A method for preparing ethylene and a method for preparing a zinc oxide nanosheet supported catalyst

Abstract

The application provides a preparation method of ethylene and a preparation method of a zinc oxide nanosheet supported catalyst. The zinc oxide nanosheet supported catalyst is subjected to a light irradiation reaction in an ethane atmosphere to obtain ethylene. The catalyst comprises a carrier, zinc oxide nanosheets, and a metal (Pd, Ag or Au) supported on the carrier. By using zinc oxide nanosheets as the carrier and supporting metal particles (Pd, Au or Ag), the response of the solar spectrum can be extended from ultraviolet light to visible light and near-infrared light regions by means of the SPR effect, the spatial separation of electron-hole pairs is promoted, the zinc oxide nanosheet supported catalyst can be used as a photocatalyst to catalyze ethane to obtain ethylene, and high selectivity and high yield of C2H4 can be obtained, and high yield of hydrogen can be obtained. In addition, the zinc oxide nanosheet supported catalyst can be prepared by a simple hydrothermal impregnation method, and large-scale production can be easily realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photocatalysis, and in particular to a preparation method of ethylene and a preparation method of zinc oxide nanosheet supported catalyst. BACKGROUND

[0002] Ethane chemical utilization is of great significance to the modern chemical industry, especially with the massive exploration of shale gas (the proven shale gas content in the world is about 214.5 trillion cubic meters, of which ethane accounts for about 10-20%). It is expected to break away from the dependence on fossil energy and develop new energy. Among various products of ethane conversion, ethylene is the most basic chemical, which can be used to synthesize polyethylene, ethylene glycol, styrene, etc. According to estimates, the global demand for ethylene in 2023 reached 182.5 million tons. Currently, ethane-to-ethylene is mainly concentrated in thermal catalytic cracking processes, but this process requires extremely high temperature input (600℃), which is easy to cause coking and uncontrollable peroxidation process. Photocatalysis is considered to be an attractive method to realize the conversion of C2H6 under mild conditions (ambient temperature and pressure), which only needs solar energy as energy input. However, the current photocatalytic ethane-to-ethylene has problems such as low yield and low selectivity. Therefore, finding an efficient and stable photocatalyst to realize the high-selectivity conversion of ethane to ethylene has attracted widespread attention from researchers. SUMMARY

[0003] Therefore, the purpose of the present application is to provide a preparation method of ethylene and a preparation method of zinc oxide nanosheet supported catalyst. The preparation method can obtain ethylene with high selectivity and high yield.

[0004] To achieve this purpose, the present application adopts the following technical solutions:

[0005] In a first aspect, the present application provides a preparation method of ethylene, comprising the following steps:

[0006] subjecting the zinc oxide nanosheet supported catalyst to a photo-illumination reaction in an ethane atmosphere to obtain ethylene;

[0007] The zinc oxide nanosheet supported catalyst comprises a carrier: zinc oxide nanosheet, and a metal supported on the carrier.

[0008] The metal is selected from any one or more of Pd, Ag or Au.

[0009] Preferably, the mass ratio of the carrier to the metal supported on the carrier is (93-97):(3-7).

[0010] Preferably, the thickness of the zinc oxide nanosheet is 4-5 nm.

[0011] Preferably, the average particle size of the metal is 10-20 nm.

[0012] Preferably, the light source of the light irradiation reaction is selected from any one of a xenon lamp, a high-pressure mercury lamp, an LED lamp or an iodine tungsten lamp.

[0013] Preferably, the power of the light source in the light irradiation reaction is 80-120 mW cm -2 .

[0014] Preferably, the time of the light irradiation reaction is 2-6 h.

[0015] Preferably, the purity of the ethane is ≥99.9%.

[0016] In a second aspect, the present application provides a preparation method of the above-mentioned zinc oxide nanosheet supported catalyst, comprising the following steps:

[0017] mixing the surfactant, the metal salt solution and the soluble zinc salt and performing a reaction at 90-150 ℃ to obtain the zinc oxide nanosheet supported catalyst;

[0018] The metal salt solution is selected from any one or more of a Na2PdCl4 solution, an AgNO3 solution or a NaAuCl4 solution.

[0019] Preferably, the surfactant is selected from any one or more of hexamethylenetetramine, trisodium citrate, urea, polyvinylpyrrolidone or cetyltrimethylammonium bromide.

[0020] Preferably, the soluble zinc salt is selected from any one or more of zinc acetate, zinc chloride, zinc nitrate or zinc sulfate.

[0021] Preferably, the molar ratio of the surfactant, the metal salt solution and the soluble zinc salt is (0.3-2):(0.01-0.07):1.

[0022] Preferably, the temperature of the reaction is 100-130 ℃ and the time is 5-12 h.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] (1) The application provides a preparation method of ethylene, which carries out a light reaction of a zinc oxide nanosheet supported catalyst in an ethane atmosphere to obtain ethylene. The zinc oxide nanosheet supported catalyst comprises a carrier, zinc oxide nanosheets, and a metal supported on the carrier, and the metal is selected from any one or more of Pd, Ag or Au. Single zinc oxide nanosheets have good photosensitivity, but their visible light capture ability is weak, the photo-generated carrier separation efficiency is poor, and the dehydrogenation performance is weak, resulting in low C-H bond cleavage efficiency in alkanes. By loading metal particles (Pd, Au, Ag) on the zinc oxide nanosheets as the carrier, the SPR effect can be used to expand the response of the solar spectrum from ultraviolet light to visible light and near-infrared light, and the metal particles can also serve as the migration center of photo-generated electrons, promote the spatial separation of electron-hole pairs, and be used as a photocatalyst to catalyze ethane to obtain high selectivity and high yield of C2H4, and high yield of hydrogen. Through research, the zinc oxide nanosheet supported palladium nanoparticles obtained a yield of 16.32 mmol g -1 of ethylene in the reaction of photocatalytic dehydrogenation of ethane to prepare ethylene and hydrogen, and the selectivity was as high as 94.83%; the yield of hydrogen also reached 14.49 mmol g -1 .

