1. A preparation method of a two-species supported catalyst is characterized by comprising the following steps: using phosphotungstic acid, bismuth salt and lithium sulfate as raw materials, heating and stirring under mild conditions, using phosphotungstic acid with rich oxygen coordination sites as a carrier, using bismuth salt as a precursor, uniformly embedding bismuth on four-fold sites of the phosphotungstic acid to form a stable structure by a vacuum rotary evaporation method, using lithium sulfate as a raw material, and coupling lithium species to the phosphotungstic acid W ═ O by a wet impregnation method_dO in (1)_dThereby obtaining the dual-species supported catalyst.

2. A process for the preparation of a two-species supported catalyst according to claim 1, wherein: the bismuth salt is bismuth nitrate pentahydrate or bismuth chloride.

3. The preparation method of the dual-species supported catalyst according to claim 1, which comprises the following steps:

(1) dissolving phosphotungstic acid in distilled water, dropwise adding a bismuth salt solution, violently stirring for 2-3 hours, placing the mixed solution in a rotary evaporator, carrying out rotary evaporation heating reaction at the temperature of 80-120 ℃ and the rotating speed of 500-600 r/min, and carrying out rotary evaporation heating reaction for 8-10 hours under a vacuum condition;

(2) and (2) adding the sample obtained by the reaction in the step (1) into a lithium sulfate solution, carrying out impregnation reaction for 24-36 h at normal temperature, fully stirring, and drying in an oven to obtain a dried sample, namely the dual-species supported catalyst.

4. A process for the preparation of a two-species supported catalyst according to claim 3, characterized in that: the molar ratio of the phosphotungstic acid to the bismuth salt solution in the step (1) is 347: 2.43-10.

5. A process for the preparation of a two-species supported catalyst according to claim 3, characterized in that: the concentration of the lithium sulfate solution in the step (2) is 0.05-0.5 mol/L, and the pH of the lithium sulfate solution is 4-5.

6. A process for the preparation of a two-species supported catalyst according to claim 3, characterized in that: the dosage ratio of the sample to the lithium sulfate solution in the step (2) is 0.3-1.0 g:30 mL.

7. A process for the preparation of a two-species supported catalyst according to claim 3, characterized in that: the temperature of the dipping reaction in the step (2) is 25-30 ℃, and the rotating speed is 1000-2000 r/min.

8. A two-species supported catalyst prepared according to the method for preparing a two-species supported catalyst of any one of claims 1 to 7.

9. Use of a two-species supported catalyst according to claim 8 in an electrocatalytic ammonia synthesis reaction.

10. The use of a two-species supported catalyst according to claim 9 in an electrocatalytic ammonia synthesis reaction, wherein: the method for preparing the double-species supported catalyst into the double-species supported catalytic electrode specifically comprises the following steps:

s1, dispersing the dual-species supported catalyst in an ethanol solution and adsorbing the dual-species supported catalyst in the multi-walled carbon nanotube through electrostatic action;

s2, then taking the multi-walled carbon nanotubes adsorbed with the dual-species supported catalyst, dispersing the multi-walled carbon nanotubes in a dispersion liquid composed of ethanol and water again, and after carrying out ultrasonic treatment for 1-2 hours, taking the dual-species supported catalyst mixed liquid and dripping the dual-species supported catalyst mixed liquid on hydrophilic carbon paper; the volume ratio of the ethanol to the water is 2: 1;

s3, spin-coating the polytetrafluoroethylene emulsion on the surface of the catalyst to prepare the double-species supported catalytic electrode for the electro-catalytic ammonia synthesis reaction.

