Intrinsic Activity of MnOx-CeO2 Catalysts in Ethanol Oxidation

Abstract

MnOx-CeO2 mixed oxides are considered efficient oxidation catalysts superior to the corresponding single oxides. Although these oxides have been the subject of numerous studies, their fundamental performance indicators, such as turnover frequency (TOF) or specific activity, are scarcely reported. The purpose of the present work is to investigate the effect of catalyst composition on the concentration of active sites and intrinsic activity in ethanol oxidation by the employment of temperature-programmed desorption and oxidation of isotopically-labelled ethanol, 12CH313CH2OH. The transformation pathways of preadsorbed ethanol in the absence of gaseous oxygen refer to dehydrogenation to acetaldehyde followed by its dissociation combined with oxidation by lattice oxygen. In the presence of gaseous oxygen, lattice oxygen is rapidly restored and the main products are acetaldehyde, CO2, and water. CO2 forms less easily on mixed oxides than on pure MnOx. The TOF of ethanol oxidation has been calculated assuming that the amount of adsorbed ethanol and CO2 produced during temperature-programmed oxidation (TPO) is a reliable indicator of the concentration of the active sites.