Method for synthesizing urea through thermoelectric coupling catalysis

Abstract

The invention belongs to the technical field of urea synthesis, and discloses a method for synthesizing urea through thermoelectric coupling catalysis. According to the method, a metal diatom catalyst is adopted as an electrode material, a metal-nonmetal mediating pair composed of metal ions and a nonmetal mediator is added into an electrolyte, mass transfer of a nitrogen source reactant from an electrode-electrolyte double electric layer to the surface of the catalyst is enhanced under the reaction condition of thermally-enhanced electricity, and the nitrogen source is obtained. The dissociation of N = N or N = O bonds of a nitrogen source by a double-atom catalyst and a metal-nonmetal mediator is enhanced, and C-N coupling of the nitrogen source and the nonmetal mediator is promoted to generate urea. Therefore, the action of the thermoelectric synergistic coupling metal-nonmetal mediation pair changes the reaction path of traditional electro-catalytic synthesis of urea, the reaction steps of traditional electro-catalytic synthesis of urea are shortened, and the yield of thermoelectric catalytic synthesis of urea is remarkably higher than that of single electro-catalytic synthesis and single thermocatalytic synthesis of urea.

Description

Technical Field

[0001] This invention belongs to the field of urea synthesis technology, specifically relating to a method for thermoelectric coupling catalytic synthesis of urea. Background Technology

[0002] Urea has been widely used in industry, agriculture, and medicine. Furthermore, urea is considered an efficient hydrogen transporter. Its availability, low cost, safe storage, and ease of transportation also make it an ideal choice for fuel cell technology.

[0003] Currently, urea synthesis mainly relies on the high-temperature, high-pressure Haber process to first synthesize ammonia, which then reacts with carbon dioxide under high temperature and pressure (400-500℃, 100-200MPa) to synthesize urea. This process results in complex urea synthesis, high costs, and severe energy consumption and environmental pollution. While electrocatalytic urea synthesis technology can be driven by renewable electricity and has advantages such as safe and simple operation, the multiple reaction steps lead to low CN coupling efficiency and low urea yield (see...). Figure 3 High-temperature thermocatalysis, however, has the disadvantages of high energy consumption and high pollution. Summary of the Invention

[0004] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the present invention proposes a method for the thermo-electric coupling catalytic synthesis of urea, which, compared with the single electrocatalytic or thermocatalytic synthesis of urea, not only reduces the number of steps in the synthesis reaction, but also significantly improves the yield of urea.

[0005] The inventive concept of this invention is as follows: This invention uses a metal diatomic catalyst as an electrode, and introduces metal cations (such as Li) into the electrolyte. + Na + K + Ca 2+ Mg 2+ 、Rb + Cs + ) and non-metallic mediators (such as CO2, CO3) 2- HCO3 -The metal-nonmetal mediated pair consists of a metal-nonmetal pair. Under thermo-enhanced electrochemical reaction conditions, the d-orbital electrons of the metal diatomic catalyst transition from a low-spin state to a high-spin state, thereby promoting the adsorption and activation of reactants and reaction intermediates. Simultaneously, the metal-nonmetal mediated pair, under the synergistic effect of the electrode-electrolyte double layer, promotes the adsorption of nitrogen source reactants by the catalyst and promotes the activation and decomposition of the nitrogen source and nonmetal mediated material themselves. Furthermore, under thermo-electric synergistic conditions, the mass transfer of nitrogen source reactants from the double layer to the catalyst surface and the dissociation of N≡N or N=O bonds are enhanced, and CN coupling between the nitrogen source and nonmetal mediated material is promoted to generate urea. Therefore, this invention provides a novel urea synthesis method. Because the thermo-electric synergistic effect optimizes the d-orbital electron spin state of the dimetallic catalyst and the mass transfer and chemical properties of the metal-nonmetal mediated pair in the electrode-electrolyte double layer, it changes the reaction mechanism of traditional electrocatalytic urea synthesis, reduces the number of reaction steps, and therefore the yield of urea synthesized by thermo-electrocatalysis in this invention is significantly higher than that of urea synthesized by electrocatalysis or thermocatalysis alone.

