CN113502489B - Preparation method and application of electrocatalyst for reduction of alkyne into olefin - Google Patents
Preparation method and application of electrocatalyst for reduction of alkyne into olefin Download PDFInfo
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Abstract
The invention relates to the technical field of electrochemical catalysts, and discloses a preparation method and application of an electrocatalyst for reducing alkyne into olefin. The invention provides a preparation method of a molybdenum disulfide supported palladium monatomic catalyst for alkyne reduction. The MoS2 supported palladium monatomic catalyst prepared by the method has a nanometer flower-shaped structure, so that more active sites can be exposed, and the catalytic activity of the catalyst is improved; the method can be applied to electrochemical catalysis alkyne reduction, does not need to introduce hydrogen from the outside, has higher safety, and has higher catalytic hydrogenation efficiency and selectivity.
Description
Technical Field
The invention relates to the technical field of electrochemical catalysts, in particular to a preparation method and application of an electrocatalyst for reducing alkyne into olefin.
Background
With the development of society, the demand of people for fine chemicals is increasing. Olefins are one of the most important commodity chemicals in the petrochemical industry, and are widely used in the production of fine chemicals, plastics, and other industrial products. Thus, olefins have a profound key role in human survival and development. However, in the modern society, olefin production is mainly achieved by cracking of petroleum hydrocarbons, but a part of alkyne byproducts are inevitably produced in the process, so that the performance is reduced or the human health is impaired when fine chemicals are produced. Such as: in the industrial production of polyethylene, acetylene is very unfriendly to the polymerization reaction, which acts to deactivate the ethylene polymerization catalyst. The selective conversion of alkynes to alkenes is therefore now of great importance for industrial production.
Palladium-based catalysts are commonly used for the hydrogenation of acetylene due to their high hydrogenation activity. Such as commercial palladium on carbon catalysts and Lindlar catalysts invented by the chemical company rochon, Lindlar (Herbert Lindlar). The Lindlar catalyst is prepared by adsorbing palladium on a carrier (calcium carbonate or barium sulfate) and adding a small amount of inhibitor (lead acetate or quinoline). In the catalytic hydrogenation reaction using this catalyst, hydrogen performs a cis-addition to an acetylene bond to produce a cis-olefin. However, the Lindlar catalyst contains heavy metal Pb, is not an environment-friendly catalyst and is not beneficial to popularization and application of a large amount of the catalyst, so that the search for a proper catalyst is urgent.
Molybdenum disulfide (MoS) 2 ) The electrochemical hydrogen production material considered as very useful is widely applied to the field of catalysis due to the unique two-dimensional layered structure, larger specific surface area and good electronic conductivity, and MoS is used at present 2 Are of widespread interest and are considered to be one of the most promising electrocatalysts. MoS 2 Has special layered morphology, can provide a large number of loading sites for the catalytic active substances, shows more catalytic active centers, and has the highest electron mobility of about 500 cm for the single-layer molybdenum disulfide 2 V · s, its metal edge activity is also calculated as: Δ G H The = 0.06eV. has the advantages of high electrocatalytic performance, no toxicity, low cost, environmental protection and the like, so that the catalyst is widely applied to aspects of electrocatalytic reduction hydrogenation, photoelectric conversion, hydrogen production by water decomposition and oxygen production and the like.
Molybdenum disulfide (MoS) 2 ) The supported palladium-based catalyst has been proved to have good electrocatalytic reduction hydrogenation performance, but the molybdenum disulfide supported palladium-based catalyst has many disadvantages, such as low atom utilization rate, poor selectivity for olefin in the electrochemical reduction process, low electron utilization in the electrochemical reduction alkyne process, and the like, and also limits the wide application thereof in the catalysis field.
CN112301369A, the invention relates to a method for synthesizing olefin by electro-catalysis semi-hydrogenation gas phase alkyne, which adopts a gas diffusion electrode, sprays a catalyst on a gas diffusion layer substrate (comprising conductive carbon paper, metal and the like), and separates the anode and the cathode by an ion exchange membrane. And (3) carrying out electrochemical performance test by adopting a three-electrode or two-electrode system constant voltage method, wherein the reaction gas is high-purity alkyne. Experimental results show that the method can be used for selectively reducing gas-phase alkyne into corresponding alkene with high efficiency. Compared with H-type electrolytic cell, the gas diffusion electrode has doubled reaction current density, and the reaction current can reach 1A cm by regulating and controlling reaction voltage 2 The Faraday efficiency of the target olefin product is remarkably improved to more than 95%; compared with the traditional thermal catalysis technology, the method can be used for preparing the catalyst at normal temperature and normal pressureThe gas phase alkyne is selectively reduced to an alkene and does not require the consumption of hydrogen, but the subject for which is a gas alkyne.
