Recyclable supported catalyst for photocatalytic dehydrogenation of ethane to ethylene

Abstract

The application belongs to the technical field of photocatalytic ethane dehydrogenation to ethylene, and particularly relates to a supported photocatalyst which can be used to catalyze ethane dehydrogenation to ethylene under mild conditions and can be recycled. 3‑x Under simulated sunlight, the supported photocatalyst can catalyze ethane dehydrogenation to ethylene with high selectivity. 3‑x The photocatalyst can be regenerated through a simple calcination-reduction treatment, thereby effectively solving the problems of poor stability and difficult regeneration of traditional dehydrogenation catalysts. The preparation method of the supported catalyst is simple, the reaction conditions are mild, and the supported catalyst has a broad application prospect in the process of ethane dehydrogenation to ethylene.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photocatalytic ethane dehydrogenation to ethylene, and particularly relates to a supported photocatalyst which can be used for catalyzing ethane dehydrogenation to ethylene under mild conditions and can be recycled. BACKGROUND

[0002] The yield of ethylene is an important indicator of the development level of a country's petroleum chemical industry. Ethylene is one of the basic raw materials in the chemical industry and is one of the basic components of synthetic plastics, fibers, styrene, ethylene glycol and other value-added compounds, and is widely used. The traditional route for producing olefins is steam cracking and catalytic cracking of petroleum distillates. These two processes are endothermic and require a large amount of energy input and a very high operating temperature (800-850 ℃), and high temperature can cause problems such as excessive oxidation and cracking. In recent years, with the increase in proven reserves, the exploitation of shale gas has become one of the most meaningful energy revolutions in the 21st century. The composition of shale gas is mainly methane, and ethane accounts for about 15% of its composition. As the second largest component of shale gas, the development and utilization of ethane has attracted widespread attention. Due to the increasing demand for ethylene worldwide, catalytic ethane dehydrogenation to prepare ethylene is considered to be a very promising method. At present, catalytic ethane dehydrogenation mainly focuses on thermal catalysis, but this route usually encounters the problem of serious deactivation of the catalyst due to coke formation and metal sintering at high temperature. Compared with thermal catalysis, photocatalysis can change the catalytic reaction path by driving the transformation of the energy form of the catalytic reaction under mild conditions, and can reduce the energy barrier of the rate-limiting step in the catalytic system, thereby improving the activity and selectivity of the reaction. Therefore, it is urgent to develop a photocatalyst for ethane dehydrogenation to ethylene under mild conditions with high activity, high selectivity and high stability.

[0003] At present, the photocatalytic ethane dehydrogenation to prepare ethylene reaction system mainly involves an ethane oxidative dehydrogenation reaction system with an oxidant (such as O2, etc.). The exothermic nature of this reaction is thermodynamically favorable, but the target product ethylene is easily overoxidized to form CO2 and other products. In contrast, the photocatalytic non-oxidative dehydrogenation reaction system can effectively prevent the overoxidation of the target product ethylene by utilizing the moderate oxidation ability of lattice oxygen, and has broad research prospects.

[0004] Tungsten oxide and various modified tungsten-based catalysts have been widely used in the light-induced selective oxidation of many organic compounds. With its rich oxidation states and oxygen vacancies, it can achieve high selectivity and high activity in the catalytic reaction process. More importantly, tungsten oxide is of great concern in industrial applications due to its high thermal stability, strong visible light absorption, long service life and moderate oxidation ability.

[0005] Platinum-based catalysts have been proven to be able to activate the C-H bond of ethane for the preparation of ethylene by ethane dehydrogenation. Compared with conventional CrOx Compared with base catalysts or other catalysts, platinum-based catalysts have the advantages of fast reaction rate, good stability, environmental friendliness, etc. Therefore, loading a small amount of noble metal Pt on the surface of visible light responsive tungsten oxide with oxygen vacancies is one of the effective strategies to improve the efficiency of photocatalytic ethane dehydrogenation to ethylene. However, based on the Mars-van Krevelen mechanism, the lattice oxygen in the metal oxide will participate in the reaction, and then be removed from the surface of the tungsten oxide catalyst, resulting in catalyst deactivation. To solve this problem, we take advantage of the multi-valence oxidation state of tungsten oxide, and regenerate and recycle the catalyst by a simple "calcination-reduction" method after the reaction. SUMMARY

[0006] The purpose of the present application is to provide a recyclable supported photocatalyst for ethane dehydrogenation to ethylene. The synthesis method of the photocatalyst is simple and has considerable yield, and can selectively activate the C-H bond of ethane molecules, and then efficiently photocatalyze ethane dehydrogenation to ethylene under mild conditions. To solve the problem of catalyst deactivation after the reaction, the catalyst can be regenerated by a simple "calcination-reduction" method, and recycled, which is conducive to the popularization and application in the existing process of catalytic ethane dehydrogenation to ethylene.

