Spherical ferro-titanite-supported photocatalyst for oxidative coupling of methane to ethane

Abstract

The present invention discloses a spherical ferro-titanium-supported photocatalyst for the oxidative coupling of methane to ethane. The spherical ferro-titanium-supported photocatalyst is prepared by first synthesizing highly crystalline Zn2Ti3O8 using a hydrothermal method, and then loading precious metal nanoparticles on the surface of the Zn2Ti3O8 using a NaBH4 reduction method. The precious metal nanoparticle loading is 0.5 to 1.5 wt%. The resulting photocatalyst promotes the separation of photogenerated carriers, effectively inhibits the recombination of photogenerated electrons and holes, and reduces the degree of overoxidation in the reaction, thereby significantly improving the efficiency of photocatalytic oxidative coupling of methane to ethane. Therefore, the photocatalyst has broad application prospects in efficiently utilizing solar energy to promote the conversion of methane into high-value-added industrial products.

Description

Technical Field

[0001] The present invention belongs to the technical field of photocatalytic methane conversion, and particularly relates to a spherical ferro-titanium-supported photocatalyst for producing ethane through oxidative coupling of methane and a preparation method thereof. Background Art

[0002] As the main component of natural gas, shale gas and combustible ice, methane (CH4) is not only cheap and abundant, but can also be used as a basic chemical raw material to be converted into other value-added chemicals. At the same time, as the second largest greenhouse gas, methane's greenhouse effect is about 25 times that of CO2. Although its emissions only account for 16% of the world's total greenhouse gas emissions, its contribution to global warming is as high as 25%. Due to the highly symmetrical tetrahedral structure of the CH4 molecule, its bond energy is high (439 kJ mol -1 ), with a dipole moment close to zero and a strong inertness, requiring high temperature and pressure for C-H bond activation. Therefore, traditional methane conversion relies primarily on energy-intensive, high-temperature reactions. However, such demanding, high-temperature reactions present challenges such as high energy consumption, severe catalyst deactivation, and significant product overoxidation. Photocatalytic technology, a green technology widely studied in recent years, is considered an effective solution to these problems. It can activate and dissociate methane C-H bonds under mild conditions, offering advantages such as low energy consumption, low cost, and high safety. It holds significant potential for methane conversion research.

[0003] Titanates are a class of functional materials with excellent electrical and optical properties and are widely used in photocatalytic research. They primarily have two structures: a perovskite-type structure belonging to the Pm3m space group, and a ferro-titanite structure with the R3 space group. ZnTiO3, a titanate with a typical ferro-titanite structure, is often accompanied by the formation of zinc orthotitanate during traditional solid-phase preparation, resulting in low sample purity. A previous invention (CN 110745863A) used a precipitant to synthesize micron-shaped Zn2Ti3O8, but its crystallinity was poor. To address this, the present invention utilizes a simple, convenient, and mild hydrothermal method. In the absence of a precipitant, high-temperature calcination is used to successfully prepare pure Zn2Ti3O8 with high crystallinity. Furthermore, by loading this material with precious metals, it can be used in the photocatalytic oxidative coupling of methane to ethane. Summary of the Invention

[0004] The present invention aims to provide an ilmenite-supported photocatalyst for the oxidative coupling of methane to ethane and its preparation method. This photocatalyst effectively promotes the separation of photogenerated charge carriers, improving the efficiency of the photoreaction while effectively reducing the degree of product overoxidation, thereby overcoming the shortcomings of conventional photocatalysts, such as poor stability, low activity, and low quantum efficiency. The photocatalyst is simple to synthesize, achieves high yields, and operates under mild photocatalytic reaction conditions, facilitating its widespread application in photocatalytic methane oxidative coupling reactions.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A spherical ferro-titanium ore-supported photocatalyst is prepared by first synthesizing high-crystallinity Zn2Ti3O8 using a hydrothermal method, and then supporting noble metal nanoparticles on the Zn2Ti3O8 using a NaBH4 reduction method. The preparation specifically comprises the following steps:

[0007] (1) A certain amount of zinc salt is dissolved in ethylene glycol, stirred for 0.5-24 h, and then a certain amount of tetrabutyl titanate is added dropwise. After stirring evenly, the mixture is transferred into a polytetrafluoroethylene kettle for reaction. The resulting solid is washed, dried, ground, and then calcined at high temperature in air to obtain Zn2Ti3O8 with high crystallinity.

