Lattice oxide ion-transfer effect demonstrated in the selective oxidation of propene over silica-supported bismuth molybdate catalysts

Silica-supported bismuth molybdate catalysts were prepared by impregnation in a highly dispersed state and by coprecipitation in a largely crystallize d state. Their catalytic behavior was investigated in the oxidation of prop ene to acrolein. The highly dispersed bismuth molybdate catalysts on silica were found to be intrinsically active but poorly selective to acrolein. Wh en we increased the loading amount the oxidation activity drastically incre ased. The poor acrolein selectivity of this catalyst was improved by contin uous use in the catalytic oxidation for making the particle size of the dis persed bismuth molybdate larger. The catalytic activity and selectivity wer e little influenced by the loading amount in the cases of the coprecipitate d catalysts. The results demonstrate that, for the activity and selectivity , bismuth molybdate catalysts need to be of a certain particle size which c an provide sufficient lattice oxide ions during the catalytic redox cycle. (C) 1999 Elsevier Science B.V. All rights reserved.