H 2S adsorption on polycrystalline UO 2

Abstract

We report results on the adsorption and desorption of H 2S on polycrystalline UO 2 at 100 and 300 K, using ultrahigh vacuum X-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS), and temperature programmed desorption (TPD). Our work is motivated by the potential for using the large stockpiles of depleted uranium in industrial applications, e.g., in catalytic processes, such as hydrodesulfurization (HDS) of petroleum. H 2S is found to adsorb molecularly at 100 K on the polycrystalline surface, and desorption of molecular H 2S occurs at a peak temperature of ∼140 K in TPD. Adsorption rates of sulfur as a function of H 2S exposure are measured using XPS at 100 K; the S 2p intensity and lineshapes demonstrate that the saturation coverage of S-containing species is ∼1 monolayer (ML) at 100 K, and is ∼0.3–0.4 ML of dissociation fragments at 300 K. LEIS measurements of adsorption rates agree with XPS measurements. Atomic S is found to be stable to >500 K on the oxide surface, and desorbs at ∼580 K. Evidence for a recombination reaction of dissociative S species is also observed. We suggest that O-vacancies, defects, and surface termination atoms in the oxide surface are of importance in the adsorption and decomposition of S-containing molecules.