[0008] (2) The prepared Zn2Ti3O8 was dispersed in deionized water, and then a noble metal precursor solution was added dropwise thereto. After continuous stirring, a NaBH4 aqueous solution was added dropwise for reduction treatment. The resulting precipitate was then filtered, washed, and dried to obtain a spherical ferro-titanium ore-supported photocatalyst.

[0009] Furthermore, the molar ratio of zinc salt to tetrabutyl titanate used in step (1) is (0.5-2):1.

[0010] Furthermore, the zinc salt in step (1) is zinc acetate, zinc nitrate or zinc chloride.

[0011] Furthermore, the reaction temperature in step (1) is 120-200°C and the reaction time is 2-48h.

[0012] Furthermore, the high temperature calcination in step (1) is carried out at a temperature of 500-800°C and a time of 0.5-8h.

[0013] Furthermore, the noble metal used in step (2) is derived from a chloride salt solution of Au, Pt, Pd or Ru.

[0014] Furthermore, the amount of NaBH4 added in step (2) is 1-10 times the mass of the precious metal precursor used.

[0015] Furthermore, the reduction treatment time in step (2) is 0.1-2 h.

[0016] Furthermore, the loading amount of the noble metal nanoparticles in the spherical ferro-titanium ore-supported photocatalyst obtained in step (2) is 0.5-1.5 wt%.

[0017] The obtained spherical ferro-titanium ore-supported photocatalyst can effectively promote the separation of photogenerated carriers, improve the efficiency of the photocatalytic reaction, and effectively reduce the degree of overoxidation of the product, and can be used for photocatalytic methane oxidative coupling to produce ethane.

[0018] The remarkable effects of the present invention are:

[0019] (1) In the present invention, a photocatalyst with good visible light response performance is prepared by reducing and loading precious metals as co-catalysts on the surface of Zn2Ti3O8 without adding a precipitant. The preparation method is simple and easy, which is conducive to its application in the photocatalytic methane oxidation to ethane reaction process.

[0020] (2) The photocatalyst obtained by the present invention can be used for oxidative coupling of methane to ethane under mild conditions with high conversion rate and good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The Zn2Ti3O8 prepared in Example 2 and the Au prepared in Example 3 1.0 / XRD spectrum of Zn2Ti3O8.

[0022] Figure 2 The Zn2Ti3O8 (a) prepared in Example 2 and the Au prepared in Example 3 1.0 / Zn2Ti3O8(b)SEM spectrum.

[0023] Figure 3 The Zn2Ti3O8 prepared in Example 2 and the Au prepared in Example 3 1.0 / DRS spectrum of Zn2Ti3O8.

[0024] Figure 4 This is a performance comparison chart of the samples prepared in Examples 2-5 for photocatalytic methane oxidative coupling to produce ethane.

[0025] Figure 5 This is a performance comparison chart of catalyst samples loaded with different precious metals for the photocatalytic oxidative coupling of methane to produce ethane. DETAILED DESCRIPTION

[0026] A spherical ferro-titanium ore-supported photocatalyst, the preparation method of which comprises the following steps:

[0027] (1) A certain amount of zinc salt is dissolved in ethylene glycol, stirred for 0.5-24 h, and then tetrabutyl titanate is added dropwise at a molar ratio of zinc salt to tetrabutyl titanate of (0.5-2):1. After stirring evenly, the mixture is transferred into a polytetrafluoroethylene kettle and hydrothermally reacted at 120-200 °C for 2-48 h. The obtained solid is washed, dried, and ground, and then calcined at 500-800 °C in air for 0.5-8 h to obtain Zn2Ti3O8 with high crystallinity.

[0028] (2) The prepared Zn2Ti3O8 was dispersed in deionized water, and then the noble metal precursor solution was added dropwise thereto. After continuous stirring, an aqueous solution of NaBH4 containing 1-10 times the mass of the noble metal precursor was added dropwise for reduction treatment for 0.1-2 h. The resulting precipitate was then filtered, washed, and dried to obtain a spherical ferro-titanium ore-supported photocatalyst M. x / Zn2Ti3O8, where the loading amount x of the noble metal nanoparticles is 0.5~1.5 wt%.

[0029] Wherein, the zinc salt in step (1) is zinc acetate, zinc nitrate or zinc chloride.

[0030] The noble metal precursor solution used in step (2) is a chloride salt solution of Au, Pt, Pd or Ru, and its concentration is 10 g / L.

[0031] In order to make the contents of the present invention easier to understand, the technical solutions of the present invention are further described below in conjunction with specific implementation methods, but the present invention is not limited thereto.

