Preparation method of Pt monatomic modified ZnO and application of Pt monatomic modified ZnO in photocatalytic oxidation of methane to generate oxygen-containing liquid product
By modifying ZnO photocatalysts with Pt single atoms, efficient conversion of methane into oxygen-containing liquid products was achieved under mild conditions, solving the problems of low selectivity and efficiency in existing technologies and showing potential for commercial applications.
Patent Information
- Application Number
- CN202510954893.1
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-11
- Publication Date
- 2025-10-17
AI Technical Summary
Existing technologies make it difficult to convert methane into high-value-added oxygen-containing liquid products, especially HCHO and CH3OH, with high selectivity under mild conditions, and traditional photocatalysts are prone to over-oxidation.
Pt single atoms were used to modify ZnO photocatalysts. Nano-ZnO was prepared by precipitation and calcination methods, and then Pt was loaded by photodeposition to achieve directional migration of photogenerated holes and precise design of methane activation sites, avoiding excessive oxidation dominated by OH.
Under low-temperature conditions, high activity and high selectivity were achieved to generate oxygen-containing liquid products, with an AQY of 14.14% and a selectivity of 95%. The mild reaction conditions simplified the catalyst preparation process and have commercial application potential.
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Figure CN120790145A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of photocatalytic materials, and particularly relates to a preparation method of Pt monatomic modified ZnO and application of the Pt monatomic modified ZnO in photocatalytic oxidation of methane to generate oxygen-containing liquid products. BACKGROUND
[0002] Methane (CH4) is the main component of coalbed methane, shale gas, and methane hydrate resources, and its efficient conversion to high-value chemicals has attracted increasing attention. However, the indirect conversion method (steam reforming to synthesis gas and then catalytic reforming) relied on by the industry usually requires high temperature and high pressure conditions. Therefore, it is an extremely attractive but challenging goal to achieve the direct and high-selectivity conversion of CH4 to liquid oxygen-containing compounds (such as HCHO and CH3OH) under mild conditions, which are key C1 platform molecules. This challenge stems from the inherent inertness of CH4 (its C-H bond dissociation energy is high) and the high reactivity of the target oxygen-containing compounds: under the conditions required to activate CH4, they are extremely prone to continuous oxidation to generate CO2 or CO.
[0003] Traditional strong activators (such as ·Cl and ·OH radicals) can effectively break the C-H bond of CH4, but they are also prone to attack the generated oxygen-containing products, leading to deep oxidation. Studies have shown that regardless of the activator used, the key step to successfully achieve high activity and high selectivity conversion is often the formation of methyl radicals (·CH3). Therefore, if CH4 can be directly activated to generate ·CH3 while avoiding highly oxidative activators (especially ·OH), it is expected to achieve high activity and high selectivity conversion.
[0004] Photocatalysis provides a possible way for this, using photogenerated holes to directly extract H from CH4 to generate ·CH3. However, previous studies have focused on generating ·OH radicals (through O2-derived reactive oxygen species ROS or adding H2O2) as the main activator, which inevitably leads to over-oxidation of the target products (Angew. Chem. Int. Ed. 2024, 63, e202409876.). To achieve a transition from the ·OH-dominated mechanism to the ·CH3-dominated mechanism, rational design of the photocatalyst is required, with the core being: ensuring sufficient CH4 supply on the surface of the catalyst; efficiently guiding photogenerated holes to specific active sites; and preferentially using holes to directly break the C-H bond of CH4 to generate ·CH3, and maximizing the inhibition of ·OH formation. Currently, there is no photocatalyst that meets all these requirements. SUMMARY
[0005] The present application aims to overcome the low activity, selectivity and quantum efficiency of liquid products in the prior art, and provides a preparation method of Pt single-atom modified ZnO and application of the Pt single-atom modified ZnO in photocatalytic oxidation of methane to generate oxygen-containing liquid products. By modifying ZnO with single-atom Pt, directional migration of photo-generated holes and accurate design of methane activation sites are successfully achieved, the problem of excessive oxidation in the traditional ·OH dominant approach is bypassed, and a new approach for methane conversion is provided.
