The reactions of acetaldehyde and ethylene have been investigated on the surfaces of UO2 and UO3 by temperature programmed desorption (TPD). On UO2 two molecules of acetaldehyde undergo reductive coupling to C4 olefins. This is due to the fluorite structure of UO2, which can accommodate large numbers of excess oxygen, up to UO2.25. The vacant surface oxygen of UO2 were titrated by N2O 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 UO3 indicated the desorption of acetaldehyde (490 K). In addition, an unexpected product was also observed. This product was identified as furan (C4H4O, m/e 68, 39) which desorbed at ca. 550 K with a carbon selectivity of ca. 40 %. Furan formation from ethylene on UO3 requiring the formation of one carbon-carbon bond and of one carbon-oxygen bond, is most likely accompanied by oxygen depletion from the UO3 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.
|Number of pages||10|
|Journal||Studies in Surface Science and Catalysis|
|Publication status||Published - 1997|