Preparation method of copper-palladium alloy loaded nano titanium dioxide material for producing methane through photocatalytic reduction of carbon dioxide

Abstract

The invention discloses a preparation method of a copper-palladium alloy loaded nano titanium dioxide semiconductor material as a catalyst for a carbon dioxide reduction reaction. Firstly, alloy nanoparticles are generated through a sol-gel method, the morphology of the nanoparticles is controlled and agglomeration is prevented through oleylamine and oleic acid, and borane-tert-butylamine is added at the temperature of 170 DEG C to regulate and control the sizes of the generated alloy nanoparticles. A series of characterizations prove that the catalyst has a very good particle loading condition, uniform particle distribution and increased reaction active sites, and shows excellent activity when being applied to a carbon dioxide reduction reaction, when the loading capacities of copper and palladium are respectively 1%, the activity of the obtained catalyst is the highest, the methane generation rate can reach 20.23 mol / g / h, and the methane generation rate can reach 20.23 mol / g / h. The selectivity of methane reaches 100%.

Description

Technical Field

[0001] This invention belongs to the technical fields of advanced nanomaterials, energy conversion and photocatalysis, and specifically relates to a method for preparing a copper-palladium alloy supported titanium dioxide surface as a carbon dioxide reduction catalyst. Background Technology

[0002] Photocatalytic reduction of carbon dioxide (CO2) is a high-value carbon-based fuel and a potential solution to the greenhouse effect and energy crisis. Among the many reduction products, methane (CH4) has attracted much attention due to its high energy density and important value as a basic chemical feedstock. The photocatalytic reduction of CO2 produces various products, but selectively converting CO2 to CH4 remains a significant challenge. This is because the reduction of CO2 to CH4 is a multi-step process involving eight electrons and eight protons, which is kinetically far more difficult than the two-electron pathway for carbon monoxide (CO). Currently, many strategies exist, such as promoting CO2 adsorption through doping or vacancy engineering to create a built-in electric field, or using morphology control engineering to promote the separation and transfer of photogenerated carriers to facilitate the photocatalytic reduction of CO2 into methanates. However, most current strategies focus on the activation of CO2 molecules in the reduction half-reaction, while the dissociation of H2O in the oxidation half-reaction is often neglected. Water molecules dissociate on the catalyst surface to produce OH- and protons, where OH-... - The process can consume photogenerated holes to reduce the recombination rate of photogenerated carriers, while protons migrate to the active sites of CO2 adsorption, driving the proton-electron coupling transfer process. Therefore, how to synergistically promote the water oxidation reaction and the CO2 reduction reaction has become a pressing technical challenge in this field.

[0003] Therefore, based on the above research background, considering both the effective separation of photogenerated charges and the creation of H2O activation sites, this invention prepared copper-palladium alloy-supported nano-titanium dioxide materials. The activity of these materials was systematically compared with that of titanium dioxide supported only by a single metal. On the one hand, the presence of copper provides abundant sites for CO2 adsorption and activation, promoting carbon dioxide reduction. On the other hand, palladium acts as an activation site for H2O, activating H2O and then migrating protons to the copper and titanium dioxide surfaces, providing protons for CO2 methanation. Furthermore, the presence of titanium dioxide also promotes charge separation, increasing the charge density participating in the photocatalytic reaction, thereby improving photocatalytic activity. The copper-palladium alloy-supported titanium dioxide material prepared in this invention achieves a highly efficient photocatalytic reduction and methanation process for CO2. Summary of the Invention

[0004] The key problem solved by this invention is to construct a photocatalytic material with excellent photocatalytic carbon dioxide reduction activity, and to conduct in-depth research on the factors and mechanisms that enhance the activity.

[0005] This invention involves adding a copper-palladium precursor to a catalyst containing a reducing agent and a surfactant. The addition of the surfactant prevents particle agglomeration. Borane-tert-butylamine is added under specific temperature conditions, and the temperature is controlled to regulate the surface morphology and particle size. Finally, copper-palladium alloy nanoparticles are loaded onto the surface of titanium dioxide using ultrasound.

[0006] The copper-palladium supported titanium dioxide material exhibits excellent selectivity in photocatalytic carbon dioxide reduction, with a methane generation rate of up to 20.23 µmol / g / h and a selectivity of 100%.

[0007] The method specifically includes the following steps:

[0008] (1) In a 50 mL three-necked flask, add 10 mL of dibenzyl ether, 7.36 mL of oleylamine, and 1.25 mL of oleic acid, along with 16.5 mg of copper acetylacetone and 11.5 mg of palladium acetylacetone. Then connect the three-necked flask to a three-way valve and connect it to a balloon, which is then filled with argon gas. The entire system is then evacuated, and the three-way valve is closed, leaving argon gas in the balloon. The mixture is stirred at 95 °C under vacuum for one hour.

