Reaction of S2 with ZnO and Cu/ZnO Surfaces: Photoemission and Molecular Orbital Studies

Abstract

The adsorption of S2 on ZnO and Cu/ZnO has been investigated using synchrotron-based high-resolution photoemission spectroscopy. On dosing a clean ZnO surface with S2 at 300 K, the molecule dissociates. The S is associated first with Zn and at medium coverages with Zn−O sites. When the sulfur coverage is increased to θS = 0.5 ML, evidence is found for sulfur bound purely to the O sites of ZnO. The sulfur species associated with O and the Zn−O sites are unstable at temperatures above 500 K. Possible reaction pathways for the dissociation of S2 on ZnO(0001)−Zn and Zn(1010) surfaces were studied using ab initio SCF calculations. At low sulfur coverages, an adsorption complex in which S2 is bridge bonded to two adjacent Zn atoms (Zn−S−S−Zn) is probably the precursor state for the dissociation for the molecule. It is possible to get much higher coverages of sulfur on ZnO (0.7 ML) than on Al2O3 (0.1 ML) at similar S2 exposures. This, in conjunction with results previously reported for H2S adsorption on Cr2O3 a...