[0006] To address the aforementioned technical problems, a first aspect of the present invention provides a method for thermoelectric coupling catalytic synthesis of urea, comprising the following steps: (1) Assemble the three-electrode system and the electrolyte into an electrolytic cell. The working electrode of the three-electrode system is a metal diatomic catalyst. The electrolyte contains a metal-nonmetal mediated pair. The metal-nonmetal mediated pair includes metal cations and nonmetal mediators. The nonmetal mediators include nonmetal molecules or nonmetal anions. (2) Add a nitrogen source to the electrolyte to form a reaction system; then energize and heat the electrolytic cell to dissociate the N≡N bond or N=O in the reaction system and couple the nitrogen source with the CN of the non-metallic mediator to generate the urea.

[0007] Specifically, this invention employs a metal diatomic catalyst as the working electrode. Under thermally enhanced electrochemical reaction conditions, the d-orbital electrons of the metal diatomic catalyst transition from a low-spin state to a high-spin state, thereby promoting the adsorption and activation of reactants and reaction intermediates (see [link to relevant documentation]). Figure 1 Simultaneously, a metal-nonmetal mediated pair, composed of metal cations and nonmetal mediators, is added to the electrolyte. Under the synergistic effect of the electrode-electrolyte double layer, the metal-nonmetal mediated pair promotes the adsorption of nitrogen source reactants by the catalyst and facilitates the activation and decomposition of the nitrogen source and the nonmetal mediators themselves (see...). Figure 2 Furthermore, the thermoelectric synergistic condition enhances the mass transfer of nitrogen source reactants from the electrode-electrolyte double layer to the catalyst surface, strengthens the dissociation of the N≡N or N=O bonds of the nitrogen source by the diatomic catalyst and the metal-nonmetal mediated pair, and promotes the CN coupling of the nitrogen source and the nonmetal mediated to generate urea (see [link to relevant documentation]). Figure 3Therefore, the thermoelectric coupling catalytic synthesis method for urea of ​​the present invention can effectively improve the yield of urea.

[0008] In some embodiments of the present invention, the metal diatomic catalyst is selected from any one of Cu-Co, Fe-Ni, Au-Pd, Ti-W, Zn-Mn, Pt-Mo, Cr-Rh, V-Ru, Ir-Bi, and In-Sn. These metals are abundant in nature, inexpensive, and easy to prepare, and have good application prospects.

[0009] In some embodiments of the present invention, the preparation process of the metal diatomic catalyst includes the following steps: dissolving two soluble metal salts, melamine and carbon black in ethanol to obtain a mixed slurry; then heating the mixed slurry to evaporate the solvent and obtain a black solid; and finally calcining the black solid to obtain the metal diatomic catalyst.

[0010] In some embodiments of the present invention, the ratio of the amount of soluble metal salt to melamine is 1 mmol: (10-30) mg; the mass ratio of melamine to carbon black is 1: (20-30); and the mass-volume ratio of melamine to ethanol is 1 mg: (3-5) mL.

[0011] In some embodiments of the present invention, the heating temperature of the mixed slurry is 50-70°C, the calcination temperature is 700-900°C, and the calcination time is 1-3 hours.

[0012] In some embodiments of the present invention, the metal cation is selected from Li. + Na + K + Ca 2+ Mg 2+ 、Rb + Cs + At least one of the following, wherein the nonmetallic molecule includes CO2, and the nonmetallic anion is selected from CO3. 2- HCO3 - At least one of the following. The metal cation may be introduced by a soluble salt containing the above-mentioned ions, CO3. 2- and HCO3 - It can be made from CO3 2- and HCO3 - The soluble salt is introduced.

[0013] In some embodiments of the present invention, the concentration of the metal-nonmetal mediator pair in the electrolyte is 0.01-5 mol / L. The electrolyte is a deionized aqueous solution of the metal-nonmetal mediator pair, that is, a solution formed by adding the metal-nonmetal mediator pair to deionized water.

