Preparation method of novel series heterojunction electrocatalyst for urea synthesis

Abstract

The invention relates to a preparation method of a novel series heterojunction electrocatalyst for urea synthesis, and belongs to the technical field of production of high value-added chemicals and catalysts. The novel bimetallic oxide series electrocatalyst (CuO / Co3O4) is prepared by taking ZIF-67 as a precursor and combining an ion exchange method with a low-temperature pyrolysis method, and green and energy-saving urea electrosynthesis can be realized through co-reduction of electrocatalytic CO2 and NO3 <->. The CuO / Co3O4 series electrocatalyst is prepared into a cathode, and under the action of specific additional bias voltage, the yield of urea electrocatalytically synthesized by the catalyst within 30 min reaches 14 mmol gcat <-1 > h <-1 >, and the highest Faraday efficiency reaches 61.1%; the stable urea yield, Faraday efficiency and current response can still be kept after six times of cyclic utilization, and a green synthesis route and a sustainable technology are provided for urea electrosynthesis. The method has the characteristics of simplicity, high efficiency and low cost, and can be applied to electro-catalytic synthesis of urea.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high value-added chemicals and catalyst production, and particularly relates to a preparation method of a novel CuO / Co3O4 tandem heterojunction electrocatalyst for urea synthesis. BACKGROUND

[0002] Urea is one of the most important nitrogen-containing raw materials in industry, not only as a major fertilizer for agriculture, but also widely used in textiles, pharmaceuticals and energy carriers. Traditional urea synthesis relies on the high-energy Haber-Bosch and Bosch-Meiser processes, which not only consume a large amount of energy, but also emit significant CO2, which is contrary to the goal of green and sustainable development. Therefore, it is urgent to develop a green, environmentally friendly and low-energy urea synthesis method to replace the traditional urea synthesis process. Electrocatalytic co-reduction of CO2 and nitrogen-containing small molecules to synthesize urea is a new green alternative. The commonly used nitrogen sources are mainly nitrogen (N2) and nitrate (NO3 - ), but N2 molecules have a very high triple bond dissociation energy (941 kJ mol -1 ) and poor water solubility (6.24×10 4 mol L -1 atm -1 ), and NO3 - can be easily obtained from industrial wastewater and domestic sewage. Based on this, electrocatalytic co-reduction of NO3 - and CO2 is more likely to achieve urea synthesis. However, the hydrogenation processes of NO3 - and CO2 are competitive, and both need to occur at similar reaction sites, which makes it extremely challenging to achieve efficient electrocatalytic co-reduction of NO3 - and CO2 to synthesize urea. Therefore, it is urgent to design high-efficiency, high-faraday-efficiency and low-cost electrocatalysts to revolutionize the urea synthesis process.

[0003] Inspired by the highly active bimetallic active center of double-metal hydroxide, tandem bimetallic oxide catalysts exhibit significant advantages in the field of catalysis due to their unique structure and synergistic effect. Compared with single-metal oxides, bimetallic oxide systems can optimize the d-band center of active sites through intermetallic interactions, thereby adjusting the adsorption energy of reaction intermediates and improving catalytic activity and selectivity. Different metal oxides may catalyze different steps in a multi-step reaction (such as reduction and hydrogenation), forming a tandem catalytic pathway to improve overall efficiency. By designing tandem active sites, the reaction can be guided along a specific path to suppress side reactions. Tandem bimetallic oxide catalysts, through careful design of components and structure, can achieve "1+1>2" catalytic performance, and are an important development direction for future efficient and sustainable catalytic systems. SUMMARY

[0004] One of the purposes of the present application is to provide a novel CuO / Co3O4 series heterojunction electrocatalyst and a preparation method thereof.

[0005] The second purpose of the present application is to provide a method for synthesizing urea by using CuO / Co3O4 electrocatalysis.

