Carbon-supported highly ordered body-centered cubic structure RuGa nanocrystal, and preparation method and application thereof

Abstract

The application relates to the technical field of nanocatalysis, and discloses carbon-loaded highly-ordered body-centered cubic structure RuGa nanocrystals as well as a preparation method and application thereof. The preparation method of the carbon-loaded highly-ordered body-centered cubic structure RuGa nanocrystals comprises the following steps: dissolving a ruthenium salt and a gallium salt in a hydrochloric acid solution and adding a carbon carrier, performing ultrasonic stirring, then performing rotary evaporation and vacuum drying, and then sequentially performing high-temperature alloying and low-temperature ordering on the obtained precursor powder in a reducing atmosphere to obtain the carbon-loaded highly-ordered body-centered cubic structure RuGa nanocrystals. The preparation method provided by the application is simple in process and convenient for large-scale commercial production. The RuGa nanocrystals have the body-centered cubic structure of high order and isolated Ru sites, can be used in an ammonia system for electrocatalytic reduction of nitrate or nitrite, can reach a Faraday efficiency of more than 97%, and can realize the application of changing nitrate or nitrite-containing wastewater into valuable ammonia.

Description

Technical Field

[0001] The present invention relates to the field of nanocatalysis technology, and in particular to a carbon-supported highly ordered body-centered cubic RuGa nanocrystal and a preparation method and application thereof. Background Art

[0002] Ammonia is an important inorganic chemical raw material and is widely used in fertilizers, explosives, medicine and other fields. Due to its high energy density (4.32kw h L -1 Ammonia is a renewable, green, and carbon-free energy carrier, boasting a high hydrogen content (17.6%), ease of transportation, and liquefied storage. Currently, over 90% of the world's ammonia is produced using the energy-intensive Haber-Bosch process, which consumes 1-2% of global fossil energy and contributes to 1.5% of global carbon emissions annually. Therefore, finding a low-energy, environmentally friendly method for producing ammonia is of great significance and value.

[0003] Furthermore, due to the overuse of fossil fuels and the increasing demand for nitrogen fertilizers in agricultural activities, large amounts of nitrate and nitrite pollutants are discharged into the natural environment, leading to contamination of groundwater and drinking water. Long-term exposure to nitrate and nitrite can cause human health problems, such as methemoglobinemia and cancer, and pose a serious threat to ecological security and human health. Traditional methods for removing nitrate and nitrite from wastewater suffer from disadvantages such as high cost and difficult post-treatment. Electrocatalytic reduction of nitrate and nitrite can be carried out under mild conditions and, combined with sustainable energy sources, is more environmentally friendly. Furthermore, electrocatalytic reduction of nitrate and nitrite can produce a high-value product—ammonia—turning waste into treasure. Currently, ruthenium (Ru)-based catalysts have demonstrated excellent performance in the electrocatalytic reduction of nitrate and nitrite to produce ammonia. However, Ru's high cost, scarcity, and strong affinity for nitrite limit its widespread application.

[0004] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a carbon-supported highly ordered body-centered cubic RuGa nanocrystal and its preparation method and application, aiming to solve the problem that Ru catalysts are limited in application due to their high cost, scarcity and strong affinity characteristics.

[0006] In order to reduce the amount of Ru and improve its catalytic activity, the introduction of carriers and the formation of alloys is an effective strategy. Compared with disordered alloys, ordered alloys have stronger geometric, electronic and ordered effects, which can more effectively adjust the interaction between the catalyst and the adsorbate, improve the activity and selectivity, and especially the Ru-based alloy with high order degree has important influence on the catalytic activity and selectivity in specific catalytic process.

[0007] The technical scheme of the present application is as follows:

[0008] In the first aspect of the present application, a preparation method of carbon-supported highly ordered body-centered cubic structure RuGa nanocrystals is provided, comprising the following steps:

[0009] After dissolving the ruthenium salt and gallium salt in the hydrochloric acid solution, a carbon carrier is added, and after ultrasonic and stirring, a precursor suspension is obtained;

[0010] After the precursor suspension is evaporated and dried, a precursor powder is obtained;

[0011] The precursor powder is subjected to alloying and ordering in a reducing atmosphere in sequence, and after cooling, the carbon-supported highly ordered body-centered cubic structure RuGa nanocrystals are obtained.

