Influence of hydrocarbon chemisorption on the NOx adspecies over supported noble-metal catalysts

In situ and time-resolved DRIFT methods were used to monitor the change in NOx adspecies on Pt(1%)–TiO2 and Rh(1%)–TiO2 catalysts during interaction with propene with the aim to determine whether or not propene chemisorption and interaction with the catalyst induces a change in the nature of the NOx adspecies prior to their reduction. The nature of NOx adspecies produced by interaction of the NO+O2/He feed with the catalyst is different on Pt- and Rh–TiO2 (in the Pt–TiO2 catalyst the IR more intense adspecies are nitrate, while in the Rh–TiO2 catalyst nitrosyl species are the IR more intense), but modification of the nature of the adspecies prior to their conversion is observed in both cases. The interpretation of the data provides indication about the nature of the reactive NOx species and the presence of multiple pathways in the mechanism of their conversion.