Preparation method of solar-driven methane-to-methanol catalytic material and application thereof in outdoor system

Abstract

The application relates to the technical field of catalytic materials, in particular to a preparation method of a solar-energy-driven catalytic material for preparing formaldehyde from methane and application of the catalytic material in an outdoor system, and the preparation method comprises the following steps: S1, dissolving nano-titanium dioxide and boron nitride powder in deionized water, adding glacial acetic acid after stirring, continuously stirring to obtain a uniform suspension; S2, adding a light absorption modifier and a structure modifier into the suspension, reacting for 3-4 hours under water bath conditions, then reducing to room temperature, washing a filter cake after solid-liquid separation; S3, drying the filter cake, grinding, and obtaining the solar-energy-driven catalytic material for preparing formaldehyde from methane. In the application, the modified carrier, the light absorption modifier and the structure modifier synergistically act together, high-efficiency activation of methane molecules, high-selectivity generation of target product formaldehyde, and wide adaptability to reaction conditions are realized, so that the catalytic material can maintain high activity and stability under strong sunlight or simulated xenon lamp illumination.

Description

Technical Field

[0001] This invention relates to the field of catalytic materials technology, specifically to a method for preparing a solar-driven methane-to-formaldehyde catalytic material and its application in outdoor systems. Background Technology

[0002] Formaldehyde, as an important basic chemical raw material, is mainly produced industrially through the "methanol oxidation method" using methanol as a raw material. This process generally suffers from problems such as high reaction temperatures (280-700℃), high energy consumption, high carbon emissions, and the easy generation of byproducts such as carbon monoxide and carbon dioxide, leading to limited formaldehyde selectivity. In contrast, photocatalytic direct conversion of methane to formaldehyde technology offers milder reaction conditions (room temperature and pressure), can utilize clean energy sources such as solar energy, and is a clean and pollution-free process, making it a highly promising green synthesis route. However, this technology still faces several key bottlenecks that restrict its industrial application.

[0003] Common photocatalysts (such as pure TiO2) generally suffer from low visible light utilization, high photogenerated carrier recombination rates, and insufficient active sites, resulting in low methane activation efficiency and formaldehyde selectivity and yield that fail to meet practical requirements. Secondly, the reaction process relies on external light, especially the ultraviolet-near-ultraviolet wavelength range, causing the naturally light-driven reaction to be interrupted at night or when light is insufficient, leading to discontinuous production, low equipment utilization, and limited capacity. Furthermore, existing photocatalytic systems often suffer from low integration, such as separation of solar energy collection from the reaction process, significant energy transfer losses, and insufficient light energy utilization. Therefore, there is an urgent need to develop a catalytic material with high catalytic activity, broad spectral response, and structural stability, and to construct an integrated reaction system capable of continuous day and night operation and energy self-sufficiency, in order to promote the practical application of photocatalytic methane-to-formaldehyde conversion technology. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing a solar-driven methane-to-formaldehyde catalyst and its application in outdoor systems.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing a solar-driven methane-to-formaldehyde catalyst includes the following preparation steps:

[0007] S1. By mass, dissolve 0.2-0.5 parts of nano titanium dioxide and 0.2-0.5 parts of boron nitride powder in 190-200 parts of deionized water, stir at 300-500 r / min for 3-5 min, add 8-10 parts of glacial acetic acid, and continue stirring for 8-10 min to obtain a uniform suspension.

[0008] S2. Add 1-3 parts of light absorption modifier and 1-3 parts of structure modifier to the suspension obtained in step S1. React for 3-4 hours at a speed of 200-300 r / min under water bath conditions of 78-82℃. After cooling to room temperature, wash the filter cake 2-3 times with a small amount of deionized water after solid-liquid separation.

[0009] S3. Transfer the filter cake obtained in step S2 to a vacuum drying oven and dry it at 58-62℃ for 10-12 hours. Then grind it gently with an agate mortar to obtain a solar-driven methane-to-formaldehyde catalyst.

[0010] The preparation of the structural modifier includes the following steps:

[0011] S21. By mass, dissolve 2-2.2 parts of citric acid and 1-1.4 parts of urea in 10-12 parts of deionized water, transfer to a high-pressure reactor lined with polytetrafluoroethylene, react at 180-200℃ for 3-4 hours, cool and dialyze for 20-24 hours to obtain a carbon quantum dot solution.

