A novel material for passive NO adsorber: Ce-based BEA zeolite

Passive NOx adsorbers (PNAs) were proposed to address the NOx emissions during the cold start phase. Here we show a novel Ce-based BEA zeolite, as a noble-metal-free passive NOx adsorber. The NOx adsorption capacity of Ce/BEA reaches 36 μmol/g in the feed gas close to realistic exhaust conditions, and the NOx desorption temperature, which is around 290 °C, is ideal for diesel exhaust after-treatment systems. Ce/BEA also behaves notable stability of high temperature CO exposure conditions. Multiple characterizations were performed to explore the NOx adsorption chemistry of Ce/BEA. The Ce(Ⅳ) species in the BEA zeolite serves as the active center for NOx adsorption. The bidentate nitrate species is responsible for the observed NOx storage capacity, and the active oxygen around Ce(Ⅳ) plays a critical role in its formation. Considering the significantly better cost efficiency of Ce compared to Pd, Ce/BEA presents an enormous potential for the PNA applications and provides a novel formulation for the noble-metal choice of PNA materials.