Noble metal modified hollow structure catalyst, preparation method thereof and application of noble metal modified hollow structure catalyst in electrosynthesis of ammonia

Abstract

The invention discloses a noble metal modified hollow structure catalyst as well as a preparation method and application thereof, and belongs to the technical field of electro-catalysis. The preparation method comprises the following steps: (1) preparing a precursor to obtain cuprous oxide; (2) constructing a hollow structure: enabling transition metal oxide to grow on the surface of cuprous oxide; adding a Na2S2O3 solution to etch cuprous oxide to obtain a hollow transition metal oxide; (3) precious metal modification: obtaining a transition metal oxide precursor modified by precious metal salt; and (4) thermal treatment growth: carrying out high-temperature annealing on the transition metal oxide precursor modified by the noble metal salt to obtain the noble metal modified hollow structure catalyst. According to the catalyst, through in-situ growth of precious metal oxide particles or precious metal state particles on the surface of the transition metal oxide, intermediate adsorption can be optimized, side reactions are inhibited, and the efficiency and selectivity of reducing nitrate into ammonia are improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrocatalysis, and particularly relates to a noble metal modified hollow structure catalyst, a preparation method thereof and application thereof in electrochemical synthesis of ammonia. BACKGROUND

[0002] Ammonia (NH3) is an important chemical raw material in modern industrial production, and is widely used in the fields of agricultural fertilizers, plastics, chemical industry, and medicine. The existing industrial synthesis of ammonia mainly relies on the Haber-Bosch (H-B) process, but the process needs to be carried out under high temperature (400-600 ℃) and high pressure (>400 atm), which is high in energy consumption and accompanied by a large amount of CO2 emission, which is not conducive to green and sustainable development. In recent years, the electrochemical nitrogen reduction reaction (NRR) is considered as a promising green ammonia synthesis method. However, due to the extremely high bond energy (941 kJ·mol -1 ) of the N≡N bond of nitrogen molecules and the extremely low solubility, the faradic efficiency and yield of ammonia in the NRR process are generally low (usually 1-2 orders of magnitude lower than the H-B process). At the same time, the competition of the side reaction of hydrogen evolution (HER) further reduces the selectivity and energy efficiency of ammonia.

[0003] At the same time, with excessive fertilization and industrial emissions, a large amount of nitrate (NO3 - ) waste accumulates in water bodies, posing a serious threat to the environment and human health. Compared with N2 reduction, the nitrate reduction reaction (NO3 - RR) has a lower N-O bond energy and a higher solubility, and shows significant advantages in green electrochemical synthesis of ammonia, and its ammonia faradic efficiency and yield are expected to approach or even rival the traditional H-B process. Therefore, the electrochemical nitrate reduction for ammonia driven by renewable energy is considered as a green ammonia synthesis technology with both environmental governance and resource utilization value. However, the NO3 - RR process involves a complex eight-electron reduction step, and is affected by the competitive hydrogen evolution reaction. At present, some transition metal (such as Cu, Co, etc.) catalysts have shown certain ammonia selectivity and yield, but generally require a higher overpotential, which further aggravates the HER competition, resulting in insufficient ammonia selectivity.

[0004] From the reaction mechanism, the key steps of NO3 - RR include the adsorption and activation of NO3 - , the gradual deoxidation and hydrogenation process. Among them, the deoxidation and hydrogenation process largely depends on the active hydrogen (*H) produced by the water splitting reaction (Volmer step, H2O+e⁻→*H+OH⁻). Studies have shown that noble metals have unique advantages in promoting the dissociation of water molecules, which can provide active hydrogen for the NO3 -RR provides an efficient source of active hydrogen. Based on this, by introducing noble metal modification on the surface of transition metal oxides, it is expected to optimize the adsorption behavior of intermediates, inhibit the Heyrovsky reaction (*H+H2O+e⁻→H2+OH⁻), and promote the Volmer reaction, thereby effectively improving the activity and selectivity of nitrate electro-reduction for ammonia synthesis. SUMMARY

[0005] The purpose of the present application is to provide a noble metal modified hollow structure catalyst and its preparation method and application in electro-synthesis of ammonia. It aims to solve the problem that the existing nitrate reduction electro-synthesis ammonia catalyst has shown certain ammonia selectivity and yield, but generally needs a higher overpotential, further aggravating the HER competition, resulting in insufficient ammonia selectivity. The catalyst of the present application can optimize the adsorption of intermediates, inhibit side reactions, and improve the efficiency and selectivity of nitrate reduction to ammonia by in-situ growth of noble metal oxide nanoparticles or noble metal metal particles on the surface of transition metal oxides.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] A preparation method of a noble metal modified hollow structure catalyst, comprising the following steps:

