Preparation method and application of metal-Ce binary solid solution oxide catalyst

Abstract

The invention discloses a preparation method and application of a metal-Ce binary solid solution oxide catalyst, and belongs to the field of catalyst synthesis. The preparation method comprises the following steps: fully stirring a soluble metal M salt solution and a Ce metal salt solution, uniformly mixing, dropwise adding a weak base solution, adjusting the pH value of the solution under a stirring condition to form a precipitate, and stirring by using dilute acid or an ammonia water solution to remove active metal M and oxides thereof which do not form a solid solution; and carrying out suction filtration, vacuum drying and the like to obtain the M-Ce-Ox solid solution catalyst, and carrying out high-temperature treatment on the M-Ce-Ox solid solution catalyst to adjust the number of oxygen vacancies in the solid solution catalyst. Compared with a traditional supported catalyst, the solid solution catalyst prepared by the method has higher target product selectivity, and can promote directional generation of CO2 to a high-added-value reduction product.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst synthesis, and particularly relates to a preparation method of a metal-Ce binary solid solution oxide catalyst and its application in the electrocatalytic reduction of CO2. Background Art

[0002] The increasing annual content of CO2 in the atmosphere has led to a series of ecological and environmental problems such as global warming and frequent extreme weather, threatening the development of human society. Converting CO2 into a series of high-value chemicals (such as HCOOH, C2H4, C2H5OH, etc.) by using electrical energy generated from renewable energy under the action of a catalyst can not only effectively reduce the carbon content in the atmosphere, but also stably store renewable energy. For an efficient CO2 conversion process, the structural design and regulation of the catalyst are particularly crucial. Taking the most widely studied Cu-based catalyst as an example, the high-valent Cu species (Cu + or Cu 2+ ) have stronger adsorption and conversion capabilities for intermediates, but in the actual CO2 reduction process, due to the existence of a high overpotential, it is difficult for such species to exist stably. For p-block metals (Sn, In) that produce formic acid, the high-valent metal species have higher formic acid formation capabilities, but they also face the problem that the high-valent metal species cannot exist stably during the CO2 conversion process. Currently, by using means such as strong interaction between the active component and the support, carbon layer coating, etc., the self-reduction phenomenon of high-valent metal species is inhibited to a certain extent, but the effect is not very ideal. In addition, the preparation process of most catalysts is too cumbersome to achieve large-scale preparation. Therefore, developing a simple electrocatalyst synthesis method with high target product selectivity to convert CO2 into high-value products at a low overpotential and high current density has very important economic value and application prospects. Summary of the Invention

[0003] Object of the Invention: Aiming at the problem that high-valent metals such as Cu and Sn in the CO2 electrocatalyst in the prior art are difficult to exist stably, the present invention provides a preparation method of a metal-Ce binary solid solution oxide catalyst. The present invention introduces CeO2 with better thermodynamic stability as the matrix, embeds the active catalytic component into the lattice of CeO2, prepares a binary solid solution oxide catalyst by the co-precipitation method, and cooperates with the atmosphere-assisted method to adjust the number of oxygen vacancies in the solid solution catalyst, so as to simultaneously achieve the effect of stabilizing high-valent metal species and maintaining high catalytic activity and target product selectivity during the CO2 reduction process. The present invention realizes the preparation of a highly selective CO2 reduction electrocatalyst by adjusting parameters such as the ratio between the active metal and Ce, the calcination atmosphere and temperature.

[0004] Technical solution: To solve the above technical problems, the technical solution adopted by the present invention is: a preparation method of a metal-Ce binary solid solution oxide catalyst, comprising the following steps:

[0005] (1) Mix a soluble metal M salt solution and a Ce metal salt solution; M is Cu, Sn, In, Au, Ag or Pd;

[0006] (2) Adjust the pH of the solution to acidic to inhibit the hydrolysis of the salt;

[0007] (3) Adjust the pH of the solution to alkaline to form a precipitate. After separating the obtained precipitate, it is dried to obtain a solid powder;

[0008] (4) Remove the active metal M and its oxides that have not formed a solid solution from the obtained solid powder, and after high-temperature treatment in different atmospheres, M-Ce-O x solid solution catalyst is obtained.

