Pillared Clays as Superior Catalysts for Selective Catalytic Reduction of NO with NH₃

Five pillared clays (PILC) have been synthesized and tested for their activities in the selective catalytic reduction (SCR) of NO by NH₃ in the temperature range 250-450 °C. They all showed considerable activities, in the decreasing order Cr₂O₃-PILC, Fe₂O₃-PILC, TiO₂-PILC, ZrO₂-PILC, and Al₂-O₃-PILC. Cr₂O₃-PILC exhibited higher activities than a “commercial” (VTT) WO₃-V₂O₅/TiO₂ catalyst, but its activity was severely decreased by SO₂. Fe₂O₃-PILC showed activities comparable to that of V₂O₅/TiO₂ and was SO₂ resistant. Doping with cerium oxide significantly enhanced the activity; for Fe₂O₃-PILC, doping with 1.5-2% CeO₂ more than doubled its activity, and the resulting activity was significantly higher than that of the VTT commercial catalyst (both with and without SO₂ and H₂O). The formed PILC catalysts will have a bimodal pore structure, with which a superior poison resistance has been demonstrated in SCR operations with a V₂Os-based catalyst. Thus, the high activities and the potential poison resistance make pillared clays a promising new class of catalysts for SCR applications.