[0008] (1) Precursor preparation: dissolve copper precursor salt in an aqueous solution containing a surfactant, add an alkali solution after stirring uniformly, and react to generate a blue precipitate; add a reducing agent solution to the reaction system, wash the precipitate after reaction, and obtain cuprous oxide nanostructure;

[0009] (2) Hollow structure construction: disperse the cuprous oxide nanostructure obtained in step (1) in a solution containing a surfactant and a transition metal precursor salt, mix by ultrasonic and stirring, and grow transition metal oxides on the surface of cuprous oxide; add Na2S2O3 solution to etch cuprous oxide, centrifuge and wash to obtain hollow transition metal oxides;

[0010] (3) Noble metal modification: disperse the hollow transition metal oxides obtained in step (2) in ethanol, mix with a noble metal precursor salt solution and stir; adjust the pH by alkali solution and stir overnight, vacuum dry to obtain a transition metal oxide precursor modified with noble metal salt;

[0011] (4) Heat treatment growth: anneal the transition metal oxide precursor modified with noble metal salt obtained in step (3) under an inert atmosphere or a reducing gas atmosphere to grow noble metal nanoparticles uniformly on the surface of transition metal oxides, and obtain a noble metal modified hollow structure catalyst.

[0012] The mass ratio of the copper precursor salt, the transition metal precursor salt and the noble metal precursor salt is 1:(0.1-100):(0.1-100). The composite catalyst with the ratio has small nano size and uniform size, and has a good catalytic effect on NO3 - The RR has a good catalytic effect.

[0013] In step (1), the copper precursor salt is one of copper chloride, copper sulfate, copper nitrate and copper acetate.

[0014] The surfactant is one of sodium citrate, PVP, CTAB, CTAC, 16BAC, SLS, CAPB or SDS; preferably, the surfactant is sodium citrate.

[0015] The alkaline solution is an aqueous NaOH solution or an aqueous KOH solution.

[0016] The reducing agent is one of ascorbic acid, sodium citrate, NaBH4, hydrogen-based sodium borohydride, N, N-dimethyl lithium borohydride or sodium triacetoxy borohydride.

[0017] The cleaning is cleaning with deionized water.

[0018] The reaction of step (1) is a solution synthesis reaction, the reaction temperature is room temperature, and the reaction time is 1-24 hours.

[0019] The cuprous oxide nano structure is at least one of a cuprous oxide nanosphere, a cuprous oxide nanowire, a cuprous oxide nanosheet, a cuprous oxide nanocolumn, a cuprous oxide nanoflower or a cuprous oxide nanobelt.

[0020] In step (2), the surfactant is one of sodium citrate, PVP, CTAB, CTAC, 16BAC, SLS, CAPB or SDS; preferably, the surfactant is PVP.

[0021] The transition metal precursor salt is one of a zirconium, scandium, molybdenum, chromium, yttrium, titanium, vanadium, manganese, cobalt, nickel or zinc transition metal salt. Preferably, the transition metal precursor salt is one of a nitrate, an acetate, a sulfate or a chloride.

[0022] In step (2), the cuprous oxide is etched by adding a Na2S2O3 solution to remove the cuprous oxide core, and a hollow-structured transition metal oxide is obtained.

[0023] The solvent of the solution is a mixed solvent of a water-miscible organic solvent and water; further preferably, the water-miscible organic solvent is at least one of ethanol, methanol, ethylene glycol or isopropyl alcohol.

[0024] The washing is washing with deionized water and ethanol in sequence.

[0025] The reaction of step (2) is a solution synthesis reaction, the reaction temperature is room temperature, and the reaction time is 1-24 hours.

[0026] In step (3), the noble metal precursor salt is one of platinum, palladium, gold, silver, ruthenium, iridium, osmium or rhodium noble metal salt; preferably, the noble metal precursor salt is at least one of rhodium chloride, platinum chloride, iridium chloride, palladium chloride, chloroplatinic acid, chloropalladic acid, sodium chloroplatinate, potassium chloroplatinate, potassium chlororuthenate, ammonium chlororuthenate, potassium chloroosmate, ammonium chloroosmate, chloroiridic acid or potassium chloroiridate.

[0027] The alkali solution is one of sodium hydroxide solution, potassium hydroxide solution or concentrated ammonia; and after pH adjustment, the pH is 10-14.

[0028] The noble metal precursor salt solution is an alcohol solution.

[0029] In step (3), the overnight reaction time is 2-24 hours.

