Method for preparing urea through co-electrolysis of CO2 and nitrite ions
By supporting copper-zinc bimetals on a non-precious metal-based catalyst and electrolyzing CO2 and nitrite ions using a carbon paper electrode, the problems of high cost of precious metal catalysts and difficulty in N2 activation are solved, achieving low-cost and high-efficiency urea production, reducing CO2 emissions, and showing promising prospects for industrial application.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-30
- Publication Date
- 2026-03-24
AI Technical Summary
In the existing electrochemical synthesis of urea, the high cost of precious metal catalysts and the difficulty of N2 activation limit its industrial application, while the large CO2 emissions cause serious environmental pollution.
A non-precious metal-based catalyst was used to synthesize nano-cerium oxide support via a hydrothermal method. Copper-zinc bimetal was loaded onto the support, and urea was generated by electrolyzing CO2 and nitrite ions using a carbon paper electrode.
It achieves low-cost and high-efficiency urea production, reduces CO2 emissions, provides an environmentally friendly industrial application path, and has excellent catalyst performance with a high urea production rate.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of electrochemical preparation of urea, and particularly relates to a method for preparing urea by co-electrolyzing CO2 and nitrite ions. BACKGROUND
[0002] Urea (CO(NH2)2) is an important chemical that plays a crucial role in both agriculture and industry. It is mainly used in agriculture as a nitrogen fertilizer to promote plant growth, supporting global food production. Urea is also an important industrial raw material, widely used in medicine, cosmetics, textiles, and plastic industries. Current industrial production of urea involves two-step reactions, i.e., N2+H2→NH3, NH3+CO2→CO(NH2)2, both of which are carried out under harsh conditions of high temperature and high pressure. These two reactions involve high-concentration NH3 consumption and, due to the fact that H2 is mainly produced from fossil energy, indirectly lead to high CO2 emissions. CO2 is one of the main greenhouse gases, and its massive emission can cause global climate change, posing a serious threat to the environment. At the same time, CO2 is a cheap C1 resource, and how to effectively reduce CO2 emissions and convert it into useful chemicals has become an important research direction in the fields of environmental protection and resource utilization. Due to the mild reaction conditions and low CO2 emissions of electrochemical reduction, electrochemical synthesis of urea from CO2 / N2 and their derivatives has become a promising sustainable strategy.
[0003] In recent years, numerous researchers have continuously explored and designed new catalysts, electrolytes, reaction devices, etc., and have made significant progress in the electrocatalytic synthesis of urea. Currently, urea can be synthesized by coupling CO2 and various nitrogen sources (N2, nitrate ions, nitrite ions) in water through an electrochemical process, which is a process involving multiple proton coupling and multiple electron transfer. Among these reactants, N2 is a cheap and abundant nitrogen source, but due to the very stable nitrogen-nitrogen triple bond in N2 molecules, its activation and reaction are extremely difficult, usually showing low performance in the synthesis of urea. Nitrate ions are a nitrogen source with a high oxidation state, which exists widely in nature and industrial wastewater. Compared with N2, the activation of nitrate ions is less difficult, so the research on the preparation of urea by coupling nitrate ions with CO2 is relatively easy. Studies have shown that this method has low energy consumption and high selectivity of urea. However, the high oxidation state of nitrate ions can lead to the occurrence of side reactions, thereby affecting the purity of the product and the efficiency of the reaction. The oxidation state of nitrite ions is lower, and its coupling reaction with CO2 to generate urea has received significant attention in recent years. This method not only has high efficiency, but also has fewer by-products. Therefore, the electrocatalytic coupling of CO2 and NO2 - to prepare urea has industrial application prospects.
[0004] For the process of electrochemical synthesis of urea, the design and preparation of electrocatalysts are crucial. The catalysts for electrochemical synthesis of urea reported in the literature include metal oxide catalysts rich in defects (Cell Reports Physical Science 2 (2021), 100378), metal oxide supported metal catalysts (Journal of Colloid and Interface Science 577 (2020) 109-114) and bimetallic catalysts such as terbium-doped palladium nanocrystals (Nano Letters., 20 (2020) 8282-8289), gold-copper nanowires (Cell Reports Physical Science 3 (2022), 100869). The above-mentioned catalysts mainly involve noble metals, which limits their industrial application due to their low reserves and high cost.
