Synergistic Effect of Co–Ni Bimetal on Plasma Catalytic Ammonia Synthesis

Plasma synthesis of ammonia is a potential and sustainable way of nitrogen fixation. In this work, a series of M/Al 2 O 3 (M =Co, Ni, Co–Ni) catalysts have been investigated to enhance the synthesis of NH 3 from N 2 and H 2 in a dielectric barrier discharge (DBD) plasma reactor. Under the conditions of a volume ratio of N 2 :H 2 of 1:1, a total gas flow rate of 200 mL min −1 , and a discharge temperature of 200 °C, the order of the ammonia synthesis rate filled with different catalysts was Co–Ni/Al 2 O 3 > Co/Al 2 O 3 > Ni/Al 2 O 3 > Al 2 O 3 > only plasma. And the highest ammonia synthesis rate could be obtained was 1500 μmol g −1 h −1 by using Co–Ni/Al 2 O 3 as the catalyst. Further research found that compared with single metal catalysis, on the one hand, the presence of Co–Ni bimetal reduced the total amount and strength of acidic sites on the catalyst surface, which is beneficial for the desorption of synthesized ammonia gas. On the other hand, the presence of Co–Ni bimetal enhanced the plasma discharge observed by the ICCD camera. At the same time, the electrical characterization was found changed with different catalysts added in the plasma synthesis process. Adding a Co–Ni bimetal loaded catalyst in the reaction system increased the average electric field (E) and improved the power efficiency.