[0009] Among them, in step (1), the metal salt M is a nitrate or chloride of Cu, Sn or In, and the Ce metal salt is a nitrate of Ce. The metal M among them is an active component for the electrocatalytic reduction of CO2, such as Cu, Sn, In, etc., and the solid solution catalyst is prepared from soluble metal salts (nitrates, chlorides, etc.).

[0010] Among them, the feeding molar ratio of M to Ce in step (1) is 0.5:9.5 to 1:1.

[0011] Further, 0.05-0.5 g of metal salt is added to every 50-200 mL of deionized water.

[0012] Among them, in step (2), an acid solution is added to adjust the pH of the solution to 1-3 to inhibit the hydrolysis of the salt.

[0013] Among them, in step (3), a weak base solution is added, and under stirring conditions, the pH of the solution is adjusted to 9-11, and a large amount of precipitate is formed. The obtained precipitate is separated by suction filtration and vacuum dried at 60-90 °C to obtain a solid powder.

[0014] Among them, in step (4), the obtained solid powder is stirred with a dilute acid or ammonia water solution for 6-24 h to remove the active metal M and its oxides that have not formed a solid solution, and then M-Ce-O x solid solution catalyst is obtained through suction filtration, vacuum drying, etc.

[0015] Further, the solid solution catalyst obtained in step (4) is subjected to high-temperature treatment in different atmospheres to obtain a M-Ce-O x solid solution catalyst with different oxygen vacancy numbers.

[0016] Among them, the obtained solid solution catalyst is treated at a high temperature of 300-500 °C for 1-3 h in different atmospheres to adjust the number of oxygen vacancies in the solid solution, and M-Ce-O is obtained. x The solid solution catalyst, and the atmosphere is air or an Ar atmosphere containing 5%-10% H2.

[0017] Preferably, in step (1), the soluble metal M salt and the Ce metal salt are respectively dissolved in deionized water in a beaker with a certain volume, and precursor solutions A and B are obtained after sufficient stirring; 0.05-0.5 g of metal salt is added to every 50-200 mL of deionized water, the metal salt M is a nitrate or chloride of Cu, Sn, or In, and the Ce salt is a nitrate of Ce; after the solutions A and B are sufficiently stirred, they are mixed evenly and stirred continuously for 1-3 h to be fully mixed evenly to form solution C.

[0018] In step (2), a certain amount of acid solution (dilute hydrochloric acid, dilute nitric acid, etc.) is added to solution C to adjust the pH of the solution to 1-3 to inhibit the hydrolysis of the salt.

[0019] In step (3), a weak base (such as ammonia water) with a certain concentration (10%-30%) is gradually added dropwise to the above-mentioned mixed solution C, and the pH of the solution is adjusted to 9-11 under stirring conditions, and a large amount of precipitation can be observed; the obtained precipitate is separated by suction filtration and vacuum dried at 60-90 °C to obtain a solid powder.

[0020] In step (4), the obtained solid powder is stirred with a dilute acid or ammonia water solution (5%-30%) as a complexing agent for 6-24 h to remove the active metal M and its oxides that have not formed a solid solution, and then a certain proportion of M-Ce-O x solid solution catalyst is obtained through suction filtration, vacuum drying, etc.

[0021] In step (5), the obtained solid solution catalyst is treated at a high temperature of 300-500 °C for a certain time of 1-3 h in a tube furnace under different atmospheres (such as hydrogen) to adjust the number of oxygen vacancies in the solid solution. Experiments of the present invention show that it is better to have a moderate number of oxygen vacancies, which can not only effectively promote water dissociation to provide adsorbed active *H species (*H is an adsorbed H species, * represents an adsorption site), but also maintain catalytic stability.

