Process for the photocatalytic oxidative dehydrogenation of alkanes to olefins

Abstract

The application provides a method for preparing olefins by photocatalytic oxidative dehydrogenation of alkanes, and belongs to the technical field of photocatalytic preparation of olefins. The method comprises the following steps: using a xenon lamp as a light source, introducing a mixed gas containing alkanes into a photocatalytic reactor loaded with a photocatalyst, and making the alkanes in the mixed gas undergo oxidative dehydrogenation under light to obtain olefins; wherein the photocatalyst comprises a TiO2{001} carrier and a bimetallic alloy loaded on the TiO2{001} carrier, the bimetallic alloy is an alloy formed by Pd and other metals, and the other metals are selected from any one of Fe, Ni, Cu, Zn, Pt, Ag and Au; wherein the mixed gas further comprises oxygen and an inert gas, the alkanes are ethane or propane, and the olefins are ethylene or propylene.

Description

Technical Field

[0001] This invention belongs to the field of photocatalytic preparation of olefins, and particularly relates to a method for photocatalytic oxidative dehydrogenation of alkanes to produce olefins. Background Technology

[0002] Ethylene (C2H4) is a fundamental raw material in the petrochemical industry and a basic chemical feedstock for synthetic fibers, synthetic rubber, and other products. Ethylene production capacity is a key indicator of the petrochemical industry's development. Currently, ethylene is mainly produced through high-temperature steam cracking of naphtha-derived hydrocarbons. This process typically takes place under harsh conditions of 800-900℃, resulting in high energy consumption and significant carbon dioxide (CO2) emissions. Against the backdrop of emission reduction, developing a low-carbon, energy-saving, and efficient new route for ethylene production is of paramount importance. Driven by this urgent need, the route for directly producing ethylene from abundant ethane has attracted widespread attention. Among these routes, the oxidative dehydrogenation (ODHE) of ethane thermodynamically avoids reaction equilibrium limitations and carbon deposition problems, making it more advantageous than the direct dehydrogenation of ethane (C2H6). However, due to the high carbon-hydrogen (CH) bond energy of ethane (415 kJ / mol), traditional thermocatalysis generally requires operation at temperatures above 500 °C. High temperatures (above 500 °C) easily induce deep oxidation of the target product, ethylene, leading to decreased selectivity and the generation of large amounts of worthless CO2. Furthermore, high temperatures pose a serious challenge to the long-term stability of the catalyst. Therefore, developing mild catalytic systems for the synthesis of alkenes is of great significance. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a method for photocatalytic oxidative dehydrogenation of alkanes to olefins, aiming to at least partially solve the above-mentioned technical problems. The technical solution provided by this invention is as follows.

[0004] According to an embodiment of the present invention, a method for photocatalytic oxidative dehydrogenation of alkanes to produce olefins is provided, comprising: using a xenon lamp as a light source, introducing a mixed gas containing alkanes into a photocatalytic reactor loaded with a photocatalyst, and subjecting the alkanes in the mixed gas to oxidative dehydrogenation to produce olefins under illumination conditions; wherein the photocatalyst comprises a TiO2{001} support and a bimetallic alloy supported on the TiO2{001} support, the bimetallic alloy being an alloy formed by Pd and other metals, the other metals being selected from any one of Fe, Ni, Cu, Zn, Pt, Ag, and Au; wherein the mixed gas further comprises oxygen and an inert gas, the alkanes being ethane or propane, and the olefins being ethylene or propylene.

[0005] In this invention, a xenon lamp is used as the external energy source, oxygen as the oxidant, an inert gas as the equilibrium gas in the photocatalytic reactor, and TiO2{001} supported on a bimetallic alloy as the photocatalyst, enabling the oxidative dehydrogenation of alkanes to produce olefins under illumination. This invention employs palladium (Pd) to form a bimetallic alloy with other metals. Pd has a stronger CH dissociation ability than other metals, effectively activating alkanes into alkyl radicals, while the other metals have a strong ability to activate oxygen, thus utilizing oxygen to activate alkyl radicals to generate weakly adsorbed olefins. Considering the weak adsorption capacity of other metals for olefins, the olefins produced by oxidative dehydrogenation can be further desorbed, resulting in more selective and active olefin products, such as ethylene or propylene. This invention uses a xenon lamp as the external energy source to achieve highly efficient conversion of alkanes to olefins. The method for preparing olefins in this invention has advantages such as low energy consumption, high conversion rate, simple operation, mild oxidative dehydrogenation reaction conditions, and lower cost. Attached Figure Description

[0006] Figure 1 This is a graph showing the photocatalytic reaction performance of the photocatalyst in Example 1 of the present invention;

[0007] Figure 2 This is a graph showing the photocatalytic reaction performance of the photocatalyst in Example 2 of the present invention;

[0008] Figure 3 This is a graph showing the photocatalytic reaction performance of the photocatalyst in Example 3 of the present invention;

[0009] Figure 4 The graph shows the photocatalytic reaction performance of ethane and oxygen at different volume ratios in Example 4 of this invention.