[0009] (2) Heat to 170°C, switch to argon atmosphere, maintain for 5 min, add 100 mg of borane-tert-butylamine, continue to heat to 290°C, stir for 1 hour under argon atmosphere, and then slowly cool to room temperature.

[0010] (3) Place the above cooling solution into a centrifuge tube, add 10 mL of n-hexane and 10 mL of isopropanol to wash once, then wash once with n-hexane, then add 400 mg of nano titanium dioxide to the precursor, sonicate for 4 hours, then wash the obtained solution three times with anhydrous ethanol and deionized water respectively, and then put it into a vacuum oven to dry.

[0011] The system in step (1) is stirred in a vacuum environment to isolate oxygen.

[0012] Borane-tert-butylamine is added at 170°C in step (2).

[0013] In step (2), the temperature is raised to 290°C and stirring is carried out continuously under an argon atmosphere.

[0014] This method utilizes a sol-gel approach to preferentially control the size of nanoparticles by adding copper-palladium precursors, reducing agents, and surfactants. The resulting material, obtained by adding nano-titanium dioxide and ultrasonically loading it, offers the following advantages as a catalyst for the photocatalytic reduction of carbon dioxide:

[0015] (1) The presence of copper provides abundant sites for CO2 adsorption and activation.

[0016] (2) The presence of palladium acts as an activation site for H2O, promoting the dissociation and transport of hydrogen.

[0017] (3) The presence of titanium dioxide can stably provide photogenerated electrons and photogenerated charges; Attached Figure Description

[0018] Figure 1 These are electron micrographs of the catalyst material. Figure 1 (a) is the HADDF-STEM image of the prepared copper-palladium alloy nanoparticles loaded with titanium dioxide. Figure 1 (b)-(d) are HRTEM images of the prepared copper-palladium alloy nanoparticles loaded with titanium dioxide. The insets are magnified views of the carrier surface and the alloy particle surface. As can be seen from the HADDF-STEM and HRTEM images, the prepared alloy particles are uniform in size and dispersed. The magnified view of the nanoparticles in Figure (d) shows the (110) crystal plane of the copper-palladium alloy, indicating that the alloy carrier was successfully synthesized.

[0019] Figure 2 (a) shows the XRD patterns of each catalyst. Figure 2 (b) shows the UV-Vis spectra of different catalysts. The XRD pattern shows that the catalyst mainly exhibits anatase titanium dioxide with some rutile peaks. The UV-Vis spectra indicate that the copper-palladium alloy loading can significantly improve the light absorption capacity of the catalyst in the UV and visible regions and reduce the overall band gap width.

[0020] Figure 3 (a), (b), (c), and (d) are the fluorescence spectra, time-resolved transient fluorescence spectra, photocurrent response density spectra, and EIS spectra of different metal catalysts, respectively. The fluorescence spectra show that the introduction of the copper-palladium alloy significantly reduces the fluorescence intensity of the catalyst. The time-resolved transient fluorescence spectra show that the copper-palladium alloy-supported titanium dioxide catalyst has the longest fluorescence lifetime. The photocurrent response density and EIS spectra show that the copper-palladium alloy-supported titanium dioxide has the largest photocurrent and the smallest impedance value. Combining the fluorescence and electrochemical data, it can be concluded that the copper-palladium alloy-supported titanium dioxide has the best photogenerated charge and carrier separation efficiency.

[0021] Figure 4(a) and (b) are the CO2-TPD and CO-TPD curves for each catalyst, respectively. The two figures show that the copper-palladium alloy-supported titanium dioxide exhibits the strongest adsorption peak in the high-temperature region, indicating that compared to single metals, the copper-palladium alloy-supported titanium dioxide has a better adsorption capacity for carbon dioxide and carbon monoxide.

[0022] Figure 5 This is a graph showing the activity data of photocatalytic carbon dioxide conversion. Figure (a) shows that the catalyst with a 1% copper-palladium alloy loading has the best methane yield; Figure (b) shows that the alloy has the highest yield and the best selectivity compared to the single metal; Figure (c) shows that the carbon source in methane is entirely carbon dioxide, and the proton source in methane is entirely hydrogen produced by water splitting, without interference from other impurities.

[0023] Figure 6 These are in-situ infrared spectra of different samples. (a)-(c) are time-dependent curves, and (d)-(f) are 2D contour plots. The in-situ infrared spectra show that the titanium dioxide catalyst supported on the copper-palladium alloy exhibits a significant peak for the COOH* intermediate, and also shows key intermediates for methane formation, such as *CH2OH, *CH3OH, and CH3*.

[0024] Figure 7 These are XPS spectra of copper and palladium before and after the reaction. The spectra show that the overall valence states of copper and palladium did not change significantly before and after the reaction, indicating that the catalyst has good reaction stability. Detailed Implementation

[0025] The present invention will now be described in detail with reference to specific embodiments.

