A preparation method of boron and nitrogen co-doped CeFeO3 catalyst

Abstract

The present invention provides a preparation method of a boron and nitrogen co-doped CeFeO3 catalyst. The preparation process of this material is divided into two steps: solution combustion method and hydrogen reduction method. The preparation time is short and the operation process is simple. The prepared catalyst can efficiently activate N2 and CO2 simultaneously and has high activity and selectivity for electrocatalytic synthesis of urea.

Description

Technical Field

[0001] The present invention relates to the field of preparation of electrocatalysts, and specifically, to a novel preparation method of a boron and nitrogen co-doped CeFeO3 catalyst. Background Art

[0002] Urea is the most widely used chemical fertilizer in the world, and its production ranks first among various nitrogen fertilizers. Therefore, the development of urea production technology is of great significance for meeting the growing food demand. Breaking the very stable N2 triple bond is the difficulty in synthesizing urea. Currently, the Haber-Bosch process under high temperature and high pressure is mainly used in industrial urea production to activate N2 and convert N2 into NH3; subsequently, under high temperature and high pressure conditions, NH3 further reacts with CO2 to be converted into urea. The Haber-Bosch process requires very high energy consumption, so many researchers have begun to try to find a more economical, environmentally friendly, and milder reaction condition method for urea synthesis.

[0003] Although electrocatalytic reduction can synthesize urea from N2 and CO2 gases under mild conditions, currently, it still faces the problems of low yield and poor selectivity. Developing a catalyst that can efficiently activate N2 and CO2 under mild conditions and efficiently promote the carbon-nitrogen coupling reaction is the key to improving the yield and selectivity of urea.

[0004] The present invention proposes a preparation method of a boron and nitrogen co-doped CeFeO3 catalyst, with a short preparation time and a simple operation process. The prepared catalyst can efficiently activate N2 and CO2 and efficiently promote the carbon-nitrogen coupling reaction, and has high activity and selectivity for urea synthesis. Summary of the Invention

[0005] The present invention provides a preparation method of a boron and nitrogen co-doped CeFeO3 catalyst. The preparation process is divided into two steps: solution combustion method and hydrogen reduction method. Its advantages are short preparation cycle, simple device, and low cost. Using the prepared catalyst as the cathode material, in a potassium bicarbonate solution, CO2 and N2 can be electrocatalytically and efficiently synthesized into urea in one step. This method is implemented by the following technical solutions:

[0006] Step 1: Dissolve an oxidant, a boride, and a fuel in water to obtain a precursor solution for the solution combustion method;

[0007] Step 2: Transfer the precursor solution for the solution combustion method to a muffle furnace for combustion, quickly take it out after keeping warm for a period of time, cool, grind, wash, and dry to obtain an orange-brown material, which is boron and nitrogen co-doped CeFeO3 powder;

[0008] Step 3: Place the prepared boron and nitrogen co-doped CeFeO3 powder in a tubular furnace for calcination, and continuously introduce H2 / Ar gas during heating and heat preservation. After the calcination is completed, a boron and nitrogen co-doped CeFeO3 catalyst is obtained.

[0009] Step 4: Mix the prepared boron and nitrogen co-doped CeFeO3 catalyst with Nafion solution and ethanol, drop-coat it on carbon paper, and obtain a boron and nitrogen co-doped CeFeO3 catalyst electrode after drying;

[0010] Step 5: Use the prepared boron and nitrogen co-doped CeFeO3 catalyst electrode as the cathode, a platinum sheet as the counter electrode, a silver / silver chloride electrode as the reference electrode, use a potassium bicarbonate solution as the electrolyte, introduce a mixed gas of CO2 and N2 into the system, and carry out an electroreduction synthesis of urea reaction.

[0011] Further, in the above step 1, the oxidant includes one or more metal salt compounds such as Ce(NO3)3, Ce(NH4)2(NO3)6, Fe(NO3)3, Fe(NO3)2; the boron-containing compound includes one or more compounds such as NaBH4, H3BO3, Na2B4O7, B2O3; the fuel includes one or more compounds such as sodium glutamate, hydroxyacetamide, glycine, formic acid hydrazide, ammonium nitrate, glucose;

[0012] Further, in the above step 1, the molar ratio of the oxidant to the boron-containing compound is 1:5 to 5:1;

[0013] Further, in the above step 1, the molar ratio of the oxidant to the fuel is 1:5 to 5:1;

[0014] Further, in the above step 2, the combustion temperature is 350 - 450 °C, and the heat preservation time is 3 - 10 min;

[0015] Further, in the above step 3, the calcination temperature is 100 - 200 °C, the heat preservation time is 1 - 3 h, and the volume ratio of the H2 and Ar mixed gas is 5:95 to 20:80. Specific Embodiments

[0016] Example 1

[0017] 1. Preparation of boron and nitrogen co-doped CeFeO3 powder by solution combustion method:

[0018] (1) Add 534 mg of Ce(NO3)3·6H2O, 496.8 mg of Fe(NO3)3·9H2O, 76 mg of H3BO3, and 461.6 mg of glycine to a 250 ml beaker, add 3 ml of deionized water and dissolve it, and perform ultrasonic mixing treatment to obtain a precursor solution for the solution combustion method;

[0019] (2) Place the beaker containing the precursor solution in a muffle furnace at 400 °C, burn it in an air atmosphere and keep it warm for 5 min. After the combustion is completed, quickly take it out to obtain a porous orange-brown material. After it cools down, grind it, wash it three times with deionized water, and dry it to obtain boron and nitrogen co-doped CeFeO3 powder.

