CN113649027B

CN113649027B - Catalyst for chlorine evolution reaction in chlor-alkali industry and preparation method thereof

Info

Publication number: CN113649027B
Application number: CN202010380340.7A
Authority: CN
Inventors: 侯仰龙; 黄晓晓; 孙圣男
Original assignee: Peking University
Current assignee: Peking University
Priority date: 2020-04-28
Filing date: 2020-04-28
Publication date: 2022-11-08
Anticipated expiration: 2040-04-28
Also published as: CN113649027A

Abstract

The invention discloses a catalyst for an anode chlorine evolution reaction of electrolysis salt water in the chlor-alkali industry and a preparation method thereof. The preparation method adopts a high-temperature solvothermal method: dissolving selenium powder, tungsten-based inorganic salt, rhenium-based inorganic salt and a reducing agent in a mixed solvent of N, N-dimethylformamide and water, reacting the mixed solution at high temperature and high pressure, cooling to room temperature, separating, precipitating and drying to obtain the catalyst. The catalyst obtained by the invention has excellent catalytic activity, catalytic selectivity and stability in an acidic electrolyte, has the characteristics of low cost and simple and feasible preparation method, and is suitable for industrial production.

Description

Catalyst for chlorine precipitation reaction in chlor-alkali industry and preparation method thereof

Technical Field

The invention relates to an electrocatalyst for chlorine evolution reaction of an anode in chlor-alkali industry and a preparation method thereof, in particular to a catalyst with a three-dimensional porous structure formed by stacking transition metal (tungsten, rhenium) selenide nanosheets.

Background

Chlorine, one of the most important industrial chemicals, is a key chemical in the production of polymers and pharmaceuticals, in the paper industry and in water treatment, with a global annual production of about 7500 million tons. For example, an average of approximately 1000 million tons of chlorine are consumed in europe for production of disinfectants and other industrial products each year. The chlor-alkali industry refers to the production of sodium hydroxide, chlorine and hydrogen by electrolysis of aqueous sodium chloride solutions and is the main route for the industrial production of chlorine at present. In the process, chloride ions are oxidized at the anode to generate chlorine, and chlorine precipitation reaction is carried out; a reduction reaction occurs at the cathode to produce hydrogen gas and sodium hydroxide.

In the chlor-alkali industry, mixed metal oxides of noble metals (iridium or ruthenium) are mainly used as electrocatalysts at the anodes where the chlorine evolution reaction takes place, such as dimensionally stable anodes (mixed solid solution of 30% ruthenium dioxide and 70% titanium dioxide). However, theoretical simulations and experimental studies show that: (1) The catalyst has high catalytic activity of oxygen precipitation reaction. There is a competitive relationship between the oxygen evolution reaction and the chlorine evolution reaction, both of which are catalyzed on similar active sites on the catalyst surface. Therefore, the mixed metal oxide catalyst has low reaction selectivity, and influences the catalytic activity of the catalyst on chlorine gas precipitation and the purity of a product; (2) The mixed metal oxide catalyst contains a large amount of noble metal elements, and the preparation cost is high; (3) At present, the industrial mixed metal oxide catalyst is a block porous material, and the surface area and the utilization rate of the catalyst are to be further improved. Therefore, the development of a non-noble metal chlorine evolution reaction catalyst with high catalytic selectivity, high catalytic activity, high utilization rate and low cost has important significance for the sustainable development of the chlor-alkali industry.

Disclosure of Invention

The invention aims to provide an electrocatalyst applied to the chlorine evolution reaction of an anode in the chlor-alkali industry, which is a non-noble metal composite catalyst obtained by carrying out solvothermal reaction on a mixed solution of a precursor material and a reducing agent material under the conditions of high temperature and high pressure, and reduces the cost of the catalyst on the premise of ensuring the catalytic activity, catalytic selectivity and stability of the catalyst.

The electrocatalyst for the chlorine evolution reaction of the anode in the chlor-alkali industry provided by the invention has a three-dimensional porous structure. Specifically, transition metal sulfur group compound nano sheets are mutually staggered to form a three-dimensional structure.

The transition metal sulfur group compound nanosheet is of a two-dimensional layered structure, and comprises the following components: rhenium selenide, tungsten selenide, and tungsten selenide/rhenium.

In the tungsten selenide/rhenium nanosheet structure, the atomic ratio of the tungsten element in the total amount of the metal cation element is 0% to 100%, and the atomic ratio of the rhenium element in the total amount of the metal cation element is 0% to 100%.