CN112301373A, a method for selective reduction of alkyne impurities in olefin by electrocatalysis, in particular to the selective hydrogenation of acetylene, propine, butyne, phenylacetylene and the like by electrocatalysis. The gas diffusion electrode is prepared by spraying a catalyst on a gas diffusion layer substrate (comprising conductive carbon paper and metal) by adopting a gas diffusion electrode electrolytic cell, and the anode and the cathode are isolated by an ion exchange membrane. A three-electrode or two-electrode system constant voltage method is adopted for carrying out electrochemical performance test, wherein reaction gas olefin contains 1% of alkyne impurities. The method does not need to introduce hydrogen from the outside, but only aims at the hydrogenation reduction of the gas alkyne and needs to improve the safety of large-scale application.
Disclosure of Invention
In order to solve the above problems, the present invention provides a method for preparing an electrocatalyst for the reduction of alkynes to alkenes. The molybdenum disulfide supported palladium single-atom electrocatalyst has a nanometer flower-layer structure, is beneficial to exposing more active sites, and improves the catalytic activity of the catalyst.
The invention provides a preparation method of an electrocatalyst for reducing alkyne into olefin, wherein the electrocatalyst is a molybdenum disulfide supported palladium single-atom catalyst, and the preparation method comprises the following steps:
(1) adding ammonium molybdate tetrahydrate and thiourea into a solvent, and uniformly stirring to obtain a mixed solution; in the mixed solution, the mass concentration of ammonium molybdate tetrahydrate and thiourea is 0.027-0.035mol/L and 0.76-1mol/L respectively;
(2) placing the mixed solution obtained in the step (1) into a reaction kettle, reacting for 16-20h at 210-230 ℃ to obtain a reaction product, and washing and drying the reaction product to obtain a molybdenum disulfide catalyst carrier;
(3) PdCl 2 Dissolving in HCl solution to obtain chloropalladate; the concentration of the HCl solution is 0.25-0.32 mol/L, and PdCl 2 HCl and MoS obtained in step (2) 2 The mass ratio of (A) is 0.09-0.13:1: 0.18-0.26;
(4) adding the molybdenum disulfide obtained in the step (2) and the chloropalladate solution obtained in the step (3) into ethanol, and uniformly stirring to obtain a mixed solution;
(5) and (3) reacting the mixed solution obtained in the step (4) at 38-42 ℃ for 10-12 h to obtain a reaction product, and washing and drying the reaction product to obtain the molybdenum disulfide supported palladium single-atom catalyst.
The invention utilizes a hydrothermal method and ammonium molybdate tetrahydrate [ (NH) 4 )Mo 7 O 24 ﹒4H 2 O)]And thiourea (CH 4 N 2 S) reaction for preparing MoS 2 Reacting for 16-20h under the condition of 210-230 ℃, and then cleaning and drying a reaction product to obtain molybdenum disulfide (MoS) 2 ) The catalyst carrier has the following reaction equation:
4((NH 4 ) 6 Mo 7 O 24 ·4H 2 O)+ 63CH 4 N 2 S+ 42H 2 O→150NH 3 +63CO 2 +7H 2 SO 4 +28 MoS 2
subsequently, the present invention utilizes PdCl 2 As a source of palladium as a molybdenum disulfide supported palladium monatomic catalyst, but due to PdCl 2 The solubility in water is not high, so the invention utilizes PdCl 2 Has the characteristic of higher solubility in HCl solution, and PdCl 2 Dissolving in HCl solution to obtain complex chloropalladate (H) 2 PdCl 4 ). In the present invention, the palladium atom is bonded to MoS 2 The S atom on the surface forms a coordinate bond to form PdS x By forming a single catalytic center of palladium atoms through coordination bonds. And washing and drying the reaction product to obtain the molybdenum disulfide supported palladium monatomic catalyst. The obtained molybdenum disulfide supported palladium single-atom catalyst has MoS 2 The nano flower-shaped structure is beneficial to exposing more active sites, and the catalytic activity of the catalyst is improved.
Preferably, the solvent in the step (1) is water; the stirring in the step (1) and the step (4) is magnetic stirring, and the stirred solution is subjected to ultrasonic treatment; washing in the step (2) and the step (5) by alternately washing with ethanol and deionized water; the drying method is drying.
