H2S adsorption on polycrystalline UO2

We report results on the adsorption and desorption of H2S on polycrystalline UO2 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. H2S is found to adsorb molecularly at 100 K on the polycrystalline surface, and desorption of molecular H2S occurs at a peak temperature of ∼140 K in TPD. Adsorption rates of sulfur as a function of H2S 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.