Preparation method of cerium-based compound catalyst for electrosynthesis of hydrogen peroxide through oxygen reduction reaction

Abstract

The invention discloses a preparation method of a cerium-based compound catalyst for electrosynthesis of hydrogen peroxide through an oxygen reduction reaction. The method comprises the following steps: 1) dissolving cerium nitrate and urea in deionized water, and carrying out hydrothermal reaction and heat treatment to obtain cerium dioxide; 2) carrying out heat treatment on a certain amount of melamine to obtain graphite-phase carbon nitride; (3) adding the prepared cerium dioxide and graphite-phase carbon nitride into methanol and stirring; and finally, performing heat treatment on a sample in a muffle furnace to obtain the cerium dioxide composite graphite phase carbon nitride catalyst. The cerium-based compound catalyst prepared by the preparation method has excellent performance on a two-electron oxygen reduction reaction.

Description

Technical Field:

[0001] The present invention relates to a catalyst for electrocatalytic two-electron oxygen reduction reaction to prepare hydrogen peroxide, and particularly to a preparation method of a cerium-based composite catalyst for electro-synthesizing hydrogen peroxide by oxygen reduction reaction, belonging to the technical field of electrocatalysis. Background Art:

[0002] With the increasing environmental protection requirements, hydrogen peroxide, as an environmentally friendly oxidant and chemical bleaching reagent, is widely used in many fields such as wastewater treatment, pulp bleaching, disinfection, and chemical synthesis due to its excellent properties such as strong oxidizing property, high efficiency, greenness, and pollution-free use.

[0003] Currently, the main method for large-scale production of hydrogen peroxide is the anthraquinone recycling method. The anthraquinone process includes sequential hydrogenation and oxidation of anthraquinone molecules, followed by extraction and distillation, which is a multi-step and energy-intensive process that requires a large amount of energy input and a complex separation process to obtain high-purity hydrogen peroxide. In addition, to minimize transportation costs, it is necessary to rely on an energy-intensive distillation method to concentrate the hydrogen peroxide solution to a concentration of up to 70 wt%, but the hydrogen peroxide solution at this concentration is highly corrosive and poses an explosion risk during transportation; secondly, the anthraquinone process also has relatively serious problems of three wastes, such as the presence of mesitylene isomers in the waste gas, waste activated alumina, and the presence of organic substances such as aromatics and potassium carbonate lye in the wastewater, which will cause very serious environmental pollution. Therefore, it is necessary to seek a cost-effective and environmentally friendly method to produce hydrogen peroxide.

[0004] In addition, hydrogen peroxide can also be directly generated from hydrogen and oxygen. Although the direct hydrogen-oxygen generation method does not cause environmental pollution during the production of hydrogen peroxide and is a green and environmentally friendly production method, the direct mixing of hydrogen and oxygen poses an explosion risk, and the direct synthesis of hydrogen peroxide from hydrogen and oxygen requires the use of precious metal catalysts, which are expensive and difficult to recycle, resulting in high costs and poor economy for this method, hindering its large-scale application.

[0005] Compared with the anthraquinone method and the direct hydrogen-oxygen generation method, the on-site production of hydrogen peroxide by two-electron oxygen reduction reaction is an economic, safe, and environmentally friendly production method, which realizes the continuous on-site production of hydrogen peroxide by using water and oxygen. This electrochemical method can effectively solve most of the problems existing in the anthraquinone method and the direct hydrogen-oxygen generation method, and has the characteristics of simple reaction conditions, clean production process, and low time consumption. Therefore, the synthesis of hydrogen peroxide by two-electron oxygen reduction reaction has attracted more and more attention from domestic and foreign researchers.