[0010] Figure 5A The graph shows the photocatalytic reaction performance under different light intensities in Example 5 of this invention.

[0011] Figure 5B The graph shows the photocatalytic reaction performance of Example 5 of the present invention at different reaction temperatures;

[0012] Figure 6 This is a graph showing the stability test results of the photocatalytic reaction in Example 6 of the present invention;

[0013] Figure 7A The images shown are transmission electron microscope (TEM) images and particle size distribution diagrams of the photocatalyst in Example 3 of this invention.

[0014] Figure 7B This is an elemental distribution diagram of the photocatalyst in Example 3 of the present invention;

[0015] Figure 8 for Figure 7ALinear scanning images of alloy particles in a magnified area using transmission electron microscopy (TEM), where a represents the alloy particles and the scanning direction from left to right, and b represents the scanning result corresponding to the scanning direction a.

[0016] Figure 9 This is a comparison chart of the photocatalytic reaction performance of different photocatalysts in Example 3, Comparative Examples 1-2 of the present invention;

[0017] Figure 10 This is a performance diagram of photocatalytic oxidation dehydrogenation to propylene in Example 7 of the present invention. Detailed Implementation

[0018] The current method of preparing olefins from alkanes involves high temperatures, harsh conditions, high energy consumption, and the emission of large amounts of CO2 gas. There is an urgent need to develop a mild catalytic system to convert alkanes into olefins.

[0019] In recent years, photocatalysis has become a green, environmentally friendly, and promising new technology. Photocatalysis utilizes energy from sunlight or other light sources to drive alkane dehydrogenation reactions, reducing dependence on high temperatures (above 500°C) and effectively reducing carbon emissions and energy consumption. The photocatalytic alkane dehydrogenation process typically involves the generation and migration of photogenerated charge carriers. These charge carriers provide effective reaction sites for the activation of alkane molecules, thereby promoting the dehydrogenation of alkenes to olefins.

[0020] Titanium dioxide (TiO2) is a common photocatalyst, widely used in photocatalysis research due to its excellent chemical stability, non-toxicity, low cost, and suitable band structure. However, the intrinsic photocatalytic activity of TiO2 is limited by its high recombination rate of photogenerated carriers, and the ability of pure TiO2 surface to regulate the adsorption and desorption behavior of reaction intermediates and products is limited, often leading to unsatisfactory selectivity for olefins (such as ethylene) in ODHE reactions. Introducing suitable metals onto TiO2 can effectively improve the separation and recombination of photogenerated charges, providing new active centers for photocatalytic dehydrogenation reactions. Among many metals, palladium (Pd), platinum (Pt), and copper (Cu) have excellent activation capabilities for the CH bonds of alkanes and are highly favored in alkane conversion reactions. However, in TiO2 photocatalysts supported on a single metal, although the single metal site can effectively activate alkanes, its stronger adsorption of intermediates and olefins can easily trigger continuous dehydrogenation and over-oxidation, resulting in high CO2 selectivity and difficulty in maximizing olefin yield.

[0021] Therefore, in order to further improve the performance of the catalyst, this invention proposes to introduce a second metal (such as Fe, Ni, Cu, etc.) and control the presence mode of the two metals (such as alloys or nanoparticles) to effectively regulate the ability of oxygen activation and alkane dehydrogenation, so that alkanes can be efficiently converted into olefins, avoiding excessive oxidation of the products and improving the yield and selectivity of olefins.

[0022] Specifically, the present invention provides a method for photocatalytic oxidative dehydrogenation of alkanes to produce olefins, comprising: using a xenon lamp as a light source, introducing a mixed gas containing alkanes into a photocatalytic reactor loaded with a photocatalyst, and oxidizing and dehydrogenating the alkanes in the mixed gas to obtain olefins under illumination conditions; wherein the photocatalyst comprises a TiO2{001} support and a bimetallic alloy supported on the TiO2{001} support, the bimetallic alloy being an alloy formed by Pd and other metals, the other metals being selected from any one of Fe, Ni, Cu, Zn, Pt, Ag, and Au; wherein the mixed gas also includes oxygen and an inert gas, the alkanes being ethane or propane (C3H8), and the olefins being ethylene (C2H4) or propylene (C3H6).

