Characterization of silica‐supported uranium–molybdenum oxide catalysts

Abstract

AbstractThe techniques of X‐ray diffraction, infrared and electron spin resonance spectroscopies, kinetics of reduction by H2, and XPS were used to investigate the chemical species present at the interface in silica‐supported uranium–molybdenum oxide catalysts. In this catalyst series, with constant MoO3 loading (16.7 wt%) and Mo/(Mo + U) atomic ratios ranging between 1 and 0, it was found that the oxidic forms of Mo and U were not well dispersed, MoO3 crystallites being detected on the catalysts with a high Mo/(Mo + U) atomic ratio. In the less‐uranium‐rich catalysts [Mo/(Mo + U) = 0.89] both MoO3 crystallites and a crystalline ‘uranyl molybdate’ phase were present. This catalyst exhibited the highest reduction degree by H2 and the highest ESR signal intensity of Mo5+ ions when reduced under very mild conditions. The information obtained with these techniques was used to explain the promotional effect of U on the MoO3/SiO2 base catalyst for the selective oxidation of isobutene.