De-reducibility mechanism of titanium on maghemite catalysts for the SCR reaction: An in situ DRIFTS and quantitative kinetics study

An environmental benign TiO2 doped maghemite catalyst, the gamma-Fe95Ti5, was prepared via the precipitation microwave pyrolysis method for the NOx removal. The gamma-Fe95Ti5 exhibited significantly higher catalytic activity and better N-2 selectivity than the pure maghemite, gamma-Fe100Ti0. The SCR active window of the catalyst is broadened and the resistances to H2O and SO2 are also preserved. Ti4+ cations could enter the lattice of y-Fe100Ti0, forming the partial solid solution on the catalyst surface, as gamma-Fe2-zeta Ti zeta O3+xi. This structure improves the quantity and stability of both Lewis and Bronsted acid sites compared with the gamma-Fe100Ti0. Meanwhile, the dopant cations suppress the reduction of Fe3+ and the percentage of active oxygen on the catalyst surface. These could suppress the N2O formation from NH3 oxidation and NOx reduction. By the combination of both DRIFTS and kinetic methods, the rate constants of the gamma-Fe95Ti5 catalyst via the Eley-Rideal and Langmuir-Hinshelwood mechanisms increase simultaneously, while the rate constant via the catalytic oxidation of NH3 decreases compared with the gamma-Fe100Ti0.