By
combining experimental measurements with <i>ab initio</i> molecular dynamics
simulations, we provide the first microscopic description of the interaction
between metal surfaces and a low-temperature nitrogen-hydrogen plasma. Our
study focuses on the dissociation of hydrogen and nitrogen as the main
activation route. We find that ammonia forms via an Eley-Rideal mechanism where
atomic nitrogen abstracts hydrogen from the catalyst surface to form ammonia on
an extremely short timescale (a few picoseconds). On copper, ammonia formation
occurs via the interaction between plasma-produced atomic nitrogen and the
H-terminated surface. On platinum, however, we find that surface saturation
with NH groups is necessary for ammonia production to occur. Regardless of the
metal surface, the reaction is limited by the mass transport of atomic
nitrogen, consistent with the weak dependence on catalyst material that we
observe and has been reported by several other groups. This study represents a significant
step towards achieving a mechanistic, microscopic-scale understanding of
catalytic processes activated in low-temperature plasma environments.
Energy loss and surface temperature effects in
ab initio
molecular dynamics simulations: N adsorption on Ag(111) as a case study