[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:
[0007] In the first aspect of the present application, a preparation method of a Pt single-atom modified ZnO photocatalyst for photocatalytic oxidation of methane to generate oxygen-containing liquid products is provided. The method uses a precipitation method and a calcination method to prepare nano-ZnO, and then uses a photodeposition method to obtain a Pt / ZnO photocatalyst, thereby preparing a photocatalyst with atomic dispersion of Pt supported on ZnO, which comprises the following steps:
[0008] (1) A certain amount of zinc nitrate Zn(NO3)2·6H2O is placed in a container containing a certain amount of deionized water, and is fully stirred until dissolved to obtain a zinc nitrate solution; a certain amount of oxalic acid H2C2O4 is placed in a container containing a certain amount of deionized water, and is fully stirred until dissolved to obtain an oxalic acid solution;
[0009] (2) Under appropriate stirring, the oxalic acid solution is added to the zinc nitrate solution at a rate of 1 drop per second to obtain a white turbid solution, which is filtered, washed and dried to obtain white zinc oxalate ZnC2O4 powder;
[0010] (3) The ZnC2O4 powder obtained by drying in step (2) is calcined in a porcelain boat to obtain nano-ZnO powder;
[0011] (4) The nano-ZnO powder in step (3) is dispersed into a mixed solution of H2O and CH3OH, and is appropriately stirred; then, a certain amount of H2PtCl6·6H2O solution is added dropwise into the ZnO suspension;
[0012] (5) The mixed solution in step (4) is continuously stirred in the dark, and then is photodeposited under a xenon lamp, and is filtered, washed and dried to obtain an x wt% Pt / ZnO photocatalyst with Pt supported on ZnO, wherein x wt% is 0.01-1 wt%.
[0013] Further, in step (1), the amount ratio of Zn(NO3)2·6H2O to deionized water is 5 mol:100 mL, and the amount ratio of H2C2O4 to deionized water is 5 mol:100 mL.
[0014] Further, in the step (2), the drying temperature is 80℃, and the drying time is 12h.
[0015] Further, in the step (3), the calcination treatment is performed at a temperature increasing rate of 5℃ / min, and the treatment is performed at 400℃ for 6h.
[0016] Further, in the step (4), the volume ratio of H2O to CH3OH is 70ml:30ml, and the concentration of H2PtCl6·6H2O is 1mol·L -1 , and the ratio of the amount of the nano-ZnO powder to H2PtCl6·6H2O is 0.5g:25μl, 0.5g:255μl or 0.5g:2540μl.
[0017] Further, in the step (5), the stirring time is 2h, and the light deposition time is 2h.
[0018] In the second aspect of the present application, the atomically dispersed Pt / The method for catalyzing methane oxidation by using the ZnO photocatalyst is performed in a batch reactor with a certain volume, and the steps are as follows: a certain amount of the catalyst is dispersed in water by ultrasonic wave, and then the mixture is added into a quartz cell, and the quartz cell is placed in the batch reactor. The batch reactor is purged with O2 for 30min to discharge air. Then, the reactor container is pressurized with O2 and CH4. Subsequently, the solution is stirred at a speed of 300rpm. A xenon lamp is used as the light source. After the reaction is completed, the reactor is cooled in an ice bath for 1h.
[0019] Further, the mass of the catalyst used is 1-10mg, preferably 10mg;
[0020] Further, the volume of the solvent water used is 0-105ml, preferably 75ml;
[0021] Further, the light source is a full-spectrum xenon lamp, preferably 300W;
[0022] Further, the light irradiation time t is 1-4h, preferably 4h.
[0023] Further, the oxygen reaction pressure is 0-1MPa, preferably 0.1MPa;
[0024] Further, the methane reaction pressure is 0-2MPa, preferably 1.9MPa; and the total pressure is preferably 2MPa.