[0006] Although the synthesis of hydrogen peroxide by the two-electron oxygen reduction reaction has many advantages, the strong four-electron competitive reaction during the oxygen reduction reaction limits the synthesis efficiency of hydrogen peroxide. Since the degree of interaction between the catalyst and the oxygen-containing species intermediate is the key factor determining the reaction path, designing and developing highly selective and highly active electrocatalysts to promote the reaction towards the two-electron oxygen reduction reaction path is the greatest challenge in this field. Currently, a variety of catalysts have been reported, including noble metals and their alloys, single-atom catalysts, and transition metal oxides. So far, the electrocatalysts with the highest reported performance are noble metal-based catalysts such as gold, palladium, and platinum. However, due to the low abundance and high cost of noble metal-based catalysts, their practical large-scale applications are limited. Summary of the Invention:

[0007] In order to overcome the above-mentioned shortcomings and deficiencies of the prior art, the purpose of the present invention is to provide a preparation method of a cerium-based composite catalyst for the electro-synthesis of hydrogen peroxide by electro-chemical oxygen reduction reaction. Cerium dioxide and graphitic carbon nitride are compounded to prepare a cerium-based composite material. The preparation method is simple and has low cost. The material of the present invention has high selectivity for hydrogen peroxide.

[0008] The preparation method of a cerium-based composite catalyst for the electro-synthesis of hydrogen peroxide by oxygen reduction reaction according to the present invention includes the following steps:

[0009] Step 1: Dissolve cerium nitrate and urea in deionized water, and obtain a dispersion after magnetic stirring for 0.5 - 1 h; transfer the dispersion to a polytetrafluoroethylene high-pressure reaction kettle for hydrothermal reaction; after the reaction is completed, wash and dry, and then perform heat treatment in air to obtain cerium dioxide;

[0010] Step 2: Weigh a certain amount of melamine and place it in a crucible for heat treatment in air to obtain graphitic carbon nitride;

[0011] Step 3: Disperse cerium dioxide and graphitic carbon nitride in methanol according to a certain ratio, stir for 0.5 h - 2 h, then place it in an oven to dry, and then perform heat treatment in air to obtain a cerium-based composite catalyst.

[0012] Preferably, in the above Step 1, the molar ratio of cerium nitrate to urea is 1:110 - 1:130; the temperature of the hydrothermal reaction is 140 - 200 °C, and the reaction time is 15 - 26 h; the conditions of the heat treatment are to treat at 300 - 700 °C for 3 - 6 h with a heating rate of 1 - 5 °C / min.

[0013] Preferably, in the above Step 2, the amount of melamine is 2 - 6 g, and the conditions of the heat treatment are to treat at 200 - 600 °C for 2 - 7 h with a heating rate of 2 - 6 °C / min.

[0014] Preferably, the mass ratio of cerium dioxide to graphitic carbon nitride in the step 3 is one of 1:0 to 1:2, 1:0 to 1:1, and 2:0 to 2:1, and the conditions of the heat treatment are to treat at 50 to 300 °C for 2 to 6 h at a heating rate of 1 to 5 °C / min.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] The method for preparing the catalyst in the present invention is simple in operation and high in efficiency. The prepared catalyst does not contain noble metal materials, reducing the cost.

[0017] In the present invention, cerium dioxide and graphitic carbon nitride have good energy band structures. The cerium-based composite catalyst prepared by compounding the two can form a heterojunction, which can improve the charge transfer ability, is beneficial to the formation of reaction intermediates, and at the same time, the formed covalent bond provides a channel for the charge transfer, thereby realizing the efficient synthesis of hydrogen peroxide.

[0018] The method for synthesizing hydrogen peroxide by the two-electron oxygen reduction reaction proposed in the present invention has the characteristics of less pollution, low cost, and being able to produce hydrogen peroxide on-site compared with the anthraquinone method and the direct synthesis method of hydrogen and oxygen. Description of the drawings:

[0019] Figure 1 It is the scanning electron microscope image of the cerium dioxide prepared in Example 1;

[0020] Figure 2 It is the scanning electron microscope image of the graphitic carbon nitride prepared in Example 1;

[0021] Figure 3 It is the scanning electron microscope image of the cerium-based composite material prepared in Example 1;