[0012] S22. Mix 20-25 parts of the modified carrier and the carbon quantum dot solution obtained in step S21, stir at 250-300 r / min for 1-2 h, and then stir and evaporate the solvent at 60℃ to obtain a preliminary composite powder.

[0013] S23. Dissolve the preliminary composite powder obtained in step S22 and 0.15-0.2 parts of silane coupling agent in 10-12 parts of anhydrous ethanol, adjust the pH to 5-6 with acetic acid, reflux and stir at 70°C for 2-3 hours, then add 0.05-0.1 parts of hexadecyltrimethylammonium bromide and continue stirring for 40-50 minutes.

[0014] S24. Separate the mixture obtained in step S23, dry it at 80°C, calcine it at 440-450°C for 1-2 hours, and grind it to obtain the structure modifier.

[0015] Preferably, the preparation of the light absorption modifier includes the following steps:

[0016] S11. Dissolve 0.3-0.4 parts by mass of silver nitrate and 0.2-0.3 parts by mass of copper nitrate in 50-60 parts by mass of deionized water to obtain solution A;

[0017] S12. Dissolve 1-1.3 parts sodium citrate and 0.1-0.2 parts ascorbic acid in 50-60 parts deionized water to obtain solution B;

[0018] S13. Mix solution A and solution B, stir at 450-500 r / min for 50-60 min in a water bath at 58-62℃, concentrate by rotary evaporation at 68-72℃, and freeze-dry to obtain the light absorption modifier.

[0019] Preferably, the preparation of the modified support includes the following steps:

[0020] S221. By mass, dissolve 0.3-0.4 parts of ammonium metatungstate, 0.1-0.3 parts of citric acid, and 0.7-0.8 parts of 1 mol / L hydrochloric acid solution in 2.5-3 parts of deionized water to obtain a precursor solution;

[0021] S222. Add nano silica dispersion to the precursor solution obtained in step S221, stir at 250-300 r / min for 3-4 h in a 40℃ water bath, and then stir at 60℃ to evaporate the solvent.

[0022] S223. The mixture obtained in step S222 is dried at 80°C for 5-6 hours, ground into fine powder, placed in a muffle furnace and calcined in air atmosphere, cooled to room temperature and then ground to obtain the modified carrier.

[0023] Preferably, the filter membrane used for solid-liquid separation in step S2 is a 0.22 μm aqueous microporous filter membrane.

[0024] Preferably, the molecular weight cutoff of the dialysis bag used in step S21 is 1000 Da.

[0025] Preferably, the silane coupling agent in step S23 is selected from KH-550.

[0026] Preferably, in step S222, the mass concentration of the nano-silica dispersion is 3%, and the solvent is anhydrous ethanol.

[0027] Preferably, in step S223, the temperature is increased to 250°C at a rate of 2°C / min, held for 1 hour, and then increased to 450°C at a rate of 2°C / min and held for 2 hours.

[0028] Application of a solar-driven methane-to-formaldehyde catalyst in an outdoor system.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1. This invention constructs a three-dimensional conductive network in the catalyst system through the synergistic effect of structural modifiers and modified supports, accelerating the migration of photogenerated electrons from the light absorber to the active sites, further inhibiting charge recombination, and improving the structural stability and durability of the composite material. The modified support not only possesses a high specific surface area, providing highly dispersed anchoring sites for the active components and preventing their aggregation, but also has certain photocatalytic activity and acidic sites, which can initially activate methane molecules. Its stable porous structure facilitates the diffusion of reactants and products, improving mass transfer efficiency.

[0031] 2. In this invention, the modified carrier, light absorption modifier, and structural modifier work synergistically to achieve efficient activation of methane molecules, highly selective generation of the target product formaldehyde, and wide adaptability to reaction conditions, so that the catalytic material can maintain high activity and stability under strong sunlight or simulated xenon lamp irradiation. Attached Figure Description

[0032] Figure 1 This is a process flow diagram for preparing the solar-driven methane-to-formaldehyde catalytic material of the present invention;

[0033] Figure 2 The above is a bar chart showing the yield of the solar-driven methane-to-formaldehyde catalyst prepared in Example 1 and Comparative Example 1 of this invention.