Secondly, the invention also provides a method for carrying out electrocatalytic reduction on alkyne by using the electrocatalyst obtained by the preparation method, which comprises the following steps:
(1) forming the electrocatalyst into a working electrode;
(2) and connecting a working electrode with a power supply cathode, inserting the working electrode into the catholyte containing the carbon-carbon triple-bond reactant, connecting an auxiliary electrode with a power supply anode, inserting the auxiliary electrode into the anolyte, communicating the catholyte with the anolyte, and reacting to obtain a carbon-carbon double-bond product.
The invention utilizes MoS 2 The characteristics that water electrolysis can be catalyzed to generate hydrogen and the Pd-based catalyst can catalyze acetylene hydrocarbon to generate hydrogenation reduction reaction are achieved, the molybdenum disulfide supported palladium single-atom catalyst prepared by the method is manufactured into a working electrode, and simultaneously the two characteristics are applied, and the hydrogen prepared by water electrolysis is added to a reactant containing carbon-carbon triple bonds through the molybdenum disulfide supported palladium single-atom catalyst; the working electrode is connected with the cathode of a power supply, the auxiliary electrode is connected with the anode of the power supply, the working electrode and the auxiliary electrode are inserted into the electrolyte containing the carbon-carbon triple bond reactant to form a passage, the hydrogen element in the solution obtains electrons on the surface of the anode, and then the carbon-carbon triple bond of the reactant in the electrolyte and hydrogen gas perform addition reaction to generate a carbon-carbon double bond under the action of the molybdenum disulfide supported palladium single-atom catalyst; the regulation of the voltage can control the selectivity of the reaction. In order to prevent the reactants or products from being oxidized by the anode, the present invention can separate the catholyte and the anolyte by means of a membrane or a salt bridge. The invention does not need to introduce hydrogen from the outside, and utilizes the liquid electrolyte, thereby having better safety and selectivity and higher conversion efficiency.
Preferably, the preparation method of the working electrode in the step (1) comprises the following steps:
(A) adding an electrocatalyst into absolute ethyl alcohol, adding a Nafion solution after uniform dispersion, and obtaining a catalyst mixed solution after uniform dispersion again;
(B) and uniformly coating the obtained catalyst mixed solution on carbon paper, and drying to obtain the working electrode.
Because the problem that a catalyst is easy to fall off on the surface is often encountered when a glassy carbon electrode is used or a carbon electrode is used in an electrocatalysis process, the working electrode is prepared by modifying the electrode with a Nafion solution. Nafion is a polymer, has certain viscosity and also has excellent conductivity. The coating process of the catalyst is to flatly place the carbon paper with a slender shape under an infrared lamp for heating, and then drop the uniform catalyst solution on the front and back surfaces of the carbon paper so as to ensure the uniformity of the catalyst. In order to improve the dispersion of the catalyst in the catalyst mixture, the electrocatalyst is first added to absolute ethanol, because absolute ethanol has similar compatibility with Nafion solution. In addition, the absolute ethyl alcohol has better volatility, and the drying speed can be improved.
Preferably, the mass ratio of the electrocatalyst to the absolute ethyl alcohol in the step (A) is 9-11: 790-810; the solid content of the Nafion solution is 4.8-5.2%, and the volume ratio of the added Nafion solution to absolute ethyl alcohol is 14-16: 1000; the dispersion method is ultrasonic dispersion.
Preferably, the coating amount of the electrocatalyst coated on the carbon paper in the step (B) is 4.5-5.5 mg/cm 2 (ii) a The drying method is infrared lamp drying.
In order to maximize the catalytic efficiency of the electrocatalyst per unit volume, the coating of the electrocatalyst on the carbon paper should not be too thick, and therefore the coating amount on the carbon paper is preferably 4.5 to 5.5mg/cm 2 (ii) a The infrared lamp is used for accelerating the evaporation of the solvent, so that the catalyst is quickly adhered to the surface of the carbon paper.
Preferably, the auxiliary electrode in the step (2) is a Pt net, the catholyte is a mixed solution of potassium hydroxide solution and saturated alcohol, the concentration of the potassium hydroxide is 0.9-1.1 mol/L, and the volume ratio of the saturated alcohol is 1.5-2.5: 1; the saturated alcohol is one or more of absolute ethyl alcohol, ethylene glycol, propanol, propylene glycol and glycerol.
In order to dissolve the reactant containing the carbon-carbon triple bond in the electrolyte, the electrolyte adopted by the invention is a mixed solution of potassium hydroxide solution and saturated alcohol.
Preferably, the concentration of the reactant in the step (2) in the electrolyte is 15-20 mmol/L, and the energizing voltage during the reaction is-0.5 to-0.1V.
