A Pd–Ag / TiO2 ultrasmall single-atom alloy photocatalyst, its preparation method and application

Abstract

The application belongs to the field of photocatalytic materials and environmental catalysis technology, and particularly relates to a Pd-Ag / TiO2 ultra-small single-atom alloy photocatalyst and a preparation method and application thereof, wherein the Pd-Ag / TiO2 ultra-small single-atom alloy photocatalyst takes anatase TiO2 as a carrier, and Pd and Ag are loaded on the surface of the carrier; the Pd exists in the form of atomic single atoms or sub-nanometer clusters, and forms a composite structure of local interaction with adjacent Ag atoms, so as to construct an ultra-small single-atom alloy active center of Pd-Ag synergistic action; the total loading amount of the Pd and the Ag is 0.05-2 wt%, and the molar ratio of the Pd to the Ag is 1:(0.05-5). A small amount of heteronuclear metal Ag is introduced on the surface of TiO2 as a regulation unit, the electronic state of a Pd active center is adjusted through intermetallic local interaction, and therefore the CO2 photocatalytic reduction activity and the methanol selectivity are improved.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic materials and environmental catalysis technology, specifically relating to a Pd–Ag / TiO2 ultra-small single-atom alloy photocatalyst, its preparation method, and its application. Background Technology

[0002] Currently, the global atmospheric carbon dioxide concentration has exceeded 420 ppm, and the greenhouse effect and ocean acidification are becoming increasingly severe. Under the macro framework of the "dual carbon" goal, how to convert CO2 into high-value-added chemicals has become a key path to achieve carbon recycling. Methanol (CH3OH), as an important C1 platform molecule, has a high energy density and is liquid at room temperature and pressure. It possesses the dual properties of a clean fuel and a hydrogen storage medium, and is therefore regarded as the core cornerstone of the methanol economy. However, at present, the mainstream production of methanol still relies on the coal chemical route, which is accompanied by high energy consumption and large carbon emissions, making it difficult to meet the needs of green and low-carbon transformation. In contrast, solar-driven photocatalytic CO2 reduction technology can achieve the synergistic conversion of CO2 and water under mild conditions, with significant advantages such as low energy consumption and green process, and is therefore regarded as the cutting-edge direction of CO2 resource utilization. Anatase TiO2, with its low cost, good chemical stability, and suitable band structure, has long occupied the dominant position in the field of photocatalysis and meets the basic thermodynamic conditions for driving the CO2 reduction reaction. By introducing metal active centers onto the TiO2 surface, its surface electronic structure can be effectively modulated, further enhancing catalytic activity and selectivity.

[0003] Existing research has shown that while TiO2-based single-atom metal catalysts achieve extremely high atomic utilization, their local coordination environment is often limited by strong metal-oxygen interactions, resulting in a restricted space for adjusting the electronic states of active centers, which in turn limits their activity and selectivity in the CO2 photoreduction process. To overcome this bottleneck, it is necessary to systematically control the local structure and interaction modes of TiO2-based single-atom active centers at the microscopic level. On the one hand, the bonding mode between single atoms and the TiO2 surface can be altered by carefully designing metal precursors, adjusting heat treatment conditions, or introducing synergistic coordinators, thereby weakening the strong metal-oxygen coupling. On the other hand, the special electronic environment constructed by surface defects, oxygen vacancies, or dopants can be utilized to achieve precise control of the electronic states of single atoms, thereby improving the efficiency of CO2 adsorption, activation, and multi-electron transfer processes.

[0004] In summary, overcoming the challenge of local coordination limitation in TiO2-based single-atom catalysts is key to improving the photocatalytic CO2 reduction performance. Therefore, how to improve the catalytic performance of TiO2-based single-atom catalysts by regulating the local structure and interaction mode of TiO2-based single-atom active centers remains a critical issue that urgently needs to be addressed in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the existing technology and provide a Pd–Ag / TiO2 ultra-small single-atom alloy photocatalyst, its preparation method and application. By introducing a small amount of heteronuclear metal Ag as a control unit on the TiO2 surface, the electronic state of the Pd active center is adjusted through intermetallic local interactions, thereby improving the photocatalytic reduction activity of CO2 and the selectivity of methanol.