[0022] The metal-Ce binary solid solution oxide catalyst prepared by the preparation method described in the present invention.

[0023] The application of the metal-Ce binary solid solution oxide catalyst described in the present invention in the electrocatalytic reduction of CO2.

[0024] Among them, the electrolytic cell used by the metal-Ce binary solid solution oxide catalyst in electrocatalytic CO2 reduction is an ion-exchange membrane-separated H-type or flow-type electrolytic cell, with an Ag / AgCl electrode or a Hg / HgO electrode as the reference electrode, a Pt sheet or nickel foam as the counter electrode, and a hydrophobic carbon paper coated with the metal-Ce binary solid solution oxide catalyst as the working electrode; the constant potential range is -0.30V to -2.0V vs. RHE, the ion-exchange membrane is an anion or cation exchange membrane, the electrolyte is a KCl, KOH or KHCO3 solution with a concentration of 0.1 to 3M, and the carbon dioxide gas flow rate is 10 to 50 sccm.

[0025] Furthermore, the prepared binary solid solution oxide catalyst is used for electrocatalytic reduction of CO2 to produce high-value-added chemicals such as formic acid and ethylene.

[0026] Among them, the preparation method of the carbon paper coated with the solid solution catalyst includes the following steps:

[0027] Add a Nafion solution to a dispersion of the solid solution catalyst with a concentration of 1 to 10 mg / mL, and then spray the catalyst dispersion on the carbon paper. After drying at room temperature, the working electrode is obtained;

[0028] Among them, 100 to 600 μL of the catalyst dispersion is sprayed per square centimeter of the carbon paper; the solvent of the dispersion is isopropanol or a mixture of isopropanol and water with a ratio of 1:3 to 3:1; the volume ratio of the Nafion solution to the dispersion is 1:10 to 100; the concentration of the Nafion solution is 1 wt% to 10 wt%.

[0029] The present invention prepares a nanoscale binary solid solution catalyst by the coprecipitation method, introducing active components M (such as Cu, Sn, In) into the CeO2 lattice with high thermodynamic stability. By forming stable M-O-Ce bonds and the excellent conduction ability of Ce 4 + / Ce 3+ electron pairs, the high valence state of the active metal M can be effectively maintained, thereby promoting the electrocatalytic conversion of CO2 to high-value-added products. The prepared nanocatalyst has a large specific surface area and more oxygen vacancies, which is beneficial to the adsorption of reactants and intermediates.

[0030] The present invention utilizes the active M species with stable structure in the solid solution, which is different from the existing strategies for improving stability such as metal-support interaction. During the synthesis of the catalyst, CeO2 has an extremely high thermodynamic reduction potential, and the active metal component M (Cu, Sn, In, etc.) is easily embedded into its lattice to form a solid solution structure. By forming stable M-O-Ce chemical bonds, the high-valence active M component is protected from being reduced, thereby maintaining its efficient CO2 catalytic performance. In the preparation process of the co-precipitation method in the present invention, the material ratio, pH adjustment, calcination atmosphere, temperature and time are all crucial. Among them, the material ratio and pH adjustment will affect the composition of the solid solution structure, and the calcination conditions will affect the number of oxygen vacancies in the final catalyst. The pH adjustment in the present invention will affect the hydrolysis degree of the two precursor salts, and only by controlling the appropriate pH range can they be co-hydrolyzed and precipitated. Further experiments found that by adjusting the ratio of Sn and Ce in the raw materials, binary solid solution structures can be synthesized, but it can be seen from the atomic emission spectrum that their ratios are different, and different ratios have different selectivities for the target product formic acid. At the same time, it can be seen from different calcination treatment times that the oxygen vacancies show a gradually increasing trend with the increase of the treatment time.

