Reactions of acetone on the surfaces of the oxides of uranium

The reactions of acetone were investigated on alpha U3O8 (stoichiometric and H-2 reduced) by temperature programmed desorption. The surface and bulk characteristics of U oxides were investigated by x-ray photoelectron spectroscopy (XPS) and x-ray diffraction (XRD). The comparison between the XPS U 4f(7/2) binding energy of beta UO3, alpha U3O8. and UO2 indicated that the U cations in U3O8 are composed of +5/+6 (2/1) or +4/+6 (1/2) oxidation states. XPS of H-2 reduced alpha U3O8 (at 800 K) indicated a shift of the U 4f(7/2) binding energy from 381.6 (unreduced) to 380.5 eV (reduced) as well as the appearance of two satellites at 387.0 and 397.4 eV. These new XPS lines' positions are characteristic of U+4 cations of UO2. Similar results were observed upon AT-ion sputtering of alpha U3O8. AT-ion sputtering of beta UO3 also results in the reduction of U+6 cations to U+4 cations. XRD of H-2 reduced alpha U3O8 indicated that all of the alpha U3O8 phase was transformed to the UO2 phase. A considerable difference between the reactivity of the surfaces of U3O8 and UO2 towards acetone was observed. A carbon-carbon bond formation reaction giving isobutene was observed only on the alpha U3O8 surface indicating its structure-sensitive nature and/or its sensitivity towards changing the oxidation state of U cations. This reaction has not been observed on the surfaces of actinide oxides before. On the other hand, acetone reacted on UO2 to give mainly propene. This latter reaction (which is a C-O bond dissociation) is most likely due to the capacity of UO2 to accommodate large numbers of atomic oxygen in interstitial positions while maintaining its structure intact. (C) 1997 American Vacuum Society.