On the mechanism for the plasma-activated N₂ dissociation on Ru surfaces

Plasma-activation of N2 via vibrational excitations or electronic excitations enhances the dissociative sticking probability on Ru-surfaces with respect to ground-state N2. We propose that this is primarily due to a weaker nitrogen-nitrogen bond, facilitating direct adsorption of both nitrogen atoms on the metallic surface, a pathway with a high barrier for ground-state N2 due to the short bond distance of 110 pm. Furthermore, we show that the increased sticking probability is not only a heating artefact, as the activation barrier for N2 dissociation decreases upon plasma-activation. Recent modelling studies show that the binding strengths of surface adsorbates, as well as the barrier for dissociation may change as a result of high electric fields, as well as high degrees of charging metal particles. We show that the effect of plasma-induced electric fields is negligible in dielectric barrier discharge reactors, and other non-thermal plasma reactors. The effect of alkali promoters on the local electric fields is orders of magnitude larger than the electric field of the plasma. The role of plasma-induced metal surface charging during N2 dissociation is currently not known for metal clusters on a support.