[0025] (2) The above-mentioned zinc oxide nanosheet supported catalyst provided by the application can be prepared by a simple hydrothermal impregnation method, which is convenient for large-scale production. At the same time, a variety of metal particles can be loaded, and the catalyst has excellent universality. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 a is a transmission electron microscope image of 5.87% Pd-ZnO nanosheets prepared in Example 1;

[0027] Figure 1 b is a scanning electron microscope image of 5.87% Pd-ZnO nanosheets prepared in Example 1;

[0028] Figure 2 is an element distribution map of 5.87% Pd-ZnO nanosheets prepared in Example 1;

[0029] Figure 3 is an XRD diffraction pattern of 5.87% Pd-ZnO nanosheets prepared in Example 1 and an XRD diffraction pattern of ZnO nanosheets prepared in Comparative Example 1;

[0030] Figure 4 is a Raman shift diagram of 5.87% Pd-ZnO nanosheets prepared in Example 1 and a Raman shift diagram of ZnO nanosheets prepared in Comparative Example 1;

[0031] Figure 5 XPS pattern of 5.87% Pd-ZnO nanoplatelets prepared in Example 1;

[0032] Figure 6 a Scanning electron micrograph of Ag-ZnO nanoplatelets prepared in Example 2;

[0033] Figure 6 b Transmission electron micrograph of Ag-ZnO nanoplatelets prepared in Example 2;

[0034] Figure 7 Elemental mapping of Ag-ZnO nanoplatelets prepared in Example 2;

[0035] Figure 8 XRD pattern of Ag-ZnO nanoplatelets prepared in Example 2;

[0036] Figure 9 a Scanning electron micrograph of Au-ZnO nanoplatelets prepared in Example 3;

[0037] Figure 9 b Transmission electron micrograph of Au-ZnO nanoplatelets prepared in Example 3;

[0038] Figure 10 Elemental mapping of Au-ZnO nanoplatelets prepared in Example 3;

[0039] Figure 11 XRD pattern of Au-ZnO nanoplatelets prepared in Example 3;

[0040] Figure 12 a Transmission electron micrograph of ZnO nanoplatelets prepared in Comparative Example 1;

[0041] Figure 12 b Scanning electron micrograph of ZnO nanoplatelets prepared in Comparative Example 1;

[0042] Figure 13 Elemental mapping of ZnO nanoplatelets prepared in Comparative Example 1;

[0043] Figure 14 Scanning electron micrograph of Pd-ZnO nanoplatelets prepared in Comparative Example 2;

[0044] Figure 15 XRD pattern of Pd-ZnO nanoplatelets prepared in Comparative Example 2;

[0045] Figure 16 a Transmission electron micrograph of Pd-ZnO nanoplatelets prepared in Comparative Example 3;

[0046] Figure 16b is a scanning electron microscope image of the Pd-ZnO nanosheet prepared in Comparative Example 3;

[0047] Figure 17 a is a static photocurrent test comparison chart of the 5.87% Pd-ZnO nanosheet prepared in Example 1 and the ZnO nanosheet prepared in Comparative Example 1;

[0048] Figure 17 b is an electrochemical impedance spectrum comparison chart of the 5.87% Pd-ZnO nanosheet prepared in Example 1 and the ZnO nanosheet prepared in Comparative Example 1;

[0049] Figure 17 c is a UV-Vis diffuse reflectance spectrum comparison chart of the 5.87% Pd-ZnO nanosheet prepared in Example 1 and the ZnO nanosheet prepared in Comparative Example 1;

[0050] Figure 17 d is a photoluminescence comparison chart of the 5.87% Pd-ZnO nanosheet prepared in Example 1 and the ZnO nanosheet prepared in Comparative Example 1;

[0051] Figure 18 is a product distribution chart of the 5.87% Pd-ZnO nanosheet, the 0.09% Pd-ZnO nanosheet, the 1.43% Pd-ZnO nanosheet, the 9.81% Pd-ZnO nanosheet prepared in Example 1, Example 4-6 and the metal nanoparticle-unloaded ZnO nanosheet prepared in Comparative Example 1 for photocatalyzing high-purity ethane (99.9%) to produce ethylene;

[0052] Figure 19 is a long-time stability chart of the 5.87% Pd-ZnO nanosheet prepared in Example 1 for photocatalyzing ethane (99.9%) to produce ethylene. DETAILED DESCRIPTION

[0053] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0054] In view of the problems of low yield and low selectivity in the prior art of photocatalyzing ethane to produce ethylene, the present application provides a preparation method of ethylene, which comprises the following steps:

[0055] The zinc oxide nanosheet-loaded catalyst is subjected to a photo-illumination reaction in an ethane atmosphere to obtain ethylene.

[0056] In the present application, the zinc oxide nanosheet supported catalyst comprises a carrier: zinc oxide nanosheet, and a metal supported on the carrier, the metal being selected from any one or more of Pd, Ag or Au.