[0012] Optionally, the ruthenium salt is one or more of anhydrous ruthenium chloride, ruthenium acetate, ruthenium carbonyl, ruthenium acetylacetone, and ammonium hexachlororuthenate.

[0013] Optionally, the gallium salt is one or more of gallium nitrate nine hydrate, gallium chloride, gallium sulfate, gallium acetate, and gallium acetylacetone.

[0014] Optionally, the molar ratio of the ruthenium salt to the gallium salt is 1:(1-3).

[0015] Optionally, the concentration of the hydrochloric acid solution is 0.5-2 mol / L.

[0016] Optionally, the carbon carrier is selected from one of carbon black Black Pearl 2000, carbon black Ketjenblack EC-600JD, carbon black Ketjenblack EC-300J, graphene, and carbon nanotube.

[0017] Optionally, the evaporation and drying of the precursor suspension is performed by rotary evaporation and vacuum drying.

[0018] Optionally, the reducing atmosphere is hydrogen gas or a mixture of hydrogen gas and argon gas.

[0019] Optionally, the alloying conditions are as follows: the temperature is 900-1100℃, the heating rate is 5-30℃ / min, and the holding time is 2-10h.

[0020] Optionally, the ordering conditions are: temperature of 400-600° C., cooling rate of 2-10° C. / min, and holding time of 4-12 h.

[0021] The second aspect of the present invention provides a carbon-supported highly ordered body-centered cubic RuGa nanocrystal, which is prepared by the method for preparing the carbon-supported highly ordered body-centered cubic RuGa nanocrystal.

[0022] Optionally, the mass fraction of RuGa nanocrystals in the carbon-supported highly ordered body-centered cubic RuGa nanocrystals is 5 to 20 wt %.

[0023] Optionally, the size of the RuGa nanocrystals in the carbon-supported highly ordered body-centered cubic RuGa nanocrystals is less than 7 nm.

[0024] The third aspect of the present invention provides an application of the carbon-supported highly ordered body-centered cubic RuGa nanocrystals in the electrocatalytic reduction of nitrate or nitrite to produce ammonia.

[0025] The present invention has the beneficial effects:

[0026] (1) The present invention prepares carbon-supported highly ordered body-centered cubic RuGa nanocrystals by precisely controlling the drying process and regulating the calcination conditions. The preparation process is simple and can be effectively expanded to realize its application in converting nitrate or nitrite-containing wastewater into valuable ammonia.

[0027] (2) The product prepared by the present invention is a body-centered cubic RuGa nanocrystal with a highly ordered structure and isolated Ru sites. The particle size is small and the distribution is uniform. It can be directly used in the electrochemical nitrate or nitrite reduction system for ammonia production at room temperature and pressure.

[0028] (3) The carbon-supported, highly ordered body-centered cubic RuGa nanocrystals provided by the present invention, as catalytic electrode materials, achieve efficient electrocatalytic reduction of nitrate or nitrite to ammonia, with a Faradaic efficiency greater than 97%. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is the X-ray diffraction pattern of the carbon-supported highly ordered body-centered cubic RuGa nanocrystals prepared in Example 1 of the present invention.

[0030] Figure 2 This is a bright-field transmission electron microscopy image of the carbon-supported highly ordered body-centered cubic RuGa nanocrystals prepared in Example 1 of the present invention.

[0031] Figure 3This is a dark-field high-resolution transmission electron microscopy image of the carbon-supported highly ordered body-centered cubic RuGa nanocrystals prepared in Example 1 of the present invention.

[0032] Figure 4 This is a graph showing the Faraday efficiency test results of the electrocatalytic reduction of nitrate to ammonia at different potentials by the carbon-supported highly ordered body-centered cubic RuGa nanocrystals prepared in Example 1 of the present invention.

