Research On The Technology Of Green Synthetic Ammonia Under Ambient Conditions

Ammonia（NH₃）is a very important chemical product,which is widely used in agriculture,industry,and other fields.More than 80%of produced NH₃is primarily used for chemical fertilizers,and more than half of agriculture depends on NH₃based fertilizers to increase production.In addition,NH₃is also an excellent carbon-free energy carrier due to its high energy density,easy liquefaction,convenient storage,and transportation.Today,industrial ammonia synthesis still adopts Haber-Bosch（HB）process.About 96%of the raw material H₂comes from fossil fuels and produces a large number of greenhouse gases.It is of great significance to develop a new green and low-carbon method under more reasonable and mild conditions,and use renewable electricity to convert water（instead of high-purity hydrogen）and N₂or air into ammonia to replace the HB process with high energy consumption and high carbon emission.This paper studies the green synthetic ammonia technology under ambient conditions from the following two aspects.（1）Given the complex preparation of catalysts for electrocatalytic ammonia synthesis,iron-based catalysts were in-situ prepared at room temperature and pressure to realize electrocatalytic N₂reduction to NH₃.An iron-based catalyst was in-situ prepared from Fe SO₄solution by using a three-electrode system and copper foam as working electrodes,and the electrochemical synthesis of ammonia was tested.The reaction product was detected by indophenol blue spectrophotometry,the content of ammonia was determined,and the yield of NH₃and Faraday efficiency were calculated.XRD,XPS,SEM,HRTEM,and other methods were used to characterize the catalyst on the surface of the working electrode.It was proved that the main component of the iron-based catalyst was Fe（0）,the morphology was lamellar structure,and the intersecting nano lamellar shape provided a large specific surface area.With the voltage of-1.0 V vs.SCE and 0.3 M Fe SO₄solution,the highest ammonia yield was 823 mg·h^-1·m^-2and the corresponding Faraday efficiency was 3.27%.This convenient,environment-friendly,and continuous method eliminates the cumbersome catalyst synthesis steps and provides a new idea for the industrial application of electrochemical ammonia synthesis.（2）Due to the competition of hydrogen evolution reaction,the Faraday efficiency of electrochemical synthesis of NH₃in the water system was still low.This work explores a lithium-mediated green ammonia synthesis technology,which includes three steps:nitridation of Li⁺,hydrolysis of Li₃N,and electrolysis of lithium salt.Ammonia synthesis at room temperature and pressure was realized by using N₂and H₂O as raw materials mediated by Li⁺.Lithium-mediated technology separates the charging and hydrogenation of nitrogen molecules in the process of electrocatalytic ammonia synthesis,completely avoids the competition of hydrogen evolution reaction,and obtains excellent efficiency and selectivity.The total current efficiency can reach 68.16%.The lithium-mediated technology provides a new way to improve the selectivity of electrochemical ammonia synthesis.