Ultra-stable Pd ions at Al T1/T2 sites on a dealuminated Pd/beta passive NOx adsorber

Pd ions as NO adsorbing sites on zeolites for PNA materials showed evident deactivation when exposed to reducing agents or treated under hydrothermal conditions. In this study, stable Pd2+ species are mainly obtained by loading palladium on a dealuminated beta zeolite, and can survive during cyclic evaluations with reducing agents and hydrothermal treatment at 850 degrees C. On the dealuminated beta zeolite, a large amount of framework Al T1/T2 is reserved by design. CO-DRIFTS and H-2-TPR results reveal that [Pd-OH] and isolated Pd(iso)(b) are mainly present on the dealuminated beta zeolite and are quite stable because of their higher energy. These [Pd-OH]/Pd(iso)(b) on the dealuminated beta zeolite contribute stable NOx storage performance. Al-27 MAS NMR suggests that the Al T1/T2 sites of PDB-F are more stable and the [Pd-OH]/Pd(iso)(b) simultaneously protects the occupied Al T1/T2 sites from being destroyed. NH3-TPD shows that [Pd-OH]/Pd(iso)(b) on the dealuminated beta zeolite contributes a more stable acid concentration after cycle evaluation or hydrothermal aging. Thus, the dealuminated Pd/beta materials, with ultra-stable Pd2+ species, can meet real exhaust conditions.