[0031] Furthermore, the CO2 electroreduction test of the present invention shows that the solid solution catalyst exhibits better selectivity for the target product.

[0032] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0033] (1) The present invention provides a simple method for preparing a binary solid solution oxide catalyst, with simple process operation, efficiently constructing a stable solid solution structure of active M species, promoting the efficient conversion of CO2 into high-value-added products, strong result repeatability, and suitable for large-scale preparation;

[0034] (2) For the catalyst prepared by the present invention, by embedding the active metal components (Cu, Sn, In, etc.) into the stable CeO2 lattice, stable metal-O-Ce bonds are formed, thereby stabilizing the high-valence active metal species, and cooperating with the regulation of oxygen vacancies in the catalyst, promoting the directional generation of high-value-added reduction products from CO2; this solid solution catalyst has higher selectivity for the target product compared with traditional supported catalysts.

[0035] (3) The strategy of protecting high-valence metal species through solid solution provided by the present invention can be extended to other electrocatalytic fields, such as electrocatalytic fields related to water electrolysis, fuel cells, etc., providing effective ideas and references for the development of efficient electrocatalysts. Description of the Drawings

[0036] Figure 1 XRD pattern of the Sn4-Ce6-O x catalyst prepared in Example 1;

[0037] Figure 2 The Sn4-Ce6-O prepared in Example 1 x Transmission electron microscope image (TEM) of the catalyst;

[0038] Figure 3 The Cu1-Ce9-O prepared in Example 2 x Transmission electron microscope image (TEM) of the catalyst;

[0039] Figure 4 For the sample Cu1-Ce9-O in Example 2 x Powder XRD diffraction pattern of the catalyst;

[0040] Figure 5 For the sample Sn4-Ce6-O in Example 1 x And the bar graph of the Faraday efficiency of electrocatalytic reduction of carbon dioxide to formic acid by the SnO2 catalyst of the comparative sample at different potentials;

[0041] Figure 6 For the sample Cu1-Ce9-O in Example 2 x And the bar graph of the Faraday efficiency of electrocatalytic reduction of carbon dioxide to methane by the CuO catalyst of the comparative sample at different potentials;

[0042] Figure 7 XRD pattern of different ratios of Sn-Ce solid solution of the sample prepared in Example 6;

[0043] Figure 8 Line graph of the Faraday efficiency of electrocatalytic reduction of carbon dioxide to formic acid by different ratios of Sn-Ce solid solution and the SnO2 catalyst of the comparative sample at different potentials in Example 6. Detailed implementation mode

[0044] The present invention will be further described below in conjunction with specific embodiments, which are only used to explain the present invention and should not be construed as a limitation to the present invention. Those of ordinary skill in the art can understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and purposes of the present invention, and the scope of the present invention is defined by the claims and their equivalents.

[0045] The experimental methods in the following examples are all conventional methods unless otherwise specified. The test materials used in the following examples are all purchased from conventional biochemical reagent companies unless otherwise specified.

[0046] Example 1

[0047] Step 1: Accurately weigh 280.6 mg of SnCl4·5H2O and dissolve it in a beaker containing 200 mL of deionized water, and stir to form a precursor solution A.

[0048] Step 2: Accurately weigh 521.0 mg of Ce(NO3)3·6H2O and dissolve it in a beaker containing 200 mL of deionized water, and stir to form precursor solution B.

[0049] Step 3: Add solution A to solution B under stirring conditions, adjust the pH of the solution to 1 with dilute hydrochloric acid to inhibit the hydrolysis of the Sn salt, and continue stirring for 1 h to obtain a mixed solution C.

[0050] Step 4: Dropwise add an ammonia aqueous solution with a mass fraction of 25% to the mixed solution C under stirring conditions until the pH of the solution reaches about 10. A large amount of light purple precipitate can be observed to form.

[0051] Step 5: Filter and wash the precipitate obtained in Step 4 with a large amount of deionized water, and then place it in a vacuum drying oven at 80 °C for drying overnight to obtain a light yellow powder D.