[0005] Therefore, the development of efficient and stable non-noble metal-based electrocatalysts is of great significance for the realization of large-scale co-electrolysis of CO2 and nitrite ions to produce urea. SUMMARY
[0006] The present application aims to provide a method for co-electrolysis of CO2 and nitrite ions to prepare urea to overcome the shortcomings of the prior art.
[0007] To achieve the above-mentioned application purposes, the present application provides the following technical solutions: The present application provides a method for co-electrolysis of CO2 and nitrite ions to prepare urea, comprising the following steps: 1) mixing cerium nitrate, water, propionic acid and ethylene glycol and then performing hydrothermal reaction to obtain a nano cerium oxide carrier; 2) mixing the nano cerium oxide carrier, ethanol and metal salt and then performing rotary evaporation to obtain a precipitate; sequentially drying and calcining the precipitate, and reducing the calcined product under a reducing gas to obtain a catalyst; In step 2), the metal salt is a copper salt or a mixture of a copper salt and a zinc salt; 3) mixing the catalyst, anhydrous ethanol and a perfluorosulfonic acid resin solution to obtain a suspension, coating the suspension on carbon paper to obtain a working electrode; 4) placing the working electrode in an electrolyte, introducing CO2 gas, and performing electrolysis reaction using a three-electrode system to obtain an electrolyte containing urea; In step 4), the electrolyte is an aqueous solution of KOH and KNO2.
[0008] Preferably, in step 1), the mass-to-volume ratio of cerium nitrate and propionic acid is 0.5~1.5 mg: 0.5~2 mL; the volume ratio of water, propionic acid and ethylene glycol is 0.5~2: 0.5~2: 20~40; the hydrothermal reaction temperature is 150~220℃, and the hydrothermal reaction time is 150~250 min.
[0009] Preferably, in step 2), the mass-to-volume ratio of the nano-cerium oxide carrier, ethanol, and metal salt is 80-120 mg: 15-25 mL: 20-45 mg; the copper salt contains copper nitrate, copper chloride, copper sulfate, or copper acetylacetonate, and the zinc salt contains zinc nitrate, zinc chloride, zinc sulfate, or zinc acetylacetonate.
[0010] Preferably, the calcination temperature in step 2) is 250~350℃ and the calcination time is 0.5~1.5h; the drying temperature is 70~90℃ and the drying time is 10~14h.
[0011] Preferably, the reducing gas in step 2) is an H2 / Ar mixture, in which the volume fraction of H2 is 3.3~99.999%; the temperature of the reduction reaction is 400~600℃, the time of the reduction reaction is 4~6h, and the rate of heating to the reduction reaction temperature is 0.5~1.5℃ / min.
[0012] Preferably, in step 3), the mass-to-volume ratio of the catalyst, anhydrous ethanol, and perfluorosulfonic acid resin solution is 5 mg: 500~2000 μL: 20~100 μL, and the mass fraction of the perfluorosulfonic acid resin solution is 3~7%.
[0013] Preferably, the mixing time in step 3) is 25-35 minutes, the coating method is drop coating, and the coating amount of suspension on carbon paper is 0.15-0.25 mg suspension / 1 cm. 2 Carbon paper.
[0014] Preferably, the concentration of CO2 gas in step 4) is 5~99.999%; in the aqueous solution of KOH and KNO2, the concentration of KOH is 0.05~0.5 mol / L and the concentration of KNO2 is 0.01~0.1 mol / L.
[0015] Preferably, the electrolysis reaction in step 4) has a potential of -1.2 to -0.6 V vs. RHE.
