Abstract
The coordination properties of surface V/sup 4 +/ ions of reduced V/sub 2/O/sub 5/ supported on silica have been studied by EPR using the adsorption of various probe molecules. The spectrum resolution, greatly enhanced with the third-derivative presentation, indicates an orthorhombic symmetry for the V/sup 4 +/ ions after CO adsorption (g/sub 1/ approx. g/sub 2/ = 1.985, g/sub 3/ = 1.931, A/sub 1/ approx. A/sub 2/ 71.4 G, A/sub 3/ = 191.4 G). The use of /sup 13/C-enriched carbon monoxide allows us to observe that the V/sup 4 +/ surface ions can coordinate two CO molecules from the gas phase to form, together with four lattice oxide ions, a distorted octahedron with one pronounced vanadyl character bond. The /sup 13/C superhyperfine coupling constant is found to be about 7 G. The influence of the adsorbed molecules (CO, H/sub 2/O, C/sub 2/H/sub 4/) on the properties of the V/sup 4 +/ ions at the surface is further discussed. 33 references, 4 figures, 1 table.
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