[0030] In step (4), the inert atmosphere is Ar or N2.

[0031] The reducing gas is CO or H2.

[0032] The treatment time of high-temperature annealing is 1-16 hours, and the treatment temperature of high-temperature annealing is 300-500℃; preferably, the temperature of high-temperature annealing is increased to the treatment temperature at a heating rate of 5℃ / min.

[0033] The noble metal nanoparticles include noble metal oxide particles or noble metal metal particles, and the particle size of the noble metal oxide particles or noble metal metal particles is 1-100 nm.

[0034] The vacuum drying is vacuum drying for 12-24 hours.

[0035] A noble metal modified hollow structure catalyst is obtained by the above preparation method. Further, in the noble metal modified hollow structure catalyst, the state of the noble metal is oxidation state or metal state.

[0036] The above noble metal modified hollow structure catalyst is applied in the electro-synthesis of ammonia.

[0037] The application discloses a preparation method of a noble metal modified hollow structure catalyst, and particularly, first, cuprous oxide nano structures are prepared through reaction by taking metal salt solution as raw materials; then, transition metal oxides are constructed on the surface of the cuprous oxide, and at the same time, hollow structures are obtained through etching reaction; then, noble metal salt modified transition metal oxide precursors are synthesized through reaction; finally, noble metal oxide particles or noble metal metal particles are grown on the surface of the transition metal oxides of the hollow structures through reaction, so that the target catalyst is obtained. - The application discloses a noble metal modified hollow structure catalyst.

[0038] The growth particles in the application are prepared by a solution synthesis method and annealing reaction; through a simple synthesis process, the noble metal oxide particles or the noble metal metal particles are uniformly grown on the transition metal oxides; and the obtained composite nano frame catalyst is not a simple physical mixture, but an orderly reaction in sequence.

[0039] The noble metal modified hollow structure catalyst in the application is a noble metal salt modified transition metal oxide composite system, wherein the noble metal can be metal particles / clusters in a metal state or an oxide state, and is uniformly grown on the transition metal oxides. - The noble metal mainly provides active hydrogen H, promotes water decomposition, and the transition metal oxide is an active material of NO3 - In the NO3 - Reduction to NH3.

[0040] The noble metal modified hollow structure catalyst prepared by the application comprises various combination forms, and the CoO@Ir composite catalyst is one of typical representatives. In the preparation process, by accurately controlling the mass percentage of the three raw material components, the following technical effects are achieved: (1) the transition metal is grown on the surface of cuprous oxide, and at the same time, the cuprous oxide is completely etched to form a hollow metal oxide structure; (2) the noble metal nanoparticles such as Ir and Ru are uniformly grown on the surface of the noble metal oxide particles or the noble metal metal particles. Especially, the optimization control of the noble metal content is crucial: too high noble metal content will intensify the competition of the hydrogen evolution reaction. The noble metal salt modified transition metal oxide binary composite material designed by the application has a reasonable component content range, so that the two components can be organically combined and synergized, thereby exhibiting excellent NO3 - RR catalytic performance.

[0041] The noble metal modified hollow structure catalyst prepared by the application has uniform noble metal particles, which are uniformly distributed on the surface of the transition metal oxide, have a large specific surface area, and are beneficial to the electrocatalytic reduction of NO3 - RR catalytic reaction, and the application also discloses the above NO3 - RR electrocatalytic material in the nitrate electro-reduction ammonia reaction.

[0042] Compared with the prior art, the application has the following advantages due to the use of the above technical solutions:

[0043] 1. The application first grows noble metal particles on the surface of a transition metal oxide to obtain a binary system catalyst, which has excellent NO3 - RR catalytic activity, compared with existing catalysts, it has a wide voltage range to maintain high FE (> 95%). And the system is conducive to promoting the generation of hydrogen radicals in water, so as to achieve the purpose of inhibiting the Heyrovsky reaction (*H+H2O+e⁻→H2+OH⁻) and activating the Volmer reaction (H2O+e⁻→*H+OH⁻), thereby promoting the reduction of NO3 - to NH3.

[0044] 2. The noble metal modified hollow structure catalyst provided by the application has reasonable material composition, so that the electronic structure of the noble metal particles and the transition metal oxide reaches the best state, so that the catalyst adsorbs NO3 - in the most appropriate state, and the NO3 - adsorbed on the surface of the noble metal is well reduced to NH3, thereby improving the ability of the catalyst to resist NO3 - RR.

[0045] 3. The noble metal modified hollow structure catalyst provided by the application has NO3 - RR electrocatalytic material performance stability, in a wide voltage range to maintain high activity and selectivity.

