A comparative study on the adsorption of benzyl alcohol, toluene and benzene on platinum

Abstract

The adsorption of benzyl alcohol, toluene and benzene on platinum was studied using cyclic voltammetry combined with on-line mass spectrometry (DEMS). Flow cell procedures allow the detection of volatile products formed during adsorption of these molecules and their displacement with CO, as well as during the oxidative and reductive stripping of the adsorbed layer. Three adsorption potentials were chosen: 0.20, 0.35 and 0.50 V versus reversible hydrogen electrode (rhe). Toluene and benzene adsorb without dissociation. Total hydrogenation of the ring with formation of methyl-cyclohexane and cyclohexane, respectively, was observed suggesting that the aromatic ring of the adsorbed species lies on the surface. For benzyl alcohol, the presence of the OH group favours the dissociative adsorption: the rupture of the CC bond between the ring and the CH 2OH group produces CO and benzene. Hydrogenolysis of benzyl alcohol also occurs in the Pt(H) region with formation of toluene. Both adsorbed toluene and benzene from benzyl alcohol react with H 2 producing methyl-cyclohexane and cyclohexane, respectively. Thus, benzene and toluene formed from benzyl alcohol also seem to adsorb with the aromatic ring parallel-oriented on the surface.