Preparation method of monatomic cocatalyst and application thereof

Abstract

The application discloses a preparation method of a single-atom cocatalyst and application thereof, and belongs to the technical field of catalysts. The preparation method comprises the following steps: (1) preparing a metal precursor containing an alkyne group; (2) dispersing the metal precursor containing the alkyne group and a semiconductor carrier in an organic solvent, and then stirring and mixing under light-proof conditions to obtain a mixed system; and (3) irradiating the mixed system with a xenon lamp at room temperature to obtain the single-atom cocatalyst. The method not only avoids a traditional high-temperature reduction process, but also effectively inhibits the agglomeration of metal atoms through a steric hindrance effect generated by the coupling of a phenylacetylene ligand at normal temperature and pressure, thereby providing a brand-new low-energy-consumption scheme for preparing a single-atom cocatalyst with high stability and high dispersity.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a method for preparing a single-atom co-catalyst and its application. Background Technology

[0002] Single-atom catalysts (SACs) exhibit extremely high activity and selectivity in heterogeneous catalysis due to their maximum atom utilization, uniform active center structure, and unique electronic properties. Especially in highly challenging reactions such as methane activation, carbon dioxide reduction, and advanced oxidation processes (AOPs), single-atom metal centers often demonstrate performance far exceeding that of traditional nanoparticle catalysts.

[0003] However, how to achieve stable dispersion of single atoms has always been a key scientific problem in this field. Currently, the common methods for preparing single-atom catalysts include: (1) Impregnation and co-precipitation: Although these methods are simple to operate, metal atoms are prone to migration and aggregation during subsequent high-temperature calcination or chemical reduction, forming nanoclusters or large particles, making it difficult to ensure the single-atom dispersion state of the active center. (2) Atomic layer deposition (ALD): Although this method can precisely control the loading, the equipment is expensive, the precursor cost is high, and the production efficiency is low, making it difficult to promote in large-scale industrial applications. (3) High-temperature pyrolysis: Metal-organic frameworks (MOFs) are used as precursors for pyrolysis. Although a stable single-atom structure can be obtained, the process is energy-intensive and easily forms complex carbon layer encapsulation, burying some active sites and affecting catalytic efficiency. (4) Freeze-drying: Its core advantage is that it can effectively suppress metal aggregation through low-temperature freezing and achieve high-density atomic-level dispersion. However, its equipment and operating costs are high, and the preparation cycle is very long (usually more than 24 hours), and it often needs to be combined with high-temperature treatment, making the process more complex.

[0004] To address the problems of complex synthesis processes, harsh conditions, easy metal aggregation, and uneven distribution of active sites in the existing technologies, there is an urgent need to develop a synthesis strategy that can achieve in-situ anchoring of metal atoms under mild conditions and with a highly controllable process. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a method for preparing a single-atom cocatalyst and its application, thereby solving problems such as complex synthesis processes, harsh conditions, easy metal agglomeration, and uneven distribution of active sites in existing technologies.

[0006] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing a single-atom co-catalyst is provided, comprising the following steps: (1) Preparation of metal precursors containing alkyne groups; (2) Disperse the alkynyl-containing metal precursor and semiconductor support in an organic solvent, and then stir and mix them under light-protected conditions to obtain a mixed system; (3) At room temperature, the mixed system was irradiated with a xenon lamp to obtain a single-atom co-catalyst.

[0007] The beneficial effects of this invention are as follows: After uniformly dispersing the alkynyl-containing metal precursor and semiconductor support in an organic solvent, they are then mixed under light-protected conditions. This step, also known as pre-adsorption treatment, aims to allow the metal precursor molecules to reach adsorption equilibrium on the support surface. Finally, the adsorption-equilibrium mixture is irradiated at room temperature to induce a coupling reaction and release of the alkynyl ligands in the alkynyl-containing metal precursor. Simultaneously, the released metal atoms are anchored on the semiconductor support surface, thus obtaining a single-atom cocatalyst. This photoinduced in-situ coupling process effectively suppresses the aggregation of metal atoms on the support surface during the reaction. The process of this invention can achieve stable loading of metal in an atomically dispersed state on the semiconductor support at room temperature.

