The surface chemistry of 1,3-cyclohexadiene and 1,4-cyclohexadiene on Pt(111) studied by surface vibrational spectroscopy with sum frequency generation

The structure and reactions of 1,3-cyclohexadiene and 1,4-cyclohexadiene on Pt(111) has been studied by sum frequency generation at a pressure of 10−10–1 Torr. It was found that 1,4-cyclohexadiene adsorbs flat on the surface at low temperature and dehydrogenates to adsorbed benzene at about 300 K. 1,3-Cyclohexadiene undergoes a rearrangement to 1,4-cyclohexadiene through a 3–5 hydrogen shift which competes with the dehydrogenation reaction pathway at low temperature (<290 K) and dehydrogenates to benzene at higher temperature. This competing reaction behavior has also been observed at 1 Torr pressure of 1,3-cyclohexadiene on Pt(111) at 285 K.