[0020] 2. Preparation of boron and nitrogen co-doped CeFeO3 catalyst by hydrogen reduction method:

[0021] (1) Place the boron and nitrogen co-doped CeFeO3 powder in a tubular furnace, set the heating rate to 5 °C / min, heat it to 150 °C and then transfer it to the heat preservation program. The heat preservation temperature is 150 °C and the heat preservation time is 2 h. Continuously introduce the H2 / Ar mixed gas during heating and heat preservation. The volume ratio of H2 to Ar is 5:95, and the flow rate of the mixed gas is 50 cm 3 / min. After the calcination is completed, the boron and nitrogen co-doped CeFeO3 catalyst is obtained.

[0022] 3. Reduction performance test of boron and nitrogen co-doped CeFeO3 catalyst:

[0023] (1) Take 20 mg of the boron and nitrogen co-doped CeFeO3 catalyst and add it to the mixed solution of Nafion and ethanol, where ethanol is 1900 μl and Nafion is 100 μl. Place the mixed solution added with the boron and nitrogen co-doped CeFeO3 catalyst in an ultrasonic cleaner and ultrasonically treat it for 30 min. Then, take 30 μl of the mixed solution and drop it on a 1×2 cm 2 carbon paper, and the dropping area is 1×1 2 cm. After it dries naturally, the boron and nitrogen co-doped CeFeO3 catalyst electrode is obtained;

[0024] (2) Prepare 0.5 mol / L KHCO3 solution as the electrolyte, use a platinum sheet as the counter electrode, a silver / silver chloride electrode as the reference electrode, and the prepared catalyst electrode as the working electrode. Introduce a mixed gas of CO2 and N2 into the system and set the potential to react for 1.5 h under the condition of -0.7 V relative to the silver / silver chloride electrode. After the reaction is completed, the urea yield is measured to be 8.38 mmol h -1 g -1 , and the Faraday efficiency is 74%.

Claims

1. Application of a boron and nitrogen co-doped CeFeO3 catalyst in electrocatalytic synthesis of urea, characterized in that, Firstly, boron and nitrogen co-doped CeFeO3 powder was prepared by solution combustion method, and then the CeFeO3 powder was treated by hydrogen reduction method to obtain boron and nitrogen co-doped CeFeO3 catalyst. Using boron and nitrogen co-doped CeFeO3 as the cathode material, in potassium bicarbonate solution, CO2 and N2 can be electrocatalytically and efficiently synthesized into urea in one step.

2. Use of a boron and nitrogen co-doped CeFeO3 catalyst according to claim 1 for electrocatalytic synthesis of urea, characterized in that, The precursor solution of the solution combustion method contains an oxidant, a fuel, and a boron-containing compound.

3. Use of a boron and nitrogen co-doped CeFeO3 catalyst according to claim 1 for electrocatalytic synthesis of urea, characterized in that, The fuel in the precursor solution of the solution combustion method contains one or more compounds among sodium glutamate, hydroxyacetamide, glycine, formic acid hydrazide, ammonium nitrate, and glucose.

4. Use of a boron and nitrogen co-doped CeFeO3 catalyst according to claim 1 for electrocatalytic synthesis of urea, characterized in that, The oxidant in the precursor solution of the solution combustion method contains one or more metal salt compounds among Ce(NO3)3, Ce(NH4)2(NO3)6, Fe(NO3)3, and Fe(NO3)2.

5. Use of a boron and nitrogen co-doped CeFeO3 catalyst according to claim 1 for electrocatalytic synthesis of urea, characterized in that, The molar ratio of the oxidant to the fuel in the precursor solution of the solution combustion method is 5:1 to 1:

5.

6. Use of a boron and nitrogen co-doped CeFeO3 catalyst according to claim 1 for electrocatalytic synthesis of urea, characterized in that, The boron-containing compound in the precursor solution of the solution combustion method contains one or more compounds among NaBH4, H3BO3, Na2B4O7, and B2O3.

7. Use of a boron and nitrogen co-doped CeFeO3 catalyst according to claim 1 for electrocatalytic synthesis of urea, characterized in that, The molar ratio of the oxidant to the boron-containing compound in the precursor solution of the solution combustion method is 5:1 to 1:

5.

8. Use of a boron and nitrogen co-doped CeFeO3 catalyst according to claim 1 for electrocatalytic synthesis of urea, characterized in that, The ignition temperature of the solution combustion method is 350 - 450 °C, and the heat preservation time is 3 - 10 min.

9. Use of a boron and nitrogen co-doped CeFeO3 catalyst according to claim 1 for electrocatalytic synthesis of urea, characterized in that, The heat preservation temperature of the hydrogen reduction method is 100 - 200 °C. During the heat preservation process, the volume ratio of the H2 and Ar mixed gas is 5:95 to 20:80, and the heat preservation time is 1 - 3 h.