Benzene chemisorption on palladium surfaces. I. High-resolution electron-energy-loss vibrational spectra and structural models

Benzene chemisorption on Pd(111) and Pd(100) crystal faces at 300 K has been studied by high-resolution electron-energy-loss spectroscopy and thermal desorption spectroscopy. Our results indicate that benzene chemisorbs associatively at only one site and is {π} bonded with its ring plane parallel to the metal surface. Thermal desorption studies indicate that benzene adsorption is only partially reversible, with decomposition evolving H₂ and leaving a carbon-covered surface as the competing mechanism to benzene thermal desorption. The similarity of the benzene vibrational spectra on Pd(100) and Pd(111) has led us to propose a new model for benzene chemisorption on transition-metal surfaces involving a lower adsorption-site symmetry (Cₛ) than has been previously suggested.