Effect of the Intrinsic Properties of Metals on the Adsorption Behavior of Molecules-Competitive and Cooperative Adsorption of Benzene and Other Species on Pt and Rh Surfaces

摘要

Our previous study of benzene adsorption on Pt groups reveals the marked effect of the intrinsic properties of the metals. In the present paper, we further investigated the competitive and cooperative adsorption effects of halogen ions, SCN-, and pyridine on benzene adsorption on Pt and Rh surfaces using in situ electrochemical surface-enhanced Raman spectroscopy (SERS). The effect of the adsorption strength and the concentration of these species, the electrode potential, and the surface morphology on the adsorption behavior of benzene were systematically studied. Very different effects have been found on Pt and Rh surfaces. On Pt surfaces, Br- and I- competed with the chemisorbed benzene; meanwhile, the chemisorbed ions induced the physisorption of benzene. However, on Rh surfaces, a much weaker coadsorption was observed for I- and benzene. With the addition of a 1/100 amount of pyridine, the chemisorbed benzene was totally removed from the Pt surface. However, on the Rh surface, signals from both benzene and pyridine were simultaneously observed due to their adsorption on different sites. On both surfaces, the adsorption of benzene was totally suppressed after the addition of the SCN- ion. The existence of benzene in the interfacial region weakened the interaction between the adsorbed species. Preliminary models have been postulated to account for the competitive and cooperative adsorption behaviors of benzene with other species on the two metal surfaces. The difference may originate from the different electronic structures of Pt and Rh.