The thickness of the transition metal sulfur group compound nanosheet is preferably in the range of 1-20nm.

The invention also provides a preparation method of the catalyst, which mainly adopts a high-temperature solvothermal method and comprises the following steps:

1) Dissolving selenium powder, tungsten-based inorganic salt, rhenium-based inorganic salt and a reducing agent in a mixed solvent of N, N-dimethylformamide and water;

2) Reacting the mixed solution obtained in the step 1) under the conditions of high temperature and high pressure, and separating, precipitating and drying after cooling to room temperature to obtain the catalyst;

in the mixed solution obtained in the step 1), the concentration of the selenium powder substances is 10-100mmol/L; the concentration of the reducing agent is preferably 0.01 to 0.1mmol/L; the concentration of the tungsten-based inorganic salt is preferably 0-50mmol/L; the concentration of the rhenium-based inorganic salt is preferably 0 to 50 mmol/L. The tungsten-based inorganic salt species is preferably sodium tungstate, the rhenium-based inorganic salt is preferably ammonium perrhenate, and the reducing agent is preferably sodium borohydride.

In the step 2), the reaction temperature is 180-240 ℃. The reaction time is 12-72 hours.

In the preparation of the catalyst, firstly, tungsten-based inorganic salt, selenium powder and a reducing agent are dissolved in N, N-dimethylformamide, and then the solution is mixed and stirred with an aqueous solution fully dissolved with rhenium-based inorganic salt for 2 hours to obtain a uniform mixed solution. The step has the advantages of helping the precursor material to be uniformly distributed in the solution, and further forming a nanosheet structure with uniform thickness and uniform element distribution in the high-temperature high-pressure treatment process. And then, nucleating and growing the mixed solution under the conditions of high temperature and high pressure to gradually grow ions in the material into a two-dimensional nanosheet material, and stacking the two-dimensional nanosheet material to form a three-dimensional porous structure. In the preparation process, the proportion of the rhenium-based inorganic salt and the tungsten-based inorganic salt in the precursor material can be adjusted to realize any proportion of the rhenium element and the tungsten element in the final product.

The preparation method of the catalyst is simple and feasible, and is suitable for industrial production. Experiments prove that the catalyst material obtained from the reactant system of 200mg to 10g has consistent object image and appearance, so that the material is suitable for industrial production of large-scale quantities.

The performance test of the prepared catalyst proves that the voltage value of the catalyst is similar to that of the commercial catalyst. And the Tafel slope of the material is small, which indicates that the material has good dynamic characteristics. In addition, after the stability test is carried out on the material, the obtained material still maintains excellent catalytic activity after long-term work.

Drawings

FIG. 1 is a diagram of the synthesis process of the catalyst of the present invention, which goes through the steps of nucleation, aggregate growth, and aging to obtain the final catalyst.

Fig. 2 is a transmission electron microscope image of tungsten selenide nanosheets.

Fig. 3 is a transmission electron microscope image of rhenium selenide nanosheets.

Fig. 4 is a transmission electron micrograph, a nitrogen desorption curve, and a catalytic performance test curve of the catalyst material No. 1, in which: the method comprises the following steps of (a) showing a transmission electron microscope, (b) showing a nitrogen adsorption and desorption curve, (c) showing cyclic voltammograms at different scanning speeds, (d) selecting data of the cyclic voltammograms at different scanning speeds, (e) showing a catalytic performance test curve, and (f) showing a tafel curve.

Fig. 5 is a transmission electron micrograph, a nitrogen desorption curve, and a catalytic performance test curve of catalyst material No. 2, in which: the method comprises the following steps of (a) showing a transmission electron microscope picture, (b) showing a nitrogen adsorption and desorption curve, (c) showing cyclic voltammograms at different scanning speeds, (d) selecting data of the cyclic voltammograms at different scanning speeds, (e) showing a catalytic performance test curve, and (f) showing a Tafel curve.

Fig. 6 is a transmission electron micrograph, a nitrogen desorption curve, and a catalytic performance test curve of the catalyst material No. 3, in which: the method comprises the following steps of (a) showing a transmission electron microscope, (b) showing a nitrogen adsorption and desorption curve, (c) showing cyclic voltammograms at different scanning speeds, (d) selecting data of the cyclic voltammograms at different scanning speeds, (e) showing a catalytic performance test curve, and (f) showing a tafel curve.

