A Pd-Cu / WO 3-x Process for the preparation of a material and use thereof

Abstract

This invention belongs to the field of photocatalysts, specifically relating to a Pd-Cu / WO3 catalyst. 3‑x Preparation method and application of the material. This invention involves mixing and grinding ammonium paratungstate and urea, calcining the resulting mixture, cooling it, and then grinding it again to obtain WO3. 3‑x Powder; then the WO 3‑x The powder was dispersed in deionized water and concentrated hydrochloric acid was added, and the mixture was stirred to form an acidic, stable suspension; then copper sulfate solution was added, and the Cu process was completed under xenon lamp irradiation. 2+ Photoreduction deposition; then PdCl2 solution is added, stirred, and subjected to a second light irradiation to promote Pd deposition. 2+ Pd-Cu bimetallic active sites were constructed by loading a copper-supported substrate onto its surface. The solid product was then washed with water, filtered, and dried at low temperature to obtain Pd-Cu / WO3. 3‑x Composite photocatalytic materials. The Pd-Cu / WO3 prepared in this invention... 3‑x The material can effectively suppress the generation of excessive oxidation products such as CO or CO2 in the photocatalytic methane oxidation reaction, achieving 98% selectivity in formaldehyde generation.

Description

Technical Field

[0001] This invention belongs to the field of photocatalysts, specifically relating to a Pd-Cu / WO3 catalyst. 3-x Preparation methods and applications of materials. Background Technology

[0002] Methane (CH4) is a significant greenhouse gas, with a greenhouse effect more than 20 times that of carbon dioxide. With the large-scale development and utilization of fossil fuels, anthropogenic methane emissions continue to increase, exacerbating the greenhouse effect and wasting carbon resources. Therefore, achieving efficient conversion and resource utilization of methane is of great significance for alleviating environmental problems and improving resource utilization efficiency.

[0003] Photocatalytic selective oxidation of methane can directly convert methane into high-value-added chemicals such as formaldehyde under mild reaction conditions. It features mild reaction conditions and low energy consumption, making it an important technological route for the resource utilization of methane. However, because the bond energy of the C–H bond in the formaldehyde molecule (approximately 368 kJ / mol) is lower than that in the methane molecule (approximately 435 kJ / mol), the formaldehyde generated during the reaction is more prone to further dehydrogenation and deep oxidation, producing byproducts such as carbon monoxide (CO) and carbon dioxide (CO2), thus reducing the selectivity of formaldehyde and the yield of the target product. To improve the selectivity of formaldehyde, existing technologies typically employ strongly acidic reaction media or add high-valence oxidants such as hydrogen peroxide or permanganate to inhibit further oxidation of formaldehyde and promote the formation of the target product. However, these methods generally suffer from problems such as complex reaction systems, high operating costs, easy equipment corrosion, and the potential for secondary pollution, which are detrimental to the large-scale application of the process and green sustainable development. Therefore, developing a catalytic system that can achieve highly selective photocatalytic oxidation of methane to formaldehyde without relying on strong acidic reaction media and high-valent oxidants has become an urgent technical problem to be solved in this field.

[0004] In recent years, bimetallic site modulation, as an efficient interface engineering strategy, has been proven to significantly enhance the activity and selectivity of photocatalytic reactions. However, systematic research on the application of bimetallic sites in photocatalytic methane conversion is still lacking, especially the regulatory mechanism of bimetallic synergy on reaction pathways and the evolution of key intermediates remains unclear. Based on this, we developed a catalytic material containing Pd-Cu bimetallic sites. In this system, the electronic interaction between Pd and Cu not only promotes the separation and transport of photogenerated carriers but also optimizes the distribution of reactive oxygen species. Simultaneously, the synergistic effect between bimetallic sites effectively regulates the adsorption and desorption behavior of key intermediates. This dual synergy of electronic structure and geometric configuration achieves precise activation of the methane CH bond and effectively suppresses excessive oxidation pathways through site isolation, enabling the reaction to directionally generate formaldehyde with a selectivity consistently above 98%. The bimetallic site strategy is expected to overcome the bottleneck of balancing activity and selectivity in current photocatalytic methane-to-formaldehyde conversion, providing new design ideas and technical pathways for achieving efficient and highly selective methane conversion without the need for external strong acids or high-valent oxidants. Summary of the Invention