[0008] Based on the above technical solution, the present invention can be further improved as follows: Furthermore, the metal loading in the single-atom co-catalyst is 0.4-1.2 wt%; preferably 1 wt%.

[0009] Furthermore, the metals in the metal precursor are copper (Cu), gold (Au), and silver (Ag).

[0010] Further, the specific process of step (1) is as follows: dissolve the metal salt in an organic solvent, then add triethylamine and phenylacetylene, mix well, separate and dry to obtain the metal precursor containing acetylene.

[0011] The beneficial effects of adopting the above-mentioned further technical solution are as follows: under the alkaline action of triethylamine, phenylacetylene loses the terminal alkyne hydrogen and then coordinates with metal ions in the metal salt to obtain a metal precursor containing an alkyne group.

[0012] Furthermore, the organic solvent in step (1) is methanol.

[0013] Further, in step (1), the mass-to-volume ratio of the metal salt, organic solvent, triethylamine, and phenylacetylene is (300-400) mg: (30-50) mL: (2-2.5) mL: (0.4-0.5) mL; preferably, the mass-to-volume ratio of the metal salt, organic solvent, triethylamine, and phenylacetylene is 365 mg: 40 mL: 2.24 mL: 0.44 mL.

[0014] Furthermore, in step (2), the semiconductor carrier is titanium dioxide.

[0015] Furthermore, in step (2), the mixture is stirred and mixed under light-protected conditions for 20-40 min; preferably, it is stirred and mixed under light-protected conditions for 30 min.

[0016] The beneficial effects of adopting the above-mentioned further technical solution are as follows: This process is a pre-adsorption process, which is carried out under light-protected conditions and involves the anchoring equilibrium of the metal precursor. The pre-adsorption time determines the uniformity of chemical adsorption and dispersion of precursor molecules on the carrier surface. If the time is insufficient, the precursor has not yet reached adsorption-desorption equilibrium, and the number of precursors anchored on the carrier surface is small and unevenly distributed, requiring a certain amount of time to reach adsorption equilibrium. Therefore, in this invention, the pre-adsorption time is 20-40 min, preferably 30 min.

[0017] Furthermore, in step (3), the lamp is irradiated with a 300 W xenon lamp for 30-60 minutes; preferably, it is irradiated with a 300 W xenon lamp for 30 minutes.

[0018] The beneficial effects of adopting the above-mentioned further technical solution are as follows: the wavelength of the photoinduced in-situ coupling reaction is not related to the substrate material. It is mainly due to the light absorption coupling of the alkyne-containing metal precursor itself. It is not necessary to use ultraviolet light; visible light can also be used.

[0019] Light intensity directly determines the rate of the coupling reaction. In the low-power range, the coupling rate increases significantly with increasing light intensity, and the exposure time of single atoms decreases; however, when the power is too high, the excessively fast reaction rate may produce localized thermal effects, which not only fail to further improve the coupling efficiency but also easily induce thermal migration and aggregation of metal atoms. This invention preferably uses a 300 W xenon lamp for irradiation.

[0020] Irradiation time is a key variable controlling the anchoring and dispersion state of single atoms. With prolonged irradiation time, the single-atom loading and activity on the catalyst surface exhibit a "volcano-like" trend of first increasing and then decreasing. When the time is insufficient (less than 30 min), the Glaser coupling reaction is incomplete, and a large number of ligands (such as phenylacetylene groups) remain on the semiconductor support surface. However, when the reaction time is controlled between 30-60 min, the coupling reaction is complete, the ligands completely leave, and the metal atoms are stably anchored as isolated single atoms at defect sites on the semiconductor support surface, achieving optimal catalytic activity. If the irradiation time is too long and continuous photogenerated carrier attack occurs, it may lead to local structural damage on the semiconductor support surface, causing the originally stably anchored single atoms to migrate and detach, subsequently agglomerating into nanoclusters or nanoparticles on the surface, reducing the atomic utilization rate of single atoms and the intrinsic catalytic activity.