[0034] Figure 3 This is a schematic diagram illustrating the selectivity of the solar-driven methane-to-formaldehyde catalytic material prepared in Example 1 and Comparative Example 1 of the present invention;

[0035] Figure 4 The graphs show the CO yield of the solar-driven methane-to-formaldehyde catalysts prepared in Examples 1 and 2 of this invention.

[0036] Figure 5 Line graphs showing the CO2 production of the solar-driven methane-to-formaldehyde catalysts prepared in Example 1 and Comparative Example 2 of this invention.

[0037] Figure 6 The image shows the XRD pattern of the solar-driven methane-to-formaldehyde catalyst obtained in Example 1 of this invention. Detailed Implementation

[0038] The present invention will now be clearly and completely described in conjunction with embodiments thereof. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0039] Please see Figures 1-6 The present invention provides a technical solution:

[0040] Example 1

[0041] A method for preparing a solar-driven methane-to-formaldehyde catalytic material:

[0042] Before preparing the solar-driven methane-to-formaldehyde catalyst, the modified support, light absorption modifier, and structural modifier are prepared:

[0043] The preparation of the modified carrier includes the following steps:

[0044] S221. Dissolve 0.3g ammonium metatungstate, 0.1g citric acid, and 0.7g 1mol / L hydrochloric acid solution in 2.5g deionized water to obtain a precursor solution;

[0045] S222. Add a 3% (w / w) nano-silica dispersion to the precursor solution obtained in step S221, stir at 250 r / min for 3 h in a 40°C water bath, and then stir at 60°C to evaporate the solvent.

[0046] S223. The mixture obtained in step S222 is dried at 80°C for 5 hours, ground into fine powder, and then placed in a muffle furnace for calcination in air atmosphere (heated to 250°C at a rate of 2°C / min, held for 1 hour, then heated to 450°C at a rate of 2°C / min, and held for 2 hours). After cooling to room temperature, it is ground to obtain the modified carrier.

[0047] The preparation of the light absorption modifier includes the following steps:

[0048] S11. Dissolve 0.3g of silver nitrate and 0.2g of copper nitrate in 50g of deionized water to obtain solution A;

[0049] S12. Dissolve 1g of sodium citrate and 0.1g of ascorbic acid in 50g of deionized water to obtain solution B;

[0050] S13. Mix solution A and solution B, stir at 450 r / min for 50 min in a 58℃ water bath, concentrate by rotary evaporation at 68℃, and freeze-dry to obtain the light absorption modifier.

[0051] The preparation of the structural modifier includes the following steps:

[0052] S21. Dissolve 2g of citric acid and 1g of urea in 10g of deionized water, transfer to a high-pressure reactor lined with polytetrafluoroethylene, react at 180℃ for 3h, cool and then dialyze (the molecular weight cutoff of the dialysis bag used for dialysis is 1000Da) for 20h to obtain a carbon quantum dot solution.

[0053] S22. Mix 20g of modified carrier with the carbon quantum dot solution obtained in step S21, stir at 250r / min for 1h, and then stir and evaporate the solvent at 60℃ to obtain preliminary composite powder;

[0054] S23. Dissolve the preliminary composite powder obtained in step S22 and 0.15g of silane coupling agent (KH-550) in 10g of anhydrous ethanol, adjust the pH to 5 with acetic acid, reflux and stir at 70℃ for 2h, then add 0.05g of cetyltrimethylammonium bromide and continue stirring for 40min.

[0055] S24. Separate the mixture obtained in step S23, dry it at 80°C, calcine it at 440°C for 1 hour, and grind it to obtain the structure modifier.

[0056] S1. Dissolve 0.2g of nano titanium dioxide and 0.2g of boron nitride powder in 190g of deionized water, stir at 300r / min for 3min, add 8g of glacial acetic acid, and continue stirring for 8min to obtain a uniform suspension.

