New Insights on the Release and Reduction of NOx Stored over PGM-Based LNT Catalysts

In this work, we have investigated the release and reduction of NOx (nitrates) stored on Rh–Ba/Al2O3 and Pt–Rh–Ba/Al2O3 catalysts and compared with Pt–Ba/Al2O3. It is shown that the release occurs at the interface between the PGM sites and the storage sites, can be probed by isotopic exchange experiments and is governed by the rate of oxygen removal from the metallic PGM sites. Accordingly the presence of a reductant, that keeps the PGM sites in a reduced state by scavenging oxygen adatoms formed upon nitrate decomposition, greatly favors the release of NO and its subsequent reduction. In these steps, not much differences have been observed considering either Pt- or Rh-based samples.