Electrochemical behavior and semiempirical approach to the electroadsorption of 3-buten-2-one and 2-butanone on platinum

The electroadsorption of 3-buten-2-one was studied on polycrystalline and f aceted Pt electrodes in aqueous 0.5 M H2SO4 between 20 and 70 degrees C usi ng voltammetric and transient techniques. The largest values of anodic char ge densities in stripping experiments were observed at the potential of zer o charge of the Pt/acid interface (ca. 0.20 V), that is. 550, 680, and 720 mu C cm(-2), on polycrystalline and (111)- and (100)-faceted electrodes, re spectively. The anodic and cathodic strippings of 3-buten-2-one showed the formation of at least two residues with different electrochemical behavior. For comparison cyclic voltammetries and current transients of 2-butanone o n Pt were also studied. To get a deeper insight into the adsorption configu rations of 3-buten-2-one and 2-butanone, the extended Huckel molecular orbi tal methodology was used to predict adsorption geometries and binding energ ies on simulated Pt(100) and Pt(lll) single-crystal surfaces. At equilibriu m potentials, two types of adsorbed species were recognized, a planar 3-but en-2-one formed by the interaction of carbonyl and alkene groups and adsorb ates coming from the single interaction of the >C=O moiety for both 3-buten -2-one and 2-butanone. At simulated positive potentials, 3-buten-2-one adso rption occurred on Pt(lll) and Pt(100) clusters through the n-orbitals of t he >C=C< moiety, whereas at negative potentials 3-buten-2-one was adsorbed via mu-bridging or di-sigma configuration(s). (C) 1999 Academic Press.