Gold-supported TiO2 catalysts with lattice shrinkage, their preparation methods and applications

Abstract

The application belongs to the technical field of photocatalysts, and particularly discloses a gold-loaded lattice-contracted TiO2 catalyst as well as a preparation method and application thereof. Firstly, by loading gold on the annealed titanium dioxide, the inert C-H bond in the methane molecule can be effectively activated in the photocatalytic process, the activation energy of the reaction is reduced, and thus the conversion rate of methane is improved, which can reach 70 mmol / g / h of C 2+ The yield of the product, wherein the yield of ethane is 66 mol / g / h. Secondly, the catalyst exhibits excellent selectivity. In the reaction of methane oxidative coupling to prepare ethane, the reaction path can be accurately guided to the direction of generating ethane, and the occurrence of other side reactions is effectively inhibited, and the selectivity of the catalyst to C 2+ The product can be as high as 95%. Finally, the catalyst of the application has excellent stability. After 50h of catalytic reaction, the performance does not change obviously, and the catalytic activity and selectivity can be relatively stable without obvious decline.

Description

Technical Field

[0001] This invention belongs to the field of photocatalyst technology, specifically relating to gold-supported lattice-shrinking TiO2 catalysts, their preparation methods, and applications. Background Technology

[0002] In the chemical industry, given the limited availability of coal and oil resources, directly and selectively converting methane (CH4), the main component of methane hydrates and shale gas reserves, into high-value hydrocarbons has become an ideal strategy to reduce dependence on coal and crude oil.

[0003] However, CH4 is inert, and its high CH bond dissociation energy (439 kJ·mol⁻¹) -1 The low polarizability and demanding nature of methane mean that its conversion typically requires harsh reaction conditions or strong oxidants, making the conversion process extremely difficult. The conversion of methane to ethane (C2H6) and ethylene (C2H4) can be achieved via non-oxidative coupling (NOCM) or oxidative coupling (OCM), but these thermocatalytic processes require high temperatures of approximately 600°C, leading to undesirable side reactions such as carbon deposition in NOCM and excessive oxidation in OCM, as well as significant energy waste.

[0004] Ethane has a wide range of uses. It can be used as fuel in household stoves and outdoor barbecues. In the petrochemical industry, it is a raw material for the production of ethylene, which can be produced through steam cracking. High-purity ethane can be used as an extraction solvent in chemical laboratories and as a reaction solvent in liquid chromatography analysis. Due to its low boiling point, it can also be used as a refrigerant.

[0005] Various photocatalysts show great potential in the coupling of methane to C2 products, with selectivity ranging from 60% to 99%, such as Pt-CuOx / TiO2, Pd-Bi / Ga2O3, Au-ZnO / TiO2, and Zn5(OH)8Cl2·H2O. However, the methane conversion rates of all methane coupling photocatalysts are at a moderate level, only reaching µmol·h⁻¹. -1 Order of magnitude, some even below 1 µmol·h -1 .

[0006] In summary, existing methane conversion technologies, whether thermocatalytic or photocatalytic, have significant drawbacks. While thermocatalysis can achieve methane conversion, it involves high reaction temperatures, numerous side reactions, and substantial energy waste. Photocatalysis, although offering better selectivity, suffers from low methane conversion rates, making it difficult to meet the demands of large-scale industrial production. Therefore, there is an urgent need to develop high-yield, highly selective, and highly stable photocatalytic oxidation coupling catalysts for methane to address these issues. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention proposes a gold-supported lattice-shrinking TiO2 catalyst, its preparation method, and its application, to achieve high yield, high selectivity, and high stability in the photocatalytic oxidative coupling of methane to ethane.

[0008] In a first aspect, the present invention provides a gold-supported lattice-shrinking TiO2 catalyst, the catalyst comprising annealed titanium dioxide and gold supported on titanium dioxide.

[0009] Secondly, the present invention provides a method for preparing the above-mentioned gold-supported lattice-shrinking TiO2 catalyst, comprising the following steps: S1. Anneal the nano-titanium dioxide to obtain annealed titanium dioxide. S2. Add deionized water to a beaker, then add a soluble gold salt solution, then add annealed titanium dioxide, stir, add a reducing agent, continue stirring to react, and after the reaction is complete, use an aqueous filter membrane to filter and wash with deionized water. S3. The powder on the filter membrane is vacuum dried to obtain a titanium dioxide catalyst supported on gold and annealed.

[0010] Preferably, the purity of the nano-titanium dioxide in S1 is 99.8%, and it is annealed in an air atmosphere at an air flow rate of 20 mL / min and a heating rate of 2 °C / min in a tube furnace at 600 °C for 3 hours.