[0057] In the present application, the thickness of the zinc oxide nanosheet is 4-5 nm, such as 4 nm, 4.1 nm, 4.2 nm, 4.3 nm, 4.4 nm, 4.5 nm, 4.6 nm, 4.7 nm, 4.8 nm, 4.9 nm or 5 nm, etc. The zinc oxide nanosheet has excellent photosensitivity, and at the same time, its nanosheet structure can make the carrier have a larger specific surface area, so that there are more surface active sites that can adsorb more reactant molecules. Controlling the thickness of the zinc oxide nanosheet to 4-5 nm can effectively shorten the transport of photo-generated electrons and improve the efficiency of photocatalysis. In the present application, if the particle size of the loaded metal particles is too large, it will cover the surface of the zinc oxide nanosheet, reducing the adsorption sites in subsequent actual photocatalysis, and causing the electron-hole recombination to intensify, resulting in reduced catalytic performance. Conversely, if the particle size is too small, it means that the amount of loaded metal is too low, which also leads to poor catalytic performance. Therefore, the average particle size of the metal particles is preferably 10-20 nm, such as 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm or 20 nm, etc.

[0058] The single zinc oxide nanosheet has good photosensitivity, but its visible light capture ability is weak, the photo-generated carrier separation efficiency is poor, and the dehydrogenation performance is weak, resulting in low C-H bond cleavage efficiency in alkanes. In the present application, by loading metal particles (Pd, Au, Ag) on the zinc oxide nanosheet as a carrier, the response of the solar spectrum can be extended from ultraviolet light to visible light and near-infrared light regions with the aid of SPR effect, and the metal particles can also serve as a migration center for photo-generated electrons to promote the spatial separation of electron-hole pairs.

[0059] In the present application, the zinc oxide nanosheet supported catalyst can be used as a photocatalyst to catalyze the preparation of ethylene from ethane, and by controlling the loading amount of metal particles, the peroxidation reaction of C2H6 can be effectively inhibited, thereby improving the selectivity of C2H4. The present application has found that when the mass content of the carrier is too high, i.e. the mass content of the metal supported on the carrier is too low, it will result in low yield of ethylene, and conversely, when the mass content of the metal supported on the carrier is too high, it will result in decreased selectivity of ethylene. Therefore, in the present application, the mass ratio of the carrier to the metal supported on the carrier is preferably (93-97):(3-7), which can be 93:7, 93.5:6.5, 94:6, 94.5:5.5, 95:5, 95.5:4.5, 96:4, 96.5:3.5 or 97:3, etc.

[0060] In some embodiments of the present application, the preparation of ethylene preferably comprises the following steps:

[0061] An appropriate amount of the above-prepared metal nanoparticle-loaded zinc oxide nanosheet catalyst is weighed, added with an appropriate amount of water to be ultrasonically dissolved, and then uniformly coated on a quartz surface dish to ensure uniform distribution of the zinc oxide nanosheet catalyst. Then, after drying, the quartz surface dish is placed in an ethane atmosphere for photoreaction. In the present application, the quartz surface dish is preferably dried and then placed in a Pfeiffer photochemical reactor, sealed, and filled with high-purity ethane gas for photoreaction. In the present application, the purity of the high-purity ethane gas is ≥ 99.9%, the light source for the photoreaction is selected from any one of a xenon lamp, a high-pressure mercury lamp, an LED lamp, or an iodine-tungsten lamp, the power of the light source is 80-120 mW cm -2 , preferably 100 mW cm -2 , and the photoreaction time is 2-6 h, preferably 4-5 h.

[0062] The above zinc oxide nanosheet-loaded catalyst can be prepared by a simple hydrothermal impregnation method. In some embodiments of the present application, the preparation method of the zinc oxide nanosheet-loaded catalyst preferably comprises the following steps:

[0063] The surfactant, metal salt solution, and soluble zinc salt are mixed and reacted at 90-150°C to obtain the zinc oxide nanosheet-loaded catalyst.

[0064] According to the present application, the surfactant, metal salt solution, and soluble zinc salt are first mixed. In some embodiments of the present application, the surfactant is preferably mixed with a solvent, and the surfactant is preferably any one or more of hexamethylenetetramine, trisodium citrate, urea, polyvinylpyrrolidone, or cetyltrimethylammonium bromide, more preferably hexamethylenetetramine and trisodium citrate, and further preferably the molar ratio of hexamethylenetetramine to trisodium citrate is (0.3-2):(0.1-1.5). The (0.3-2) can be 0.3, 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, or 2.0, etc.; the (0.1-1.5) can be 0.1, 0.2, 0.5, 0.8, 1.0, 1.2, or 1.5, etc. The mixing is preferably carried out under stirring. It should be noted that zinc oxide cannot form nanosheet structures in a neutral environment, and the present application preferably uses hexamethylenetetramine and trisodium citrate as surfactants, wherein hexamethylenetetramine provides a weak alkaline environment and releases OH - , which is conducive to the subsequent control of the formation of zinc oxide nanosheets with sodium citrate; at the same time, the sodium citrate structure contains a reducing hydroxyl group, which can reduce the metal (Au, Ag, Pd) salt solution to metal nanoparticles.

