Characterization of Ceria’s Interaction with NOx and NH3

Ceria is a common component of engine aftertreatment catalysts due to its oxygen storage ability, its redox properties, and its role in stabilizing Pt against sintering. The interactions between ceria and NH 3 or NO x were investigated to better understand the role of ceria in oxidation reactions occurring over a diesel oxidation catalyst, in the reduction of NO x on lean NO x traps, and in the selective catalytic oxidation (SCO) of NH 3 . Ceria proved active in NO oxidation, selective catalytic reduction of NO by NH 3 (NH 3 –SCR), and NH 3 –SCO reactions. Between 100 and 450 °C, both NH 3 and NO x adsorbed on ceria simultaneously. In the absence of NO x, NH 3 was oxidized over CeO 2 forming N 2 via a two-step selective catalytic reduction mechanism at low temperature and NO x at high temperature. In the presence of NO x, NH 3 reacted with adsorbed NO x species, again forming N 2 at lower temperatures (250–450 °C), while at higher temperature, a significant portion of the NH 3 was oxidized, with product NO formed.