[0033] Figure 5 This is a bright-field transmission electron microscopy image of the carbon-supported highly ordered body-centered cubic RuGa nanocrystals prepared in Example 2 of the present invention.

[0034] Figure 6 This is a bright-field transmission electron microscopy image of the carbon-supported highly ordered body-centered cubic RuGa nanocrystals prepared in Example 3 of the present invention.

[0035] Figure 7 This is the X-ray diffraction pattern of the carbon-supported close-packed hexagonal Ru nanocrystals prepared in Comparative Example 1 of the present invention.

[0036] Figure 8 This is a bright-field transmission electron microscopy image of the carbon-supported close-packed hexagonal Ru nanocrystals prepared in Comparative Example 1 of the present invention.

[0037] Figure 9 This is a dark field high-resolution transmission electron microscopy image of the carbon-supported close-packed hexagonal Ru nanocrystals prepared in Comparative Example 1 of the present invention.

[0038] Figure 10 This is a graph showing the Faraday efficiency test results of the electrocatalytic reduction of nitrate to ammonia at different potentials using carbon-supported close-packed hexagonal Ru nanocrystals prepared in Comparative Example 1 of the present invention.

[0039] Figure 11 This is a bright-field transmission electron microscope image of the carbon-supported highly ordered body-centered cubic RuGa nanocrystals prepared in Comparative Example 2 of the present invention.

[0040] Figure 12 This is the X-ray diffraction pattern of the carbon support centered cubic structure RuGa nanocrystals prepared in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0041] The present invention provides carbon-supported, highly ordered, body-centered cubic RuGa nanocrystals, and their preparation methods and applications. To clarify the objectives, technical solutions, and effects of the present invention, the present invention is described in further detail below. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention.

[0042] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0043] The present invention provides a method for preparing carbon-supported RuGa nanocrystals with a highly ordered body-centered cubic structure, comprising the following steps:

[0044] S1. Add ruthenium salt and gallium salt into hydrochloric acid solution and dissolve them, then add carbon support, sonicate and stir to obtain a precursor suspension;

[0045] S2, evaporating and drying the precursor suspension to obtain a precursor powder;

[0046] S3. Placing the precursor powder in a crucible, and successively performing high-temperature alloying and low-temperature ordering in a reducing atmosphere to obtain the carbon-supported highly ordered body-centered cubic RuGa nanocrystals.

[0047] The present invention uses a carbon support with a high specific surface area (such as commercial carbon black) to prepare carbon-supported, highly ordered body-centered cubic (BCC) RuGa nanocrystals by utilizing an impregnation-thermal reduction method. The preparation method not only helps suppress the agglomeration and growth of catalyst particles during the high-temperature alloying-ordering process, but also helps provide good conductivity during the electrocatalytic process and can significantly reduce costs. The present invention uses a rotary evaporation-vacuum drying technology, which helps avoid adverse factors such as agglomeration or delamination of precursor powder particles during the drying process, so that the nanocrystals obtained after calcination have a smaller size and are evenly distributed on the carbon black, which helps expose more catalytic active sites, thereby promoting the reduction of nitrate or nitrite. In the present invention, highly ordered BCC RuGa nanocrystals are obtained through the process of high-temperature alloying and low-temperature ordering. The isolated Ru sites formed by this specific structure have a stable and fixed coordination environment, are neatly arranged, and are abundant and compact. The unique BCC structure and its specific isolated Ru sites can effectively reduce the adsorption of hydrogen and inhibit the HER reaction, thereby facilitating the highly selective reduction of nitrate or nitrite to ammonia. Compared with independent Ru atoms, the ordered nanocrystals ensure that the isolated Ru sites formed in the specific crystal structure have higher stability.

[0048] In some embodiments, in step S1, the ruthenium salt is one or more of anhydrous ruthenium chloride, ruthenium acetate, carbonyl ruthenium, ruthenium acetylacetonate, and ammonium hexachlororuthenate.

[0049] In some embodiments, in step S1, the gallium salt is one or more of gallium nitrate nonahydrate, gallium chloride, gallium sulfate, gallium acetate, and gallium acetylacetonate.