[0023] In this invention, a xenon lamp is used as the external energy source, oxygen as the oxidant, an inert gas as the equilibrium gas in the photocatalytic reactor, and TiO2{001} supported on a bimetallic alloy as the photocatalyst, enabling the oxidative dehydrogenation of alkanes to produce olefins under illumination. This invention utilizes a bimetallic alloy formed by Pd and other metals. Pd exhibits stronger CH dissociation capabilities compared to other metals, effectively activating alkanes into alkyl radicals. The other metals, however, possess strong oxygen activation capabilities, allowing for the effective activation of alkyl radicals to generate weakly adsorbed olefins. Furthermore, considering the weak adsorption capacity of other metals for olefins, the olefins produced by oxidative dehydrogenation can be further desorbed, resulting in more selective and active olefin products, such as ethylene or propylene. This invention, using a xenon lamp as the external energy source, achieves highly efficient conversion from alkanes to olefins. The method for preparing olefins in this invention offers advantages such as lower energy consumption, higher conversion rate, simple operation, milder oxidative dehydrogenation reaction conditions, and lower cost.

[0024] According to an embodiment of the present invention, the power of the xenon lamp is 130W-300W, preferably 300W; the illuminance of the xenon lamp is 4.7mW / cm². 2 -10.7mW / cm 2 For example, it can be 4.7mW / cm 2 6.3mW / cm 2 7.6mW / cm 2 8.9mW / cm 2 10.7mW / cm 2The illuminance of the xenon lamp is preferably 10.7 mW / cm², or any value within this range. 2 .

[0025] According to embodiments of the present invention, the volume ratio of oxygen, inert gas, and alkanes in the mixed gas is (2-5):(45-48):50, for example, it can be 2:48:50, 3.3:46.7:50, 4:46:50, 5:45:50, or any value within this range. Preferably, the volume ratio of oxygen, inert gas, and alkanes is 3.3:46.7:50. The inert gas used in the present invention is nitrogen or argon, which is used as the balance gas in the photocatalytic reactor. Nitrogen (N2) is preferred as the inert gas. The flow rate of the mixed gas is 10 mL / min to 75 mL / min, for example, it can be 10 mL / min, 20 mL / min, 25 mL / min, 30 mL / min, 35 mL / min, 40 mL / min, 45 mL / min, 50 mL / min, 55 mL / min, 60 mL / min, 65 mL / min, 70 mL / min, 75 mL / min, or any value within this range. Preferably, the flow rate of the mixed gas is 30-50 mL / min, and more preferably, the flow rate of the mixed gas is 50 mL / min. By controlling the flow rate of the mixed gas (10 mL / min-75 mL / min), continuous dehydrogenation and over-oxidation in the alkane oxidative dehydrogenation reaction can be effectively avoided, thereby preventing the increase in CO2 selectivity from reducing the selectivity and yield of olefins.

[0026] According to embodiments of the present invention, the bimetallic alloy can be a Pd-Fe alloy, a Pd-Ni alloy, a Pd-Cu alloy, a Pd-Zn alloy, a Pd-Pt alloy, a Pd-Ag alloy, or a Pd-Au alloy, with a preference for a Pd-Ag alloy. Taking ethane as an example, the active sites of the Pd-Ag alloy are spatially close, and Pd has a stronger CH dissociation ability, which can effectively activate ethane (C2H6) into ethyl radicals (·C2H5); while Ag has a higher ability to activate oxygen and a weaker adsorption capacity for ethylene (C2H4), which can effectively activate ·C2H5 with O2 to produce weakly adsorbed ethylene, which can then be further desorbed to obtain a more selective and more active ethylene product.

[0027] According to embodiments of the present invention, the amount of photocatalyst used is 5 mg to 100 mg, for example, 5 mg, 10 mg, 20 mg, 30 mg, 40 mg, 50 mg, 60 mg, 70 mg, 80 mg, 90 mg, 100 mg, etc., more preferably 5-20 mg, or any value within this range. The amount of photocatalyst can also be adjusted according to the actual reaction. By controlling the amount of photocatalyst, excessive dissociation of CH in alkanes can be effectively avoided, while carbon deposition on the photocatalyst can be avoided, which would lead to photocatalyst deactivation.

[0028] According to embodiments of the present invention, in the photocatalyst, the loading of Pd, based on the mass of the TiO2{001} support, is 0.1wt%-1wt%, for example, 0.1wt%, 0.2wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.8wt%, 1.0wt%, etc.; the loading of other metals is 0.1wt%-1wt%, for example, 0.1wt%, 0.2wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.8wt%, 1.0wt%, etc. The loading ratio of the two metals in the Pd-Fe alloy, Pd-Ni alloy, Pd-Cu alloy, Pd-Zn alloy, Pd-Pt alloy, and Pd-Au alloy is 1:1.

