CN113881955A

CN113881955A - Electrocatalyst for electrocatalytic reduction of carbon monoxide to acetic acid and application thereof

Info

Publication number: CN113881955A
Application number: CN202111188530.XA
Authority: CN
Inventors: 郑耿锋; 纪亚丽
Original assignee: Fudan University
Current assignee: Fudan University
Priority date: 2021-10-12
Filing date: 2021-10-12
Publication date: 2022-01-04
Anticipated expiration: 2041-10-12
Also published as: CN113881955B

Abstract

The invention belongs to the technical field of carbon monoxide electrocatalytic reduction, and particularly relates to an electrocatalyst for electrocatalytic reduction of carbon monoxide to generate acetic acid and application thereof. The invention firstly prepares an electrocatalyst-copper-palladium alloy nanoparticle electrocatalyst for electrocatalytic reduction of carbon monoxide to generate acetic acid, and then uses the electrocatalyst as a catalytic reaction cathode, adopts potassium hydroxide electrolyte to electrocatalytic carbon monoxide reduction, and selectively generates acetic acid. The partial current density of the catalyst for catalyzing the electro-reduction of carbon monoxide to generate acetic acid can reach 425mA cm^‑2The Faraday efficiency can reach 70%; the catalyst can continuously and stably run for 500h in a membrane electrode device at the total current of 2.5ACan keep higher faradaic efficiency of acetic acid. The invention has the advantages of wide raw material source, simple preparation method, environmental protection and low price, efficiently converts carbon monoxide into acetic acid and has wide market application prospect.

Description

Electrocatalyst for electrocatalytic reduction of carbon monoxide to acetic acid and application thereof

Technical Field

The invention belongs to the technical field of carbon monoxide electrocatalytic reduction, and particularly relates to an electrocatalyst for electrocatalytic reduction of carbon monoxide to generate acetic acid and application thereof.

Background

Energy, one of the three major industries in the 21 st century, consumes large amounts of fossil fuels and thus emits large amounts of carbon dioxide (CO)₂) Greenhouse gases, have accelerated the progress of global warming very rapidly. By utilizing the electrochemical technology, the carbon dioxide greenhouse molecules can be efficiently converted into chemical energy to be stored in chemical fuels and products under the driving of clean, easily obtained and stable electric energy, and an important foundation is laid for reducing the utilization rate of fossil energy and realizing carbon peak reaching and carbon neutralization. The reduction of carbon dioxide in alkaline electrolytes enables higher conversion activity to be obtained compared to neutral or acidic electrolyte environments, however, CO₂Is easy to react with alkaline electrolyte to cause the accumulation of a large amount of bicarbonate, and influences the high-activity conversion of carbon monoxide. Carbon monoxide is a key intermediate in the electrochemical reduction of CO2, and commercial SOFC devices are now capable of converting CO₂And efficiently converted into carbon monoxide on a large scale. Therefore, by the two-step method, the carbon monoxide is directly subjected to electrochemical catalytic reduction, the formation of a byproduct bicarbonate can be avoided, the high-alkalinity electrolyte is convenient to react, and a larger current density is obtained.

As an important chemical, acetic acid is widely applied to important fields of polymer material manufacturing industry, food industry, drug synthesis and the like, and the electrochemical reduction of carbon monoxide to obtain acetic acid has important significance. However, at present, the faradaic efficiency of the electrochemical reduction of carbon monoxide to acetic acid is still lower than 50%, and the fractional current density is still lower than 200mA cm^-2And has a large difference with the industrial application level. Ketene is reported to be an important intermediate in the electrochemical reduction of carbon monoxide to acetic acid, while high carbon monoxide coverage favors the electrochemical conversion of carbon monoxide to oxygenated products. Based on the above, the invention provides a new catalyst design idea. According to the invention, palladium is introduced into the metallic copper, so that the coverage of carbon monoxide on a three-phase interface of a catalytic reaction is improved, the stability of a ketene intermediate is enhanced, the selectivity and activity of the material for catalyzing the reduction of carbon monoxide to acetic acid are enhanced, and the purpose of reaching the industrial level is achievedThe partial current density of acetic acid, and the catalyst designed by the invention has extremely high stability under the reaction condition, and can continuously and efficiently work for 500 hours. In addition, the catalyst designed by the invention has wide raw material source, simple preparation process and convenient large-scale utilization.