[0065] In some embodiments of the present application, after the surfactant is completely dissolved, a soluble zinc salt is introduced into the system, which can be selected from any one or more of zinc acetate, zinc chloride, zinc nitrate or zinc sulfate, and after stirring until the soluble zinc salt is completely dissolved, a metal salt solution is added to the system, which is selected from any one or more of Na2PdCl4 solution, AgNO3 solution or NaAuCl4 solution. In the present application, after the metal salt solution is added, it is preferably stirred for 5-10 min to ensure that the metal salt solution is fully mixed with the surfactant and the soluble zinc salt, and then the reaction is carried out at 90-150°C for 5-12 h, more preferably at 100-130°C for 6-10 h. In some embodiments of the present application, the reaction system after the addition of the metal salt solution is preferably transferred to a polytetrafluoroethylene liner, sealed with a stainless steel reaction kettle, and then reacted in a constant temperature oven.

[0066] In the present application, the above-mentioned point values are only for listing and are not limited thereto, and other point values within the numerical range can also be applicable. To avoid complexity, they will not be repeated here.

[0067] After the above reaction is completed, the present application preferably cools to room temperature, centrifuges the reaction solution, and collects the solid. In some embodiments of the present application, the collected solid is preferably washed with deionized water, and the number of washes is generally more than 3 times. After washing is completed, the solid is dried. Since the loaded metal particles may be at risk of oxidation during drying, the present application preferably uses vacuum freeze-drying for drying, which can avoid oxidation of the loaded metal particles in a low-temperature, vacuum environment. The drying time is generally more than 8 h. After drying is completed, the zinc oxide nanosheet loaded with metal particles, i.e., the zinc oxide nanosheet supported catalyst, is obtained. To prevent the loaded metal particles from being oxidized, the present application preferably stores the obtained zinc oxide nanosheet supported catalyst in a vacuum dryer for subsequent characterization and application.

[0068] The preparation method of the above-mentioned zinc oxide nanosheet supported catalyst provided by the present application is simple and easy to implement. By adjusting the addition of raw materials, zinc oxide nanosheet catalysts loaded with different metal particles can be prepared, which has universality and is conducive to large-scale production.

[0069] Compared with the single ZnO nanosheet catalyst, the Pd-ZnO nanosheet catalyst provided by the application enhances the absorption of visible light, promotes the migration of photo-generated electron-hole pairs, effectively inhibits the recombination efficiency of photo-generated carriers, and effectively improves the efficiency of photocatalytic C2H6 dehydrogenation to prepare C2H4. Under the same conditions, the Ag-ZnO nanosheet and the Au-ZnO nanosheet have similar technical effects.

[0070] According to the photocatalytic application example: research on photocatalytic C2H6 dehydrogenation to prepare C2H4, the zinc oxide nanosheet loaded with 5.87wt% palladium nanoparticles (i.e., 5.87% Pd-ZnO) is used as a catalyst for photocatalytic dehydrogenation of ethane to prepare ethylene and hydrogen with high efficiency, and after 4 hours of reaction, 16.32mmolg -1 of ethylene yield can be obtained, and the selectivity is as high as 94.83%; the hydrogen yield can reach 14.49mmolg -1 . In addition, the prepared Ag-ZnO nanosheet catalyst and Au-ZnO nanosheet catalyst are tested for photocatalytic application under the same conditions, and it is found that they have similar experimental results with the Pd-ZnO, and can obtain ethylene with high selectivity and high yield, and also can obtain hydrogen with high yield.

[0071] In order to further illustrate the application, the following examples are used for detailed description. The experimental raw materials used in the following examples of the application are all general commercially available products.

[0072] Example 1

[0073] This embodiment provides a Pd-ZnO nanosheet catalyst, which takes ZnO nanosheet as a carrier and is loaded with metal Pd, and the preparation method is as follows:

[0074] Take 140 mg of hexamethylenetetramine (National Pharmaceutical Group Chemical Reagent Co., Ltd., purity ≥ 99%) and 29.4 mg of trisodium citrate dihydrate (National Pharmaceutical Group Chemical Reagent Co., Ltd., purity ≥ 99%) into 30 mL of deionized water, place it on a magnetic stirrer at 300 r / min for 5 min, then add 297 mg of zinc nitrate hexahydrate (aladdin, purity ≥ 99%). After complete dissolution, add 100 μL of 0.5 mol / L Na2PdCl4 solution, place it on a magnetic stirrer at 300 r / min for 5 min, then transfer the mixed solution to a 50 mL polytetrafluoroethylene liner, seal it with a stainless steel reaction kettle, and place it in a constant temperature oven (Shanghai Jinghong Experimental Equipment Co., Ltd., DHG-9036Y) with a temperature of 100 ℃. The reaction time is 6 h. After the reaction is completed, cool it to room temperature naturally, wash it with deionized water several times, and centrifuge to collect the solid. Finally, dry it in a vacuum freeze dryer (Shanghai Lichengbangxi Instrument Technology Co., Ltd., LC-10N-50A) for at least 8 h or more, obtain a black solid powder, and place the powder sample in a vacuum dryer for subsequent characterization and application.

[0075] The obtained black solid powder was characterized by transmission electron microscopy (JEOL JEM-ARM200F), scanning electron microscopy (GeminiSEM450), X-ray photoelectron spectroscopy (ESCALAB 250), XRD instrument (Philips X’Pert Pro Super diffractometer), and laser Raman spectrometer (LabRAM HR Evolution), respectively. The specific content of Pd was determined by inductively coupled plasma emission spectrometry (5.87%). Figure 1 The transmission electron microscopy (TEM) image is shown in Figure 1 The scanning electron microscopy (SEM) image is shown in Figure 2 The element distribution map is shown in Figure 3 The XRD diffraction pattern is shown in Figure 4 The Raman spectrum is shown in Figure 5 The photoelectron spectroscopy (XPS) is shown in Figures 1-2 It can be seen from Figures 3-5 that the thickness of the Pd-ZnO nanosheet is about 4-5 nm, and the Pd nanoparticles are uniformly distributed on the ZnO nanosheet.

