Preparation method of tungsten carbide supported metal monatomic catalyst and application of tungsten carbide supported metal monatomic catalyst in electrocatalytic synthesis of ammonia
The tungsten carbide-supported metal single-atom catalyst addresses the instability and low selectivity of existing catalysts by providing high N conversion rates and ammonia yields, enhancing the efficiency of electrocatalytic ammonia synthesis.
Patent Information
- Application Number
- CN202411294762.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-09-14
- Publication Date
- 2024-12-17
AI Technical Summary
The instability of catalysts, low selectivity, and limited ammonia yield are significant challenges in the electrocatalytic synthesis of ammonia, which hinders the efficient conversion of nitrate/nitrite to ammonia.
A method for preparing a tungsten carbide-supported metal single-atom catalyst involves steps such as preparing a dopamine hydrochloride solution, adding metal chloride and sodium tungstate, ultrasonic and filtration treatments, and high-temperature carbonization to create a catalyst that is stable and efficient for ammonia synthesis.
The catalyst achieves high N conversion rates and ammonia yields, with selectivities up to 96% and Faraday efficiencies up to 63%, demonstrating improved stability and efficiency in electrocatalytic ammonia synthesis.
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Figure CN119145002A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of electrocatalytic synthesis of ammonia, and in particular to a preparation method of a tungsten carbide supported metal single atom catalyst and application thereof in electrocatalytic synthesis of ammonia. Background Art
[0002] Ammonia is extremely important to human beings in fertilizer production, fertilizer raw materials, oil refining industry, etc. It is an indispensable basic chemical in modern industry. At the same time, nitrate / nitrite pollution is a serious environmental problem, posing a threat to human health and ecosystems. Electrocatalytic reduction of nitrate / nitrite to synthesize ammonia is a sustainable ammonia synthesis pathway that can not only convert nitrate / nitrite into high-value-added ammonia, but also control the nitrate / nitrite content in water to maintain ecological balance. In recent years, electrocatalytic synthesis of ammonia has been a hot research field due to its advantages such as environmental friendliness, sustainability and mild conditions. The conversion of nitrate / nitrite to ammonia through electrochemical reactions is considered to be a promising strategy to balance the global nitrogen cycle and has attracted much attention from researchers. However, the instability of catalysts, low selectivity and Faraday efficiency, and limited ammonia yield have always been huge challenges in the field of electrocatalytic synthesis of ammonia, which need to be further improved. To this end, researchers at home and abroad have developed a variety of strategies, including developing more efficient catalysts, optimizing reaction conditions, and in-depth research on reaction mechanisms. Summary of the invention
[0003] Based on this, it is necessary to propose a preparation method of tungsten carbide-supported metal single-atom catalyst and its application in electrocatalytic synthesis of ammonia to solve the following problems in the prior art: Electrocatalytic synthesis of ammonia is a hot research field due to its advantages such as environmental friendliness, sustainability and mild conditions. The conversion of nitrate / nitrite to ammonia through electrochemical reaction is considered to be a promising strategy for balancing the global nitrogen cycle and has attracted much attention from researchers. However, the instability of the catalyst, low selectivity and Faraday efficiency, and limited ammonia yield have always been huge challenges in the field of electrocatalytic synthesis of ammonia, which need to be further improved.
[0004] Specifically, the present invention includes the following contents.
[0005] The first aspect of the present invention provides a method for preparing a tungsten carbide supported metal single atom catalyst, characterized in that it comprises: step 1, preparing a dopamine hydrochloride solution, and dripping a hydrochloric acid solution into the dopamine hydrochloride solution, and controlling the pH value of the dopamine hydrochloride solution to be 1.5-2.5; step 2, adding a metal chloride to the dopamine hydrochloride solution and stirring evenly to obtain a first mixed solution, wherein the metal chloride is one of cobalt chloride, copper chloride and zinc chloride, but is not limited to cobalt chloride, copper chloride and zinc chloride; step 3, preparing a sodium tungstate solution, and adding the sodium tungstate solution dropwise to the first mixed solution, and stirring for a period of time. Continue stirring evenly to obtain a second mixed solution; step 4, using ultrapure water to perform multiple ultrasonic and filtration treatments on the second mixed solution to obtain a first ultrasonic mixed filtrate; step 5, after the first ultrasonic mixed filtrate is clarified, ethanol is added to the clarified first ultrasonic mixed filtrate to perform multiple ultrasonic and filtration treatments to obtain a second ultrasonic mixed filtrate; step 6, after the second ultrasonic mixed filtrate is clarified, the clarified second ultrasonic mixed filtrate is placed in a vacuum drying oven for drying treatment to obtain a catalyst precursor; step 7, the catalyst precursor is placed in an argon furnace for high temperature carbonization treatment to obtain a tungsten carbide supported metal single atom catalyst.
