Pb-CeO2 composite catalyst as well as preparation method and application thereof

Abstract

The invention discloses a Pb-CeO2 composite catalyst as well as a preparation method and application thereof. The method comprises the following steps: calcining cerium salt in air to obtain CeO2, and mixing the CeO2 with lead salt in a solvent in proportion, or directly mixing the cerium salt and the lead salt in the solvent in proportion, heating and stirring, drying, grinding and uniformly mixing, and calcining in oxygen to obtain the Pb-CeO2 composite catalyst. The preparation method is simple, large-scale production can be achieved, the Pb-CeO2 composite catalyst is used for electrochemical carbon dioxide reduction, the formic acid synthesis Faraday efficiency close to 100% can be obtained, and when the applied voltage is-1.2 V, the current density can reach about 1 A / cm < 2 >.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts for preparing formic acid by electrochemical reduction of carbon dioxide, and relates to a Pb-CeO2 composite catalyst, a preparation method and an application thereof. Background Art

[0002] With the development of human industrial society, a large amount of carbon dioxide gas is emitted into the atmosphere, which has caused a significant greenhouse effect and global climate problems, seriously affecting human survival and development. Reducing the carbon dioxide content in the atmosphere is urgent. Using electricity generated by renewable energy to drive electrochemical carbon dioxide reduction to synthesize high-value-added chemicals provides an effective way to achieve artificial carbon cycle. The development and application of 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 the sustainable development of mankind.

[0003] Formic acid is a very important chemical product, widely used in dye, food, leather and other industrial fields. At the same time, formic acid is also an important liquid fuel, mainly used in fuel cells. At present, formic acid is mainly prepared by methanol conversion in industry. Since methanol mainly comes from fossil resources, industrial formic acid synthesis is heavily dependent on fossil fuels and emits a large amount of carbon dioxide. By selecting a suitable electrocatalyst, electrochemical carbon dioxide reduction technology can effectively synthesize formic acid, which is expected to replace the current industrial formic acid synthesis technology and achieve low-cost, high-efficiency, sustainable and zero-carbon emission formic acid synthesis. However, the lead-containing or cerium-containing catalysts commonly used for the electrochemical reduction of carbon dioxide to produce formic acid have certain limitations. For example, the single-atom lead alloy copper catalyst (Pb1Cu) prepared by Zeng et al. has a formic acid selectivity of up to 96% and a carbon dioxide reduction of more than 1Acm -2The current density is high, but its preparation method limits the large-scale preparation of the catalyst (Zheng T, Liu C, Guo C, et al. Copper-catalysed exclusive CO2 to pure formic acid conversion via single-atomalloying [J]. Nature Nanotechnology, 2021, 16.). Existing studies have shown that CeO2 can obtain a higher formic acid selectivity after being composited with bismuth-based materials. Du et al. prepared CeO2 / Bi3NbO7 catalyst by electrospinning and calcination, which can obtain 84.73% formic acid selectivity. The formic acid selectivity of this catalyst is not very high and the current density is small (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. mixed CeO2 with Bi ions and added Na2CO3 for co-precipitation, and then calcined to obtain Bi2O3 / CeO x The composite catalyst has a formic acid selectivity of 98.28%, but the current density is also low (Wang C, Pang R, Pan Z, et al. The interfacial aspect of Bi2O3 / CeO x heterostructure catalysts for HCOOH production from CO2 electroreduction[J].Journal of MaterialsChemistry A,2022,10). In summary, the 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 selectivity for formic acid at high current density. Therefore, it is urgent to develop new electrocatalysts with high activity, high selectivity, simple synthesis methods, readily available raw materials, and low cost. Summary of the invention

[0004] The object of the present invention is to provide a Pb-CeO2 composite catalyst, a preparation method and an application thereof. The Pb-CeO2 composite catalyst has high formic acid selectivity at a high current density in the process of catalytic electrochemical carbon dioxide reduction to synthesize formic acid.

[0005] The technical solution for achieving the purpose of the present invention is as follows:

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

[0007] According to the mass ratio of Pb element to CeO2 of 0.1-0.2, CeO2 obtained by calcining cerium salt in air is mixed with lead salt in a solvent, or cerium salt and lead salt are directly mixed in a solvent in proportion, dried and ground evenly after heating and stirring, and then calcined at 600-800°C in oxygen to obtain a Pb-CeO2 composite catalyst.

[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 acetylacetonate, lead chloride or lead nitrate.

[0010] Preferably, the CeO2 obtained by calcining a cerium salt in air is prepared by placing the cerium salt in air, heating it to 350-600°C at a heating rate of 4-6°C / min, and calcining it to obtain CeO2 for 1-5 hours.

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

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

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

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

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

[0016] Compared with the prior art, the present invention has the following beneficial effects:

[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 has a very high selectivity for the synthesis of formic acid in electrochemical carbon dioxide reduction applications, with a Faradaic efficiency close to 100%.

