A simple redox model of low-T NO + CO adsorption onto Pd-CHA as effective Passive NOx Adsorbers

• Published in: Reaction chemistry & engineering 2024
• Main Authors: Iacobone, Umberto, Gjetja, Andrea, Usberti, Nicola, Nova, Isabella, Tronconi, Enrico, Bounechada, Djamela, Villamaina, Roberta, Ruggeri, Maria Pia, York, Andrew, Mantarosie, Loredana, Collier, Jillian
• Format: Article
• Language: English
• ISSN: 2058-9883; 2058-9883
• DOI: 10.1039/D4RE00324A

Pd-exchanged chabazite (Pd-CHA) catalysts show NO adsorption and desorption features which comply well with the requirements for low-T Passive NOx Adsorber (PNA) applications. An earlier work based on transient adsorption tests investigated the NO storage pathway on Pd-CHA, a still debated topic in the literature. Such research highlighted a Pd-redox mechanism (Pd2+ ↔ Pd+) underlying the NO storage chemistry over these systems. CO and NO were capable to reduce Pd2+ at low temperatures, and the newly formed Pd+ acted as the main NO storage site. Increasing temperatures activated a Pd-oxidation process, which reduced the fraction of Pd+ sites, and consequently the NO storage, but was inhibited by H2O. Herein we challenge quantitatively such a scheme relying on transient kinetic analysis. We show that a simple redox kinetic model of NO + CO storage on Pd-CHA, based on the above, reproduces the main features of the species evolution and of the NO storage observed under variable operating conditions over Pd-CHA samples with two Pd-loadings, thus lending support to the proposed Pd-redox chemistry.