[0076] Example 2

[0077] This example provides an Ag-ZnO nanosheet catalyst, which takes ZnO nanosheet as the carrier and loads metal Ag. Its preparation method is as follows:

[0078] Take 140 mg of hexamethylenetetramine (National Pharmaceutical Group Chemical Reagent Co., Ltd., purity ≥ 99%) and 60 mg of trisodium citrate dihydrate (National Pharmaceutical Group Chemical Reagent Co., Ltd., purity ≥ 99%) into 30 mL of deionized water, and place it on a magnetic stirrer at 400 r / min for 8 minutes. Then add 297 mg of zinc nitrate hexahydrate (aladdin, purity ≥ 99%). After complete dissolution, add 70 μL of 0.6 mol / L AgNO3 solution, and place it on a magnetic stirrer at 350 r / min for 6 minutes. Then transfer the mixed solution to a 50 mL polytetrafluoroethylene liner, seal it with a stainless steel reaction kettle, and place it in a constant temperature oven (Shanghai Jinghong Experimental Equipment Co., Ltd., DHG-9036Y) with a temperature of 110°C and a reaction time of 8h. After the reaction is completed, cool it to room temperature naturally, wash it with deionized water several times, and centrifuge to collect the solid. Finally, dry it in a vacuum freeze dryer (Shanghai Lichengbangxi Instrument Technology Co., Ltd., LC-10N-50A) for at least 8h, obtain a solid powder, and place the powder sample in a vacuum dryer for storage for subsequent characterization and application.

[0079] The solid powder was characterized by transmission electron microscopy (JEOL JEM-ARM200F), scanning electron microscopy (Gemini SEM450), and XRD (Philips X’Pert Pro Super diffractometer), respectively. The scanning electron microscopy image is shown in Figure 6 , the transmission electron microscopy image (TEM) is shown in Figure 6 , the element distribution map is shown in Figure 7 , and the XRD diffraction pattern is shown in Figure 8 . As can be seen from Figure 6 and Figure 7 , the thickness of the obtained Ag-ZnO nanosheet is about 4 to 5 nanometers, and the Ag nanoparticles are uniformly distributed on the ZnO nanosheet. As can be seen from Figure 8 , the silver nanoparticle loaded zinc oxide nanosheet (Ag-ZnO) is indeed successfully prepared.

[0080] Example 3

[0081] This example provides a Au-ZnO nanosheet catalyst, which takes ZnO nanosheet as the carrier and loads metal Au. Its preparation method is as follows:

[0082] Take 180 mg of hexamethylenetetramine (National Pharmaceutical Group Chemical Reagent Co., Ltd., purity ≥ 99%) and 45 mg of trisodium citrate dihydrate (National Pharmaceutical Group Chemical Reagent Co., Ltd., purity ≥ 99%) into 30 mL of deionized water, and place it on a magnetic stirrer at 500 r / min for 7 minutes. Then add 297 mg of zinc nitrate hexahydrate (aladdin, purity ≥ 99%). After complete dissolution, add 80 μL of 0.5 mol / L NaAuCl4 solution, and place it on a magnetic stirrer at 450 r / min for 10 minutes. Then transfer the mixed solution to a 50 mL polytetrafluoroethylene liner, seal it with a stainless steel reaction kettle, and place it in a constant temperature oven (Shanghai Jinghong Experimental Equipment Co., Ltd., DHG-9036Y) with a temperature setting of 90°C. The reaction time is 10 h. After the reaction is completed, cool it to room temperature naturally, wash it with deionized water several times, and centrifuge to collect the solid. Finally, dry it in a vacuum freeze dryer (Shanghai Licenbangxi Instrument Technology Co., Ltd., LC-10N-50A) for at least 8 h or more to obtain a solid powder. Place the powder sample in a vacuum dryer for subsequent characterization and application.

[0083] The solid powder was characterized by transmission electron microscopy (JEOL JEM-ARM200F), scanning electron microscopy (Gemini SEM450), and XRD (Philips X’Pert Pro Super diffractometer). The scanning electron micrograph is shown in FIG. 4a, the transmission electron micrograph (TEM) is shown in FIG. 4b, the elemental distribution map is shown in FIG. 4c, and the XRD diffraction pattern is shown in FIG. 4d. Figure 9 Figure 9 Figure 10 Figure 11 Figures 9-10 It can be seen from FIG. 4d that the Au-ZnO nanosheet obtained has a thickness of about 4 to 5 nanometers, and the Au nanoparticles are uniformly distributed on the ZnO nanosheet. Figure 11

[0084] Examples 4-6

[0085] Compared with Example 1, the only difference is that the amount of 0.5 mol / L Na2PdCl4 solution added is 20 μL, 60 μL and 200 μL, respectively, corresponding to Pd-ZnO nanosheets with loading amounts of 0.09%, 1.43% and 9.81%, respectively. The remaining parameters and steps are consistent with Example 1.

[0086] The products obtained in Examples 4-6 were characterized according to the characterization methods in Reference Examples 1-3, and the results were similar to those of Examples 1-3.