[0025] Compared with the prior art, the present application has the following beneficial effects:
[0026] 1. The application loads atomically dispersed Pt on the photocatalyst of polar material ZnO for the field of high-pressure gas-solid-liquid phase light-driven methane oxidation to produce oxygen-containing liquid products. The application uses ZnO as a catalyst base material, which produces a surface polarization electric field due to its polar crystal surface. This not only significantly enhances the adsorption capacity of CH4 (through specific interaction between C-H bond dipole and Zn 2+ site), but also promotes the directional separation of photo-generated electron-hole pairs, providing an efficient charge transport basis for the reaction system. At the same time, the conduction band position of ZnO reduces O2 to generate ·O2 - , which provides a mild oxidant for radical chain reaction, while preventing the excessive accumulation of highly oxidized ·OH. This "moderate reduction and oxidation ability" is the key to balancing methane activation and product selectivity. The valence band hole captured by the Pt monatomic site is directionally transferred to the adsorbed CH4 molecule, triggering C-H bond dissociation to generate ·CH3. This avoids the traditional multi-step oxidation path mediated by ·OH and thermodynamically inhibits over-oxidation. Through the precise modification of Pt monatomic sites, we have achieved a ·CH3-dominated path in the ZnO system, with both AQY (14.14%) and selectivity (95%) reaching a high level.
[0027] 2. Compared with the prior art, the catalyst preparation process of the application breaks through the bottleneck of complex process and high energy consumption - simple raw materials and preparation method are selected, and the catalyst synthesis can be completed in a short time at low temperature. The whole preparation process is not only simple to operate, but also has significant energy saving advantage. The core lies in the prepared metal oxide, which has small particle size and large specific surface area. In addition, only single-atom metal needs to be loaded on the oxide carrier, without additional consumption of a large amount of energy, showing strong commercial application potential. What is particularly important is that the raw materials and process of the catalyst preparation method are simple, but it has excellent methane oxidation catalytic performance. In the reaction process, only light source irradiation can promote the conversion of methane to high value-added chemicals, and the reaction conditions are very mild. The whole system uses solar energy as the only energy supply, completely abandoning other energy consumption such as electricity, and truly realizes the maximization of solar energy to chemical energy. BRIEF DESCRIPTION OF DRAWINGS
[0028] Figure 1 X-ray diffraction patterns of the ZnO catalyst prepared in Example 1, and the Pt / ZnO catalysts prepared in Examples 2-4.
[0029] Figure 2 Nitrogen adsorption-desorption graphs of the ZnO catalyst prepared in Example 1, and the Pt1 / ZnO catalyst prepared in Example 3.
[0030] Figure 3 Scanning electron microscope graph of the ZnO prepared in Example 1.
[0031] Figure 4 This is a scanning electron microscope image of 0.1wt% Pt / ZnO prepared in Example 3.
[0032] Figure 5 This is a transmission electron micrograph of the Pt1 / ZnO catalyst prepared in Example 3.
[0033] Figure 6 This is the spherical aberration corrected electron microscope image of the Pt1 / ZnO catalyst prepared in Example 3.
[0034] Figure 7 This is a graph showing the yield of liquid products of the ZnO catalyst prepared in Example 1 and the Pt / ZnO photocatalysts prepared in Examples 2-4 under 4 hours of illumination.
[0035] Figure 8 This is a graph showing the yield of liquid products over Au1 / ZnO, Pd1 / ZnO, and Ru1 / ZnO catalysts prepared in Examples 5-7 under 4 hours of illumination.
[0036] Figure 9 This is a relationship diagram between the liquid product yield of the 0.1wt% Pt / ZnO catalyst prepared in Example 3 and the illumination time.