[0050] In some embodiments, in step S1, the molar ratio of the ruthenium salt to the gallium salt is 1:(1-3).

[0051] In some embodiments, in step S1, the concentration of the hydrochloric acid solution is 0.5 to 2 mol / L.

[0052] In some embodiments, in step S1, the carbon support is selected from one of carbon black Black Pearl 2000, carbon black Ketjenblack EC-600JD, carbon black Ketjenblack EC-300J, graphene, and carbon nanotubes.

[0053] In some embodiments, in step S3, the reducing atmosphere is hydrogen or a mixture of hydrogen and argon.

[0054] In some embodiments, in step S3, the high-temperature alloying and low-temperature ordering steps are specifically as follows: heating the precursor powder to 900-1100°C at 5-30°C / min and keeping it warm for 2-10 hours; then cooling it to 400-600°C at 2-10°C / min, keeping it warm for 4-12 hours, and then cooling it naturally.

[0055] In the synthesis process of RuGa nanocrystals in the present invention, the degree of alloying has a significant impact on the formation of an ordered structure. Increasing the temperature and improving the degree of alloying are conducive to the progress of ordering. However, under normal circumstances, the driving force for the transformation of a disordered structure into an ordered structure is still relatively small, and direct cooling cannot provide sufficient thermodynamic driving force. Therefore, by extending the low-temperature annealing time, the kinetic energy barrier of atomic ordering is overcome, thereby obtaining highly ordered RuGa nanocrystals.

[0056] The embodiment of the present invention provides a carbon-supported highly ordered body-centered cubic RuGa nanocrystal, which is prepared by using the method for preparing the carbon-supported highly ordered body-centered cubic RuGa nanocrystal.

[0057] The highly ordered RuGa nanocrystals of the present invention exhibit a typical body-centered structure. The isolated Ru sites formed by this specific structure have a stable, fixed coordination environment, are neatly arranged, and are abundant and compact. This unique body-centered structure and its specific isolated Ru sites can effectively reduce hydrogen adsorption and inhibit the HER reaction, thereby facilitating the highly selective reduction of nitrates or nitrites to ammonia. In addition, compared to independent Ru atoms, the ordered nanocrystals ensure that the isolated Ru sites formed in the specific crystal structure have higher stability.

[0058] In some embodiments, the mass fraction of RuGa nanocrystals in the carbon-supported highly ordered body-centered cubic RuGa nanocrystals is 5 to 20 wt %.

[0059] In some embodiments, the size of the RuGa nanocrystals in the carbon-supported highly ordered body-centered cubic RuGa nanocrystals is less than 7 nm.

[0060] An embodiment of the present invention provides an application of the carbon-supported highly ordered body-centered cubic RuGa nanocrystals in the electrocatalytic reduction of nitrate or nitrite to produce ammonia.

[0061] In the application of electrocatalytic ammonia production using nitrate or nitrite, in order to improve selectivity, the HER reaction must be avoided as much as possible. The key is to make the Ru site discontinuous and become an isolated active site. Therefore, how to construct RuGa nanocrystals with isolated Ru sites of a highly ordered carbon-supported specific structure by designing a simple and easy method is of great significance. The size of the RuGa nanocrystals in the carbon-supported highly ordered body-centered cubic structure RuGa nanocrystals prepared by the present invention is less than 7nm, and presents a highly ordered body-centered cubic structure. The isolated Ru sites formed by this specific structure enable it to achieve a Faraday efficiency of greater than 97% in the application of electrocatalytic nitrate or nitrite reduction to ammonia production. By regulating the alloy composition, loading amount, sintering system, etc., the order, size and electrocatalytic performance of the RuGa nanocrystals in the reduction of nitrate or nitrite to ammonia can be effectively regulated.

[0062] The following describes it in detail through specific examples.

