 hours to obtain a molybdenum-doped tungsten oxide powder.

[0043] (3) A suspension obtained by dispersing 60 mg of the molybdenum-doped tungsten oxide powder and 0.3 mg of sodium chloroplatinate in 27 mL of deionized water was transferred to a quartz photo reactor, 1.4 mL of methanol was added, and the reactor was replaced with an argon atmosphere. Under irradiation of a 300 W xenon lamp at an irradiation intensity of 180 mW·cm -2 for 1 hour, the product was collected by centrifugation, and after washing with deionized water, it was dried overnight at 70 o C to obtain a Pt-MoWO3 photocatalyst.

[0044] The Pt-MoWO3 photocatalyst prepared in this example 2 was subjected to a photo-thermal catalytic methane conversion test. The test method was as follows: 5 mg of the above-prepared Pt-MoWO3 photocatalyst was dispersed in 180 mL of deionized water under continuous stirring at 700 rpm, and after adjusting the pH to 1.5 by adding concentrated sulfuric acid, it was transferred to a high-pressure reaction kettle with a light-transmitting window at the top. After replacing the air in the high-pressure reaction kettle with oxygen, 0.2 MPa of oxygen and 2.8 MPa of methane were introduced, and after heating to 45 o C under continuous stirring in the dark, a 100 W LED lamp (365 nm) was applied for irradiation, and the reaction was continued for 2 hours.

[0045] The XRD patterns of the Pt-MoWO3 photocatalyst before and after the methane conversion test reaction are shown in Figure 6 , and no obvious change was observed after the reaction, indicating that the Pt-MoWO3 photocatalyst has good chemical stability.

[0046] Example 3:

[0047] This example provides a method for preparing a molybdenum-doped tungsten oxide photocatalyst with platinum-oxygen vacancy active sites, which is realized by the following steps:

[0048] (1) 0.02 g of potassium molybdate was dissolved in 95 mL of deionized water with 1.5 g of potassium tungstate, 0.9 mL of hydrochloric acid solution (37 wt%) was added under stirring, and 0.5 g of anhydrous citric acid and 3.3 mL of hydrogen peroxide solution (30%) were added to the solution. After stirring for 20 minutes, the system was transferred to a Teflon-lined high-pressure reactor, and heated at 150 o C for 8 hours. After cooling, the product was filtered and washed with deionized water, and dried at 60 o C overnight to obtain a molybdenum-doped tungsten oxide precursor.

[0049] (2) The molybdenum-doped tungsten oxide precursor powder after drying was uniformly ground, and annealed at 450 o C for 2 hours in a muffle furnace to obtain a molybdenum-doped tungsten oxide powder.

[0050] (3) A suspension obtained by dispersing 125 mg of molybdenum tungsten oxide powder and 0.04 mg of potassium chloroplatinate in 25 mL of deionized water was transferred to a quartz photo-reactor, 5 mL of methanol was added, and the atmosphere was replaced with argon. Under the irradiation of a 300 W xenon lamp, the light intensity was 180 mW·cm -2 for 0.5 hours, and the product was collected by centrifugation and washed with deionized water, and then dried at 60 o C overnight to obtain a Pt-MoWO3 photocatalyst.

[0051] The Pt-MoWO3 photocatalyst prepared in this example was subjected to a photo-thermal catalytic methane conversion test. The test method was as follows: 20 mg of the above-prepared photocatalyst was dispersed in 180 mL of deionized water under continuous stirring at 700 rpm, and the pH was adjusted to 2.3 by adding concentrated sulfuric acid, and then transferred to a high-pressure reactor with a light-transmitting window at the top. After replacing the air in the high-pressure reactor with oxygen, 0.6 MPa of oxygen and 2.4 MPa of methane were introduced, and after heating to 80 o C under continuous stirring in the dark, a 100 W LED lamp (365 nm) was applied for irradiation, and the reaction was carried out for 0.5 hours.

[0052] Comparative Example 1: Platinum-loaded tungsten oxide photocatalyst

[0053] The preparation method of the platinum-loaded tungsten oxide photocatalyst in this comparative example was realized in the following steps:

[0054] (1) 1.0 g of ammonium tungstate was dissolved in 95 mL of deionized water, 0.7 mL of hydrochloric acid solution (37 wt%) was added under stirring, and 0.4 g of anhydrous citric acid and 2 mL of hydrogen peroxide solution (30 wt%) were added to the solution. After stirring for 15 minutes, the system was transferred to a Teflon-lined high-pressure reactor, and heated at 160 o C for 5 hours. After cooling, the product was filtered and washed with deionized water, and dried at 80o Dry overnight at C.