The selectivity and the speed of the hydrogenation reduction reaction of the reactant containing the carbon-carbon triple bond in the electrolyte can be realized by controlling the concentration of the reactant containing the carbon-carbon triple bond in the electrolyte, the concentration of the electrolyte and the size of electrified voltage in the reaction.
The invention has the following beneficial effects:
(1) MoS prepared by the invention 2 The palladium-loaded monatomic catalyst has a nanometer flower-shaped structure, so that more active sites can be exposed, and the catalytic activity of the catalyst is improved;
(2) MoS prepared by the invention 2 The supported palladium monatomic catalyst is applied to electrochemical catalysis of alkyne reduction, does not need to be introduced with hydrogen from the outside, and has higher safety, higher catalytic hydrogenation efficiency and selectivity.
Drawings
FIG. 1 is a TEM test chart of the prepared catalyst;
FIG. 2 is a scanning electron microscope test chart of the prepared catalyst;
FIG. 3 is an XRD pattern of the catalyst as prepared;
FIG. 4 is a graph of conversion of the catalytic reaction of the prepared catalyst;
FIG. 5 is a graph of the selectivity of the catalytic reaction of the prepared catalyst;
FIG. 6 is a graph of the conversion of a commercial palladium on carbon catalyst reaction prepared;
fig. 7 is a graph of the selectivity of the reaction of a commercial palladium on carbon catalyst prepared.
Detailed Description
The present invention will be further described with reference to the following examples. The devices, reagents and methods referred to in the present invention are, unless otherwise indicated, all devices, reagents and methods known in the art.
Example 1
Preparing a molybdenum disulfide supported palladium monatomic catalyst:
(1) mixing ammonium molybdate tetrahydrate [ (NH) 4 )Mo 7 O 24 ﹒4H 2 O)]Thiourea (CH) 4 N 2 S) adding the mixed solution into a solvent, and uniformly stirring to obtain a mixed solution; in the mixed solution, the mass concentration of ammonium molybdate tetrahydrate and thiourea is 0.03mol/L and 0.86mol/L respectively;
(2) placing the mixed solution obtained in the step (1) into a reaction kettle, reacting for 16-20h at 210-230 ℃ to obtain a reaction product, and washing and drying the reaction product to obtain a molybdenum disulfide catalyst carrier;
(3) PdCl 2 Dissolving in HCl solution to obtain chloropalladate (H) 2 PdCl 4 ) (ii) a The concentration of the HCl solution is 0.25 mol/L, and PdCl 2 HCl and MoS obtained in step (2) 2 The ratio of the amounts of the substances of (a) is 0.11:1: 0.22;
(4) adding the molybdenum disulfide obtained in the step (2) and the chloropalladate solution obtained in the step (3) into ethanol, and uniformly stirring to obtain a mixed solution;
(5) reacting the mixed solution obtained in the step (4) for 11 hours at 40 ℃ to obtain a reaction product, and washing and drying the reaction product to obtain the molybdenum disulfide supported palladium single-atom catalyst;
preparing a working electrode:
(A) adding an electrocatalyst into absolute ethyl alcohol, wherein the mass ratio of the electrocatalyst to the absolute ethyl alcohol is 1: 80; after uniform ultrasonic dispersion, adding 5.0% Nafion solution, wherein the volume ratio of the Nafion solution to the absolute ethyl alcohol is 15:1000, and obtaining a catalyst solution after uniform ultrasonic dispersion again;
(B) the obtained catalyst mixed solution is evenly coated on carbon paper, and the coating amount of the electrocatalyst on the carbon paper is 5.0 mg/cm 2 Drying by an infrared lamp to obtain the working electrode;
the application of the electrocatalyst to the alkyne electrocatalytic reduction method comprises the following steps:
and respectively connecting the working electrode with the anode and the cathode of a power supply, wherein the anode electrolyte and the cathode electrolyte both contain 1.0mol/L of potassium hydroxide and absolute ethyl alcohol, the volume ratio of the potassium hydroxide to the absolute ethyl alcohol is 2:1, the cathode electrolyte also contains 20mmol/L of carbon-carbon triple bond reactant, the cathode electrolyte and the anode electrolyte are communicated, and the reaction is started under the condition that the voltage is-0.4V.