[0022] Figure 4 It is the linear cyclic voltammetry test curve of the cerium-based composite material prepared in Example 1 in 0.1 M KOH solution;

[0023] Figure 5 It is the selectivity of hydrogen peroxide calculated by the linear cyclic voltammetry test curve of the cerium-based composite material prepared in Example 1 in 0.1 M KOH solution;

[0024] Figure 6 It is the linear cyclic voltammetry test curve of the cerium-based composite material prepared in Example 2 in 0.1 M KOH solution;

[0025] Figure 7 It is the selectivity of hydrogen peroxide calculated by the linear cyclic voltammetry test curve of the cerium-based composite material prepared in Example 2 in 0.1 M KOH solution;

[0026] Figure 8Linear cyclic voltammetry test curve of the cerium-based composite material prepared in Example 3 in 0.1 M KOH solution;

[0027] Figure 9 Selectivity of hydrogen peroxide calculated from the linear cyclic voltammetry test curve of the cerium-based composite material prepared in Example 3 in 0.1 M KOH solution. Specific implementation method:

[0028] The above content of the present invention will be further specifically described below in conjunction with specific embodiments. However, these implementation methods are not limited to the following embodiments.

[0029] Example 1

[0030] This example provides a preparation method of a cerium-based composite catalyst, which specifically includes the following steps:

[0031] First step: Control the molar ratio of cerium nitrate to urea at 1:120, then dissolve it in deionized water, stir for a period of time to completely dissolve it, wash it repeatedly with deionized water and ethanol, dry it, and heat-treat the dried sample in air at a heating rate of 4 °C / min at 400 °C for 4 h to obtain cerium dioxide.

[0032] Second step: Heat-treat melamine in air at a heating rate of 5 °C / min at 550 °C for 4 h to obtain graphitic carbon nitride.

[0033] Third step: Disperse the cerium dioxide and graphitic carbon nitride prepared in the first step and the second step in a mass ratio of 1:2 in 50 ml of methanol, stir to make them completely mixed, and then heat-treat them in air at a heating rate of 2 °C / min at 150 °C for 4 h to obtain a cerium-based composite catalyst.

[0034] The scanning electron microscope image of the cerium dioxide obtained in this example is as Figure 1 shown. It can be concluded that the morphology of the prepared cerium dioxide is spherical and the sizes are different. The spherical shape has a larger specific surface area and can provide more active sites during the process of preparing hydrogen peroxide by the two-electron oxygen reduction reaction; Figure 2 It shows that the prepared graphitic carbon nitride is sheet-like, and this sheet-like graphitic carbon nitride is beneficial to the loading of cerium dioxide; the scanning electron microscope ( Figure 3 ) of the cerium-based composite material shows that cerium dioxide is successfully loaded on graphitic carbon nitride. At the same time, the cerium dioxide and graphitic carbon nitride in the present invention have a good energy band structure. The cerium-based composite material prepared by combining the two can form a heterojunction, and the formed covalent bond provides a channel for the transfer of charges. The initial potential for the electrocatalytic two-electron oxygen reduction reaction in 0.1 M KOH solution is 0.72 V (relative to the reversible hydrogen electrode, see Figure 4) The selectivity for hydrogen peroxide reaches 84% at 0 - 0.5 V (versus reversible hydrogen electrode) (see Figure 5 ).

[0035] Example 2

[0036] This example provides a preparation method of a cerium-based composite catalyst. Among them, except for the third step, the rest of the preparation methods are the same as those in Example 1:

[0037] Third step: Disperse the cerium dioxide and graphitic carbon nitride prepared in the first and second steps in 50 ml of methanol at a mass ratio of 1:1, stir to make them fully mixed, and then heat-treat at 150 °C for 4 h in air at a heating rate of 2 °C / min to obtain a cerium-based composite catalyst.

