Single-atom photocatalyst for hydrogen evolution reaction to produce ethylene, preparation method and application thereof

Abstract

The present invention discloses a single-atom photocatalyst for hydrogen evolution reaction to produce ethylene, a preparation method and an application thereof, wherein Au is loaded on a sheet-like carbon nitride polymer PCN to obtain Au. h / PCN, and a single-atom catalyst, Au1 / PCN, was prepared by water-bath etching. This catalyst carrier is a flake-like carbon nitride polymer, which is inexpensive, readily available, and has a low production cost. It has a high specific surface area and a wider band gap, providing more active sites and promoting carrier separation and migration. This single-atom catalyst, with gold anchored to the carbon nitride polymer as independent atoms, greatly improves atom utilization and reaction activity. When used in the hydrogen evolution reaction, it can promote the production of ethylene, and compared to similar catalysts, it produces higher amounts of ethylene.

Description

Technical Field

[0001] The present invention relates to a single-atom photocatalyst used in the field of photocatalysis and a preparation method thereof, belonging to the technical field of photocatalysts. Background Art

[0002] Among many new energy sources, solar energy has attracted widespread attention due to its huge volume and wide distribution. Photocatalytic reaction is a specific means to achieve the conversion of solar energy into chemical energy. In essence, it is a redox reaction that uses solar energy on a photocatalyst. Photocatalytic reaction is driven by and occurs on a photocatalyst. Photocatalyst is the hub for achieving energy conversion. In the artificial field, to achieve the process of converting solar energy into chemical energy, stable low-energy substances (H2O, CO2, N2, etc.) can be converted into energy substances or chemical raw materials such as H2, CO, NH3, alcohols, hydrocarbons (including liquid fuels such as gasoline and diesel), aldehydes, etc. through photocatalytic reaction driven by photocatalysts. These substances can be directly used in existing industrial equipment and power devices, have huge application potential in the future, and have become a research hotspot in the energy field.

[0003] At present, the overall efficiency of photocatalysis is still very low. The production of ethylene in the hydrogen evolution reaction involves CC coupling and dehydrogenation of organic groups, which is very complex and difficult. Summary of the Invention

[0004] The present invention aims to provide a single-atom photocatalyst for use in hydrogen evolution reaction to produce ethylene and a preparation method thereof. The catalyst can produce both hydrogen and ethylene in the hydrogen evolution reaction, and gold is anchored on a carrier in the form of independent atoms rather than clusters, thereby greatly improving the atomic utilization rate.

[0005] The technical solution adopted by the present invention is: a single-atom photocatalyst and a preparation method thereof, wherein gold is loaded on a sheet-like polymer carbon nitride (PCN) to obtain Au. h / PCN, and the single atom catalyst Au1 / PCN was prepared by water bath etching.

[0006] Preferably, a thermodynamic etching method is used to synthesize sheet-like polymer carbon nitride (PCN).

[0007] Preferably, Au is loaded on the sheet-like polymer carbon nitride (PCN) by photodeposition method. h / PCN.

[0008] Preferably, the single-atom catalyst Au1 / PCN is prepared by water bath etching, and the specific steps are: h / PCN and CuCl2 are placed in dimethylformamide, uniformly dispersed by ultrasonication, maintained at a temperature of 60-80°C and a rotation speed of 400-600r for 6-10 hours, washed and dried.

[0009] The present invention also provides use of the single-atom photocatalyst in preparing ethylene through hydrogen evolution reaction.

[0010] The carbon nitride polymer-supported gold single-atom catalyst prepared by the present invention has the following advantages:

[0011] 1. The catalyst carrier is made of flaky carbon nitride polymer, which is cheap, easy to obtain and has low production cost. It has a high specific surface area and a wider band gap, which is conducive to providing more active sites and promoting the separation and migration of carriers.

[0012] 2. The preparation method of the catalyst is simple to operate, does not require complex equipment, has mild conditions, and the preparation process is simple and controllable.

[0013] 3. The catalyst is used in hydrogen evolution reaction. When the sacrificial agent is methanol, the products are generally hydrogen and methane, and it is difficult to generate ethylene. However, this catalyst can promote the generation of ethylene and the amount of ethylene generated is larger than that of similar catalysts.

[0014] 4. After the catalyst participates in the hydrogen evolution reaction, under suitable reaction conditions, a higher yield can be obtained and the catalyst can be recycled and reused after participating in the reaction.

[0015] 5. The catalyst is a single-atom catalyst. Gold is anchored to the carbon nitride polymer in the form of independent atoms, which greatly improves the atomic utilization rate and reaction activity. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The sample color images are respectively: sheet-like carbon nitride polymer (a), etched gold pre-catalyst (b), and etched single atom catalyst (c).

[0017] Figure 2 XRD pattern of gold single-atom catalyst supported on a flake-like carbon nitride polymer support.

