Surface oxide-support interaction (SOSI) for surface redox sites

Abstract

Recent studies of supported vanadium oxide catalysts have revealed that the vanadium oxide component is present as a two-dimensional metal oxide overlayer on oxide supports (i.e., Al{sub 2}O{sub 3}, TiO{sub 2}). These surface vanadium oxide species are generally more selective and active than bulk, crystalline V{sub 2}O{sub 5} for the partial oxidation of hydrocarbons. The molecular structures of these surface vanadium oxide species have recently been characterized under in situ conditions with Raman spectroscopy, infrared spectroscopy, solid-state {sup 51}V NMR spectroscopy and x-ray absorption near edge structure (XANES) spectroscopy. The characterization results uniformly agree that under in situ conditions the surface vanadium oxide species appears to be four coordinated. In addition, the Raman and infrared vibrational spectroscopy measurements reveal that two different surface vanadium oxide species can be present on the oxide supports. The in situ Raman spectra exhibit a sharp band at {approximately} 1,030 cm{sup {minus}1} and a broad band at {approximately} 900 cm{sup {minus}1}, and the relative intensities of these two Raman bands varies with surface vanadium oxide coverage on the oxide support. In the present investigation, the physical and chemical properties of the isolated surface vanadate species, corresponding to the Raman band at {approximately} 1,030 cm{sup {minus}1},more » are examined on different oxide supports in order to determine the extent of surface oxide-support interactions for supported vanadium oxide catalysts.« less