[0011] Preferably, the soluble gold salt solution in S2 is a HAuCl4·3H2O solution.

[0012] Preferably, the reducing agent in S2 is NaBH4.

[0013] Preferably, in step S2, 160 mL of deionized water is added to the beaker, followed by the addition of 0.8 mL of HAuCl4·3H2O solution with a concentration of 5 mg / mL, and 200 mg of annealed titanium dioxide is added. After stirring for 10 minutes, 30 mg of NaBH4 is added and stirred at room temperature for 3 hours.

[0014] Preferably, the vacuum drying temperature in step S3 is 60°C.

[0015] Preferably, the gold loading in the gold-loaded annealed titanium dioxide catalyst obtained in S3 is 2%.

[0016] Thirdly, the present invention provides the application of the above-mentioned gold-supported lattice-shrinking TiO2 catalyst in the photocatalytic oxidative coupling of methane to ethane.

[0017] The beneficial effects of this invention are: First, by loading gold onto annealed titanium dioxide, a unique catalytic active center structure is formed, and a synergistic effect is generated between the gold nanoparticles and titanium dioxide. This synergistic effect significantly enhances the catalytic activity of the catalyst for the methane oxidative coupling reaction. During photocatalysis, it can effectively activate the inert CH bonds in the methane molecule, reduce the activation energy of the reaction, and thus improve the methane conversion rate, achieving a Cconversion of 70 mmol / g / h. 2+ The product yield was high, with ethane yielding 66 mol / g / h. Secondly, the catalyst exhibited excellent selectivity. In the oxidative coupling of methane to ethane, it precisely guided the reaction pathway towards ethane production, effectively suppressing other side reactions. Its effect on C2C... 2+ The product selectivity can reach up to 95%. Finally, the catalyst of this invention exhibits excellent stability. No significant change in performance was observed after 50 hours of catalytic reaction; both its catalytic activity and selectivity remained relatively stable without any noticeable decline. This is attributed to the stable chemical bonding between gold and annealed titanium dioxide, as well as the stability of the catalyst structure. This reduces the risk of catalyst deactivation during the reaction process, extends the catalyst's lifespan, and lowers the frequency and cost of catalyst replacement in industrial applications. Therefore, this catalyst shows promising application prospects in the large-scale industrial production of methane through oxidative coupling to ethane, effectively promoting the efficient utilization of methane resources in the chemical industry, reducing dependence on traditional resources such as coal and crude oil, and providing strong technical support for the development of sustainable energy and the chemical industry. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a transmission electron microscope image of the 2% Au / TiO2(600) catalyst.

[0020] Figure 2 This is a mapping diagram of the 2% Au / TiO2(600) catalyst.

[0021] Figure 3 This is a particle size distribution diagram of gold nanoparticles corresponding to the 2% Au / TiO2(600) catalyst.

[0022] Figure 4 These are emission spectra of the 2% Au / TiO2(600) catalyst at different temperatures. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0024] Example 1 This embodiment provides a method for preparing a gold-supported lattice-shrinking TiO2 catalyst, including the following steps: S1. The 99.8% nano titanium dioxide (anatase) of the product is annealed in an air atmosphere at an air flow rate of 20 mL / min and a heating rate of 2℃ / min in a tube furnace at 600℃ for 3 hours. S2. Add 160 mL of deionized water to a 400 mL beaker, then add 0.8 mL of 5 mg / mL HAuCl4·3H2O solution dropwise, add 200 mg of annealed titanium dioxide, stir for 10 minutes, and then add 30 mg of NaBH2O. 4， Stir for 3 hours at room temperature; after stirring, filter the above solution, wash the filter with deionized water, and use an aqueous filter membrane with specifications of 50mm×0.45um. S3. The catalyst powder on the filter paper was placed in a vacuum drying oven at 60℃ and dried overnight to obtain a gold-loaded annealed titanium dioxide catalyst, wherein the gold loading was 2%. Its transmission electron microscope image is shown below. Figure 1 As shown, the mapping diagram is as follows: Figure 2 As shown, the corresponding particle size distribution diagram of gold nanoparticles is as follows. Figure 3 As shown.

[0025] Example 2: Based on Example 1, the performance of the 2% Au / TiO2 catalyst was tested, and the specific process is as follows: 2.5 mg of catalyst was weighed and dissolved in 2 mL of anhydrous ethanol by ultrasonication. The solution was then filtered through a 37 mm diameter glass fiber membrane with a 1.2 μm pore size, allowing the catalyst to adsorb onto the membrane surface. The membrane was dried using a heater to remove the anhydrous ethanol. The membrane was then placed in a continuous flow reactor, illuminated by a 300 W xenon lamp. A mixture of pure CH4 gas at a flow rate of 89 mL / min and a 5% O2 and N2 mixture at a flow rate of 11 mL / min was introduced to initiate the reaction. The reactant gases flowed into the reactor from the bottom, passed through the catalyst, and finally entered a gas chromatograph for product analysis.

