Ammonia Synthesis via Nitrogen-Coupled Methane Conversion at Ambient Temperature and Plasma Conditions

Ammonia synthesis has been coupled with methane conversion under plasma conditions by using Fe–Al composite metal oxides as the catalyst. The process for ammonia production starting from natural gas is thus shortened, and meanwhile, C2 hydrocarbons are generated as a byproduct with high selectivity. In order to overcome the high barrier for the activation of methane and nitrogen, dielectric barrier discharge (DBD) technology is used to input high-quality energy into the reaction system. A thorough examination of the performance of quite a few 3d-metal oxides, SiO2, and Al2O3 has been done to screen out the cheap, promising elements for CH4–N2 coupled conversion. Based on these results, the Fe–Al composite metal oxide is selected as the catalyst and prepared by a hydrothermal method. Under the condition of SEI (specific energy input, kJ/L) = 12 kJ/L, CH4/N2 = 3:1, and an optimal Al–Fe ratio of 2:1, the ammonia concentration reaches 1185.86 ppm. Upon further optimization of the specific energy input and feed gas ratio, with CH4/N2 = 1:3 and SEI = 24 kJ/L, the highest ammonia concentration reaches 3534.32 ppm. The highest methane conversion rate was 15.71% when the SEI was 24 kJ/L and CH4/N2 = 1:5. The highest concentration of C2 products was 1.74% with CH4/N2 = 1:1 and SEI = 24 kJ/L. Under this condition, the selectivity of ethane, ethylene, acetylene, propane, and propylene was 52.83, 4.37, 2.71, 18.03, and 0.59%, respectively. The structure of the catalyst was characterized by XRD, XPS, TGA, and BET.