Fe3+-ion-exchanged delaminated pillared clays (PILCs) have been found previously to be more active than the vanadia-based catalysts for selective catalytic reduction (SCR) of NO by NH3. The effects of acid treatment of the clay (before pillaring) and base treatments of the TiO2-PILC (before ion exchange) on the activities of the Fe-TiO2-PILC catalysts were studied. It was found that the acid treatment increased the activity (by 33%), but the base treatments decreased the activity (although they increased the cation exchange capacity of the pillared clay and, hence, the Fe content). The activities of the catalysts were directly related to their surface Bronsted acidities as identified by FT-IR of chemisorbed NH3.