Background

Ammonia is one of the highest-yield chemicals in the world and is widely applied to production of chemical fertilizers, plastics, explosives and the like; previously, global ammonia production was about 5 million tons, with considerable importance in food, energy chemistry, and ammonia is considered to be a potential hydrogen storage molecule and liquid fuel in the future. The synthetic ammonia is one of the most important inventions in the 20 th century, and makes a great contribution to the promotion of social progress. Currently, the Haber-Bosch process (Haber-Bosch process) is widely used for industrial ammonia synthesis, i.e. ammonia synthesis is carried out by nitrogen and hydrogen under high temperature and high pressure and under the action of iron-based catalyst, and N is synthesized by the Haber-Bosch process under severe reaction conditions (15-25MPa, 300-₂Reduction to NH₃The method has the problems of complex process, high energy consumption, low yield, large amount of greenhouse gas emission, shortage of fossil fuel, global climate change and the like. Therefore, the development of a high-efficiency, low-energy-consumption and clean ammonia synthesis process is of great significance.

In recent years, electrocatalysis nitrogen fixation under normal temperature and pressure by using renewable energy electric energy has attracted extensive attention of scholars all over the world, and is considered to be one of the most promising technologies for replacing industrial synthetic ammonia. However, since nitrogen reduction involves cleavage of a strong triple bond (N ≡ N), kinetic difficulties arise, and since the hydrogen evolution potential and the nitrogen reduction potential are very close, hydrogen evolution as a competing reaction severely limits the efficiency of nitrogen reduction to ammonia. In order to solve the above problems, many researchers have adopted different strategies to improve the nitrogen reduction performance, such as defect engineering, heterojunction engineering, spatial cooperation strategy or hydrophobic layer construction, etc., and the patent with application number CN201910483691.8 discloses a normal temperature nitrogen-fixing electrocatalyst, a preparation method of an electrocatalytic electrode and a nitrogen-fixing method, and specifically discloses a Na method for fixing nitrogen_0.26CoO₂Electrocatalytic nitrogen fixation electrode, and adding Na_0.26CoO₂Electrocatalytic nitrogen fixation electrode and Hg/HgSO₄The electrodes are assembled into an electrocatalytic nitrogen fixation battery, and nitrogen in the atmosphere is catalytically converted into ammonia in a sulfuric acid solution under the voltage of-0.1 to-1.0V; the patent with the application number of CN201910339033.1 discloses an iron trioxide nitrogen fixation catalyst rich in oxygen vacancies based on reductive ionic liquid,The preparation method and the application of electrocatalysis nitrogen fixation thereof, in particular discloses preparation of ferric oxide nano cubic particles with rich oxygen vacancies and smaller particles, and the application of the ferric oxide nano cubic particles in electrocatalysis nitrogen fixation reaction; however, the processes disclosed in the above patents and the catalysts utilized are still very slow and ultra-low in selectivity in the kinetics of the nitrogen reduction reaction at ambient conditions. Therefore, the development of an efficient nitrogen reduction catalyst remains the most major challenge for nitrogen fixation reaction at normal temperature and pressure.

Phosphotungstic acid with a Keggin structure is used as a novel multifunctional catalyst, has rich oxygen coordination sites, and can accurately anchor metal species, particularly four-fold sites and W ═ O ═ on the metal species_dAnd (d is a terminal) can modify metal species, so that phosphotungstic acid can establish a good carrier platform for modification of two species. In addition, the polyanion in the phosphotungstic acid has rich electrons which can be transferred to the anchored double species and adjust the electronic structure of the double species, and meanwhile, the phosphotungstic acid has poor hydrogen evolution performance, can reduce the reduction rate of hydrogen protons, and is an ideal carrier for inhibiting the hydrogen evolution competitive reaction. Therefore, the modification of two species on phosphotungstic acid is expected to become a catalyst for efficient electro-catalytic reduction of nitrogen.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a bi-species supported catalyst and a preparation method thereof, wherein phosphotungstic acid, bismuth salt and lithium sulfate are used as raw materials, batch feeding and heating and stirring are carried out under mild conditions, phosphotungstic acid with rich oxygen coordination sites is used as a carrier, bismuth salt and lithium sulfate are used as bi-species modified precursors, and a high-performance bi-lithium bi-species supported phosphotungstic acid electrocatalyst for electrocatalysis nitrogen fixation is developed.

