Remarkably, in the larger crystallite size sample O2 conversion rises much more than necessary to satisfy 2-propanol conversion stoichiometrically from 65 °C and 55 °C respectively (according to the temperature programmed reaction profiles in figure ), as one equivalent of oxygen ideally converts two equivalents of 2-propanol to two equivalents of acetone. The levels of O2 conversion cannot be explained by partial oxidation or total combustion either as neither CO2 nor H2 evolution occur at these temperatures. This might possibly indicate the formation of a reactive oxygen species or its precursors at low temperatures and the reaction to (a selection of) the products at higher temperatures. Such an oxygen species has to be considered as stable at higher temperatures only as the sample was oxidatively pretreated in synthetic air before the temperature programmed reaction experiment, which is why such an oxygen species should be already available on the surface, if it was stable at lower temperatures as well. In the smaller crystallite size sample, this observation can be made as well to a much lower extend close to the onset temperatures of partial oxidation in the first cycles (280 °C), which could indicate the ongoing formation of reactive species and explain the over-stoichiometric O2 consumption.