[0021] Application of the single-atom cocatalyst prepared by the above method in the photocatalytic methane conversion reaction.

[0022] Furthermore, the application of the single-atom co-catalyst prepared by the above method in the photocatalytic conversion of methane to methanol and formaldehyde.

[0023] The present invention has the following beneficial effects: (1) This invention utilizes the principle of in-situ photoinduced chemistry. Under light irradiation, the in-situ coupling reaction of an alkyne-containing metal precursor on the surface of a semiconductor support achieves ligand departure while simultaneously loading metal atoms directly onto the semiconductor support surface. This method not only avoids the traditional high-temperature reduction process but also effectively suppresses the aggregation of metal atoms through the spatial confinement effect generated by the coupling of phenylacetylene ligands at room temperature and pressure. This provides a novel low-energy-consumption scheme for preparing highly stable and highly dispersed single-atom catalysts.

[0024] (2) The preparation method of this invention is simple, and the preparation of single-atom cocatalysts can be completed at room temperature and pressure without the need for high-temperature calcination or low-temperature treatment, which greatly reduces costs and energy consumption. The single-atom cocatalysts prepared by this invention achieve maximum atom utilization. Attached Figure Description

[0025] Figure 1 The UV-Vis diffuse reflectance spectra of Cu / P25 obtained by phenylacetylene copper, irradiation for 0 min and irradiation for 60 min are shown.

[0026] Figure 2 The image shows aberration-corrected electron microscopy image and elemental mapping of the single-atom cocatalyst Cu / P25 prepared in Example 1.

[0027] Figure 3 Aberration-corrected electron microscopy image and elemental mapping of the catalyst Cu / P25-PD prepared in Comparative Example 1.

[0028] Figure 4 The image shows a spherical aberration electron microscope image (scale bar 10 nm) and elemental mapping of the catalyst Cu / P25-NaBH4 prepared in Comparative Example 2.

[0029] Figure 5 The image shows aberration-corrected electron microscopy (SEM) image of the catalyst Cu / P25-NaBH4 prepared in Comparative Example 2 (scale bar: 2 nm).

[0030] Figure 6 The results show the photocatalytic methane conversion activity of the single-atom co-catalyst Cu / P25.

[0031] Figure 7 The results show the photocatalytic methane conversion activity of the catalyst Cu / P25-PD prepared in Comparative Example 1.

[0032] Figure 8 The results show the photocatalytic methane conversion activity of the catalyst Cu / P25-NaBH4 prepared in Comparative Example 2. Detailed Implementation

[0033] The examples given below are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, conditions in the examples are performed under standard conditions or as recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0034] Example 1: A method for preparing a single-atom cocatalyst includes the following steps: (1) Weigh 365 mg CuCl2·2H2O into a beaker, add 40 mL of methanol to dissolve it completely, then slowly add 2240 μL of triethylamine and 440 μL of phenylacetylene dropwise at a uniform rate, mix well, then filter, dry, grind to obtain a yellow solid powder, which is copper phenylacetylene. (2) Take 0.48, 0.72, 0.96, 1.2 and 1.44 mg of copper phenylacetylene (so that the mass percentage of copper in the final single-atom co-catalyst is 0.4%, 0.6%, 0.8%, 1% and 1.2% respectively) and 50 mg of titanium dioxide (P25) respectively and dissolve them in 40 mL of methanol. Then stir for 30 min under the dark and then irradiate for 30 min under a 300W xenon lamp at room temperature to form atomically dispersed catalyst Cu / P25. Wash, centrifuge and dry to obtain solid powder, which is the single-atom co-catalyst.