[0063] Example 1

[0064] 0.121g of anhydrous ruthenium chloride and 0.288g of gallium nitrate nonahydrate were added to 150mL of 1mol / L hydrochloric acid solution. Once completely dissolved, 0.4g of Black Pearl 2000 was added. After sonication for 2h, the mixture was stirred overnight to thoroughly mix the precursor and carbon black support. The mixed solution was then subjected to rotary evaporation to separate the solvent and dried to obtain a powdery mixture. The dried powder was placed in a corundum crucible and placed in a tube furnace. Under a hydrogen-argon reducing atmosphere, the temperature was increased at 10°C / min to 900°C and maintained for 4h. The mixture was then cooled at 10°C / min to 500°C and maintained for 4h. After natural cooling, carbon-supported highly ordered body-centered cubic RuGa nanocrystals were obtained.

[0065] Figure 1 The X-ray diffraction pattern of the product was obtained and it was concluded through analysis that the product was RuGa nanocrystals with a typical body-centered cubic structure (PDF#65-9718).

[0066] from Figure 2 Bright-field transmission electron microscopy images show that body-centered cubic RuGa nanocrystals are evenly dispersed on the surface of the carbon black carrier, with an average particle size of about 5 nm and no obvious agglomeration.

[0067] Figure 3 The dark-field high-resolution transmission electron microscopy images in the figure show that the nanocrystals have a clear RuGa body-centered structure and are highly ordered.

[0068] Figure 4 The performance of the catalyst in a 1 mol / L potassium hydroxide solution containing a nitrate concentration of 2000 ppm is shown. The carbon-supported highly ordered body-centered cubic RuGa nanocrystals have a maximum ammonia Faraday efficiency of 97.1%.

[0069] Example 2

[0070] 0.121g of anhydrous ruthenium chloride and 0.337g of gallium nitrate nonahydrate were added to 150mL of 1mol / L hydrochloric acid solution. Once completely dissolved, 0.4g of Black Pearl 2000 was added. After sonication for 2h, the mixture was stirred overnight to thoroughly mix the precursor and carbon black support. The mixed solution was then subjected to rotary evaporation to separate the solvent and dried to obtain a powdery mixture. The dried powder was placed in a corundum crucible and placed in a tube furnace. Under a hydrogen-argon reducing atmosphere, the temperature was increased at 20°C / min to 1000°C and maintained for 2h. The temperature was then cooled at 2°C / min to 500°C and maintained for 12h. After natural cooling, carbon-supported highly ordered body-centered cubic RuGa nanocrystals were obtained.

[0071] Depend on Figure 5 From the bright field transmission electron microscope images, it can be found that highly ordered body-centered cubic RuGa nanocrystals are evenly dispersed on the surface of the carbon black carrier, with an average particle size of about 6nm and no obvious agglomeration.

[0072] In a 1 mol / L potassium hydroxide solution containing 2000 ppm nitrate concentration, the carbon-supported highly ordered body-centered cubic RuGa nanocrystals have a maximum ammonia Faraday efficiency of up to 96%.

[0073] Example 3

[0074] 0.121g of anhydrous ruthenium chloride and 0.203g of gallium nitrate nonahydrate were added to 150mL of 1mol / L hydrochloric acid solution. Once completely dissolved, 0.4g of Black Pearl 2000 was added. After sonication for 2h, the mixture was stirred overnight to thoroughly mix the precursor and carbon black support. The mixed solution was then subjected to rotary evaporation to separate the solvent and dried to obtain a powdery mixture. The dried powder was placed in a corundum crucible and placed in a tube furnace. Under a hydrogen-argon reducing atmosphere, the temperature was increased at 30°C / min to 1100°C and maintained for 10h. The mixture was then cooled at 5°C / min to 600°C and maintained for 6h. After natural cooling, highly ordered carbon-supported body-centered cubic RuGa nanocrystals were obtained.

[0075] Depend on Figure 6 From the bright field transmission electron microscope image, it can be found that highly ordered body-centered cubic RuGa nanocrystals are evenly dispersed on the surface of the carbon black carrier, with an average particle size of about 6.8nm and no obvious agglomeration.

[0076] In a 1 mol / L potassium hydroxide solution containing 2000 ppm nitrate concentration, the carbon-supported highly ordered body-centered cubic RuGa nanocrystals have a maximum ammonia Faraday efficiency of 95.3%.