[0005] This invention aims to overcome the problems of low product selectivity and poor stability in existing photocatalytic methane conversion technologies, and provides a Pd-Cu / WO3 solution. 3-x Preparation methods and applications of materials.

[0006] This invention is achieved through the following technical solution: a Pd-Cu / WO3 3-x The method for preparing the material includes the following steps: (1) Ammonium paratungstate and urea are mixed and ground. The resulting mixture is heated and calcined, then cooled and ground again to obtain WO3. 3-x powder; (2) Take the WO obtained in step (1) 3-x The powder was dispersed in deionized water, and then concentrated hydrochloric acid was added and stirred to form an acidic and stable suspension. (3) Add copper sulfate solution to the solution obtained in step (2), stir the reaction, and use a 300 W xenon lamp as the light source with a working current set to 10 A for irradiation to achieve Cu 2+ Photoreduction deposition; (4) Then add PdCl2 solution to the solution obtained in step (3) and continue stirring to allow PdCl2 to form a precipitate. 2+ Adsorption occurs on the surface of a Cu-loaded support, followed by photodeposition under the same illumination conditions as described above to form Pd-Cu bimetallic sites. (5) After the reaction, the solution was stirred and the solid product was washed with deionized water, filtered, and dried at low temperature to obtain Pd-Cu / WO3. 3-x Material.

[0007] As a further improvement to the technical solution of the present invention, the molar ratio of urea to ammonium paratungstate in step (1) is 25~175:1.

[0008] As a further improvement to the technical solution of this invention, the specific operation of heating and calcining in step (1) is as follows: using 2 o Heating rate increased to 400 °C / min o Keep warm at 1°C for 35 minutes, then add 1 o Heating rate increased to 650 °C / min o Calcination with C for 5 hours.

[0009] As a further improvement to the technical solution of the present invention, the low-power illumination in steps (3) and (4) is performed using a 300 W xenon lamp as the light source, with the working current set to 10 A.

[0010] As a further improvement to the technical solution of the present invention, in step (2), WO 3-x The mass-to-volume ratio of powder to concentrated hydrochloric acid is 1 g: 43 μL. As a further improvement to the technical solution of this invention, in step (3), WO3 in the acidic stable suspension... 3-x The molar ratio of powder to copper sulfate is 9.3:1.

[0011] As a further improvement to the technical solution of the present invention, in step (4), the mass ratio of Cu in copper sulfate and Pd in ​​PdCl2 solution is 0.5:0.1~0.9.

[0012] The present invention also provides a Pd-Cu / WO prepared by the aforementioned preparation method. 3-x Material.

[0013] The present invention further provides the Pd-Cu / WO 3-x Application of materials as photocatalysts in the photocatalytic oxidation of methane to formaldehyde.

[0014] As a further improvement to the application technology solution of the present invention, the specific method of the application includes: adding Pd-Cu / WO to water. 3-x The material was placed in a high-pressure reactor, and the air was replaced multiple times with a mixture of methane and oxygen until the reaction pressure was reached at 0.1~2.5 MPa. The high-pressure reactor was then irradiated with a light source with a wavelength of 300~850 nm to catalyze the oxidation of methane to formaldehyde.

