2007 Volume 40 Issue 12 Pages 1064-1071
In order to improve the catalytic activity of magnesium ortho-vanadate (Mg3V2O8) for the oxidative dehydrogenation of propane, Mg3V2O8 doped with Fe3+ (Fe–Mg3V2O8) was prepared. The improvement of the conversion of propane from 4.8% on Mg3V2O8 to 8.2% on 5% Fe–Mg3V2O8 together with the rather similar selectivity to propylene on un-doped and doped catalysts (62.3 and 61.0%, respectively). To evaluate the redox nature of Fe–Mg3V2O8 during the oxidative dehydrogenation, the catalysts used for the conversion of propane with and without gaseous oxygen were analyzed by XRD, solid state 51V MAS NMR, XAFS, and XPS. After the propane conversion without oxygen, complete conversion of Fe–Mg3V2O8 to Mg2VO4 and MgO together with a small amount of Fe2O3 was observed by XRD, while the reduction of V5+ to V4+ was detected by 51V MAS NMR and V K-edge XAFS from the catalyst. However XPS analysis showed that such a reduction was not observed over the surface of Fe–Mg3V2O8 since oxygen was supplied from bulk to the surface of the catalyst to keep V5+ over the surface. After the treatment of the reduced catalysts with gaseous oxygen, the complete regeneration of Fe–Mg3V2O8 from the reduced phase was confirmed by those analyses.
