Adsorption of cyclopentene on Pt(111) and ordered PtnSn/Pt(111) surface alloys

The adsorption of cyclopentene (C5H8) on Pt(111) and the two ordered Pt3Sn/Pt(111) and Pt2Sn/Pt(111) surface alloys has been investigated experimentally using high-resolution electron energy loss spectroscopy, ultraviolet photoelectron spectroscopy, low-energy electron diffraction, and temperature-programmed desorption as well as theoretically by ab initio density functional theory (DFT) calculations. On the Pt(111) and the respective surface alloys, a di-sigma bonding of cyclopentene has been found both experimentally as well as in the DFT calculations. Even though the bonding mechanism on Pt(111) and the two surface alloys is very similar, large differences in the bond energy and the thermal stability of the cyclopentene have been detected. On Pt(111), part of the C5H8 desorbs intact at similar to280 K whereas the remaining amount is converted to C5H5. This species completely dehydrogenates to carbon upon heating above 450 K. On the surface alloys, the temperature of desorption is reduced to 244 K (Pt3Sn) and 198 K (Pt2Sn), respectively, and no dehydrogenation is detected. The influence of the aliphatic ring on the interaction between the olefinic bond and the substrate is weak even though an interaction of the beta-hydrogen with the surface atoms has been found experimentally and theoretically for cyclopentene on Pt(111) and on the Pt3Sn/Pt(111) surface alloy.