An X-ray absorption study of two VOCl3-modified silicas: evidence for chloride-silica interactions.
The structures of the sites formed in the gas-solid reactions of VOCl3 with the surfaces of a fumed silica (Aerosil) and a silica gel (Sylopol) were investigated by using X-ray absorption spectroscopy. XANES and EXAFS analysis at the vanadium K-edge reveal that the sites have a uniform first coordination sphere regardless of the origin or the extent of hydroxylation of the silica support (controlled by thermal treatment in vacuo at 100 and 500 degrees C). Analysis of the second coordination sphere was limited by the lack of structural uniformity. EXAFS curve-fitting confirmed that the sites are [triple bond]SiOVOCl2, but revealed an unexpected asymmetry in the V-Cl bond distances. The latter is suggested to be a manifestation of silicon-chloride interactions.
Deguns
Eric W
EW
Department of Chemistry, University of California, Santa Barbara, California 93106-5080, USA.
Taha
Ziyad
Z
Meitzner
George D
GD
Scott
Susannah L
SL