Vibrationally excited molecule-metal surface reactions in heterogeneous and plasma catalysis: going beyond the Fridman-Macheret α model.

Abstract

Vibrational excitation of reactants plays an important role in heterogeneous and plasma catalysis by increasing the reactivity of various rate-controlling steps. Therefore, state-of-the-art microkinetic models attempt to include this effect by modelling the change in reaction rate with the Fridman-Macheret α approach. Although this approach is ubiquitous in simulations of plasma catalysis, it is not well established how accurate it is. In this work, we evaluate the Fridman-Macheret α approach by comparing it to vibrational efficacies obtained with molecular dynamics simulations. Unfortunately, the agreement is extremely poor (R ² = -0.35), raising questions about the suitability of using this method in describing vibrationally excited dissociative chemisorption on metal surfaces, as is currently the norm in plasma catalysis. Furthermore, the approach lacks vibrational mode specificity. Instead, we propose an alternative model at comparable computational cost, which is fitted to theoretical vibrational efficacies obtained with molecular dynamics. Our model uses (1) the barrier height to dissociative chemisorption, (2) an indication of how "late" the barrier is, and (3) the overlap of vibrational modes and the reaction coordinate at the barrier. These three features lead to a considerable qualitative and quantitative (R ² = 0.52) improvement over the Fridman-Macheret α approach. Therefore, we advise to make use of our new model, since it can be readily plugged into existing microkinetic models for heterogeneous and plasma catalysis.