[0087] Comparative Example 1 ​​​​​

[0088] Preparation of ZnO nanosheets without metal nanoparticle loading: 140 mg of methenamine (National Pharmaceutical Group Chemical Reagent Co., Ltd., purity > 99%) and 29.4 mg of trisodium citrate dihydrate (National Pharmaceutical Group Chemical Reagent Co., Ltd., purity > 99%) were weighed into a 100 mL round-bottom flask and added to 30 mL of deionized water, and placed on a magnetic stirrer at 300 r / min for 5 minutes, then 297 mg of zinc nitrate hexahydrate (aladdin, purity > 99%) was added. After complete dissolution, the flask was transferred to a water bath, the temperature was set to 90°C, and the reaction time was 6h. After the reaction was completed, it was naturally cooled to room temperature, washed several times with deionized water, and the solid was collected by centrifugation. Finally, it was dried in a 80°C drying oven to obtain a white solid powder.

[0089] The solid powder was characterized and tested by scanning electron microscopy (GeminiSEM 450), transmission electron microscopy (JEOL JEM-ARM200F), laser Raman spectrometer (LabRAM HR Evolution), X-ray photoelectron spectrometer (ESCALAB 250), and XRD instrument (Philips X’Pert Pro Super diffractometer), respectively. The transmission electron microscopy image obtained is shown in FIG. 1a, the scanning electron microscopy image is shown in FIG. 1b, the element distribution map is shown in FIG. 1c, the XRD is shown in FIG. 1d, the Raman shift map is shown in FIG. 1e, and the results show that the zinc oxide nanosheets without metal nanoparticle loading are successfully synthesized. Figure 12 a, the scanning electron microscopy image is shown in FIG. 1b, the element distribution map is shown in FIG. 1c, the XRD is shown in FIG. 1d, the Raman shift map is shown in FIG. 1e, and the results show that the zinc oxide nanosheets without metal nanoparticle loading are successfully synthesized. Figure 12 a, the scanning electron microscopy image is shown in FIG. 1b, the element distribution map is shown in FIG. 1c, the XRD is shown in FIG. 1d, the Raman shift map is shown in FIG. 1e, and the results show that the zinc oxide nanosheets without metal nanoparticle loading are successfully synthesized. Figure 13 a, the scanning electron microscopy image is shown in FIG. 1b, the element distribution map is shown in FIG. 1c, the XRD is shown in FIG. 1d, the Raman shift map is shown in FIG. 1e, and the results show that the zinc oxide nanosheets without metal nanoparticle loading are successfully synthesized. Figure 3 a, the scanning electron microscopy image is shown in FIG. 1b, the element distribution map is shown in FIG. 1c, the XRD is shown in FIG. 1d, the Raman shift map is shown in FIG. 1e, and the results show that the zinc oxide nanosheets without metal nanoparticle loading are successfully synthesized. Figure 4 a, the scanning electron microscopy image is shown in FIG. 1b, the element distribution map is shown in FIG. 1c, the XRD is shown in FIG. 1d, the Raman shift map is shown in FIG. 1e, and the results show that the zinc oxide nanosheets without metal nanoparticle loading are successfully synthesized.

[0090] Comparative Example 2

[0091] Synthesis at 70°C: 140 mg of hexamethylenetetramine (National Pharmaceutical Group Chemical Reagent Co., Ltd., purity ≥ 99%) and 29.4 mg of trisodium citrate dihydrate (National Pharmaceutical Group Chemical Reagent Co., Ltd., purity ≥ 99%) were weighed into 30 mL of deionized water and stirred at 300 r / min on a magnetic stirrer for 5 min, then 297 mg of zinc nitrate hexahydrate (aladdin, purity ≥ 99%) was added. After complete dissolution, 100 μL of 0.5 mol / L Na2PdCl4 solution was added, and the mixture was stirred at 300 r / min on a magnetic stirrer for 5 min. The mixed solution was then transferred to a 50 mL polytetrafluoroethylene liner, sealed with a stainless steel reaction kettle, and placed in a constant temperature oven (Shanghai Jinghong Experimental Equipment Co., Ltd., DHG-9036Y) with a temperature setting of 70°C. The reaction time was 6 h. After the reaction was completed and the temperature was naturally cooled to room temperature, the sample was washed several times with deionized water and centrifuged to collect the solid. Finally, the sample was dried in a vacuum freeze dryer (Shanghai Lichengbangxi Instrument Technology Co., Ltd., LC-10N-50A) for at least 8 h, and the black solid powder was placed in a vacuum desiccator for subsequent characterization and application.

[0092] The solid powder was characterized by scanning electron microscopy (GeminiSEM 450) and XRD (Philips X’Pert Pro Super diffractometer), and the obtained scanning electron micrograph is shown in Figure 14 and the XRD diffraction pattern is shown in Figure 15 The results show that the obtained sample is agglomerated together and has no obvious nanosheet structure. This indicates that the crystal structure of zinc oxide has not been formed under low temperature conditions (70°C), and therefore zinc oxide nanosheet structures cannot be synthesized when the reaction temperature is below 90°C.