[0006] Preferably, the preparation of the dopamine hydrochloride solution comprises: dissolving dopamine hydrochloride in pure water to obtain the dopamine hydrochloride solution with a concentration of 0.01M-0.15M.
[0007] Preferably, the preparing of the sodium tungstate solution comprises: dissolving sodium tungstate in pure water to obtain the sodium tungstate solution having a concentration of 0.01M-0.15M.
[0008] Preferably, the ratio of the amount of dopamine hydrochloride in the dopamine hydrochloride solution to the amount of sodium tungstate in the sodium tungstate solution is 1:1.
[0009] Preferably, the ratio of the amount of the metal chloride to the amount of dopamine hydrochloride in the dopamine hydrochloride solution is 1:10.
[0010] Preferably, the vacuum drying temperature of placing the clarified second ultrasonic mixed filtrate in a vacuum drying oven for drying is 50-70°C.
[0011] Preferably, the temperature of placing the catalyst precursor into an argon furnace for high-temperature carbonization treatment is 800-1000° C., and the carbonization treatment time is 2-3 hours.
[0012] The second aspect of the present invention provides an application of the above-mentioned tungsten carbide supported metal single atom catalyst in the electrocatalytic synthesis of ammonia, which comprises: making the tungsten carbide supported metal single atom catalyst into a tungsten carbide supported metal single atom modified electrode; placing the tungsten carbide supported metal single atom modified electrode into an H-type electrolytic cell, wherein the electrolyte in the H-type electrolytic cell is a mixed solution of 0.2M K2SO4 and KNO3 with a nitrogen concentration of 100ppm, and electrocatalytically reducing nitrate to synthesize ammonia under normal temperature and pressure conditions.
[0013] Preferably, the tungsten carbide-supported metal single-atom catalyst is made into a tungsten carbide-supported metal single-atom modified electrode, comprising: step one, placing the tungsten carbide-supported metal single-atom catalyst in a plastic centrifuge tube, adding anhydrous ethanol to the plastic centrifuge tube, then ultrasonically dispersing the plastic centrifuge tube evenly and then dripping a naphthol solution, and then ultrasonically treating the solution in the plastic centrifuge tube in an ultrasonic machine; step two, measuring the solution of the plastic centrifuge tube after ultrasonic treatment with a pipette, dripping it on conductive carbon paper, and drying it to obtain the tungsten carbide-supported metal single-atom modified electrode.
[0014] Preferably, the tungsten carbide supported metal single atom catalyst is made into a tungsten carbide supported metal single atom modified electrode, comprising: step 1, weighing 5 mg of the prepared tungsten carbide supported metal single atom catalyst and placing it in a 2 ml plastic centrifuge tube, then adding 480 μL of anhydrous ethanol to the plastic centrifuge tube, then ultrasonically dispersing the plastic centrifuge tube evenly, then dripping 20 μL of naphthol solution, and then ultrasonically treating the solution in the plastic centrifuge tube in an ultrasonic machine for 1 hour; step 2, using a pipette to measure 50 μL of the solution in the plastic centrifuge tube and dripping it on a 1×1 cm 2 The conductive carbon paper was dried to obtain 0.5 mg / cm 2 The tungsten carbide supports a metal single atom modified electrode.
[0015] The beneficial effects of the preparation method of the present invention and the obtained tungsten carbide supported metal single atom catalyst include but are not limited to:
[0016] The raw materials used in the present invention are easily available, the reaction steps are simple and uncomplicated, the catalyst has good stability, can maintain high activity under long-term reaction conditions, and can efficiently synthesize ammonia under conditions of different nitrogen sources, and has high N conversion rate, yield and FE. The highest ammonia nitrogen yield is 997.35 μg h -1 mg -1 cat .,N conversion rate can reach up to 96%, which has very good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS
[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.