[0037] Figure 10 The apparent quantum yield and ultraviolet absorption diagram of 0.1wt% Pt / ZnO prepared in Example 3. DETAILED DESCRIPTION
[0038] In order to better understand the present invention, the content of the present invention is further illustrated below in conjunction with the examples, but the content of the present invention is not limited to the following examples.
[0039] Example 1
[0040] The preparation method of ZnO photocatalyst is as follows:
[0041] First, prepare Zn(NO3)2·6H2O aqueous solution (0.05 mol·L -1 , 100mL) and H2C2O4 aqueous solution (0.05mol·L -1 , 100mL). Then, under appropriate stirring, 100mL of H2C2O4 solution was dripped into the Zn(NO3)2·6H2O solution at a rate of 1 drop / second, yielding a white, turbid solution. This solution was filtered, washed, and dried at 80°C to obtain white zinc oxalate (ZnC2O4) powder. Finally, the ZnC2O4 powder was evenly distributed on the bottom of a porcelain ark and transferred to a muffle furnace, where it was heated to 400°C at a rate of 5°C / min and maintained at 400°C for 6 hours. After cooling naturally, it was ground to yield the ZnO photocatalyst.
[0042] Example 2
[0043] The preparation method of 0.01wt% Pt / ZnO photocatalyst is as follows:
[0044] 0.5g of the original nano-ZnO powder prepared in Example 1 was dispersed into 70mL of mixed liquid (the mixed liquid was composed of 70mL H2O and 30mL methanol, here 70mL was used, and the remaining 30ml was used to disperse H2PtCl6·6H2O), and stirred properly. Then, 25μl of H2PtCl6·6H2O solution (1mol·L -1 ) was diluted to 30mL with the above mixed liquid, and dripped into the ZnO suspension. Then, it was continuously stirred in the dark for 2h, and then photodeposited under the xenon lamp for 2h. Finally, after filtration, washing, and drying at 80°C, 0.01wt% Pt / ZnO photocatalyst was obtained.
[0045] Example 3
[0046] The preparation method of 0.1wt% Pt / ZnO photocatalyst is as follows:
[0047] 0.5g of the original nano-ZnO powder prepared in Example 1 was dispersed into 70mL of mixed liquid (the mixed liquid was composed of 70mL H2O and 30mL methanol, here 70mL was used, and the remaining 30ml was used to disperse H2PtCl6·6H2O), and stirred properly. Then, 255μl of H2PtCl6·6H2O solution (1mol·L -1 ) was diluted to 30mL with the above mixed liquid, and dripped into the ZnO suspension. Then, it was continuously stirred in the dark for 2h, and then photodeposited under the xenon lamp for 2h. Finally, after filtration, washing, and drying at 80°C, 0.1wt% Pt / ZnO (hereinafter referred to as Pt1 / ZnO) photocatalyst was obtained.
[0048] Example 4
[0049] The preparation method of 1wt% Pt / ZnO photocatalyst is as follows:
[0050] 0.5g of the original nano-ZnO powder prepared in Example 1 was dispersed into 70mL of mixed liquid (the mixed liquid was composed of 70mL H2O and 30mL methanol, here 70mL was used, and the remaining 30ml was used to disperse H2PtCl6·6H2O), and stirred properly. Then, 2540μl of H2PtCl6·6H2O solution (1mol·L -1 ) was diluted to 30mL with the above mixed liquid, and dripped into the ZnO suspension. Then, it was continuously stirred in the dark for 2h, and then photodeposited under the xenon lamp for 2h. Finally, after filtration, washing, and drying at 80°C, 1wt% Pt / ZnO photocatalyst was obtained.