[0016] The beneficial effects of this invention are: 1) This invention first synthesizes a nano-cerium oxide support using a hydrothermal method, and then prepares a nano-catalyst for electrocatalytic urea production using a precursor containing non-precious metals (copper and zinc) through a simple impregnation and calcination method. By supporting this catalyst on carbon paper and using a potassium hydroxide-potassium nitrite aqueous solution as the electrolyte, urea can be produced through efficient co-electrolysis of CO2 and nitrite. The method of this invention is mild and low-cost, opening up a practically feasible path for electrocatalytic urea production, and has significant economic and social benefits.
[0017] 2) This invention uses a mesoporous cerium oxide support with a large specific surface area to load copper-zinc bimetal or copper metal for electrochemical synthesis of urea. At -1.0V vs. RHE potential, the urea production rate reaches 787.5 mg·h⁻¹. -1 ·g -1 .
[0018] 3) This invention uses a non-precious metal catalyst to react CO2 and NO2. - The coupling process to produce urea can not only produce high-value chemicals, but also alleviate environmental problems caused by CO2 emissions to a certain extent, and has great application prospects. Attached Figure Description
[0019] Figure 1 Cu prepared in Example 1 100 Transmission electron microscopy image of the CeO2 catalyst; Figure 2 Cu from Example 1 100 @Urea yield of CeO2 catalyst and CeO2-supported bimetallic catalysts in Examples 2 and 1-3 at -1.0V vs. RHE potential; Figure 3 Cu for Example 3 30 Zn 70 @CeO2 catalyst yields of urea and ammonia at different potentials; Figure 4 The yields of urea and ammonia at -1.0V vs. RHE potentials for catalysts with different copper-zinc ratios in Examples 1-3, Example 5, and Comparative Example 4. Detailed Implementation
[0020] This invention provides a method for preparing urea by co-electrolysis of CO2 and nitrite ions, comprising the following steps: 1) A hydrothermal reaction was carried out after mixing cerium nitrate, water, propionic acid and ethylene glycol to obtain nano-cerium oxide carrier; 2) The nano-cerium oxide support, ethanol and metal salt were mixed and then rotary evaporated to obtain a precipitate; the precipitate was then dried and calcined in sequence, and the calcined product was subjected to a reduction reaction under a reducing gas to obtain a catalyst; Step 2) The metal salt is a copper salt or a mixture of copper and zinc salts; 3) Mix the catalyst, anhydrous ethanol and perfluorosulfonic acid resin solution (Nafion solution) to obtain a suspension, and coat the suspension onto carbon paper to obtain the working electrode; 4) Place the working electrode in the electrolyte, introduce CO2 gas, and use a three-electrode system to carry out the electrolysis reaction to obtain an electrolyte containing urea; Step 4) The electrolyte is an aqueous solution of KOH and KNO2.
[0021] This invention uses CO2 and nitrite ions as raw materials, a catalyst drop-coated on carbon paper as the working electrode material, and an aqueous solution of potassium hydroxide and potassium nitrite as the electrolyte to form an electrochemical system for electrolytic reaction to obtain the product urea; the surface of copper can effectively adsorb CO2 and NO2. - As an intermediate, copper lowers the activation energy of the reaction, thus exhibiting excellent performance in the electrochemical reduction of CO2 and possessing great potential and application prospects.
[0022] In this invention, the preferred mass-to-volume ratio of cerium nitrate and propionic acid in step 1) is 0.5-1.5 mg: 0.5-2 mL, more preferably 0.7-1.2 mg: 0.7-1.5 mL, and even more preferably 1 mg: 1-1.2 mL; the preferred volume ratio of water, propionic acid, and ethylene glycol is 0.5-2: 0.5-2: 20-40, more preferably 0.7-1.5: 0.7-1.5: 25-35, and even more preferably 1-1.2: 1-1.2: 30; the preferred temperature of the hydrothermal reaction is 150-220°C, more preferably 180-200°C, and the preferred time of the hydrothermal reaction is 150-250 min, more preferably 180-220 min, and even more preferably 200 min.
[0023] In this invention, the cerium nitrate in step 1) is preferably cerium nitrate hexahydrate; after the hydrothermal reaction is completed, the mixture is sequentially cooled and centrifuged to obtain a nano-cerium oxide carrier.
