A red phosphorus supported metal monatomic photocatalyst for reduction of carbon dioxide to ethylene

Abstract

The application discloses a red phosphorus (RP) supported metal monatomic photocatalyst for reduction of carbon dioxide to ethylene, and belongs to the field of catalysis. A crystalline RP carrier is prepared by a chemical vapor deposition method, monatomic Pt is uniformly anchored on the RP surface by an impregnation-calcination method, a Pt-P coordination structure is constructed, and a Pt1 / RP photocatalyst is obtained. The RP carrier provides stable and uniform surface phosphorus coordination sites, monatomic Pt promotes photo-induced charge separation and CO2 protonation, surface coordination P serves as a core active site and cooperates with Pt to dominate C-C coupling, and the limitation that traditional single-metal catalysts are difficult to generate C2 products is broken. Under visible light, the C2H4 yield of the Pt1 / RP can reach 21.03 micromoles per gram per hour ‑1 h ‑1 , and the selectivity is more than 93%. The application can be expanded to Co, Ni, Ag, Fe, Ir, Cu, Rh, Pd and other monatomic metals, and high-selectivity C2H4 synthesis is achieved, which exhibits excellent universality.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic carbon dioxide (CO2) resource utilization technology, and more specifically, relates to a method for preparing a photocatalyst based on red phosphorus (RP) supported on metal single atoms, and its application in the highly selective photocatalytic reduction of CO2 to produce ethylene (C2H4). Background Technology

[0002] C2H4 is an indispensable cornerstone raw material in the chemical industry, widely used in the production of polymers and various high-value-added chemicals. Traditional C2H4 production mainly relies on the steam cracking of petroleum hydrocarbons, a process that is energy-intensive and produces significant greenhouse gas emissions. Solar-driven photocatalysis to convert CO2 and water into C2H4 offers a highly attractive sustainable carbon-neutralization route. However, the highly selective reduction of CO2 to C2H4 is technically challenging due to the significant thermodynamic and kinetic barriers to C-C bond formation.

[0003] Conventional photocatalytic CO2 reduction catalysts (such as metal oxides and sulfides) mainly produce C1 products such as CO and CH4. Currently, there are few photocatalysts that can successfully generate C2H4, and most rely on finely regulated bimetallic catalysts. These traditional systems generally neglect the crucial role of the support in the C2H4 coupling process, making it difficult to provide a universal and easily implemented strategy for C2H4 synthesis.

[0004] To address the aforementioned issues, this invention proposes using RP elemental semiconductor materials with narrow bandgap structures and wide visible light absorption capabilities as carriers for metal single atoms. By constructing a single-atom metal-RP coordination structure and utilizing phosphorus atoms coordinated with the metal as key active centers, a synergistic effect is generated with the single-atom metal to precisely drive the CC coupling step in the CO2 reduction process. This achieves highly selective photocatalytic reduction of CO2 to C2H4, providing a simple and universal new approach for utilizing solar energy to convert greenhouse gases into high-value-added multi-carbon chemicals. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of low C2H4 selectivity and complex catalyst design in existing photocatalytic CO2 reduction systems, and to provide a highly efficient, universal and highly selective metal single-atom / red phosphorus (M1 / RP) photocatalyst for C2H4 production.

[0006] The preparation method of this photocatalyst is characterized by comprising the following steps:

[0007] (1) Commercial RP was purified by hydrothermal method to remove surface impurities;

[0008] (2) Preparation of RP support by chemical vapor deposition (CVD): Purified commercial RP was mixed with iodine to promote crystallization, vacuum sealed in a quartz tube, and placed in a muffle furnace for high-temperature calcination; after the reaction was completed, it was thoroughly washed with deionized water and dried by centrifugation to obtain RP support;

[0009] (3) The single-atom metal M1-RP coordination structure was constructed by impregnation-calcination method: the RP support was dispersed in deionized water to form a suspension, and the single-atom metal precursor solution was added dropwise while stirring continuously to make the metal atoms uniformly anchored on the RP surface.

[0010] (4) The catalyst powder collected by rotary evaporation is dried and then calcined in a mixed atmosphere of 5% H2 / Ar to remove surface oxides and further strengthen the chemical bond between the metal single atom and the coordinated RP, and finally the M1 / RP photocatalyst is obtained.