Example 2 (different from example 1 in that the electrocatalyst is applied to the alkyne electrocatalytic reduction method, and the voltage value is different)
Preparing the molybdenum disulfide supported palladium monatomic catalyst:
(1) mixing ammonium molybdate tetrahydrate [ (NH) 4 )Mo 7 O 24 ﹒4H 2 O)]Thiourea (CH) 4 N 2 S) adding the mixed solution into a solvent, and uniformly stirring to obtain a mixed solution; in the mixed solution, the mass concentration of ammonium molybdate tetrahydrate and thiourea is 0.03mol/L and 0.86mol/L respectively;
(2) placing the mixed solution obtained in the step (1) into a reaction kettle, reacting for 16-20h at 210-230 ℃ to obtain a reaction product, and washing and drying the reaction product to obtain a molybdenum disulfide catalyst carrier;
(3) PdCl 2 Dissolving in HCl solution to obtain chloropalladate (H) 2 PdCl 4 ) (ii) a The concentration of the HCl solution is 0.25 mol/L, and PdCl 2 HCl and MoS obtained in step (2) 2 The amount ratio of the substances of (a) is 0.11:1: 0.22;
(4) adding the molybdenum disulfide obtained in the step (2) and the chloropalladate solution obtained in the step (3) into ethanol, and uniformly stirring to obtain a mixed solution;
(5) reacting the mixed solution obtained in the step (4) for 11 hours at 40 ℃ to obtain a reaction product, and washing and drying the reaction product to obtain the molybdenum disulfide supported palladium monatomic catalyst;
preparing a working electrode:
(A) adding an electrocatalyst into absolute ethyl alcohol, wherein the mass ratio of the electrocatalyst to the absolute ethyl alcohol is 1: 80; after ultrasonic dispersion is uniform, adding 5.0% Nafion solution, wherein the volume ratio of the Nafion solution to absolute ethyl alcohol is 15:1000, and performing ultrasonic dispersion again to obtain catalyst solution;
(B) uniformly coating the obtained catalyst mixed solution on carbon paper, wherein the coating amount of the electrocatalyst on the carbon paper is 5.0 mg/cm 2 Drying the working electrode by an infrared lamp to obtain the working electrode;
the application of the electrocatalyst to the alkyne electrocatalytic reduction method comprises the following steps:
and respectively connecting the working electrode with the anode and the cathode of a power supply, wherein the anode electrolyte and the cathode electrolyte both contain 1.0mol/L of potassium hydroxide and absolute ethyl alcohol, the volume ratio of the potassium hydroxide to the absolute ethyl alcohol is 2:1, the cathode electrolyte also contains 20mmol/L of carbon-carbon triple bond reactant, the cathode electrolyte and the anode electrolyte are communicated, and the reaction is started under the condition that the voltage is-0.3V.
Example 3 (different from example 1 in that the electrocatalyst was used in the alkyne electrocatalytic reduction method, the voltage value was different)
Preparing a molybdenum disulfide supported palladium monatomic catalyst:
(1) mixing ammonium molybdate tetrahydrate [ (NH) 4 )Mo 7 O 24 ﹒4H 2 O)]Thiourea (CH) 4 N 2 S) adding the mixed solution into a solvent, and uniformly stirring to obtain a mixed solution; in the mixed solution, the mass concentration of ammonium molybdate tetrahydrate and thiourea is 0.03mol/L and 0.86mol/L respectively;
(2) placing the mixed solution obtained in the step (1) into a reaction kettle, reacting for 16-20h at 210-230 ℃ to obtain a reaction product, and washing and drying the reaction product to obtain a molybdenum disulfide catalyst carrier;
(3) PdCl 2 Dissolving in HCl solution to obtain chloropalladate (H) 2 PdCl 4 ) (ii) a The concentration of the HCl solution is 0.25 mol/L, and PdCl 2 HCl and MoS obtained in step (2) 2 The amount ratio of the substances of (a) is 0.11:1: 0.22;
(4) adding the molybdenum disulfide obtained in the step (2) and the chloropalladate solution obtained in the step (3) into ethanol, and uniformly stirring to obtain a mixed solution;
(5) reacting the mixed solution obtained in the step (4) for 11 hours at 40 ℃ to obtain a reaction product, and washing and drying the reaction product to obtain the molybdenum disulfide supported palladium monatomic catalyst;
preparing a working electrode:
(A) adding an electrocatalyst into absolute ethyl alcohol, wherein the mass ratio of the electrocatalyst to the absolute ethyl alcohol is 1: 80; after ultrasonic dispersion is uniform, adding 5.0% Nafion solution, wherein the volume ratio of the Nafion solution to absolute ethyl alcohol is 15:1000, and performing ultrasonic dispersion again to obtain catalyst solution;
(B) uniformly coating the obtained catalyst mixed solution on carbon paper, wherein the coating amount of the electrocatalyst on the carbon paper is 5.0 mg/cm 2 Drying by an infrared lamp to obtain the working electrode;
the application of the electrocatalyst in the alkyne electrocatalytic reduction method comprises the following steps:
and respectively connecting the working electrode with the anode and the cathode of a power supply, wherein the anode electrolyte and the cathode electrolyte both contain 1.0mol/L of potassium hydroxide and absolute ethyl alcohol, the volume ratio of the potassium hydroxide to the absolute ethyl alcohol is 2:1, the cathode electrolyte also contains 20mmol/L of carbon-carbon triple bond reactant, the cathode electrolyte and the anode electrolyte are communicated, and the reaction is started under the condition that the voltage is-0.2V.
