Effect of hydrocarbon chain length and cyclization on the adsorption strength of unsaturated hydrocarbons on Pt/3d bimetallic surfaces

Pt-based 3d bimetallic surfaces are known to display higher activities and/or selectivities for various important surface reactions. They exhibit properties that can be entirely different from the parent metal surfaces. Various linear and cyclic unsaturated hydrocarbons were examined over a range of Pt bimetallic surfaces in the present work to help understand the influence of the adsorbate structure and the electronic structure of bimetallic surface on their adsorption properties and reactivity. Density functional theory (DFT) calculations were performed to study the binding of these molecules on the 3d-Pt(1 1 1) surface (over-layer structure) and Pt-3d-Pt (subsurface) structure. The effect of hydrocarbon chain length as well as cyclization was also studied on these surfaces. The DFT results for linear alkenes (1-butene, 1-pentene, 1-hexene) showed that the binding energies of these molecules decreased as the d-band centers moved away from the Fermi level, for 3d as well as 5d surfaces. Cyclohexene adsorption and reactivity were also studied using both theory and experiments. Cyclohexene adsorbed in a boat-type configuration and bonded weakly to the surface as compared to 1-hexene. Benzene adsorption was investigated on the bridge as well as the hollow adsorption sites. Benzene bonded more weakly than 1-hexene and cyclohexene on the subsurface Pt-3d-Pt(1 1 1) bimetallic structures.