[0052] Step 6: Disperse the light yellow powder D obtained in Step 5 in 200 mL of deionized water, and adjust the pH of the dispersion to 2 with dilute hydrochloric acid. Continuously stir at room temperature for 12 h to remove the unformed solid solution SnO x , and then obtain the Sn4-Ce6-O x solid solution catalyst after filtration, washing with deionized water, and vacuum drying at 80 °C;

[0053] Step 7: Heat-treat the Sn4-Ce6-O x solid solution catalyst obtained in Step 6 in a tubular furnace. The treatment atmosphere is a 5% H2 / Ar mixed gas, and the calcination condition is to treat at 350 °C for 1 h to obtain the Sn4-Ce6-O x solid solution catalyst with moderate oxygen vacancies.

[0054] Figure 1 For the XRD test patterns of CeO2 and the Sn4-Ce6-O x catalyst prepared in Step 7. It can be seen from the figure that a single substance appears in the XRD, and it is very close to CeO2 in the standard card. After magnifying the spectrum, it is found that its main peaks are slightly shifted to a higher angle relative to CeO2. According to the Bragg formula 2dsinθ = nλ, nλ is a constant value. Then, when θ increases, it indicates that the interplanar spacing d decreases, which also means that smaller atoms of Sn are embedded in the CeO2 lattice, resulting in lattice contraction. This also indicates the formation of the solid solution structure Sn4-Ce6-O x .

[0055] Figure 2 For the Sn4-Ce6-O xTEM image of the catalyst. As can be seen from the figure, the catalyst is composed of small particles with a size of 3-5 nm. The small particles aggregate together, and their smaller particle size gives it a high specific surface area, enabling more reactive sites to be exposed.

[0056] Table 1 shows the proportion of oxygen vacancies obtained by peak fitting of XPS O1s before and after treatment with 5% H2-Ar at 350 °C. Through comparison, it can be seen that the content of oxygen vacancies has been significantly increased after high-temperature calcination treatment. Oxygen vacancies can effectively promote water dissociation and provide more active *H species for CO2 reduction. However, the content of oxygen vacancies is not the more the better, and a moderate content of oxygen vacancies is required. Excessive content will reduce the stability and formic acid selectivity. In the experiments of the present invention, it was found that when the calcination condition was treatment at 350 °C for 1 h, a Sn4-Ce6-O x solid solution catalyst with moderate oxygen vacancies was obtained, and the performance was the best. Continuing to increase the content of oxygen vacancies would significantly reduce the stability and formic acid selectivity.

[0057] Table 1 XPS determination of the effect of different calcination times on the oxygen vacancy content in Sn4Ce6O x solid solution

[0058]

[0059] Example 2

[0060] Step 1: Accurately weigh 48.3 mg of Cu(NO3)3·3H2O and dissolve it in a beaker containing 200 mL of deionized water, and stir to form precursor solution A.

[0061] Step 2: Accurately weigh 781.4 mg of Ce(NO3)3·6H2O and dissolve it in a beaker containing 200 mL of deionized water, and stir to form precursor solution B.

[0062] Step 3: Under stirring conditions, add solution A to solution B, adjust the pH of the solution to 2 with dilute hydrochloric acid to inhibit the hydrolysis of Cu salts, and continue stirring for 1 h to obtain a mixed solution C.

[0063] Step 4: Under stirring conditions, add an aqueous ammonia solution with a mass fraction of 25% to the mixed solution C until the pH of the solution reaches about 11. A large amount of light purple precipitate can be observed to form.

[0064] Step 5: Filter and wash the precipitate obtained in Step 4 with a large amount of deionized water, and then place it in a vacuum drying oven at 80 °C to dry overnight to obtain a light yellow powder D.

