Comprehensive study of the promotional mechanism of F on Ce–Mo/TiO2 catalysts for wide temperature NH3-SCR performance: the activation of surface Ti–F bonds

Abstract

CeTiO_x, CeFTiO_x, CeMoTiO_x and CeFMoTiO_x catalysts were prepared by solvothermal synthesis, and the effect of element doping on the structures, chemical properties and SCR reactivity of the catalysts has been investigated by experimental analysis and density functional theory (DFT) calculations. The selective catalytic reduction (SCR) performance, operation window, H₂O/SO₂ durability and airspeed resistance of the CeFMoTiO_x catalyst were notably improved or optimized via the simultaneous introduction of fluorine and molybdenum. The CeFMoTiO_x catalyst presented satisfactory SCR performance by employing the advantages of inorganic element F and transition metal element Mo, which could increase the trapping sites and oxygen vacancies and enhance the synergistic interaction among metal oxide particles. Moreover, it was verified that O_α was generated except for the transformation between Ce⁴⁺ and Ce³⁺, and released from F⁻ species instead of O₂⁻ into the lattice of TiO₂ during the resistance SO₂ test at 300 °C, which was favorable for the SCR reaction. Significantly, the internal electron transfer function between metal oxides and oxygen vacancies, as well as the activation of surface Ti–F bonds played important roles in the process of SCR operation.