A DEMS study of the electroreduction and oxidation of 3-buten-2-one and 2-butanone adsorbates on platinum in sulphuric solutions

The electrochemical adsorption characteristics of 3-buten-2-one and 2-butanone on porous platinum electrodes were investigated by differential electrochemical mass spectrometry (DEMS) in aqueous 0.5 M H2SO4. The study was conducted through the oxidation and reduction of residues formed at different adsorption potentials (E-ad). The maximum adsorption for both organic substances was observed at the potential of zero charge of the interface, that is, ca 0.20 V. At this potential an adsorbate species with the C-O bond lying parallel to the surface is proposed. The sole oxidation product for both molecules was carbon dioxide. Anodic current transients were detected for 3-buten-2-one at adsorption potentials higher than 0.20 V. Between 0.40 and 0.60 V, it is possible to admit a 1-3e(-) loss during adsorption with a progressive fragmentation of the original molecule at increasing E-ad. After three cycles in the H-adatom region, about 75% of the 3-buten-2-one adsorbate is desorbed; the main products being butane, 1-butene and propane. The ratio of these products depends on E-ad, as is expected for the fragmentation of the molecule upon increasing potentials. On the other hand, 2-butanone was adsorbed in the 0.10-0.60 V potential range without current transients associated with the dissociative reactions of the molecule. The surface coverage diminished drastically at both sides of the maximum adsorption (0.20 V). Butane was the main reduction product of 2-butanone. (C) 1998 Elsevier Science S.A. All rights reserved.