DRIFTS study of the role of alkaline earths in promoting the catalytic activity of HC and NOx conversion over Pd-only three-way catalysts

Abstract

To reveal the role of alkaline earths modification in promoting the catalytic activity of HC and NO_x conversion, catalytic activity tests and DRIFT experiments under different reaction conditions were performed. The introduction of alkaline earths promotes the catalytic activities of both HC and NO_x elimination under stoichiometric NO_x–CO–HC–O₂ conditions, especially for Pd/CZBa, whereas it inhibits CO oxidation. In addition, the operation window of NO_x conversion is also obviously widened as a result of enhanced NO_x storage ability. DRIFTS results demonstrate that modification with alkaline earths improves the formation rate of nitrites and nitrates due to enhanced electron transfer and oxygen mobility, as well as the dissociation of NO species on the active metal, which increases the storage ability and reduction performance of NO_x. On the other hand, the doping of alkaline earths could weaken the inhibiting effect arising from strongly bonded HC species on NO adsorption and dissociation due to the promoted catalytic activity of HC deep oxidation, which promotes the reaction of CO and NO_x at low temperature.