[0057] S2. Add 1g of light absorption modifier and 1g of structure modifier to the suspension obtained in step S1. React for 3 hours at 200r / min in a water bath at 78℃. After cooling to room temperature, the filter cake is washed twice with a small amount of deionized water after solid-liquid separation (0.22μm aqueous microporous filter membrane).

[0058] S3. Transfer the filter cake obtained in step S2 to a vacuum drying oven, dry it at 58°C for 10 hours, and then gently grind it with an agate mortar to obtain a solar-driven methane-to-formaldehyde catalyst.

[0059] Example 2

[0060] A method for preparing a solar-driven methane-to-formaldehyde catalytic material:

[0061] Before preparing the solar-driven methane-to-formaldehyde catalyst, the modified support, light absorption modifier, and structural modifier are prepared:

[0062] The preparation of the modified carrier includes the following steps:

[0063] S221. Dissolve 0.4g ammonium metatungstate, 0.3g citric acid, and 0.8g 1mol / L hydrochloric acid solution in 3g deionized water to obtain a precursor solution;

[0064] S222. Add a 3% (w / w) nano-silica dispersion to the precursor solution obtained in step S221, stir at 300 r / min for 4 h in a 40°C water bath, and then stir at 60°C to evaporate the solvent.

[0065] S223. The mixture obtained in step S222 is dried at 80°C for 6 hours, ground into fine powder, and then placed in a muffle furnace for calcination in air atmosphere (heated to 250°C at a rate of 2°C / min, held for 1 hour, then heated to 450°C at a rate of 2°C / min, and held for 2 hours). After cooling to room temperature, it is ground to obtain the modified carrier.

[0066] The preparation of the light absorption modifier includes the following steps:

[0067] S11. Dissolve 0.4g of silver nitrate and 0.3g of copper nitrate in 60g of deionized water to obtain solution A;

[0068] S12. Dissolve 1.3g sodium citrate and 0.2g ascorbic acid in 60g deionized water to obtain solution B;

[0069] S13. Mix solution A and solution B, stir at 500 r / min for 60 min in a 62℃ water bath, concentrate by rotary evaporation at 72℃, and freeze-dry to obtain the light absorption modifier.

[0070] The preparation of the structural modifier includes the following steps:

[0071] S21. Dissolve 2.2g of citric acid and 1.4g of urea in 12g of deionized water, transfer to a high-pressure reactor lined with polytetrafluoroethylene, react at 200℃ for 4h, cool and then dialyze (the molecular weight cutoff of the dialysis bag used for dialysis is 1000Da) for 24h to obtain a carbon quantum dot solution.

[0072] S22. Mix 25g of modified carrier with the carbon quantum dot solution obtained in step S21, stir at 300r / min for 2h, and then stir and evaporate the solvent at 60℃ to obtain preliminary composite powder;

[0073] S23. Dissolve the preliminary composite powder obtained in step S22 and 0.2g of silane coupling agent (KH-550) in 12g of anhydrous ethanol, adjust the pH to 6 with acetic acid, reflux and stir at 70℃ for 3h, then add 0.1g of cetyltrimethylammonium bromide and continue stirring for 50min.

[0074] S24. Separate the mixture obtained in step S23, dry it at 80°C, calcine it at 450°C for 2 hours, and grind it to obtain the structure modifier.

[0075] S1. Dissolve 0.5g of nano titanium dioxide and 0.5g of boron nitride powder in 200g of deionized water, stir at 500r / min for 5min, add 10g of glacial acetic acid, and continue stirring for 10min to obtain a uniform suspension.

[0076] S2. Add 3g of light absorption modifier and 3g of structure modifier to the suspension obtained in step S1. React for 4 hours at 300r / min in a water bath at 82℃. After cooling to room temperature, the filter cake is washed three times with a small amount of deionized water after solid-liquid separation (0.22μm aqueous microporous filter membrane).

[0077] S3. Transfer the filter cake obtained in step S2 to a vacuum drying oven, dry it at 62°C for 12 hours, and then gently grind it with an agate mortar to obtain a solar-driven methane-to-formaldehyde catalyst.