[0032] Example 1 Preparation of Zn2Ti3O8

[0033] 8 mmol of zinc acetate dihydrate was dissolved in 80 mL of ethylene glycol and stirred overnight. Then, 7 mmol of tetrabutyl titanate was added dropwise and stirred thoroughly. The solution was then transferred to a 100 mL polytetrafluoroethylene kettle and hydrothermally reacted in a 140°C oven for 12 hours. After cooling to room temperature, the resulting solid was filtered, washed, dried, and ground to a uniform consistency. It was then calcined in a muffle furnace at 550°C for 2 hours to obtain Zn2Ti3O8.

[0034] Example 2 Preparation of Zn2Ti3O8

[0035] Dissolve 10 mmol of zinc acetate dihydrate in 60 mL of ethylene glycol and stir overnight. Then, add 8 mmol of tetrabutyl titanate dropwise and stir until uniform. The solution is then transferred to a 100 mL polytetrafluoroethylene kettle and hydrothermally reacted in a 160°C oven for 20 hours. After cooling to room temperature, the resulting solid is filtered, washed, dried, and ground to a uniform consistency. It is then calcined in a muffle furnace at 700°C for 2 hours to obtain Zn2Ti3O8.

[0036] Example 3 Au 1.0 Preparation of Zn2Ti3O8

[0037] 400 mg of Zn2Ti3O8 prepared in Example 2 was dispersed in 60 mL of deionized water. After stirring and dispersing evenly, 0.4 mL of chloroauric acid aqueous solution (concentration of 10 g / L) was added dropwise thereto. Stirring was continued until the sample was evenly dispersed. Subsequently, 2 mL of the freshly prepared 6 mg / mL NaBH4 solution was added dropwise. After stirring for 15 min, the obtained sample was filtered, washed with deionized water, and dried in an oven to obtain Au 1.0 / Zn2Ti3O8.

[0038] Figure 1 For the prepared Zn2Ti3O8 and Au 1.0 / Zn2Ti3O8 XRD pattern. Figure 1 As shown in the figure, all the diffraction peaks in the XRD spectrum of the Zn2Ti3O8 sample match the standard XRD spectrum of Zn2Ti3O8 (PDF#87-1781), and the peaks are narrow and sharp, and no other impurity peaks are detected, indicating that a high crystallinity Zn2Ti3O8 sample is obtained. 1.0 In the XRD spectrum of the / Zn2Ti3O8 sample, no characteristic peaks of Au species were detected except the diffraction peaks of Zn2Ti3O8.

[0039] Figure 2 For the prepared Zn2Ti3O8 and Au 1.0 / Zn2Ti3O8 SEM image. As shown in the figure, Zn2Ti3O8 is a spherical structure, and the sample morphology does not change significantly before and after loading.

[0040] Figure 3 For the prepared Zn2Ti3O8 and Au 1.0 / Zn2Ti3O8 DRS map. As shown in the figure, Zn2Ti3O8 and Au 1.0 / Zn2Ti3O8 have good light absorption ability, but compared with Zn2Ti3O8, Au 1.0 / Zn2Ti3O8 light absorption is significantly increased.

[0041] Example 4 Au 0.5 Preparation of Zn2Ti3O8

[0042] 200 mg of Zn2Ti3O8 prepared in Example 2 was dispersed in 35 mL of deionized water. After stirring and dispersing evenly, 0.2 mL of chloroauric acid solution (concentration of 5 g / L) was added dropwise thereto. Stirring was continued until the sample was evenly dispersed. Subsequently, 5 mL of the freshly prepared 3 mg / mL NaBH4 solution was added dropwise. After stirring for 80 min, the obtained sample was filtered, washed with deionized water, and dried in an oven to obtain Au 0.5 / Zn2Ti3O8.

[0043] Example 5 Au 1.5 Preparation of Zn2Ti3O8

[0044] 200 mg of Zn2Ti3O8 prepared in Example 2 was dispersed in 100 mL of deionized water. After being uniformly dispersed by stirring, 0.3 mL of chloroauric acid solution (concentration of 10 g / L) was added dropwise thereto. Stirring was continued until the sample was uniformly dispersed. Subsequently, 3 mL of the freshly prepared 3 mg / ml NaBH4 solution was added dropwise. After stirring for 12 min, the obtained sample was filtered, washed with deionized water, and dried in an oven to obtain Au 1.5 / Zn2Ti3O8.

