Mechanisms of N-2 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 N-2 desorption were obtained by calculations, both of which released more than 1,000 kJ/mol. The energy barrier of the rate-limiting step for N-2 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 x 10(11) s(-1) and 7.52 x 10(7) s(-1) at 1,400 K for the two foregoing reactions, respectively.