[0018] in:
[0019] Figure 1 Schematic diagram of the electrochemical test LSV corresponding to tungsten carbide-supported copper single atom, tungsten carbide-supported cobalt metal single atom and tungsten carbide-supported zinc metal single atom;
[0020] Figure 2 X-ray diffraction patterns corresponding to tungsten carbide supported copper single atom catalyst, tungsten carbide supported cobalt single atom catalyst and tungsten carbide supported zinc single atom catalyst;
[0021] Figure 3 The yield and FE diagram of the electrocatalytic reduction of nitrate by tungsten carbide supported copper single atom catalyst at different voltages for two hours;
[0022] Figure 4 The yield and FE diagram of the electrocatalytic reduction of nitrate by tungsten carbide supported cobalt single atom catalyst at different voltages for two hours;
[0023] Figure 5 The yield and FE diagram of the electrocatalytic reduction of nitrate by tungsten carbide supported zinc single atom catalyst at different voltages for two hours;
[0024] Figure 6 Figure 2 is a graph of N selectivity for electrocatalytic reduction of nitrite / nitrate to ammonia over tungsten carbide supported copper single atom catalyst, tungsten carbide supported cobalt single atom catalyst, and tungsten carbide supported zinc single atom catalyst;
[0025] The Cu SACs@WC in the figure is a copper single-atom catalyst supported by tungsten carbide, the Co SACs@WC is a cobalt single-atom catalyst supported by tungsten carbide, and the Zn SACs@WC is a zinc single-atom catalyst supported by tungsten carbide. LSV, or linear sweep voltammetry, is an electrochemical test method used to evaluate the electrochemical activity and properties of electrode materials. This method analyzes the reaction occurring on the electrode surface by linearly changing the electrode potential within a specific potential range and recording the change in current. FE stands for Faraday efficiency. DETAILED DESCRIPTION
[0026] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0027] Example 1
[0028] The method for preparing a tungsten carbide supported copper metal single atom catalyst for efficient electrocatalytic synthesis of ammonia according to the present invention comprises the following steps:
[0029] 1) Preparation of catalyst precursor: 10 mmol dopamine hydrochloride is dissolved in 100 mL pure water to obtain a 0.1 M dopamine hydrochloride solution, and hydrochloric acid solution is added dropwise to control the pH to 2, 0.5 mmol copper chloride dihydrate is added to the obtained dopamine hydrochloride solution and stirred evenly to obtain a first mixed solution; secondly, 100 mL 0.1 M sodium tungstate solution is prepared (sodium tungstate is dissolved in pure water for preparation), and the sodium tungstate solution is slowly added dropwise to the above-mentioned first mixed solution, and stirring is continued for 1 hour to obtain a second mixed solution; secondly, the second mixed solution is subjected to ultrasonic and filtration treatment 3 times using ultrapure water to obtain a first ultrasonic mixed filtrate; secondly, after the first ultrasonic mixed filtrate is clarified, ethanol is added to the clarified first ultrasonic mixed filtrate for 3 ultrasonic and filtration treatments to obtain a second ultrasonic mixed filtrate; finally, after the second ultrasonic mixed filtrate is clarified, the clarified second ultrasonic mixed filtrate is placed in a vacuum drying oven for vacuum drying at 60° C. to obtain a catalyst precursor. Wherein, M is mol / L, the same below.
[0030] 2) High-temperature carbonization: The catalyst precursor is carbonized at 900°C in an argon furnace at a heating rate of 2°C / min for 2 h to obtain a copper metal single atom catalyst supported on a tungsten carbide substrate.
[0031] The copper metal single atom catalyst supported by tungsten carbide was made into a working electrode. In an H-type electrolytic cell, 0.2M K2SO4 and KNO3 with a nitrogen concentration of 100ppm were used as electrolytes to electrocatalytically reduce nitrate to synthesize ammonia at room temperature and pressure. The ammonia concentration was characterized by Nessler's reagent spectrophotometry. The FE was about 52% and the N selectivity was 90%. Among them, the role of K2SO4 (i.e. potassium sulfate) is to increase the ion concentration and improve the conductivity. KNO3 (i.e. potassium nitrate) is a reactant. The principle reaction formula for electrocatalytic reduction of nitrate to synthesize ammonia is: 9H + +NO3 - +8e -→NH3+3H2O. Among them, ppm (parts per million) is the unit of mass fraction, and its definition is one part per million, the same below.