[0029] In this invention, a mixed gas consisting of alkanes, oxygen, and an inert gas is introduced into a photocatalytic reactor (such as a planar mobile phase reactor) loaded with a photocatalyst, and then placed under a xenon lamp to carry out the photocatalytic oxidative dehydrogenation of alkanes to produce olefins, while the performance of the photocatalytic oxidative dehydrogenation of alkanes is monitored. By adjusting the composition and amount of the photocatalyst, the composition and flow rate of the mixed gas, and the light intensity, the activity and selectivity of the photocatalytic oxidative dehydrogenation of alkanes to produce olefins can be adjusted.

[0030] According to an embodiment of the present invention, a method for preparing a photocatalyst includes: mixing a Pd source and a TiO2{001} support in water, adding a reducing agent to reduce the Pd source, and drying under vacuum to obtain a Pd-loaded TiO2{001}; mixing the Pd-loaded TiO2{001} with other metal sources in water, adding a reducing agent to reduce the other metal sources, and drying under vacuum to obtain a TiO2{001} loaded with a bimetallic alloy; wherein, the other metal sources include any one of Fe source, Ni source, Cu source, Zn source, Pt source, Ag source, and Au source.

[0031] In embodiments of the present invention, a bimetallic alloy can be obtained by first reducing the Pd source and then reducing other metal sources. While a bimetallic alloy can still be obtained by reversing the order of addition of the Pd source and other metal sources, the activity of the resulting photocatalyst in catalyzing the oxidative dehydrogenation of alkanes decreases, leading to a reduction in olefin selectivity. Furthermore, the method for preparing the photocatalyst in this invention is relatively simple. By mixing different amounts of Pd source with TiO2{001} in water, and then reducing with a reducing agent and vacuum drying, TiO2{001} with different Pd loadings can be obtained. Subsequently, different amounts of other metal sources are mixed with TiO2{001} with different Pd loadings in water, and then reduced with a reducing agent and vacuum dried to obtain different bimetallic alloys and TiO2{001} with different loadings.

[0032] According to embodiments of the present invention, the Pd source is selected from Na₂PdCl₄; the Ni source is selected from Ni(NO₃)₂; the Cu source is selected from Cu(NO₃)₂; the Zn source is selected from ZnCl₂; the Pt source is selected from H₂PtCl₆; the Ag source is selected from AgNO₃; and the Au source is selected from HAuCl₄. The reducing agent is selected from sodium borohydride (NaBH₄).

[0033] Taking Na₂PdCl₄ and AgNO₃ as examples, the method for preparing the photocatalyst includes: mixing Na₂PdCl₄ with a TiO₂{001} support in water, adding NaBH₄ and reducing at 30°C for 1 h, followed by vacuum drying (200 Pa) at 60°C for 10-12 h to obtain Pd-supported TiO₂{001}. Then, mixing AgNO₃ with the Pd-supported TiO₂{001} in water, adding NaBH₄ and reducing at 30°C for 1 h, followed by vacuum drying at 60°C for 10-12 h to obtain a photocatalyst with a Pd-Ag bimetallic alloy supported on a TiO₂{001} support.

[0034] According to embodiments of the present invention, Pd and Ag sources are preferably used to prepare the photocatalyst. When the bimetallic alloy is a Pd-Ag alloy, the amount of Pd-Ag alloy used is 10 mg; in the Pd-Ag alloy, the loading of Pd is 0.5 wt% and the loading of Ag is 0.25 wt%. When the bimetallic alloy is a Pd-Ag alloy, the volume ratio of oxygen, nitrogen, and ethane in the mixed gas is 3.3:46.7:50, and the flow rate of the mixed gas is 50 mL / min; the power of the xenon lamp is 300 W, and the illuminance of the xenon lamp is 10.7 mW / cm². 2 The activity and selectivity of photocatalytic ethane oxidative dehydrogenation to ethylene can be adjusted by regulating the amount of photocatalyst composed of Pd-Ag alloy and TiO2{001} support, the composition and flow rate of the mixed gas, and the light intensity of the xenon lamp.

[0035] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0036] It should be noted that the ethane, oxygen, nitrogen, Pd source, Fe source, Ni source, Cu source, Zn source, Pt source, Ag source, Au source, and NaBH4 used in this invention are all commercially available products, and the water used is deionized water. A gas chromatograph (Furi GC-9790II) was used to detect a series of organic compounds such as methane and ethane, as well as H2, O2, and CO. y Inorganic gases (including CO and CO2) and others.

