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 O^2– anions of the surface lattice. In USbO₅, they could also be considered as O^2– 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.