Synergistic Effect Of Dielectric Barrier Discharge Plasma Catalytic Ammonia Synthesis

Ammonia（NH₃）is one of the most important chemicals in modern society.In industry,the Haber-Bosch method is used to synthesize ammonia,which has harsh reaction conditions,high energy consumption and a large amount of greenhouse gas emissions.Non-thermal plasma technology offers a potential route for ammonia synthesis.In addition,the combination of plasma and catalyst can greatly improve the ammonia synthesis rate and energy yield.Therefore,the selection of suitable catalysts and the exploration of the synergistic effect between plasma and catalyst will play a very important role in guiding the plasma synergistic catalytic synthesis of ammonia.This work firstly investigated the research progress of low temperature plasma synthesis of ammonia.In this regard,applying plasma technology,in a coaxial packed-bed DBD plasma reactor designed by our team,H₂ and N₂ were used as raw materials to carry out research work related to ammonia synthesis.The content and main research conclusions of this work are as follows:（1）The effect of different reaction conditions on the synthesis of ammonia was investigated by using transition metal supported on alumina as catalyst（M/Al₂O₃,M=Co,Ni,Co-Ni）.The results show that when the volume ratio of N₂:H₂ is 1:1,the total gas flow rate is 200 m L·min^-1,and the discharge temperature is 200℃,the sequence of ammonia synthesis rate under different catalytic conditions is:Co-Ni/Al₂O₃>Co/Al₂O₃>Ni/Al₂O₃>Al₂O₃>plasma only,and the ammonia synthesis rate can reach up to 1500μmol·g^-1·h^-1 when the Co-Ni/Al₂O₃ catalyst is filled.Further research found that,compared with single-metal catalysis,the presence of Co-Ni bimetal on the one hand reduced the number and strength of acid sites on the catalyst surface,which was conducive to the timely desorption of synthesized ammonia from the catalyst surface.On the other hand,the presence of the Co-Ni bimetal enhanced the plasma discharge as observed by the ICCD camera.At the same time,adding different catalysts into the reaction system will affect the electrical properties of the plasma discharge.Among them,the catalyst loaded with Co-Ni bimetal was added to the reaction,which improved the average electric field（E）and power efficiency.（2）Co-Ni bimetals were supported on different supports as catalysts（Co-Ni/MOF-74,Co-Ni/MCM-41,MCM-41,Co-Ni/Al₂O₃ and Al₂O₃）for the reaction.The effects of catalytic conditions,temperature,specific energy input,N₂:H₂ volume ratio and other factors on the rate of ammonia synthesis and energy yield were systematically studied.It was found that compared with conventional catalysts,the developed Co-Ni/MOF-74 can enhance the plasma discharge and has the advantages of large specific surface area and abundant pore structure which promotes the transfer of active particles during the reaction process.It has high catalytic activity and is an ideal catalyst.When the volume ratio of N₂:H₂ is 1:1,the specific energy input is 33.27 k J·L^-1,and the discharge temperature is 200℃,the highest ammonia synthesis rate can be obtained as high as 2608.70μmol·g^-1·h^-1with Co-Ni/MOF-74 catalyst.In addition,it was proposed that the synergistic catalysis of DBD plasma for ammonia synthesis was carried out both in the gas phase and on the surface of the catalyst through the characterization of catalyst combined with the preliminary exploration of the plasma diagnosis.