A method for preparing a monatomic alloy and applications thereof

Abstract

The application relates to a preparation method and application of a monatomic alloy, and belongs to the technical field of photocatalysis. The FeV@FeVO monatomic alloy catalyst prepared by a solid-phase sintering and high-temperature reduction method is simple in preparation method, can realize large-scale production, can regulate reaction activity, can obtain green preparation of synthesis gas, and is also at the world top level in reaction yield. In addition, the application also provides a characterization method of photoactive sites, and provides a train of thought for photocatalysis mechanism analysis.

Description

Technical Field

[0001] This invention relates to a method for preparing a single-atom alloy and its application, belonging to the field of photocatalysis technology. Background Technology

[0002] The overuse of coal, oil, and natural gas has inevitably led to energy depletion and an environmental crisis. Large amounts of carbon dioxide emissions have also significantly impacted human survival and development, making energy conservation and emission reduction a growing focus of attention.

[0003] Among a range of solutions, inspired by photosynthesis in nature, capturing solar energy to convert carbon dioxide into high-value chemicals is an effective way to promote the development of clean energy. However, currently reported photocatalysts have relatively low catalytic efficiency, which cannot meet the requirements of green photosynthesis. Therefore, developing highly efficient catalysts for photo-driven carbon dioxide conversion is particularly important.

[0004] Single-atom alloy catalysts have become an important research subject in the field of photocatalysis due to their unique coordination environment and abundant catalytic active sites. Designing the composition of single-atom alloys to regulate the products of photocatalytic carbon dioxide reduction is a challenging research topic.

[0005] The preparation of single-atom alloys includes wet impregnation, physical vapor deposition, and laser ablation in liquid technology. Moreover, most current single-atom alloy catalysts contain noble metal elements (such as Au, Ag, Cu, Ru, Pt, etc.), which greatly increases the synthesis cost of the catalyst and is not conducive to its large-scale commercial use.

[0006] Furthermore, no single-atom alloy catalysts have been reported to produce high-yield, tunable syngas (CO+H2) in the field of light-driven carbon dioxide reduction. Summary of the Invention

[0007] The purpose of this invention is to overcome the efficiency problem in existing light-driven CO2 reduction processes, propose a method for preparing non-precious metal single-atom alloys, and combine it with applications to achieve green and efficient synthesis of syngas.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] In a first aspect of the invention, a method for preparing a single-atom alloy is provided, comprising a two-step solid-state sintering and high-temperature reduction, including the following steps:

[0010] (1) Take ferric nitrate nonahydrate crystals and ammonium metavanadate and dissolve them in water respectively to obtain ferric nitrate precursor solution and ammonium metavanadate precursor solution respectively. Then add the ferric nitrate precursor solution dropwise to the ammonium metavanadate precursor solution and heat and stir the mixed solution until the water is completely evaporated.

[0011] (2) After grinding the sample obtained in step (1) evenly, calcine it at 350℃ for 2 hours to obtain the precursor sample;

[0012] (3) After thoroughly grinding the precursor sample obtained in step (2), place it in a muffle furnace and calcine it at 650°C for 2 hours to obtain the FeVO4 sample, abbreviated as FeVO;

[0013] (4) Take out the FeVO4 catalyst obtained in step (3) and mix it with NaBH4 in a weight ratio of 2:1 and grind it. Then put it into a tube furnace (in Ar atmosphere) and calcine it at 400℃, 500℃, 600℃ and 700℃ for 2 hours respectively. Take out the sample.

[0014] (5) After washing, filtering and drying the sample obtained in step (4), four single-atom alloy samples were obtained and named FeV@FeVO-4, FeV@FeVO-5, FeV@FeVO-6 (hereinafter referred to as FeV@FeVO) and FeV@FeVO-7, respectively.

[0015] Furthermore, in step 1), the molar ratio of ferric nitrate to ammonium metavanadate in the mixed solution is 1:1.

[0016] In a second aspect of the invention, the application of a single-atom alloy prepared by the method described in the first aspect as a catalyst in the field of light-driven carbon dioxide reduction is provided.

[0017] In a third aspect of the invention, a method for performing a light-driven carbon dioxide reduction reaction using a single-atom alloy prepared by the method described in the first aspect as a catalyst is provided, the method comprising the following steps:

[0018] (1) Place the single-atom alloy catalyst in a quartz solid reactor, purge it thoroughly with high-purity CO2 gas to remove impurities from the environment, then inject 0.5 ml of deionized water into the container and let it stand in the dark for 8 hours.

[0019] (2) Turn on the light and stop after 3 hours.