Example 4 (different from example 1 in that the electrocatalyst is applied to the alkyne electrocatalytic reduction method, and the voltage value is different)
Preparing a molybdenum disulfide supported palladium monatomic catalyst:
(1) mixing ammonium molybdate tetrahydrate [ (NH) 4 )Mo 7 O 24 ﹒4H 2 O)]Thiourea (CH) 4 N 2 S) adding the mixed solution into a solvent, and uniformly stirring to obtain a mixed solution; in the mixed solution, the mass concentration of ammonium molybdate tetrahydrate and thiourea is 0.03mol/L and 0.86mol/L respectively;
(2) placing the mixed solution obtained in the step (1) into a reaction kettle, reacting for 16-20h at 210-230 ℃ to obtain a reaction product, and washing and drying the reaction product to obtain a molybdenum disulfide catalyst carrier;
(3) PdCl 2 Dissolving in HCl solution to obtain chloropalladate (H) 2 PdCl 4 ) (ii) a The concentration of the HCl solution is 0.25 mol/L, and PdCl 2 HCl and MoS obtained in step (2) 2 The amount ratio of the substances of (a) is 0.11:1: 0.22;
(4) adding the molybdenum disulfide obtained in the step (2) and the chloropalladate solution obtained in the step (3) into ethanol, and uniformly stirring to obtain a mixed solution;
(5) reacting the mixed solution obtained in the step (4) for 11 hours at 40 ℃ to obtain a reaction product, and washing and drying the reaction product to obtain the molybdenum disulfide supported palladium single-atom catalyst;
preparing a working electrode:
(A) adding an electrocatalyst into absolute ethyl alcohol, wherein the mass ratio of the electrocatalyst to the absolute ethyl alcohol is 1: 80; after ultrasonic dispersion is uniform, adding 5.0% Nafion solution, wherein the volume ratio of the Nafion solution to absolute ethyl alcohol is 15:1000, and performing ultrasonic dispersion again to obtain catalyst solution;
(B) the obtained catalyst mixed solution is evenly coated on carbon paper, and the coating amount of the electrocatalyst on the carbon paper is 5.0 mg/cm 2 Drying the working electrode by an infrared lamp to obtain the working electrode;
the application of the electrocatalyst to the alkyne electrocatalytic reduction method comprises the following steps:
and respectively connecting the working electrode with the anode and the cathode of a power supply, wherein the anode electrolyte and the cathode electrolyte both contain 1.0mol/L of potassium hydroxide and absolute ethyl alcohol, the volume ratio of the potassium hydroxide to the absolute ethyl alcohol is 2:1, the cathode electrolyte also contains 20mmol/L of carbon-carbon triple bond reactant, the cathode electrolyte and the anode electrolyte are communicated, and the reaction is started under the condition that the voltage is-0.15V.
Example 5 (different from example 1 in that the electrocatalyst was used in the alkyne electrocatalytic reduction method, the voltage value was different)
Preparing the molybdenum disulfide supported palladium monatomic catalyst:
(1) mixing ammonium molybdate tetrahydrate [ (NH) 4 )Mo 7 O 24 ﹒4H 2 O)]Thiourea (CH) 4 N 2 S) adding the mixed solution into a solvent, and uniformly stirring to obtain a mixed solution; in the mixed solution, the quantity concentration of ammonium molybdate tetrahydrate and thiourea is 0.03mol/L and 0.86mol/L respectively;
(2) placing the mixed solution obtained in the step (1) into a reaction kettle, reacting for 16-20h at 210-230 ℃ to obtain a reaction product, and washing and drying the reaction product to obtain a molybdenum disulfide catalyst carrier;
(3) PdCl 2 Dissolving in HCl solution to obtain chloropalladate (H) 2 PdCl 4 ) (ii) a The concentration of the HCl solution is 0.25 mol/L, and PdCl 2 HCl and MoS obtained in step (2) 2 The amount ratio of the substances of (a) is 0.11:1: 0.22;
(4) adding the molybdenum disulfide obtained in the step (2) and the chloropalladate solution obtained in the step (3) into ethanol, and uniformly stirring to obtain a mixed solution;
(5) reacting the mixed solution obtained in the step (4) for 11 hours at 40 ℃ to obtain a reaction product, and washing and drying the reaction product to obtain the molybdenum disulfide supported palladium single-atom catalyst;
preparing a working electrode:
(A) adding an electrocatalyst into absolute ethyl alcohol, wherein the mass ratio of the electrocatalyst to the absolute ethyl alcohol is 1: 80; after ultrasonic dispersion is uniform, adding 5.0% Nafion solution, wherein the volume ratio of the Nafion solution to absolute ethyl alcohol is 15:1000, and performing ultrasonic dispersion again to obtain catalyst solution;
(B) uniformly coating the obtained catalyst mixed solution on carbon paper, wherein the coating amount of the electrocatalyst on the carbon paper is 5.0 mg/cm 2 Drying by an infrared lamp to obtain the working electrode;
the application of the electrocatalyst to the alkyne electrocatalytic reduction method comprises the following steps:
and respectively connecting the working electrode with the anode and the cathode of a power supply, wherein the anode electrolyte and the cathode electrolyte both contain 1.0mol/L of potassium hydroxide and absolute ethyl alcohol, the volume ratio of the potassium hydroxide to the absolute ethyl alcohol is 2:1, the cathode electrolyte also contains 20mmol/L of carbon-carbon triple bond reactant, the cathode electrolyte and the anode electrolyte are communicated, and the reaction is started under the condition that the voltage is-0.1V.