The technical scheme of the invention is as follows:

the invention discloses a preparation method of a dual-species supported catalyst, which comprises the steps of taking phosphotungstic acid, bismuth salt and lithium sulfate as raw materials, heating and stirring the raw materials under mild conditions, using phosphotungstic acid with rich oxygen coordination sites as a carrier, taking the bismuth salt as a precursor, uniformly embedding bismuth on four-fold sites of the phosphotungstic acid to form a stable structure by a vacuum rotary evaporation method, and then using sulfuric acidLithium is used as raw material, and a wet impregnation method is adopted to couple lithium species in phosphotungstic acid W ═ O_dO in (1)_dThereby obtaining the dual-species supported catalyst.

Further, the bismuth salt is bismuth nitrate pentahydrate or bismuth chloride.

Further, the preparation method of the dual-species supported catalyst specifically comprises the following steps:

(3) dissolving phosphotungstic acid in distilled water, dropwise adding a bismuth salt solution, violently stirring for 2-3 hours, placing the mixed solution in a rotary evaporator, and carrying out rotary evaporation heating reaction for 8-10 hours under a vacuum condition;

(4) and (2) adding the sample obtained by the reaction in the step (1) into a lithium sulfate solution, carrying out impregnation reaction for 24-36 h at normal temperature, fully stirring, and drying in an oven to obtain a dried sample, namely the dual-species supported catalyst.

Further, the molar ratio of the phosphotungstic acid to the bismuth salt solution is 347: 2.43-10.

Further, the temperature of the rotary evaporation heating reaction in the step (1) is 80-120 ℃, and the rotating speed is 500-600 r/min.

Further, the concentration of the lithium sulfate solution in the step (2) is 0.05-0.5 mol/L, and the pH of the lithium sulfate solution is 4-5.

Further, the dosage ratio of the sample to the lithium sulfate solution in the step (2) is 0.3-1.0 g:30 mL.

Further, the temperature of the dipping reaction in the step (2) is 25-30 ℃, and the rotating speed is 1000-2000 r/min.

The invention also discloses the dual-species supported catalyst prepared by the preparation method of the dual-species supported catalyst.

The invention also discloses application of the double-species supported catalyst in the electrocatalytic ammonia synthesis reaction.

Further, the application of the dual-species supported catalyst in the electrocatalytic ammonia synthesis reaction, which is to prepare the dual-species supported catalyst into a dual-species supported catalytic electrode, specifically comprises the following steps:

s1, dispersing the dual-species supported catalyst in an ethanol solution and adsorbing the dual-species supported catalyst in the multi-walled carbon nanotube through electrostatic action;

s2, then taking the multi-walled carbon nanotubes adsorbed with the dual-species supported catalyst, dispersing the multi-walled carbon nanotubes in a dispersion liquid composed of ethanol and water again, and after carrying out ultrasonic treatment for 1-2 hours, taking the dual-species supported catalyst mixed liquid and dripping the dual-species supported catalyst mixed liquid on hydrophilic carbon paper; the volume ratio of the ethanol to the water is 2: 1;

s3, spin-coating the polytetrafluoroethylene emulsion on the surface of the catalyst to prepare the double-species supported catalytic electrode for the electro-catalytic ammonia synthesis reaction.

Compared with the prior art, the invention has the beneficial effects that:

(1) the preparation method of the two-species supported catalyst provided by the invention has the advantages that the phosphotungstic acid is used as a carrier for the first time, the bismuth-lithium double-metal-species modified phosphotungstic acid is used for realizing the multi-functionalization of the catalyst, meanwhile, the electrocatalytic electrode prepared by the two-species supported catalyst is used for realizing the nitrogen reduction with high activity and high selectivity, and the prepared two-species supported catalyst and the prepared catalytic electrode are applied to the ammonia synthesis reaction, so that the two-species supported catalyst has excellent ammonia synthesis performance, particularly the Faraday efficiency of the ammonia synthesis and exceeds the efficiency value reported by the current same-system work.