[0037] Ethane conversion rate = (Total ethane before reaction - Total ethane after reaction) / Total ethane before reaction

[0038] Ethylene selectivity = Ethylene production / (Total ethane before reaction - Total ethane after reaction).

[0039] CO y Selectivity = 2 × CO y Amount produced / (Total ethane before reaction - Total ethane after reaction).

[0040] Example 1

[0041] TiO2{001} support was mixed with different amounts of Na2PdCl4 in deionized water, and Na2PdCl4 was reduced by NaBH4 reduction method. After vacuum drying at 60℃ for 12 h, photocatalysts with different Pd loadings (referred to as "Xwt%Pd-TiO2{001}") were obtained, where the Pd loading X was 0.1, 0.25, 0.5, 0.75, and 1.

[0042] 10 mg of photocatalysts with different Pd loadings (Xwt%Pd-TiO2{001}) were evenly spread at the bottom of a planar mobile phase photocatalytic reactor. A mixed gas of oxygen, nitrogen, and ethane in a volume ratio of 3.3:46.7:50 was then introduced into the reactor at a flow rate of 50 mL / min. After venting for 1 hour, the reactor was placed under a 300W xenon lamp to directly irradiate the photocatalyst, with the lamp intensity controlled at 10.7 mW / cm². 2 The photocatalytic reaction to produce ethylene via oxidative dehydrogenation was carried out. Gas chromatography was used to detect the gas content and composition before and after the reaction to evaluate the photocatalytic performance. Specific test results are as follows: Figure 1 As shown.

[0043] Figure 1 This is a graph showing the photocatalytic reaction performance of the photocatalyst in Example 1 of the present invention.

[0044] like Figure 1 As shown, when only TiO2{001} is used as a photocatalyst, the main product of the oxidative dehydrogenation reaction of ethane is CO. y As the Pd loading increases, ethylene (C2H4) is gradually produced, with the highest selectivity for ethylene and ethane conversion rate observed at a Pd loading of 0.5 wt%. As the Pd loading further increases from 0.5 wt% to 0.75 wt%-1 wt%, the selectivity for ethylene and the ethane conversion rate gradually decrease. Therefore, the preferred Pd loading is 0.5 wt%.

[0045] Example 2

[0046] Based on Example 1, a second metal is introduced to form a bimetallic alloy. Specifically, the method for preparing the TiO2{001} photocatalyst supported on the bimetallic alloy is as follows: 0.5wt% Pd-TiO2{001} is mixed with 0.5wt% of other metal sources (M source, M = Fe, Ni, Cu, Zn, Pt, Ag, Au) in deionized water. The other metal sources are reduced by NaBH4 reduction method. After vacuum drying at 60°C for 12 h, a photocatalyst containing Pd and other metals forming a bimetallic alloy (referred to as "0.5wt%-Pd-0.5wt%M-TiO2{001}") is obtained.

[0047] 10 mg of a photocatalyst containing a bimetallic alloy (0.5 wt% Pd-0.5 wt% M-TiO2{001}) was evenly spread at the bottom of a planar mobile phase photocatalytic reactor. A mixed gas of oxygen, nitrogen, and ethane in a volume ratio of 3.3:46.7:50 was then introduced into the reactor at a flow rate of 50 mL / min. After venting for 1 hour, the reactor was placed under a 300 W xenon lamp to directly irradiate the photocatalyst, with the lamp's intensity controlled at 10.7 mW / cm². 2 The photocatalytic reaction to produce ethylene via oxidative dehydrogenation was carried out. Gas chromatography was used to detect the gas content and composition before and after the reaction to evaluate the photocatalytic performance. Specific test results were obtained. Figure 2 As shown.

[0048] Figure 2 This is a graph showing the photocatalytic reaction performance of the photocatalyst in Example 2 of the present invention.

[0049] like Figure 2As shown, under the same test conditions, among bimetallic alloys formed by Pd and other metals, Pd-Ag alloy has higher ethylene selectivity and ethane conversion rate, followed by Pd-Au alloy. However, Pd-Au alloy is more expensive, so Pd-Ag alloy is preferred.

[0050] Example 3

[0051] Based on Example 2, the effect of Ag loading on the photocatalytic performance of the formed photocatalyst containing bimetallic alloy was investigated.

