Mechanism of the Selective Catalytic Reduction of NOx with NH3 over W-Doped Fe/TiO2 Catalyst

The W-doped Fe/TiO2 catalyst prepared by an impregnation method exhibited a good NH3-selective catalytic reduction(SCR) activity and N-2 selectivity with broad operation temperature window. The interaction between Fe and W could increase the amount of surface chemisorbed oxygen, and thus enhances the low temperature SCR activity by facilitating the fast SCR of 2NH(3)+NO+NO2 -> 2N(2)+3H(2)O. The NH3-SCR reaction mechanism over the W-Fe/TiO2 was fully investigated via in situ diffuse reflectance infrared Fourier transform spectroscopy(in situ DRIFTS). In the low temperature range(<250 degrees C), the reactive surface species were mainly coordinated NH3, ionic NH4+ and adsorbed NO2 species, and the SCR mainly followed the Langmuir-Hinshelwood mechanism, during which the adsorbed NO2 species became the important active sites. In the high temperature range(>250 degrees C), the reactive surface species were mainly NH2, and the SCR mainly followed the Eley-Rideal mechanism, during which the formation of NH2NO intermediate species after H-abstraction of NH3 was the rate-determining step.