[0078] Example 3

[0079] A method for preparing a solar-driven methane-to-formaldehyde catalytic material:

[0080] Before preparing the solar-driven methane-to-formaldehyde catalyst, the modified support, light absorption modifier, and structural modifier are prepared:

[0081] The preparation of the modified carrier includes the following steps:

[0082] S221. Dissolve 0.32g ammonium metatungstate, 0.15g citric acid, and 0.72g 1mol / L hydrochloric acid solution in 2.6g deionized water to obtain a precursor solution;

[0083] S222. Add a 3% (w / w) nano-silica dispersion to the precursor solution obtained in step S221, stir at 260 r / min for 3.5 h in a 40°C water bath, and then stir at 60°C to evaporate the solvent.

[0084] S223. The mixture obtained in step S222 is dried at 80°C for 5.5 h, ground into fine powder, and then placed in a muffle furnace for calcination in air atmosphere (heated to 250°C at a rate of 2°C / min, held for 1 h, then heated to 450°C at a rate of 2°C / min, and held for 2 h). After cooling to room temperature, it is ground to obtain the modified carrier.

[0085] The preparation of the light absorption modifier includes the following steps:

[0086] S11. Dissolve 0.32g of silver nitrate and 0.22g of copper nitrate in 52g of deionized water to obtain solution A;

[0087] S12. Dissolve 1.1g sodium citrate and 0.12g ascorbic acid in 52g deionized water to obtain solution B;

[0088] S13. Mix solution A and solution B, stir at 460 r / min for 52 min in a 59℃ water bath, concentrate by rotary evaporation at 69℃, and freeze-dry to obtain the light absorption modifier.

[0089] The preparation of the structural modifier includes the following steps:

[0090] S21. Dissolve 2.05g of citric acid and 1.1g of urea in 10.5g of deionized water, transfer to a high-pressure reactor lined with polytetrafluoroethylene, react at 185℃ for 3.5h, cool and then dialyze (the molecular weight cutoff of the dialysis bag used for dialysis is 1000Da) for 21h to obtain a carbon quantum dot solution.

[0091] S22. Mix 21g of modified carrier with the carbon quantum dot solution obtained in step S21, stir at 260r / min for 1.5h, and then stir and evaporate the solvent at 60℃ to obtain preliminary composite powder;

[0092] S23. Dissolve the preliminary composite powder obtained in step S22 and 0.16g of silane coupling agent (KH-550) in 10.5g of anhydrous ethanol, adjust the pH to 5.5 with acetic acid, reflux and stir at 70℃ for 2.5h, then add 0.06g of cetyltrimethylammonium bromide and continue stirring for 42min.

[0093] S24. Separate the mixture obtained in step S23, dry it at 80°C, calcine it at 442°C for 1.5 hours, and grind it to obtain the structure modifier.

[0094] S1. Dissolve 0.3g of nano titanium dioxide and 0.3g of boron nitride powder in 192g of deionized water, stir at 350r / min for 4min, add 8.5g of glacial acetic acid, and continue stirring for 9min to obtain a uniform suspension;

[0095] S2. Add 1.5g of light absorption modifier and 1.5g of structure modifier to the suspension obtained in step S1. React at 220r / min for 3.5h under water bath conditions of 79℃. After cooling to room temperature, the filter cake is washed twice with a small amount of deionized water after solid-liquid separation (0.22μm aqueous microporous filter membrane).

[0096] S3. Transfer the filter cake obtained in step S2 to a vacuum drying oven, dry it at 59°C for 10.5 hours, and then gently grind it with an agate mortar to obtain a solar-driven methane-to-formaldehyde catalyst.

[0097] Example 4

[0098] A method for preparing a solar-driven methane-to-formaldehyde catalytic material:

[0099] Before preparing the solar-driven methane-to-formaldehyde catalyst, the modified support, light absorption modifier, and structural modifier are prepared:

[0100] The preparation of the modified carrier includes the following steps:

[0101] S221. Dissolve 0.38g ammonium metatungstate, 0.21g citric acid, and 0.78g 1mol / L hydrochloric acid solution in 2.8g deionized water to obtain a precursor solution;

[0102] S222. Add a 3% (w / w) nano-silica dispersion to the precursor solution obtained in step S221, stir at 280 r / min for 3.5 h in a 40°C water bath, and then stir at 60°C to evaporate the solvent.