[0014] In some embodiments of the present invention, the nitrogen source is selected from N2 and NO2. - NO3 - At least one of the following. The NO2 -- and NO3 - They are introduced by their respective soluble salts.

[0015] In some embodiments of the present invention, the reference electrode of the three-electrode system is Hg / HgO, and the counter electrode is a platinum sheet.

[0016] In some embodiments of the present invention, in step (2), the heating temperature is 30-80°C.

[0017] In some embodiments of the present invention, in step (2), the voltage applied is -1.674V to -1.274V relative to the Hg / HgO reference electrode.

[0018] Compared with the prior art, the above-described technical solution of the present invention has at least the following technical effects or advantages: (1) This invention uses a metal diatomic catalyst as the working electrode and adds a metal-nonmetal mediated pair composed of metal ions and nonmetal mediators to the electrolyte. Under thermo-enhanced electrochemical reaction conditions, the mass transfer of nitrogen source reactants from the electrode-electrolyte double layer to the catalyst surface is enhanced, the dissociation of the nitrogen source N≡N or N=O bonds by the diatomic catalyst and the metal-nonmetal mediated pair is enhanced, and the CN coupling of the nitrogen source and the nonmetal mediator is promoted to generate urea. Therefore, the thermo-electrochemical synergistic coupling of the metal-nonmetal mediated pair in this invention changes the reaction pathway of traditional electrocatalytic urea synthesis, shortens the reaction steps of traditional electrocatalytic urea synthesis, and the yield of thermo-electrocatalytic urea synthesis is significantly higher than that of urea synthesis by electrocatalysis and thermocatalysis alone.

[0019] (2) The thermoelectric coupling catalytic synthesis method for urea provided by the present invention does not involve high temperature and high pressure, the reaction process is simple and efficient, and can effectively reduce the cost of urea industrial production. Attached Figure Description

[0020] Figure 1 This is a schematic diagram showing the transition of the d-orbital spin state of a metal diatomic catalyst from a low-spin state to a high-spin state under thermoelectric synergy. Figure 2 Schematic diagram of thermoelectric synergistic promotion of metal-nonmetal-mediated activation and pyrolysis of reactants; Figure 3 This is a schematic diagram of the reaction steps for the electrocatalytic synthesis of urea and the thermoelectric synergistic CN-coupled catalytic synthesis of urea. Detailed Implementation

[0021] The present invention will now be described in detail with reference to embodiments to facilitate understanding of the invention by those skilled in the art. It is particularly important to note that the embodiments are merely illustrative of the invention and should not be construed as limiting the scope of protection of the invention. Non-essential improvements and adjustments made to the invention by those skilled in the art based on the above description should still fall within the scope of protection of the invention. Furthermore, all raw materials mentioned below, unless otherwise specified, are commercially available products; all process steps or preparation methods not mentioned in detail are process steps or preparation methods known to those skilled in the art.

[0022] Example 1 A method for thermoelectric coupling catalytic synthesis of urea includes the following steps: (1) Preparation of Cu-Co metal diatomic catalysts: 0.2 mmol Co(Ac)₂·4H₂O, 0.2 mmol Cu(Ac)₂·H₂O, 4 mg melamine, and 100 mg carbon black were dissolved in 15 mL of ethanol and treated with alternating ultrasonic and stirring for 5 hours to obtain a mixed slurry. The mixed slurry was then placed in an oil bath at 60 °C and heated with continuous magnetic stirring until the solvent was completely evaporated to obtain a black solid. Finally, the black solid was ground and dispersed, then transferred to a tube furnace and calcined at 800 °C for 2 hours under an Ar atmosphere to obtain the final product, a Cu-Co metal diatomic catalyst.

[0023] (2) Assembly of the electrolytic cell An H-type electrolytic cell was used, with the Cu-Co metal diatomic catalyst prepared in step (1) as the working electrode, Hg / HgO as the reference electrode, and a platinum sheet as the counter electrode; 1.0 mol / L Li was added to deionized water. + and CO3 2- The metal-nonmetal mediator pairs are used as electrolytes.