Comparative example 1
The catalyst used in the comparative example was commercial palladium on carbon, which was different from that used in example 1 in that commercial palladium on carbon was directly used for the electrode and applied to the electrocatalytic reduction of alkyne, and the electrode made of palladium on carbon was used for the cathode, and the electrochemical performance test procedure was the same as that used in example 1, and the applied voltage was-0.4V.
Comparative example 2
The catalyst used in the comparative example was commercial palladium on carbon, which was different from that used in example 1 in that commercial palladium on carbon was directly used for the electrode and applied to the electrocatalytic reduction of alkyne, and the electrode made of palladium on carbon was used for the cathode, and the electrochemical performance test procedure was the same as that used in example 1, and the applied voltage was-0.3V.
Comparative example 3
The catalyst used in the comparative example was commercial palladium on carbon, which was different from that used in example 1 in that commercial palladium on carbon was directly used for the electrode and applied to the electrocatalytic reduction of alkyne, and the electrode made of palladium on carbon was used for the cathode, and the electrochemical performance test procedure was the same as that used in example 1, and the applied voltage was-0.2V.
Comparative example 4
The catalyst used in the comparative example was commercial palladium on carbon, which was different from that used in example 1 in that commercial palladium on carbon was directly used for the electrode and applied to the electrocatalytic reduction of alkyne, and the electrode made of palladium on carbon was used for the cathode, and the electrochemical performance test procedure was the same as that used in example 1, and the applied voltage was-0.1V.
The test method comprises the following steps:
microscopic morphology and phase analysis:
the microscopic appearances of the molybdenum disulfide supported palladium single-atom catalyst prepared in the examples 1-5 are observed through TEM and SEM, as shown in figures 1 and 2, the catalyst is seen to be in a nanometer flower-shaped layered structure, no particles exist on the surface of the carrier, and the noble metal Pd on MoS can be fully proved 2 Uniform dispersion of the surface. The XRD patterns of the molybdenum disulfide supported palladium monatomic catalysts prepared in examples 1-5 were obtained by XRD, see fig. 3;
and (3) electrochemical performance testing:
the test method was carried out using a three-electrode system (working electrode (W), counter electrode (C) and reference electrode (R)). The test environment is an electrolytic cell which takes a cation exchange membrane as a separation chamber and a negative chamber. Then adding the same electrolyte on the anode and the cathode respectively, adding reactants on the cathode, taking one side with the catalyst as a working electrode, and connecting the working electrode as an electrolytic cathode with a cathode wire of an electrochemical workstation; a reference electrode (Ag/AgCl) is placed at the cathode side and is connected with a reference line of an electrochemical workstation; one side with a platinum mesh electrode is used as a counter electrode and is connected with the anode of the electrochemical workstation as an electrolytic anode. The conversion rate of the catalyst prepared in examples 1-5 for converting alkyne into olefin is shown in fig. 4, fig. 5 is the selectivity of the catalyst prepared in examples 1-5 for alkyne, and it can be seen that at-0.3V, the catalytic reaction reaches 98% after reaching 5 hours, and the selectivity is still maintained above 93%; comparative examples 1-4 the conversion of alkynes to alkenes is shown in fig. 6 and fig. 7 is the selectivity of the commercial catalysts of comparative examples 1-4 to alkynes, it can be seen that when the potential is-0.3V, the catalytic reaction reaches 86% after 5 hours, 98% after 9 hours, and 60% with selectivity decreasing with increasing potential. Compared with commercial palladium-carbon catalyst, the catalyst synthesized by the method of the invention has the advantages of fast conversion rate and good selectivity.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, changes and equivalent reagent changes made on the above embodiment according to the technical spirit of the present invention still belong to the protection scope of the technical solution of the present invention.