[0020] Furthermore, in step 2), the illumination conditions are: a 300W xenon lamp with an intensity equivalent to 10 suns.

[0021] In a fourth aspect of the invention, a method for characterizing photoactive sites is provided.

[0022] Single-atom alloys exhibit high activity in the photo-driven reduction of carbon dioxide to syngas. The inventors hypothesize that this activity is related to the abundance of photoactive sites in the single-atom alloys. However, there is currently no testing method for these photoactive sites, so we provide a characterization method.

[0023] The method mainly includes the following steps:

[0024] 1) Take the sample to be tested and dry it at 100℃ for 3 hours;

[0025] 2) It is loaded into a quartz tube reactor and saturated with CO2 in a gas stream;

[0026] 3) Purge the system with high-purity helium as the carrier gas for about 2 hours. After the system stabilizes, turn on the illumination using a 300W xenon lamp.

[0027] 4) By recording the signal of activated CO2 using a TCD detector, the photoactive sites on the sample surface can be characterized.

[0028] The inventors unexpectedly discovered that the single-atom alloy of this invention, as a catalyst, can achieve the green and efficient preparation of syngas. Furthermore, single-atom alloy catalysts prepared under different conditions achieved different syngas (CO+H2) preparation ratios, thus enabling the regulation of catalytic products. Regarding the reaction mechanism, the inventors elucidated the crucial role of photoactive sites through a photoexcited adsorption-desorption testing method.

[0029] Compared with existing technologies, this invention has the following advantages and beneficial effects: The single-atom alloy catalyst prepared by this invention has a simple process, high reproducibility, and can achieve large-scale production. It exhibits superior activity in light-driven carbon dioxide water addition tests, realizing green synthesis of syngas. The photoexcited adsorption-desorption test method used in this invention is the first to characterize the number of photoactive sites in single-atom alloys. Attached Figure Description

[0030] Figure 1 This is a spherical aberration electron microscope image of FeV@FeVO.

[0031] Figure 2 The image shows the XRD pattern of the sample.

[0032] Figure 3 This is the light absorption spectrum of the sample.

[0033] Figure 4 This is a comparison chart showing the reaction activity of samples with CO2 and water under xenon lamp irradiation.

[0034] Figure 5 The graph shows the CO2 temperature-programmed adsorption-desorption test results for the sample.

[0035] Figure 6 CO2 photoexcitation adsorption-desorption test of the sample. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to specific examples and accompanying drawings. These examples will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. Furthermore, it is noted that for those skilled in the art, the optimal data in this invention are only applicable to this invention, and reasonable adjustments and improvements made without departing from the concept of the invention are all within the scope of protection of this invention.

[0037] Example 1

[0038] Weigh 1 mmol Fe(NO3)2·9H2O and 1 mmol NH4VO3, and dissolve them separately in 100 mL of deionized water. Then, slowly add the iron-containing precursor solution dropwise to the NH4VO3 solution, followed by heating to 80 °C until the solution evaporates to dryness. Transfer the evaporated sample to a muffle furnace and sinter at 350 °C for 2 h to obtain the precursor. Then transfer the precursor to a muffle furnace and sinter at 650 °C for 2 h to obtain the FeVO4 (FeVO) sample.

[0039] Example 2

[0040] Weigh 0.5g of the FeVO4 sample from Example 1, mix it with NaBH4 at a weight ratio of 2:1, grind it evenly, and then place it in a tube furnace for calcination at 400℃, 500℃, 600℃, and 700℃ for 2 hours (with argon as the protective gas). Remove the sample. After washing, filtering, and drying the obtained sample, four single-atom alloy catalysts can be obtained, named FeV@FeVO-4, FeV@FeVO-5, FeV@FeVO-6 (abbreviated as FeV@FeVO), and FeV@FeVO-7, respectively.

[0041] from Figure 1 The aberration-corrected electron microscopy images clearly show the island-like single-atom alloys exposed on the FeV@FeVO surface, confirming the successful preparation of the single-atom alloys.

[0042] Figure 2 As can be seen from the XRD pattern, the alloy phase on the surface gradually emerges as the sintering temperature increases.

[0043] Figure 3 The UV-vis test spectrum of the prepared sample shows that the light absorption capacity of the single-atom alloy catalyst has been greatly improved.

[0044] Example 3

[0045] Performance tests were conducted on five samples: FeVO, FeV@FeVO-4, FeV@FeVO-5, FeV@FeVO, and FeV@FeVO-7. 50 mg of sample was weighed for each test, and the photocatalytic CO2 reduction performance was tested. A reactor (quartz material) containing the sample was filled with pure CO2 gas, and 0.5 ml of water was injected. After adsorption in the dark for 8 hours, illumination (300W xenon lamp, intensity of 10 suns) was turned on, and the reaction products were detected by gas chromatography every 30 minutes. The reaction was terminated after 3 hours, and the changes in the reaction products were analyzed and compared.