[0046] 4. The noble metal modified hollow structure catalyst disclosed by the application is simple to prepare, the raw materials are widely available, and the price is lower than that of existing noble metal catalysts, especially the proportion of noble metal in the catalyst is small, which greatly reduces the cost of the noble metal NO3 - RR catalyst. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 X-ray diffraction spectrum of the CoO@Ir catalyst of Example 1 and the hollow structure CoO nanocube;

[0048] Figure 2Scanning electron microscope images of Cu2O nanocubes and hollow CoO nanocubes from Example 1;

[0049] Figure 3 The images shown are scanning electron microscope (SEM) and transmission electron microscope (TEM) images of the CoO@Ir catalyst from Example 1.

[0050] Figure 4 The X-ray photoelectron spectra of the CoO@Ir catalyst and hollow CoO nanocubes in Example 1 are shown.

[0051] Figure 5 Electrochemical data for the CoO@Ir catalyst and hollow CoO nanocubes of Example 1, as well as commercial IrO2;

[0052] Figure 6 The CoO@Ir catalyst of Example 1 was tested for stability over 20 cycles at a standard hydrogen potential of –0.3 V;

[0053] Figure 7 The CoO@Ir catalyst of Example 1 was subjected to long-term stability testing at a standard hydrogen potential of –0.3 V. Detailed Implementation

[0054] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0055] Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0056] Currently, existing catalysts for the electroreduction of nitrate to ammonia have shown certain ammonia selectivity and yield, but they generally require high overpotentials, further intensifying competition with the electroreduction reaction (HER), resulting in insufficient ammonia selectivity. To address these technical problems, this invention proposes a highly efficient catalyst for the electroreduction of nitrate to ammonia, its preparation method, and its applications. The catalyst of this invention optimizes intermediate adsorption, suppresses side reactions, and improves the efficiency and selectivity of nitrate reduction to ammonia by in-situ growth of noble metal oxide nanoparticles or noble metal particles on the surface of transition metal oxides.

[0057] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0058] Example 1 Preparation of noble metal modified hollow structure catalyst (Ir / CoO system catalyst)

[0059] A preparation method of a noble metal modified hollow structure catalyst (Ir / CoO system catalyst), the specific steps are as follows:

[0060] (1) Preparation of precursor (Cu2O): 0.375 g of CuSO4·5H2O and 0.13 g of sodium citrate were dissolved in 80 mL of deionized water, and stirred until completely dissolved to form a blue solution; 20 mL of 1.25 mol / L NaOH solution was added to the above solution, and stirred for several minutes to generate a blue precipitate; 0.265 g of ascorbic acid (AA) was dissolved in 50 mL of deionized water, and the obtained AA solution was added to the blue precipitate system, and the color of the precipitate was observed to gradually change from blue to green, and finally a brick red precipitate was formed; the brick red precipitate was collected, washed with deionized water for three times, and a pure Cu2O nanocube sample was obtained.

[0061] (2) Hollow structure construction (CoO): The prepared Cu2O nanocube was dispersed in 80 mL of deionized water; 5.32 g of PVP (polyvinylpyrrolidone) and 44 mg of CoCl2 were dissolved in 80 mL of ethanol, and ultrasonic treatment was performed until completely dissolved; the above two solutions were mixed and ultrasonic treatment was performed for 30 minutes, followed by magnetic stirring for 50 minutes; 10 g of Na2S2O3 in 50 mL of aqueous solution was added, and it was observed that the solution gradually generated a light green precipitate; after continuing to stir for 15 minutes and standing for 1 hour, the color of the precipitate gradually deepened to dark green; the precipitate was collected by centrifugation, and was washed with deionized water and ethanol for five times respectively, and finally a hollow transition metal oxide (precursor CoO) was obtained.

[0062] (3) Noble metal modification (preparation of CoO@Ir): 5 mg of IrCl3 was dissolved in 10 mL of deionized water, and heated to completely dissolve; the prepared CoO was dispersed in 8 mL of ethanol; the IrCl3 solution and the CoO ethanol dispersion were mixed, and concentrated ammonia water was added dropwise to adjust the pH value of the system to 12; the reaction was stirred at room temperature for 12 hours, and vacuum drying was performed at 60°C to obtain a transition metal oxide precursor modified by noble metal salt (CoO@Ir precursor).

[0063] (4) Heat treatment growth: The precursor was placed in a tube furnace, and was heated to 400°C at a heating rate of 5°C / min under N2 protection; after constant temperature calcination for 2 hours, natural cooling was performed, and finally a noble metal modified hollow structure catalyst (Ir / CoO system catalyst, i.e. CoO@Ir catalyst) was obtained.

