Electrochemical reactions of benzoic acid on platinum and palladium studied by DEMS. Comparison with benzyl alcohol

The electrochemical reactivity of benzoic acid on porous platinum and palla dium electrodes has been studied by cyclic voltammetry and differential ele ctrochemical mass spectrometry (DEMS) in aqueous 0.1 M HClO4. The objective of this work is to investigate the adsorption processes and the reactivity of this compound on different noble metals, in order to compare these resu lts with those obtained for related aromatic compounds. On-line mass spectr oscopy analysis of volatile products reveals that the adsorption of benzoic acid is irreversible at platinum while it is mainly reversible on palladiu m. Accordingly, different catalytic activity of platinum and palladium is d emonstrated during the electrooxidation process. The anodic stripping of th e adsorbates formed from benzoic acid yields CO2 as the sole oxidation prod uct of platinum. Cathodic stripping of the residues results in the partial desorption of the organic adlayer from the electrode. At palladium, only sm all amounts of irreversibly adsorbed species, which also oxidise to CO2 are detected. The effect of the nature of the electrode on the electrochemical behaviour of these substances is also analysed. (C) 2000 Elsevier Science B.V. All rights reserved.