FIG. 7 is a plot of cyclic voltammograms of catalyst 3 (a) in different solutions and (b) the time stability.

Fig. 8 is an atomic force microscope picture of catalyst 3.

Fig. 9 is a transmission electron microscope diffraction image and an element distribution image of the catalyst 3. (a) Diffraction images of catalyst 3, and (b-f) high angle dark field electron micrographs and corresponding elemental distribution maps of catalyst 3.

Detailed Description

The present invention will be further described with reference to the following examples, but the scope of the present invention is not limited to these examples.

EXAMPLE I preparation of tungsten selenide nanosheet network Structure

2mmol of selenium powder, 0.05mmol of sodium borohydride and 1mmol of sodium tungstate are simultaneously dissolved in 20mL of N, N-dimethyl formamide, ultrasonic dispersion is carried out for 30 minutes, then the obtained solution is transferred into a reaction kettle, and then solvothermal reaction is carried out for 24 hours at 220 ℃. Cooling to room temperature, washing, and freeze-drying. The transmission electron micrograph of the nanosheet is shown in fig. 2.

EXAMPLE II preparation of rhenium selenide nanosheet network Structure

2mmol of selenium powder and 0.05mmol of sodium borohydride are simultaneously dissolved in 20mL of N, N-dimethylformamide; 1mmol of ammonium perrhenate was dissolved in 10mL of deionized water, and the two solutions were ultrasonically dispersed for 30 minutes and then mixed well. The above solution was transferred to a reaction vessel, followed by a solvothermal reaction at 220 ℃ for 24 hours. Cooling to room temperature, washing, and freeze-drying. The transmission electron microscope image of the nanosheet is shown in fig. 3.

EXAMPLE III preparation of catalyst 1 and Performance testing

2mmol selenium powder, 0.05mmol sodium borohydride and x mmol (x is more than 0 and less than 1) sodium tungstate are simultaneously dissolved in 20mL N, N-dimethylformamide; (1-x) mmol of ammonium perrhenate was dissolved in 10mL of deionized water, and the two solutions were ultrasonically dispersed for 30 minutes and then mixed well. The above solution was transferred to a reaction vessel, followed by solvothermal reaction at 240 ℃ for 48 hours. Cooling to room temperature, washing, and freeze-drying. Specific values of x and the amount of precursor used are shown below,

the catalyst obtained in example three was subjected to a test of catalytic performance for a chlorine evolution reaction. By comparing the catalyst performances at different cation ratios, it can be concluded that the catalyst performs a solvothermal reaction at 240 ℃ for 48 hours, wherein the catalyst performance is best when the molar charge ratio of sodium tungstate and high ammonium rhenate is 1: 3, which is numbered 1. The transmission electron microscope photograph of the catalyst No. 1 is shown in fig. 4 (a), and the catalyst is in a nano-sheet structure which is staggered with each other. FIG. 4 (b) shows the nitrogen desorption curve for catalyst No. 1, which has a BET specific surface area of 64.91m ² (iv) g. FIG. 4 (c)Selecting specific data points for cyclic voltammetry curves of the catalyst 1 at different sweep rates to obtain a graph (d) of FIG. 4, and calculating to obtain a catalyst with a capacitance of 7.82e-4F/cm ² . As shown in FIGS. 4 (e) - (f), the catalyst concentration was 10mA/cm ² The corresponding voltage value at the current density of (1) was 1.48V, and the Tafel slope was 57mV/dec (see Table 1).

EXAMPLE four preparation of catalyst 2 and testing of the Properties

2mmol selenium powder, 0.05mmol sodium borohydride and x mmol (x is more than 0 and less than 1) sodium tungstate are simultaneously dissolved in 20mL N, N-dimethylformamide; (1-x) mmol of ammonium perrhenate was dissolved in 10mL of deionized water, and the two solutions were ultrasonically dispersed for 30 minutes and then mixed well. The above solution was transferred to a reaction kettle, followed by solvothermal reaction at various temperatures for 48 hours. Cooling to room temperature, washing, and freeze-drying. Specific x-values reaction temperatures are shown below.