[0024] In this invention, the mass-to-volume ratio of the nano-cerium oxide carrier, ethanol, and metal salt in step 2) is preferably 80-120 mg: 15-25 mL: 20-45 mg, more preferably 90-110 mg: 17-22 mL: 25-40 mg, and even more preferably 100 mg: 20 mL: 28-33 mg; the copper salt preferably contains copper nitrate, copper chloride, copper sulfate, or copper acetylacetonate, and the zinc salt preferably contains zinc nitrate, zinc chloride, zinc sulfate, or zinc acetylacetonate.
[0025] In this invention, the calcination temperature in step 2) is preferably 250~350℃, more preferably 270~330℃, and even more preferably 300~310℃, and the calcination time is preferably 0.5~1.5h, more preferably 0.8~1.2h, and even more preferably 1h; the drying temperature is preferably 70~90℃, more preferably 75~85℃, and even more preferably 80℃, and the drying time is preferably 10~14h, more preferably 11~13h, and even more preferably 12h.
[0026] In this invention, the calcined product in step 2) is washed, dried, and then subjected to a reduction reaction. The washing reagent is preferably anhydrous ethanol, and the number of washings is preferably 2 to 4 times, more preferably 3 times. The drying temperature is preferably 70 to 90°C, more preferably 75 to 85°C, more preferably 80°C, and the drying time is preferably 10 to 14 hours, more preferably 11 to 13 hours, more preferably 12 hours.
[0027] In this invention, the reducing gas in step 2) is preferably an H2 / Ar mixture, wherein the volume fraction of H2 in the H2 / Ar mixture is preferably 3.3~99.999%, more preferably 10~50%, and even more preferably 20~40%; the temperature of the reduction reaction is preferably 400~600℃, more preferably 450~550℃, and even more preferably 500℃; the time of the reduction reaction is preferably 4~6h, more preferably 4.5~5.5h, and even more preferably 5h; and the rate of heating to the reduction reaction temperature is preferably 0.5~1.5℃ / min, more preferably 0.7~1.3℃ / min, and even more preferably 0.9~1℃ / min.
[0028] In this invention, the preferred mass-to-volume ratio of the catalyst, anhydrous ethanol, and perfluorosulfonic acid resin solution in step 3) is 5 mg: 500~2000 μL: 20~100 μL, more preferably 5 mg: 700~1500 μL: 40~70 μL, and even more preferably 5 mg: 950~1100 μL: 50~60 μL. The preferred mass fraction of the perfluorosulfonic acid resin solution is 3~7%, more preferably 4~6%, and even more preferably 5%.
[0029] In this invention, the mixing time in step 3) is preferably 25-35 min, more preferably 27-33 min, and even more preferably 30 min. The coating method is preferably drop coating, and the coating amount of the suspension on the carbon paper is preferably 0.15-0.25 mg suspension / 1 cm. 2 The carbon paper is further preferably prepared with a suspension concentration of 0.18~0.22 mg / cm³. 2 Carbon paper, more preferably 0.2 mg suspension / 1 cm 2 Carbon paper.
[0030] In this invention, the concentration of CO2 gas in step 4) is preferably 5~99.999%, more preferably 50~99%; in the aqueous solution of KOH and KNO2, the concentration of KOH is preferably 0.05~0.5 mol / L, more preferably 0.1~0.4 mol / L, more preferably 0.2~0.3 mol / L, and the concentration of KNO2 is preferably 0.01~0.1 mol / L, more preferably 0.02~0.05 mol / L, more preferably 0.03~0.04 mol / L.
[0031] In this invention, the electrolysis potential in step 4) is preferably -1.2 to -0.6V vs. RHE, and more preferably -1.0 to -0.8V vs. RHE.
[0032] In this invention, the urea-containing electrolyte in step 4) is subjected to qualitative and quantitative analysis using the urease decomposition method and the indophenol blue method; the volume-to-mass ratio of electrolyte to urease is preferably 2 mL: 1~3 mg, more preferably 2 mL: 1.5~2.5 mg, and even more preferably 2 mL: 2 mg.