[0052] 0.5wt% Pd-TiO2{001} was mixed with different amounts of AgNO3 in deionized water, and AgNO3 was reduced by NaBH4 reduction. After vacuum drying at 60℃ for 12 h, a photocatalyst containing bimetallic alloys with different Ag loadings (referred to as "0.5wt%Pd-Xwt%Ag-TiO2{001}") was obtained, where the Ag loading X was 0.1, 0.25, 0.5, 0.75, and 1.

[0053] Ten mg of photocatalyst containing bimetallic alloys with varying Ag loadings was spread evenly at the bottom of a planar mobile phase photocatalytic reactor. A mixed gas of oxygen, nitrogen, and ethane in a volume ratio of 3.3:46.7:50 was then introduced into the reactor at a flow rate of 50 mL / min. After venting for 1 hour, the reactor was placed under a 300W xenon lamp for direct irradiation of the photocatalyst, with the lamp intensity controlled at 10.7 mW / cm². 2 The photocatalytic reaction to produce ethylene via oxidative dehydrogenation was carried out. Gas chromatography was used to detect the gas content and composition before and after the reaction to evaluate the photocatalytic performance. Specific test results are as follows: Figure 3 As shown.

[0054] Figure 3 This is a graph showing the photocatalytic reaction performance of the photocatalyst in Example 3 of the present invention.

[0055] like Figure 3 As shown, under the same test conditions, the Pd-Ag alloy formed by 0.5 wt% Pd and 0.25-1 wt% Ag exhibits higher ethylene selectivity, with the 0.5 wt% Pd-0.25 wt% Ag combination showing a higher ethane conversion rate compared to 0.5-1 wt% Ag. Therefore, the preferred photocatalyst is 0.5 wt% Pd-0.25 wt% Ag-TiO2{001}.

[0056] Example 4

[0057] The photocatalytic performance was tested using 10 mg of the 0.5 wt% Pd-0.25 wt% Ag-TiO2{001} photocatalyst from Example 3 and the method of ethane oxidative dehydrogenation to ethylene. The difference was that the volume ratio of ethane to oxygen in the mixed gas was adjusted (ethane (C2H6): oxygen (O2) = 50:0, 50:2, 50:3.3, 50:5), with the remainder being nitrogen. The photocatalytic performance was evaluated by detecting the gas content and composition before and after the reaction in the planar mobile phase photocatalytic reactor using gas chromatography. Specific test results are shown below. Figure 4 As shown.

[0058] Figure 4 The graph shows the photocatalytic reaction performance of ethane and oxygen at different volume ratios in Example 4 of this invention.

[0059] like Figure 4 As shown, under the same 0.5wt%Pd-0.25wt%Ag-TiO2{001} photocatalyst, increasing the volume ratio of oxygen (e.g., increasing the volume ratio of ethane to oxygen from 50:0 to 50:3.3) can improve the selectivity of ethylene and the conversion rate of ethane. Further, increasing the volume ratio of ethane to oxygen from 50:3.3 to 50:5 results in excessive oxidation of the system, leading to a decrease in both ethylene selectivity and ethane conversion rate.

[0060] Example 5

[0061] The method for producing ethylene from ethane by oxidative dehydrogenation was employed using 10 mg of the 0.5 wt% Pd-0.25 wt% Ag-TiO2{001} photocatalyst from Example 3. The volume ratio of ethane to oxygen was kept constant at 50:3.3 for photocatalytic reaction performance testing. The difference was that the light intensity of the xenon lamp was changed to 4.7 mW / cm². 2 6.3mW / cm 2 7.6mW / cm 2 8.9mW / cm 2 10.7mW / cm 2 All other conditions remained the same. The photocatalytic reaction performance was evaluated by detecting the gas content and composition before and after the reaction in the planar mobile phase photocatalytic reactor using gas chromatography. Specific test results are shown below. Figures 5A-5B As shown.

[0062] Figure 5A This is a graph showing the photocatalytic reaction performance under different light intensities in Example 5 of the present invention.

[0063] like Figure 5AAs shown, the conversion rate of ethane increases rapidly with increasing xenon lamp light intensity. For example, under the same light intensity, the 0.5wt%Pd-0.25wt%Ag-TiO2{001} photocatalyst exhibits higher photocatalytic performance (e.g., ethane conversion rate) compared to the 0.5wt%Pd-TiO2{001} photocatalyst and TiO2{001} photocatalyst. Furthermore, under the same light intensity, the reaction temperature changes significantly for different photocatalysts; however, with increasing xenon lamp light intensity, the corresponding reaction temperature gradually increases, reaching 10.7 mW / cm². 2 At that time, the reaction temperature reaches 150-160℃.

[0064] Figure 5B The graph shows the photocatalytic reaction performance of Example 5 of the present invention at different reaction temperatures.