(2) According to the invention, bismuth species are creatively and accurately anchored on the four-fold site of phosphotungstic acid, and the electronic structure of the bismuth species is adjusted, so that the bismuth species with rich electrons can promote the adsorption and activation of inert dinitrogen molecules, and the activity of synthesizing ammonia by electrocatalysis effectively improved.

(3) The invention creatively couples lithium species to W ═ O of phosphotungstic acid_dO of (A) to (B)_dEffectively reduces the reduction rate of hydrogen protons, inhibits hydrogen evolution competition reaction, and effectively improves the electron selectivity of the catalyst

Drawings

FIG. 1 is an X-ray powder diffraction pattern (XRD) of a Bi-Li dual-species supported phosphotungstic acid catalyst prepared according to example 1 of the present invention;

FIG. 2 is a Fourier infrared spectrum (FTIR) of Bi-Li dual-species supported phosphotungstic acid catalyst prepared according to example 1 of the present invention, phosphotungstic acid, and Bi-species supported phosphotungstic acid in different proportions;

FIG. 3 is a graph showing the comparison of the performance of the Bi-Li dual-species supported phosphotungstic acid catalyst prepared in example 1 of the present invention in ammonia synthesis by electro-catalytic nitrogen reduction.

Detailed Description

In order to facilitate understanding of the present invention, the technical solutions of the present invention will be further described with reference to the following detailed description and the accompanying drawings, but the present invention is not limited thereto.

Example 1

In the preparation method of the two-species supported catalyst, bismuth nitrate pentahydrate is adopted as bismuth salt, phosphotungstic acid, bismuth nitrate pentahydrate and lithium sulfate are used as raw materials, heating and stirring are carried out under mild conditions, phosphotungstic acid with rich oxygen coordination sites is used as a carrier, bismuth nitrate pentahydrate is used as a precursor, bismuth species are uniformly embedded on four-fold sites of phosphotungstic acid to form a stable structure through a vacuum rotary evaporation method, lithium sulfate is used as a raw material, and a wet impregnation method is adopted to couple lithium species on W ═ O ═ phosphotungstic acid_dO in (1)_dThereby obtaining the dual-species supported catalyst, which comprises the following steps:

(1) dissolving 347 mu mol of phosphotungstic acid in 10mL of distilled water, dropwise adding 2.43 mu mol of bismuth nitrate pentahydrate solution, violently stirring for 2h, placing the mixed solution in a rotary evaporator, carrying out rotary evaporation heating reaction for 8h under a vacuum condition, wherein the temperature of the rotary evaporation heating reaction is 100 ℃, and the rotating speed is 500 r/min;

(2) and (2) adding 0.3g of sample obtained by the reaction in the step (1) into 30mL of lithium sulfate solution, wherein the concentration of the lithium sulfate solution is 0.1mol/L, the pH value of the lithium sulfate solution is 4, carrying out impregnation reaction at normal temperature for 24h, the temperature of the impregnation reaction is 25 ℃, the rotating speed is 1000r/min, fully stirring, and then putting into an oven for drying to obtain a dried sample, namely the dual-species supported catalyst.

Example 2

Preparation of two-species Supported catalyst, bismuth salt mining in this exampleBismuth chloride, phosphotungstic acid, bismuth chloride and lithium sulfate are used as raw materials, heating and stirring are carried out under mild conditions, phosphotungstic acid with rich oxygen coordination sites is used as a carrier, bismuth nitrate pentahydrate is used as a precursor, bismuth species are uniformly embedded on four-fold sites of the phosphotungstic acid to form a stable structure through a vacuum rotary evaporation method, lithium sulfate is used as a raw material, and a wet impregnation method is adopted to couple lithium species to the phosphotungstic acid W ═ O_dO in (1)_dThereby obtaining the dual-species supported catalyst, which comprises the following steps:

(1) dissolving 347 mu mol of phosphotungstic acid in 10mL of distilled water, dropwise adding 4.43 mu mol of bismuth chloride solution, violently stirring for 3h, placing the mixed solution in a rotary evaporator, carrying out rotary evaporation heating reaction for 10h under a vacuum condition, wherein the temperature of the rotary evaporation heating reaction is 80 ℃, and the rotating speed is 500 r/min;

