Technical Challenges and Prospects in Sustainable Plasma Catalytic Ammonia Production from Methane and Nitrogen.

Ammonia is crucial for human life as an important ingredient for fertilizer, industrial and household chemicals, and is considered as a future fuel alternative and hydrogen storage molecule. There remain no viable alternatives to the energy-and capital-intensive Haber-Bosch (H-B) process. Efforts in the development of novel catalytic processes operated at milder conditions (low temperatures and ambient pressure), prominently electrochemistry and non-thermal plasma (NTP), and utilization of lower-cost H sources for ammonia formation than the ultrapure H2 have been witnessed in the last few years. Yet, limited progress from these routes has been made to date given unresolved low ammonia yield and technical challenges. Several rare works attempted to activate methane (CH4 ) and nitrogen (N2 ) by non-thermal plasma to produce ammonia and valued-added hydrocarbons have proven to be a promising research direction, rivalling the reaction between N2 and ultrapure H2 or water. The direct conversion of CH4 and N2 to ammonia is still at the beginning level, and it remains unclear that what extent these technologies must be improved to develop a commercial process. Toward this goal, this Perspective critiques current steps and miss-steps of sustainable plasma catalytic ammonia production from CH4 and N2 in terms of technology, plasma-catalyst synergy, mechanistic insights, and experimental protocols. We discuss mechanistic understandings of catalyst-promoted ammonia production and translate such discussions as well as key metrics achieved in the field into recommendations of feasible processes for ammonia and value-added hydrocarbons formation from CH4 and N2 .