[0051] Example 5
[0052] The 0.1wt% Au / ZnO photocatalyst was prepared as follows:
[0053] The 0.5g of the original ZnO nanopowder prepared in Example 1 was dispersed into 70mL of the mixed liquid (the mixed liquid was composed of 70mL H2O and 30mL methanol, here 70mL was used, the rest 30ml was used to disperse AuCl3-HCl-4H2O), with proper stirring. Then, 255μl of AuCl3-HCl-4H2O solution (1 mol-L -1 ) was diluted to 30mL with the above mixed liquid, and was dropped into the ZnO suspension. Then, continuous stirring in the dark for 2h, and then photodeposition under the xenon lamp for 2h. Finally, the 0.1wt% Au / ZnO (hereinafter referred to as Au1 / ZnO) photocatalyst was obtained after filtration, washing, and drying at 80°C.
[0054] Example 6
[0055] The 0.1wt% Pd / ZnO photocatalyst was prepared as follows:
[0056] The 0.5g of the original ZnO nanopowder prepared in Example 1 was dispersed into 70mL of the mixed liquid (the mixed liquid was composed of 70mL H2O and 30mL methanol, here 70mL was used, the rest 30ml was used to disperse PdCl2-HCl-4H2O), with proper stirring. Then, 255μl of PdCl2-HCl-4H2O solution (1 mol-L -1 ) was diluted to 30mL with the above mixed liquid, and was dropped into the ZnO suspension. Then, continuous stirring in the dark for 2h, and then photodeposition under the xenon lamp for 2h. Finally, the 0.1wt% Pd / ZnO (hereinafter referred to as Pd1 / ZnO) photocatalyst was obtained after filtration, washing, and drying at 80°C.
[0057] Example 7
[0058] The 0.1wt% Ru / ZnO photocatalyst was prepared as follows:
[0059] The 0.5g of the original ZnO nanopowder prepared in Example 1 was dispersed into 70mL of the mixed liquid (the mixed liquid was composed of 70mL H2O and 30mL methanol, here 70mL was used, the rest 30ml was used to disperse RuCl3), with proper stirring. Then, 255μl of RuCl3 solution (1 mol-L -1) The above mixture was diluted to 30 mL and added dropwise to the ZnO suspension. Then, it was continuously stirred in the dark for 2 h and then photodeposited under a xenon lamp for 2 h. Finally, 0.1 wt% Ru / ZnO (hereinafter referred to as Ru1 / ZnO) photocatalyst was obtained by filtration, washing and drying at 80 °C.
[0060] The results of product detection of each example are as follows:
[0061] Figure 1 X-ray diffraction patterns of the ZnO catalyst prepared in Example 1 and the Pt / ZnO catalyst prepared in Example 2-4. Figure 1 The characteristic diffraction peaks appearing at 2Q = 31.8° and 36.2° correspond to the (100) and (101) crystal planes of the hexagonal wurtzite structure, indicating that the ZnO photocatalyst was successfully prepared. No diffraction signal related to Pt was detected, indicating that its volume fraction on the ZnO was low and highly dispersed, and the introduction of metallic Pt had no obvious effect on the lattice structure of ZnO.
[0062] Figure 2 Nitrogen adsorption-desorption isotherms of the ZnO catalyst prepared in Example 1 and the Pt1 / ZnO catalyst prepared in Example 3. Figure 2 The specific surface areas of ZnO and Pt1 / ZnO are similar, with that of Pt1 / ZnO being 32.7 m 2 g -1 , which provides a large number of active sites for redox reactions.
[0063] Figure 3 Scanning electron micrograph of the ZnO catalyst prepared in Example 1. Figure 3 The pattern presented in
[0064] Figure 4 Scanning electron micrograph of the Pt1 / ZnO catalyst prepared in Example 3. Figure 4 The pattern presented in Figure 3 is not significantly different, indicating that the deposition of Pt does not change the morphology of the ZnO base material. Figure 4 a shows that at a small size, the ZnO as a whole presents a loose block, and when the scale is enlarged, as shown in Figure 4 b, it can be more clearly seen that it is stacked by particles of about 20 nm, and this special structure has a larger specific surface area.