[0024] (3) Thermoelectric coupling catalytic synthesis of urea Add KNO3 to the electrolyte at a concentration of 1.5 mol / L NO3. - As a nitrogen source, a constant negative potential of -1.424V was applied to the cathode, the reaction temperature was 60℃, the reaction was carried out for 2 hours, and the gaseous products generated by the reaction were collected.

[0025] Example 2 A method for thermoelectric coupling catalytic synthesis of urea includes the following steps: (1) Preparation of Fe-Ni metal diatomic catalysts: 0.2 mmol Fe(Ac)2·4H2O, 0.2 mmol Ni(Ac)2·H2O, 4 mg melamine, and 100 mg carbon black were dissolved in 15 mL of ethanol and treated with alternating ultrasonic and stirring for 5 hours to obtain a mixed slurry. The mixed slurry was then placed in an oil bath at 60 °C and heated with continuous magnetic stirring until the solvent was completely evaporated to obtain a black solid. Finally, the black solid was ground and dispersed, then transferred to a tube furnace and calcined at 800 °C for 2 hours under an Ar atmosphere to obtain the final product, the Fe-Ni metal diatomic catalyst.

[0026] (2) Assembly of the electrolytic cell An H-type electrolytic cell was used, with the Fe-Ni metal diatomic catalyst prepared in step (1) as the working electrode, Hg / HgO as the reference electrode, and a platinum sheet as the counter electrode; 0.2 mol / L Na2O was added to deionized water. + A metal-nonmetal mediated pair composed of CO2 serves as the electrolyte.

[0027] (3) Thermoelectric coupling catalytic synthesis of urea Add KNO3 to the electrolyte at a concentration of 0.5 mol / L NO3. - As a nitrogen source, a constant negative potential of -1.674V was applied to the cathode, and the electrolyte was heated to 70°C. The reaction was carried out for 2 hours, and the gaseous products generated by the reaction were collected.

[0028] Example 3 A method for thermoelectric coupling catalytic synthesis of urea includes the following steps: (1) Preparation of Au-Pd metal diatomic catalysts: 0.2 mmol Au(Ac)₂·4H₂O, 0.2 mmol Pd(Ac)₂·H₂O, 4 mg melamine, and 100 mg carbon black were dissolved in 15 mL of ethanol and treated with alternating ultrasonic and stirring for 5 hours to obtain a mixed slurry. The mixed slurry was then placed in an oil bath at 60 °C and heated with continuous magnetic stirring until the solvent was completely evaporated to obtain a black solid. Finally, the black solid was ground and dispersed, then transferred to a tube furnace and calcined at 800 °C for 2 hours under an Ar atmosphere to obtain the final product, an Au-Pd metal diatomic catalyst.

[0029] (2) Assembly of the electrolytic cell An H-type electrolytic cell was used, with the Au-Pd metal diatomic catalyst prepared in step (1) as the working electrode, Hg / HgO as the reference electrode, and a platinum sheet as the counter electrode; a K2O solution with a concentration of 1.0 mol / L was added to deionized water. + and HCO3 - The metal-nonmetal mediator pairs are used as electrolytes.

[0030] (3) Thermoelectric coupling catalytic synthesis of urea Add KNO2 to the electrolyte at a concentration of 1.0 mol / L NO2. - As a nitrogen source, a constant negative potential of -1.274V was applied to the cathode, and the electrolyte was heated to 70°C. The reaction was carried out for 2 hours, and the gaseous products generated by the reaction were collected.

[0031] Example 4 A method for thermoelectric coupling catalytic synthesis of urea includes the following steps: (1) Preparation of Ti-W metal diatomic catalysts: 0.2 mmol Ti(Ac)₂·4H₂O, 0.2 mmol W(Ac)₂·H₂O, 4 mg melamine, and 100 mg carbon black were dissolved in 15 mL of ethanol and treated with alternating ultrasonic and stirring for 5 hours to obtain a mixed slurry. The mixed slurry was then placed in an oil bath at 60 °C and heated with continuous magnetic stirring until the solvent was completely evaporated to obtain a black solid. Finally, the black solid was ground and dispersed, then transferred to a tube furnace and calcined at 800 °C for 2 hours under an Ar atmosphere to obtain the final product, a Ti-W metal diatomic catalyst.