[0015] This invention provides a Pd-Cu / WO 3-x The preparation method and application of the material have the following advantages compared with existing technologies: 1. Pd-Cu / WO prepared by the method of the present invention 3-xCompared to commercially available P25 photocatalysts, this material has a wider light absorption range, which can broaden the absorption band edge to about 537 nm and has higher light utilization efficiency. 2. The method of this invention prepares Pd-Cu / WO3 with a broad spectral response via wet photodeposition. 3-x The materials and preparation methods are simple to operate and easy to repeat, providing a good technical foundation and material guarantee for commercial applications; 3. Pd-Cu / WO prepared by the method of the present invention 3-x The material, due to the Pd-Cu bimetallic active sites and WO3 3-x The carriers exhibit strong interactions, high formaldehyde selectivity, excellent catalytic activity, and good cycle stability, with a selectivity consistently above 98%. 4. The Pd-Cu / WO prepared by this invention 3-x The material can promote the efficient separation of photogenerated electrons, thereby facilitating oxygen activation. It can efficiently generate ·OOH with moderate oxidizing power as the main active species, further improving the photocatalytic activity and target product selectivity of the catalyst. Attached Figure Description

[0016] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 The Pd-Cu / WO prepared in Example 1 2.72 X-ray diffraction pattern of photocatalyst.

[0019] Figure 2 The Pd-Cu / WO prepared in Example 1 2.72 Scanning electron microscope image.

[0020] Figure 3 The Pd-Cu / WO prepared in Example 1 2.72 WO prepared in Comparative Examples 1-3 2.72 Pd / WO 2.72 and Cu / WO 2.72 Transmission electron microscope image of a photocatalyst.

[0021] Figure 4 The Pd-Cu / WO prepared in Example 12.72 WO prepared in Comparative Examples 1-3 2.72 Pd / WO 2.72 and Cu / WO 2.72 UV-Vis diffuse reflectance spectrum of photocatalyst.

[0022] Figure 5 The Pd-Cu / WO prepared in Example 1 2.72 WO prepared in Comparative Examples 1-3 2.72 Pd / WO 2.72 and Cu / WO 2.72 Comparison of infrared spectra of photocatalysts.

[0023] Figure 6 The Pd-Cu / WO prepared in Example 1 2.72 WO prepared in Comparative Examples 1-3 2.72 Pd / WO 2.72 and Cu / WO 2.72 Raman spectroscopy results of photocatalyst.

[0024] Figure 7 The Pd-Cu / WO prepared in Examples 1 and 2 2.72 Compared with the Pd / WO prepared in Comparative Examples 2-3 2.72 Cu / WO 2.72 Comparison of product distribution in the photocatalytic reaction of methane to formaldehyde.

[0025] Figure 8 The Pd-Cu / WO prepared in Example 1 2.72 Product distribution diagram in the photocatalytic methane-to-formaldehyde reaction under different water addition conditions.

[0026] Figure 9 The Pd-Cu / WO prepared in Example 1 2.72 Product distribution diagram in the photocatalytic reaction of methane to formaldehyde under different oxygen partial pressures.

[0027] Figure 10 The Pd-Cu / WO prepared in Example 1 2.72 WO prepared in Comparative Examples 1-3 2.72 Pd / WO 2.72 and Cu / WO 2.72 Schematic diagram of the photocatalyst producing ·OOH.

[0028] Figure 11 The Pd-Cu / WO prepared in Example 3 2.72 Figure showing the results of the cycle stability test of the photocatalyst. Detailed Implementation

[0029] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0030] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0031] This invention provides a Pd-Cu / WO 3-x A specific embodiment of the material preparation method includes the following steps: (1) Ammonium paratungstate and urea are mixed and ground. The resulting mixture is heated and calcined, then cooled and ground again to obtain WO3. 3-x powder; (2) Take the WO obtained in step (1) 3-x The powder was dispersed in deionized water, and then concentrated hydrochloric acid was added and stirred to form an acidic and stable suspension. (3) Add copper sulfate solution to the solution obtained in step (2), stir the reaction, and use a 300 W xenon lamp as the light source with a working current set to 10 A for irradiation to achieve Cu 2+ Photoreduction deposition; (4) Then add PdCl2 solution to the solution obtained in step (3) and continue stirring to allow PdCl2 to form a precipitate. 2+ Adsorption occurs on the surface of a Cu-loaded support, followed by photodeposition under the same illumination conditions as described above to form Pd-Cu bimetallic sites. (5) After the reaction, the solution was stirred and the solid product was washed with deionized water, filtered, and dried at low temperature to obtain Pd-Cu / WO3. 3-x Material.

