Two new pathways starting from a representative oxygen-containing char model are characterized to account for the role played by oxygen during NO-char interaction. The stable species and transition states present in the pathways are calculated at B3LYP/6-31G(d). One pathway provides theoretical evidence for the experimental hypothesis that the major reason for the enhancement is mainly due to the generated new active sites. The other clarifies the role of oxygen responsible for C(N) formation and interaction between NO and C(N). The highest energy barriers for both pathways are calculated to be similar to 200 kJ/mol, which may be accessible at the actual coal combustion system. The N-2 formation mechanisms suggested by Suuberg and Arana (1997) [46] and Tomita et al. (1998) [48] have been therefore improved with the combination of density functional theory (DFT) and the available experimental results. (C) 2016 The Combustion Institute. Published by Elsevier Inc. All rights reserved.