[0033] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.
[0034] In this embodiment, the cathode chamber and anode chamber of the H-type electrolytic cell are separated by a Nafion 117 membrane; the three electrodes include a reference electrode, a counter electrode, and a working electrode, with silver / silver chloride as the reference electrode, a graphite rod as the counter electrode, and carbon paper with a catalyst drop-coated as the working electrode.
[0035] Example 1
[0036] 1 mg of cerium nitrate hexahydrate, 1 mL of deionized water, 1 mL of propionic acid, and 30 mL of ethylene glycol were stirred evenly and then placed in a 30 mL Teflon-sealed autoclave at 180 °C for hydrothermal reaction for 200 min. After natural cooling to room temperature, the mixture was centrifuged to obtain nano-cerium oxide (CeO2) support. 100 mg of nano-CeO2 support was dispersed in 20 mL of anhydrous ethanol, and 31.8 mg of copper chloride was added. The mixture was ultrasonically dispersed at 40 kHz for 40 min. After uniform dispersion, the anhydrous ethanol was removed by rotary evaporation. The resulting precipitate was dried at 80 °C for 12 h and then calcined in a muffle furnace at 300 °C for 1 h. After cooling, the calcined product was washed three times with anhydrous ethanol, dried at 80 °C for 12 h, and then heated to 500 °C at a rate of 1 °C / min in an H2 / Ar mixed gas (H2 volume fraction of 10%). It was reduced at 500 °C for 5 h and then naturally cooled to room temperature to obtain Cu. 100 @CeO2 catalyst (the mass fraction of Cu in the catalyst is 15%).
[0037] 5mg Cu 100 @CeO2 catalyst, 950 μL anhydrous ethanol, and 50 μL Nafion D520 solution (5% by mass) were ultrasonically mixed for 30 min to obtain a suspension. The suspension was then diluted with 0.2 mg suspension / 1 cm⁻¹. 2 Carbon paper is evenly dripped onto a 2cm layer 2 The carbon paper is dried naturally to obtain the working electrode.
[0038] The working electrode was placed in an H-type electrolytic cell containing electrolytes (an aqueous solution of KOH and KNO2, with a KOH concentration of 0.1 mol / L and a KNO2 concentration of 0.02 mol / L). 99% pure CO2 gas was continuously introduced (CO2 introduction rate of 20 mL / min). Electrolysis was carried out using a three-electrode system at a potential of -1.0 V vs. RHE to obtain an electrolyte containing urea.
[0039] In this embodiment, the electrolyte (2 mL) after electrolysis was tested using the urease (2 mg) and indophenol blue (prepared by mixing 2 mL of 1 mol / L NaOH aqueous solution containing 5 wt% sodium citrate and 5 wt% salicylic acid, 1 mL of 0.05 mol / L NaClO aqueous solution, and 200 μL of 1 wt% C₅FeN₆Na₂O aqueous solution). The test results showed that the main products of the electrolyte were urea and ammonia. When the applied potential was -1.0 V vs. RHE, the urea formation rate was 274.3 mg·h⁻¹. -1 ·g -1 .
[0040] Cu prepared in Example 1 100 Transmission electron microscopy image of the @CeO2 catalyst as shown in the image. Figure 1 As shown.
[0041] Example 2
[0042] In Example 1, the 31.8 mg copper chloride was replaced with 15.9 mg copper chloride and 15.7 mg zinc chloride, while other process conditions remained the same as in Example 1, yielding Cu. 50 Zn 50 @CeO2 catalyst (in which the sum of the mass fractions of Cu and Zn is 15%); the preparation process of the working electrode and the electrolyte containing urea obtained by electrolysis is the same as in Example 1.
[0043] In this embodiment, the electrolyte (2 mL) after electrolysis was analyzed using urease (2 mg) and indophenol blue method. The results showed that the main products of the electrolyte were urea and ammonia. When the applied potential was -1.0 V vs. RHE, the urea formation rate was 407 mg / h. -1 ·g -1 .