[0011] In step (3) above, the single-atom metal M1 is selected from any one of Co, Ni, Ag, Fe, Ir, Cu, Rh, Pd or Pt; specifically, when the single-atom metal M is Pt, its mass loading is 0.18 wt.%~1.12 wt.% (preferably 0.59 wt.%); to ensure the lateral comparability of the intrinsic catalytic activity between different metal atoms, when the single-atom metal M1 is selected from Co, Ni, Ag, Fe, Ir, Cu, Rh or Pd, its mass loading is controlled within a range close to the optimal Pt loading, i.e., 0.5 wt.%~0.7 wt.%.

[0012] The hydrothermal purification conditions in (1) are: 200 °C, 12 h.

[0013] The high-temperature calcination conditions in (2) are as follows: the temperature is raised to 550 ℃ at a heating rate of 2 ℃ / min and held for 4 h; then cooled to 280 ℃ at a rate of 1 ℃ / min and held for 4 h; finally cooled to room temperature at a rate of 0.2 ℃ / min.

[0014] The impregnation conditions in (3) are: continuous magnetic stirring for 6 h.

[0015] The calcination conditions in (4) are: calcination at 200 °C for 2 h at a flow rate of 5% H2 / Ar of 50 mL / min.

[0016] The performance evaluation of the M1 / RP photocatalyst prepared by this invention for the photocatalytic reduction of CO2 to ethylene is as follows: The M1 / RP photocatalyst is ultrasonically dispersed in deionized water, uniformly drop-coated onto a quartz glass slide and dried, and placed in a reactor with a quartz window; after the reactor is evacuated, high-purity CO2 and water vapor are introduced, and a 300 W xenon lamp is used as the light source to irradiate the sample for photocatalytic reaction. The composition of the gaseous products in the reactor is analyzed by gas chromatography.

[0017] This invention utilizes phosphorus phosphate (RP) as a universal coordination platform, opening a new pathway for the synthesis of C2 products via C2 coupling using single-metal catalysts. Taking the Pt1 / RP system as an example, at a loading of 0.59 wt%, the visible light-driven C2H4 yield reached 21.03 μmol g⁻¹ h⁻¹, with a selectivity of 93%. Research indicates that the phosphorus atom coordinated with the metal acts as a key active center, synergistically interacting with the single-atom metal to precisely dominate the highly selective synthesis of C2H4. This strategy provides a promising technical route for the field of green and low-carbon chemical engineering. Attached Figure Description

[0018] Figure 1 (a) SEM, (b) HRTEM, (c) Aberration-corrected HAADF-STEM, (d) STEM, and corresponding (e, f) EDS elemental distribution maps of the Pt1 / RP (0.59 wt.% Pt) sample prepared for this invention. These images demonstrate that single-atom Pt is highly uniformly dispersed at the atomic level on the RP support surface.

[0019] like Figure 2 The image shows the XRD patterns of the prepared RP support and Pt1 / RP samples with different Pt loadings. This demonstrates that the RP support in the Pt1 / RP samples is crystalline RP, and that the loading of single-atom Pt does not alter the bulk crystal structure of the RP support.

[0020] like Figure 3 The figure shows the Pt 4f and P 2p XPS spectra of Pt1 / RP samples with different Pt loadings according to the present invention. As the Pt content increases, the Pt 4f peak gradually shifts towards lower binding energies, while the P 2p peak shifts towards higher binding energies. This indicates that the Pt single atom forms a Pt-P coordination with the P atoms on the RP support surface, accompanied by electron transfer from P to Pt, revealing a strong electronic interaction at the interface between the two.

[0021] like Figure 4The figure shows a comparison of the photocatalytic CO2 reduction product formation rates of Pt1 / RP samples with different Pt loadings. It indicates that the C2H4 yield exhibits a "volcano-like" trend with increasing Pt loading, with the sample having a Pt loading of approximately 0.59 wt.% showing the best photocatalytic C2H4 synthesis performance.

[0022] like Figure 5 The figure shows the photocatalytic CO2 reduction activity and C2H4 selectivity of RP catalysts supported on different single-atom metals (M1 / RP, M = Co, Ni, Ag, Fe, Ir, Cu, Rh, Pd, Pt). This demonstrates that the RP coordination platform proposed in this invention has broad applicability and can activate various single-atom metals to achieve highly selective photocatalytic C2H4 synthesis. Detailed Implementation

[0023] The technical solution of the present invention will be further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present disclosure.

