The oxidation of propene over bismuth oxide, molybdenum oxide, and bismuth molybdate catalysts: II. ESR studies of bismuth molybdate and MoO 3 catalysts

Abstract

The ESR signals ascribed to Mo 5+ have been found when bismuth molybdate or molybdenum oxide catalysts were exposed to propene at temperatures between 225 and 500 °C. With molybdenum oxide the signal intensities increase steadily with time; with bismuth molybdates they increase continuously at lower temperatures, but increase and then decay rapidly at higher temperatures. When 1:1 mixtures of propene and oxygen contact the catalysts, no Mo 5+ signals are seen while gaseous oxygen is still present. With bismuth molybdate and 1-butene, the Mo 5+ signals behave as with propene, but with hydrogen the Mo 5+ signals increase continuously. These changes are discussed in relation to the reduction of the catalysts, as revealed in parts III and IV, and some deductions are made about the possible bonding of the hydrocarbon radicals to the molybdenum ions and the effects of oxygen gas and bismuth ions on that bonding.