[0055] (2) After the dried powder is ground evenly, it is placed in a muffle furnace at 500°C. o Annealing at C for 2 hours yields tungsten oxide powder.

[0056] (3) The suspension obtained by dispersing 100 mg of tungsten oxide powder and 0.1 mg of chloroplatinic acid in 27 mL of deionized water was transferred to a quartz photoreactor, and 3 mL of methanol was added to replace the atmosphere with argon gas. The reactor was then irradiated with a 300 W xenon lamp at a light intensity of 180 mW·cm. -2 After sedimentation for 2 hours, the product was collected by centrifugation and washed with deionized water for 80 hours. o Dry at C overnight to obtain platinum-supported tungsten oxide photocatalyst (Pt-WO3).

[0057] The Pt-WO3 photocatalyst prepared in this comparative example was subjected to photothermal catalytic methane conversion test, and the test method was the same as in Example 1.

[0058] Comparative Example 2: Molybdenum-doped tungsten oxide photocatalyst

[0059] The preparation process of this comparative example is basically the same as that of Example 1, except that only steps (1) and (2) are performed to obtain molybdenum-doped tungsten oxide photocatalyst (MoWO3).

[0060] The MoWO3 photocatalyst prepared in this comparative example was subjected to photothermal catalytic methane conversion test, and the test method was the same as in Example 1.

[0061] Comparative Example 3: Pure Tungsten Oxide Photocatalyst

[0062] The preparation process of this comparative example is basically the same as that of comparative example 1, except that only steps (1) and (2) are performed to obtain pure tungsten oxide photocatalyst (WO3).

[0063] The WO3 photocatalyst prepared in this comparative example was subjected to photothermal catalytic methane conversion test, and the test method was the same as in Example 1.

[0064] A comparison of the TEM morphology of the Pt-MoWO3 photocatalyst prepared in Example 1 with that of the Pt-WO3 photocatalyst prepared in Comparative Example 1 and the WO3 photocatalyst prepared in Comparative Example 3 is shown below. Figure 5 As shown, a is a TEM image of the Pt-MoWO3 photocatalyst, which shows that the Pt-MoWO3 photocatalyst has a nanobulk structure. The morphology comparison with b and c shows that after molybdenum doping and platinum photochemical deposition, the crystal structure does not change significantly except that the surface of the photocatalyst becomes rougher.

[0065] Using gas chromatography (GC) 1H-NMR and UV-Vis diffuse reflectance spectroscopy were used to quantify the reaction products of photothermal catalytic methane conversion in Examples 1-3 and Comparative Examples 1-3, and to detect the yield of the reaction products and the selectivity of formic acid. The results are shown in Table 1.

[0066] Table 1. Methane conversion test results of Examples 1-3 and Comparative Examples 1-3

[0067]

[0068] Table 1 shows that the platinum-oxygen vacancy dual-site synergistic molybdenum-doped tungsten oxide photocatalyst provided by this invention exhibits excellent catalytic activity, with high formic acid yield and selectivity. A comparison of Example 1 with Comparative Examples 2 and 3 shows that the pure tungsten oxide photocatalyst has insufficient activation capacity for methane, making it difficult to deeply oxidize methane to formic acid, thus resulting in low catalytic activity. While molybdenum doping enhances the adsorption capacity for intermediates, slightly increasing the formic acid yield, its methane activation capacity remains insufficient, and the catalytic activity remains low. A comparison of Example 1 with Comparative Example 1 demonstrates a synergistic effect between platinum and oxygen vacancies. Compared to a single platinum-supported cocatalyst, the constructed platinum-oxygen vacancy active site not only improves the formic acid yield but also enhances formic acid selectivity by regulating the adsorption capacity of intermediates.

[0069] In summary, this invention designs and precisely constructs a molybdenum-doped tungsten oxide photocatalyst with platinum-oxygen vacancy active sites. Under photo-thermal synergistic catalytic conditions, using oxygen as the oxidant, methane is efficiently catalyzed to formic acid under light irradiation through the synergistic effect of platinum and oxygen vacancies, achieving a formic acid production rate as high as 69.26 mmol·g. -1 ·h -1 With a selectivity of up to 80.21%, mild reaction conditions, and a green and environmentally friendly catalytic process, it has the potential for large-scale industrial application.