[0007] To achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0008] A recyclable supported photocatalyst for ethane dehydrogenation to ethylene is prepared by loading metal Pt on the surface of WO3 and further treating it in a 5% H2 / Ar atmosphere to obtain the supported catalyst Pt / WO3. 3-x The optimal loading amount of Pt is about 1 wt%, and the loading amount is controllable.

[0009] The preparation method of the supported catalyst comprises the following steps:

[0010] (1) WO3 is prepared by a hydrothermal method;

[0011] (2) The supported catalyst Pt / WO3 is prepared by an impregnation-reduction method. 3-x

[0012] The specific steps are as follows:

[0013] (1) 3 g of oxalic acid dihydrate and 0.3 g of tungsten chloride are dissolved in 60 mL of ethanol, stirred for 30 min, and then reacted at 100 ℃ for 24 h, and naturally cooled to room temperature. The obtained precipitate is washed and dried to obtain WO3;

[0014] (2) 400 mg of WO3 is dispersed in 20 mL of water, and 80-800 μL of chloroplatinic acid solution (concentration of 10 mg mL-1) is added. -1 ​), stirring for 30 min, drying at 100 ℃, collecting the product, and calcining the product at 300 ℃ under a 5% H2 / Ar atmosphere for 1 h to prepare a supported catalyst Pt / WO 3-x .

[0015] The obtained supported catalyst can be used for the photocatalytic dehydrogenation of ethane to ethylene.

[0016] The significant effect of the present application is that:

[0017] (1) The present application loads metal Pt on the surface of WO3, significantly promotes the activation of ethane, and significantly improves the efficiency of the catalytic reaction.

[0018] (2) The present application realizes catalyst regeneration by a simple “dipping-reduction” method, so that the catalyst can maintain good stability.

[0019] (3) The preparation method of the present application is simple, has a high yield, and is conducive to application in the existing process of photocatalytic dehydrogenation of ethane to ethylene. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 are XRD patterns of WO3, WO 3-x , and Pt / WO 3-x .

[0021] Figure 2 are EPR patterns of WO3, WO 3-x , and Pt / WO 3-x .

[0022] Figure 3 are DRS patterns of WO3, WO 3-x , and Pt / WO 3-x .

[0023] Figure 4 is a Pt 4f pattern of Pt / WO 3-x .

[0024] Figure 5 The a-c figures in FIG. 1 are SEM, HRTEM, and element distribution pictures of Pt / WO 3-x .

[0025] Figure 6 is a reaction activity comparison chart of WO 3-x and Pt / WO 3-x loaded with different proportions of metal Pt.

[0026] Figure 7 is a recycling activity chart of Pt / WO 3-x . DETAILED DESCRIPTION

[0027] In order to make the content of the present application more convenient to understand, the technical solutions of the present application are further described below in combination with specific embodiments, but the present application is not limited thereto.

[0028] Example 1 Preparation of WO3

[0029] 3 g of oxalic acid dihydrate and 0.3 g of tungsten chloride were dissolved in 60 mL of ethanol, and after stirring for 30 min, the solution was reacted at 100 ℃ for 24 h, and then naturally cooled to room temperature. The obtained precipitate was washed and dried to obtain WO3.

[0030] Example 2 Preparation of Pt / WO 3-x

[0031] 400 mg of WO3 obtained in Example 1 was dissolved in 20 mL of water, and 80-800 μL of chloroplatinic acid solution (concentration of 10 mg mL -1 ) was added, and the solution was stirred for 30 min, dried at 100 ℃, and the product was collected and calcined at 300 ℃ for 1 h in a 5vol% H2 / Ar atmosphere to obtain the supported catalyst Pt / WO 3-x .

