Mechanisms of N2 desorption from NO heterogeneous reduction on char surface were investigated by molecular modeling using density functional theory. All geometric optimization and single point energy calculations were performed at B3LYP/6-31G(d) level. Adsorption of NO on a char surface was a strongly exothermic process. Two different reaction pathways for N2 desorption were obtained by calculations, both of which released more than 1,000 kJ/mol. The energy barrier of the rate-limiting step for N2 desorption was 95 kJ/mol by reaction of surface carbon-nitrogen species with another NO molecule and was 205 kJ/mol by combination of two neighboring surface carbon-nitrogen species. The forward reaction rate of each intermediate reaction was calculated employing conventional transition state theory. Predicted rate constants of rate-limiting steps were 3.17 × 1011 s−1 and 7.52 × 107 s−1 at 1,400 K for the two foregoing reactions, respectively.