The oxidation of propene over bismuth oxide, molybdenum oxide and bismuth molybdate catalysts: III. Electrical conductivities of bismuth molybdate, MoO 3 and Bi 2O 3

Abstract

On exposure to propene, 1-butene or hydrogen, pressed discs of the catalysts bismuth molybdate and molybdenum oxide show rapid and reproducible increases of electrical conductivity at temperatures between 400 and 550 °C. The conductivities decrease to their original values on reoxidation by gaseous oxygen. At any selected stage of reduction or reoxidation, the rates of reduction or reoxidation are linear functions of the gas pressures. If the gases are removed at a given extent of reduction, the conductivities then change with temperature as expected for semiconductors, and the energy gaps fall to very low values on moderately-reduced catalysts. In the presence of an excess of a 1:1 mixture of propene and oxygen, bismuth molybdate shows a nearly constant conductivity corresponding to roughly 10% reduction, and this extent of reduction varies only slightly as the proportions of propene and oxygen are changed from 9:1 to 1:9. With 1:1 mixtures of the gases molybdenum oxide appears to be reduced to only a very small extent. Bismuth oxide shows an initial decrease of conductivity followed by an increase when contacted with propene, and the conductivity falls on reoxidation.