[0006] To achieve the above objectives, one of the technical solutions of the present invention is: a Pd–Ag / TiO2 ultrasmall single-atom alloy photocatalyst, comprising a TiO2 support and Pd and Ag loaded on its surface, wherein the total loading of Pd and Ag is 0.05–2 wt%, the molar ratio of Pd to Ag is 1:(0.05–5), the Pd and Ag are dispersed in an atomic-level manner on the surface of the TiO2 support, and the Pd atoms form a composite structure with localized interactions with neighboring Ag atoms, thereby constructing an ultrasmall single-atom alloy active center with Pd–Ag synergistic effect.

[0007] Pd and Ag form localized interactions, thereby altering the electronic state of the Pd active center and enhancing its catalytic performance for CO2 reduction.

[0008] In a preferred embodiment of the present invention, the TiO2 is anatase TiO2 with a spherical or near-spherical microstructure.

[0009] In a preferred embodiment of the present invention, the Pd and Ag are mainly dispersed in single-atom form on the surface of the TiO2 support.

[0010] In a preferred embodiment of the present invention, the total loading of Pd and Ag is 0.6–1 wt%, and the molar ratio of Pd to Ag is 1:(0.8–1).

[0011] To achieve the above objectives, the second technical solution of the present invention is: a method for preparing a Pd–Ag / TiO2 ultrasmall single-atom alloy photocatalyst, comprising the following steps:

[0012] (1) Disperse TiO2 in anhydrous ethanol and sonicate for 10–20 min to obtain a TiO2 anhydrous ethanol dispersion with a molar concentration of 0.05–0.15 mol / L;

[0013] (2) Purge with inert gas N2 for 30–40 min to remove dissolved oxygen;

[0014] (3) Add Ag precursor solution and react under ultraviolet light for 30–40 min to deposit Ag on TiO2 surface;

[0015] (4) Add Pd precursor solution and react under ultraviolet light for 30–40 min to deposit Pd on TiO2 surface;

[0016] (5) Pd–Ag / TiO2 ultra-small single-atom alloy photocatalyst was obtained after washing, centrifugation and vacuum drying.

[0017] In a preferred embodiment of the present invention, in step (3), the Ag precursor is one of inorganic silver salt, organic acid silver salt, or inorganic cation-coordinated silver complex, and the Pd precursor is one of inorganic palladium salt or organic acid palladium salt.

[0018] In a preferred embodiment of the present invention, steps (3) and (4) can be combined and implemented simultaneously by adding Ag precursor solution and Pd precursor solution, reacting under ultraviolet light, and simultaneously completing the co-deposition of Ag and Pd on the TiO2 surface.

[0019] In a preferred embodiment of the present invention, the centrifugation speed in step (5) is 6000–9000 rpm and the time is 3–5 min.

[0020] The anatase TiO2 used was prepared by the sol-gel method, and the specific preparation method is as follows: Tetrabutyl titanate was added to anhydrous ethanol and stirred at 6000-8000 rpm to obtain a tetrabutyl titanate anhydrous ethanol suspension with a molar concentration of 0.5-3 mol / L; deionized water, glacial acetic acid, and anhydrous ethanol were mixed in a volume ratio of (1-3):(1-3):(2-4) to obtain a mixed solvent; the mixed solvent was added to the tetrabutyl titanate anhydrous ethanol suspension, magnetically stirred at 600-800 rpm, and aged for 8-16 h to obtain a gel; the obtained gel was dried at 60-80 ℃ for 8-14 h, then ground, washed, and dried again; the dried sample was calcined at a temperature of 500-550 ℃, a heating rate of 3-5 ℃ / min, and a holding time of 4-6 h to obtain anatase TiO2 support.

