Characterization and Quantification of Reduced Sites on Supported Vanadium Oxide Catalysts by Using High-Frequency Electron Paramagnetic Resonance

摘要

VOx (1.41.7 V?nm-2) supported on SBA-15, Al2O3, or TiO2 was studied before and after exposure to oxidative dehydrogenation of propane (ODP), and pure hydrogen or propane. After treatment, samples were quenched and frozen in quartz vials and characterized by using high-frequency electron paramagnetic resonance (HF-EPR). For SBA-15- and Al2O3-supported vanadia, V4+ sites were the most abundant paramagnetic species, whereas Ti3+ was dominant in TiO2-supported V2O5. For the quantification of paramagnetic reduced sites, Mn2+ was used as reference. The maximum relative numbers of reduced V4+ or Ti3+ sites were found to increase in the sequence SBA-15 (11?% V4+/V)