[0032] Specifically, this embodiment uses Chenhua CHI-660E electrochemical workstation, in an H-type electrolytic cell, 0.2M K2SO4 and KNO3 with a N concentration of 100ppm are used as electrolytes to carry out it test electrocatalytic reduction of nitrate to synthesize ammonia under normal temperature and pressure conditions, the reference electrode is Ag / AgCl, the counter electrode is a platinum sheet, the reaction time is two hours, and the samples obtained before and after the reaction are characterized by Nessler's reagent spectrophotometry for ammonia concentration, and it is calculated that FE is about 52%, and N selectivity is 90%.
[0033] Example 2
[0034] The method for preparing a tungsten carbide supported cobalt single atom catalyst for efficient electrocatalytic synthesis of ammonia according to the present invention comprises the following steps:
[0035] 1) Preparation of catalyst precursor: 10 mmol dopamine hydrochloride is dissolved in 100 mL pure water to obtain a 0.1 M dopamine hydrochloride solution, and hydrochloric acid solution is added dropwise to control the pH to 1.5, 0.5 mmol cobalt chloride hexahydrate is added to the obtained dopamine hydrochloride solution and stirred evenly to obtain a first mixed solution; secondly, 100 mL 0.1 M sodium tungstate solution is prepared (sodium tungstate is dissolved in pure water for preparation), and the sodium tungstate solution is slowly added dropwise to the above-mentioned first mixed solution, and stirring is continued for 1 hour to obtain a second mixed solution; secondly, the second mixed solution is subjected to ultrasonic and filtration treatment 3 times using ultrapure water to obtain a first ultrasonic mixed filtrate; secondly, after the first ultrasonic mixed filtrate is clarified, ethanol is added to the clarified first ultrasonic mixed filtrate for 3 ultrasonic and filtration treatments to obtain a second ultrasonic mixed filtrate; finally, after the second ultrasonic mixed filtrate is clarified, the clarified second ultrasonic mixed filtrate is placed in a vacuum drying oven for vacuum drying at 60° C. to obtain a catalyst precursor.
[0036] 2) High-temperature carbonization: The catalyst precursor is carbonized at 800°C in an argon furnace at a heating rate of 2°C / min for 2 h to obtain a cobalt single-atom catalyst supported on a tungsten carbide substrate.
[0037] The tungsten carbide supported cobalt single atom catalyst was made into a working electrode. In an H-type electrolytic cell, 0.2M K2SO4 and KNO3 with a N concentration of 100ppm were used as electrolytes to electrocatalytically reduce nitrate to synthesize ammonia at room temperature and pressure. The ammonia concentration was characterized by Nessler's reagent spectrophotometry. The FE was about 49% and the N selectivity was 83%. Among them, the role of K2SO4 (i.e. potassium sulfate) is to increase the ion concentration and improve the conductivity. KNO3 (i.e. potassium nitrate) is a reactant. The principle reaction formula for electrocatalytic reduction of nitrate to synthesize ammonia is: 9H + +NO3 - +8e - →NH3+3H2O.
[0038] Specifically, this embodiment uses Chenhua CHI-660E electrochemical workstation, in an H-type electrolytic cell, 0.2M K2SO4 and KNO3 with a N concentration of 100ppm are used as electrolytes to carry out it test electrocatalytic reduction of nitrate to synthesize ammonia under normal temperature and pressure conditions, the reference electrode is Ag / AgCl, the counter electrode is a platinum sheet, the reaction time is two hours, and the samples obtained before and after the reaction are characterized by Nessler's reagent spectrophotometry for ammonia concentration, and it is calculated that FE is approximately 49% and N selectivity is 83%.
[0039] Example 3
[0040] The method for preparing a tungsten carbide supported zinc single atom catalyst for efficient electrocatalytic ammonia synthesis according to the present invention comprises the following steps:
[0041] 1) Preparation of catalyst precursor: 10 mmol dopamine hydrochloride was dissolved in 100 mL pure water to obtain a 0.1 M dopamine hydrochloride solution, and hydrochloric acid solution was added dropwise to control the pH to 2.5, 0.5 mmol zinc chloride dihydrate was added to the obtained dopamine hydrochloride solution and stirred evenly to obtain a first mixed solution; secondly, 100 mL 0.1 M sodium tungstate solution was prepared (sodium tungstate was dissolved in pure water for preparation), and the sodium tungstate solution was slowly added dropwise to the above first mixed solution, and stirred for 1 hour to obtain a second mixed solution; secondly, the second mixed solution was subjected to ultrasonic and filtration treatment 3 times using ultrapure water to obtain a first ultrasonic mixed filtrate; secondly, after the first ultrasonic mixed filtrate was clarified, ethanol was added to the clarified first ultrasonic mixed filtrate for 3 ultrasonic and filtration treatments to obtain a second ultrasonic mixed filtrate; finally, after the second ultrasonic mixed filtrate was clarified, the clarified second ultrasonic mixed filtrate was placed in a vacuum drying oven for vacuum drying at 60° C. to obtain a catalyst precursor.