(2) and (2) adding 0.4g of sample obtained by the reaction in the step (1) into 30mL of lithium sulfate solution, wherein the concentration of the lithium sulfate solution is 0.05mol/L, the pH value of the lithium sulfate solution is 5, carrying out impregnation reaction at normal temperature for 28h, the temperature of the impregnation reaction is 30 ℃, the rotating speed is 2000r/min, fully stirring, and then putting into an oven for drying to obtain a dried sample, namely the dual-species supported catalyst.

Example 3

In the preparation method of the two-species supported catalyst, bismuth nitrate pentahydrate is adopted as bismuth salt, phosphotungstic acid, bismuth nitrate pentahydrate and lithium sulfate are used as raw materials, heating and stirring are carried out under mild conditions, phosphotungstic acid with rich oxygen coordination sites is used as a carrier, bismuth nitrate pentahydrate is used as a precursor, bismuth species are uniformly embedded on four-fold sites of phosphotungstic acid to form a stable structure through a vacuum rotary evaporation method, lithium sulfate is used as a raw material, and a wet impregnation method is adopted to couple lithium species on W ═ O ═ phosphotungstic acid_dO in (1)_dThereby obtaining the dual-species supported catalyst, which comprises the following steps:

(1) dissolving 347 mu mol of phosphotungstic acid in 10mL of distilled water, dropwise adding 6.43 mu mol of pentahydrate bismuth nitrate solution, violently stirring for 2h, placing the mixed solution in a rotary evaporator, carrying out rotary evaporation heating reaction for 9h under a vacuum condition, wherein the temperature of the rotary evaporation heating reaction is 120 ℃, and the rotating speed is 600 r/min;

(2) and (2) adding 1.0g of sample obtained by the reaction in the step (1) into 30mL of lithium sulfate solution, wherein the concentration of the lithium sulfate solution is 0.2mol/L, the pH value of the lithium sulfate solution is 4, carrying out impregnation reaction at normal temperature for 36h, the temperature of the impregnation reaction is 26 ℃, the rotating speed is 1500r/min, fully stirring, and then putting into an oven for drying to obtain a dried sample, namely the dual-species supported catalyst.

Example 4

In the preparation method of the two-species supported catalyst, bismuth chloride is adopted as bismuth salt, phosphotungstic acid, bismuth chloride and lithium sulfate are used as raw materials, heating and stirring are carried out under mild conditions, phosphotungstic acid with rich oxygen coordination sites is used as a carrier, bismuth nitrate pentahydrate is used as a precursor, bismuth species are uniformly embedded on four-fold sites of the phosphotungstic acid to form a stable structure through a vacuum rotary evaporation method, then lithium sulfate is used as a raw material, and a wet impregnation method is adopted to couple lithium species on W ═ O ═ phosphotungstic acid_dO in (1)_dThereby obtaining the dual-species supported catalyst, which comprises the following steps:

(1) dissolving 347 mu mol of phosphotungstic acid in 10mL of distilled water, dropwise adding 10 mu mol of bismuth chloride solution, violently stirring for 2.5h, placing the mixed solution in a rotary evaporator, carrying out rotary evaporation heating reaction for 8h under a vacuum condition, wherein the temperature of the rotary evaporation heating reaction is 110 ℃, and the rotating speed is 550 r/min;

(2) and (2) adding 0.8g of sample obtained by the reaction in the step (1) into 30mL of lithium sulfate solution, wherein the concentration of the lithium sulfate solution is 0.5mol/L, the pH value of the lithium sulfate solution is 5, carrying out impregnation reaction for 30h at normal temperature, the temperature of the impregnation reaction is 25 ℃, the rotating speed is 1000r/min, fully stirring, and then putting into an oven for drying to obtain a dried sample, namely the dual-species supported catalyst.

