Enhancement of Catalytic Activity Over the Iron-Modified Ce/TiO₂ Catalyst for Selective Catalytic Reduction of NOx with Ammonia

A series of iron-modified Ce/TiO 2 catalysts with different Fe/Ti molar ratios were prepared by an impregnation method and used for selective catalytic reaction (SCR) of NO x with NH 3 . The Fe–Ce/TiO 2 catalyst with a Fe/Ti molar ratio of 0.2 had good low-temperature activity and sulfur-poisoning resistance compared with the Ce/TiO 2 catalyst. The introduction of Fe could increase the amount of Ce 3+ and chemisorbed oxygen species on the catalyst surface and thereafter generate more ionic NH 4 + and in situ formed NO 2, respectively. In addition, the dispersion of cerium oxide could be improved by the addition of iron, and no visible phase of iron oxide could be observed at low Fe/Ti molar ratios (≤0.2). All of these factors played significant roles in the enhanced catalytic activity, especially the low-temperature activity. Furthermore, mechanisms of the SCR reaction and the SO 2 poisoning of the Fe(0.2)–Ce/TiO 2 catalyst were studied using in situ diffuse reflectance infrared Fourier transform spectroscopy. Coordinated NH 3 and ionic NH 4 + species as well as adsorbed NO 2 might be the key intermediates in the SCR reaction in the relatively low-temperature range. The formation of ammonium sulfate appeared to be the dominant cause for the catalyst deactivation in SO 2 -containing gases.