[0024] Example 1: Purification of Commercial Red RP: An appropriate amount of commercial RP was weighed and placed in a reaction vessel, and deionized water was added and mixed thoroughly. The suspension was then placed in a high-pressure reactor and subjected to hydrothermal treatment at 200 °C for 12 h. After the reaction was completed, the mixture was centrifuged, washed, and dried sequentially to remove impurities from the initial material, yielding purified RP.

[0025] Example 2: Preparation of RP support: Purified commercial RP precursor and elemental iodine were mixed, vacuum-sealed in a quartz tube, and subjected to high-temperature programmed calcination in a muffle furnace. The specific high-temperature programmed calcination parameters were: heating to 550 °C at a rate of 2 °C / min and holding at this temperature for 4 h; then cooling to 280 °C at a rate of 1 °C / min and holding for 4 h; finally, slowly cooling to room temperature at a rate of 0.2 °C / min. The final product was washed with water to remove residual impurities and dried at 60 °C to obtain the RP support.

[0026] Example 3: Preparation of M1 / RP single-atom photocatalyst: 100 mg of the RP support prepared in Example 2 was dispersed in 25 mL of deionized water and magnetically stirred to form a homogeneous suspension. A predetermined volume of a 0.2 mol / L single-atom metal salt precursor aqueous solution was added dropwise, and stirring was continued for 6 h. The single-atom metal precursor solution was selected from any one of CoCl2·6H2O, NiCl2·6H2O, IrCl3, AgNO3, FeCl3·6H2O, CuCl2, RhCl3·3H2O, PdCl2, and H2PtCl6·6H2O. Subsequently, the solid was dried and collected at 60 °C using rotary evaporation, and then placed in a tube furnace and calcined at 200 °C for 2 h under a 5% H2 / Ar mixed atmosphere at a flow rate of 50 mL / min. The final M1 / RP sample was obtained.

[0027] Specifically, to investigate the effect of single-atom loading on photocatalytic performance, when the single-atom metal was Pt, the precursor used was H2PtCl6·6H2O. By adjusting the dropping volume of this 0.2 mol / L precursor aqueous solution, gradient samples with actual mass loading ranging from 0.18 wt.% to 1.12 wt.% were prepared, and the optimal embodiment of the present invention was determined to be a Pt1 / RP sample with an actual mass loading precisely controlled at 0.59 wt.%. Meanwhile, to ensure the lateral comparability of intrinsic catalytic activity among different metal atoms, when the single-atom metal was selected from Pd, Rh, Cu, Ir, Fe, Ag, Ni, or Co, the dropping volume of the corresponding 0.2 mol / L metal salt precursor aqueous solution was precisely controlled, and the actual mass loading of these comparative samples was controlled within a range close to the optimal Pt loading, i.e., between 0.57 wt.% and 0.62 wt.%.

[0028] Example 4: Application and Performance Testing of M1 / RP Photocatalyst in CO2 Reduction to C2H4 The M1 / RP photocatalyst prepared in the above examples was ultrasonically dispersed in deionized water, uniformly drop-coated onto a quartz glass slide, and dried. The quartz glass slide loaded with the photocatalyst was placed in a photocatalytic reactor with a quartz window. After evacuating the reactor, high-purity CO2 and water vapor (water was added dropwise, and then water vapor was generated by irradiation with a 300 W xenon lamp) were introduced as reaction gases. A 300 W xenon lamp was used as the light source to irradiate the sample for photocatalytic CO2 reduction. During the reaction, the gaseous product components in the reactor were sampled and analyzed periodically by gas chromatography to evaluate the catalyst's rate and selectivity for C2H4 formation. See details below. Figure 5Under similar metal loading conditions, the C2H4 formation rate and selectivity of each M1 / RP photocatalyst are as follows (data in parentheses are, in order: actual loading, C2H4 formation rate, C2H4 selectivity): Co1 / RP (0.58 wt.%, 2.81 μmol g) -1 h -1 , 62%), Ni1 / RP (0.61 wt.%, 3.99 μmol g -1 h -1 , 72%), Ag1 / RP (0.60 wt.%, 4.35 μmol g -1 h -1 , 71%), Fe1 / RP (0.62 wt.%, 5.60 μmol g -1 h -1 , 82%), Ir1 / RP (0.59 wt.%, 6.71 μmol g -1 h -1 , 75%), Cu1 / RP (0.61 wt.%, 6.94 μmol g -1 h -1 , 71%), Rh1 / RP (0.58 wt.%, 10.13 μmol g -1 h -1 , 83%), Pd1 / RP (0.57 wt.%, 15.32 μmol g -1 h -1 ,86%) and Pt1 / RP (0.59 wt.%, 21.03 μmolg). -1 h -1 (93%). Among them, the Pt1 / RP sample had the highest C2H4 formation rate (21.03 μmol g). -1 h -1 The optimal embodiment exhibits C2H4 selectivity (93%) and C2H4 selectivity.

