Mechanistic aspects of the release and the reduction of NOx stored on Pt–Ba/Al2O3

• The NOx release is not driven by the ads–des equilibrium of stored NOx.
• 15NO isotopic exchange allows decoupling NOx release from its further reduction.
• 15NO isotopic exchange is catalyzed by Pt.
• Reduced Pt sites activate stored NOx that are destabilized and released as NO.

The release and reduction of NOx stored on Pt–Ba/Al2O3 is here investigated under nearly isothermal conditions. It is shown that the release driven by adsorption–desorption equilibrium of stored NOx is negligible. It is also shown that NO isotopic exchange between stored 14NOx and 15NO in absence of O2, which implies the release of stored NOx and has the potential to decouple NOx release from its further reduction, is catalyzed by Pt and is observed from temperatures well below that of the NOx thermal desorption. It is suggested that reduced Pt sites activate stored NOx that are destabilized and eventually released as NOx in the gas phase or adsorbed onto Pt. Therefore, under nearly isothermal conditions, the NOx release is a chemical reaction catalyzed by Pt occurring at the Pt/Ba interface. In the presence of reductants, the release of stored NOx and its further reduction cannot be decoupled. The higher is the reducing power the more effective is the reduction of Pt and activation of stored NOx by metal Pt that represent the first step of release and reduction of stored NOx.

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