[0064] The catalyst is loaded on carbon paper as the working electrode, platinum mesh as the counter electrode, and Hg / HgO electrode as the reference electrode. The cyclic voltammogram is tested in a mixed solution of 1 M potassium hydroxide and 0.1 M potassium nitrate. The catalyst is activated by the cyclic voltammogram, and the scanning rate is 50 mV / s. The linear sweep voltammogram and the time-current curve are measured in a mixed solution of 1 M KOH and 0.1 M potassium nitrate by using a three-electrode system, and the catalyst loaded on carbon paper as the working electrode, and saturated Hg / HgO as the reference electrode, and platinum mesh as the counter electrode.

[0065] The detection results are shown in Table 1, and are as follows: Figures 1 to 7

[0066] Figure 1 The X-ray diffraction patterns of the catalyst CoO@Ir and the precursor CoO can be seen in the X-ray diffraction patterns corresponding to CoO (PDF #89-2803, PDF #48-1719), which preliminarily indicates that the hollow structure CoO nanocube and the CoO@Ir catalyst are successfully synthesized, and the Ir doping does not significantly change the original structure of CoO.

[0067] Figure 2 a is the scanning electron microscope (SEM) image of the Cu2O nanocube, and it can be seen that the Cu2O is a uniform cubic block. Subsequently, the hollow structure CoO nanocube and the catalyst CoO@Ir are synthesized based on the Cu2O cubic block. Figure 2 b is the scanning electron microscope (SEM) image of the hollow structure CoO nanocube, and it can be seen that the Cu2O cubic block is etched to obtain a hollow structure. This indicates the successful synthesis of the precursor CoO.

[0068] Figure 3 a, b, and c are the scanning electron microscope (SEM) images and the transmission electron microscope (TEM) images of the CoO@Ir catalyst, and the uniformly distributed nanoparticles on the CoO hollow structure can be clearly seen in the images. Figure 3 d, e, and f can be seen that the O, Cu, Co, and Ir elements are uniformly distributed. This preliminarily confirms the successful incorporation of Ir into the precursor CoO. It is shown that the noble metal particles of the CoO@Ir catalyst prepared by the present application are uniform in size, uniformly distributed on the CoO hollow structure, have a large specific surface area, and can be used as a catalyst for the reduction of NO3 – RR promotes the generation of hydrogen radicals in water, thereby facilitating the conversion of NO3 – to NH3.

[0069] Figure 4 a, b, and c are the X-ray photoelectron spectroscopy of the CoO@Ir catalyst and the hollow structure CoO nanocube, and it can be seen that the Ir 4f spectrum of the CoO@Ir indicates that the Ir is in the form of Ir 3+ and Ir​4+ The mixed valence state. And the ratio of Co 2p spectra Co 3+ / Co 2+ changes, and shifts to the direction of higher binding energy, indicating that CoO has undergone electron transfer after doping Ir. In addition, a new peak appears in the O 1s spectrum of CoO@Ir, which corresponds to lattice oxygen, which further proves the successful modification of Ir.

[0070] Figure 5 a CoO@Ir catalyst in 1 M KOH + 0.1 M KNO3 and 1 M KOH electrolyte to compensate for 25% of the linear sweep voltammetry curve, it can be seen that in the presence of NO3 – , the current density increases significantly, which indicates that CoO@Ir has high catalytic activity for NO3 – . In Figure 5 b, c catalyst CoO@Ir and precursor CoO and commercial IrO2 in 1 M KOH + 0.1 M KNO3 mixed electrolyte to compensate for 25% of the linear sweep voltammetry curve and ammonia production rate at different potentials (0.3 V ~ –0.3 V) vs. RHE, it can be seen that the current density and ammonia production rate of CoO@Ir are significantly higher than those of precursor CoO and commercial IrO2, which further indicates that CoO@Ir has higher NO3 – RR activity. Figure 5 d is the FE of the catalyst CoO@Ir, it can be seen that CoO@Ir has higher NH3FE at the beginning, and the byproduct NO2 - almost none, and maintains a high FE in a wide voltage range (0.3 V ~ –0.3 V) vs. RHE, which indicates that CoO@Ir catalyst maintains high activity in the NO3 – RR process.

[0071] Figure 6 is the 20 cycle stability test of CoO@Ir catalyst at –0.3 V vs. RHE, it can be seen that the current density and NH3faraday efficiency remain constant throughout the running time. This indicates that the CoO@Ir catalyst has good stability.

