A DEMS STUDY OF THE ELECTROREDUCTION AND OXIDATION OF 3-BUTEN-2-ONE AND 2-BUTANONE ADSORBATES ON PLATINUM IN SULFURIC SOLUTIONS

The electrochemical adsorption characteristics of 3-buten-2-one and 2- butanone on porous platinum electrodes were investigated by differenti al electrochemical mass spectrometry (DEMS) in aqueous 0.5 M H2SO4. Th e study was conducted through the oxidation and reduction of residues formed at different adsorption potentials (E-ad). The maximum adsorpti on for both organic substances was observed at the potential of zero c harge of the interface, that is, ca 0.20 V. At this potential an adsor bate species with the C-O bond lying parallel to the surface is propos ed. The sole oxidation product for both molecules was carbon dioxide. Anodic current transients were detected for 3-buten-2-one at adsorptio n potentials higher than 0.20 V. Between 0.40 and 0.60 V, it is possib le to admit a 1-3e(-) loss during adsorption with a progressive fragme ntation of the original molecule at increasing E-ad. After three cycle s 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 ra tio of these products depends on E-ad, as is expected for the fragment ation of the molecule upon increasing potentials. On the other hand, 2 -butanone was adsorbed in the 0.10-0.60 V potential range without curr ent transients associated with the dissociative reactions of the molec ule. 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.