[0032] (2) Assembly of the electrolytic cell An H-type electrolytic cell was used, with the Ti-W metal diatomic catalyst prepared in step (1) as the working electrode, Hg / HgO as the reference electrode, and a platinum sheet as the counter electrode; a 1.0 mol / L Ca solution was added to deionized water. 2+ A metal-nonmetal mediated pair composed of CO2 serves as the electrolyte.

[0033] (3) Thermoelectric coupling catalytic synthesis of urea Add KNO2 to the electrolyte at a concentration of 1.5 mol / L NO2. - As a nitrogen source, a constant negative potential of -1.424V was applied to the cathode, and the electrolyte was heated to 80°C. The reaction was carried out for 2 hours, and the gaseous products generated by the reaction were collected.

[0034] Example 5 A method for thermoelectric coupling catalytic synthesis of urea includes the following steps: (1) Preparation of Zn-Mn metal diatomic catalysts: 0.2 mmol Zn(Ac)₂·4H₂O, 0.2 mmol Mn(Ac)₂·H₂O, 4 mg melamine, and 100 mg carbon black were dissolved in 15 mL of ethanol and treated with alternating ultrasonic and stirring for 5 hours to obtain a mixed slurry. The mixed slurry was then placed in an oil bath at 60 °C and heated with continuous magnetic stirring until the solvent was completely evaporated to obtain a black solid. Finally, the black solid was ground and dispersed, then transferred to a tube furnace and calcined at 800 °C for 2 hours under an Ar atmosphere to obtain the final product, a Zn-Mn metal diatomic catalyst.

[0035] (2) Assembly of the electrolytic cell An H-type electrolytic cell was used, with the Zn-Mn metal diatomic catalyst prepared in step (1) as the working electrode, Hg / HgO as the reference electrode, and a platinum sheet as the counter electrode; 0.1 mol / L of Mg was added to deionized water. 2+ and CO3 2- The metal-nonmetal mediator pairs are used as electrolytes.

[0036] (3) Thermoelectric coupling catalytic synthesis of urea Add KNO2 to the electrolyte at a concentration of 0.1 mol / L NO2. - As a nitrogen source, a constant negative potential of -1.374V was applied to the cathode, and the electrolyte was heated to 65°C. The reaction was carried out for 2 hours, and the gaseous products generated by the reaction were collected.

[0037] Example 6 A method for thermoelectric coupling catalytic synthesis of urea includes the following steps: (1) Preparation of Pt-Mo metal diatomic catalysts: 0.2 mmol Pt(Ac)₂·4H₂O, 0.2 mmol Mo(Ac)₂·H₂O, 4 mg melamine, and 100 mg carbon black were dissolved in 15 mL of ethanol and treated with alternating ultrasonic and stirring for 5 hours to obtain a mixed slurry. The mixed slurry was then placed in an oil bath at 60 °C and heated with continuous magnetic stirring until the solvent was completely evaporated to obtain a black solid. Finally, the black solid was ground and dispersed, then transferred to a tube furnace and calcined at 800 °C for 2 hours under an Ar atmosphere to obtain the final product, a Pt-Mo metal diatomic catalyst.

[0038] (2) Assembly of the electrolytic cell An H-type electrolytic cell was used, with the Pt-Mo metal diatomic catalyst prepared in step (1) as the working electrode, Hg / HgO as the reference electrode, and a platinum sheet as the counter electrode; 2 mol / L of Rb was added to deionized water. 2+ and HCO3 - The metal-nonmetal mediator pairs are used as electrolytes.

[0039] (3) Thermoelectric coupling catalytic synthesis of urea Add KNO3 to the electrolyte at a concentration of 2.0 mol / L NO3. - As a nitrogen source, a constant negative potential of -1.674V was applied to the cathode, and the electrolyte was heated to 70°C. The reaction was carried out for 2 hours, and the gaseous products generated by the reaction were collected.

