(653d) Synthesis, Characterization And Catalytic Performance Of Highly Dispersed Vanadium Grafted Sba-15 Catalyst
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, i.e., N2-physisorption, X-ray diffraction, transmission electron microscopy (TEM), Raman spectroscopy, H2 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, predominantly composed of isolated VO4 units with distorted tetrahedral coordination. The suggested (≡SiO)3-V=O sites on the silica surface comprises one short bond (~1.54 Å) and three long bonds (1.74 Å). Methanol oxidation was employed 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 as compared to 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 Brönsted acid sites of the surface.