Disclosure of Invention

The first purpose of the invention is to provide a catalyst which has high activity and high stability and is convenient for industrialized use and is used for electrocatalytic reduction of carbon monoxide to generate acetic acid;

a second object of the present invention is to provide a novel and efficient catalyst preparation method, which can achieve controllability of the catalyst structure and maximization of the active site density by forming intermetallic compounds.

The third purpose of the invention is to provide a method for producing acetic acid by electrocatalytic reduction of carbon monoxide by using the catalyst.

The invention provides an electrocatalyst for generating acetic acid by electrocatalytic reduction of carbon monoxide, which is copper-palladium alloy nano powder (particles) and is prepared by the following steps:

(1) dissolving a copper salt precursor in ethylene glycol ethyl ether, and dissolving a palladium salt precursor in acetone;

(2) stirring the two solutions at room temperature for more than 5 min;

(3) after the two solutions are completely dissolved respectively, uniformly mixing the two solutions, and stirring for 1-180 minutes at room temperature;

(4) preparing a sodium borohydride solution with the volume of 5-1000 mL and the concentration of 0.1-10 mol/L, and dropwise adding the sodium borohydride solution into the mixed solution;

(4) after the dropwise addition of the sodium borohydride solution is finished, stirring the solution at room temperature for 1-180 minutes to completely react;

(5) after the reaction is finished, centrifuging the obtained solution to obtain a black solid, washing the black solid for a plurality of times by using water and ethanol, and then placing the black solid in a vacuum drying oven to be dried to obtain unordered copper-palladium alloy nano powder;

(6) putting the black copper-palladium alloy nano powder obtained by drying into a tube furnace, and using H₂Calcining the mixture in a mixed atmosphere of/Ar for 0.5 to 10 hours at the temperature of between 100 and 600 ℃ to obtain atomsOrdered copper-palladium intermetallic compounds.

In the invention, the copper salt is one or more of copper chloride, copper acetate, copper sulfate and copper nitrate; the palladium salt is one or more of palladium chloride, palladium acetate, palladium sulfate and palladium nitrate.

The molar ratio of the copper salt to the palladium salt is 1 (0.1-10), the molar ratio of the copper salt to the palladium salt is preferably 1 (0.5-5), and the molar ratio of the copper salt to the palladium salt is more preferably 1 (0.8-2).

The copper-palladium alloy nanoparticle electrocatalyst is applied to electrocatalysis carbon monoxide reduction reaction to obtain products with two or more carbons. Among them, the copper palladium intermetallic compound has the highest reactive site density and the best electrocatalytic performance.

The method for generating acetic acid by using the catalyst to carry out electrocatalytic reduction on carbon monoxide adopts potassium hydroxide electrolyte, promotes the electrocatalytic reduction on carbon monoxide by using the stability of a ketene intermediate and the improvement of the coverage of carbon monoxide on a catalytic reaction three-phase interface, and generates acetic acid, and comprises the following specific steps:

(1) dispersing a copper-palladium alloy nanoparticle electrocatalyst in a solvent, adding a Nafion solution, and dispersing the solution uniformly under an ultrasonic condition; spraying the catalyst on the gas diffusion electrode layer by adopting a spraying mode, and drying, wherein the catalyst loading amount is controlled to be 0.1-1000 mg/cm²As an electrocatalytic reaction cathode;

(2) introducing carbon monoxide gas to make the carbon monoxide contact with one side of the electrode not loaded with the electrocatalyst, and making the potassium hydroxide electrolyte contact with one side of the electrode loaded with the electrocatalyst; the electrode is subjected to hydrophobic treatment, carbon monoxide can contact with the catalyst through the electrode, and the electrolyte cannot diffuse to the other side;

(3) negative voltage is applied to the electrode, and the current is controlled to be 0.02-50A/cm²The carbon monoxide is selectively reduced into acetic acid as a main product and other multi-carbon products (such as products of carbon and more than carbon), specifically one or more of ethyl, ethanol, ethylene and propanol; among these, acetic acid is the main product.

In the step (2), the carbon monoxide gas is introduced, and the flow rate is controlled to be 5mL/min to 1000 mL/min.

In the step (2), the electrolyte is a potassium hydroxide solution, and the concentration is 1-10 mol/L.

