Bond Order Conservation Strategies in Catalysis Applied to the NH3 Decomposition Reaction

On the basis of an extensive set of density functional theory calculations, it is shown that a simple scheme provides a fundamental understanding of variations in the transition state energies and structures of reaction intermediates on transition metal surfaces across the periodic table. The scheme is built on the bond order conservation principle and requires a limited set of input data, still achieving transition state energies as a function of simple descriptors with an error smaller than those of approaches based on linear fits to a set of calculated transition state energies. We have applied this approach together with linear scaling of adsorption energies to obtain the energetics of the NH3 decomposition reaction on a series of stepped fcc(211) transition metal surfaces. This information is used to establish a microkinetic model for the formation of N-2 and H-2, thus providing insight into the components of the reaction that determines the activity.