Pb-ceo2 composite catalyst, preparation method and application thereof

Abstract

This invention discloses a Pb-CeO2 composite catalyst, its preparation method, and its application. The method involves mixing CeO2 obtained by calcining cerium salt in air with lead salt in a solvent in a specific ratio, or directly mixing cerium salt and lead salt in a solvent in a specific ratio. After heating and stirring, the mixture is dried, ground, and ground until homogeneous, then calcined in oxygen to obtain the Pb-CeO2 composite catalyst. The preparation method of this invention is simple and can be mass-produced. The Pb-CeO2 composite catalyst, used for electrochemical carbon dioxide reduction, can achieve a formic acid synthesis Faradaic efficiency close to 100%, and at an applied voltage of -1.2 V, the current density can reach 1 A / cm². 2 about.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology for the electrochemical reduction of carbon dioxide to prepare formic acid, and relates to a Pb-CeO2 composite catalyst, its preparation method and its application. Background Technology

[0002] With the development of human industrial society, large amounts of carbon dioxide gas have been emitted into the atmosphere, causing a significant greenhouse effect and global climate problems, seriously affecting human survival and development. Reducing atmospheric carbon dioxide levels is now urgent. Utilizing electricity generated from renewable energy sources to drive electrochemical carbon dioxide reduction for the synthesis of high-value-added chemicals provides an effective pathway to achieving an artificial carbon cycle. Developing and applying electrocatalytic carbon dioxide reduction technology can not only reduce the concentration of carbon dioxide gas in the atmosphere but also realize the conversion of renewable energy into high-value-added chemicals, which is of great significance to human sustainable development.

[0003] Formic acid is a crucial chemical widely used in industries such as dyes, food, and leather tanning. It is also an important liquid fuel, primarily used in fuel cells. Currently, formic acid is mainly produced industrially through methanol conversion. Since methanol is primarily derived from fossil fuels, industrial formic acid synthesis heavily relies on fossil fuels and emits large amounts of carbon dioxide. With suitable electrocatalysts, electrochemical carbon dioxide reduction technology can effectively synthesize formic acid, potentially replacing current industrial formic acid synthesis technologies and achieving low-cost, high-efficiency, sustainable, and zero-carbon emission formic acid production. However, commonly used lead- or cerium-containing catalysts for the electrochemical reduction of carbon dioxide to formic acid have limitations. For example, the single-atom lead-copper alloy catalyst (Pb1Cu) prepared by Zeng et al. exhibits a formic acid selectivity as high as 96% and a carbon dioxide emission rate exceeding 1 Acm. -2While CeO2 exhibits high current density, its preparation method limits its large-scale preparation (Zheng T, Liu C, Guo C, et al. Copper-catalyzed exclusive CO2 to pure formic acid conversion via single-atomalloying[J]. Nature Nanotechnology, 2021, 16.). Existing research indicates that CeO2 combined with bismuth-based materials can achieve high formic acid selectivity. Du et al. prepared a CeO2 / Bi3NbO7 catalyst with 84.73% formic acid selectivity by electrospinning followed by calcination. However, this catalyst does not have very high formic acid selectivity and also has a low current density (Song L, Liang Z, Sun M et al. The interfacial effect induced by rare earth oxide inboosting the conversion of CO2 to formate[J]. Energy & Environmental Science, 2022, 15). Liu et al. obtained Bi2O3 / CeO7 by mixing CeO2 with Bi ions, adding Na2CO3 for co-precipitation, and then calcining. x A composite catalyst exhibits 98.28% formic acid selectivity; however, its current density is also relatively low (Wang C, Pang R, Pan Z, et al. The interfacial aspect of Bi₂O₃ / CeO₂). x Heterostructure catalysts for HCOOH production from CO2 electroreduction [J]. Journal of Materials Chemistry A, 2022, 10. In summary, existing catalysts for the electrochemical reduction of carbon dioxide to formic acid generally face problems such as complex preparation methods that are not conducive to industrial scale-up, high raw material costs, and insufficient formic acid selectivity at high current densities. Therefore, there is an urgent need to develop novel electrocatalysts with high activity, high selectivity, simple synthesis methods, readily available raw materials, and low cost. Summary of the Invention

[0004] The purpose of this invention is to provide a Pb-CeO2 composite catalyst, its preparation method, and its application. This Pb-CeO2 composite catalyst exhibits high formic acid selectivity at high current densities during the catalytic electrochemical reduction of carbon dioxide to formic acid.