[0026] This invention provides a method for preparing titanium dioxide nanoparticles supported on copper-palladium alloy nanoparticles as a raw material for photocatalytic carbon dioxide reduction, and the specific steps are as follows:

[0027] Step 1: In a 50 mL three-necked flask, add 10 mL of dibenzyl ether, 7.36 mL of oleylamine, and 1.25 mL of oleic acid, along with 16.5 mg of copper acetylacetone and 11.5 mg of palladium acetylacetone. Connect the three-necked flask to a three-way valve and then connect it to a balloon, which is then filled with argon gas. Evacuate the entire system, close the three-way valve, leaving argon gas in the balloon, and stir at 95°C under vacuum for one hour.

[0028] Step 2: Heat to 170℃, switch to argon atmosphere, maintain for 5 min, add 100 mg of borane-tert-butylamine, continue heating to 290℃, stir for 1 hour under argon atmosphere, and then slowly cool to room temperature.

[0029] Step 3: Place the above cooling solution into a centrifuge tube, add 10 mL of n-hexane and 10 mL of isopropanol for washing once, then wash once more with n-hexane. Add 400 mg of nano-titanium dioxide to the precursor, sonicate for 4 hours, and then wash the resulting solution three times with anhydrous ethanol and deionized water, and then dry it in a vacuum oven.

[0030] The copper-palladium alloy prepared by the above method has a uniform nanoparticle structure. It exhibits the best photocatalytic activity in reducing carbon dioxide to methane when the loading of copper and palladium is 1% respectively. The methane generation rate can reach 20.23 µmol / g / h, and the methane selectivity reaches 100%.

Claims

1. A method for preparing a copper-palladium alloy-supported nano-titanium dioxide material as a photocatalytic carbon dioxide reduction material, characterized in that, This method uses nano-titanium dioxide as a carrier and controls the size and morphology of nanoparticles by solvent control. A solvent that controls the particle size is added to the precursor, followed by the addition of a reducing agent and ultrasonic treatment to uniformly load copper-palladium alloy onto the surface of titanium dioxide, thus obtaining copper-palladium alloy / titanium dioxide composite materials with different loading amounts. At the same time, this method is also applicable to the preparation of titanium dioxide catalysts supported by single metal copper or palladium.

2. The application of the material according to claim 1 in the photocatalytic carbon dioxide reduction reaction, characterized in that: The loaded alloy particles are uniform in size and evenly dispersed, providing abundant active sites; titanium dioxide provides photogenerated holes and electrons in the reaction; the presence of copper enhances the adsorption and activation efficiency of carbon dioxide, and the presence of palladium promotes the adsorption, dissociation and proton transfer efficiency of water molecules, thus enabling the material to exhibit excellent selectivity in the photocatalytic reduction of carbon dioxide to methane.

3. Specifically, it includes the following steps: First, in a 50 mL three-necked flask, add 10 mL of dibenzyl ether, 7.36 mL of oleylamine, and 1.25 mL of oleic acid, along with 16.5 mg of copper acetylacetone and 11.5 mg of palladium acetylacetone. Then, connect the three-necked flask to a three-way valve and connect it to a balloon, which is then filled with argon gas. Next, evacuate the entire system, close the three-way valve, leaving argon gas still in the balloon, and stir at 95°C under vacuum for one hour. The second step is to raise the temperature to 170°C, switch the three-way valve to an argon atmosphere, maintain for 5 minutes, add 100 mg of borane-tert-butylamine, continue to raise the temperature to 290°C, stir for 1 hour under an argon atmosphere, and then slowly cool to room temperature. The third step involves placing the above-mentioned cooling solution into a centrifuge tube, washing it once with 10 mL of n-hexane and 10 mL of isopropanol, then washing it once more with n-hexane, adding 400 mg of nano-titanium dioxide to the precursor, sonicating it for 4 hours, and then washing the resulting solution three times with anhydrous ethanol and deionized water, and finally drying it in a vacuum oven.

4. A copper-palladium alloy-supported titanium dioxide photocatalytic carbon dioxide reduction raw material and its preparation method, as claimed in claim 1, characterized in that... The presence of copper enhances the absorption and activation efficiency of carbon dioxide, while the presence of palladium enhances the adsorption and dissociation of water molecules and the efficiency of proton transfer, thus exhibiting excellent selectivity in the photocatalytic reduction of carbon dioxide to methane.

5. The preparation method according to claim 2, characterized in that: In the first step, the system is stirred in a vacuum environment to isolate oxygen.

6. The preparation method according to claim 2, characterized in that: In the second step, borane-tert-butylamine is added at 170°C.

7. The preparation method according to claim 2, characterized in that: In the second step, the temperature is raised to 290°C and stirred continuously under an argon atmosphere to prevent oxidation.

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