Propene adsorption on Cu 2O single-crystal surfaces

Abstract

The interaction of propene with Cu 2O surfaces was investigated using thermal desorption spectroscopy (TDS), ultraviolet photoelectron spectroscopy (UPS), and X-ray photoelectron spectroscopy (XPS). Propene adsorption was studied on clean, deuterium-predosed, and oxygen-predosed Cu 2O(100) and (111) surfaces. Clear differences in the numbers and temperatures of the desorption states on the (111) and (100) surfaces demonstrate that propene adsorption is structure-sensitive on Cu 2O. Propene adsorption at low temperature is primarily molecular on both the (100) and (111) surfaces. However, evidence for a small amount of propene dissociation to allyl (C 3H 5) was found for the (111) surface, and is believed to occur at surface oxygen vacancies and defects. CO was the only desorption product besides propene, and was detected after propene adsorption at low temperature on the (111) surface only. A change in the (111) surface structure from a nearly stoichiometric (1 × 1) surface to an oxygen-deficient (√3 × √3) R30° surface was observed due to the removal of lattice oxygen to form CO. These changes in surface structure were accompanied by changes in the propene desorption spectra, and demonstrated that the highest temperature propene desorption feature is associated with lattice oxygen vacancies. For adsorption at 300 K, evidence for propene dissociation to allyl was found for both the (100) and (111) surface. However, the coverages of adsorbed propene were small, and the sticking coefficient at 300 K was estimated to be less than 10 −5.