[0006] The technical solution adopted by the present application is:

[0007] A preparation method of a CuO / Co3O4 series heterojunction electrocatalyst for urea synthesis, comprising the following steps:

[0008] 1) Co(NO3)3·6H2O and CTAB are dissolved in deionized water, marked as solution A; 2-methylimidazole is dissolved in deionized water, marked as solution B; solution B is added to solution A at room temperature, and after stirring for 30 min, purple solid is obtained by centrifugation, and is washed with methanol, and dried at 80℃ to obtain ZIF-67;

[0009] 2) ZIF-67 is dispersed in anhydrous ethanol, stirred for 10 min, and marked as dispersion C; Cu(NO3)3·4H2O is dissolved in deionized water, marked as solution D; dispersion C is directly added to solution D, and stirred vigorously for 30 min, and the solid is obtained by centrifugation, and washed with anhydrous ethanol three times, and dried at 60℃ to obtain a composite precursor;

[0010] 3) The composite precursor is uniformly ground and laid in a quartz porcelain boat, transferred to a muffle furnace for calcination, and cooled to room temperature to obtain a CuO / Co3O4 catalyst.

[0011] Further, in the above preparation method, in step 1), 290 mg of Co(NO3)3·6H2O and 5 mg of CTAB are dissolved in 10 mL of deionized water, and 4.54 g of 2-methylimidazole is dissolved in 70 mL of deionized water.

[0012] Further, in the above preparation method, in step 2), 0.3 g of ZIF-67 is dispersed in 20 mL of anhydrous ethanol, and 0.3 g of Cu(NO3)3·4H2O is dissolved in 10 mL of deionized water.

[0013] Further, in the above preparation method, in step 3), the calcination conditions are: under the atmosphere of air, the temperature is raised to 400℃ at a speed of 5℃ / min -1 and lasts for 2 h.

[0014] The CuO / Co3O4 series heterojunction electrocatalyst prepared by the preparation method of any one of the above is applied in the electrocatalytic synthesis of urea.

[0015] Further, the application has the characteristics that the application method comprises the following steps:

[0016] 1) Preparation of CuO / Co3O4 / CP electrode: 2 mg CuO / Co3O4 series heterojunction electrocatalyst was weighed and dispersed in 1000 μL ethanol / water mixed solution containing 5% Nafion, and ultrasonic treatment was performed for 30 min to obtain a dispersion liquid; the dispersion liquid was dropped and coated on a carbon paper electrode, and dried at room temperature;

[0017] 2) Electro-catalytic synthesis of urea by CuO / Co3O4 / CP: in an H-type reactor with a proton exchange membrane as a separator, CuO / Co3O4 / CP was used as the working electrode, Ag / AgCl was used as the reference electrode, and Pt sheet was used as the counter electrode; the electrolyte solution was a neutral mixed electrolyte of CO2-saturated NaHCO3 and NaNO3, and CO2 was continuously introduced during the reaction; before the reaction, a CV scan was performed at a speed of 100 mVs -1 -1.0 V vs. RHE potential range for 30 cycles until a stable solid / liquid interface was obtained; and urea was synthesized by catalytic reaction under constant potential driving.

[0018] Further, in the step 1) of the application method, the volume ratio of ethanol to water in the ethanol / water mixed solution is 15 / 1.

[0019] Further, in the step 1) of the application method, the loading amount of the CuO / Co3O4 series heterojunction electrocatalyst on the carbon paper electrode is 0.1 mg cm -2 .

[0020] Further, in the step 2) of the application method, the concentration of NaHCO3 and NaNO3 in the neutral mixed electrolyte of NaHCO3 and NaNO3 is 0.1 M.

[0021] The application has the following beneficial effects:

[0022] 1) The application adopts ion exchange method combined with low-temperature pyrolysis method to prepare a new type of bimetallic oxide series electrocatalyst (CuO / Co3O4), which has simple preparation process, low carbon and environmental protection, and meets the green chemistry concept. - In the process of co-reduction of CO2 and NO3

[0023] 2、The application has the characteristics of simple, efficient, low cost, high selectivity and low voltage required for electrocatalysis. The cathode prepared by the CuO / Co3O4 series electrocatalyst under the action of a specific additional bias can electrocatalytically synthesize urea at a yield of up to 14 mmol g cat -1 h -1 The highest faradic efficiency reaches 61.1%; after 6 cycles, the urea yield, faradic efficiency and current response can still be maintained, which provides a green, efficient and low-cost synthesis route and sustainable technical support for urea electro-synthesis. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a scanning electron microscope (SEM) image of Co3O4 (a) and CuO / Co3O4 (b).

