© 2016 The Royal Society of Chemistry. The reaction mechanism of nitric oxide (NO) reduction to nitrous oxide (N 2 O) and N 2 catalyzed by a Cr-phthalocyanine sheet (CrPc) was investigated using periodic density functional theory (DFT). The results show that direct NO dissociation on the catalyst is inhibited by a large energy barrier owing to the difficulty of direct cleavage of the strong NO bond. The dimer mechanism in which two NO molecules meet together is more preferred via three competitive mechanistic pathways consisting of two Langmuir-Hinshelwood (LH1 and LH2) and one Eley-Rideal (ER) mechanism. N 2 O is produced from LH1 and ER which have activation barriers (E a ) of 0.35 and 1.17 eV, respectively, while N 2 is a product from LH2 with an E a of 0.57 eV. All the three pathways are highly exothermic processes. Based on energetic aspects, LH1 is the kinetically and exothermically most favorable pathway (the E a of the rate-determining step is 0.35 eV). Therefore, we predict that NO can be easily reduced by CrPc under mild conditions. In an environmental application, CrPc would be a promising catalyst for the abatement of NO at low temperature.