[0032] In one example provided by the present invention, the molar ratio of urea to ammonium paratungstate in step (1) is 25-175:1. In different embodiments, the mixing and grinding of ammonium paratungstate and urea in step (1) is carried out at room temperature, and the molar ratio of urea to ammonium paratungstate can be 25:1, 50:1, 75:1, 100:1, 125:1, 150:1, 175:1, or any molar ratio between any two specified values. In the present invention, the WO obtained in step (1) 3-x The value of x in the powder is related to the molar ratio of urea and ammonium paratungstate, as well as the calcination conditions, and the value of x ranges from 0 to 1.

[0033] In another example provided by the present invention, the specific operation of heating and calcining in step (1) is as follows: using 2o Heating rate increased to 400 °C / min o Keep warm at 1°C for 35 minutes, then add 1 o Heating rate increased to 650 °C / min o Calcination with C for 5 hours.

[0034] In one example provided by the present invention, the low-power illumination in steps (3) and (4) is performed using a 300 W xenon lamp as the light source, with the operating current set to 10 A.

[0035] In another example provided by the present invention, in step (2), WO 3-x The mass-to-volume ratio of powder to concentrated hydrochloric acid is 1 g: 43 μL.

[0036] In one example provided by the present invention, in step (3), WO3 in the acidic stable suspension 3-x The molar ratio of powder to copper sulfate is 9.3:1.

[0037] In another example provided by the present invention, in step (4), the mass ratio of Cu in copper sulfate and Pd in ​​PdCl2 solution is 0.5:0.1~0.9.

[0038] The present invention also provides the Pd-Cu / WO 3-x Application of materials as photocatalysts in the photocatalytic oxidation of methane to formaldehyde.

[0039] Furthermore, the specific method of the application includes: adding Pd-Cu / WO to water. 3-x The materials were placed in a high-pressure reactor, including Pd-Cu / WO3. 3-x The mass-to-volume ratio of photocatalyst to water is 0.1~2 g / L. The air is replaced multiple times with a mixture of methane and oxygen and the reaction pressure is increased to 0.1~2.5 MPa. The high-pressure reactor is irradiated with a light source with a wavelength of 300~850 nm to catalyze the oxidation of methane to formaldehyde.

[0040] The present invention also provides Pd-Cu / WO prepared by the aforementioned preparation method. 3-x Photocatalysts can promote the formation of formaldehyde through photocatalysis. This invention also provides a method for detecting formaldehyde as follows: (1) Mix the reaction solution with the acetylacetone solution at a volume ratio of 1:1, and heat at 35°C. o React at C for 60 min; (2) The absorbance at a wavelength of 412 nm was measured using a UV-Vis spectrophotometer, and the formaldehyde yield was calculated based on the standard curve of formaldehyde concentration versus absorbance.

[0041] To further demonstrate the Pd-Cu / WO of this invention3-x The photocatalyst promotes the generation of ·OOH under photocatalytic conditions. This invention also provides a method for detecting ·OOH as follows: (1) Add Pd-Cu / WO to methanol 3-x Photocatalyst, Pd-Cu / WO 3-x The concentration of the photocatalyst in methanol is 5~30 mg / mL; (2) Add DMPO as an OOH scavenger to the mixed solution in step (1) above, maintain the DMPO concentration at 3~5 mmol / L, and purge with oxygen for 30 min; (3) Transfer the solution after processing in step (2) above into a capillary tube and place it in a special tube for EPR testing. Install the special tube into the EPR detection instrument, irradiate the reaction system with a light source of wavelength 300~850 nm, and collect the EPR signal under the set illumination time to complete the detection of ·OOH.

