Propene oxidation and hydrogenation on a porous platinum electrode in acidic solution

The electrochemical reactivity of propene at the polycrystalline Pt/acidic solution interface was studied by on line differential electrochemical mass spectrometry (DEMS). It was shown that a relatively fast adsorption of hydrocarbon molecules on the electrode surface preceded their electroreduction and electrooxidation at E < 0.2 V and E > 0.6 V, respectively. The adsorbate consisted of associatively bonded propene, partially dehydrogenated C-3-hydrocarbon residues, as well as C-3-, C-2-, and/or C-1-oxygen-containing species in relative amounts dependent on the adsorption potential and the subsequent potential sequence. The maximum electrode coverage of 0.58 nmol cm(-2) was achieved in the potential range 0.3-0.5 V, where the major part of the surface species was propene itself, oriented with the carbon chain almost parallel relative to the electrode/ solution interface. The oxygenated C-3-species were formed favorably in the presence of coadsorbed water and/or OH species, at 0.5 V < E < 0.8 V. Propane was identified as the main volatile product of the cathodic hydrogenation of the adsorbate. Additionally, the reductive decomposition of the oxygenated C3-species yielded methane along with the C-2-oxygen-containing moieties remaining on the Pt surface and/or undergoing further fragmentation to the C-1-oxygen-containing residues. The only final volatile oxidation product of all the adsorbates was CO2.