[0005] The technical solution for achieving the objective of this invention is as follows:

[0006] The preparation method of Pb-CeO2 composite catalyst includes the following steps:

[0007] The Pb-CeO2 composite catalyst is obtained by calcining cerium salt in air to obtain CeO2 with a mass ratio of Pb to CeO2 of 0.1 to 0.2, mixing CeO2 obtained by calcining cerium salt in air with lead salt in a solvent, or by directly mixing cerium salt and lead salt in a solvent in a certain proportion, heating and stirring, drying and grinding evenly, and then calcining in oxygen at 600 to 800°C.

[0008] Preferably, the cerium salt is selected from cerium nitrate hexahydrate, cerium chloride hexahydrate, or cerium acetate hydrate.

[0009] Preferably, the lead salt is selected from lead acetate trihydrate, lead acetylacetone, lead chloride, or lead nitrate.

[0010] Preferably, CeO2 is obtained by calcining cerium salt in air. The specific steps for preparation are as follows: place cerium salt in air, heat it to 350-600℃ at a heating rate of 4-6℃ / min to obtain CeO2, and calcination time is 1-5 hours.

[0011] Preferably, the solvent is a mixed solution of water and ethanol with a volume ratio of 20:1.

[0012] Preferably, during the calcination process in oxygen, the heating rate is 1–4 °C / min, and the holding time is 8–12 hours.

[0013] This invention provides a Pb-CeO2 composite catalyst prepared by the above method.

[0014] Furthermore, the present invention provides the application of the above-mentioned Pb-CeO2 composite catalyst in the electrochemical reduction of carbon dioxide to prepare formic acid.

[0015] Specifically, in the above applications, the Pb-CeO2 composite catalyst is used as the catalyst for the cathode reaction.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] (1) The preparation method of Pb-CeO2 composite catalyst is simple and can be produced on a large scale.

[0018] (2) The Pb-CeO2 composite catalyst exhibits very high selectivity for the synthesis of formic acid in electrochemical carbon dioxide reduction applications, with a Faraday efficiency approaching 100%.

[0019] (3) The Pb-CeO2 composite catalyst can achieve very high current densities in the electrochemical reduction of carbon dioxide to formic acid. For example, when a voltage of -1.2V is applied (relative to the reversible hydrogen electrode), the current density can reach 1A / cm. 2 about. Attached Figure Description

[0020] Figure 1 This is a powder X-ray diffraction pattern of CeO2 and the Pb-CeO2 composite catalyst in Example 1.

[0021] Figure 2 This is a transmission electron microscope image of CeO2 and the Pb-CeO2 composite catalyst in Example 1.

[0022] Figure 3 This is the X-ray photoelectron spectrum of CeO2 and the Pb-CeO2 composite catalyst in Example 1.

[0023] Figure 4 These are the performance graphs and current graphs of electrochemical carbon dioxide reduction for CeO2 and the Pb-CeO2 composite catalyst in Example 1.

[0024] Figure 5 The graphs show the performance of the catalysts for electrochemical carbon dioxide reduction in Examples 1-4 and Comparative Examples 1-4 at -1.0V (relative to the reversible hydrogen electrode). Detailed Implementation

[0025] The following embodiments are provided to better understand the present invention, but are not intended to limit the invention. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0026] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0027] 1. Electrochemical carbon dioxide reduction test conditions:

[0028] The electrochemical carbon dioxide reduction performance of all catalysts was tested using the Wuhan Koster electrochemical workstation. The tests were conducted in a flow cell using a 1 mol / L KOH aqueous solution as the electrolyte.

[0029] In a typical test, 8 mg of Pb-CeO2 composite catalyst was added to a mixed solution containing 985 μL isopropanol and 15 μL Nafion-117 solution (5%, Sigma-Aldrich), and sonicated for half an hour to obtain a well-dispersed catalyst coating solution. Then, the catalyst was coated with a solution at 1 mg / cm³. 2 The Pb-CeO2 composite catalyst was coated onto a gas diffusion electrode and dried to serve as the working electrode. All tests were performed at room temperature with a CO2 gas flow rate of 40 mL / min. A platinum sheet electrode and a mercury-mercury oxide electrode were used as the counter electrode and reference electrode, respectively.