[0042] The specific embodiments of the present invention will be described in detail below.

[0043] Example 1

[0044] (1) At room temperature, urea and ammonium paratungstate are thoroughly ground at a molar ratio of 100:1 to ensure uniform mixing and obtain a mixed powder. The mixed powder is placed in a covered crucible and calcined in a muffle furnace in stages: first at 2 o Heating to 400°C at a heating rate of C / min o C, keep warm for 35 minutes, then at 1 o Continue heating at a rate of C / min to 650 o C, and calcined at this temperature for 5 hours. After calcination, allow it to cool naturally to room temperature, then grind the product into a fine powder to obtain WO3. 2.72 .

[0045] (2) Take the WO prepared above 2.72 0.1 g of Cu was dispersed in 45 mL of deionized water, and 4.3 μL of concentrated hydrochloric acid (36%) was added to form a stable suspension. While continuously stirring, 5 mL of copper sulfate solution was added to the dispersion, and the reaction was continued for 30 min to allow Cu to react. 2+ Adsorbed on WO 2.72 Surface; the copper sulfate solution was prepared by dissolving 11.8 mg CuSO4 5H2O in 30 mL of deionized water; (3) Add copper sulfate solution to the solution obtained in step (2), stir the reaction, and use a 300 W xenon lamp as the light source with a working current set to 10 A for irradiation to achieve Cu 2+ Photoreduction deposition; (4) Then add 83 μL (10 g / L) PdCl2 solution and continue stirring for 30 min to allow Pd to settle. 2+ Adsorption occurs on the surface of a Cu-loaded support, followed by photodeposition under the same illumination conditions as described above to form Pd-Cu bimetallic sites. (5) After the reaction, the solution was stirred and the solid product was washed with deionized water, filtered, and dried at low temperature to obtain Pd-Cu / WO3. 2.72 Materials (attached) Figure 7 Pd in 0.5 Cu 0.5 -WO 2.72 The result is as follows: Figure 2 As shown.

[0046] Pd-Cu / WO 2.72 The material was used for the photocatalytic oxidation of methane. The specific reaction conditions were as follows: the catalyst and water were mixed at a mass-to-volume ratio of 0.2 g / L. The mixture was added to a micro high-pressure reactor. The air inside the reactor was repeatedly replaced with a mixture of methane and oxygen (volume ratio 1.9:0.1) until the pressure inside the reactor reached 2 MPa. Finally, the reaction system was irradiated with a light source with a wavelength of 300–850 nm, and formaldehyde was produced. The results are as follows. Figure 7 As shown.

[0047] Based on the above reaction conditions, Pd 0.5 Cu 0.5 -WO 2.72 The catalyst exhibited the best catalytic performance, therefore it was selected, and the amount of deionized water and the partial pressure of oxygen in the reaction system were further optimized. The results showed that the catalyst exhibited the best photocatalytic performance when the amount of deionized water added was 100 mL and the partial pressure of oxygen was 0.1 MPa. The test results are as follows: Figure 8 and Figure 9 As shown.

[0048] For Pd-Cu / WO 2.72 The detection conditions and procedures for reactive oxygen species during photocatalysis are as follows: Under light-protected conditions, 5 mg of Pd-Cu / WO3 was added to 200 μL of methanol. 2.72 The photocatalyst was ultrasonically treated to ensure uniform dispersion, resulting in a suspension. 2 μL of DMPO (as a ·OOH scavenger) was added to this suspension, and oxygen was bubbled through for 30 min. The treated solution was then loaded into a capillary tube, which was placed in a dedicated EPR testing tube. This tube was then connected to an EPR detection instrument, and the capillary tube was irradiated with a light source of 300–850 nm. The corresponding EPR signal was acquired after 3 min of illumination. Specific detection results are as follows: Figure 10 As shown.

