Application of the unique redox properties of magnesium ortho-vanadate incorporated with palladium in the unsteady-state operation of the oxidative dehydrogenation of propane

摘要

The oxidative dehydrogenation of propane on Pd2+-incorporated magnesium ortho-vanadate (Pd-ortho-MgVO) was examined, despite the long-held belief that magnesium ortho-vanadate (Mg3V2O8) demonstrates scant catalytic activity in oxidative dehydrogenation. At 0.75 h on-stream, a higher activity than that on magnesium pyro-vanadate (monoclinic Mg2V2O7), which is believed to be one of the more active catalysts for oxidative dehydrogenation, was observed using 5% Pd-ortho-MgVO. Unfortunately, the higher catalytic activity decreased with time on stream due to the rapid abstraction of lattice oxygen from 5% Pd-ortho-MgVO. Although the abstracted lattice oxygen was not regenerated during oxidative dehydrogenation in the presence of excess gaseous oxygen, it was easily regenerated during reoxidation in the absence of propane in the feedstream. Redox cycles of palladium and vanadium species during the catalytic reaction and reoxidation were confirmed using extended X-ray absorption fine structure around the Pd K-edge and V-51 magic-angle spinning nuclear magnetic resonance, respectively. The results of the present study suggest that the higher catalytic activity observed using 5% Pd-ortho-MgVO at 0.75 h on-stream can be maintained by using an unsteady-state operation in combination with the catalytic reaction and catalyst reoxidation. (C) 2008 Elsevier Inc. All rights reserved.