[0045] Example 6 Preparation of Catalysts Loaded with Different Precious Metals

[0046] 200 mg of Zn2Ti3O8 prepared in Example 2 was dispersed in 60 mL of deionized water. After being uniformly dispersed by stirring, 0.2 mL of palladium chloride solution, ruthenium chloride solution and platinum chloride solution (concentration of 10 g / L) were added dropwise thereto respectively. The stirring was continued until the sample was uniformly dispersed. Subsequently, 10 ml of the freshly prepared 3 mg / ml NaBH4 solution was added dropwise. After stirring for 23 min, the obtained sample was filtered, washed with deionized water and dried in an oven to obtain Pd 1.0 / Zn2Ti3O8、Ru 1.0 / Zn2Ti3O8、Pt 1.0 / Zn2Ti3O8.

[0047] Application Example: Photocatalytic oxidative coupling of CH4 to produce C2H6

[0048] 30 mg of the catalyst was placed in a quartz dish, 1 mL of H₂O was added dropwise, and ultrasonic dispersion was achieved. The mixture was then transferred to an oven and baked for 20 minutes to form a uniform catalyst film. In a batch glass reactor equipped with a quartz window, the quartz dish containing the treated catalyst was fixed in the center of the reactor. CH₄ and O₂ were pumped in, and the product was detected after illumination.

[0049] Figure 4This is a performance comparison chart of the catalyst samples prepared in Examples 2-5 for photocatalytic methane oxidative coupling to produce ethane. As shown in the figure, under light irradiation, Au 1.0 / Zn2Ti3O8 has the best photocatalytic performance, and its photocatalytic reduction of CH4 to produce C2H6 by oxidative coupling is 609.5 μmol·g -1 ·h -1 , which is about 175 times that of the Zn2Ti3O8 sample.

[0050] Figure 5 The following chart compares the performance of catalyst samples loaded with different precious metals in the photocatalytic oxidative coupling of methane to ethane. As can be seen from the figure, under the same precious metal loading conditions, Au-loaded Zn2Ti3O8 has the best photocatalytic activity for the oxidative coupling of methane to ethane.

[0051] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. Use of a spherical ferro-titanium-supported photocatalyst in photocatalytic oxidative coupling of methane to ethane, characterized by: The spherical ferro-titanium ore-loaded photocatalyst is prepared by first synthesizing high-crystallinity Zn2Ti3O8 using a hydrothermal method, and then loading precious metal nanoparticles on the Zn2Ti3O8 using a NaBH4 reduction method, wherein the obtained Zn2Ti3O8 has a spherical structure, and the precious metal nanoparticles are specifically Au nanoparticles, and their loading amount is 0.5~1.5 wt%.

2. The use according to claim 1, characterized in that: The preparation of the spherical ferro-titanium ore-supported photocatalyst comprises the following steps: (1) A certain amount of zinc salt is dissolved in ethylene glycol, stirred for 0.5-24 h, and then a certain amount of tetrabutyl titanate is added dropwise. After stirring evenly, the reaction is carried out in a hydrothermal reactor. The obtained solid is washed, dried, ground, and then calcined at high temperature in air to obtain Zn2Ti3O8 with high crystallinity. (2) The prepared Zn2Ti3O8 is dispersed in deionized water, and then a noble metal precursor solution is added dropwise thereto. After continuous stirring, a NaBH4 aqueous solution is added dropwise for reduction treatment. The resulting precipitate is then filtered, washed, and dried to obtain the spherical ferro-titanium ore-supported photocatalyst.

3. The use according to claim 2, characterized in that: The molar ratio of zinc salt to tetrabutyl titanate used in step (1) is (0.5-2):

1.

4. The use according to claim 2 or 3, characterized in that: The zinc salt is zinc acetate, zinc nitrate or zinc chloride.

5. The use according to claim 2, characterized in that: The reaction temperature in step (1) is 120-200°C and the reaction time is 2-48 h.

6. The use according to claim 2, characterized in that: The high-temperature calcination in step (1) is carried out at a temperature of 500-800°C and a time of 0.5-8 h.

7. The use according to claim 2, characterized in that: The noble metal precursor used in step (2) is the chloride of the noble metal element Au.

8. The use according to claim 2, characterized in that: The amount of NaBH4 added in step (2) is 1-10 times the mass of the precious metal precursor used.

9. The use according to claim 2, characterized in that: The reduction treatment time in step (2) is 0.1-2h.

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