Sol–Gel Pd Exhaust Catalysts and N2O Production

Abstract

Al2O3, CeO2–Al2O3, CeO2–Tb4O7–Al2O3 and ZrO2–Al2O3 supported Pd samples have been prepared by sol–gel methods. Extents and mechanisms of N2O production in CO–NO and CO–NO–O2 reactions on these have been considered. This occurs most selectively under oxidising (lean-burn) conditions or in the presence of CeO2 and CeO2–Tb4O7 promoters near the CO–NO light off temperature. Over Pd/ZrO2–Al2O3 the CO–NO reaction at 573 K has CO and NO conversions that are second order with respect to p CO and p NO. Over this catalyst NO conversion is faster than that of CO until O2(g) is added, causing CO conversion and N2O production at 573 K to rise simultaneously. CeO2 or CeO2–Tb4O7 incorporation into a Pd/Al2O3 catalyst enhances N2O production near the CO–NO light-off temperature in the absence of added O2 without CO conversion being raised. There is current attention on pollution control opportunities through lean-burn conditions, Pd catalysts and oxygen storage capacity enhancement. The present work suggests that their role in N2O production may need to be better understood and controlled. For the moment N2O formation provides a window on mechanisms of TWC operation.