[0065] Step 6: Disperse the light yellow powder D obtained in Step 5 in 100 mL of concentrated ammonia water with a mass fraction of 10%, and continuously stir at room temperature for 12 h to remove the CuO that has not formed a solid solution x, and after being filtered with deionized water, washed, and vacuum-dried at 80 °C, Cu1-Ce 9- O x solid solution catalyst was obtained.

[0066] Step 7: The Cu1-Ce9-O x solid solution catalyst obtained in Step 6 was heat-treated in a tubular furnace. The treatment atmosphere was a 5% H2 / Ar mixed gas, and the calcination conditions were treatment at 350 °C for 1 h to obtain a Cu1-Ce9-O x solid solution catalyst rich in oxygen vacancies.

[0067] Figure 3 The TEM image of the Cu1-Ce9-O x catalyst prepared in Step 7 of Example 2. It can be seen from the figure that the catalysts are all composed of small particles with a size of 3 - 5 nm. The small particles aggregate together, and their smaller particle size gives them a high specific surface area, enabling more reactive sites to be exposed.

[0068] Figure 4 The XRD pattern of the Cu1-Ce9-O x catalyst prepared in Step 7 of Example 2. The catalyst shows the diffraction peaks of CeO2, and no diffraction peaks of other substances appear, indicating the formation of a single phase. In addition, the position of the catalyst diffraction peak is slightly shifted towards a higher angle relative to CeO2. According to Bragg's formula, this is because the smaller Cu atoms are incorporated into the lattice of CeO2, causing lattice contraction, indicating that the Cu1-Ce9-O x solid solution catalyst was successfully prepared.

[0069] Example 3

[0070] Electrocatalytic reduction of carbon dioxide to high-value products by solid solution catalyst

[0071] In an H-type electrolytic cell separated by a cation exchange membrane, an electrocatalytic reduction of carbon dioxide reaction was carried out in a three-electrode system with an Ag / AgCl electrode as the reference electrode, a Pt sheet as the counter electrode, and a 2 cm × 0.5 cm carbon paper sprayed with 1.2 mg of the solid solution catalyst as the working electrode. The preparation method of the working electrode is as follows: Take 10 mg of the catalyst Sn4-Ce6-O prepared in Example 1 above xDispersed in 5 mL of isopropanol, 10 μL of 5 wt% Nafion solution was added. Subsequently, the catalyst dispersion was sprayed onto a 2 cm × 0.5 cm carbon paper in three portions using an airbrush, 200 μL each time. After natural drying at room temperature, the working electrode was obtained. In the electroreduction test, 0.1 M KCl solution was used as the electrolyte, and the potentiostatic reduction test was carried out under the condition of continuously introducing pure carbon dioxide with a flow rate of 30 mL / min. The range of the applied potential was -1.0 V to -1.8 V vs. RHE.

[0072] Example 4

[0073] Example 4 adopted the method of Example 3, except that the solid solution catalyst was replaced with the catalyst Cu1-Ce9-O prepared in Example 2. x .

[0074] Example 5

[0075] Example 5 adopted the method of Example 3, except that the electrolyte was replaced with 1 M KOH or KHCO3 solution, the electrolytic cell was a flow-through electrolytic cell, the reference electrode was a Hg / HgO electrode, and the ion exchange membrane was an anion exchange membrane.

[0076] Comparative Example 1

[0077] Accurately weigh 140.3 mg of SnCl4·5H2O and dissolve it in a beaker containing 200 mL of deionized water, stir and mix. Under stirring, add 5 wt% aqueous NaOH solution until the pH of the solution reaches about 10. A large amount of light purple precipitate can be observed. After the precipitate is filtered by suction and washed with a large amount of deionized water, it is placed in a vacuum drying oven at 80 °C and dried overnight to obtain SnO2.

