New Insights into NO−Carbon and N2O−Carbon Reactions from Quantum Mechanical Calculations

Abstract

Density functional theory calculations were used to investigate the mechanisms of NO−carbon and N2O−carbon reactions. It was the first time that the importance of surface nitrogen groups was addressed in the kinetic behaviors of the NO−carbon reaction. It was found that the off-plane nitrogen groups that are adjacent to the zigzag edge sites and in-plane nitrogen groups that are located on the armchair sites make the bond energy of oxygen desorption even ca. 20% lower than that of the off-plane epoxy group adjacent to zigzag edge sites and in-plane o-quinone oxygen atoms on armchair sites; this may explain the reason why the experimentally obtained activation energy of the NO−carbon reaction is ca. 20% lower than that of the O2−carbon reaction over 923 K. A higher ratio of oxygen atoms can be formed in the N2O−carbon reaction, because of the lower dissociation energy of N2O, which results in a higher ratio of off-plane epoxy oxygen atoms. The desorption energy of semiquinone with double adjacent off-plane oxygen groups is ca. 20% less than that of semiquinone with only one adjacent off-plane oxygen group. This may be the reason why the activation energy of N2O is also ca. 20% less than that of the O2−carbon reaction. The new mechanism can also provide a good qualitative comparison for the relative reaction rates of NO−, N2O−, and O2−carbon reactions. The anisotropic characters of these gas−carbon reactions can also be well explained.