Acid-Base Properties of Vanadium Oxide Catalysts

4 Acid-Base Properties of Vanadium Oxide Catalysts 

As noted, for example by van der Wiele and van den Berg,4 the interaction between the molecule to be oxidized and the catalyst is based on the electron-donating and -accepting properties and can be described in terms of the acid-base properties. Activity and selectivity are thus expected to depend on the relative acidity and basicity. Thus Boreskov et al.80 observed a clear correlation between the acidity of a V205/Ti02 catalyst modified with different alkali metals and the selectivity for 0-xylene oxidation. The most acidic site was assumed to be responsible for the destructive oxidation. Thus the selectivity increased with the basicity, i.e., with the atomic number of the alkali metal. 

Chakrabarthy et al.81 found for the dehydration of propan-2-ol by V205 and lithium vanadium bronzes, that lithium increases the dehydration, in contradiction with the view that this reaction takes place at the acid centers, but correlating well with the semiconductor properties. 

Krupay and Ross83 studied the influence of the addition of alkali metal sulphates to V205 on the reaction between CO and N20. Some curious discrepancies in their paper unfortunately invalidate some of their conclusions. 

As mentioned on p. 108, Spiridinova et a/.40,41 only find evidence for Lewis acid adsorption sites, whereas Goldberg et al 2 and Nowinska43 also find evidence for Br nsted acid sites. Similarly Belokopytov et al. 8 observe the adsorption of NH3 on both types of acid centers, Lewis sites showing a greater acid strength. On the other hand Inomata et al28,81,82 report that on V205 itself adsorption of NH3 only occurs as NH4 and that adsorption as 

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