[0044] Comparative Example 1
[0045] In Example 1, the 31.8 mg copper chloride was replaced with 15.9 mg copper chloride and 11.9 mg silver nitrate, while other process conditions remained the same as in Example 1, yielding Cu. 50 Ag 50 @CeO2 catalyst; the preparation process of the working electrode and the electrolyte containing urea obtained by electrolysis is the same as in Example 1.
[0046] Comparative Example 2
[0047] In Example 1, the 31.8 mg copper chloride was replaced with 15.9 mg copper chloride and 14.6 mg indium chloride, while other process conditions remained the same as in Example 1, yielding Cu. 50 In 50 @CeO2 catalyst; the preparation process of the working electrode and the electrolyte containing urea obtained by electrolysis is the same as in Example 1.
[0048] Comparative Example 3
[0049] In Example 1, the 31.8 mg copper chloride was replaced with 15.9 mg copper chloride and 12.1 mg tin chloride, while other process conditions remained the same as in Example 1, yielding Cu. 50 Sn 50 @CeO2 catalyst; the preparation process of the working electrode and the electrolyte containing urea obtained by electrolysis is the same as in Example 1.
[0050] Cu in Example 1 100 @Urea yields at -1.0 V vs. RHE potential for CeO2 catalysts and CeO2-supported bimetallic catalysts in Examples 2 and 1-3 are as follows: Figure 2 As shown, by Figure 2 It can be seen that Cu 50 Zn 50 @CeO2 exhibits a significantly higher urea yield than other bimetallic catalysts.
[0051] Example 3
[0052] In Example 1, the 31.8 mg copper chloride was replaced with 9.5 mg copper chloride and 21.9 mg zinc chloride, while other process conditions remained the same as in Example 1, yielding Cu. 30Zn 70 @CeO2 catalyst (in which the sum of the mass fractions of Cu and Zn is 15%); the preparation process of the working electrode and the electrolyte containing urea obtained by electrolysis is the same as in Example 1.
[0053] In this embodiment, the electrolyte (2 mL) after electrolysis was completed was tested using urease (2 mg) and indophenol blue method. The test results showed that the main products of the electrolyte were urea and ammonia.
[0054] Example 4
[0055] The applied potential in Example 3 was changed from -1.0V vs. RHE to -1.2V vs. RHE, -0.8V vs. RHE, and -0.6V vs. RHE, respectively, while other process conditions remained the same as in Example 3.
[0056] Cu in Examples 3 and 4 30 Zn 70 @CeO2 catalyst yields of urea and ammonia at different potentials, as follows Figure 3 As shown. By Figure 3 It can be seen that the urea production rate is the highest when the applied potential is -1.0V vs. RHE, which is 787.5 mg·h⁻¹. -1 ·g -1 .
[0057] Example 5
[0058] In Example 1, the 31.8 mg copper chloride was replaced with 3.2 mg copper chloride and 28.2 mg zinc chloride, while other process conditions remained the same as in Example 1, yielding Cu. 10 Zn 90 @CeO2 catalyst (in which the sum of the mass fractions of Cu and Zn is 15%); the preparation process of the working electrode and the electrolyte containing urea obtained by electrolysis is the same as in Example 1.
[0059] In this embodiment, the electrolyte (2 mL) after electrolysis was analyzed using urease (2 mg) and the indophenol blue method. The results showed that the main products of the electrolyte were urea and ammonia. When the applied potential was -1.0 V vs. RHE, the urea formation rate was 526.5 mg·h⁻¹. -1 ·g -1 .
[0060] Comparative Example 4
[0061] In Example 1, the 31.8 mg copper chloride was replaced with 31.4 mg zinc chloride, and other process conditions were the same as in Example 1, to obtain Zn. 100@CeO2 catalyst (in which the mass fraction of Zn is 15%); the preparation process of the working electrode and the electrolyte containing urea obtained by electrolysis is the same as in Example 1.