Claims (10)
1. A preparation method of an electrocatalyst for reducing alkyne into olefin is characterized in that the electrocatalyst is a molybdenum disulfide supported palladium monatomic catalyst, and the preparation method comprises the following steps:
(1) adding ammonium molybdate tetrahydrate and thiourea into a solvent, and uniformly stirring to obtain a mixed solution; in the mixed solution, the mass concentration of ammonium molybdate tetrahydrate and thiourea is 0.027-0.035mol/L and 0.76-1mol/L respectively;
(2) placing the mixed solution obtained in the step (1) into a reaction kettle, reacting for 16-20h at 210-230 ℃ to obtain a reaction product, and washing and drying the reaction product to obtain a molybdenum disulfide catalyst carrier;
(3) PdCl 2 Dissolving in HCl solution to obtain chloropalladate; the concentration of the HCl solution is 0.25-0.32 mol/L, and PdCl 2 HCl and MoS obtained in step (2) 2 In an amount of 0.09 to 0.13:1:0.18-0.26；
(4) Adding the molybdenum disulfide obtained in the step (2) and the chloropalladate solution obtained in the step (3) into ethanol, and uniformly stirring to obtain a mixed solution;
(5) and (3) reacting the mixed solution obtained in the step (4) at 38-42 ℃ for 10-12 h to obtain a reaction product, and washing and drying the reaction product to obtain the molybdenum disulfide supported palladium single-atom catalyst.
2. The method for preparing an electrocatalyst according to claim 1, wherein the solvent in step (1) is water.
3. The method for preparing the electrocatalyst according to claim 1, wherein the stirring in step (1) and step (4) is magnetic stirring, and the stirred solution is subjected to ultrasonic treatment.
4. The method for preparing the electrocatalyst according to claim 1, wherein the washing in step (2) and step (5) is alternately washed with ethanol and deionized water; the drying method is drying.
5. A method for carrying out electrocatalytic reduction on alkyne by using the electrocatalyst obtained by the preparation method according to any one of claims 1 to 4, characterized by comprising the following steps:
(1) forming the electrocatalyst into a working electrode;
(2) and connecting the working electrode with the negative electrode of a power supply, inserting the working electrode into the catholyte containing the carbon-carbon triple-bond reactant, connecting the auxiliary electrode with the positive electrode of the power supply, inserting the auxiliary electrode into the anolyte, communicating the catholyte and the anolyte, and reacting to obtain a carbon-carbon double-bond product.
6. The electrocatalytic reduction method according to claim 5, wherein the working electrode preparation method of step (1) includes the steps of:
(A) adding the electrocatalyst into absolute ethyl alcohol, adding a Nafion solution after uniform dispersion, and obtaining a catalyst mixed solution after uniform dispersion again;
(B) and uniformly coating the obtained catalyst mixed solution on carbon paper, and drying to obtain the working electrode.
7. The electrocatalytic reduction method as set forth in claim 6, wherein the mass ratio of the electrocatalyst to the absolute ethanol in the step (A) is 9-11: 790-810; the solid content of the Nafion solution is 4.8-5.2%, and the volume ratio of the added Nafion solution to absolute ethyl alcohol is 14-16: 1000; the dispersion method is ultrasonic dispersion.
8. The electrocatalytic reduction method according to claim 6, wherein the coating amount of the electrocatalyst applied to the carbon paper in the step (B) is 4.5 to 5.5mg/cm 2 (ii) a The drying method is infrared lamp drying.
9. The electrocatalytic reduction method according to claim 5, wherein the auxiliary electrode in the step (2) is a Pt mesh, the catholyte is a mixed solution of a potassium hydroxide solution and a saturated alcohol, the concentration of the potassium hydroxide is 0.9 to 1.1mol/L, and the volume ratio of the saturated alcohol is 1.5 to 2.5: 1; the saturated alcohol is one or more of absolute ethyl alcohol, ethylene glycol, propanol, propylene glycol and glycerol.
10. The electrocatalytic reduction method according to claim 5, wherein the concentration of the reactant in the step (2) in the electrolyte is 15 to 20mmol/L, and the energizing voltage during the reaction is-0.5 to-0.1V.
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