[0025] Figure 2 is an X-ray diffraction (XRD) spectrum of CuO, Co3O4 and CuO / Co3O4.

[0026] Figure 3 is a full spectrum of X-ray photoelectron spectroscopy (XPS) (a), XPS high-resolution O 1s (b) and Co 2p (c) and Cu 2p (d) spectrum of CuO, Co3O4 and CuO / Co3O4.

[0027] Figure 4 (a) is a linear sweep curve (LSV) of CuO, Co3O4 and CuO / Co3O4, (b) is a (LSV) of CuO / Co3O4 in different electrolyte solutions, (c) is a cyclic voltammogram (CV) of CuO, Co3O4 and CuO / Co3O4.

[0028] Figure 5 (a) is a urea yield catalytic synthesis of CuO, Co3O4 and CuO / Co3O4, (b) is a faradic efficiency of different products in the process of CuO / Co3O4 catalytic CO2 and NO3 - reduction reaction, (c) is a cycle utilization of CuO / Co3O4 catalytic synthesis of urea. DETAILED DESCRIPTION

[0029] Example 1 Preparation of CuO / Co3O4 series heterojunction electrocatalyst

[0030] Accurately weigh 290 mg Co(NO3)3·6H2O and 5 mg CTAB and dissolve them in 10 mL of deionized water, labeling this solution A. Weigh 4.54 g 2-methylimidazole and dissolve it in 70 mL of deionized water, labeling this solution B. Add solution B to solution A at room temperature, stir for 30 min, centrifuge to obtain a purple solid, wash several times with methanol, and dry at 80 °C to obtain ZIF-67. Weigh 0.3 g ZIF-67 and disperse it in 20 mL of anhydrous ethanol, stir for 10 min, labeling this dispersion C. Accurately weigh 0.3 g Cu(NO3)3·4H2O and dissolve it in 10 mL of deionized water, labeling this solution D. Add dispersion C directly to solution D and stir vigorously for 30 min. Centrifuge to obtain a solid, wash three times with anhydrous ethanol, and dry at 60 °C to obtain the composite precursor. Grind the obtained composite precursor evenly and spread it in a quartz ceramic boat, transfer it to a muffle furnace, and heat it at 5 °C for 1 min under an air atmosphere. -1 The temperature was increased to 400℃ and maintained for 2 h. After cooling to room temperature, CuO / Co3O4 catalyst was obtained.

[0031] For comparison, a Co3O4 catalyst was prepared by adding only cobalt nitrate hexahydrate according to the above method.

[0032] For comparison, CuO catalysts were prepared using the method described above, but with only copper nitrate tetrahydrate added.

[0033] Figure 1 These are SEM images of Co3O4 and CuO / Co3O4. From... Figure 1 As can be seen from a, the prepared Co3O4 exhibits a cubic morphology (around 500 nm) and a relatively smooth surface; the CuO / Co3O4 obtained after ion exchange ( Figure 1 b) It transforms into a hollow cube with a rough surface and numerous pores.

[0034] Figure 2 These are the XRD patterns of CuO, Co3O4, and CuO / Co3O4. From... Figure 2 As can be seen from the data, the synthesized CuO monomer corresponds to the monoclinic CuO system (JCPDS 80-1917); the Co3O4 monomer corresponds to the cubic crystal system (PDF 74-2120). The XRD pattern of CuO / Co3O4 is dominated by the characteristic diffraction peaks of CuO, with some minor characteristic diffraction peaks of Co3O4, indicating that CuO... 2+ Ion exchange gradually occurs from the outside in, eventually leading to the formation of the CuO / Co3O4 heterocatalyst.

[0035] Figure 3are the photoelectron spectroscopy and high resolution spectra of CuO, Co3O4 and CuO / Co3O4. From Figure 3 a, it can be seen that the CuO / Co3O4 heterojunction contains Cu, Co and O elements. From Figure 3 b, it can be observed that the three materials all contain lattice oxygen (O L ), oxygen vacancy (O V ) and chemisorbed oxygen (O C ), and the O V contained in CuO / Co3O4 is obviously higher than that of the other two comparative catalysts. Figure 3 c-d, it can be seen that the Co 2p of CuO / Co3O4 heterojunction catalyst has a significant negative shift compared with Co3O4, while the Cu 2p has a positive shift compared with CuO, indicating that the surface electrons flow from CuO to Co3O4, and this surface electron transfer leads to the lack of electrons on the surface of the catalyst, which is beneficial to the electrocatalytic reaction.