[0030] Example 1

[0031] 5g of cerium nitrate hexahydrate was calcined in air at 350℃ with a heating rate of 5℃ / min and held at that temperature for 2h. The resulting product was then ground to obtain CeO2. 1g of CeO2 was mixed with 240mg of lead nitrate in a solution of water and ethanol (volume ratio 20:1), dried at 75℃, ground, and then dried in a vacuum drying oven for 12h. Finally, it was calcined in an oxygen atmosphere at 800℃ for 10h with a heating rate of 2℃ / min. After natural cooling, the product was ground to obtain the Pb-CeO2 composite catalyst.

[0032] Example 2

[0033] 2.25 g of cerium nitrate hexahydrate and 240 mg of lead nitrate were mixed in a mixed solution of water and ethanol (volume ratio 20:1), dried at 75 °C, ground, and then dried in a vacuum drying oven for 12 h. Finally, it was calcined at 800 °C for 10 h in an oxygen atmosphere at a heating rate of 2 °C / min. After natural cooling, it was ground to obtain the Pb-CeO2 composite catalyst.

[0034] Example 3

[0035] 5g of cerium nitrate hexahydrate was calcined in air at 350℃ with a heating rate of 5℃ / min and held at that temperature for 2h. The resulting product was then ground to obtain CeO2. 1g of CeO2 was mixed with 160mg of lead nitrate in a solution of water and ethanol (volume ratio 20:1), dried at 75℃, ground, and then dried in a vacuum drying oven for 12h. Finally, it was calcined in an oxygen atmosphere at 800℃ for 10h with a heating rate of 2℃ / min. After natural cooling, the product was ground to obtain the Pb-CeO2 composite catalyst.

[0036] Example 4

[0037] 5g of cerium nitrate hexahydrate was calcined in air at 350℃ with a heating rate of 5℃ / min and held at that temperature for 2h. The resulting product was then ground to obtain CeO2. 1g of CeO2 was mixed with 320mg of lead nitrate in a mixture of water and ethanol (volume ratio 20:1), dried at 75℃, ground, and then dried in a vacuum drying oven for 12h. Finally, it was calcined in an oxygen atmosphere at 800℃ for 10h with a heating rate of 2℃ / min. After natural cooling, the product was ground to obtain the Pb-CeO2 composite catalyst.

[0038] Comparative Example 1

[0039] 5g of cerium nitrate hexahydrate was calcined in air at 350℃ with a heating rate of 5℃ / min and held at that temperature for 2h. The resulting product was then ground to obtain CeO2. 1g of CeO2 was mixed with 80mg of lead nitrate in a solution of water and ethanol (volume ratio 20:1), dried at 75℃, ground, and then dried in a vacuum drying oven for 12h. Finally, it was calcined in an oxygen atmosphere at 800℃ for 10h with a heating rate of 2℃ / min. After natural cooling, the product was ground to obtain the Pb-CeO2 composite catalyst.

[0040] Comparative Example 2

[0041] 5g of cerium nitrate hexahydrate was calcined in air at 350℃ with a heating rate of 5℃ / min and held at that temperature for 2h. The resulting product was then ground to obtain CeO2. 1g of CeO2 was mixed with 400mg of lead nitrate in a solution of water and ethanol (volume ratio 20:1), dried at 75℃, ground, and then dried in a vacuum drying oven for 12h. Finally, it was calcined in an oxygen atmosphere at 800℃ for 10h with a heating rate of 2℃ / min. After natural cooling, the product was ground to obtain the Pb-CeO2 catalyst.

[0042] Comparative Example 3

[0043] 5g of cerium nitrate hexahydrate was calcined in air at 350℃ with a heating rate of 5℃ / min and held at that temperature for 2h. The calcined product was then ground to obtain CeO2. 1g of CeO2 was dissolved in a mixed solution of water and ethanol (volume ratio 20:1), dried at 75℃, ground, and then dried in a vacuum drying oven for 12h. Finally, it was calcined in an oxygen atmosphere at 800℃ for 10h with a heating rate of 2℃ / min. After natural cooling, the calcined product was ground to obtain the CeO2 catalyst.