[0077] Comparative Example 1

[0078] 0.205g of anhydrous ruthenium chloride was added to 150mL of 1mol / L hydrochloric acid solution. Once completely dissolved, 0.4g of Black Pearl 2000 was added. After ultrasonication for 2h, the mixture was stirred overnight to thoroughly mix the precursor and carbon black support. The mixed solution was then subjected to rotary evaporation to separate the solvent and dried to obtain a powdery mixture. The dried powder was placed in a corundum crucible and placed in a tube furnace. Under a hydrogen-argon reducing atmosphere, the temperature was increased at 10°C / min to 900°C and maintained for 4h. The temperature was then cooled at 10°C / min to 500°C and maintained for 4h. After natural cooling, carbon-supported close-packed hexagonal Ru nanocrystals were obtained.

[0079] Figure 7 Figure 2 is the X-ray diffraction pattern of the heat-treated product, from which it can be concluded that it is a typical close-packed hexagonal structure Ru nanocrystal (PDF#06-0663).

[0080] Depend on Figure 8 From the bright field transmission electron microscope images, it can be found that the close-packed hexagonal Ru nanocrystals are evenly dispersed on the surface of the carbon black carrier, with an average particle size of about 5.2 nm and no obvious agglomeration.

[0081] Depend on Figure 9 It can be seen from the dark field high-resolution transmission electron microscopy image in that the nanocrystals prepared in Comparative Example 1 have a clear Ru close-packed hexagonal structure.

[0082] Figure 10 The performance of the catalyst in a 1 mol / L potassium hydroxide solution containing a nitrate concentration of 2000 ppm is shown. As shown in the figure, the highest ammonia Faraday efficiency of the carbon-supported close-packed hexagonal Ru nanocrystals is about 91%.

[0083] Comparative Example 2

[0084] 0.101 g of anhydrous ruthenium chloride and 0.305 g of gallium nitrate nine hydrate were added to 150 mL of 1 mol / L hydrochloric acid solution, after complete dissolution, 0.4 g of Black Pearl 2000 was added, after ultrasonic treatment for 2 h, the mixture was stirred overnight to make the precursor and carbon black carrier fully mixed and uniform, then the mixed solution was dried by the conventional method to obtain a powdery mixture. The above dry powder was placed in a corundum crucible and put into a tube furnace, under a hydrogen-argon reducing atmosphere, the temperature was raised to 900℃ at a rate of 10℃ / min and kept for 4 h; then cooled to 500℃ at a rate of 10℃ / min and kept for 4 h, and then naturally cooled to obtain carbon-supported highly ordered body-centered cubic structure RuGa nanocrystals.

[0085] From the bright-field transmission electron microscopy images in Figure 11 It can be found that the highly ordered body-centered cubic structure RuGa nanocrystals are unevenly dispersed on the surface of the carbon black carrier, and the particle size distribution is large, from 5 nm to 20 nm

[0086] In a 1 mol / L potassium hydroxide solution containing 2000 ppm of nitrate, the highest ammonia Faraday efficiency of the carbon-supported highly ordered body-centered cubic structure RuGa nanocrystals is 89%.

[0087] Comparative Example 3

[0088] 0.101 g of anhydrous ruthenium chloride and 0.305 g of gallium nitrate nine hydrate were added to 150 mL of 1 mol / L hydrochloric acid solution, after complete dissolution, 0.4 g of Black Pearl 2000 was added, after ultrasonic treatment for 2 h, the mixture was stirred overnight to make the precursor and carbon black carrier fully mixed and uniform, then the mixed solution was dried by the conventional method to obtain a powdery mixture. The above dry powder was placed in a corundum crucible and put into a tube furnace, under a hydrogen-argon reducing atmosphere, the temperature was raised to 900℃ at a rate of 10℃ / min and kept for 4 h; then cooled to 500℃ at a rate of 10℃ / min and kept for 4 h, and then naturally cooled to obtain carbon-supported highly ordered body-centered cubic structure RuGa nanocrystals.