[0103] S223. The mixture obtained in step S222 is dried at 80°C for 5.5 h, ground into fine powder, and then placed in a muffle furnace for calcination in air atmosphere (heated to 250°C at a rate of 2°C / min, held for 1 h, then heated to 450°C at a rate of 2°C / min, and held for 2 h). After cooling to room temperature, it is ground to obtain the modified carrier.

[0104] The preparation of the light absorption modifier includes the following steps:

[0105] S11. Dissolve 0.38g of silver nitrate and 0.28g of copper nitrate in 58g of deionized water to obtain solution A;

[0106] S12. Dissolve 1.2g sodium citrate and 0.18g ascorbic acid in 58g deionized water to obtain solution B;

[0107] S13. Mix solution A and solution B, stir at 480 r / min for 57 min in a 61℃ water bath, concentrate by rotary evaporation at 70℃, and freeze-dry to obtain the light absorption modifier.

[0108] The preparation of the structural modifier includes the following steps:

[0109] S21. Dissolve 2.15g of citric acid and 1.3g of urea in 11g of deionized water, transfer to a high-pressure reactor lined with polytetrafluoroethylene, react at 195℃ for 3.5h, cool and then dialyze (the molecular weight cutoff of the dialysis bag used for dialysis is 1000Da) for 23h to obtain a carbon quantum dot solution.

[0110] S22. Mix 24g of modified carrier with the carbon quantum dot solution obtained in step S21, stir at 280r / min for 1.5h, and then stir and evaporate the solvent at 60℃ to obtain preliminary composite powder;

[0111] S23. Dissolve the preliminary composite powder obtained in step S22 and 0.18g of silane coupling agent (KH-550) in 11g of anhydrous ethanol, adjust the pH to 5.5 with acetic acid, reflux and stir at 70℃ for 2.5h, then add 0.08g of cetyltrimethylammonium bromide and continue stirring for 48min.

[0112] S24. Separate the mixture obtained in step S23, dry it at 80°C, calcine it at 448°C for 1.5 hours, and grind it to obtain the structure modifier.

[0113] S1. Dissolve 0.4g of nano titanium dioxide and 0.4g of boron nitride powder in 198g of deionized water, stir at 450r / min for 4min, add 9g of glacial acetic acid, and continue stirring for 9min to obtain a uniform suspension.

[0114] S2. Add 2g of light absorption modifier and 2g of structure modifier to the suspension obtained in step S1. React at 280r / min for 3.5h under water bath conditions at 80℃. After cooling to room temperature, the filter cake is washed 3 times with a small amount of deionized water after solid-liquid separation (0.22μm aqueous microporous filter membrane).

[0115] S3. Transfer the filter cake obtained in step S2 to a vacuum drying oven, dry it at 60°C for 11 hours, and then gently grind it with an agate mortar to obtain a solar-driven methane-to-formaldehyde catalyst.

[0116] Comparative Example 1

[0117] The only difference between Comparative Example 1 and Example 1 is that no modified carrier was added in this comparative example; the other steps are exactly the same in Comparative Example 1 and Example 1.

[0118] Comparative Example 2

[0119] The only difference between Comparative Example 2 and Example 1 is that no light absorption modifier or structural modifier was added in this comparative example. The remaining steps are exactly the same in Comparative Example 2 and Example 1.

[0120] Performance testing:

[0121] To verify the successful composite of the catalytic materials, the phase and crystal structure of the solar-driven methane-to-formaldehyde catalytic material obtained in Example 1 were analyzed by XRD. The test results are attached. Figure 6 As shown in the figure, the diffraction peaks of the catalytic material correspond to those of the standard card (PDF#21-1272), with no impurity peaks and relatively sharp peaks. For pure TiO2, the strongest diffraction peak corresponding to the (101) plane appears at 25.2°, indicating that the main exposure of TiO2 is (101). The synthesized catalytic material (TiO2 / BN) composite sample has an XRD pattern similar to that of TiO2, and the positions of the diffraction peaks have not changed significantly compared to TiO2. The catalytic material was successfully composited. In addition, the diffraction peak shape of BN was not observed in the XRD pattern of the catalytic material, which may be due to the low diffraction intensity of BN in TiO2 / BN and the random distribution of TiO2 on BN.

