Mechanism of the selective catalytic reduction of NO _x with NH₃ over W-doped Fe/TiO₂ catalyst

Abstract

The W-doped Fe/TiO₂ catalyst prepared by an impregnation method exhibited a good NH₃-selective catalytic reduction(SCR) activity and N₂ 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 2NH₃+NO+NO₂→2N₂+3H₂O. 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 °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 °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.

Keywords

Selective catalytic reduction / Iron / Tungsten / Reaction mechanism

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