[0018] Figure 3 These are TEM images of sheet-like carbon nitride polymer (a), etched gold pre-catalyst (b), and etched single-atom catalyst (c).

[0019] Figure 4 XPS of a single-atom gold catalyst supported on a sheet-like carbon nitride polymer. DETAILED DESCRIPTION

[0020] This invention uses a flaky carbon nitride polymer as a catalyst support due to its high specific surface area and larger band gap. It is then combined with the precious metal gold (Au) to prepare a gold single-atom catalyst. The initial goal was to increase the gold loading and improve the atomic utilization rate. However, when applied to the hydrogen evolution reaction, it was unexpectedly discovered that it can promote ethylene production, providing an effective solution to the problems of the prior art.

[0021] Example 1

[0022] The preparation method of the sheet-like carbon nitride polymer-supported gold single atom catalyst is as follows:

[0023] (1) Preparation of sheet-like polymer carbon nitride (PCN): PCN was synthesized by using an improved thermodynamic etching method. First, dicyandiamide was heated in a muffle furnace at 550 °C in air for 4 h (heating rate 2.3 °C min -1 ), and the cooling rate was controlled at 1℃min -1 Then, the yellow block C3N4 was moved to a mortar for fine grinding to form a fine powder, and spread it flat in an open container, and then placed in a muffle furnace again to react at 480℃ for 4h (heating rate 2℃min -1 ), and then rapidly cooled, eventually forming a pale yellow flake carbon nitride polymer (PCN), the photo and morphology of which are shown in Figure 1 a and Figure 3 a.

[0024] (2) A large amount of Au is loaded on PCN to form Au h / PCN: 1g chloroauric acid is dissolved in 20ml water and fully dissolved under ultrasonication to prepare a 50mg / ml chloroauric acid solution. 25ml H2O, 25ml methanol (CH3OH), 100mg PCN and 2.7ml chloroauric acid solution are placed in a transparent glass reaction container and then fully dissolved under ultrasonication. The glass reactor is placed in visible light and irradiated at room temperature for about 14h. The sample is centrifuged and washed three times with deionized water. Then it is dried at 70℃ overnight to finally form Au. h / PCN powder, its photos and morphology are as follows Figure 1 b and Figure 3 b.

[0025] (3)Au h / PCN selectively etched to form Au1 / PCN: 0.4g CuCl2 and 40ml dimethylformamide (DMF) were placed in a 100ml beaker, and the Au synthesized in step (2) was added under ultrasonic conditions. h / PCN powder. After fully dissolved, transfer the beaker to a water bath and maintain it at a temperature of 60°C and a rotation speed of 450r for 8 hours. Recover the etching waste liquid and collect the samples, wash them twice with DMF solution, wash the precipitate three times with deionized water, place it in an oven and dry it at 70°C overnight to form a single-atom catalyst powder. The results of inductively coupled plasma emission spectroscopy (ICP) tests show that the loading of Au on the sheet-like carbon nitride polymer is 0.34wt%, marked as catalyst 1, and its photo and morphology are shown in Figure 1. Figure 1 c and Figure 3 c, XRD and XPS analyses were as follows Figure 2 and Figure 4 The catalytic performance is shown in Tables 1 and 2.

[0026] Example 2

[0027] Example 2 The remaining steps were the same as in Example 1, except that gold was not loaded in step (2). Specifically, in step (2), 25 ml of H₂O, 25 ml of methanol (CH₃OH), and 100 mg of PCN were placed in a transparent glass reaction vessel and then fully dissolved under ultrasound. The glass reactor was exposed to visible light at room temperature for approximately 14 hours. The sample was centrifuged and washed three times with deionized water. It was then dried at 70°C overnight to form a catalyst powder, designated Catalyst 2. The catalytic properties are shown in Table 2.

[0028] Example 3

[0029] The other steps of Example 3 are the same as those of Example 1, except that water bath etching is not performed, i.e., step (3) is omitted. The resulting catalyst powder is labeled as Catalyst 3, and the catalytic performance is shown in Table 2.

[0030] Example 4

[0031] The other steps of Example 4 are the same as those of Example 1, except that the flaky carbon nitride polymer (PCN) is replaced by titanium dioxide (TiO2). The resulting catalyst powder is labeled as Catalyst 4, and the catalytic performance is shown in Table 2.

[0032] Example 5

[0033] The other steps of Example 5 are the same as those of Example 1, except that the loaded metal is changed from gold (Au) to palladium (Pd). The specific operation steps are as follows:

[0034] (1) The preparation of sheet-like polymer carbon nitride (PCN) is the same as in Example 1.

