In this proposal the reaction mechanism of N2O decomposition and oxidation of CO to CO2 over metal-catalysts such as metal-zeolites or metal-porphyrin catalysts will be studied with M06 functional. The obtained results will be compared with the sophisticated method namely second-order Møller-Plesset perturbation theory (MP2). This study would provide the understanding of the utilizing metal-catalysts for deducing the environmental toxic gases and may guide us for future development of catalysts for other toxic gases.