[0078] The catalysts before and after the 5% H2-Ar treatment at 350 °C in Example 1 and the sample of Comparative Example 1 were used to electrocatalytically reduce carbon dioxide to formic acid with 0.1 M KCl as the electrolyte, and the other steps were carried out according to the method of Example 3. The Faraday efficiency varied with the applied potential as Figure 5 shown. By comparison, it was found that within a wide electrochemical window range (-1.0 to -1.8 V vs. RHE), Sn4-Ce6-O x showed a higher formic acid Faraday efficiency (>80%), indicating that it showed better catalytic activity for the conversion of CO2 to formic acid. The better catalytic activity of the solid solution catalyst was mainly because after Sn was embedded in the lattice of Ce, it could maintain a higher valence state without being reduced, and the high-valent Sn was beneficial to adsorb and convert CO2 to formic acid.

[0079] Comparative Example 2

[0080] Accurately weigh 48.3 mg of Cu(NO3)3·3H2O and dissolve it in a beaker containing 200 mL of deionized water, stir and mix. Under stirring conditions, add 5 wt% NaOH aqueous solution dropwise until the pH of the solution reaches about 11. A large amount of blue precipitate can be observed to form. After the precipitate is filtered by suction and washed with a large amount of deionized water, it is placed in a vacuum drying oven at 80 °C and dried overnight to obtain CuO.

[0081] The samples of the catalyst before and after being treated at 350 °C with 5% H2-Ar in Example 2 and the sample of Comparative Example 2 were used. With 0.1 M KCl as the electrolyte, and the rest of the steps were carried out according to the method of Example 3 for electrocatalytic reduction of carbon dioxide to methane. The Faraday efficiency changes with the applied potential as Figure 6 shown. By comparison, it is found that the synthesized Cu1-Ce 9- O x solid solution catalyst has a higher Faraday efficiency for methane, indicating that it has better catalytic activity for CO2 to methane. This is because after Cu atoms are highly dispersed into the lattice of CeO2, they can serve as catalytic sites to first reduce CO2 to *CO. The oxygen vacancies in CeO2 can accelerate the dissociation process of water and provide abundant active *H species, promoting the further hydrogenation of adsorbed *CO on the Cu sites and generating methane. On the other hand, the formation of a solid solution lattice with Cu dispersed in the CeO2 lattice also enables the Cu sites to maintain a relatively high valence state, which is beneficial to the adsorption and conversion process of CO2.

[0082] It can be seen from the above Comparative Examples 1 and 2 that the catalyst prepared by the present invention has very excellent selectivity, mainly because the high-valent M active species can stably exist.

[0083] Example 6

[0084] The method of Example 1 was adopted, with the difference that the feeding ratios of Sn and Ce precursors were adjusted (the molar ratios of Sn and Ce feeding were 2:8, 3:7, 4:6, 5:5 respectively), and solid solution materials after calcination treatment with different compositions were obtained. The results are as Figure 7 and Table 2 show.

[0085] Table 2 Determination of Sn atom content in solid solutions with different Sn-Ce ratios by atomic emission spectroscopy

[0086]

[0087] As Figure 7As shown in Table 2, by changing the feeding ratio of Sn and Ce precursors, Sn-Ce binary solid solution structures were obtained. It can be seen from the XRD peaks that the diffraction peaks in the solid solution shifted to a higher angle relative to CeO2, indicating that Sn was embedded in the CeO2 lattice to form a solid solution structure. The proportion of Sn in different solid solutions measured by atomic emission spectroscopy is shown in Table 2, and it can be seen that it is close to the feeding ratio. When the content of Sn is relatively high, a solid solution structure can still be formed. At the same time, it is also proved that SnO2 and CeO2 have similar crystal structures, and more Sn can be dissolved in CeO2, thus providing more active sites for CO2 reduction.

[0088] Example 7

[0089] Using the testing method of Example 3, the CO2 electroreduction performance was tested, and the results are as Figure 8 shown.

