Metal porphyrins (M = Ti, Fe, Co, Ni, Cu, or Zn) as potential catalysts for the oxidation of CO by NO: insight from DFT calculations

The oxidation of CO by N 2 O over M-porphyrin (M = Ti, Fe, Co, Ni, Cu, and Zn) catalysts has been investigated via density functional theory calculations. The whole reaction process is divided into two steps: the catalytic decomposition of N 2 O that breaks the N-O bond resulting in O-M active species, and the carbon atoms of the CO molecule reaction with O-M to form CO 2 . For the rate-controlled step of the reaction, the porphyrins of different metal centers appear in different positions. The barrier height of N 2 O decomposition on Ti-porphyrin is 3.8 kcal mol −1 , and the barrier height of CO oxidation is 21.9 kcal mol −1 . The rate-controlled step appears in the process of oxidation of CO. However, for Fe-porphyrin, the barrier height of N 2 O decomposition is 24.2 kcal mol −1 , and the barrier height of CO oxidation is 11.4 kcal mol −1 . The rate-controlled step appears in the process of N 2 O decomposition. For the catalytic decomposition of N 2 O, the Ti-porphyrin has a low activation energy barrier, which may be due to the smaller gap between the highest occupied molecular orbital (HOMO) of the metal porphyrin and the lowest unoccupied molecular orbital (LUMO) of N 2 O for Tiporphyrin compared to Fe-porphyrin. A highly active metal porphyrin catalyst for the treatment of harmful CO and N 2 O into N 2 and CO 2 was theoretically screened by DFT calculation.