Density functional theory calculations, with corrections for London dispersion interactions, have here been used in studying the generation and decomposition of N2O through the heterogeneous reduction of NO on a biochar surface. The effect of K-decoration on this specific mechanism has also been investigated.The results show that there are two possible pathways for the generation and decomposition of N2O on the pristine char surface, depending on type of reaction site. In the formation stage of N2O, the reactions rates of the two pathways are remarkably similar. However, the activation energies of those pathways are different for the decomposition stage of N2O (166.75 kJ/mol and 117.51 kJ/mol respectively).Decoration by K does not change these original reaction pathways. However, it decreases the activation energy for the rate-determining step and, thus, increases the total reaction rate. The activation energy is reduced by 13 kJ/mol for the generation of N2O and the effect is even larger for the process of N2O decomposition. For this latter type of process, the K-induced activation energies for the two pathways are reduced by 97.69 kJ/mol and 48.45 kJ/mol in comparison to pristine char.Moreover, the reaction rates of the different reaction pathways were observed to gradually increase with an increase in temperature. In addition, the difference between the reaction rates for the pathway of the pristine char, and that of the K-decorated char, was found to decrease, which is most probably due to the sublimation of K atoms at higher temperatures.