DRIFT Study of Manganese/Titania-Based Catalysts for Low-Temperature Selective Catalytic Reduction of NO with NH3

Abstract

Manganese oxides and iron-manganese oxides supported on TiO₂ were prepared by the sol−gel method and used for low-temperature selective catalytic reduction (SCR) of NO with NH₃. Base on the previous study, Mn(0.4)/TiO₂ and Fe(0.1)−Mn(0.4)/TiO₂ were then selected to carry out the in situ diffuse reflectance infrared transform spectroscopy (DRIFT) investigation for revealing the reaction mechanism. The DRIFT spectroscopy for the adsorption of NH₃ indicated the presence of coordinated NH₃ and NH₄⁺ on both of the two catalysts. When NO was introduced, the coordinated NH₃ on the catalyst surface was consumed rapidly, indicating these species could react with NO effectively. When NH₃ was introduced into the sample preadsorbed with NO + O₂, SCR reaction would not proceed on Mn(0.4)/TiO₂. However, for Fe(0.1)−Mn(0.4)/TiO₂ the bands due to coordinated NH₃ on Fe₂O₃ were formed. Simultaneously, the bidentate nitrates were transformed to monodentate nitrates and NH₄⁺ was detected. And NO₂ from the oxidation of NO on catalyst could react with NH₄⁺ leading to the reduction of NO. Therefore, it was suggested that the SCR reaction on Fe(0.1)−Mn(0.4)/TiO₂ could also take place in a different way from the reactions on Mn(0.4)/TiO₂ proposed by other researchers. Furthermore, the SCR reaction steps for these two kinds of catalysts were proposed.