Conceptual chemistry approach towards the support effect in supported vanadium oxides: Valence bond calculations on the ionicity of vanadium catalysts

The concept of bond ionicity, obtained via a valence bond analysis, is invoked in the interpretation of the catalytic activity of supported vanadium oxides, in analogy with previous work conducted within the framework of conceptual DFT. For a set of model clusters representing the vanadium oxide supported on SiO2, Al2O3, TiO2, ZrO2, the ionic character of the vanadium-oxygen bond, involved in the dissociative adsorption of methanol on the catalyst, was quantified. Detailed scrutiny shows that this ionicity increases from the Al through the Zr support, in agreement with the increasing catalytic activity through this series; the case of the Si supported oxide is found to be an exception however, giving rise to the most ionic V–O bond of the different compounds studied. This finding is confirmed by calculations on smaller clusters focusing on detail in the π back bonding.