[0062] The electrolyte (2 mL) after electrolysis in this comparative example was analyzed using urease (2 mg) and the indophenol blue method. The results showed that the main products of the electrolyte were urea and ammonia. When the applied potential was -1.0 V vs. RHE, the urea formation rate was 17.7 mg / h. -1 ·g -1 .
[0063] The yields of urea and ammonia for catalysts with different copper-zinc ratios in Examples 1-3, Example 5, and Comparative Example 4 at -1.0V vs. RHE potential are as follows: Figure 4 As shown.
[0064] The electrocatalytic system of this invention has mild reaction conditions and a simple reaction device. The key cathode catalyst is easy to prepare and readily available, and has industrial development value. It provides an important and practical approach for CO2 fixation and wastewater denitrification.
[0065] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.
Claims
1. A method for preparing urea by co-electrolysis of CO2 and nitrite ions, characterized in that, It includes the following steps: 1) A hydrothermal reaction was carried out after mixing cerium nitrate, water, propionic acid and ethylene glycol to obtain nano-cerium oxide carrier; 2) The nano-cerium oxide support, ethanol and metal salt were mixed and then rotary evaporated to obtain a precipitate; the precipitate was then dried and calcined in sequence, and the calcined product was subjected to a reduction reaction under a reducing gas to obtain a catalyst; Step 2) The metal salt is a copper salt or a mixture of copper and zinc salts; 3) Mix the catalyst, anhydrous ethanol and perfluorosulfonic acid resin solution to obtain a suspension, and coat the suspension onto carbon paper to obtain the working electrode; 4) Place the working electrode in the electrolyte, introduce CO2 gas, and use a three-electrode system to carry out the electrolysis reaction to obtain an electrolyte containing urea; Step 4) The electrolyte is an aqueous solution of KOH and KNO2.
2. The method according to claim 1, characterized in that, Step 1) The mass-to-volume ratio of cerium nitrate and propionic acid is 0.5~1.5mg:0.5~2mL; the volume ratio of water, propionic acid and ethylene glycol is 0.5~2:0.5~2:20~40; the hydrothermal reaction temperature is 150~220℃, and the hydrothermal reaction time is 150~250min.
3. The method according to claim 1 or 2, characterized in that, Step 2) The mass-to-volume ratio of the nano-cerium oxide carrier, ethanol, and metal salt is 80~120mg:15~25mL:20~45mg; the copper salt includes copper nitrate, copper chloride, copper sulfate, or copper acetylacetonate, and the zinc salt includes zinc nitrate, zinc chloride, zinc sulfate, or zinc acetylacetonate.
4. The method according to claim 3, characterized in that, Step 2) The calcination temperature is 250~350℃ and the calcination time is 0.5~1.5h; the drying temperature is 70~90℃ and the drying time is 10~14h.
5. The method according to claim 4, characterized in that, Step 2) The reducing gas is an H2 / Ar mixture, in which the volume fraction of H2 is 3.3~99.999%; the temperature of the reduction reaction is 400~600℃, the time of the reduction reaction is 4~6h, and the rate of heating to the reduction reaction temperature is 0.5~1.5℃ / min.
6. The method according to claim 4 or 5, characterized in that, Step 3) The mass-to-volume ratio of the catalyst, anhydrous ethanol, and perfluorosulfonic acid resin solution is 5 mg: 500~2000 μL: 20~100 μL, and the mass fraction of the perfluorosulfonic acid resin solution is 3~7%.
7. The method according to claim 6, characterized in that, Step 3) The mixing time is 25-35 minutes, and the coating method is drop coating. The coating amount of the suspension on the carbon paper is 0.15-0.25 mg suspension / 1 cm. 2 Carbon paper.
8. The method according to claim 7, characterized in that, Step 4) The concentration of CO2 gas is 5~99.999%; in the aqueous solution of KOH and KNO2, the concentration of KOH is 0.05~0.5 mol / L and the concentration of KNO2 is 0.01~0.1 mol / L.
9. The method according to claim 8, characterized in that, Step 4) The electrolysis reaction potential is -1.2~-0.6V vs. RHE.