[0035] (2) A large amount of Pd is loaded on PCN to form Pd h / PCN: 10ml H2O, 200mg PdCl2 and 1g NaCl were placed in a 50ml beaker and ultrasonicated for 10 minutes to completely mix. Transfer to a stirring table and stir at room temperature for 2 hours. Add 100mg carbon nitride polymer (PCN) and keep it at 80°C for 15 hours. Then the mixed solution was dried by rotary evaporator to obtain a sample, which was then dispersed in 20ml H2O and poured into a sealed transparent container. It was kept in a vacuum state and under visible light irradiation for 18 hours. The sample was obtained by centrifugation, washed three times with deionized water, and kept at 80°C in a vacuum for 12 hours to form Pd h / PCN powder.

[0036] (3)Pd h / PCN selectively etched to form Pd1 / PCN: 1.5g KBr, 500mg FeCl3 and 25ml H2O were placed in a 50ml beaker, and 25mg Pd was added under ultrasonic conditions. h / PCN. 10 ml of 1 M hydrochloric acid was then added. The mixture was heated to 97°C and maintained at this temperature for 8 hours. A sample was obtained by centrifugation, and the precipitate was washed three times with deionized water while the waste liquid was recovered. The mixture was then maintained at 80°C under vacuum for 12 hours, resulting in a Pd1 / PCN powder, labeled Catalyst 5.

[0037] (4) The hydrogen evolution reaction was the same as in Example 1, and the catalytic performance was shown in Table 2.

[0038] Example 6

[0039] The sheet-like polymer carbon nitride (PCN) carrier in Example 1 was used as catalyst 6 to directly participate in the reaction. The catalytic performance is shown in Table 2.

[0040] Example 7

[0041] The flaky polymer carbon nitride (PCN) carrier in Example 5 was replaced with titanium dioxide (TiO2), and the rest was the same as Example 5, marked as catalyst 7. The catalytic performance is shown in Table 2.

[0042] Catalytic performance:

[0043] The homemade photocatalytic reactor consists of a sealed glass reactor. The reactor is connected to a gas circulation system with a ten-way valve (VICI) for online sampling to a gas chromatograph (Shanghai Ruimin GC 2060). The system is first evacuated to remove air and then placed in a state close to vacuum. The incident light source is provided by a 300W xenon lamp and a visible light filter (Beijing PerfectLight Co.), which can provide visible light with a wavelength greater than 400nm (λ>400nm). Specifically, 25ml of H2O, 25ml of methanol, and 30mg of catalyst (Examples 1-7) are placed in the homemade photocatalytic reactor. They are thoroughly mixed under ultrasonication. After 2 minutes, the reactor is connected to a gas circulation system with a ten-way valve (VICI) for online sampling to a gas chromatograph (Shanghai Ruimin GC 2060). The system is first evacuated to remove air and then placed in a state close to vacuum. The incident light source is provided by a 300W xenon lamp. After 8 hours of reaction at room temperature, the product is detected by an analytical system. The final products include hydrogen (H2), methane (CH4), carbon monoxide (CO), ethylene (C2H4), etc. The catalytic performance is shown in Tables 1 and 2.

[0044] Table 1 Catalytic performance of the catalyst in Example 1

[0045]

[0046] It can be seen from Table 1 that the gold-loaded single-atom catalyst of sheet-like polymer carbon nitride (PCN) of Example 1 of the present invention can be applied to hydrogen evolution reaction under appropriate conditions, and when the sacrificial agent is methanol, it can promote the production of ethylene.

[0047] Table 2 Comparison of catalytic performance of catalysts in Examples 1 to 7

[0048]

[0049] As can be seen from Table 2, the gold-loaded single-atom catalyst of the present invention, when applied to the hydrogen evolution reaction under suitable conditions and when the sacrificial agent is methanol, can effectively promote the production of ethylene compared with other catalysts.

[0050] In order to be environmentally friendly and save resources, the present invention can recycle the catalyst after the reaction is completed.

Claims

1. Use of a single-atom photocatalyst in the preparation of ethylene by hydrogen evolution reaction, characterized in that: Au is obtained by loading gold on sheet-like carbon nitride polymer PCN. h / PCN, a single-atom catalyst Au1 / PCN was prepared by a water bath etching method, and the single-atom catalyst Au1 / PCN, methanol and water were placed in a photocatalytic reactor to carry out hydrogen evolution reaction to prepare ethylene.

2. The use according to claim 1, characterized in that Sheet-like carbon nitride polymer PCN was synthesized by thermodynamic etching method.

3. The use according to claim 1, characterized in that Au was loaded on the sheet-like carbon nitride polymer PCN by photodeposition. h / PCN.

4. The use according to claim 1, wherein The single-atom catalyst Au1 / PCN was prepared by water bath etching. The specific steps are: h / PCN and CuCl2 are placed in dimethylformamide and uniformly dispersed by ultrasonication. The mixture is kept at a temperature of 60-80°C and a rotation speed of 400-600r for 6-10 hours, and then washed and dried.

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