[0072] Figure 7 is the 72-hour long-term stability test of CoO@Ir catalyst at –0.3 V vs. RHE, it can be seen that during each 24-hour stability measurement, the current density decreases slightly, but after the electrolyte is updated, the current density quickly recovers. This further indicates that the CoO@Ir catalyst has good stability.

[0073] Example 2 Preparation of noble metal modified hollow structure catalyst (Ru / CoO system catalyst)

[0074] A preparation method of a noble metal modified hollow structure catalyst (Ru / CoO system catalyst), the specific steps are as follows:

[0075] (1) Preparation of precursor (Cu2O): 0.375 g of CuSO4·5H2O and 0.25 g of CTAB were dissolved in 80 mL of deionized water, stirred until completely dissolved, forming a blue solution; 20 mL of 3 mol / L NaOH solution was added to the above solution, and after stirring for a few minutes, a blue precipitate was formed; 0.265 g of ascorbic acid (AA) was dissolved in 50 mL of deionized water, and the obtained AA solution was added to the blue precipitate system, and the color of the precipitate was observed to gradually change from blue to green, and finally a brick red precipitate was formed; The brick red precipitate was collected and washed with deionized water three times to obtain pure Cu2O nanobands.

[0076] (2) Hollow structure construction (CoO): The prepared Cu2O nanocubes were dispersed in 80 mL of deionized water; 5.32 g of PVP (polyvinylpyrrolidone) and 44 mg of CoCl2 were dissolved in 80 mL of ethanol, and ultrasonic treatment was performed until completely dissolved; The above two solutions were mixed and ultrasonic treated for 30 minutes, and then magnetically stirred for 50 minutes; 10 g of Na2S2O3 in 50 mL of aqueous solution was added, and it was observed that the solution gradually formed a black precipitate; Continue to stir for 15 minutes and stand for 1 hour, the color of the precipitate gradually deepens; The precipitate was collected by centrifugation, and washed with deionized water and ethanol five times in turn, and finally the CoO product was obtained.

[0077] (3) Noble metal modification (preparation of CoO@Ru): 5 mg of RuCl3 was dissolved in 10 mL of deionized water, and heated to completely dissolve; The prepared CoO was dispersed in 8 mL of ethanol; The RuCl3 solution and the CoO ethanol dispersion were mixed, and concentrated ammonia water was added dropwise to adjust the pH value of the system to 12; Stir at room temperature for 12 hours, vacuum dry at 60°C to obtain hollow transition metal oxide (CoO@Ru precursor);

[0078] (4) Heat treatment growth: The precursor was placed in a tube furnace, and heated to 400°C at a rate of 5°C / min under N2 protection; After constant temperature calcination for 2 hours, natural cooling was carried out, and finally the noble metal modified hollow structure catalyst (Ru / CoO system catalyst, i.e. CoO@Ru catalyst) was obtained

[0079] Example 3 Preparation of noble metal modified hollow structure catalyst (Rh / CoO system catalyst)

[0080] A preparation method of a noble metal modified hollow structure catalyst (Rh / CoO system catalyst), the specific steps are as follows:

[0081] (1) Preparation of precursor (Cu2O): 0.375 g of CuSO4·5H2O and 0.25 g of SDS were dissolved in 80 mL of deionized water, stirred until completely dissolved, and a blue solution was formed; 20 mL of 2 mol / L NaOH solution was added to the above solution, and after stirring for several minutes, a blue precipitate was formed; 0.265 g of ascorbic acid (AA) was dissolved in 50 mL of deionized water, and the obtained AA solution was added to the blue precipitate system, and the color of the precipitate was observed to change from blue to green, and finally a brick red precipitate was formed; the brick red precipitate was collected, washed with deionized water for three times, and pure Cu2O nanospheres were obtained.

[0082] (2) Hollow structure construction (CoO): the prepared Cu2O nanocubes were dispersed in 80 mL of deionized water; 5.32 g of PVP (polyvinylpyrrolidone) and 33 mg of CoCl2 were dissolved in 80 mL of ethanol, and ultrasonic treatment was performed until completely dissolved; the above two solutions were mixed and ultrasonic treatment was performed for 30 minutes, and then magnetic stirring was performed for 50 minutes; 10 g of Na2S2O3 in 50 mL of aqueous solution was added, and it was observed that the solution gradually formed a black precipitate; after continuing to stir for 15 minutes and standing for 1 hour, the color of the precipitate gradually deepened; the precipitate was collected by centrifugation, and was washed with deionized water and ethanol for five times respectively, and finally a hollow transition metal oxide (precursor CoO) was obtained.

