Abstract
Pd-loaded CHA zeolites (e.g., Pd-SSZ-13) have been identified as a promising candidate for passive NO (x) adsorption (PNA) in low-temperature environments. The inclusion of lubricant oil additives or biofuels in automotive exhaust after-treatment systems subjects Pd-SSZ-13 to chemical poisoning from contaminants such as alkali metals (e.g., Na and K). In this study, we present a straightforward yet highly effective approach to regenerate Pd-SSZ-13 that has been poisoned by alkali metals, achieved through washing with a dilute NH(4)Cl solution. The underlying mechanisms of both poisoning and regeneration were thoroughly explored, revealing that the deactivation due to alkali-metal poisoning is primarily attributed to the transformation of the active Pd(2+) ion into PdO (x) and a concomitant reduction in Brønsted acid sites. The NH(4)Cl washing not only removes alkali metal contaminants, thereby restoring the Brønsted acid sites previously occupied by them, but also converts the inert PdO (x) back into their active states (i.e., isolated Pd(2+)). This investigation unveils a simplified yet highly efficient NH(4)Cl washing technique for the regeneration of the deactivated Pd-SSZ-13, offering profound implications for extending the catalyst's lifespan and enhancing its performance in cold-start exhaust after-treatment applications.