[0042] 2) High-temperature carbonization: The catalyst precursor is carbonized at 1000°C in an argon furnace at a heating rate of 2°C / min for 2 h to obtain a zinc single-atom catalyst supported on a tungsten carbide substrate.
[0043] The tungsten carbide supported zinc single atom catalyst was made into a working electrode. In an H-type electrolytic cell, 0.2M K2SO4 and KNO3 with a N concentration of 100ppm were used as electrolytes to electrocatalytically reduce nitrate to synthesize ammonia under normal temperature and pressure conditions. The ammonia concentration was characterized by Nessler's reagent spectrophotometry. The FE was about 48% and the N selectivity was 78%. Among them, the role of K2SO4 (i.e. potassium sulfate) is to increase the ion concentration and improve the conductivity. KNO3 (i.e. potassium nitrate) is a reactant. The principle reaction formula for electrocatalytic reduction of nitrate to synthesize ammonia is: 9H + +NO3 - +8e - →NH3+3H2O.
[0044] Specifically, this embodiment uses Chenhua CHI-660E electrochemical workstation, and in an H-type electrolytic cell, 0.2M K2SO4 and KNO3 with a N concentration of 100ppm are used as electrolytes to carry out it test electrocatalytic reduction of nitrate to synthesize ammonia at room temperature and pressure. The reference electrode is Ag / AgCl, the counter electrode is a platinum sheet, and the reaction time is two hours. The samples obtained before and after the reaction are characterized by Nessler's reagent spectrophotometry for ammonia concentration, and it is calculated that FE is approximately 48%, and N selectivity is 78%.
[0045] Example 4
[0046] The method for preparing a tungsten carbide supported copper metal single atom catalyst for efficient electrocatalytic synthesis of ammonia according to the present invention comprises the following steps:
[0047] 1) Preparation of catalyst precursor: 10 mmol dopamine hydrochloride is dissolved in 100 mL pure water to obtain a 0.1 M dopamine hydrochloride solution, and hydrochloric acid solution is added dropwise to control the pH to 2.2, 0.5 mmol copper chloride dihydrate is added to the obtained dopamine hydrochloride solution and stirred evenly to obtain a first mixed solution; secondly, 100 mL 0.1 M sodium tungstate solution is prepared (sodium tungstate is dissolved in pure water for preparation), and the sodium tungstate solution is slowly added dropwise to the above-mentioned first mixed solution, and stirring is continued for 1 hour to obtain a second mixed solution; secondly, the second mixed solution is subjected to ultrasonic and filtration treatment 3 times using ultrapure water to obtain a first ultrasonic mixed filtrate; secondly, after the first ultrasonic mixed filtrate is clarified, ethanol is added to the clarified first ultrasonic mixed filtrate for 3 ultrasonic and filtration treatments to obtain a second ultrasonic mixed filtrate; finally, after the second ultrasonic mixed filtrate is clarified, the clarified second ultrasonic mixed filtrate is placed in a vacuum drying oven for vacuum drying at 60° C. to obtain a catalyst precursor.
[0048] 2) High-temperature carbonization: The catalyst precursor is carbonized at 900°C in an argon furnace at a heating rate of 2°C / min for 2 h to obtain a copper metal single atom catalyst supported on a tungsten carbide substrate.
[0049] The copper metal single atom catalyst supported by tungsten carbide was made into a working electrode. In an H-type electrolytic cell, 0.2M K2SO4 and KNO2 with a nitrogen concentration of 100ppm were used as electrolytes to electrocatalytically reduce nitrite to synthesize ammonia under normal temperature and pressure conditions. The ammonia concentration was characterized by Nessler's reagent spectrophotometry. The FE was about 63% and the N selectivity was 96%. Among them, the role of K2SO4 (i.e. potassium sulfate) is to increase the ion concentration and improve the conductivity. KNO2 (i.e. potassium nitrite) is a reactant. The principle reaction formula for electrocatalytic reduction of nitrate to synthesize ammonia is: 9H + +NO2 - +6e - →NH3+3H2O.
