Vanadium-titanium oxides with a V coverage ≤1.6 of the theor. monolayer (bidimensional sheet of V oxide on the TiO2 surface), prepd. by wet impregnation, grafting, and exchange techniques, were studied by x-ray diffraction, ESR, IR, UV-near-IR diffuse reflectance, and chem. anal. of the valence state and of the total amt. of V present, before and after washing with a basic soln. Results indicate that 3 V-oxide surface structures can be formed. At the lower coverages, V reacts with surface OH groups of TiO2, forming strongly interacting and stabilized V(IV) ions, part of which are coordinatively unsatd. This species is present also at higher coverages together with a 2nd V oxide species, interpreted as a bidimensional cluster of V(V) ions weakly interacting with the TiO2 surface. The V oxide in excess of a monolayer is present as multilayer cryst. V2O5. The nature of the V oxide monolayer is discussed in relation to the presence of these species and to IR anal. of the 1st overtone of ν(V:O), which suggests the presence of V ions with a single oxo group and a higher frequency of ν(V:O) as compared to the bulk V2O5. The shift to lower frequencies found by other authors is probably related to the presence of adsorbed H2O. [on SciFinder(R)]
Chemical and spectroscopic study of the nature of vanadium-oxide monolayer supported on a high-surface-area TiO2 anatase
CENTI, Gabriele;
1986-01-01
Abstract
Vanadium-titanium oxides with a V coverage ≤1.6 of the theor. monolayer (bidimensional sheet of V oxide on the TiO2 surface), prepd. by wet impregnation, grafting, and exchange techniques, were studied by x-ray diffraction, ESR, IR, UV-near-IR diffuse reflectance, and chem. anal. of the valence state and of the total amt. of V present, before and after washing with a basic soln. Results indicate that 3 V-oxide surface structures can be formed. At the lower coverages, V reacts with surface OH groups of TiO2, forming strongly interacting and stabilized V(IV) ions, part of which are coordinatively unsatd. This species is present also at higher coverages together with a 2nd V oxide species, interpreted as a bidimensional cluster of V(V) ions weakly interacting with the TiO2 surface. The V oxide in excess of a monolayer is present as multilayer cryst. V2O5. The nature of the V oxide monolayer is discussed in relation to the presence of these species and to IR anal. of the 1st overtone of ν(V:O), which suggests the presence of V ions with a single oxo group and a higher frequency of ν(V:O) as compared to the bulk V2O5. The shift to lower frequencies found by other authors is probably related to the presence of adsorbed H2O. [on SciFinder(R)]Pubblicazioni consigliate
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