[0065] like Figure 5B As shown, when only the reaction temperature changes, different photocatalysts do not exhibit any catalytic activity, indicating that the oxidative dehydrogenation of the present invention is controlled by the photocatalytic reaction rather than by temperature.

[0066] Example 6

[0067] The method for producing ethylene by ethane oxidation and deoxygenation was employed using 10 mg of the 0.5 wt% Pd-0.25 wt% Ag-TiO2{001} photocatalyst from Example 3, while maintaining a xenon lamp illumination intensity of 10.7 mW / cm². 2 The ethane-oxygen oxidative dehydrogenation reaction to ethylene was carried out in a mixed gas with a volume ratio of 50:3.3 and a flow rate of 50 mL / min to evaluate the stability of the photocatalytic performance. Specific test results are as follows: Figure 6 As shown.

[0068] Figure 6 The figure shows the results of the photocatalytic reaction stability test in Example 6 of the present invention.

[0069] like Figure 6 As shown, the 0.5wt%Pd-0.25wt%Ag-TiO2{001} photocatalyst in Example 3 of this invention maintained high ethylene selectivity (76.9%) and ethane conversion rate (115.7 mmol·g) in a long-term stability test of 150 h. -1 ·h -1 ).

[0070] Furthermore, the 0.5wt%Pd-0.5wt%Ag-TiO2{001} photocatalyst in Example 3 of the present invention was characterized by electron microscopy, and the specific characterization results are shown in the figure below. Figures 7A-7B As shown.

[0071] Figure 7A The images show the transmission electron microscope (TEM) image and particle size distribution of the photocatalyst in Example 3 of this invention.

[0072] like Figure 7A As shown, the particle size of the Pd-Ag alloy particles in Example 3 of this invention is mainly concentrated at around 3.3 nm.

[0073] Figure 7B This is an elemental distribution diagram of the photocatalyst in Example 3 of the present invention.

[0074] like Figure 7B As shown in the elemental distribution diagram, the distribution patterns of Pd and Ag are very similar, and both are evenly dispersed.

[0075] Figure 8 for Figure 7A Linear scanning images of alloy particles in a magnified area using transmission electron microscopy (TEM), where a represents the alloy particles and the scanning direction from left to right, and b represents the scanning result corresponding to the scanning direction a.

[0076] like Figure 8 As shown, TEM linear scanning revealed that Pd and Ag were uniformly distributed, proving that Pd-Ag were alloy particles grown together, and that the loading of Pd was 0.5 wt% and the loading of Ag was 0.25 wt%.

[0077] Comparative Example 1

[0078] Na₂PdCl₄, AgNO₃, and TiO₂{001} support were mixed in deionized water and deposited by photodeposition. After vacuum drying at 60℃ for 12 h, a photocatalyst with Pd and Ag nanoparticles loaded on the TiO₂{001} support was obtained. The Pd loading was 0.5 wt%, and the Ag loading was 0.25 wt%. This photocatalyst was named Pd001. 0.5wt% -Ag 0.25wt% -TiO2{001}.

[0079] Comparative Example 2

[0080] AgNO3 and TiO2{001} support were mixed in deionized water, and the Ag source was reduced by NaBH4 reduction. After vacuum drying at 60℃ for 12 h, 0.25wt% Ag-TiO2{001} was obtained. Then, 0.25wt% Ag-TiO2{001} was mixed with Na2PdCl4 in deionized water, reduced by NaBH4 reduction, and vacuum dried at 60℃ for 12 h. The resulting photocatalyst was named 0.25wt% Ag-0.5wt% Pd-TiO2{001}.

[0081] 10 mg of the 0.5 wt% Pd-0.25 wt% Ag-TiO2{001} from Example 3 above, as well as the photocatalysts prepared in Comparative Examples 1 and 2, were respectively spread evenly at the bottom of a planar mobile phase photocatalytic reactor. A mixed gas of oxygen, nitrogen, and ethane in a volume ratio of 3.3:46.7:50 was then introduced into the planar mobile phase photocatalytic reactor at a flow rate of 50 mL / min. After venting for 1 hour, the reactor was placed under a 300W xenon lamp to directly irradiate the photocatalyst. The xenon lamp was turned on, and the light intensity was controlled at 10.7 mW / cm². 2 An oxidative dehydrogenation reaction was carried out, and the gas content and composition before and after the reaction were detected by gas chromatography to evaluate the photocatalytic performance. Specific test results were obtained. Figure 9 As shown.

[0082] Figure 9 This is a comparison chart of the photocatalytic reaction performance of different photocatalysts in Example 3, Comparative Examples 1-2 of the present invention.