[0021] To achieve the above objectives, the third technical solution of the present invention is: the application of a Pd-Ag / TiO2 ultra-small single-atom alloy photocatalyst in the photocatalytic reduction of CO2 to prepare methanol.

[0022] To achieve the above objectives, the fourth technical solution of the present invention is: a method for photocatalytic reduction of CO2 to methanol using a Pd-Ag / TiO2 ultra-small single-atom alloy photocatalyst, comprising the following steps: placing the Pd-Ag / TiO2 ultra-small single-atom alloy photocatalyst in a photocatalytic reactor; introducing high-purity CO2 gas into the photocatalytic reactor and introducing water or water vapor as a proton source; establishing a high-purity CO2 reaction environment by vacuuming and circulating gas to replace air; conducting the catalytic reaction under simulated sunlight irradiation, controlling the catalytic reaction temperature at 30–50℃, and generating C1 products mainly composed of methanol.

[0023] In a preferred embodiment of the invention, the light source is preferably a xenon lamp with an AM1.5 filter.

[0024] In a preferred embodiment of the present invention, the purity of the CO2 gas is not less than 99.9%.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] 1. Compared with traditional TiO2-based single-atom metal catalysts, this invention constructs a double single-atom active site with M–M1 weak coordination characteristics, which exhibits higher catalytic activity and methanol selectivity in the photocatalytic reduction of CO2 to methanol reaction.

[0027] 2. The preparation process of this invention is simple and can be mass-produced in conventional chemical equipment, giving it a strong cost advantage.

[0028] 3. The preparation conditions of this invention are mild, do not require high temperature and high pressure, and can be converted into clean energy. Attached Figure Description

[0029] Figure 1 Pd1-Ag in Example 1 x STEM image of TiO2 ultra-small single-atom alloy photocatalyst;

[0030] Figure 2 Pd1-Ag in Example 1 x XRD pattern of TiO2 ultrasmall single-atom alloy photocatalyst;

[0031] Figure 3 The graph shows the performance of the catalyst in Example 1. Detailed Implementation

[0032] To make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in more detail below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0033] Example 1

[0034] A Pd–Ag / TiO2 ultrasmall single-atom alloy photocatalyst is proposed, which uses anatase TiO2 with spherical or near-spherical microstructure as a support. Pd and Ag are loaded on the surface of the TiO2 support. Pd and Ag exist in an atomic-level dispersion, mainly in the form of single atoms. Pd atoms form a composite structure with local interactions with neighboring Ag atoms, thereby constructing an ultrasmall single-atom alloy active center with Pd–Ag synergistic effect. The total metal loading of Pd and Ag is about 0.8 wt%, and the molar ratio is 1:1.

[0035] This embodiment also provides a method for preparing a Pd–Ag / TiO2 ultrasmall single-atom alloy photocatalyst, comprising the following steps:

[0036] Ag and Pd were loaded onto the surface of anatase TiO2 using a stepwise photodeposition method: 1 g of anatase TiO2 was added to 150 mL of anhydrous ethanol and sonicated to form a homogeneous suspension; then N2 was purged for 30 min to remove dissolved oxygen; silver nitrate solution was added, and the mixture was stirred under UV irradiation for 30 min at 8000 rpm for 45 min to deposit Ag on the TiO2 surface; then palladium nitrate solution was added, and irradiation was continued under the same conditions for another 45 min to deposit Pd on the TiO2 surface; the mixture was then washed with deionized water and centrifuged at 8000 rpm for 3 min, followed by vacuum drying at 60 °C for 24 h to obtain Pd1‒Ag. x / TiO2 ultra-small single-atom alloy photocatalyst.