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

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

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

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

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

[0024] Figure 5 It is a performance diagram of the electrochemical carbon dioxide reduction of the catalysts of Examples 1-4 and Comparative Examples 1-4 at -1.0 V (relative to the reversible hydrogen electrode). DETAILED DESCRIPTION

[0025] The following examples are provided to facilitate a better understanding of the present invention, but are not intended to limit the present invention. The experimental methods in the following examples are conventional methods unless otherwise specified. The experimental materials used in the following examples are commercially available unless otherwise specified.

[0026] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[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 test was carried out in a flow cell with an electrolyte of KOH aqueous solution at a concentration of 1 mol / L.

[0029] In a typical test, 8 mg of Pb-CeO2 composite catalyst was added to a mixed solution containing 985 μL of isopropanol and 15 μL of Nafion-117 solution (5%, Sigma-Aldrich), ultrasonicated for half an hour to obtain a well-dispersed catalyst coating solution, and then heated to 1 mg / cm 2 The Pb-CeO2 composite catalyst was coated on the gas diffusion electrode with a loading amount of , and used as the working electrode after drying. All tests were carried out at room temperature, with a CO2 gas flow rate of 40mL / min, and 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 at 350℃ in air at a heating rate of 5℃ / min, and kept warm for 2h, then ground to obtain CeO2. 1g of CeO2 was mixed with 240mg of lead nitrate in a mixed solution of water and ethanol (volume ratio of 20:1), dried at 75℃, ground, and then dried in a vacuum drying oven for 12h. Finally, it was placed in an oxygen atmosphere and calcined at 800℃ for 10h at a heating rate of 2℃ / min. After natural cooling, it was ground to obtain a 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 of 20:1), dried at 75°C, ground, and then dried in a vacuum drying oven for 12 hours. Finally, the mixture was calcined at 800°C in an oxygen atmosphere for 10 hours at a heating rate of 2°C / min. After natural cooling, the mixture was ground to obtain a Pb-CeO2 composite catalyst.

[0034] Example 3

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

[0036] Example 4

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

[0038] Comparative Example 1

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

[0040] Comparative Example 2

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

[0042] Comparative Example 3

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

[0046] Figure 1 It is the X-ray diffraction pattern of Pb-CeO2 in Example 1. It can be seen from the figure that the Pb-CeO2 composite catalyst only shows the diffraction pattern of CeO2, indicating that the introduction of Pb element does not change the crystal structure of CeO2, and may exist in the crystal lattice of CeO2 in the form of doping.

[0047] Figure 2 This is the transmission electron microscope image of CeO2 and Pb-CeO2. It can be seen from the image that after adding Pb, the particle size of the material particles is significantly reduced and has a higher degree of crystallinity.

[0048] Figure 3 It is the X-ray photoelectron spectrum of CeO2 and Pb-CeO2 in Example 1, from which Ce-O bond and Pb-O bond can be seen.

[0049] Figure 4 The electrochemical carbon dioxide reduction product selectivity data and electrochemical reaction current density of CeO2 and Pb-CeO2 composite catalyst in Example 1. It can be seen from the figure that the Pb-CeO2 composite catalyst can obtain a formic acid synthesis Faraday efficiency close to 100% in a wide potential range, and when the applied voltage is -1.2V (relative to the reversible hydrogen electrode), the current density can reach 1A / cm 2 about.

[0050] Figure 5 The performance diagram of the electrochemical carbon dioxide reduction of the catalysts of Examples 1-4 and Comparative Examples 1-4 at -1.0V vs. RHE. It can be seen from the figure that Examples 1 and 2 have the highest formic acid selectivity, which is close to 100%, while the formic acid selectivity of Examples 3 and 4, where the Pb content is at the borderline, is slightly reduced. It can be seen from Comparative Examples 1 and 2 that when the lead ratio is lower than 0.1 or higher than 0.2, the formic acid selectivity decreases more. The formic acid selectivity of pure PbO and pure CeO2 is low, and most of the product is hydrogen.

Claims

1. A method for preparing a Pb-CeO2 composite catalyst, characterized in that: The following steps are involved: According to the mass ratio of Pb element to CeO2 of 0.1-0.2, CeO2 obtained by calcining cerium salt in air is mixed with lead salt in a solvent, or cerium salt and lead salt are directly mixed in a solvent in proportion, dried and ground evenly after heating and stirring, and then calcined at 600-800°C in oxygen to obtain a Pb-CeO2 composite catalyst.

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: The lead salt is selected from lead acetate trihydrate, lead acetylacetonate, lead chloride or lead nitrate.

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

5. The preparation method according to claim 1, characterized in that: The solvent is a mixed solution 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 obtained according to the preparation method described in any one of claims 1 to 6.

8. Use of the Pb-CeO2 composite catalyst according to claim 7 in the preparation of formic acid by electrochemical reduction of carbon dioxide.

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

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