Example 5

The application of the double-species supported catalyst in the electrocatalytic ammonia synthesis reaction is characterized in that the double-species supported catalyst is prepared into a catalytic electrode, and the preparation method specifically comprises the following steps:

s1, in the embodiment, 20mg of the dual-species supported catalyst is dispersed in 12mL of ethanol solution and is adsorbed in 200mg of multi-wall carbon nano-tubes through electrostatic action;

s2, then taking 15mg of multi-walled carbon nanotubes adsorbed with the dual-species supported catalyst, dispersing the multi-walled carbon nanotubes in a dispersion liquid composed of 1mL of ethanol and 500 mu L of water again, carrying out ultrasonic treatment for 1-2 h, and then taking 100 mu L of the dual-species supported catalyst mixed liquid to be dripped on hydrophilic carbon paper;

s3, spin-coating 15 mu L of polytetrafluoroethylene emulsion on the surface of a catalyst to prepare a double-species supported catalytic electrode for the electro-catalytic ammonia synthesis reaction, and finally performing electro-catalytic ammonia synthesis by using a traditional three-electrode system.

And (3) performance testing:

the performance test of the two-species supported catalyst prepared by the preparation method provided by the invention is as follows:

FIG. 1 is an X-ray powder diffraction pattern of a bismuth lithium dual species supported phosphotungstic acid catalyst prepared according to example 1 of the present invention, and it can be seen that only a diffraction peak of phosphotungstic acid is detected without a characteristic peak of bismuth lithium species because bismuth lithium dual species are highly dispersed in phosphotungstic acid and the modification amount thereof is too low to reach the detection line of an instrument;

FIG. 2 is a Fourier infrared spectrum of the Bi-Li double-species supported phosphotungstic acid catalyst prepared according to the embodiment 1 of the present invention, phosphotungstic acid and different ratios of Bi species supported phosphotungstic acid, and it can be seen from FIG. 2(a) that the phosphotungstic acid carrier has P-O_a，W＝O_d，W-O_c-W and W-O_e-a W stretching vibration peak, indicating that it has a typical Keggin structure; W-O on bismuth species modified phosphotungstic acid_c-W and W-O_ethe-W stretching vibration peak is blue-shifted compared with the corresponding peak in the phosphotungstic acid, which indicates that the bismuth species and the W-O_c-W and W-O_eThe W peak presents a chemical interaction, the bismuth species should be anchored at the four-fold site of phosphotungstic acid consisting of W-Oc-W and W-Oe-W; by comparing the infrared spectrograms of the bismuth lithium dual-species modified phosphotungstic acid and the bismuth species phosphotungstic acid in fig. 2(b), it can be seen that the introduction of the lithium species causes W ═ O_dA red shift occurs indicating that the lithium species is red-shifted with W ═ O_dThere is a strong chemical interaction, lithium speciesW ═ O to be modified with phosphotungstic acid_dThe above step (1);

FIG. 3 is a comparative diagram of the performance of ammonia synthesis by electrocatalytic nitrogen reduction of a bismuth-lithium dual-species supported phosphotungstic acid catalytic electrode prepared in example 5 of the present invention, wherein the reaction is performed in an H-shaped reactor, a three-electrode system is adopted in the test, the bismuth-lithium dual-species supported phosphotungstic acid catalytic electrode is used as a working electrode, platinum is used as a counter electrode, and silver/silver chloride is used as a reference electrode; before testing, nitrogen is blown into the electrolyte in the system, when the nitrogen in the electrolyte is saturated, different bias voltages are applied for reaction, all potentials are relative to a standard hydrogen electrode, as can be seen from the figure, the bismuth-lithium double-metal co-modified phosphotungstic acid has excellent electro-catalytic ammonia synthesis performance, the modification of the bismuth-lithium double-metal co-modified phosphotungstic acid can synergistically promote the electro-catalytic ammonia synthesis reaction, the maximum ammonia synthesis yield is 61 mu g h^-1mg_cat- ^-1The Faraday efficiency can reach 85%.

The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by the present specification, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.