[0029] The preparation process of this invention is simple, and the RP platform used not only greatly improves the atom utilization rate, but also exhibits extremely high C2H4 selectivity under mild visible light conditions, which proves the great advantages of this non-metallic coordination platform in converting CO2 to produce high-value-added multi-carbon chemicals.

Claims

1. A method for preparing a red phosphorus-supported metal single-atom photocatalyst for the reduction of carbon dioxide to ethylene, characterized in that, Includes the following steps: (1) Commercial RP was purified by hydrothermal method to remove surface impurities; (2) Preparation of RP support by chemical vapor deposition (CVD): Purified commercial RP was mixed with iodine to promote crystallization, vacuum sealed in a quartz tube, and placed in a muffle furnace for high-temperature calcination; after the reaction was completed, it was thoroughly washed with deionized water and dried by centrifugation to obtain RP support; (3) The single-atom metal M1-RP coordination structure was constructed by impregnation-calcination method: the RP support was dispersed in deionized water to form a suspension, and the single-atom metal precursor solution was added dropwise while stirring continuously to make the metal atoms uniformly anchored on the RP surface. (4) The catalyst powder collected by rotary evaporation is dried and then calcined in a mixed atmosphere of 5% H2 / Ar to remove surface oxides and further strengthen the chemical bond between the metal single atom and the coordinated RP, and finally the M1 / RP photocatalyst is obtained.

2. The method according to claim 1, characterized in that, The single-atom metal M1 mentioned in step (3) is selected from any one of Co, Ni, Ag, Fe, Ir, Cu, Rh, Pd or Pt.

3. The method according to claim 2, characterized in that, When the single-atom metal M is Pt, its mass loading is 0.18 wt.%~1.12 wt.%, preferably 0.5 wt.%~0.7 wt.%, more preferably 0.59 wt.%; when the single-atom metal M1 is selected from Co, Ni, Ag, Fe, Ir, Cu, Rh or Pd, its mass loading is 0.5 wt.%~0.7 wt.%.

4. The method according to claim 1, characterized in that, The hydrothermal purification conditions in step (1) are: 200 °C for 12 h.

5. The method according to claim 1, characterized in that, The high-temperature calcination conditions in step (2) are as follows: heat up to 550 ℃ at a heating rate of 2℃ / min and hold for 4 h; then cool down to 280 ℃ at a rate of 1℃ / min and hold for 4 h; finally cool down to room temperature at a rate of 0.2℃ / min.

6. The method according to claim 1, characterized in that, The impregnation conditions in step (3) are: continuous magnetic stirring for 6 hours.

7. The method according to claim 1, characterized in that, The calcination conditions in step (4) are: calcination at 200 °C for 2 h at a flow rate of 5% H2 / Ar of 50 mL / min.

8. A red phosphorus-supported metal single-atom photocatalyst prepared according to any one of claims 1-7.

9. The application of the red phosphorus-supported metal single-atom photocatalyst prepared according to any one of claims 1-7 for photocatalytic CO2 reduction to ethylene.

10. According to the application of claim 9, the M1 / RP photocatalyst is ultrasonically dispersed in deionized water, uniformly drop-coated onto a quartz glass slide and dried, and placed in a reactor with a quartz window; after the reactor is evacuated, high-purity CO2 and water vapor are introduced, and a 300 W xenon lamp is used as a light source to irradiate the sample for photocatalytic reaction.

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