Thulium modified MnO_x/TiO₂ catalyst for the low-temperature selective catalytic reduction of NO with ammonia

A new thulium (Tm) modified Mn/TiO₂ catalyst is firstly prepared to remove NO at low temperature, where the TiO₂ with relatively high specific surface area (184.3 m²/g) is used as carrier to support the active component MnO_x, and Tm is utilized as promoter to modify the MnO_x. The developed Tm–Mn/TiO₂ catalyst presents significantly improved selective catalytic reduction (SCR) de-NO_x performance at low temperature with NH₃ as reducing agent. It is found that after an appropriate content of Tm is introduced, the surface concentration of Mn⁴⁺, the chemical adsorbed oxygen, the chemisorption of NH₃ and NO, and the reducibility of the Tm–Mn/TiO₂ catalyst are improved, which are helpful to the enhancement of NH₃-SCR de-NO_x performance. Moreover, it is discovered that, over Tm–Mn/TiO₂ catalyst, an Eley-Rideal (E-R) mechanism occurs in the reaction between adsorbed NH₃ species connected by Lewis acid sites and gaseous NO, meanwhile, a Langmuir-Hinshelwood (L-H) mechanism occurs between adsorbed NH₃ species and adsorbed NO species, where the E-R mechanism dominates the NH₃-SCR de-NO_x process.