Low-temperature selective catalytic reduction of NO with NH₃ over Ti_0.9M_0.1O_2-δ (M = Cr, Mn, Fe, Co, Cu)

Abstract

The catalysts, Ti_0.9M_0.1O_2-δ (M = Cr, Mn, Fe, Co, Cu), were synthesized in anatase phase by solution combustion. Selective catalytic reduction (SCR) of NO with NH₃ was investigated over these catalysts. The reaction occurred at the lowest temperature over Ti_0.9M_0.1O_2-δ, but the selectivity for N₂ was highest over Ti_0.9M_0.1O_2-δ. Therefore, both Mn and Fe were substituted in TiO₂ (Ti_0.9Mn_0.05Fe_0.05O_2-δ). The reaction occurred at low temperature with a high selectivity over this catalyst. In order to understand the reaction mechanism and the nature of the active sites, temperature programmed desorption (TPD) of NH₃ and hydrogen uptake studies were carried out. The relation between the Lewis acid sites and SCR window and the relation between Bronsted acid sites and low temperature was established. The order of the SCR reaction with respect to NO, NH₃, and O₂ was also investigated. It was also shown that the N₂ selectivity of the SCR reaction has a strong inverse correlation with the oxidation of ammonia.