Journal
JOURNAL OF CATALYSIS
Volume 253, Issue 1, Pages 74-90Publisher
ACADEMIC PRESS INC ELSEVIER SCIENCE
DOI: 10.1016/j.jcat.2007.10.019
Keywords
vanadium grafted SBA-15; methanol oxidation; XRD; Raman; H2-TPR; TEM; X-ray absorption (XANES and EXAFS)
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Vanadium oxide grafted on mesoporous silica SBA-15 has been synthesized using a controlled grafting process. Its structure has been thoroughly investigated using different characterization techniques, including N-2-physisorption, X-ray diffraction, transmission electron microscopy (TEM), Raman spectroscopy, H-2 temperature-programmed reduction, X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS). The spectroscopic results revealed that under dehydrated conditions, the grafted vanadium domains are highly dispersed on the SBA-15 surface, composed predominately of isolated VO4 units with distorted tetrahedral coordination. The suggested ( SiO)(3)V=O sites on the silica surface include one short bond (similar to 1.54 angstrom) and three long bonds (1.74 angstrom). Methanol oxidation was used as a chemical probe reaction to examine the catalytic properties of these catalysts. At low vanadium loading, the vanadium species grafted on the surface show structural properties similar to those of vanadium-incorporated MCM-41 catalyst. However, the present mesoporous V-SBA-15 catalysts in the oxidation of methanol to formaldehyde show remarkable catalytic performance compared with that of VOx/SBA-15 catalysts synthesized through a conventional wet impregnation method, which has been attributed to the homogeneous dispersion and uniformity of the catalytic vanadium species achieved on the SBA-15 support with large pore diameter and surface area. The acidic properties of V-SBA-15 was investigated by pyridine temperature-programmed desorption, which indicated the existence of both Lewis and Bronsted acid sites of the surface. (C) 2007 Published by Elsevier Inc.
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