[0065] Figure 5Transmission electron microscope image of the Pt1 / ZnO catalyst prepared in Example 3. From the image, lattice fringes of 0.281 nm can be clearly resolved, which is in good agreement with the (100) plane of ZnO, and no evidence of Pt nanoparticles on the surface of ZnO was observed.
[0066] Figure 6 High-angle annular dark field scanning transmission electron microscope image of the Pt1 / ZnO catalyst prepared in Example 3. It was verified that Pt was highly dispersed on ZnO in the form of single atoms.
[0067] Example 8
[0068] Method for catalyzing methane oxidation under light irradiation using the Pt1 / ZnO photocatalyst prepared in Example 3:
[0069] 10 mg of the Pt1 / ZnO photocatalyst prepared in Example 3 was dispersed in 75 ml of water by ultrasonic for 5 min, and then the mixture was added to a quartz cell, which was placed in a batch reactor. The batch reactor was purged with O2 for 30 min to remove air. Then, the reactor vessel was pressurized with 0.1 MPa of O2 and 1.9 MPa of CH4. Subsequently, the solution was stirred at a speed of 300 rpm. A 300 W xenon lamp was used as the light source. After the reaction, the reactor was cooled in an ice bath for 1 h. The collected catalytic products were quantitatively analyzed using a gas chromatograph, ultraviolet colorimetry, and the like.
[0070] The above method was repeated to catalyze methane oxidation under light irradiation using the ZnO photocatalyst prepared in Example 1, the Pt / ZnO photocatalyst prepared in Example 2, and the Pt / ZnO photocatalyst prepared in Example 4, respectively.
[0071] Example 9
[0072] Method for catalyzing methane oxidation under light irradiation using the Au1 / ZnO photocatalyst prepared in Example 5:
[0073] 10 mg of the Au1 / ZnO photocatalyst prepared in Example 5 was dispersed in 75 ml of water by ultrasonic for 5 min, and then the mixture was added to a quartz cell, which was placed in a batch reactor. The batch reactor was purged with O2 for 30 min to remove air. Then, the reactor vessel was pressurized with 0.1 MPa of O2 and 1.9 MPa of CH4. Subsequently, the solution was stirred at a speed of 300 rpm. A 300 W xenon lamp was used as the light source. After the reaction, the reactor was cooled in an ice bath for 1 h. The collected catalytic products were quantitatively analyzed using a gas chromatograph, ultraviolet colorimetry, and the like.
[0074] Example 10
[0075] Method for catalyzing methane oxidation under light irradiation using the Pd1 / ZnO photocatalyst prepared in Example 6:
[0076] A 10 mg Pd1 / ZnO photocatalyst prepared in Example 6 was dispersed in 75 ml of water by ultrasonic for 5 min, and then the mixture was added to a quartz cell which was placed in a batch reactor. The batch reactor was purged with O2 for 30 min to remove air. Then the reactor vessel was pressurized with 0.1 MPa O2 and 1.9 MPa CH4. Subsequently, the solution was stirred at 300 rpm. A 300 W Xenon lamp was used as the light source. After the reaction, the reactor was cooled in an ice bath for 1 h. The collected catalytic products were quantitatively analyzed by gas chromatography, UV colorimetry, etc.
[0077] Example 11
[0078] A method for catalyzing methane oxidation under light irradiation using the Ru1 / ZnO photocatalyst prepared in Example 7:
[0079] A 10 mg Ru1 / ZnO photocatalyst prepared in Example 7 was dispersed in 75 ml of water by ultrasonic for 5 min, and then the mixture was added to a quartz cell which was placed in a batch reactor. The batch reactor was purged with O2 for 30 min to remove air. Then the reactor vessel was pressurized with 0.1 MPa O2 and 1.9 MPa CH4. Subsequently, the solution was stirred at 300 rpm. A 300 W Xenon lamp was used as the light source. After the reaction, the reactor was cooled in an ice bath for 1 h. The collected catalytic products were quantitatively analyzed by gas chromatography, UV colorimetry, etc.
