Determination of the active surface area of vanadia by electrophoretic migration and XPS measurements

Abstract

Electrophoresis migration and X-ray photoelectron spectroscopy techniques were applied to measure the active surface area of vanadia in titania- and alumina-supported vanadium oxide catalysts. For V-oxide contents ranging between 0 and 2.3 × 10 14 cm −2 for Al 2O 3 and 0 and 7.2 × 10 14 cm −2 for TiO 2, it was found that V-oxide has a very high degree of dispersion mainly as monolayer. The V 2p T 2p and V 2p Al 2p intensity ratios, taken from the XPS spectra, increase monotonically with the V content. However, for V TiO 2 catalysts the straight line declines for V contents above 4.9 × 10 14 cm −2, thus indicating the end of the first vanadium layer. For the V Al 2O 3 catalyst series both apparent surface coverage and V 2p Al 2p intensity ratio steadily increase with V content, indicating that in all these preparations, even with the highest V content, the V-layered structures do not fully cover the surface of the carrier.