[0036] Example 2: Test of electrocatalytic performance

[0037] 2 mg of the prepared catalyst was weighed and dispersed in 1000 μL of ethanol / water mixed solution containing 5% Nafion (v / v, 15 / 1) to obtain a uniform dispersion liquid by ultrasonic dispersion for 30 min. 5 μL of the above dispersion liquid was dropped on a glassy carbon electrode (the electrode was polished with 0.05 μm Al2O3 polishing powder before use) to prepare a catalyst modified glassy carbon electrode as a working electrode. In a standard three-electrode system, a CHI 760E electrochemical workstation was used for selective test. The glassy carbon electrode loaded with the catalyst was used as the working electrode, an Ag / AgCl electrode was used as the reference electrode, a Pt sheet was used as the counter electrode, and the electrolyte solution was a neutral mixed electrolyte of CO2 saturated 0.1 M NaHCO3 and 0.1 M NaNO3, and CO2 was continuously introduced during the reaction. The linear sweep voltammetry (LSV) scan potential range was 0 to -1.0 V vs. RHE, the scan rate was 5 mV s -1 , and the rotation speed was 200 rpm. The cyclic voltammetry (CV) scan potential range was -0.8 to 2.0 V vs. RHE, the scan rate was 10 mVs -1 , and the rotation speed was 200 rpm. The working potential (vs. Ag / AgCl) was converted to the potential relative to the standard hydrogen electrode (vs. RHE) according to formula (1).

[0038] (1)

[0039] From Figure 4It can be seen that CuO / Co3O4 exhibits higher catalytic activity for CO2 and NO3 - co-reduction than CuO and Co3O4. Meanwhile, the co-reduction current response indicates that it has higher catalytic activity. At the same time, the Figure 4 b It can be seen that CuO / Co3O4 catalyzes CO2 and NO3 - co-reduction much better than CO2 reduction (CO2RR) and NO3 - reduction (NO3RR). From the Figure 4 c It can be seen that CuO / Co3O4 catalyzes CO2 and NO3 - co-reduction, and produces obvious CO oxidation peak (0.6 V vs. RHE) and NO2 - oxidation peak (1.45 V vs. RHE) peaks, which are beneficial to the synthesis of urea from CO2 and NO3 - co-reduction. Co3O4 does not produce NO2 - oxidation peak during the catalytic process, indicating that Co3O4 in the composite mainly plays a role in CO2RR; CuO also produces CO and NO2 - two oxidation peaks during the catalytic process, but the peak intensity is obviously lower than that of CuO / Co3O4, indicating that it has catalytic effect on NO3RR and CO2RR.

[0040] Example 3 Electro-catalytic synthesis of urea

[0041] Preparation of CuO / Co3O4 / CP electrode: 2 mg of catalyst was weighed and dispersed in 1000 μL of ethanol / water mixed solution (v / v, 15 / 1) containing 5% Nafion, and ultrasonicated for 30 min to make it uniformly dispersed. 50 μL of the above dispersion was dropped on a 1×1 cm 2 carbon paper (CP) electrode (catalyst loading amount was 0.1 mg cm -2 ), and dried at room temperature.

[0042] CuO / Co3O4 / CP electro-catalytic synthesis of urea: In a H-type reactor with a proton exchange membrane as a separator, CuO / Co3O4 / CP was used as the working electrode, Ag / AgCl as the reference electrode, Pt sheet as the counter electrode, and the electrolyte solution was a neutral mixture of 0.1 M NaHCO3 and 0.1 M NaNO3 saturated with CO2, and CO2 was continuously supplied during the reaction. Before testing, a CV scan was performed at a speed of 100 mV s -1 in the potential range of 0~ -1.0 V vs. RHE for 30 cycles until a stable solid / liquid interface was obtained. During the constant potential driven catalytic reaction, 1 mL of solution was taken out every 30 min, and the amount of urea produced during the reaction was detected by the diacetyl monoxime method.