[0093] Comparative Example 3

[0094] Synthesis at 180 °C: 140 mg of hexamethylenetetramine (National Pharmaceutical Group Chemical Reagent Co., Ltd., purity ≥ 99%) and 29.4 mg of trisodium citrate dihydrate (National Pharmaceutical Group Chemical Reagent Co., Ltd., purity ≥ 99%) were weighed into 30 mL of deionized water, stirred at 300 r / min on a magnetic stirrer for 5 min, and then 297 mg of zinc nitrate hexahydrate (aladdin, purity ≥ 99%) was added. After complete dissolution, 100 μL of 0.5 mol / L Na2PdCl4 solution was added, stirred at 300 r / min on a magnetic stirrer for 5 min, and then the mixed solution was transferred to a 50 mL polytetrafluoroethylene liner, sealed with a stainless steel reaction kettle, and placed in a constant temperature oven (Shanghai Jinghong Experimental Equipment Co., Ltd., DHG-9036Y) with a temperature of 180 °C. The reaction time was 6 h. After the reaction was completed and the temperature was naturally cooled to room temperature, the sample was washed several times with deionized water and centrifuged to collect the solid. Finally, the sample was dried in a vacuum freeze dryer (Shanghai Lichengbangxi Instrument Technology Co., Ltd., LC-10N-50A) for at least 8 h, and a black solid powder was obtained. The powder sample was placed in a vacuum dryer for subsequent characterization and application.

[0095] The solid powder was characterized by transmission electron microscopy (JEOL JEM-ARM200F), scanning electron microscopy (Gemini SEM450), and XRD (Philips X’Pert Pro Super diffractometer), respectively. The obtained transmission electron micrograph (TEM) is shown in FIG. 1a, and the scanning electron micrograph is shown in FIG. 1b. It can be seen that under this condition, the temperature is too high (180 °C), which causes the metal nanoparticles to agglomerate seriously, and the larger metal particles cover the zinc oxide nanosheets. Figure 16 Figure 16

[0096] Photoelectrochemical characterization

[0097] Static photocurrent test: Taking the pure ZnO nanosheets prepared in Comparative Example 1 and the Pd-ZnO nanosheets prepared in Example 1 as examples, 3 mg of pure ZnO nanosheets and 5.87% Pd-ZnO nanosheets were weighed and added to 750 μL and 250 μL of H2O, respectively, and ultrasonicated for 10 min. After complete dissolution, 100 μL of the solution was spread on ITO conductive glass (effective area 1 cm*1 cm) and naturally dried. Then, the Zahner electrochemical workstation (Zahner PP211) was used for photocurrent test, with 0.5 mol / L Na2SO4 solution as the electrolyte. The test used a three-electrode system, with a carbon rod as the counter electrode, a silver chloride silver electrode as the reference electrode, and ITO glass as the working electrode. The bias voltage was 1 V vs. Ag / AgCl. The test results are shown in FIG. 2a. Figure 17 a. ​​

[0098] Electrochemical impedance spectroscopy test: pure ZnO nanosheets prepared by Comparative Example 1 and 5.87% Pd-ZnO nanosheets prepared by Example 1 were weighed, added into a mixed solution of 4 mL anhydrous ethanol and 1 mL deionized water and ultrasonicated for 10 min, and after complete dissolution, 200 μL of the solution was spread on a glassy carbon electrode (effective area 1 cm*1 cm) and naturally dried. Then a multi-channel electrochemical workstation (Solartron analytical 1470E) was used to test the impedance of the sample. A three-electrode system was used, with a platinum sheet as the counter electrode, a silver-silver chloride electrode as the reference electrode, and a glassy carbon electrode as the working electrode, without applying bias. The electrolyte was a mixed solution of 0.3 mol / L K3[Fe(CN)3] and 0.5 mol / L KCl, and the test results are as follows Figure 17 b.

[0099] In addition, the pure ZnO nanosheets prepared by Comparative Example 1 and the 5.87% Pd-ZnO nanosheets prepared by Example 1 were characterized by ultraviolet-visible-near infrared diffuse reflectance spectroscopy (Uv-Vis DRS) and photoluminescence (PL), and the results are as follows Figure 17 c and 17d. It can be seen from Figure 17 a~d that compared with single ZnO nanosheets, the Pd-ZnO nanosheets loaded with Pd enhanced the absorption of visible light, promoted the migration of photo-generated electron-hole pairs, effectively inhibited the recombination efficiency of photo-generated carriers, and effectively improved the efficiency of photocatalytic C2H6 dehydrogenation to ethylene.

[0100] Photocatalytic application example: photocatalytic C2H6 dehydrogenation to C2H4

[0101] Pure ZnO nanosheets prepared by Comparative Example 1 and Pd-ZnO nanosheets prepared by Example 1 were added to 1.5 mL deionized water and ultrasonicated for 5 min to disperse. The obtained solution was all drop-coated on a quartz sheet, which was dried at 50°C for 2 h. The dried quartz sheet was transferred to a sealed off-line photocatalytic reactor (Beijing Pheilabs Technology Co., Ltd., volume 450 mL), and 500 μL deionized water was added to the bottom. The reactor was purged several times with high-purity Ar (99.9%) and then filled with high-purity C2H6 (99.9%) at normal pressure. The photocatalytic light source was a 300W Xe lamp (CEL-HXF300, Beijing Zhongjiao Jin Yuan Technology Co., Ltd.) equipped with a standard AM1.5G filter. Each test was irradiated for 4 hours, and 1 mL of gaseous product was taken from the reactor and injected into a gas chromatograph for qualitative detection (Agilent GC-7890B equipped with a TDX-01 chromatographic column, a thermal conductivity detector (TCD) and a flame ionization detector (FID), with ultra-high-purity argon as the carrier gas).

