Reaction Mechanism Revisited: Oxidation of Propylene on a Supported Palladium Catalyst

Achieving the complete oxidation of hydrocarbons in automobile exhaust requires a firm understanding of the reaction mechanisms. We investigated catalytic oxidation of C₃H₆ on Pd/La-Al₂O₃ as a model reaction using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) in combination with a transient method, i.e., modulation excitation spectroscopy. A conventional steady-state DRIFTS study demonstrated the formation of surface formate and acetate species, which have been considered to be reaction intermediate species. However, MES-DRIFTS overturned the previously considered mechanism and suggested an involvement of newly discovered acyl species as a potential intermediate species.