By comparing catalysts with different reaction temperatures and different sodium tungstate contents, the catalyst has good chlorine precipitation reaction catalytic activity under the condition of 180-240 ℃ and different metal proportions, the catalyst has the best activity under the condition of 220 ℃, the catalyst is numbered as 2, and the catalytic activity is shown in table 1. The transmission electron micrograph of the catalyst No. 2 is shown in fig. 5 (a), and the morphology thereof is an interdigitated nanosheet structure. FIG. 5 (b) shows a nitrogen adsorption/desorption curve of the catalyst, and the BET specific surface area of catalyst No. 2 is 69.81m ² (ii) in terms of/g. FIG. 5 (c) is a cyclic voltammogram of catalyst 2 at different sweep rates, and the specific data points are selected to obtain FIG. 5 (d), which is calculated to obtain a catalyst capacitance of 6.17e-4F/cm ² . As shown in FIGS. 5 (e) - (f), the catalyst was at 10mA/cm ² The corresponding voltage value at the current density of (1) was 1.43V, and the Tafel slope was 46mV/dec.

EXAMPLE V preparation of catalyst 3 and Performance testing

2mmol selenium powder, 0.05mmol sodium borohydride and x mmol (x is more than 0 and less than 1) sodium tungstate are simultaneously dissolved in 20mL N, N-dimethylformamide; (1-x) mmol of ammonium perrhenate was dissolved in 10mL of deionized water, and the two were dispersed by ultrasonic for 30 minutes and then mixed well. The above solution was transferred to a reaction kettle, followed by solvothermal reaction at a temperature of 220 ℃ for various reaction times. Cooling to room temperature, washing, and freeze-drying. Specific values of x and reaction time are shown below.

By comparing catalysts with different reaction times and different sodium tungstate contents, the catalyst has good chlorine precipitation reaction catalytic activity under the condition of 12-72 hours of reaction time and different metal proportions, the catalyst activity under the condition of 24 hours is the best, the catalyst is numbered as 3, and the catalytic activity is shown in table 1. The transmission electron micrograph of catalyst No. 3 is shown in fig. 6 (a), and the morphology thereof is an interdigitated nanosheet structure. FIG. 6 (b) shows the nitrogen desorption curve of the catalyst, and the BET specific surface area of the catalyst No. 3 is 71.63m ² (iv) g. FIG. 6 (c) is a plot of cyclic voltammetry for catalyst # 3 at different sweep rates, with the specific data points selected to give FIG. 6 (d), which was calculated to give a catalyst capacitance of 8.02e-4F/cm ² . As shown in FIGS. 6 (e) - (f), the catalyst was at 10mA/cm ² The corresponding voltage value at the current density of (1) was 1.41V, and the Tafel slope was 57 mV/dec. Fig. 7 (a) shows that catalyst No. 3 caused only a chlorine evolution reaction and no oxygen evolution reaction in a mixed aqueous solution of sodium chloride and sulfuric acid, and still maintained good catalytic activity after 35,000s cycles (as shown in fig. 7 (b)). FIG. 8 is an atomic force microscope photograph of catalyst No. 3 with a catalyst lamella thickness of 3nm. The catalyst material is polycrystalline as shown in fig. 9 (a). Fig. 9 (b-f) are high angle dark field electron micrographs and corresponding elemental distribution plots for catalyst 3 demonstrating the uniform distribution of the four elements oxygen, selenium, rhenium, and tungsten on the surface of the material.

TABLE 1 Performance of the catalyst

Claims

1. A catalyst for the chlorine evolution reaction of an electrolytic salt water anode is a three-dimensional porous structure formed by folding nanosheets, the nanosheets are 1-20nm thick, metal elements in the nanosheets are tungsten and rhenium, and non-metal elements are oxygen and selenium.

2. The method for preparing the catalyst of claim 1, comprising:

2) Reacting the mixed solution obtained in the step 1) under the conditions of high temperature and high pressure, cooling to room temperature, separating, precipitating and drying to obtain the catalyst.

3. The method of claim 2, wherein the solvent of step 1) is a mixture of deionized water and N, N-dimethylformamide.

4. The method of claim 2, wherein the solvothermal reaction time of the step 2) is 12 to 72 hours.

5. The method of claim 2, wherein the solvothermal reaction temperature of step 2) is 180 to 240 ℃.

6. The preparation method according to claim 2, wherein the concentration of the selenium powder is preferably 10 to 100mmol/L; the concentration of the reducing agent is preferably 0.01-0.1 mmol/L; the concentration of the tungsten-based inorganic salt is preferably 0-50mmol/L; the concentration of the rhenium-based inorganic salt is preferably 0 to 50mmol/L; the concentration of the tungsten-based inorganic salt and the rhenium-based inorganic salt is not 0.