[0080] Figure 7Liquid product yield plot for ZnO catalyst prepared for Example 1, Pt / ZnO photocatalysts prepared for Examples 2-4 under 4 h light illumination. For pure ZnO, a total of 57.3 pmol oxygenates (including 31.6 pmol HCHO, 25 pmol CH3OH and 0.7 pmol HCOOH) were produced within the optimized 4 h reaction time; this photocatalytic behavior of ZnO is consistent with its unique polar structure for efficient CH4 adsorption and conversion. The introduction of Pt onto the ZnO surface led to a significant enhancement in activity, peaking at 0.1% Pt mass ratio, with 119.0 pmol and 63.0 pmol of HCHO and CH3OH produced, respectively. At a higher 1 wt% Pt loading, the amount of CH3OH produced remained almost unchanged (60.0 pmol) compared to 0.1 wt% Pt supported ZnO (Pt1 / ZnO), while the amount of HCHO was halved (66.0 pmol). Interestingly, the 0.01 wt% Pt / ZnO and 0.1 wt% Pt / ZnO photocatalysts exhibited different product distributions (more specifically, the ratio of HCHO to CH3OH) compared to ZnO and Pt nanoparticle-modified ZnO (1 wt% Pt / ZnO), indicating different reaction mechanisms.
[0081] Figure 8 Liquid product distribution for Au1 / ZnO, Pd1 / ZnO and Ru1 / ZnO catalysts prepared for Examples 5-7 under 4 h light illumination. The performance trends of these catalysts were similar to Pt1 / ZnO, but were lower overall. Among them, Pd1 / ZnO exhibited the highest catalytic activity, with a total of about 135 pmol oxygenates produced (mainly about 95 pmol HCHO and about 37 pmol CH3OH), but also the highest production of deep oxidation product CO2, resulting in a liquid product selectivity of only 91.5%, indicating that Pd sites tend to initiate deep oxidation reactions. Au1 / ZnO activity was in the middle (about 117 pmol oxygenates total), with a selectivity of 91.8%. Ru1 / ZnO had the relatively highest selectivity, reaching 98%, but the lowest activity (about 80 pmol oxygenates total). Due to the differences between Pt and Au / Pd / Ru in key electronic structure parameters such as d-band center, electron affinity, etc., these systems could not simultaneously meet the three key conditions of strong methane adsorption, efficient hole capture, and directional transport of photo-generated holes to active sites, resulting in lower activity and selectivity than Pt1 / ZnO, further confirming the unique advantages of the Pt1 / ZnO catalyst.
[0082] Figure 9The plot of liquid product yield vs. irradiation time for the 0.1 wt% Pt / ZnO catalyst prepared in Example 3. Liquid oxygenate HCHO and CH3OH gradually increased with irradiation time and appreciable peroxidation product CO2 was produced at 4 hours, so the reaction duration was optimized to 4 hours.
[0083] Figure 10 The trend of AQY vs. wavelength for the 0.1 wt% Pt / ZnO photocatalyst prepared in Example 3 was consistent with its optical absorption spectrum, and increased with decreasing photon wavelength, reaching a maximum of 14.14% at 350 nm.
[0084] The above only is the preferred embodiment of the present application, should be noted that for those skilled in the art, without departing from the principles of the present application, can also make a number of improvements and refinements, these improvements and refinements are also within the scope of the present application.
