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.

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► Chemical concepts are valuable tools to interpret structural and reactivity data.
► Valence bond theory, among others, provides a direct measure of the concept of ionicity of a bond.
► The ionicity of the V–O–Support bond was proposed recently to explain the support effect in the catalytic activity of supported vanadium oxides.
► Bond ionicity from valence bond theory to a large extent supports previously made observations of this quantity.