[0083] like Figure 9 As shown, the 0.5wt%Pd-0.5wt%Ag-TiO2{001} photocatalyst in Example 3 of this invention exhibits higher ethylene selectivity and ethane conversion rate, with ethylene as the main product; while the Pd photocatalyst in Comparative Example 1... 0.5wt% -Ag 0.25wt% The main product of the oxidative dehydrogenation reaction of TiO2{001} photocatalyst is methane, with low selectivity for ethylene. Although the 0.25wt%Ag-0.5wt%Pd-TiO2{001} prepared by changing the order of Ag and Pd source addition is also a bimetallic alloy, its application in the oxidative dehydrogenation reaction will reduce the ethylene selectivity and ethane conversion rate.

[0084] Example 7

[0085] 10 mg of the 0.5 wt% Pd-0.25 wt% Ag-TiO2{001} photocatalyst from Example 3 was spread evenly at the bottom of the planar mobile phase photocatalytic reactor. A mixed gas of oxygen, nitrogen, and propane in a volume ratio of 3.3:46.7:50 was then introduced into the reactor at a flow rate of 50 mL / min. After venting for 1 hour, the reactor was placed under a 300W xenon lamp to directly irradiate the photocatalyst. The xenon lamp was turned on, and its light intensity was controlled at 10.7 mW / cm². 2 An oxidative dehydrogenation reaction was conducted to evaluate the photocatalytic performance; specific test results were obtained. Figure 10 As shown.

[0086] Figure 10 This is a performance diagram of photocatalytic oxidation dehydrogenation to propylene in Example 7 of the present invention.

[0087] like Figure 10 As shown, the 0.5wt%Pd-0.25wt%Ag-TiO2{001} photocatalyst in Example 3 of this invention exhibits high propylene selectivity (over 50%) and propane conversion rate in the reaction of propane oxidative dehydrogenation to propylene.

[0088] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are 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 photocatalytic oxidative dehydrogenation of alkanes to olefins, characterized in that, include: A reaction in which a xenon lamp is used as a light source and a mixed gas containing alkanes is introduced into a photocatalytic reactor loaded with a photocatalyst, and the alkanes in the mixed gas undergo oxidative dehydrogenation to produce olefins under light irradiation conditions; The photocatalyst includes a TiO2{001} support and a bimetallic alloy supported on the TiO2{001} support. The bimetallic alloy is an alloy formed by Pd and other metals, and the other metals are selected from either Ag or Au. The mixed gas further includes oxygen and inert gas, and the volume ratio of oxygen, inert gas and alkane in the mixed gas is (2-5):(45-48):50; The alkane is ethane or propane, and the olefin is ethylene or propylene.

2. The method according to claim 1, characterized in that, The flow rate of the mixed gas is 10 mL / min to 75 mL / min.

3. The method according to claim 1, characterized in that, The xenon lamp has a power of 130W-300W and a luminous intensity of 4.7-10.7mW / cm². 2 .

4. The method according to claim 1, characterized in that, The inert gas is nitrogen or argon.

5. The method according to claim 1, characterized in that, The photocatalyst is obtained by the following method: The Pd source and TiO2{001} support were mixed in water, and a reducing agent was added to reduce the Pd source. After vacuum drying, TiO2{001} loaded with Pd was obtained. The Pd-loaded TiO2{001} and other metal sources are mixed in water, a reducing agent is added to reduce the other metal sources, and the mixture is dried under vacuum to obtain TiO2{001} loaded with a bimetallic alloy. The other metal sources are selected from either Ag or Au sources.

6. The method according to claim 5, characterized in that, The Ag source is selected from AgNO3; The Au source is selected from HAuCl4.

7. The method according to claim 1, characterized in that, The amount of the photocatalyst used is 5mg-100mg; In the photocatalyst, the loading of Pd is 0.1wt%-1wt% based on the mass of the TiO2{001} support, and the loading of the other metals is 0.1wt%-1wt%.

8. The method according to any one of claims 1-7, characterized in that, The bimetallic alloy is a Pd-Ag alloy; The amount of the Pd-Ag alloy used is 10 mg; In the Pd-Ag alloy, the loading of Pd is 0.5 wt% and the loading of Ag is 0.25 wt%.

9. The method according to claim 8, characterized in that, In the mixed gas, the volume ratio of oxygen, inert gas and alkane is 3.3:46.7:50; The flow rate of the mixed gas is 50 mL / min, and the alkane is ethane.

10. The method according to claim 9, characterized in that, The xenon lamp has a power of 300W and a luminous intensity of 10.7mW / cm². 2 .

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