[0049] Example 2

[0050] To investigate the effect of Pd loading on Pd-Cu / WO2. 72 The effect of photocatalytic performance was investigated by keeping the Cu loading constant and only varying the amount of PdCl2 precursor solution added, while all other preparation conditions remained the same as in Example 1. Specifically, the amounts of PdCl2 precursor solution added were 17 μL, 50 μL, 116 μL, and 149 μL, respectively, to prepare Cu… 0.5 Pd 0.1 -WO 2.72 Cu 0.5 Pd 0.3 / WO 2.72 Cu 0.5 Pd 0.7 / WO 2.72 and Cu 0.5 Pd 0.9 / WO 2.72 Photocatalyst. Specific test results are as follows: Figure 7 As shown.

[0051] Comparative Example 1

[0052] Using the above preparation method, this comparative example does not introduce copper sulfate or palladium chloride, two metal precursors, and only uses deionized water to prepare WO3. 2.72 The substrate material was treated, and the resulting photocatalyst was used to directly photocatalyze the oxidation of methane, with the reactive oxygen species detected. The reaction conditions and procedures were the same as in Example 1 above. The results of the reactive oxygen species detection are as follows: Figure 10 As shown.

[0053] Comparative Example 2

[0054] Using the above preparation method, this comparative example only introduces palladium chloride as a metal precursor and does not introduce copper sulfate, resulting in a Pd / WO3 photocatalyst. 2.72 Materials (attached) Figure 7 Pd in 0.5 -WO 2.72 Pd / WO 2.72 The material was used for direct photocatalytic methane oxidation, and the reactive oxygen species were detected. The reaction conditions and operation were the same as in Example 1 above. The product distribution comparison diagram and the reactive oxygen species detection results are shown below. Figure 7 and Figure 10 As shown.

[0055] Comparative Example 3

[0056] Using the above preparation method, this comparative example only introduces copper sulfate as a metal precursor and does not introduce palladium chloride, resulting in a Cu / WO photocatalyst. 2.72 Materials (attached) Figure 7 Cu in 0.5 -WO 2.72 Cu / WO 2.72 The material was used for direct photocatalytic methane oxidation, and the reactive oxygen species were detected. The reaction conditions and operation were the same as in Example 1 above. The product distribution comparison diagram and the reactive oxygen species detection results are shown below. Figure 7 and Figure 10 As shown.

[0057] The material characterization results are as follows: Figure 1 The X-ray powder diffraction pattern shows that the prepared sample is a monoclinic Pd-Cu / WO3 crystal. 2.72 .from Figure 2 The scanning electron microscope image shows the bimetallic modified Pd-Cu / WO3. 2.72 The photocatalyst particles are uniformly distributed, with moderate agglomeration, close particle contact, and retained mesoporous voids. From Figure 3 The transmission electron microscope image shows the synthesized Pd-Cu / WO3. 2.72 The photocatalyst has a near-spherical structure, with Pd and Cu metal nanoparticles uniformly supported on WO3. 2.72 No obvious metal agglomeration was observed on the carrier surface. Figure 4 The UV-Vis diffuse reflectance spectrum indicates that Pd-Cu / WO 2.72 The photocatalyst exhibits a wide light absorption range, with the absorption band edge extending to approximately 537 nm. Its band gap, calculated using the Kubelka-Munk function, is 2.31 eV, which makes Pd-Cu / WO3... 2.72 Photocatalysts have become a very promising photocatalytic material.

