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Reaction mechanism of nitrous oxide(N2O)decomposition to N2 and O2 catalyzed by oxotitanium(IV)porphyrin(TiO-por)photoassisted condition in the presence of water interface was investigated by density functional theory(DFT).The entire reaction mechanism was divided into four elementary steps.Firstly,water dissociation to produce Ti(OH)2-por active site,it requires 23.17 kcal/mol for activation barrier.Then,the first N2O decomposes over the Ti(OH)2-por,the dissociation of N-O bond is the rate determining step by requiring activation barrier of 27.29 kcal/mol.Next,there are two alternative routes; Path A: N2O decomposition followed by H2O desorption or Path B: H2O desorption firstly and then the N2O decomposition.Based on the activation energies,Path B is a favorable route,due to an exothermic process for the H2O releasing from TiOH(OOH)-por catalyst intermediates(activation energy-4.8 kcal/mol),and the second N2O decomposition over the TiO2-por requiring lower activation barrier for 17.19 kcal/mol as compared to its decomposition in Path A.At the last step of O2 desorption which is the key reaction step for catalyst regeneration,its activation barrier is less than 1 kcal/mol since the unstable four memberedring structure in the TiO3-porphyrin intermediate.Remarkably,the O2 molecule desorption from the surface catalyst is easy process by requiring desorption energy only 3.40 kcal/mol.Therefore,based on the theoretical activation energies,the N2O decomposition doesnt inhibit by the water interface over the active site TiO-por and the TiO-por is theoretically purposed as candidate photocatalytic N2O decomposition.