Deactivation of Pd/SSZ-13 passive NOx adsorber from the perspectives of phosphorus poisoning and hydrothermal aging

Abstract

Phosphorus is one of the typical derivatives that cause irreversible deactivation of passive NOx adsorber (PNA). In this work, the deactivation effects of phosphorus on Pd/SSZ-13 were investigated in combination with hydrothermal aging treatment to gain deeper insights into phosphorus-induced deactivation. It was found that phosphorus decreased the porosity and acidity of Pd/SSZ-13 and the deactivation behavior mainly resulted from the decrease of active sites. Specifically, the isolated Pd sites (Pd2+ and [Pd(OH)]+) were poisoned by phosphorus species, leading to the transformation of isolated Pd sites to bulk PdO. After hydrothermal aging treatment, the phosphorus induced the extensive formation of AlPO4 that significantly accelerated the dealumination of zeolite framework, thus resulting in the decrease in activity and stability. Our work sheds light on the deactivation mechanism of Pd/SSZ-13 from the perspectives of phosphorus poisoning and hydrothermal aging, expecting to provide guidance on the design of Pd-based zeolites with high tolerance and high stability for cold-start application.