[0050] Specifically, this embodiment uses Chenhua CHI-660E electrochemical workstation, in an H-type electrolytic cell, 0.2M K2SO4 and KNO2 with a N concentration of 100ppm are used as electrolytes to carry out it test electrocatalytic reduction of nitrate to synthesize ammonia at room temperature and pressure. The reference electrode is Ag / AgCl, the counter electrode is a platinum sheet, and the reaction time is two hours. The samples obtained before and after the reaction are characterized by Nessler's reagent spectrophotometry for ammonia concentration, and the calculated FE is approximately 63%, and the N selectivity is 96%.
[0051] Example 5
[0052] The method for preparing a tungsten carbide supported cobalt single atom catalyst for efficient electrocatalytic synthesis of ammonia according to the present invention comprises the following steps:
[0053] 1) Preparation of catalyst precursor: 10 mmol dopamine hydrochloride is dissolved in 100 mL pure water to obtain a 0.1 M dopamine hydrochloride solution, and hydrochloric acid solution is added dropwise to control the pH to 1.8, 0.5 mmol cobalt chloride hexahydrate is added to the obtained dopamine hydrochloride solution and stirred evenly to obtain a first mixed solution; secondly, 100 mL 0.1 M sodium tungstate solution is prepared (sodium tungstate is dissolved in pure water for preparation), and the sodium tungstate solution is slowly added dropwise to the above-mentioned first mixed solution, and stirring is continued for 1 hour to obtain a second mixed solution; secondly, the second mixed solution is subjected to ultrasonic and filtration treatment 3 times using ultrapure water to obtain a first ultrasonic mixed filtrate; secondly, after the first ultrasonic mixed filtrate is clarified, ethanol is added to the clarified first ultrasonic mixed filtrate for 3 ultrasonic and filtration treatments to obtain a second ultrasonic mixed filtrate; finally, after the second ultrasonic mixed filtrate is clarified, the clarified second ultrasonic mixed filtrate is placed in a vacuum drying oven for vacuum drying at 60° C. to obtain a catalyst precursor.
[0054] 2) High-temperature carbonization: The catalyst precursor is carbonized at 800°C in an argon furnace at a heating rate of 2°C / min for 2 h to obtain a cobalt single-atom catalyst supported on a tungsten carbide substrate.
[0055] The tungsten carbide supported cobalt single atom catalyst was made into a working electrode. In an H-type electrolytic cell, 0.2M K2SO4 and KNO2 with a nitrogen concentration of 100ppm were used as electrolytes to electrocatalytically reduce nitrite to synthesize ammonia at room temperature and pressure. The ammonia concentration was characterized by Nessler's reagent spectrophotometry. The FE was about 59% and the N selectivity was 92%. Among them, the role of K2SO4 (i.e. potassium sulfate) is to increase the ion concentration and improve the conductivity. KNO2 (i.e. potassium nitrite) is a reactant. The principle reaction formula for electrocatalytic reduction of nitrate to synthesize ammonia is: 9H + +NO2 - +6e - →NH3+3H2O.
[0056] Specifically, this embodiment uses Chenhua CHI-660E electrochemical workstation, in an H-type electrolytic cell, 0.2M K2SO4 and KNO2 with a N concentration of 100ppm are used as electrolytes to carry out it test electrocatalytic reduction of nitrate to synthesize ammonia under normal temperature and pressure conditions, the reference electrode is Ag / AgCl, the counter electrode is a platinum sheet, the reaction time is two hours, and the samples obtained before and after the reaction are characterized by Nessler's reagent spectrophotometry for ammonia concentration, and it is calculated that FE is approximately 59%, and N selectivity is 92%.