[0090] Figure 8 Figure showing the variation of the Faraday efficiency of CO2 electrocatalytic reduction to formic acid with potential for Sn-Ce binary solid solution structures with different ratios in Example 6 and the comparative sample SnO2. It can be seen from the figure that the Sn-Ce binary solid solutions all show higher formic acid selectivity than SnO2. This is because the solid solution structure can effectively maintain the high-valent Sn species and can effectively promote water dissociation to provide active *H species, jointly promoting the formation of formic acid products. By comparison, it can also be found that the Sn4Ce6O x solid solution has the best formic acid selectivity.

Claims

1. A preparation method of a metal-Ce binary solid solution oxide catalyst, characterized in that, It includes the following steps: (1) Mix the soluble metal M salt solution and the Ce metal salt solution; M is Cu, Sn, In, Au, Ag or Pd; (2) Adjust the pH of the solution to acidic to inhibit the hydrolysis of the salt; (3) Adjust the pH of the solution to basic to form a precipitate. After separating the obtained precipitate and drying, a solid powder is obtained; (4) Remove the active metal M and its oxide that have not formed a solid solution from the obtained solid powder, and perform high-temperature treatment in different atmospheres to obtain the M-Ce-O x solid solution catalyst.

2. The preparation method of the metal-Ce binary solid solution oxide catalyst according to claim 1, characterized in that, In step (1), the metal salt M is preferably a nitrate or chloride of Cu, Sn, In, Au, Ag or Pd, and the Ce metal salt is a nitrate of Ce.

3. The preparation method of the metal-Ce binary solid solution oxide catalyst according to claim 1, characterized in that, In step (1), the molar ratio of M to Ce in the feed is 0.5:9.5 to 1:

1.

4. The preparation method of the metal-Ce binary solid solution oxide catalyst according to claim 1, characterized in that, In step (2), an acid solution is added to adjust the pH of the solution to 1-3 to inhibit the hydrolysis of the salt.

5. The preparation method of the metal-Ce binary solid solution oxide catalyst according to claim 1, characterized in that, In step (3), a weak base solution is added, and the pH of the solution is adjusted to 9-11 under stirring conditions to form a large amount of precipitate. The obtained precipitate is separated by suction filtration and vacuum dried at 60-90 °C to obtain a solid powder.

6. The preparation method of the metal-Ce binary solid solution oxide catalyst according to claim 1, characterized in that, In step (4), the obtained solid powder is stirred with a dilute acid or an ammonia aqueous solution for 6 to 24 h to remove the active metal M and its oxide that have not formed a solid solution, and then M-Ce-O x solid solution catalyst is obtained through suction filtration, vacuum drying, etc.

7. The preparation method of the metal-Ce binary solid solution oxide catalyst according to claim 1, characterized in that, The solid solution catalyst obtained in step (4) is treated at a high temperature of 300-500 °C for 1-3 h in different atmospheres to adjust the number of oxygen vacancies in the solid solution, obtaining M-Ce-O x solid solution catalyst, and the atmosphere is air or an Ar atmosphere containing 5%-10% H2.

8. A metal-Ce binary solid solution oxide catalyst prepared by the preparation method described in claim 1.

9. An application of the metal-Ce binary solid solution oxide catalyst described in claim 8 in electrocatalytic CO2 reduction.

10. The application according to claim 9, wherein The electrolytic cell used for the metal-Ce binary solid solution oxide catalyst in electrocatalytic CO2 reduction is an ion-exchange membrane-separated H-type or flow-type electrolytic cell, with an Ag / AgCl electrode or a Hg / HgO electrode as the reference electrode, a Pt sheet or nickel foam as the counter electrode, and a hydrophobic carbon paper coated with the metal-Ce binary solid solution oxide catalyst as the working electrode; the constant potential range is -0.30V to -2.0V vs. RHE, the ion-exchange membrane is an anion or cation exchange membrane, the electrolyte is a KCl, KOH or KHCO3 solution with a concentration of 0.1-3M, and the carbon dioxide gas flow rate is 10-50 sccm.

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