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

•Ti4+ modified γ-Fe2O3 catalyst exhibited high catalytic activity and SO2/H2O resistance.•Solid solution structure as γ-Fe2O3 crystal phase formed after doping.•The reducibility of catalyst decreased, but both Lewis and Brönsted acid sites increased.•The rates of E-R and L-H mechanisms increased while that of C-O reaction decreased.

An environmental benign TiO2 doped maghemite catalyst, the γ-Fe95Ti5, was prepared via the precipitation microwave pyrolysis method for the NOx removal. The γ-Fe95Ti5 exhibited significantly higher catalytic activity and better N2 selectivity than the pure maghemite, γ-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 γ-Fe100Ti0, forming the partial solid solution on the catalyst surface, as γ-Fe2-ζTiζO3+ξ. This structure improves the quantity and stability of both Lewis and Brönsted acid sites compared with the γ-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 γ-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 γ-Fe100Ti0.

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