Condition‐dependent NO_x adsorption/desorption over Pd/BEA: A combined microreactor and in situ DRIFTS study

Abstract

Pd/BEA is chosen as a model passive NOx adsorber (PNA) to elucidate the effect of the feed gas composition on the NOx adsorption/desorption behavior. The Brønsted acid and the partially hydrolyzed framework Al (P‐HAl(OH)) sites in HBEA adsorb NO and NO2 under dry conditions. Moreover, the performance of HBEA is not affected by CO, while CO inhibits nitrate formation and promotes NO adsorption via the Pd(NO)(CO) complexes formation over Pd/BEA. H2O inhibits NO adsorption over the Brønsted acid and P‐HAl(OH) sites, and ionic Pd is the only active site for NOx adsorption under wet conditions. Furthermore, NO adsorption over hydrated Pd (Pd2+(OH)(NO)(H2O)3) is weaker than NO adsorption over bare ionic Pd (Z2[Pd2+(NO)], Z[Pd2+(OH)(NO)]). Dehydration of Pd2+(OH)(NO)(H2O)3 forms more stable Z[Pd2+(OH)(NO)] during desorption. The NO adsorption capacity of Pd/BEA improves in the presence of CO under both dry and wet conditions by forming a stable carbonyl–nitrosyl complex.