[0026] Example 3 Based on Example 2, the results obtained by gas chromatography in this example by changing the annealing temperature of titanium dioxide are shown in Table 1.

[0027] Table 1 Catalytic effect of catalysts at different titanium dioxide annealing temperatures ; The reaction results in the table above indicate that the catalyst of the present invention achieves the best catalytic effect when titanium dioxide is annealed at 600°C and loaded with gold.

[0028] Example 4 Based on Example 3, this example involves loading different proportions of gold onto titanium dioxide that has been annealed at the optimal temperature of 600°C. The results obtained by gas chromatography are shown in Table 2.

[0029] Table 2 Catalytic effects of catalysts with different proportions of gold loading ; The reaction results in the table above show that the addition of gold co-catalyst in the catalyst of the present invention greatly improves the yield of methane to ethane, and the best catalytic effect is achieved when the gold loading is 2%.

[0030] Example 5 Based on Example 4, the performance of 2% Au / TiO2 (600) was tested by changing different gas flow rates. The results obtained by gas chromatography are shown in Table 3.

[0031] Table 3 Effect of different gas flow rates on the catalytic effect of 2% Au / TiO2 (600) ; The reaction results in the table above show that the catalyst of the present invention achieves the best performance at a total flow rate of 110 mL / min.

[0032] Example 6 Based on Example 5, the performance of 2% Au / TiO2 (600) was tested by changing different gas ratios, and the results obtained by gas chromatography are shown in Table 4.

[0033] Table 4 Effect of different gas ratios on the catalytic effect of 2% Au / TiO2 (600) ; The reaction results in the table above show that the catalyst of the present invention achieves the best performance under the condition of CH4 / O2=160 / 1.

[0034] Example 7 Based on Example 1, this example uses fluorescence spectroscopy to test titanium dioxide with a 2% Au loading and annealed at different temperatures. The emission spectra are as follows: Figure 4As shown, the results indicate that 2% Au / TiO2 (600) has the weakest emission intensity, indicating that it has the strongest separation ability between photogenerated electrons and holes, and has better performance than titanium dioxide annealed at other temperatures.

[0035] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not describe all details exhaustively, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification.

Claims

1. A method for preparing a gold-supported TiO2 catalyst with lattice shrinkage, characterized in that, Includes the following steps: S1. Anneal the nano-titanium dioxide to obtain annealed titanium dioxide. S2. Add deionized water to a beaker, then add a soluble gold salt solution, then add annealed titanium dioxide, stir, add a reducing agent, continue stirring to react, and after the reaction is complete, use an aqueous filter membrane to filter and wash with deionized water. S3. The powder on the filter membrane is vacuum dried to obtain a titanium dioxide catalyst supported on gold and annealed.

2. The method for preparing the gold-supported lattice-shrinking TiO2 catalyst according to claim 1, characterized in that, The nano-titanium dioxide in S1 has a purity of 99.8%. It is annealed in an air atmosphere at an air flow rate of 20 mL / min and a heating rate of 2 °C / min in a tube furnace at 600 °C for 3 hours.

3. The method for preparing the gold-supported lattice-shrinking TiO2 catalyst according to claim 1, characterized in that, The soluble gold salt solution in S2 is HAuCl4·3H2O solution.

4. The method for preparing the gold-supported lattice-shrinking TiO2 catalyst according to claim 3, characterized in that, The reducing agent in S2 is NaBH4.

5. The method for preparing the gold-supported lattice-shrinking TiO2 catalyst according to claim 4, characterized in that, In step S2, 160 mL of deionized water is added to a beaker, followed by the addition of 0.8 mL of HAuCl4·3H2O solution with a concentration of 5 mg / mL. Then, 200 mg of annealed titanium dioxide is added, and the mixture is stirred for 10 minutes. Finally, 30 mg of NaBH4 is added and the mixture is stirred at room temperature for 3 hours.

6. The method for preparing the gold-supported lattice-shrinking TiO2 catalyst according to claim 5, characterized in that, The vacuum drying temperature in S3 is 60°C.

7. The method for preparing the gold-supported lattice-shrinking TiO2 catalyst according to claim 6, characterized in that, The gold loading in the gold-loaded annealed titanium dioxide catalyst obtained in S3 is 2%.

8. The application of the gold-supported lattice-shrinking TiO2 catalyst prepared according to any one of claims 1-7 in the photocatalytic oxidative coupling of methane to ethane.

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