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Article

An X-ray Absorption Study of Two VOCl₃-Modified Silicas: Evidence for Chloride−Silica Interactions

Supporting Info

Eric W. Deguns,^† Ziyad Taha,^‡ George D. Meitzner,^§ and Susannah L. Scott*^†^‡

Departments of Chemistry and Chemical Engineering, University of California, Santa Barbara, California 93106-5080, and Materials Research & Technology Institute, University of Texas, El Paso, Texas 79968-0685

J. Phys. Chem. B, 2005, 109 (11), pp 5005–5011

DOI: 10.1021/jp045886y

Publication Date (Web): March 1, 2005

†

Department of Chemistry, University of California.

‡

Department of Chemical Engineering, University of California.

University of Texas.

To whom correspondence should be addressed. Fax: 1-805-893-4731. E-mail: sscott@engineering.ucsb.edu.

Abstract

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 °C). Analysis of the second coordination sphere was limited by the lack of structural uniformity. EXAFS curve-fitting confirmed that the sites are SiOVOCl₂, but revealed an unexpected asymmetry in the V−Cl bond distances. The latter is suggested to be a manifestation of silicon−chloride interactions.