Reactions of weak organic acids with oxygen atoms on Ag(100): Facile and selective conversion of cyclohexene to benzene

The reactions of cyclohexene with atomically adsorbed oxygen on Ag(100) have been examined by both temperature programmed reaction mass spectrometry and electron energy loss vibrational spectroscopy. Cyclohexene reacts with adsorbed oxygen atoms to form benzene and surface hydroxyl groups, with benzene formation complete by 200 K, as evidenced by the vibrational spectra. Benzene formed from cyclohexene dehydrogenation remains chemisorbed on the silver surface until 275 K, when it desorbs. Surface hydroxyls undergo disproportionation at 300 K to form gaseous water and chemisorbed oxygen atoms. Competing with benzene formation is another reaction pathway which leads to cyclohexene combustion. Vibrational spectroscopy indicates that a key intermediate on the pathway to cyclohexene contains an intact C-O bond.