Selective catalytic reduction of nitric oxide by ethylene in the presence of oxygen over Cu2+ ion-exchanged pillared clays

Cu2+ ion-exchanged pillared days are substantially more active than Cu2+-ZSM-5 for selective catalytic reduction (SCR) of NO by hydrocarbons. More importantly, H2O (or SO2) has only mild effects on their activities. First results on Cu2+-exchanged TiO2-pillared montmorillonite were reported by this laboratory (Yang and Li, Ref. [1]), that showed overall activities two to four times higher than Cu2+-ZSM-5. A delaminated pillared clay was subjected to Cu2+ ion-exchange and studied for SCR by C2H4 in this work. The Cu2+ ion-exchanged delaminated Al2O3-pillared clay yielded substantially higher SCR rates than both Cu2+-exchanged TiO2-pillared clay and Cu2+-ZSM-5 at temperatures above 400 degrees C. The peak NO conversion was 90% at 550 degrees C and at a space velocity of 15,000 h(-1) (with O-2 = 2%). The peak temperature decreased as the concentration of O-2 was increased. The macroporosity in the delaminated pillared clay was partially responsible for its higher peak temperatures (than that for laminated pillared clays). At 1000 ppm each for NO and C2H4, the NO conversion peaked at 2% O-2 for all temperatures. H2O and SO2 caused only mild deactivation, likely due to competitive adsorption (of SO2 on Cu2+ sites and H2O on acid sites). The high activity of Cu2+-exchanged Al2O3-pillared clay was due to a unique combination of the redox property of the Cu2+ sites and the strong Lewis acidity of the pillared clay. The suggested mechanism involved NO chemisorption (in the presence of O-2) on Cu2+-O-Al3+-on the pillars, and C2H4 activation on the Lewis acid sites to form an oxygenated species.