[0035] The phenylacetylene copper (PhC2Cu) prepared above, and the Cu / P25 obtained by irradiation for 0 min and 60 min, were analyzed, and their ultraviolet-visible diffuse reflectance (UV-DS) spectra are shown in the figure. Figure 1 As shown.

[0036] Depend on Figure 1 It is known that phenylacetylene copper has a characteristic absorption at 400-500 nm. After phenylacetylene copper and P25 are adsorbed in the dark, without light exposure (0 min of light exposure), a relatively obvious characteristic peak of phenylacetylene copper can still be seen. However, after 60 min of light exposure, the characteristic peak of phenylacetylene copper disappears, indicating that the alkynyl ligand undergoes a coupling reaction and leaves under light exposure, releasing metal atoms.

[0037] Aberration-corrected electron microscopy images of the single-atom co-catalyst Cu / P25 prepared above are shown below. Figure 2 As shown in Figure (A) (the yellow circle represents a single atom), the EDS-mapping diagram (elemental mapping diagram) is as follows: Figure 2 As shown in Figure (B) of the document.

[0038] Depend on Figure 2 It can be seen that Cu single atoms with a mass fraction of 1 wt% are uniformly distributed on the catalyst surface.

[0039] Comparative Example 1: The catalyst Cu / P25-PD was prepared by photodeposition, and the specific process is as follows: 200 mg of titanium dioxide (P25) was added to a mixed solution containing 25 mL of distilled water and 5 mL of methanol. Then, 304, 456, 608, 760, and 912 μL of Cu(NO3)3·3H2O (10 mg / L) solution were added respectively (resulting in copper loading percentages of 0.4%, 0.6%, 0.8%, 1%, and 1.2% in the final catalyst). The reaction system was first stirred at room temperature under argon atmosphere for 20 min, then stirred for another 1 h under a 300W xenon lamp at room temperature. The mixture was washed with ultrapure water, centrifuged, and dried to obtain the catalyst Cu / P25-PD.

[0040] Aberration-corrected electron microscopy images of the catalyst Cu / P25-PD (copper loading of 0.8 wt%) prepared above are shown below. Figure 3 As shown in Figure (A) (the yellow circle represents nanoclusters), the EDS-mapping diagram (elemental mapping diagram) is as follows: Figure 3 As shown in Figure (B) of the document.

[0041] Depend on Figure 3 It can be seen that the metal in the catalyst prepared by the above method is a nanocluster rather than a single atom.

[0042] Comparative Example 2: The catalyst Cu / P25-NaBH4 was prepared by sodium borohydride reduction, and the specific process is as follows: Take 200 mg of titanium dioxide (P25) and add it to a beaker containing 40 mL of distilled water. Add 304, 456, 608, 760, and 912 μL of Cu(NO3)3·3H2O (10 mg / L) solution respectively (so that the final copper loading percentage in the catalyst is 0.4%, 0.6%, 0.8%, 1%, and 1.2% respectively). Stir at a constant temperature for 0.5 h, and then slowly and uniformly add NaBH4 solution (0.8, 1.2, 1.6, 2, and 2.4 mL). React at room temperature for 0.5 h, wash with ultrapure water, centrifuge, and dry to obtain the catalyst Cu / P25-NaBH4.

[0043] Aberration-corrected electron microscopy images of the catalyst Cu / P25-NaBH4 (copper loading of 0.4 wt%) prepared above are shown below. Figure 4 As shown in Figure (A) (scale bar is 10 nm, yellow circle represents nanoclusters), the EDS-mapping diagram (elemental mapping diagram) is as follows: Figure 4 As shown in Figure (B) of the document.

[0044] Aberration-corrected electron microscopy images of the catalyst Cu / P25-NaBH4 (copper loading of 0.4 wt%) prepared above are shown below. Figure 5 As shown (scale bar is 2 nm, yellow circle represents a single atom).

[0045] Depend on Figure 4 and 5 It can be seen that the best sample of the catalyst prepared by the above method has a copper loading of 0.4 wt%, which is extremely small. Some atoms are difficult to agglomerate, and very few single atoms can be observed.