[0032] Example 3 Evaluation of the activity of Pt / WO 3-x photocatalytic ethane dehydrogenation to prepare ethylene

[0033] Example 2 Pt / WO 3-x photocatalytic ethane dehydrogenation to prepare ethylene

[0034] Figure 1 are the XRD patterns of WO3, WO 3-x and Pt / WO 3-x . As shown in the figure, the XRD pattern of the Pt / WO 3-x supported catalyst contains all the characteristic peaks of WO3. No characteristic peaks of Pt are shown in the pattern, mainly because at a low loading amount, the Pt nanoparticles are highly dispersed and have a small particle size. Figure 1

[0035] Figure 2 are the XRD patterns of WO3, WO 3-x and Pt / WO​​3-x EPR map. For example... Figure 2 As shown, under the same conditions, WO 3-x It exhibits a strong EPR signal. This can be attributed to the intense vibration of oxygen atoms on the material surface caused by the reducing atmosphere of H2, which facilitates the diffusion and overflow of oxygen from the surface lattice, leading to the generation of oxygen vacancies. (Compared to WO3) 3-x In comparison, Pt / WO 3-x The weak EPR signal intensity is due to the small amount of Pt species loaded on the surface oxygen vacancies, which reduces the signal intensity.

[0036] Figure 3 For WO3, WO 3-x and Pt / WO 3-x DRS map. For example... Figure 3 As shown, introducing oxygen vacancies into WO3 can significantly extend the photoresponse. (The last sentence appears to be incomplete and possibly refers to a different topic.) 3-x In comparison, Pt / WO 3-x It exhibits stronger light absorption in the visible light region, which corresponds to the gradual change in color from light yellow to dark blue.

[0037] Figure 4 Pt / WO 3-x The Pt 4f spectrum. (e.g.) Figure 4 As shown, the Pt 4f plot demonstrates the successful loading of Pt species. The plot indicates that Pt species are mainly composed of Pt4f. 0 The form of Pt species is loaded on the WO3 surface, while a small amount of Pt species are loaded as platinum oxide (Pt). 2+ It exists in the form of )

[0038] Figure 5 Pt / WO 3-x SEM, HRTEM, and elemental distribution images. For example... Figure 5 As shown in Figure a, Pt / WO 3-x It exhibits a sheet-like structure. For example... Figure 5 As shown in Figure b, in Pt / WO 3-x In the HRTEM image of the sample, the lattice spacing of the substrate material is 0.37 nm, which can be attributed to the (200) plane of tungsten oxide. Meanwhile, lattice fringes of the Pt (111) plane with a lattice spacing of 0.22 nm are clearly observed. Figure 5 As shown in Figure c, the W, O, and Pt elements are uniformly distributed throughout the structure.

[0039] Figure 6 For WO 3-x Pt / WO4 with different proportions of metallic Pt loading 3-x A comparison chart of reactivity. (Example) Figure 6 As shown, compared to WO 3-x Pt / WO3-x The supported catalysts can significantly improve the efficiency of photocatalytic dehydrogenation of ethane to ethylene. This is mainly due to the fact that the noble metal Pt species can significantly promote the activation of the C-H bond of ethane molecules. When the loading is 1%, the catalyst shows the highest selectivity for ethylene (84.9%).

[0040] Figure 7 The cycle regeneration activity of Pt / WO 3-x Figure 7 As shown, the catalyst after cycle regeneration shows good stability in six cycles of cycle test.

[0041] The above merely describes preferred embodiments of the present application, and any equivalent changes and modifications made within the scope of the patent application of the present application shall fall within the scope of the present application.​

Claims

1. Supported catalyst Pt / WO 3-x Its application in the photocatalytic dehydrogenation of ethane to ethylene is characterized by: The supported catalyst Pt / WO 3-x It is prepared by loading Pt onto the surface of WO3 and treating it with a 5 vol% H2 / Ar atmosphere. The loading amount of Pt on WO3 is 1 wt%.

2. The application according to claim 1, characterized in that: Supported catalyst Pt / WO 3-x The preparation method includes the following steps: (1) Preparation of WO3 by hydrothermal method; (2) Preparation of supported catalyst Pt / WO using impregnation-reduction method 3-x .

3. The application according to claim 2, characterized in that: The specific steps are as follows: (1) Dissolve oxalic acid dihydrate and tungsten chloride in ethanol, stir for 30 min, then perform hydrothermal reaction and cool naturally to room temperature; (2) The precipitate obtained in step (1) was washed and dried, then chloroplatinic acid solution was added, stirred for 30 min, and dried at 100℃; the product was collected and calcined at 300℃ in a 5 vol% H2 / Ar atmosphere for 1 h to obtain the catalyst Pt / WO. 3-x .

4. The application according to claim 3, characterized in that: Step (1) The hydrothermal reaction is specifically carried out at 100℃ for 24 hours.

5. The application according to claim 3, characterized in that: Step (2) The concentration of chloroplatinic acid solution is 10 mg / mL -1 .

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