[0122] Appendix Figure 2 The bar charts shown are of the yields of the solar-driven methane-to-formaldehyde catalysts prepared in Example 1 and Comparative Example 1 of this invention. Figure 3 This diagram illustrates the selectivity of the solar-driven methane-to-formaldehyde catalyst prepared in Example 1 and Comparative Example 1 of this invention. As can be seen from the diagram, the CH3OH yield of the solar-driven methane-to-formaldehyde catalyst prepared in Example 1 reaches approximately 330 μmol g. -1 ·h -1The selectivity of the modified support is 1.27 times that of an aerobic atmosphere, and its selectivity increases to 65%; while the selectivity of the solar-driven methane-to-formaldehyde catalyst prepared in Comparative Example 1 is only 41%. This indicates that the modified support plays a key role in the photocatalytic direct conversion of methane to formaldehyde.

[0123] Appendix Figure 4 The attached graphs show the CO yield of the solar-driven methane-to-formaldehyde catalysts prepared in Examples 1 and 2 of this invention. Figure 5 The graphs show the CO2 production of the solar-driven methane-to-formaldehyde catalysts prepared in Example 1 and Comparative Example 2 of this invention. In Comparative Example 2, the CO and CO2 production of the solar-driven methane-to-formaldehyde catalyst continuously increased over time (CO reached 12.02 μmol g / L at 2 hours). -1 CO2 reached 506.21 μmol g -1 Meanwhile, the CO yield of the solar-driven methane-to-formaldehyde catalyst prepared in Example 1 remained at a low level (only 5 μmol g at 2h). -1 The lack of significant accumulation in CO2 production confirms the synergistic effect of the modified carrier, light absorption modifier, and structural modifier, which together achieved highly selective generation of the target product formaldehyde, inhibited the production of peroxidation products, and significantly increased methanol production.

[0124] The solar-driven methane-to-formaldehyde catalyst prepared in Examples 1-4 was uniformly distributed on the flat-plate reactor of the device (PLR STPRS-03, Beijing Pofilai Technology Co., Ltd., Beijing, China) using a coating method. After connecting the gas path, the entire reaction system was started. During the day when there is sufficient sunlight, sunlight shines through the quartz window at the top of the flat-plate reactor, directly illuminating the TiO2-BN catalyst below. As the direction of sunlight changes, the flat-plate reactor can always track the light source, undergoing a photocatalytic reaction to convert the reactant methane into formaldehyde. At the same time, the solar panels on the sidewalls are fully extended, absorbing solar energy and charging the battery pack through the solar panel controller. At this time, the xenon lamp is lowered and stored, and does not work. As darkness falls and the ambient light intensity decreases, the circuit is reconnected, the solar panels on the sidewalls are folded back, the energy storage battery pack begins to supply power to the xenon lamp, the flat-plate reactor is lowered, the xenon lamp is raised and lit, and the strong light emitted shines on the catalyst, driving the photocatalytic reaction to continue. The next day, when the ambient light intensity exceeds the threshold, the xenon lamp power is cut off. At this point, the system switches back to daytime mode, and the solar panels resume charging the battery pack that has consumed some power, and the system enters the next 24-hour cycle.

[0125] Analysis confirmed that a considerable amount of formaldehyde products could be detected under both sunlight and xenon lamp illumination at night. The entire system successfully achieved continuous reaction, eliminating the reaction interruption period of more than ten hours. Simultaneously, during the eight hours of effective daylight, the electrical energy collected by the solar panels was sufficient to support the xenon lamp at its set power, achieving a positive energy cycle and self-sufficiency.