[0038] The electrochemical performance of the cerium-based composite catalyst obtained in this example was tested by an electrochemical workstation; linear sweep voltammetry was performed in an oxygen-saturated 0.1 M KOH solution, and the initial potential was 0.78 V (versus reversible hydrogen electrode, see Figure 6 ), and the selectivity for hydrogen peroxide reached 95% at 0 - 0.5 V (versus reversible hydrogen electrode) (see Figure 7 ); compared with the cerium-based composite catalyst prepared in Example 1, the cerium-based composite catalyst prepared in this example has a higher initial potential and higher hydrogen peroxide selectivity, because the loading of an appropriate amount of cerium dioxide is beneficial to the formation of a heterojunction; and the large specific surface area is also beneficial to the transfer of charges, thus improving the electrochemical performance.

[0039] Example 3

[0040] This example provides a preparation method of a cerium-based composite catalyst. Among them, except for the third step, the rest of the preparation methods are the same as those in Example 1:

[0041] Third step: Disperse the cerium dioxide and graphitic carbon nitride prepared in the first and second steps in 50 ml of methanol at a mass ratio of 3:1, stir to make them fully mixed, and then heat-treat at 150 °C for 4 h in air at a heating rate of 2 °C / min to obtain a cerium-based composite catalyst.

[0042] When the cerium-based composite catalyst prepared in this example is used for the two-electron oxygen reduction reaction to produce hydrogen peroxide, its initial potential is 0.74 V, (versus reversible hydrogen electrode, see Figure 8 ), and the selectivity for hydrogen peroxide reaches 90% at 0 - 0.5 V (versus reversible hydrogen electrode) (see Figure 9) Compared with the cerium-based composite catalyst prepared in Example 2, the initial potential is reduced, and the selectivity for peroxide is reduced by about 5%. This may be because the excessive loading of cerium dioxide is not conducive to the formation of heterojunctions and also affects the electron transfer, resulting in a decrease in electrochemical performance.

Claims

1. A preparation method of a cerium-based composite catalyst for electro-synthesizing hydrogen peroxide through an oxygen reduction reaction, characterized in that, It includes the following steps: Step 1: Dissolve cerium nitrate and urea in deionized water, and obtain a dispersion after magnetic stirring for 0.5 - 1 h; transfer the dispersion to a polytetrafluoroethylene high-pressure reactor for hydrothermal reaction; after the reaction, wash and dry, and then perform heat treatment in air to obtain cerium dioxide; Step 2: Weigh a certain amount of melamine and place it in a crucible, and perform heat treatment in air to obtain graphitic carbon nitride; Step 3: Disperse cerium dioxide and graphitic carbon nitride in methanol according to a certain ratio, stir for 0.5 h - 2 h, then place it in an oven to dry, and then perform heat treatment in air to obtain a cerium-based composite catalyst.

2. The preparation method of a cerium-based composite catalyst for electro-synthesizing hydrogen peroxide through oxygen reduction reaction according to claim 1, characterized in that, In the said Step 1, the molar ratio of cerium nitrate to urea is 1:110 - 1:130; the temperature of the hydrothermal reaction is 140 - 200 °C, and the reaction time is 15 - 26 h; the conditions of the heat treatment are to heat at a rate of 1 - 5 °C / min to 300 - 700 °C for 3 - 6 h.

3. The preparation method of a cerium-based composite catalyst for electro-synthesizing hydrogen peroxide through oxygen reduction reaction according to claim 1, characterized in that, In the said Step 2, the amount of melamine is 2 - 6 g, and the conditions of the heat treatment are to heat at a rate of 2 - 6 °C / min to 200 - 600 °C for 2 - 7 h.

4. The preparation method of a cerium-based composite catalyst for electro-synthesizing hydrogen peroxide through oxygen reduction reaction according to claim 1, characterized in that, In the said Step 3, the mass ratio of cerium dioxide to graphitic carbon nitride is one of 1:0 - 1:2, 1:0 - 1:1, and 2:0 - 2:1, and the conditions of the heat treatment are to heat at a rate of 1 - 5 °C / min to 50 - 300 °C for 2 - 6 h.

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