Mechanism of the selective catalytic reduction of NO x with NH 3 over environmental-friendly iron titanate catalyst

Abstract

The reaction mechanism of the selective catalytic reduction (SCR) of NO x with NH 3 over environmental-friendly iron titanate catalyst (FeTiO x ) was investigated in detail. Over the iron titanate crystallite with specific Fe–O–Ti structure, both Brønsted and Lewis acid sites were present and involved in the SCR reaction. NH 3 mainly adsorbed on titanium sites in the form of ionic NH 4 + and coordinated NH 3, while NO x mainly adsorbed on iron sites in the form of monodentate nitrate. In a relatively low temperature range (<200 °C), the SCR process mainly followed the Langmuir–Hinshelwood (L–H) mechanism, in which the formation of monodentate nitrate from NO oxidation by O 2 over Fe 3+ was the rate-determining step. In contrast, in a relatively high temperature range (>200 °C), the SCR process mainly followed the Eley-Rideal (E–R) mechanism, in which the formation of NH 2NO intermediate species following the H-abstraction of NH 3 by neighboring Fe 3+ was the rate-determining step.