[0044] Comparative Example 4

[0045] 0.5 g of lead nitrate was dissolved in a mixed solution of water and ethanol (volume ratio 20:1), dried at 75 °C, ground, and then dried in a vacuum drying oven for 12 h. Finally, it was calcined at 800 °C for 10 h in an oxygen atmosphere with a heating rate of 2 °C / min. After natural cooling, it was ground to obtain the PbO catalyst.

[0046] Figure 1 The image shows the X-ray diffraction pattern of Pb-CeO2 in Example 1. As can be seen from the image, the Pb-CeO2 composite catalyst only exhibits the diffraction pattern of CeO2, indicating that the introduction of Pb element did not change the crystal structure of CeO2, and it may exist in the CeO2 lattice in the form of dopant.

[0047] Figure 2 These are transmission electron micrographs of CeO2 and Pb-CeO2. As can be seen from the figures, the particle size of the material is significantly reduced after the addition of Pb, and it has a higher degree of crystallinity.

[0048] Figure 3 The X-ray photoelectron spectra of CeO2 and Pb-CeO2 in Example 1 are shown in the figure. Ce-O bonds and Pb-O bonds can be seen from the figure.

[0049] Figure 4 The figures show the electrochemical carbon dioxide reduction product selectivity data and electrochemical reaction current density of CeO2 and the Pb-CeO2 composite catalyst in Example 1. As can be seen from the figures, the Pb-CeO2 composite catalyst achieves a formic acid synthesis Faradaic efficiency close to 100% over a wide potential range, and the current density reaches 1 A / cm² when an applied voltage of -1.2 V (relative to the reversible hydrogen electrode) is reached. 2 about.

[0050] Figure 5 This is a graph showing the performance of the catalysts for electrochemical carbon dioxide reduction in Examples 1-4 and Comparative Examples 1-4 at -1.0V vs. RHE. As can be seen from the graph, Examples 1 and 2 exhibit the highest formic acid selectivity, approaching 100%, while Examples 3 and 4, with Pb content at the borderline, show a slight decrease in formic acid selectivity. Comparative Examples 1 and 2 show that the formic acid selectivity decreases significantly when the lead content is below 0.1% or above 0.2%. Pure PbO and pure CeO2 show lower formic acid selectivity, with the majority of the product being hydrogen gas.

Claims

1. A method for preparing a Pb-CeO2 composite catalyst, characterized in that, Includes the following steps: The Pb-CeO2 composite catalyst is obtained by calcining cerium salt in air to obtain CeO2 with a mass ratio of Pb to CeO2 of 0.1 to 0.2, mixing CeO2 obtained by calcining cerium salt in air with lead salt in a solvent, or by directly mixing cerium salt and lead salt in a solvent in a certain proportion, heating and stirring, drying and grinding evenly, and then calcining in oxygen at 600 to 800 °C.

2. The preparation method according to claim 1, characterized in that, The cerium salt is selected from cerium nitrate hexahydrate, cerium chloride hexahydrate, or cerium acetate hydrate.

3. The preparation method according to claim 1, characterized in that, Lead salts are selected from lead acetate trihydrate, lead acetylacetone, lead chloride, or lead nitrate.

4. The preparation method according to claim 1, characterized in that, The specific steps for preparing CeO2 by calcining cerium salt in air are as follows: place cerium salt in air and calcine it at a heating rate of 4~6 ℃ / min to 350~600 ℃ to obtain CeO2, with a calcination time of 1~5 hours.

5. The preparation method according to claim 1, characterized in that, The solvent is a mixture of water and ethanol in a volume ratio of 20:

1.

6. The preparation method according to claim 1, characterized in that, During the calcination process in oxygen, the heating rate is 1~4 ℃ / min, and the holding time is 8~12 hours.

7. The Pb-CeO2 composite catalyst prepared by any one of the preparation methods according to claims 1 to 6.

8. The application of the Pb-CeO2 composite catalyst according to claim 7 in the electrochemical reduction of carbon dioxide to prepare formic acid.

9. The application according to claim 8, characterized in that, Pb-CeO2 composite catalyst was used as a catalyst for the cathode reaction.

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