Designing Heterogeneous Catalysts for Microwave Assisted Selective Oxygenation

Microwave dielectric heating is an emerging technology in heterogeneous catalysis. However, catalyst design in this field is not as well developed as when conventional heating is used. In this study the selective oxidation of propene to acrolein has been used as a model reaction to understand the how the properties of bismuth mixed metal oxide catalysts can be tuned for use in microwave assisted catalysis. The role of the dielectric properties, that are crucial to enable the catalyst to be heated in the microwave electric field, were determined using cavity perturbation methods. Catalysts with a very high loss tangent reached high temperatures leading to combustion products, whereas materials with a low loss tangent could not be heated and were inactive. Bi 2 MoO 6 and BiVO 4 both showed promising performance during an initial screening and were investigated further. For Bi 2 MoO 6 , a partial substitution of molybdenum with vanadium resulted in the formation of Bi 1−X/3 V 1−x Mo x O 4 , with a decrease in particle size and dielectric loss tangent, and the highest rate of acrolein production was found when x=0.6 at 15 W microwave power. Higher microwave power resulted in thermal runaway which decreased the activity of the catalyst.