[0126] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a solar-driven methane-to-formaldehyde catalytic material, characterized in that, The preparation steps include the following: S1. By mass, dissolve 0.2-0.5 parts of nano titanium dioxide and 0.2-0.5 parts of boron nitride powder in 190-200 parts of deionized water, stir at 300-500 r / min for 3-5 min, add 8-10 parts of glacial acetic acid, and continue stirring for 8-10 min to obtain a uniform suspension. S2. Add 1-3 parts of light absorption modifier and 1-3 parts of structure modifier to the suspension obtained in step S1. React for 3-4 hours at a speed of 200-300 r / min under water bath conditions of 78-82℃. After cooling to room temperature, wash the filter cake 2-3 times with a small amount of deionized water after solid-liquid separation. S3. Transfer the filter cake obtained in step S2 to a vacuum drying oven and dry it at 58-62℃ for 10-12 hours. Then grind it gently with an agate mortar to obtain a solar-driven methane-to-formaldehyde catalyst. The preparation of the structural modifier includes the following steps: S21. By mass, dissolve 2-2.2 parts of citric acid and 1-1.4 parts of urea in 10-12 parts of deionized water, transfer to a high-pressure reactor lined with polytetrafluoroethylene, react at 180-200℃ for 3-4 hours, cool and dialyze for 20-24 hours to obtain a carbon quantum dot solution. S22. Mix 20-25 parts of the modified carrier and the carbon quantum dot solution obtained in step S21, stir at 250-300 r / min for 1-2 h, and then stir and evaporate the solvent at 60℃ to obtain a preliminary composite powder. S23. Dissolve the preliminary composite powder obtained in step S22 and 0.15-0.2 parts of silane coupling agent in 10-12 parts of anhydrous ethanol, adjust the pH to 5-6 with acetic acid, reflux and stir at 70°C for 2-3 hours, then add 0.05-0.1 parts of hexadecyltrimethylammonium bromide and continue stirring for 40-50 minutes. S24. Separate the mixture obtained in step S23, dry it at 80°C, calcine it at 440-450°C for 1-2 hours, and grind it to obtain the structure modifier; The preparation of the light absorption modifier includes the following steps: S11. Dissolve 0.3-0.4 parts by mass of silver nitrate and 0.2-0.3 parts by mass of copper nitrate in 50-60 parts by mass of deionized water to obtain solution A; S12. Dissolve 1-1.3 parts sodium citrate and 0.1-0.2 parts ascorbic acid in 50-60 parts deionized water to obtain solution B; S13. Mix solution A and solution B, stir at 450-500 r / min for 50-60 min in a water bath at 58-62℃, concentrate by rotary evaporation at 68-72℃, and freeze-dry to obtain the light absorption modifier; The preparation of the modified carrier includes the following steps: S221. By mass, dissolve 0.3-0.4 parts of ammonium metatungstate, 0.1-0.3 parts of citric acid, and 0.7-0.8 parts of 1 mol / L hydrochloric acid solution in 2.5-3 parts of deionized water to obtain a precursor solution; S222. Add nano silica dispersion to the precursor solution obtained in step S221, stir at 250-300 r / min for 3-4 h in a 40℃ water bath, and then stir at 60℃ to evaporate the solvent. S223. The mixture obtained in step S222 is dried at 80°C for 5-6 hours, ground into fine powder, placed in a muffle furnace and calcined in air atmosphere, cooled to room temperature and then ground to obtain the modified carrier.

2. The method for preparing a solar-driven methane-to-formaldehyde catalytic material according to claim 1, characterized in that, The filter membrane used for solid-liquid separation in step S2 is a 0.22μm aqueous microporous filter membrane.

3. The method for preparing a solar-driven methane-to-formaldehyde catalytic material according to claim 1, characterized in that, In step S21, the molecular weight cutoff of the dialysis bag used for dialysis is 1000 Da.

4. The method for preparing a solar-driven methane-to-formaldehyde catalytic material according to claim 1, characterized in that, In step S23, the silane coupling agent is selected from KH-550.

5. The method for preparing a solar-driven methane-to-formaldehyde catalytic material according to claim 1, characterized in that, In step S222, the mass concentration of the nano-silica dispersion is 3%, and the solvent is anhydrous ethanol.

6. The method for preparing a solar-driven methane-to-formaldehyde catalytic material according to claim 1, characterized in that, In step S223, the temperature is increased to 250°C at a rate of 2°C / min, held for 1 hour, and then increased to 450°C at a rate of 2°C / min and held for 2 hours.

7. The application of the solar-driven methane-to-formaldehyde catalyst prepared by the preparation method according to any one of claims 1-6 in an outdoor system.

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