[0057] Example 6
[0058] The method for preparing a tungsten carbide supported zinc single atom catalyst for efficient electrocatalytic ammonia synthesis according to the present invention comprises the following steps:
[0059] 1) Preparation of catalyst precursor: First, 10 mmol of dopamine hydrochloride was dissolved in 100 mL of pure water to obtain a 0.1 M dopamine hydrochloride solution, and hydrochloric acid solution was added dropwise to control the pH to 1.9; secondly, 0.5 mmol of zinc chloride dihydrate was added to the obtained dopamine hydrochloride solution and stirred evenly to obtain a first mixed solution; secondly, 100 mL of 0.1 M sodium tungstate solution was prepared (sodium tungstate was dissolved in pure water for preparation), and the sodium tungstate solution was slowly added dropwise to the above-mentioned first mixed solution, and stirred continuously for 1 hour to obtain a second mixed solution; secondly, the second mixed solution was subjected to ultrasonic treatment and filtration for 3 times using ultrapure water to obtain a first ultrasonic mixed filtrate; secondly, after the first ultrasonic mixed filtrate was clarified, ethanol was added to the clarified first ultrasonic mixed filtrate for 3 ultrasonic treatments and filtration to obtain a second ultrasonic mixed filtrate; finally, after the second ultrasonic mixed filtrate was clarified, the clarified second ultrasonic mixed filtrate was placed in a vacuum drying oven for vacuum drying at 60° C. to obtain a catalyst precursor.
[0060] 2) High-temperature carbonization: The catalyst precursor is carbonized at 1000°C in an argon furnace at a heating rate of 2°C / min for 2 h to obtain a zinc single-atom catalyst supported on a tungsten carbide substrate.
[0061] The tungsten carbide supported zinc single atom catalyst was made into a working electrode. In an H-type electrolytic cell, 0.2M K2SO4 and KNO2 with a N concentration of 100ppm were used as electrolytes to electrocatalytically reduce nitrite to synthesize ammonia under normal temperature and pressure conditions. The ammonia concentration was characterized by Nessler's reagent spectrophotometry. The FE was about 51% and the N selectivity was 88%. Among them, the role of K2SO4 (i.e. potassium sulfate) is to increase the ion concentration and improve the conductivity. KNO2 (i.e. potassium nitrite) is a reactant. The principle reaction formula for electrocatalytic reduction of nitrate to synthesize ammonia is: 9H + +NO2 - +6e - →NH3+3H2O.
[0062] Specifically, this embodiment uses Chenhua CHI-660E electrochemical workstation, in an H-type electrolytic cell, 0.2M K2SO4 and KNO2 with a N concentration of 100ppm as electrolytes to carry out it test electrocatalytic reduction of nitrate to synthesize ammonia under normal temperature and pressure conditions, the reference electrode is Ag / AgCl, the counter electrode is a platinum sheet, the reaction time is two hours, and the samples obtained before and after the reaction are characterized by Nessler's reagent spectrophotometry for ammonia concentration, and it is calculated that FE is approximately 51% and N selectivity is 88%.
[0063] The present invention overcomes the shortcomings of the prior art. Aiming at the poor stability and low selectivity of the existing catalysts, the present invention selects a carbide substrate with high thermal stability and good electrical conductivity. At the same time, the single-atom catalyst has high atomic utilization and selectivity. It proposes to use sodium tungstate and dopamine hydrochloride as raw materials, adsorb the metal by impregnation, and then obtain a tungsten carbide-supported metal single-atom material by high-temperature carbonization, including: copper atoms, cobalt atoms and zinc atoms, which can efficiently reduce nitrate / nitrite to electrocatalytically synthesize ammonia under ambient conditions. The present invention is simple to operate, and the prepared tungsten carbide-supported metal single-atom catalyst has the ability to efficiently electrocatalytically reduce nitrate / nitrite to synthesize ammonia, and has great application prospects in the field of electrocatalytic synthesis of ammonia.
[0064] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0065] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.
Claims
1. A method for preparing a tungsten carbide-supported metal single-atom catalyst, characterized in that: include: Step 1, preparing a dopamine hydrochloride solution, and adding a hydrochloric acid solution dropwise into the dopamine hydrochloride solution to control the pH value of the dopamine hydrochloride solution to be 1.5-2.5; Step 2, adding a metal chloride to the dopamine hydrochloride solution and stirring evenly to obtain a first mixed solution, wherein the metal chloride is one of cobalt chloride, copper chloride and zinc chloride, but is not limited to cobalt chloride, copper chloride and zinc chloride; Step 3, preparing a sodium tungstate solution, and adding the sodium tungstate solution dropwise into the first mixed solution, and continuously stirring to obtain a second mixed solution; Step 4, using ultrapure water to perform multiple ultrasonic and filtration treatments on the second mixed solution to obtain a first ultrasonic mixed filtrate; Step 5, after the first ultrasonic mixed filtrate is clarified, ethanol is added to the clarified first ultrasonic mixed filtrate to perform multiple ultrasonic and filtering treatments to obtain a second ultrasonic mixed filtrate; Step 6, after the second ultrasonic mixed filtrate is clarified, the clarified second ultrasonic mixed filtrate is placed in a vacuum drying oven for drying to obtain a catalyst precursor; Step seven, placing the catalyst precursor into an argon furnace for high-temperature carbonization treatment to obtain a tungsten carbide-supported metal single-atom catalyst.