[0037] In this embodiment, the obtained photocatalyst sample was characterized using aberration-corrected scanning transmission electron microscopy (STEM), and the results are as follows: Figure 1 .from Figure 1 The results showed that Pd and Ag mainly existed in a highly dispersed single-atom form on the TiO2 surface, with Ag accounting for 0.38 wt% and Pd accounting for 0.40 wt%. Aberration-corrected HAADF-STEM images showed numerous isolated bright spots uniformly distributed on the TiO2 support, with no distinguishable nanoparticles. XRD analysis revealed only diffraction peaks on the TiO2 support, consistent with the characteristics of single-atom dispersion, where Pd atoms were distributed in close proximity to neighboring Ag atoms, with an interatomic distance of approximately 2.7–2.9 Å. Further energy dispersive spectroscopy (EDS) analysis of the obtained catalyst sample yielded the following results: Figure 2 As shown, Pd and Ag elements are uniformly distributed on the TiO2 surface, and a neighboring distribution pattern of Ag elements can be observed around Pd. These characterization results indicate that Pd and Ag form a highly dispersed local composite structure on the TiO2 surface, providing experimental evidence for constructing an ultra-small single-atom alloy catalytic system.

[0038] A Pd1-Ag x Application of TiO2 ultra-small single-atom alloy photocatalyst in the photocatalytic reduction of CO2 to methanol.

[0039] The Pd1‒Ag obtained in this embodiment x The Pd-Ag / TiO2 ultra-small single-atom alloy photocatalyst is used for the photocatalytic reduction of CO2 to produce methanol, comprising the following steps: placing the Pd-Ag / TiO2 ultra-small single-atom alloy photocatalyst in a photocatalytic reactor; introducing high-purity CO2 gas with a purity of over 99.9% into the photocatalytic reactor, and introducing water vapor as a proton source; establishing a high-purity CO2 reaction environment by vacuuming and circulating gas to replace air; conducting the catalytic reaction under simulated sunlight irradiation using a xenon lamp with an AM1.5 filter, controlling the catalytic reaction temperature at 50℃, and generating C1 products mainly composed of methanol.

[0040] Comparative Example 1

[0041] A Pd / TiO2 photocatalyst was prepared by the following method: 1 g TiO2 was added to 150 mL of anhydrous ethanol and ultrasonically treated to form a uniform suspension; then N2 was purged for 30 min to remove dissolved oxygen; palladium nitrate solution was added to make the Pd loading 0.5 wt%, and the reaction was carried out under ultraviolet light for 30 min; the obtained product was centrifuged, washed, and vacuum dried at 80 ℃ for 24 h to obtain the Pd / TiO2 photocatalyst.

[0042] Comparative Example 2

[0043] An Ag1 / TiO2 photocatalyst was prepared by the following method: 1 g TiO2 was added to 150 mL of anhydrous ethanol and ultrasonically treated to form a uniform suspension; then N2 was purged for 30 min to remove dissolved oxygen; silver nitrate solution was added to make the Ag loading 0.5 wt%, and the reaction was carried out under ultraviolet light for 30 min; the obtained product was centrifuged (8000 rpm for 3 min), washed, and vacuum dried at 80 ℃ for 24 h to obtain the Ag / TiO2 photocatalyst.

[0044] To compare the catalytic performance of the photocatalysts obtained in Example 1, Comparative Example 1, and Comparative Example 2, the Pd-Ag / TiO2 ultra-small single-atom alloy photocatalyst was placed in a photocatalytic reactor along with Ag / TiO2 and Pd / TiO2 photocatalysts. High-purity CO2 gas (purity above 99.9%) was introduced into the photocatalytic reactor, and water vapor was introduced as a proton source. A high-purity CO2 reaction environment was established by vacuuming and circulating gas to replace air. The catalytic reaction was carried out under simulated sunlight, with the reaction temperature controlled at 50°C, producing C1 products, primarily methanol. The results are as follows: Figure 3 As shown. From Figure 3 The results show that the Pd-Ag / TiO2 ultra-small single-atom alloy photocatalyst has the highest methanol production rate, with a maximum methanol production rate of 372.70 μmol / h. -1 g -1 The highest selectivity was 93.12%, while the highest methanol yield of the Ag / TiO2 photocatalyst was only 71.01 μmol / h. -1 g -1 The yield of methanol produced by the Pd-Ag / TiO2 photocatalyst is about 5 times that of Ag / TiO2. The Pd / TiO2 photocatalyst mainly produces gaseous C1 products and basically no methanol is produced.