[0046] from Figure 4 As can be seen, single-atom alloy catalysts can achieve photo-driven carbon dioxide reduction to produce syngas, and the efficiency of single-atom alloy catalytic conversion is significantly improved compared with ordinary catalysts. Furthermore, the proportion of syngas can also be controlled by adjusting the preparation conditions of single-atom alloys.

[0047] Figure 5 It can also be seen that FeV@FeVO has a higher ability to adsorb and activate CO2, which corresponds to its significantly improved performance.

[0048] Example 4

[0049] The photoexcitation adsorption-desorption method was used to characterize FeVO and FeV@FeVO.

[0050] 50 mg of FeVO and FeV@FeVO samples were dried at 100 °C for 3 h. They were then placed in a quartz tube reactor and subjected to saturated adsorption in a CO2 gas stream. Afterward, high-purity helium was used as the carrier gas to purge for approximately 2 h. Once the system stabilized, illumination (300W xenon lamp) was applied. The signal of the activated CO2 was recorded using a TCD detector, thus characterizing the photoactive sites on the FeVO and FeV@FeVO sample surfaces.

[0051] like Figure 6 As shown, by analyzing the signal changes of CO2 gas, it can be reflected that under photoexcitation, the surface of the single-atom alloy exposes more photoactive sites, which promotes the efficient execution of photo-driven chemical reactions.

[0052] The above are merely embodiments of the present invention and do not limit the scope of the patent. Any equivalent modifications made based on the content of this specification, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A method for preparing a single-atom alloy, characterized in that, It includes two steps: solid-state sintering and high-temperature reduction, including the following steps: (1) Take ferric nitrate crystals nonahydrate and ammonium metavanadate and dissolve them in water respectively to obtain ferric nitrate precursor solution and ammonium metavanadate precursor solution respectively. Then add the ferric nitrate precursor solution dropwise to the ammonium metavanadate precursor solution and heat and stir the mixed solution until the water is completely evaporated. (2) After grinding the sample obtained in step (1) evenly, calcine it at 350℃ for 2 hours to obtain the precursor sample; (3) After thoroughly grinding the precursor sample obtained in step (2), place it in a muffle furnace and calcine it at 650°C for 2 hours to obtain FeVO4 catalyst, abbreviated as FeVO; (4) Take out the FeVO4 catalyst obtained in step (3) and mix it with NaBH4 in a weight ratio of 2:1 and grind it. Then put it into a tube furnace and calcine it at 400℃, 500℃, 600℃ and 700℃ for 2 hours under Ar atmosphere. Take out the sample. (5) The sample obtained in step (4) was washed, filtered and dried to obtain four single-atom alloy catalysts, which were named FeV@FeVO-4, FeV@FeVO-5, FeV@FeVO and FeV@FeVO-7 respectively.

2. The method for preparing a single-atom alloy according to claim 1, characterized in that, In step (1), the molar ratio of ferric nitrate to ammonium metavanadate in the mixed solution is 1:

1.

3. The application of the single-atom alloy prepared by the method according to any one of claims 1-2 as a catalyst in the field of light-driven carbon dioxide reduction.

4. A method for photo-driven carbon dioxide reduction reaction using a single-atom alloy prepared by any one of claims 1-2 as a catalyst, characterized in that, The method includes the following steps: (1) Place the single-atom alloy catalyst in a quartz solid reactor, purge it thoroughly with high-purity CO2 gas to remove impurities from the environment, then inject 0.5 ml of deionized water into the container and let it stand in the dark for 8 hours. (2) Turn on the light and stop after 3 hours.

5. The method according to claim 4, characterized in that, In step (2), the lighting conditions are: 300W xenon lamp, intensity of 10 suns.

6. A method for characterizing photoactive sites, characterized in that, The method mainly includes the following steps: 1) Take the sample to be tested and dry it at 100°C for 3 hours; wherein the sample to be tested is a single-atom alloy prepared by the method described in any one of claims 1-2; 2) It is loaded into a quartz tube reactor and saturated with CO2 in a gas stream; 3) Purge the system with high-purity helium as the carrier gas for 2 hours. After the system stabilizes, turn on the illumination using a 300W xenon lamp. 4) By recording the signal of activated CO2 using a TCD detector, the photoactive sites on the sample surface can be characterized.

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