2. The method for preparing a tungsten carbide supported metal single atom catalyst according to claim 1, characterized in that: The preparation of dopamine hydrochloride solution comprises: Dopamine hydrochloride is dissolved in pure water to obtain the dopamine hydrochloride solution with a concentration of 0.01M-0.15M.
3. The method for preparing a tungsten carbide supported metal single atom catalyst according to claim 1, characterized in that: The sodium tungstate solution is prepared, comprising: Sodium tungstate is dissolved in pure water to obtain the sodium tungstate solution with a concentration of 0.01M-0.15M.
4. The method for preparing a tungsten carbide supported metal single atom catalyst according to claim 1, characterized in that: The ratio of the amount of dopamine hydrochloride in the dopamine hydrochloride solution to the amount of sodium tungstate in the sodium tungstate solution is 1:
1.
5. The method for preparing a tungsten carbide supported metal single atom catalyst according to claim 1, characterized in that: The ratio of the amount of the metal chloride to the amount of dopamine hydrochloride in the dopamine hydrochloride solution is 1:
10.
6. The method for preparing a tungsten carbide supported metal single atom catalyst according to claim 1, characterized in that: The clarified second ultrasonic mixed filtrate is placed in a vacuum drying oven for drying at a vacuum drying temperature of 50-70°C.
7. The method for preparing a tungsten carbide supported metal single atom catalyst according to claim 1, characterized in that: The catalyst precursor is placed in an argon furnace for high-temperature carbonization treatment at a temperature of 800-1000° C., and the carbonization treatment time is 2-3 hours.
8. Use of the tungsten carbide supported metal single atom catalyst according to any one of claims 1 to 7 in electrocatalytic synthesis of ammonia, characterized in that: include: The tungsten carbide-supported metal single atom catalyst is made into a tungsten carbide-supported metal single atom modified electrode; The tungsten carbide supported metal single atom modified electrode is placed in an H-type electrolytic cell, wherein the electrolyte in the H-type electrolytic cell is a mixed solution of 0.2M K2SO4 and KNO3 with a nitrogen concentration of 100 ppm, and nitrate is electrocatalytically reduced to synthesize ammonia under normal temperature and pressure conditions.
9. The use of the tungsten carbide supported metal single atom catalyst in electrocatalytic synthesis of ammonia according to claim 8, characterized in that: The method of preparing the tungsten carbide supported metal single atom catalyst into a tungsten carbide supported metal single atom modified electrode comprises: Step 1, placing the tungsten carbide supported metal single atom catalyst in a plastic centrifuge tube, adding anhydrous ethanol to the plastic centrifuge tube, then uniformly dispersing the plastic centrifuge tube by ultrasonication, then dropping a naphthol solution, and then ultrasonically treating the solution in the plastic centrifuge tube in an ultrasonic machine; Step 2: Use a pipette to measure the solution in the plastic centrifuge tube after ultrasonic treatment, drop it on the conductive carbon paper and let it dry to obtain the tungsten carbide supported metal single atom modified electrode.
10. The use of the tungsten carbide supported metal single atom catalyst in electrocatalytic synthesis of ammonia according to claim 9, characterized in that: The method of preparing the tungsten carbide supported metal single atom catalyst into a tungsten carbide supported metal single atom modified electrode comprises: Step 1, weighing 5 mg of the prepared tungsten carbide supported metal single atom catalyst and placing it in a 2 ml plastic centrifuge tube, then adding 480 μL of anhydrous ethanol to the plastic centrifuge tube, then ultrasonically dispersing the plastic centrifuge tube evenly, then dropping 20 μL of naphthol solution, and then ultrasonically treating the solution in the plastic centrifuge tube in an ultrasonic machine for 1 hour; Step 2: Use a pipette to measure 50 μL of the solution in the plastic centrifuge tube and apply it on a 1×1 cm 2 The conductive carbon paper was dried to obtain 0.5 mg / cm 2 The tungsten carbide supports a metal single atom modified electrode.