Temperature programmed desorption of ethylene and acetaldehyde on uranium oxides. Evidence of furan formation from ethylene.

The reactions of acetaldehyde and ethylene have been investigated on the surfaces of UO(2) and UO(3) by temperature programmed desorption (TPD). On UO(2) two molecules of acetaldehyde undergo reductive coupling to C4 olefins. This is due to the fluorite structure of UO(2), which can accommodate large numbers of excess oxygen, up to UO(2.25). The vacant surface oxygen of UO(2) were titrated by N(2)O adsorption and were equal to 1.86 x 1O(19) molecules/g, representing an apparent surface area of vacant oxygen sites of 1.9 m(2)/g. On the other hand, ethylene-TPD on beta UO(3) indicated the desorption of acetaldehyde (490 K). In addition, an unexpected product was also observed. This product was identified as furan (C(4)H(4)O, m/e 68, 39) which desorbed at ca. 550 K with a carbon selectivity of ca. 40 %. Furan formation from ethylene on UO(3) requiring the formation of one carbon-carbon bond and of one carbon-oxygen bond, is most likely accompanied by oxygen depletion from the UO(3) surfaces and subsequent reduction of U cations into lower oxidation states. The observation of furan from ethylene shows that one may obtain oxygenated products with a high carbon number from ethylene (a relatively abundant feed stock) via one single step.