[0046] The single-atom co-catalyst Cu / P25 prepared in Example 1, the catalyst Cu / P25-PD prepared in Comparative Example 1, and the catalyst Cu / P25-NaBH4 prepared in Comparative Example 2 were used in the methane conversion reaction, as follows: 1. Application of single-atom co-catalyst Cu / P25 10 mg of the catalysts prepared in Example 1, Comparative Example 1, and Comparative Example 2 were placed in a high-pressure reactor, 100 mL of water was added, and the reactor was purged with O2 for 20 min. Then, CH4 (methane) at 1.9 MPa was introduced, and the reaction was carried out under a 300 W xenon lamp for 1 h. The supernatant was filtered through a filter membrane, and its photocatalytic performance in the conversion of methane to methanol (CH3OH) and formaldehyde (HCHO) was tested. The results are as follows. Figure 6-8 As shown.

[0047] Depend on Figure 6 It can be seen that the optimal Cu loading in the single-atom co-catalyst Cu / P25 sample is 1 wt%, with a total yield as high as 6.5 mmol·g. -1 ·h -1 Its performance is significantly better than that of Comparative Example 1 and Comparative Example 2.

[0048] Depend on Figure 7 It can be seen that the optimal Cu loading in the sample of the Cu / P25-PD catalyst is 0.8 wt%, and the total yield is less than 4 mmol·g. -1 ·h -1 .

[0049] Depend on Figure 8 It can be seen that the optimal Cu loading in the sample of the catalyst Cu / P25-NaBH4 is 0.4 wt%, and the total yield is approximately 3 mmol·g. -1 ·h -1 .

[0050] In summary, the single-atom cocatalyst Cu / P25 prepared in this invention exhibits superior performance in photocatalytic methane conversion compared to Comparative Examples 1 and 2. When the single-atom cocatalyst formed in this invention has a Cu loading of 1 wt%, no significant atomic aggregation was observed, maximizing atom utilization. In contrast, atomic aggregation was observed in the optimal samples prepared by the sodium borohydride reduction method and the photodeposition method when the copper loading was 0.4 wt% and 0.8 wt%, respectively.

[0051] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a monatomic promoter, characterized by, Includes the following steps: (1) Preparation of metal precursors containing alkyne groups; (2) Disperse the alkynyl-containing metal precursor and semiconductor support in an organic solvent, and then stir and mix them under light-protected conditions to obtain a mixed system; (3) At room temperature, the mixed system was irradiated with a xenon lamp to obtain a single-atom co-catalyst.

2. The production method according to claim 1, characterized by, The metal loading in the single-atom co-catalyst is 0.4-1.2 wt%.

3. The preparation method according to claim 2, characterized in that, The metal loading in the single-atom co-catalyst is 1 wt%.

4. The preparation method according to any one of claims 1-3, characterized in that, The metals in the metal precursors are copper, gold, and silver.

5. The preparation method according to claim 1, characterized in that, The specific process of step (1) is as follows: dissolve the metal salt in an organic solvent, then add triethylamine and phenylacetylene, mix well, separate and dry to obtain a metal precursor containing an alkyne group; the organic solvent is methanol; the mass-volume ratio of metal salt, organic solvent, triethylamine and phenylacetylene is (300-400) mg: (30-50) mL: (2-2.5) mL: (0.4-0.5) mL.

6. The preparation method according to claim 1, characterized in that, In step (2), the semiconductor carrier is titanium dioxide.

7. The preparation method according to claim 1, characterized in that, In step (2), stir and mix for 20-40 minutes under light-protected conditions.

8. The preparation method according to claim 1, characterized in that, In step (3), irradiate with a 300 W xenon lamp for 30-60 minutes.

9. A single-atom co-catalyst, characterized in that, It is prepared by the preparation method according to any one of claims 1-8.

10. The application of the single-atom cocatalyst according to claim 9 in the photocatalytic methane conversion reaction.

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