Reactions of Unsaturated Hydrocarbons at the Gold/Electrolyte Interface in Acid Solution

The electrochemical reactivity of ethine, ethene, and propene on polycrystalline gold in perchloric and sulfuric acid is compared. The product analysis of oxidation/reduction reactions was performed by on-line mass spectrometry and in situ FTIR spectroscopy. It was found that ethine interacts strongly with the gold/electrolyte interface, forming a chemisorbate. On the other hand, ethene and propene show a weak interaction and no adsorbed intermediates were identified after replacing the organic-containing solution by pure electrolyte. The different adsorption behavior influences the product distribution during hydrocarbon oxidation. The sole product of ethine oxidation is CO 2, whereas ethene and propene react also to partial oxidized products. The experimental results are interpreted on the basis of the electronic structures of the hydrocarbons and gold.