Distinguishing between reaction intermediates and spectators: A kinetic study of acetone oxidation using ozone on a silica-supported manganese oxide catalyst

A detailed mechanistic study of acetone oxidation using ozone was performed on a 10 wt% silica-supported manganese oxide catalyst using in situ Raman spectroscopy. Two adsorbed intermediates were identified at reaction conditions: an acetone species with a band at 2930 cm−1 and an adsorbed peroxide species on the manganese oxide with a band at 890 cm−1. Quantitative temperature-programmed desorption measurements showed that the acetone species resided on the silica support, which thus acted as a noninnocent support. The rates of the acetone and ozone reactions at 318-373 K were equally well described by the power-rate law and Langmuir-Hinshelwood expressions. Transient experiments showed that the rates of formation and reaction of the peroxide surface species did not correspond to the overall reaction rate, and it was concluded that it was not directly involved in the main reaction pathway. A mechanism is proposed involving the migration of the adsorbed acetone intermediate from the silica support to manganese centers, where it reacts with atomically adsorbed oxygen species to form complete oxidation products.