[0058] Combination Figure 5 The loading of Pd, Cu monometals and Pd-Cu bimetals did not damage WO3. 2.72 The main chemical bond structure of WO was preserved in all samples. 2.72 Typical vibrational peaks of W=O double bonds and OWO-bridged oxygen bonds. (From...) Figure 6 It can be seen that metal loading did not induce new Raman characteristic peaks, but it did cause significant changes in peak intensity. Specifically, Pd-Cu / WO 2.72 The sample showed the most significant peak intensity enhancement, and the stretching vibration peak position exhibited a slight red shift, indicating that the Pd-Cu bimetallic compound and WO3... 2.72 There are strong interactions between the carriers, which alter the local chemical environment of the WO bonds, thereby causing enhanced polarization of lattice vibrations.

[0059] from Figure 7 The distribution diagram of photocatalytic methane partial oxidation products shows that Pd-Cu / WO3 with different Pd / Cu ratios... 2.72All photocatalysts can achieve selective oxidation of methane, with formaldehyde (HCHO) as the main liquid-phase product and only small amounts of methanol (CH3OH) and carbon dioxide (CO2) generated. Previous control experiments showed that unmodified WO3... 2.72 Extremely low activity, with an overall yield of less than 200 μmol·g -1 ·h -1 Furthermore, the selectivity for HCHO is poor. In contrast, the selective oxidation performance of methane by the catalyst is significantly improved after the introduction of Pd and Cu bimetals. With increasing Pd content, the partial oxidation performance of methane by the catalyst shows a trend of first increasing and then decreasing. When Pd... 0.1 Gradually increase to Pd 0.5 At that time, the overall yield increased significantly. Further increasing the Pd content to Pd... 0.7 and Pd 0.9 Subsequently, the overall catalyst yield decreased significantly, indicating that excessively high Pd loading is detrimental to the selective oxidation of methane. Figure 7 It can be seen that Pd 0.5 Cu 0.5 -WO 2.72 This catalyst exhibited the best catalytic performance, therefore it was selected for further optimization of the reaction conditions. Figure 8 and Figure 9 It can be seen that by optimizing the amount of water added and the partial pressure of oxygen, Pd 0.5 Cu 0.5 -WO 2.72 The total yield was further increased to 6493.2 μmol·g. -1 ·h -1 Meanwhile, it exhibits optimal photocatalytic performance with a formaldehyde selectivity consistently above 98%. (The last sentence appears to be incomplete and unrelated to the preceding text. It likely refers to a specific metal, Cu.) 0.5 -WO 2.72 and Pd 0.5 -WO 2.72 In comparison, Pd-Cu bimetallic catalysts all exhibited higher formaldehyde yields and better selectivity, indicating a significant synergistic effect between Pd and Cu, which can effectively inhibit the deep oxidation of methane and improve the selective formation of formaldehyde.

[0060] from Figure 10 In the characterization experiment of DMPO capturing ·OOH, it can be seen that Pd-Cu / WO 2.72 The photocatalyst increased the ·OOH generation rate by nearly 9 times, indicating that it can generate ·OOH reactive oxygen free radicals more efficiently.

[0061] from Figure 11 It can be seen that after five cycles of testing, Pd-Cu / WO 2.72 The formaldehyde yield showed only a slight decrease, remaining stable at 6000 μmol·g. -1 ·h-1 The formaldehyde selectivity remained relatively stable, with the levels around 100 μL / min, while no significant decrease was observed in the Pd-Cu bimetallic species. This result indicates that Pd-Cu bimetallic species are compatible with WO3. 2.72 The supports are firmly bonded together, and no significant deactivation of the active components was observed during the reaction. The catalyst exhibits good structural stability and cycle life.

[0062] Example 3

[0063] To test the Pd-Cu / WO prepared in Example 1 2.72 The stability of the material was assessed, and it was used in a photocatalytic methane cycle reaction. The specific reaction conditions were as follows: the catalyst and water were mixed at a mass-to-volume ratio of 0.2 g / L, and then the mixture was added to a micro high-pressure reactor. The air inside the reactor was replaced multiple times with a mixture of methane and oxygen (volume ratio 1.9:0.1) until the pressure reached 2 MPa. Finally, the reaction system was irradiated with a light source with a wavelength of 300~850 nm to generate formaldehyde.

