Laser flash photolysis of metal oxide supported vanadyl catalysts. Spectroscopic evidence for the ligand-to-metal charge-transfer state

Abstract

A series of vanadyl containing samples supported on metal oxides (SiO₂, Al₂O₃, K-doped Al₂O₃, TiO₂, MgO and ZnO) have been studied by laser flash photolysis. Excitation at 266 or 308 nm generated transients (300 nm < λ_max < 500 nm) with lifetimes on the microsecond time scale. These were assigned to the ligand-to-metal charge-transfer triplet excited state. The absorption maximum varied with the nature of the support. Samples having higher vanadium loading showed additional transients attributed to vanadyl aggregates.