The invention has the advantages that: the cathode catalyst can enhance the adsorption of the material to carbon monoxide, promote the promotion of the carbon monoxide coverage of a three-phase interface of a catalytic reaction, stabilize a ketene intermediate and promote the efficient reduction of the carbon monoxide to acetic acid under mild conditions. Meanwhile, the combination of copper and palladium weakens the adsorption capacity of palladium on carbon monoxide, weakens the poisoning phenomenon of carbon monoxide and enhances the stability of the catalyst under reaction conditions. The copper-palladium alloy nano electro-catalyst synthesized by the invention has good chemical stability and electro-catalytic activity. The ratio of the copper and palladium two components, the applied potential and the partial pressure of carbon monoxide in the reaction feed gas influence the product selectivity and the partial current density of the carbon monoxide reduction. Thus, the ratio of copper to palladium bi-components is preferred in the present invention, the applied potential and the partial pressure of carbon monoxide in the reaction feed gas are preferred.

The partial current density of the catalyst for catalyzing the electro-reduction of carbon monoxide to generate acetic acid can reach 425mA cm^-2The Faraday efficiency can reach 70 percent, which is the highest value reported in the current literature; in addition, the catalyst can be continuously and stably operated for 500h in a membrane electrode device at the total current of 2.5A, and simultaneously can keep higher faradaic efficiency of acetic acid. The invention has wide source of raw materials, simple preparation method, environmental protection and low price, and can convert greenhouse gas carbon dioxide (CO)₂) The carbon monoxide is efficiently converted into the carbon monoxide by a commercial Solid Oxide Electrolysis (SOEC) device, and then the carbon monoxide is efficiently converted into the acetic acid by the method, so that the method has wide market application prospect.

Drawings

FIG. 1 is a schematic representation of the method of the present invention. The formation of copper palladium intermetallic compounds promotes the improvement of carbon monoxide coverage on the catalytic reaction interface, and stabilizes ketene intermediates, thereby being beneficial to promoting the catalytic reduction of carbon monoxide into acetic acid.

FIG. 2 shows the ratio of the present invention is 1:1, X-ray diffraction pattern of the copper palladium random alloy.

FIG. 3 is an X-ray diffraction pattern of the copper palladium intermetallic compound of the present invention.

FIG. 4 shows the morphology of the Cu-Pd intermetallic compound nanoelectrocatalyst according to the present invention.

FIG. 5 is an elemental distribution image of the copper palladium intermetallic compound of the present invention. Green is copper and red is palladium (scale 50 nm).

FIG. 6 is a line scan image of a TEM element of the Cu-Pd intermetallic compound of the present invention.

In FIG. 7, (a) is an image of a high-angle toroidal dark-field scanning transmission electron microscope of the copper palladium intermetallic compound of the present invention, and (b) is an enlarged view of an image in a blue box in the image (a).

FIG. 8 is a graph showing the distribution of the Faraday efficiency and the distribution of the current density of the product obtained by electrocatalytic reduction of carbon monoxide by the Cu-Pd intermetallic compound of the present invention.

FIG. 9 is a graph showing the stability of the electrocatalytic reduction of carbon monoxide by the Cu-Pd intermetallic compound of the present invention.

Detailed Description

The invention is further illustrated by the following examples, which will aid the understanding of the invention, but do not limit the content of the invention.

Example 1:

the ratio is 1:1, the preparation method comprises the following specific steps:

(1) disordered copper-palladium alloy nanoparticles in a ratio of 1:1 were synthesized by a wet chemical method, and the X-ray diffraction pattern thereof is shown in fig. 2. 1.5mmol of copper acetate was dissolved in 250mL of ethylene glycol ethyl ether, and 1.5mmol of palladium acetate was dissolved in 10mL of acetone. The above solutions were stirred at room temperature for 30 minutes, respectively, and after complete dissolution, the above solutions were mixed and stirred at room temperature for another 30 minutes. 30mL of a 1mol/L sodium borohydride solution was added dropwise to the above mixed solution, and the mixture was stirred while being added dropwise. After completion of the dropwise addition, the above mixed solution was further stirred at room temperature for 10 minutes. Separating the black precipitate by centrifugation and separatingThe seed water and the ethanol are washed for several times respectively. At 60^oAnd C, drying in a vacuum drying oven, and sealing and storing the catalyst.

(2) The synthesis ratio is 1:1 the disordered copper-palladium alloy is placed in a quartz tube of a tube furnace in H₂Calcining at 300 ℃ for 3 hours in an/Ar atmosphere to obtain the copper-palladium intermetallic compound with ordered atomic arrangement, wherein an X-ray diffraction image of the copper-palladium intermetallic compound is shown in figure 3.

