Spectroscopic characterization of vanadium(V) oxo species deposited on zirconia

Abstract

A method for deposition of vanadium(V) oxo species from acidic solutions of ammonium metavanadate on zirconia is described. The samples are synthesized by suspension of the support (powder) in solutions containing three different vanadium(V) precursor ions: the dioxovanadium(V) ion, VO₂⁺, the yellow diperoxo anion [VO(O–O)₂]⁻ and the red monoperoxo cation [VO(O–O)]⁺. Application of vanadium(V) peroxo complexes increases significantly the uptake of vanadium by zirconia. The state and localization of the VO_x species on the surface of zirconia were studied by FTIR, UV/VIS and XP spectroscopies. The materials prepared from VO₂⁺ ions contain isolated VO₄ groups and domains of orthovanadate species, (VO₄)_n. The FTIR spectra of adsorbed CO revealed that the number of exposed Zr⁴⁺ ions decreased markedly when vanadium(V) peroxo ions were used as precursors. The predominant surface structure in this case was identified as pyrovanadates, V₂O₇. On all of the samples studied no separate phase of V₂O₅ was detected.