[0040] Example 7 A method for thermoelectric coupling catalytic synthesis of urea includes the following steps: (1) Preparation of Cr-Rh metal diatomic catalysts: 0.2 mmol Cr(Ac)₂·4H₂O, 0.2 mmol Rh(Ac)₂·H₂O, 4 mg melamine, and 100 mg carbon black were dissolved in 15 mL of ethanol and treated with alternating ultrasonic and stirring for 5 hours to obtain a mixed slurry. The mixed slurry was then placed in an oil bath at 60 °C and heated with continuous magnetic stirring until the solvent was completely evaporated to obtain a black solid. Finally, the black solid was ground and dispersed, then transferred to a tube furnace and calcined at 800 °C for 2 hours under an Ar atmosphere to obtain the final product, a Cr-Rh metal diatomic catalyst.

[0041] (2) Assembly of the electrolytic cell An H-type electrolytic cell was used, with the Cr-Rh metal diatomic catalyst prepared in step (1) as the working electrode, Hg / HgO as the reference electrode, and a platinum sheet as the counter electrode; a 4 mol / L concentration of Cs was added to deionized water. + A metal-nonmetal mediated pair composed of CO2 serves as the electrolyte.

[0042] (3) Thermoelectric coupling catalytic synthesis of urea N2 was introduced into the electrolyte as a nitrogen source, a constant negative potential of -1.424V was applied to the cathode, and the electrolyte was heated to 75°C. The reaction was carried out for 2 hours, and the gaseous products generated by the reaction were collected.

[0043] Example 8 A method for thermoelectric coupling catalytic synthesis of urea includes the following steps: (1) Preparation of V-Ru metal diatomic catalysts: 0.2 mmol V(Ac)2·4H2O, 0.2 mmol Ru(Ac)2·H2O, 4 mg melamine, and 100 mg carbon black were dissolved in 15 mL of ethanol and treated with alternating ultrasonic and stirring for 5 hours to obtain a mixed slurry. The mixed slurry was then placed in an oil bath at 60 °C and heated with continuous magnetic stirring until the solvent was completely evaporated to obtain a black solid. Finally, the black solid was ground and dispersed, then transferred to a tube furnace and calcined at 800 °C for 2 hours under an Ar atmosphere to obtain the final product, a V-Ru metal diatomic catalyst.

[0044] (2) Assembly of the electrolytic cell An H-type electrolytic cell was used, with the V-Ru metal diatomic catalyst prepared in step (1) as the working electrode, Hg / HgO as the reference electrode, and a platinum sheet as the counter electrode; a 5 mol / L solution of Na was added to deionized water. + and HCO3 - The metal-nonmetal mediator pairs are used as electrolytes.

[0045] (3) Thermoelectric coupling catalytic synthesis of urea N2 was introduced into the electrolyte as a nitrogen source, a constant negative potential of -1.574V was applied to the cathode, and the electrolyte was heated to 80°C. The reaction was carried out for 2 hours, and the gaseous products generated by the reaction were collected.

[0046] Example 9 A method for thermoelectric coupling catalytic synthesis of urea includes the following steps: (1) Preparation of Ir-Bi metal diatomic catalysts: 0.2 mmol Ir(Ac)₂·4H₂O, 0.2 mmol Bi(Ac)₂·H₂O, 4 mg melamine, and 100 mg carbon black were dissolved in 15 mL of ethanol and treated with alternating ultrasonic and stirring for 5 hours to obtain a mixed slurry. The mixed slurry was then placed in an oil bath at 60 °C and heated with continuous magnetic stirring until the solvent was completely evaporated to obtain a black solid. Finally, the black solid was ground and dispersed, then transferred to a tube furnace and calcined at 800 °C for 2 hours under an Ar atmosphere to obtain the final product, an Ir-Bi metal diatomic catalyst.

[0047] (2) Assembly of the electrolytic cell An H-type electrolytic cell was used, with the Ir-Bi metal diatomic catalyst prepared in step (1) as the working electrode, Hg / HgO as the reference electrode, and a platinum sheet as the counter electrode; a solution of K at a concentration of 2.5 mol / L was added to deionized water. + A metal-nonmetal mediated pair composed of CO2 serves as the electrolyte.

