Role of intermolecular interactions in determining structure and reactivity on surfaces: Benzenethiol on Rh(111)

The reactions of benzenethiol on clean Rh(lll) have been studied using a combination of temperature-programmed reaction, high-resolution electron energy loss, and X-ray photoelectron spectroscopies. Benzenethiol adsorbs dissociatively on Rh(111) at 100 K, affording adsorbed phenylthiolate and hydrogen. The adsorption geometry of phenylthiolate is shown to depend on the coverage, with a low coverage favoring a parallel geometry of the phenyl ring. Phenylthiolate reacts by C-S bond breakage starting at 250 K, forming benzene. At saturation coverage (0.21 monolayers), the benzene is forced into the gas phase upon formation, because of molecular crowding on the surface. Comparison is made to the chemistry of benzenethiol on other transition metal surfaces, and there is no simple correlation between the metal-sulfur bonding properties and the activity or selectivity for benzenethiol desulfurization.