[0070] The embodiments described above are merely illustrative of implementation methods of the present invention and should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A platinum-oxygen vacancy dual-site synergistic molybdenum-doped tungsten oxide photocatalyst, characterized in that, Platinum is atomically dispersed on the surface of molybdenum-doped tungsten oxide photocatalyst and selectively deposited around photogenerated oxygen vacancies formed at the adjacent sites of molybdenum, forming platinum-oxygen vacancy active sites.

2. The platinum-oxygen vacancy dual-site synergistic molybdenum-doped tungsten oxide photocatalyst according to claim 1, characterized in that, The molybdenum content in the molybdenum-doped tungsten oxide photocatalyst is 0.125-1 wt%.

3. The platinum-oxygen vacancy dual-site synergistic molybdenum-doped tungsten oxide photocatalyst according to claim 1, characterized in that, In the platinum-oxygen vacancy dual-site synergistic molybdenum-doped tungsten oxide photocatalyst, the platinum mass ratio is 0.03-0.3wt%.

4. A method for preparing a platinum-oxygen vacancy dual-site synergistic molybdenum-doped tungsten oxide photocatalyst according to any one of claims 1-3, characterized in that, Includes the following steps: Step 1: At room temperature, dissolve molybdate and tungstate in deionized water. The concentrations of molybdate and tungstate in the mixed solution are 0.025-0.2 mg / mL and 5-15 mg / mL, respectively. Add 37 wt% hydrochloric acid solution to the mixed solution and stir until homogeneous. The volume ratio of the mixed solution to the hydrochloric acid solution is 200-100:

1. Step 2: Add anhydrous citric acid to the solution to a concentration of 4-5 mg / mL. Then add 30 wt% hydrogen peroxide solution to the mixed solution, with a volume ratio of the mixed solution to hydrogen peroxide solution of 50-30:

1. Stir for 10-20 minutes, then transfer to a Teflon-lined high-pressure reactor and heat at 150-180°C. o Heating at C for 5-8 hours, cooling, filtering, washing, and then refrigerating at 60-90°C. o Drying under C yields a molybdenum-doped tungsten oxide precursor. Step 3: Place the obtained molybdenum-doped tungsten oxide precursor in a muffle furnace at 450-600°C. o Annealing at C for 2 hours yielded molybdenum-doped tungsten oxide powder. Step 4: Molybdenum-doped tungsten oxide and platinum salt are added to deionized water to prepare a suspension, wherein the concentrations of molybdenum-doped tungsten oxide and platinum salt are 2-5 mg / mL and 0.0016-0.01 mg / mL, respectively. The suspension is transferred to a quartz reactor, and methanol is added at a volume ratio of 19-5:

1. The reactor is then purged with an argon atmosphere and exposed to a xenon lamp with an irradiation intensity of 180 mW·cm⁻¹. -2 After irradiation for 0.5-2 hours, the samples are centrifuged, washed, and then dried at 60-80 °C. o Drying at C yields a molybdenum-doped tungsten oxide photocatalyst with platinum-oxygen vacancy active sites.

5. The preparation method according to claim 4, characterized in that, In step 1, the molybdate is one or more of ammonium molybdate, sodium molybdate, and potassium molybdate.

6. The preparation method according to claim 4, characterized in that, In step 1, the tungstate is one or more of ammonium tungstate, sodium tungstate, and potassium tungstate.

7. The preparation method according to claim 4, characterized in that, In step 4, the platinum salt is one or more of chloroplatinic acid, ammonium chloroplatinate, potassium chloroplatinate, and sodium chloroplatinate.

8. The application of a platinum-oxygen vacancy dual-site synergistic molybdenum-doped tungsten oxide photocatalyst as described in any one of claims 1-3 in the conversion of methane to formic acid.

9. The application of the platinum-oxygen vacancy dual-site synergistic molybdenum-doped tungsten oxide photocatalyst according to claim 8 in the conversion of methane to formic acid, characterized in that, The steps are as follows: The platinum-oxygen vacancy dual-site synergistic molybdenum-doped tungsten oxide photocatalyst was ultrasonically dispersed in deionized water at a solid-liquid ratio of (5-20) mg:180 mL. After adjusting the pH to 1.5-2.3 with concentrated sulfuric acid, the mixture was transferred to a high-pressure reactor with a top light-transmitting window, and oxygen and methane were introduced. The oxygen partial pressure was 0.2-0.6 MPa, and the methane partial pressure was 2.4-2.8 MPa. The mixture was continuously stirred in the dark and heated to 45-80°C. o After C, the reaction is carried out under light with a wavelength of 365nm for 0.5-2 hours.

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