Taking the copper-palladium intermetallic compound of the embodiment as an example, the morphology and element distribution can be determined by a Transmission Electron Microscope (TEM) and a high-angle annular dark-field scanning transmission electron microscope (HADDF-STEM). As can be seen from the TEM picture of fig. 4, the material is nanoparticles having a particle size of about tens of nanometers; as can be seen from the element distribution image of fig. 5, the copper element and the palladium element are uniformly distributed in the material; as can be seen from the line scan of the transmission mirror element of fig. 6, the material has no segregation of elements; as can be seen from the HADDF-STEM element distribution picture of FIG. 7, copper atoms and palladium atoms are arranged in order.

Promoting electrocatalytic reduction of carbon monoxide to generate acetic acid in potassium hydroxide electrolyte, and specifically comprising the following steps:

the testing device adopts a flow electrolytic cell of a three-electrode system. Preparing a cathode: ultrasonically dispersing 20mg of the catalyst in 3ml of isopropanol solution, adding 60 muL Nafion, and ultrasonically mixing uniformly; uniformly spraying the uniformly mixed solution on the surface of a gas diffusion electrode in a spraying way to be used as a reaction cathode, and controlling the loading amount of a catalyst to be 0.5mg/cm². Preparing an anode: taking 20mg of commercial iridium sesquioxide powder, dispersing the powder in 3mL of isopropanol, adding 60 mu L of Nafion, and ultrasonically mixing uniformly; uniformly spraying the uniformly mixed solution on the surface of a gas diffusion electrode in a spraying way to be used as a reaction anode, and controlling the loading amount of iridium trioxide powder to be 0.5mg/cm². Reference electrode: Ag/AgCl electrode. Electrolyte solution: 1mol/L potassium hydroxide solution, and the flow rate of the electrolyte is controlled to be 5 mL/min. Reaction gas: high purity carbon monoxide gas, the flow rate of the gas is controlled at 40 mL/min. In the reaction process, the cathode is controlled by an electrochemical workstation to be applied to the cathode within-1.6-At a voltage of 2.4V, carbon monoxide is selectively reduced to a carbon two/carbon three product, with acetic acid being the major product. After the reaction was complete, 90% IR correction was performed with a resistance of 1 ohm. After the correction by IR, under the potential of-1.03V, the Faraday efficiency of acetic acid can reach 70%, and the partial current density of acetic acid can reach 425mA/cm^-2. The electrochemical performance is shown in fig. 8.

Thirdly, utilizing the membrane electrode to carry out the stability test of the catalyst under the reaction condition, and comprising the following specific steps:

a commercial membrane electrode system (two-electrode system) was used, the effective electrode area of which was 5cm². The gas diffusion electrode loaded with the copper-palladium intermetallic compound was used as a cathode for the reaction, and the nickel mesh loaded with iridium trioxide was used as an anode for the reaction. The loading of the catalyst materials of the anode and the cathode are controlled to be 0.5mg/cm²Left and right. The current and the potential of the reaction system are controlled by a direct current power supply, and the total current is 2.5A and 500mA/cm²Under the current density of (1), the copper-palladium intermetallic compound synthesized by the invention realizes 500h continuous and stable reaction, and the electrochemical stability curve of the compound is shown in figure 9. Meanwhile, the method can keep higher acetic acid selectivity, and has excellent electrochemical stability and wide application prospect.

Example 2:

the ratio is 10: 1, the preparation method of the copper-palladium alloy electrocatalyst comprises the following specific steps:

synthesis by wet chemistry 10: 1 ratio of copper palladium alloy nanoparticles. 1.5mmol of copper acetate were dissolved in 250mL of ethylene glycol ethyl ether, and 0.15 mmol of palladium acetate were dissolved in 1mL of acetone. The above solutions were stirred at room temperature for 30 minutes, respectively, and after complete dissolution, the above solutions were mixed and stirred at room temperature for another 30 minutes. 15mL of a 1mol/L sodium borohydride solution was added dropwise to the above mixed solution, and the mixture was stirred while being added dropwise. After completion of the dropwise addition, the above mixed solution was further stirred at room temperature for 10 minutes. And (4) centrifugally separating black precipitates, and washing 3-5 times by using deionized water and ethanol respectively. At 60^oAnd C, drying in a vacuum drying oven, and sealing and storing the catalyst.

