The catalysts, Ti0.9M0.1O2-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 Ti0.9Mn0.1O2-δ, but the selectivity for N2 was highest over Ti0.9Fe0.1O 2-δ. Therefore, both Mn and Fe were substituted in TiO 2 (Ti0.9Mn0.05Fe0.05O 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. © 2008 American Chemical Society.