[0083] (3) Noble metal modification (preparation of CoO@Rh): 5 mg of RhCl3 was dissolved in 10 mL of deionized water, and was heated to completely dissolve; the prepared CoO was dispersed in 8 mL of ethanol; the RhCl3 solution and the CoO ethanol dispersion were mixed, and concentrated ammonia water was added dropwise to adjust the pH value of the system to 12; the reaction was stirred at room temperature for 12 hours, and vacuum drying was performed at 60°C to obtain a transition metal oxide precursor modified by noble metal salt (CoO@Rh precursor).

[0084] (4) Heat treatment growth: the precursor was placed in a tube furnace, and was heated to 400°C at a heating rate of 5°C / min under N2 protection; after constant temperature calcination for 2 hours, natural cooling was performed, and finally a noble metal modified hollow structure catalyst (Rh / CoO system catalyst, i.e. CoO@Rh catalyst) was obtained.

[0085] Example 4 Noble metal modified hollow structure catalyst (Pd / NiO system catalyst)

[0086] A preparation method of a noble metal modified hollow structure catalyst (Pd / NiO system catalyst), the specific steps are as follows:

[0087] (1) Preparation of precursor (Cu2O): 0.375 g CuSO4·5H2O and 0.13 g sodium citrate were dissolved in 80 mL deionized water, and stirred until completely dissolved to form a blue solution; 20 mL 1.25 mol / L NaOH solution was added to the above solution, and stirred for several minutes to generate a blue precipitate; 0.265 g ascorbic acid (AA) was dissolved in 50 mL deionized water, and the obtained AA solution was added to the blue precipitate system, and the color of the precipitate was observed to gradually change from blue to green, and finally a brick red precipitate was formed; the brick red precipitate was collected, and after three deionized water washes, a pure Cu2O sample was obtained.

[0088] (2) Hollow structure construction (NiO): the prepared Cu2O nanocubes were dispersed in 80 mL deionized water; 5.32 g PVP (polyvinylpyrrolidone) and 66 mg NiCl2 were dissolved in 80 mL ethanol, and ultrasonically treated until completely dissolved; the above two solutions were mixed and ultrasonically treated for 30 minutes, and then magnetically stirred for 50 minutes; 10 g Na2S2O3 in 50 mL water was added, and it was observed that the solution gradually generated a light green precipitate; after continuing to stir for 15 minutes and standing for 1 hour, the color of the precipitate gradually deepened; the precipitate was collected by centrifugation, and was washed with deionized water and ethanol five times in turn, and finally a hollow transition metal oxide (precursor NiO) was obtained.

[0089] (3) Noble metal modification (preparation of NiO@Pd): 5 mg PdCl2 was dissolved in 10 mL deionized water, and heated until completely dissolved; the above prepared NiO was dispersed in 8 mL ethanol; the PdCl2 solution and the NiO ethanol dispersion were mixed, and concentrated ammonia water was added dropwise to adjust the pH value of the system to 12; the reaction was stirred at room temperature for 12 hours, and vacuum dried at 60°C to obtain a transition metal oxide precursor modified with a noble metal salt (NiO@Pd precursor).

[0090] (4) Heat treatment growth: the precursor was placed in a tube furnace, and was heated to 400°C at a heating rate of 5°C / min under H2 protection; after constant temperature calcination for 2 hours, it was naturally cooled, and finally a noble metal modified hollow structure catalyst (NiO@Pd system catalyst, namely NiO@Pd catalyst) was obtained, and the noble metal Pd was a metallic state nanoparticle.

[0091] The above examples and their detection results prove that the present application has the following advantages compared with the prior art:

[0092] 1. The present application first grows noble metal particles on the surface of a transition metal oxide to obtain a binary system catalyst, which not only has excellent NO3 -The RR catalytic activity has a wider voltage range compared to existing catalysts, and maintains high FE (> 90%) in the range. The system is conducive to promoting the generation of hydrogen radicals in water, thereby achieving the purpose of inhibiting the Heyrovsky reaction (*H + H2O + e⁻→ H2 + OH⁻), activating the Volmer reaction (H2O + e⁻→ *H + OH⁻), and promoting the NO3 - Reduction to NH3.

[0093] 2、The noble metal modified hollow structure catalyst provided by the application has reasonable material composition, so that the electronic structure of noble metal particles and transition metal oxides reaches an optimal state, thereby making the catalyst adsorb NO3 - In the most appropriate state, and making the NO3 - adsorbed on the surface of the noble metal is well reduced to NH3, thereby improving the NO3 - RR resistance of the catalyst.