The ratio is 1: 10 the preparation of the copper-palladium alloy electrocatalyst comprises the following specific steps:

synthesis of 1: copper palladium alloy nanoparticles in a proportion of 10. 0.15 mmol of copper acetate was dissolved in 25 mL of ethylene glycol ethyl ether, and 1.5mmol of palladium acetate was dissolved in 10mL of acetone. The above solutions were stirred at room temperature for 30 minutes, respectively, and after complete dissolution, the above solutions were mixed and stirred at room temperature for another 30 minutes. 15mL of a 1mol/L sodium borohydride solution was added dropwise to the above mixed solution, and the mixture was stirred while being added dropwise. After completion of the dropwise addition, the above mixed solution was further stirred at room temperature for 10 minutes. And (4) centrifugally separating black precipitates, and washing 3-5 times by using deionized water and ethanol respectively. At 60^oAnd C, drying in a vacuum drying oven, and sealing and storing the catalyst.

The ratio of the carbon monoxide applied to electrocatalysis reduction is 10: 1 and 10: 1, preparing an electrode of the copper-palladium alloy catalyst and performing electrochemical test, wherein the specific steps are as follows:

the testing device adopts a flow electrolytic cell of a three-electrode system. Preparing a cathode: ultrasonically dispersing 20mg of the catalyst in 3ml of isopropanol solution, adding 60 muL Nafion, and ultrasonically mixing uniformly; uniformly spraying the uniformly mixed solution on the surface of a gas diffusion electrode in a spraying way to be used as a reaction cathode, and controlling the loading amount of a catalyst to be 0.5mg/cm². Preparing an anode: taking 20mg of commercial iridium sesquioxide powder, dispersing the powder in 3mL of isopropanol, adding 60 mu L of Nafion, and ultrasonically mixing uniformly; uniformly spraying the uniformly mixed solution on the surface of a gas diffusion electrode in a spraying way to be used as a reaction anode, and controlling the loading amount of iridium trioxide powder to be 0.5mg/cm². Reference electrode: Ag/AgCl electrode. Electrolyte solution: 1mol/L potassium hydroxide solution, and the flow rate of the electrolyte is controlled to be 5 mL/min. Reaction gas: high purity carbon monoxide gas, the flow rate of the gas is controlled at 40 mL/min. In the reaction process, the cathode is controlled by an electrochemical workstation to apply a voltage of-1.6 to-2.4V, and carbon monoxide is selectively reduced into a carbon two/carbon three product, wherein the main carbon monoxide reduction product is acetic acid.

Claims

1. An electrocatalyst for the electrocatalytic reduction of carbon monoxide to acetic acid, characterized by being copper palladium alloy nanoparticles, prepared by the steps of:

(2) stirring the two solutions at room temperature for more than 5 min;

(6) putting the black copper-palladium alloy nano powder obtained by drying into a tube furnace, and using H₂Calcining for 0.5-10 h at the temperature of 100-600 ℃ in the/Ar mixed atmosphere to obtain the copper-palladium intermetallic compound with orderly arranged atoms.

2. The electrocatalyst according to claim 1, wherein the copper salt is one or more of copper chloride, copper acetate, copper sulfate, copper nitrate; the palladium salt is one or more of palladium chloride, palladium acetate, palladium sulfate and palladium nitrate.

3. The electrocatalyst according to claim 2, wherein the molar ratio of the copper salt to the palladium salt is 1 (0.1-10).

4. The electrocatalyst according to claim 3, wherein the molar ratio of the copper salt to the palladium salt is 1 (0.8-2).

5. A method for producing acetic acid by electrocatalytic reduction of carbon monoxide with the electrocatalyst according to any one of claims 1-4, wherein the electrocatalytic reduction of carbon monoxide to acetic acid is promoted by using potassium hydroxide electrolyte, utilizing the stabilization of ketene intermediate and the enhancement of carbon monoxide coverage of three-phase interface of catalytic reaction, and comprises the following specific steps:

(2) contacting carbon monoxide with the side of the electrode not loaded with the electrocatalyst, and contacting a potassium hydroxide electrolyte with the side of the electrode loaded with the electrocatalyst; the electrode is subjected to hydrophobic treatment, carbon monoxide can contact with the catalyst through the electrode, and the potassium hydroxide electrolyte cannot diffuse to the other side;

(3) negative voltage is applied to the electrode, and the current is controlled to be 0.02-5A/cm²Carbon monoxide is selectively reduced to acetic acid-based multi-carbon products.

6. The method according to claim 5, wherein the carbon monoxide gas is introduced in the step (2) at a flow rate of 5mL/min to 1000 mL/min.

7. The method according to claim 5, wherein the concentration of the potassium hydroxide electrolyte in the step (2) is 1-10 mol/L.

8. The process according to claim 5, wherein the acetic acid is a predominantly multi-carbon product in step (3), in particular one or more of ethyl, ethylene, propyl alcohol; among these, acetic acid is the main product.