SEMICONDUCTIVE PROPERTIES OF SOME URANIUM-ANTIMONY OXIDE PHASES USED AS CATALYSTS IN THE MILD OXIDATION OF BUT-1-ENE TO BUTADIENE

Three uranium-antimony mixed oxides have been prepared and characteris ed. They corresponded to USb3O10, USbO5 and an equimolar mixture of th e latter oxides with an atomic ratio U/Sb of 1/2. Their electrical con ductivity was studied as a function of temperature and oxygen pressure and was followed with time during sequential exposures to oxygen and but-1-ene in conditions close to those of catalysis. USb3O10 was found to be an intrinsic semiconductor in pure oxygen with an energy band g ap equal to 1.96 eV and became an n-type semiconductor in a but-1-ene atmosphere. By contrast USbO5 and the U-Sb-O sample with U/Sb = 1/2 we re found to be p-type semiconductors. The catalysts appeared as redox relays in but-l-ene oxy-dehydrogenation. In the case of USb3O10, the a ctive oxygen species can be estimated to be O2- anions of the surface lattice. In USbO5, they could also be considered as O2- anions, either from the lattice or as interstitial ions in accordance with the p-typ e character of the solid. The mixed phase (U/Sb = 1/2) is ca. 30% more active than both constituents, exhibiting a synergy effect, possibly due to the coexistence of both types of oxide semiconductors.