Semiconductive properties of some uranium–antimony oxide phases used as catalysts in the mild oxidation of but-1-ene to butadiene
Abstract
Three uranium–antimony mixed oxides have been prepared and characterised. They corresponded to USb3O10, USbO5 and an equimolar mixture of the latter oxides with an atomic ratio U/Sb of 1/2. Their electrical conductivity 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 gap 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 were found to be p-type semiconductors. The catalysts appeared as redox relays in but-1-ene oxy-dehydrogenation. In the case of USb3O10, the active 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-type 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.