Mechanistic insights and application potentials for CeO2-Al2O3 passive NOx adsorber (PNA) materials

Abstract

A series of CeO2/Al2O3 with Ce loading from 0.5 to 5.0 wt% were studied as PNA materials for low temperature NOx abatement. Via XRD, TEM imaging and UV–vis spectroscopy studies, it was demonstrated that CeO2 is present as nanoparticles on the Al2O3 support, and the particle size increases with increasing Ce loading. PNA performance of these materials was investigated by NOx trapping followed by TPD. The PNA chemistry was further probed with in situ NO-DRIFT spectroscopy. PNA chemistry involves a rapid direct NO trapping route that leads to surface nitrite formation, and a slower NO2 trapping route that leads to surface nitrate species. Surface nitrite decomposition releases NO at 200–300 °C, suitable for PNA application. Based on NO yields during TPD, the atomic efficiency of surface Ce was calculated, which demonstrates that dispersing CeO2 on high surface area supports is a viable strategy for improving PNA efficiency of CeO2-based materials.