[0043] Results are shown in Figure 5 a, the CuO / Co3O4 / CP catalytic synthesis of urea yield was 14.0 mmol g cat -1 h -1 , the faradic efficiency was 40.1%, significantly higher than Co3O4 / CP and CuO / CP. From Figure 5 b, it can be seen that at -0.2 V vs. RHE potential, the faradic efficiency of CuO / Co3O4 / CP catalytic synthesis of urea is the highest (61.1%). From Figure 5 c, it can be seen that after 6 cycles at -0.4 V vs. RHE potential, the urea yield does not decrease significantly, indicating that CuO / Co3O4 / CP has good recycling property; the current remains stable during the electrocatalysis process, indicating that CuO / Co3O4 / CP has excellent stability for urea electro-synthesis.

Claims

1. A method for the preparation of a novel CuO / Co304 tandem heterojunction electrocatalyst for urea synthesis, characterized by, Comprising the following steps: 1) Take Co(NO3)3·6H2O and CTAB dissolved in deionized water, marked as solution A; take 2-methylimidazole dissolved in deionized water, marked as solution B; add solution B to solution A at room temperature, centrifuge after stirring for 30 min to obtain purple solid, wash with methanol, dry at 80℃ to obtain ZIF-67; 2) Take ZIF-67 dispersed in anhydrous ethanol, stir for 10 min, marked as dispersion C; take Cu(NO3)3·4H2O dissolved in deionized water, marked as solution D; add dispersion C directly to solution D, stir vigorously for 30 min, centrifuge to obtain solid, wash with anhydrous ethanol three times, dry at 60℃ to obtain a composite precursor; 3) Grind the composite precursor evenly and lay it in a quartz boat, transfer it to a muffle furnace for calcination, cool to room temperature to obtain a CuO / Co3O4 catalyst.

2. The production method according to claim 1, characterized by, In step 1), 290 mg of Co(NO3)3·6H2O and 5 mg of CTAB were dissolved in 10 mL of deionized water, and 4.54 g of 2-methylimidazole was dissolved in 70 mL of deionized water.

3. The preparation method according to claim 1, characterized in that, In step 2), 0.3 g of ZIF-67 was dispersed in 20 mL of anhydrous ethanol, and 0.3 g of Cu(NO3)3·4H2O was dissolved in 10 mL of deionized water.

4. The method of claim 1, wherein, In step 3), the conditions of the calcination are: temperature increase to 400°C at a rate of 5°C min -1 under an atmosphere of air and for 2 h.

5. The use of the CuO / Co3O4 tandem heterojunction electrocatalyst prepared by the preparation method of any one of claims 1-4 in the electrocatalytic synthesis of urea.

6. Use according to claim 5, characterized in that, The application method comprises the following steps: 1) Preparation of CuO / Co3O4 / CP electrode: weigh 2 mg of CuO / Co3O4 tandem heterojunction electrocatalyst and disperse it in 1000 μL of ethanol / water mixed solution containing 5% Nafion, ultrasonic for 30 min to obtain a dispersion; remove the dispersion and drop coat it on a carbon paper electrode, dry at room temperature; 2) CuO / Co3O4 / CP electrocatalytic synthesis of urea: In a H-type reactor with proton exchange membrane as a separator, CuO / Co3O4 / CP as the working electrode, Ag / AgCl as the reference electrode, Pt sheet as the counter electrode, the electrolyte solution is CO2 saturated NaHCO3 and NaNO3 neutral mixed electrolyte, and CO2 is continuously introduced during the reaction; before the reaction, 30 cycles of CV scanning at a speed of 100 mV s -1 vs. RHE potential range of 0 to -1.0 V is carried out until a stable solid / liquid interface is obtained, and urea is synthesized by catalytic reaction under constant potential driving.

7. Use according to claim 6, characterized in that, In step 1), the volume ratio of ethanol to water in the ethanol / water mixed solution is 15 / 1.

8. Use according to claim 6, characterized in that, In step 1), the loading of the CuO / Co3O4 tandem heterojunction electrocatalyst on the carbon paper electrode was 0.1 mg cm -2 .

9. Use according to claim 6, characterized in that, In step 2), the concentration of NaHCO3 and NaNO3 in the neutral mixed electrolyte of NaHCO3 and NaNO3 is 0.1 M.

Images