Plasma catalysis is gaining increasing interest for various gas conversion applications, such as CO₂ conversion into value-added chemicals and fuels, CH₄ activation into hydrogen, higher hydrocarbons or oxygenates, and NH₃ synthesis. Other applications are already more established, such as for air pollution control, e.g. volatile organic compound remediation, particulate matter and NO_x removal. In addition, plasma is also very promising for catalyst synthesis and treatment. Plasma catalysis clearly has benefits over ‘conventional’ catalysis, as outlined in the Introduction. However, a better insight into the underlying physical and chemical processes is crucial. This can be obtained by experiments applying diagnostics, studying both the chemical processes at the catalyst surface and the physicochemical mechanisms of plasma-catalyst interactions, as well as by computer modeling. The key challenge is to design cost-effective, highly active and stable catalysts tailored to the plasma environment. Therefore, insight from thermal catalysis as well as electro- and photocatalysis is crucial. All these aspects are covered in this Roadmap paper, written by specialists in their field, presenting the state-of-the-art, the current and future challenges, as well as the advances in science and technology needed to meet these challenges.

This review describes the history and development of ammonia synthesis from its discovery to the early development of the Haber–Bosch process to the current use of plasma catalysis as an alternative to the possible process decentralization of this essential commodity. Proposed reaction mechanisms to-date for vacuum and atmospheric pressure discharges are summarized and discussed. The use of different discharges and materials employed as catalysts as well as the observed interactions between the plasma and the catalyst that can modify and activate the catalytic surface and the possible effects of the catalyst on plasma are herein summarized. Moreover, important differences between thermal catalysis and plasma catalysis are contrasted. It is intended that this review can also help to develop an understanding of the current knowledge and gaps for the ammonia synthesis through plasma catalysis with an emphasis on the challenges presently faced.