[0048] (3) Thermoelectric coupling catalytic synthesis of urea Add KNO3 to the electrolyte at a concentration of 2.0 mol / L NO3. - As a nitrogen source, a constant negative potential of -1.274V was applied to the cathode, and the electrolyte was heated to 75°C. The reaction was carried out for 2 hours, and the gaseous products generated by the reaction were collected.

[0049] Example 10 A method for thermoelectric coupling catalytic synthesis of urea includes the following steps: (1) Preparation of In-Sn metal diatomic catalysts: 0.2 mmol In(Ac)2·4H2O, 0.2 mmol Sn(Ac)2·H2O, 4 mg melamine, and 100 mg carbon black were dissolved in 15 mL of ethanol and treated with alternating ultrasonic and stirring for 5 hours to obtain a mixed slurry. The mixed slurry was then placed in an oil bath at 60 °C and heated with continuous magnetic stirring until the solvent was completely evaporated to obtain a black solid. Finally, the black solid was ground and dispersed, then transferred to a tube furnace and calcined at 800 °C for 2 hours under an Ar atmosphere to obtain the final product, an In-Sn metal diatomic catalyst.

[0050] (2) Assembly of the electrolytic cell An H-type electrolytic cell was used, with the In-Sn metal diatomic catalyst prepared in step (1) as the working electrode, Hg / HgO as the reference electrode, and a platinum sheet as the counter electrode; 0.1 mol / L Ca was added to deionized water. 2+ and HCO3 - The metal-nonmetal mediator pairs are used as electrolytes.

[0051] (3) Thermoelectric coupling catalytic synthesis of urea Add KNO3 to the electrolyte at a concentration of 0.2 mol / L NO3. - As a nitrogen source, a constant negative potential of -1.574V was applied to the cathode, and the electrolyte was heated to 70°C. The reaction was carried out for 2 hours, and the gaseous products generated by the reaction were collected.

[0052] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that the reaction temperature for synthesizing urea in Comparative Example 1 is room temperature.

[0053] Comparative Example 2 The only difference between Comparative Example 2 and Example 1 is that a constant negative potential was not applied to the cathode during the synthesis of urea in Comparative Example 2.

[0054] Comparative Example 3 The only difference between Comparative Example 3 and Example 1 is that Comparative Example 3 uses a Cu single-atom catalyst, and its preparation process is as follows: 0.2 mmol Cu(Ac)2·H2O, 4 mg melamine, and 100 mg carbon black were dissolved in 15 mL of ethanol and treated with alternating ultrasonic and stirring for 5 hours to obtain a mixed slurry. The mixed slurry was then placed in an oil bath at 60 °C and heated under continuous magnetic stirring until the solvent was completely evaporated to obtain a black solid. Finally, the black solid was ground and dispersed, then transferred to a tube furnace and calcined at 800 °C for 2 hours under an Ar atmosphere to obtain the final product, a Cu single-atom catalyst.

[0055] Comparative Example 4 The only difference between Comparative Example 4 and Example 2 is that no nitrogen source was added to the electrolyte during the synthesis of urea in Comparative Example 4.

[0056] Comparative Example 5 The only difference between Comparative Example 5 and Example 2 is that the reaction temperature for synthesizing urea in Comparative Example 5 is room temperature.

[0057] Comparative Example 6 The only difference between Comparative Example 6 and Example 2 is that Comparative Example 6 uses 0.2 mol / L NO3. - and Na + Metal-nonmetal mediators.

[0058] Performance testing The gaseous products generated by the reactions in Examples 1-10 and Comparative Examples 1-6 were analyzed by gas chromatography, and the yield of urea was quantitatively measured by diacetyl-oxime method and ¹H NMR method. The results are shown in Table 1.

[0059] Table 1:

[0060] As shown in Table 1, Examples 1-10 used Cu-Co and other metal diatomic catalysts as working electrodes and introduced specific metal cations and non-metal mediators into the electrolyte to form metal-nonmetal pairs. Under thermoelectric coupling catalysis, the ammonia yield reached 86.88-851.20 mmol / h. -1 g -1 .

