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.

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