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.
Highlights
Volatile organic compounds (VOCs) include all organic compounds that exist in the gaseous state in air
We have reported on the performance of a series of MnOx -CeO2 catalysts, prepared by the urea combustion method, in ethanol oxidation [8]
It was found that a major fraction of Mn ions get incorporated in the ceria lattice with a homogeneous distribution of Mn ions in the bulk and the surface for Mn/(Mn + Ce) ratios up to 0.25
Summary
Volatile organic compounds (VOCs) include all organic compounds that exist in the gaseous state in air. Noble metals [2,3,4] and oxides of the transition metals [5,6,7] have been mostly investigated for the complete oxidation of ethanol. The possibility of forming partial oxidation products that are more harmful than the original organic compound is very high during the oxidation process of compounds like ethanol. Side reactions are mainly dehydrogenation to acetaldehyde and dehydration to ethylene or diethyl ether [4,8]. Due to secondary reactions of these primary products, the formation of molecules with more than two carbon atoms, such as ethyl acetate, crotonaldehyde, and acetone has been reported [9,10]
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