Computational and Experimental Investigations into N2O Decomposition over MgO Nanocrystals from Thorough Molecular Mechanism to ab initio Microkinetics

Abstract

In this article a comprehensive molecular modeling of the reaction mechanism complemented by ab initio microkinetic modeling of the catalytic decomposition of N2O on MgO nanocrystals is discussed. The density functional level of theory was used to study the molecular mechanism of conceivable elementary steps of the deN2O reaction over the most stable (100) surface, including the effect of surface morphology. It is shown that terrace sites are responsible for steady state reactivity, whereas the more basic and reactive sites located on edges and corners are involved only in the initial stages of the reaction because of poisoning. Detailed analysis of the reaction progress in terms of the energy profiles and the evolution of partial charges and bond orders for each step allowed for an in-depth insight at the atomic scale into the nature of the catalytic N2O decomposition over anionic redox active sites constituted by surface O2– ions. The harmonic transition state theory along with the calculated free enthalpies of activation were used to model the reaction progress in pulse (transient) and steady state regimes as well as to predict the kinetic isotopic effects (KIE) for 15N and 18O labeled reactants. The proposed kinetic scheme was able to reproduce the results of temperature-programmed surface reaction and KIE experiments with high accuracy without fitting of any parameters.