[0102] Figure 18The product distribution of different Pd nanoparticle loading ZnO nanosheet and Pd-free nanoparticle loading ZnO nanosheet prepared in Example 1 and Examples 4-6 photocatalytic dehydrogenation of high purity ethane (99.99%) to ethylene is shown. As can be seen from the figure, the metal nanoparticle-free ZnO nanosheet has almost no activity for photocatalytic dehydrogenation of ethane, while the Pd-ZnO nanosheet obtained by the present application can significantly enhance the efficiency of photocatalytic dehydrogenation of C2H6 to C2H4 under mild conditions. With the increase of Pd content, the yield of C2H4 increases significantly, but when the Pd content exceeds 5.87%, the selectivity of C2H4 product drops sharply, while the yield of by-products (CO2 and CO) increases. Therefore, by controlling the loading amount of Pd to be 3-7%, the Pd-ZnO nanosheet obtained can realize high efficiency and high selectivity of photocatalytic dehydrogenation of C2H6 to C2H4 under mild conditions. After 4h of reaction, the yield of ethylene reached 16.32 mmol g -1 , and the selectivity was as high as 94.83%; in addition, 14.49 mmolg -1 of H2 was also obtained. In addition, Figure 19 The long-time stability of 5.87% Pd-ZnO nanosheet prepared in Example 1 for photocatalytic dehydrogenation of ethane (99.99%) to ethylene is shown. It can be seen that in a reaction of up to 26h, the yield and selectivity of photocatalytic dehydrogenation of C2H6 to C2H4 almost do not decay, which proves that the Pd-ZnO nanosheet catalyst has excellent stability.

[0103] According to the above examples and comparative examples, different types of metal (Pd, Ag, Au, etc.) nanoparticle loading ZnO nanosheet can be prepared by the hydrothermal impregnation reduction method of the present application. The hydrothermal temperature is controlled between 90-150°C. When the temperature is too low, the crystal structure of the ZnO nanosheet cannot be well formed, and when the temperature is higher than 150°C, the metal nanoparticles will be aggregated. According to the spectroscopy test, it is shown that the metal loading ZnO nanosheet has stronger light absorption ability and electron-hole separation efficiency, and thus has good photocatalytic properties. Taking the prepared Pd nanoparticle loading ZnO nanosheet (Pd-ZnO) as an example, the material has good performance for photocatalytic dehydrogenation of ethane to ethylene and hydrogen, which provides a new idea for high-efficiency photocatalytic conversion of ethane to high-value chemicals under mild conditions. The prepared silver nanoparticle loading ZnO nanosheet (Ag-ZnO) and gold nanoparticle loading ZnO nanosheet (Au-ZnO) have similar test results to Pd-ZnO through photoelectrochemical characterization test, ultraviolet-visible near-infrared diffuse reflectance spectroscopy (Uv-Vis DRS) test, and photoluminescence (PL) test, and can also obtain high yield and high selectivity of ethylene when applied to photocatalytic dehydrogenation of C2H6 to C2H4. With the increase of Ag and Au content, similar trends to the Pd-ZnO nanosheet catalyst are shown, and excellent stability is also obtained.

[0104] The foregoing description of the disclosed embodiments enables one of ordinary skill in the art to make or use the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing ethylene, characterized in that, Includes the following steps: Ethylene was obtained by photo-reacting a zinc oxide nanosheet-supported catalyst in an ethane atmosphere. The zinc oxide nanosheet supported catalyst includes a support: zinc oxide nanosheets, and a metal supported on the support; The metal is selected from any one or more of Pd, Ag, or Au; The preparation method of the zinc oxide nanosheet supported catalyst includes the following steps: A zinc oxide nanosheet supported catalyst was obtained by mixing a surfactant, a metal salt solution, and a soluble zinc salt and reacting them at 90-150°C. The metal salt solution is selected from any one or more of Na2PdCl4 solution, AgNO3 solution or NaAuCl4 solution; The surfactant is selected from hexamethylenetetramine and trisodium citrate.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the carrier to the metal loaded on the carrier is (93~97):(3~7).

3. The preparation method according to claim 1, characterized in that, The zinc oxide nanosheets have a thickness of 4-5 nm; The average particle size of the metal is 10~20 nm.

4. The preparation method according to claim 1, characterized in that, The light source for the photoreaction is selected from any one of xenon lamps, high-pressure mercury lamps, LED lamps, or tungsten iodine lamps.

5. The preparation method according to claim 1, characterized in that, The power of the light source in the photoluminescence reaction is 80~120mW cm. -2 ; The photoreaction time is 2-6 hours.

6. The preparation method according to claim 1, characterized in that, The purity of the ethane is ≥99.9%.

7. A method for preparing a zinc oxide nanosheet supported catalyst, characterized in that, Includes the following steps: A zinc oxide nanosheet supported catalyst was obtained by mixing a surfactant, a metal salt solution, and a soluble zinc salt and reacting them at 90-150°C. The metal salt solution is selected from any one or more of Na2PdCl4 solution, AgNO3 solution or NaAuCl4 solution; The surfactant is selected from hexamethylenetetramine and trisodium citrate.

8. The preparation method according to claim 7, characterized in that, The soluble zinc salt is selected from any one or more of zinc acetate, zinc chloride, zinc nitrate, or zinc sulfate.

9. The preparation method according to claim 7, characterized in that, The molar ratio of the surfactant, metal salt solution, and soluble zinc salt is (0.3~2): (0.01~0.07):

1.

10. The preparation method according to claim 7, characterized in that, The reaction is carried out at a temperature of 100-130°C for 5-12 hours.

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