[0045] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail 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. Such 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 of the present invention.

Claims

1. A Pd–Ag / TiO2 ultrasmall single-atom alloy photocatalyst, characterized in that, The device includes a TiO2 support and Pd and Ag loaded on its surface, wherein the total loading of Pd and Ag is 0.05–2 wt%, the molar ratio of Pd to Ag is 1:(0.05–5), and Pd and Ag are dispersed in an atomic-level manner on the surface of the TiO2 support, wherein the Pd atoms form a composite structure with local interactions with neighboring Ag atoms.

2. The Pd–Ag / TiO2 ultrasmall single-atom alloy photocatalyst as described in claim 1, characterized in that, The TiO2 is anatase TiO2 with a spherical or near-spherical microstructure.

3. The Pd–Ag / TiO2 ultrasmall single-atom alloy photocatalyst as described in claim 1, characterized in that... The Pd and Ag are mainly dispersed in single-atom form on the surface of the TiO2 support.

4. The preparation method of the Pd–Ag / TiO2 ultrasmall single-atom alloy photocatalyst as described in claims 1-3, characterized in that, Includes the following steps: (1) Disperse TiO2 in anhydrous ethanol and sonicate for 10–20 min to obtain a TiO2 anhydrous ethanol dispersion with a molar concentration of 0.05–0.15 mol / L; (2) Purge with inert gas N2 for 30–40 min to remove dissolved oxygen; (3) Add Ag precursor solution and react under ultraviolet light for 30–40 min to deposit Ag on TiO2 surface; (4) Add Pd precursor solution and react under ultraviolet light for 30–40 min to deposit Pd on TiO2 surface; (5) Pd–Ag / TiO2 ultra-small single-atom alloy photocatalyst was obtained after washing, centrifugation and vacuum drying.

5. The preparation method of the Pd–Ag / TiO2 ultrasmall single-atom alloy photocatalyst as described in claim 4, characterized in that, In step (3), the Ag precursor is one of inorganic silver salt, organic acid silver salt, or inorganic cation-coordinated silver complex. In step (4), the Pd precursor is one of inorganic palladium salt or organic acid palladium salt.

6. The preparation method of the Pd–Ag / TiO2 ultrasmall single-atom alloy photocatalyst as described in claim 4, characterized in that, Steps (3) and (4) can be combined and implemented at the same time. Ag precursor solution and Pd precursor solution are added and reacted under ultraviolet light to simultaneously complete the co-deposition of Ag and Pd on the TiO2 surface.

7. The preparation method of the Pd–Ag / TiO2 ultrasmall single-atom alloy photocatalyst as described in claim 4, characterized in that, In step (5), the centrifugation speed is 6000–9000 rpm and the time is 3–5 min.

8. The application of the Pd-Ag / TiO2 ultrasmall single-atom alloy photocatalyst as described in any one of claims 1-3 in the photocatalytic reduction of CO2 to methanol.

9. A method for photocatalytic reduction of CO2 to methanol using a Pd-Ag / TiO2 ultrasmall single-atom alloy photocatalyst as described in any one of claims 1-3, characterized in that, The process includes the following steps: placing the Pd-Ag / TiO2 ultra-small single-atom alloy photocatalyst in a photocatalytic reactor; introducing high-purity CO2 gas into the photocatalytic reactor and introducing water or water vapor as a proton source; establishing a high-purity CO2 reaction environment by evacuating and circulating air to replace the air; conducting the catalytic reaction under simulated sunlight irradiation, controlling the catalytic reaction temperature at 30–50℃, and generating C1 products mainly composed of methanol.

10. The method for photocatalytic reduction of CO2 to methanol using the Pd-Ag / TiO2 ultrasmall single-atom alloy photocatalyst as described in claim 9, characterized in that, The purity of the CO2 is not less than 99.9%.

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