Abstract

This study investigates NO adsorption on Pd-exchanged chabazite (Pd/H-CHA), a promising passive NOx adsorber (PNA) for capturing cold-start NOx emissions of gasoline- and diesel-powered vehicles. Temperature-programed desorption (TPD) and IR spectroscopy are combined with theoretical calculations to elucidate how and where NO is stored, and how water and O₂ affect this process. NO adsorption on Pd/H-CHA produces two TPD features, around 423 and 753 K, and IR bands centered at 1860 and 1810 cm⁻¹. Calculated NO stretching frequencies and maximum-desorption temperatures reveal that Pd²⁺ and Pd⁺ sites are responsible for these low- and high-temperature features, respectively, and that while the IR feature at 1810 cm⁻¹ is due to NO adsorption on Pd⁺, the 1860 cm⁻¹ feature contains contributions from both weakly-bound NO on Pd²⁺ and more strongly bound NO on Pd⁺, consistent with experimentally observed effects of water and O₂.

Get Full Text