DFT Modeling of Reaction Mechanism and Ab Initio Microkinetics of Catalytic N₂O Decomposition over Alkaline Earth Oxides: From Molecular Orbital Picture Account to Simulation of Transient and Stationary Rate Profiles

A comprehensive molecular modeling of the reaction mechanism, complemented by ab initio microkinetic studies of the catalytic decomposition of N₂O on a series of the alkaline earth oxides (MgO, CaO, and SrO), was performed. The DFT level of theory was used to study the intimate mechanism of conceivable elementary steps of the deN₂O reaction over the terrace sites of the most stable (100) planes. The principal mechanistic events were thoroughly analyzed in terms of the frontier molecular orbital picture, and a multiple role of the anionic redox active centers constituted by surface O^2–_(surf) ions was revealed. The harmonic transition state theory along with the calculated free enthalpies of activation were used to model the reaction progress with the elementary step resolution in pulse (transient) and steady state regimes. For modeling the surface diffusion and recombination of the reaction key intermediates (peroxy groups), a Monte Carlo approach was applied to rationalize dioxygen formation along the static and dynamic routes. The developed kinetic scheme was able to reproduce the results of temperature-programmed surface reaction (TPSR) and isothermal steady state experiments with high accuracy without fitting any parameters. On the basis of obtained results, a complete molecular mechanistic description of the deN₂O reaction was proposed, resolving definitely the dependence of the particular elementary steps on the strength of anionic redox centers and their Lewis basicity.