Insights on cold plasma ammonia synthesis and decomposition using alkaline earth metal-based perovskites

Abstract

The synergistic combination of solid catalysts and plasma for the synthesis of ammonia has recently attracted considerable scientific interest. Herein, we explore MgTiO₃, CaTiO₃, SrTiO₃, and BaTiO₃ perovskites as effective catalysts for the synthesis and decomposition of ammonia via cold plasma. MgTiO₃ perovskite, which contains the most electronegative alkaline metal of all the studied perovskites, resulted in the highest ammonia synthesis rate with a value of 12.16 μmol min⁻¹ m⁻², which is around 50 times the value of only plasma, 0.24 μmol min⁻¹. The high electronegativity of Mg can be assisting the dissociation of the triple nitrogen covalent bond. This intrinsic property of Mg perovskite added to the homogeneity of the plasma arising from the dielectric constant value of this perovskite might be synergistically responsible for the high ammonia synthesis rate observed. Interestingly, ammonia production over MgTiO₃ perovskite is almost double the performance of traditional oxides and some microporous crystals. We also explored the ammonia decomposition reaction due to the possibility of the importance of the reversible reaction owing to the electron collision with the ammonia molecules formed. Ammonia decomposition increased as plasma power increased. This points out the benefit of running at low plasma power and the need to design plasma reactors where the newly formed ammonia molecules can be removed from the reaction system to avoid further electron collision. The highest ammonia decomposition yield was 44.37% at 20 W corresponding to an energy yield of 5.06 g-NH₃ kW h⁻¹.