[0089] Figure 12 To prepare the X-ray diffraction pattern of the product, it is analyzed that the product is a typical body-centered cubic structure RuGa nanocrystal (PDF #65-9718), but several typical diffraction peaks do not appear (29.5°, 52.7° and 69.8°), and the order degree is poor.

[0090] In a 1 mol / L potassium hydroxide solution containing 2000 ppm of nitrate, the highest ammonia Faraday efficiency of the carbon-supported highly ordered body-centered cubic structure RuGa nanocrystals is 89%.

[0091] In summary, the embodiment of the present invention utilizes the impregnation-thermal reduction method to obtain carbon-supported highly ordered body-centered cubic structure RuGa nanocrystals with small particle size and uniform distribution by precisely controlling the drying process and regulating the calcination conditions. The preparation method provided by the present invention has a simple process and is convenient for large-scale commercial production, realizing its application in converting nitrate- or nitrite-containing wastewater into valuable ammonia. Carbon-supported RuGa nanocrystals exhibit a highly ordered body-centered cubic structure with isolated Ru sites, and can be directly used in an electrochemical nitrate or nitrite reduction ammonia production system at room temperature and pressure to achieve efficient electrocatalytic reduction of nitrate or nitrite to ammonia, with a Faraday efficiency greater than 97%.

[0092] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for preparing carbon-supported highly ordered body-centered cubic RuGa nanocrystals, characterized in that: Including steps: After adding ruthenium salt and gallium salt into hydrochloric acid solution and dissolving them, adding carbon support, ultrasonicating and stirring to obtain precursor suspension; The precursor suspension is evaporated to dryness to obtain a precursor powder; alloying and ordering the precursor powder in succession under a reducing atmosphere to obtain the carbon-supported highly ordered body-centered cubic RuGa nanocrystals; The molar ratio of the ruthenium salt to the gallium salt is 1:(1-3); The alloying conditions are: temperature of 900-1100°C, heating rate of 5-30°C / min, and holding time of 2-10h; the ordering conditions are: temperature of 400-600°C, cooling rate of 2-10°C / min, and holding time of 4-12h.

2. The method for preparing carbon-supported highly ordered body-centered cubic RuGa nanocrystals according to claim 1, characterized in that: The ruthenium salt is one or more of anhydrous ruthenium chloride, ruthenium acetate, carbonyl ruthenium, ruthenium acetylacetonate, and ammonium hexachlororuthenate; the gallium salt is one or more of gallium nitrate nonahydrate, gallium chloride, gallium sulfate, gallium acetate, and gallium acetylacetonate.

3. The method for preparing carbon-supported highly ordered body-centered cubic RuGa nanocrystals according to claim 1, characterized in that: The concentration of the hydrochloric acid solution is 0.5-2 mol / L.

4. The method for preparing carbon-supported highly ordered body-centered cubic RuGa nanocrystals according to claim 1, characterized in that: The carbon support is selected from one of carbon black Black Pearl 2000, carbon black Ketjenblack EC-600JD, carbon black Ketjenblack EC-300J, graphene, and carbon nanotubes.

5. The method for preparing carbon-supported highly ordered body-centered cubic RuGa nanocrystals according to claim 1, characterized in that: The reducing atmosphere is hydrogen or a mixture of hydrogen and argon.

6. A carbon-supported, highly ordered body-centered cubic RuGa nanocrystal, characterized in that: The RuGa nanocrystals are prepared by the method for preparing carbon-supported highly ordered body-centered cubic structure RuGa nanocrystals according to any one of claims 1 to 5.

7. The carbon-supported highly ordered body-centered cubic RuGa nanocrystal according to claim 6, characterized in that: The mass fraction of RuGa nanocrystals in the carbon-supported highly ordered body-centered cubic RuGa nanocrystals is 5-20wt%; and the size of the RuGa nanocrystals is less than 7nm.

8. Use of the carbon-supported highly ordered body-centered cubic RuGa nanocrystals according to claim 6 or 7 in electrocatalytic reduction of nitrate or nitrite to produce ammonia.

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