Claims
1. A method for preparing Pt single atom modified ZnO, characterized in that: The method adopts precipitation and calcination methods to prepare nano ZnO, and then uses optical deposition method to obtain Pt / ZnO photocatalyst, thereby preparing a photocatalyst in which atomically dispersed Pt is loaded on ZnO, comprising the following steps: (1) Place a certain amount of zinc nitrate (Zn(NO3)2·6H2O) in a container containing a certain amount of deionized water and stir thoroughly until dissolved to obtain a zinc nitrate solution; place a certain amount of oxalic acid (H2C2O4) in a container containing a certain amount of deionized water and stir thoroughly until dissolved to obtain an oxalic acid solution; (2) Under appropriate stirring, the oxalic acid solution is added to the zinc nitrate solution at a rate of 1 drop / second to obtain a white turbid solution, which is then filtered, washed, and dried to obtain white zinc oxalate ZnC2O4 powder; (3) calcining the ZnC2O4 powder obtained by drying in step (2) in a porcelain boat to obtain nano ZnO powder; (4) Dispersing the nano ZnO powder in step (3) into a mixed solution of H2O and CH3OH and stirring appropriately; then, dropping a certain amount of H2PtCl6·6H2O solution into the ZnO suspension; (5) The mixed solution in step (4) was continuously stirred in the dark, and then photodeposited under a xenon lamp. After filtering, washing, and drying, x wt% Pt loaded on ZnO was obtained. / ZnO photocatalyst, x wt% is 0.01-1 wt%.
2. The method for preparing a Pt single-atom modified ZnO photocatalyst for photocatalytic oxidation of methane to generate oxygen-containing liquid products according to claim 1, characterized in that: In the step (1), the ratio of Zn(NO3)2·6H2O to deionized water is 5 mol:100 mL, and the ratio of H2C2O4 to deionized water is 5 mol:100 mL.
3. The method for preparing a Pt single-atom modified ZnO photocatalyst for photocatalytic oxidation of methane to generate oxygen-containing liquid products according to claim 1, characterized in that: In the step (2), the drying temperature is 80° C. and the drying time is 12 h.
4. The method for preparing a Pt single-atom modified ZnO photocatalyst for photocatalytic oxidation of methane to generate oxygen-containing liquid products according to claim 1, characterized in that: In the step (3), during the calcination treatment, the temperature is increased at a heating rate of 5°C / min and the treatment is carried out at 400°C for 6 hours.
5. The method for preparing a Pt single-atom modified ZnO photocatalyst for photocatalytic oxidation of methane to generate oxygen-containing liquid products according to claim 1, characterized in that: In step (4), the volume ratio of H2O to CH3OH is 70ml:30ml, and the concentration of H2PtCl6·6H2O is 1mol·L -1 The usage ratio of nano ZnO powder to H2PtCl6·6H2O is 0.5g:25μl or 0.5g:255μl or 0.5g:2540μl.
6. The method for preparing a Pt single-atom modified ZnO photocatalyst for photocatalytic oxidation of methane to generate oxygen-containing liquid products according to claim 1, characterized in that: In the step (5), the stirring time is 2 hours and the photodeposition time is 2 hours.
7. Atomically dispersed Pt prepared by the method according to any one of claims 1 to 6 / The method for catalyzing methane oxidation by ZnO photocatalyst is characterized in that: The method is carried out in a batch reactor of a certain capacity, and the steps are as follows: a certain amount of catalyst is dispersed in water by ultrasonication, and then the mixture is added to a quartz cell, which is placed in the batch reactor; the batch reactor is purged with O2 for 30 minutes to expel air; then the reactor container is pressurized with O2 and CH4; then, the solution is stirred at a speed of 300 rpm; a xenon lamp is used as a light source; and after the reaction is completed, the reactor is cooled in an ice bath for 1 hour.
8. The method according to claim 7, characterized in that The mass of the catalyst used is 1-10 mg, the volume of the solvent water used is 0-105 ml, the light source is a full-spectrum xenon lamp, the illumination time t is 1-4 hours, the oxygen reaction pressure is 0-1 MPa, and the methane reaction pressure is 0-2 MPa.
9. The method according to claim 8, characterized in that The mass of the catalyst used is 10 mg; the volume of the solvent water used is 75 ml; the light source is a 300W full-spectrum xenon lamp; the illumination time t is 4 h; the oxygen reaction pressure is 0.1 MPa; the methane reaction pressure is 1.9 MPa; and the total pressure is preferably 2 MPa.