[0061] Compared to Example 1, the urea yields of Comparative Examples 1-3 were significantly reduced due to the use of single thermal catalysts, electrocatalysts, and single-atom catalysts, respectively.

[0062] Compared to Example 2, Comparative Examples 4 and 6 failed to synthesize urea successfully due to the absence of a nitrogen source and the use of other non-metallic mediators, respectively. Comparative Example 5, compared to Example 2, also showed a significant decrease in urea yield due to the use of a single electrocatalyst.

[0063] For those skilled in the art, several simple deductions or substitutions can be made without departing from the inventive concept, without requiring creative effort. Therefore, any simple improvements made to this invention by those skilled in the art based on the disclosure of this invention should be within the scope of protection of this invention. The above embodiments are preferred embodiments of this invention, and all processes similar to this invention and equivalent changes should fall within the scope of protection of this invention.

Claims

1. A method for thermoelectric coupling catalytic synthesis of urea, characterized in that, Includes the following steps: (1) Assemble the three-electrode system and the electrolyte into an electrolytic cell. The working electrode of the three-electrode system is a metal diatomic catalyst. The electrolyte contains a metal-nonmetal mediated pair. The metal-nonmetal mediated pair includes metal cations and nonmetal mediators. The nonmetal mediators include nonmetal molecules or nonmetal anions. (2) Add a nitrogen source to the electrolyte to form a reaction system; then energize and heat the electrolytic cell to dissociate the N≡N bond or N=O in the reaction system and couple the nitrogen source with the CN of the non-metallic mediator to generate the urea.

2. The method for thermoelectric coupling catalytic synthesis of urea according to claim 1, characterized in that, The metal diatomic catalyst is selected from any one of Cu-Co, Fe-Ni, Au-Pd, Ti-W, Zn-Mn, Pt-Mo, Cr-Rh, V-Ru, Ir-Bi, and In-Sn.

3. The method for thermoelectric coupling catalytic synthesis of urea according to claim 2, characterized in that, The preparation process of the metal diatomic catalyst includes the following steps: dissolving two soluble metal salts, melamine and carbon black in ethanol to obtain a mixed slurry; then heating the mixed slurry to evaporate the solvent and obtain a black solid; finally calcining the black solid to obtain the metal diatomic catalyst.

4. The method for thermoelectric coupling catalytic synthesis of urea according to claim 3, characterized in that, The ratio of the amount of soluble metal salt to melamine is 1 mmol: (10-30) mg; the mass ratio of melamine to carbon black is 1: (20-30); and the mass-volume ratio of melamine to ethanol is 1 mg: (3-5) mL.

5. The method for thermoelectric coupling catalytic synthesis of urea according to claim 3, characterized in that, The heating temperature of the mixed slurry is 50-70℃, the calcination temperature is 700-900℃, and the calcination time is 1-3 hours.

6. The method for thermoelectric coupling catalytic synthesis of urea according to claim 1, characterized in that, The metal cation is selected from Li + Na + K + Ca 2+ Mg 2+ 、Rb + Cs + At least one of the following, wherein the nonmetallic molecule includes CO2, and the nonmetallic anion is selected from CO3. 2- HCO3 - At least one of them.

7. The method for thermoelectric coupling catalytic synthesis of urea according to claim 1, characterized in that, The concentration of the metal-nonmetal mediator pair in the electrolyte is 0.01-5 mol / L.

8. The method for thermoelectric coupling catalytic synthesis of urea according to claim 1, characterized in that, The nitrogen source is selected from N2 and NO2. - NO3 - At least one of them.

9. The method for thermoelectric coupling catalytic synthesis of urea according to claim 1, characterized in that, In step (2), the heating temperature is 30-80℃.

10. The method for thermoelectric coupling catalytic synthesis of urea according to claim 1, characterized in that, In step (2), the voltage applied is -1.674V to -1.274V relative to the Hg / HgO reference electrode.

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