[0094] 3、The noble metal modified hollow structure catalyst provided by the application has NO3 - RR electrocatalytic material has stable performance, and maintains high activity and selectivity in a wider voltage range.

[0095] 4、The noble metal modified hollow structure catalyst disclosed by the application is simple to prepare, has a wide source of raw materials, and has a lower price compared to existing noble metal catalysts, especially the small proportion of noble metals in the catalyst, which greatly reduces the cost of noble metal NO3 - RR catalyst.

[0096] The above only describes the preferred embodiments of the application and is not intended to limit the application. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A method for preparing a noble metal-modified hollow structure catalyst, characterized by: The method comprises the following steps: (1) precursor preparation: dissolving copper precursor salt in an aqueous solution containing a surfactant, adding an alkali solution after stirring uniformly, and generating blue precipitate through reaction; adding a reducing agent solution to the reaction system, and cleaning the precipitate after reaction to obtain cuprous oxide nanostructure; (2) hollow structure construction: dispersing the cuprous oxide nanostructure obtained in step (1) in a solution containing a surfactant and a transition metal precursor salt, mixing through ultrasonic and stirring, and growing transition metal oxide on the surface of cuprous oxide; adding Na2S2O3 solution to etch cuprous oxide, and obtaining hollow transition metal oxide through centrifugation and washing; (3) noble metal modification: dispersing the hollow transition metal oxide obtained in step (2) in ethanol, mixing with a noble metal precursor salt solution and stirring; adjusting pH through alkali solution and stirring overnight, and obtaining transition metal oxide precursor modified by noble metal salt through vacuum drying; (4) heat treatment growth: annealing the transition metal oxide precursor modified by noble metal salt obtained in step (3) under inert atmosphere or reducing gas atmosphere, growing noble metal nanoparticles uniformly on the surface of transition metal oxide, and obtaining noble metal modified hollow structure catalyst.

2. The method of claim 1, wherein the method is characterized by: The mass ratio of the copper precursor salt, the transition metal precursor salt and the noble metal precursor salt is 1:(0.1-100):(0.1-100).

3. The method of claim 1, wherein the method is characterized by: In step (1), the copper precursor salt is one of copper chloride, copper sulfate, copper nitrate or copper acetate; The cuprous oxide nanostructure is at least one of cuprous oxide nanosphere, nanowire, nanosheet, nanocolumn, nanoflower or nanobelt; The surfactant is one of PVP, CTAB, CTAC, 16BAC, SLS, CAPB or SDS; The alkali solution is NaOH aqueous solution or KOH aqueous solution; The reducing agent is one of ascorbic acid, sodium citrate, NaBH4, hydrogen-based sodium borohydride, N,N-dimethyl lithium borohydride or sodium triacetoxy borohydride.

4. The method of claim 1, wherein the method is characterized by: In step (1), the cleaning is cleaning with deionized water; The reaction of step (1) is solution synthesis reaction, the reaction temperature is room temperature, and the reaction time is 1-24 hours.

5. The method of claim 1, wherein the method is characterized by: In step (2), the surfactant is one of sodium citrate, PVP, CTAB, CTAC, 16BAC, SLS, CAPB or SDS; The transition metal precursor salt is one of zirconium, scandium, molybdenum, chromium, yttrium, titanium, vanadium, manganese, cobalt, nickel or zinc transition metal salt.

6. The method of claim 1, wherein the method is characterized by: In step (2), the solvent of the solution is mixed solvent of water-miscible organic solvent and water; the water-miscible organic solvent is at least one of ethanol, methanol, ethylene glycol or isopropyl alcohol; The washing is washing with deionized water and ethanol in sequence; The reaction of step (2) is solution synthesis reaction, the reaction temperature is room temperature, and the reaction time is 1-24 hours.

7. The method of claim 1, wherein the method is characterized by: In step (3), the noble metal precursor salt is one of platinum, palladium, gold, silver, ruthenium, iridium, osmium or rhodium noble metal salt; The alkali solution is one of sodium hydroxide solution, potassium hydroxide solution or concentrated ammonia water; and the pH after adjustment is 10-14. The noble metal precursor salt solution is an alcohol solution. The reaction time in step (3) is 2-24 hours.

8. The method of claim 1, wherein the method is characterized by: In step (4), the inert atmosphere is Ar or N2. The reducing gas is CO or H2. The treatment time of high-temperature annealing is 1-16 hours, and the treatment temperature of high-temperature annealing is 300-500℃.

9. A noble metal modified hollow structure catalyst obtained by the preparation method in any one of claims 1-8.

10. Application of the noble metal modified hollow structure catalyst in claim 9 in electro-synthesis of ammonia.

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