ABSTRACT3+ -exchanged pillared clay is found to be the most active. The catalytic activity of Fe-TiO 2 -PILC could be further improved by the addition of a small amount of cerium ions or cerium oxide. H 2 O and SO 2 increase both the activity and the product selectivity to N 2 . The maximum activity on the Ce-Fe-TiO 2 -PILC is more than 3 times as active as that on a vanadium catalyst. Moreover, compared to the V 2 O 5 -WO 3 /TiO 2 catalyst, the Fe-TiO 2 -PILC catalysts show higher N 2 /N 2 O product selectivities and substantially lower activities (by ~85%) for SO 2 oxidation to SO 3 under the same reaction conditions. A 100-hr run in the presence of H 2 O and SO 2 for the CeO 2 /Fe-TiO 2 -PILC catalyst showed no decrease in activity. INTRODUCTIONSelective catalytic reduction (SCR) of nitrogen oxides (NO + NO 2 ) with NH 3 is of increasing commercial interest for stationary source applications. A large number of catalysts, such as V 2 O 5 -WO 3 (or MoO 3 )/TiO 2 , other transitionmetal oxides (e.g., Fe, Cr, Co, Ni, Cu, Nb), and doped catalysts, as well as zeolite-type catalysts (e.g., H-ZSM-5,

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