The Operating Cycle of NO Adsorption and Desorption in Pd-Chabazite for Passive NO Adsorbers.

Pd-doped chabazite (Pd/CHA) offers unique opportunities to adsorb and desorb NO in the target temperature range for application as a passive NO adsorber (PNA). The ability of Pd/CHA to trap NO emissions at low temperatures (<200 °C) is facilitated by the binding of NO species at various Pd sites available in the CHA framework. Density functional theory (DFT) simulations are performed to understand Pd speciation in CHA and the interaction of NO with Pd/CHA to explain the mechanisms of NO adsorption, oxidation, and desorption processes.