[0064] After the reaction was completed, the Pd-Cu bimetallic modified WO3 was recovered. 2.72 The photocatalyst, after washing and drying, was reused in the next round of photocatalytic reaction, and the above reaction steps were repeated for cycle stability testing. After five cycles, the Pd-Cu / WO3 photocatalyst showed good stability. 2.72 The formaldehyde yield showed only a slight decrease, remaining stable at 6000 μmol·g. -1 ·h -1 Around [a certain value], while the selectivity of formaldehyde did not show a significant decrease. The results are as follows: Figure 11 As shown.

[0065] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered within the protection scope of the claims.

Claims

1. A Pd-Cu / WO3 3-x The method for preparing the material is characterized by, Includes the following steps: (1) ammonium paratungstate is mixed with urea and ground, the obtained mixture is calcined by heating, and after cooling, grinding is performed to obtain WO 3-x powder; (2) Take the WO obtained in step (1) 3-x The powder was dispersed in deionized water, and then concentrated hydrochloric acid was added and stirred to form an acidic and stable suspension. (3) Add copper sulfate solution to the solution obtained in step (2), stir the reaction, and use a 300 W xenon lamp as the light source with a working current set to 10 A for irradiation to achieve Cu 2+ Photoreduction deposition; (4) Then add PdCl2 solution to the solution obtained in step (3) and continue stirring to allow PdCl2 to form a precipitate. 2+ Adsorption occurs on the surface of a Cu-loaded support, followed by photodeposition under the same illumination conditions as described above to form Pd-Cu bimetallic sites. (5) After the reaction, the solution was stirred and the solid product was washed with deionized water, filtered, and dried at low temperature to obtain Pd-Cu / WO3. 3-x Material.

2. A Pd-Cu / WO3 according to claim 1 3-x The method for preparing the material is characterized by, The molar ratio of urea to ammonium paratungstate in step (1) is 25~175:

1.

3. A Pd-Cu / WO3 according to claim 1 3-x The method for preparing the material is characterized by, The specific operation of heating and calcining in step (1) is as follows: 2 o Heating rate increased to 400 °C / min o Keep warm at 1°C for 35 minutes, then add 1 o Heating rate increased to 650 °C / min o Calcination with C for 5 hours.

4. A Pd-Cu / WO3 according to claim 1 3-x The method for preparing the material is characterized by, The low-power illumination in steps (3) and (4) uses a 300 W xenon lamp as the light source and the operating current is set to 10 A for illumination.

5. A Pd-Cu / WO3 according to claim 1 3-x The method for preparing the material is characterized by, In step (2), WO 3-x The mass-to-volume ratio of powder to concentrated hydrochloric acid was 1 g : 43 μL.

6. A Pd-Cu / WO3 according to claim 1 3-x The method for preparing the material is characterized by, In step (3), WO3 in the acidic stable suspension 3-x The molar ratio of powder to copper sulfate is 9.3:

1.

7. A Pd-Cu / WO3 according to claim 1 3-x The method for preparing the material is characterized by, In step (4), the mass ratio of Cu in copper sulfate to Pd in ​​PdCl2 solution is 0.5:0.1~0.

9.

8. A Pd-Cu / WO3 prepared by the preparation method according to any one of claims 1 to 7 3-x Material.

9. The Pd-Cu / WO as described in claim 8 3-x Application of materials as photocatalysts in the photocatalytic oxidation of methane to formaldehyde.

10. The application according to claim 9, characterized in that, The specific method of the application includes: adding Pd-Cu / WO to water. 3-x The material was placed in a high-pressure reactor, and the air was replaced multiple times with a mixture of methane and oxygen until the reaction pressure was reached at 0.1~2.5 MPa. The high-pressure reactor was then irradiated with a light source with a wavelength of 300~850 nm to catalyze the oxidation of methane to formaldehyde.

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