Raman, UV-vis, and X-ray photoelectron spectroscopy were combined in one experimental setup to directly study the interplay between the structure and dispersion of SBA-15-supported vanadium oxide during dehydration. The fully hydrated catalyst is slightly reduced but consists mainly of V5+ species with pseudo-octahedral V coordination strongly resembling the xerogel V2O5-1.2H(2)O. After dehydration, a highly dispersed surface vanadium oxide species with tetrahedrally coordinated vanadium and significantly smaller ensemble size is formed. (C) 2007 Elsevier Inc. All rights reserved.