Effect of support on the vanadyl oxygen abstraction in supported vanadia

TL;DR

This study uses cluster DFT modeling to explore how support materials influence vanadia catalysts' activity, revealing that oxygen mobility results from a compensation effect in surface bonding.

Contribution

It provides a detailed mechanistic insight into how support interactions affect vanadyl oxygen dissociation energy in supported vanadia catalysts.

Findings

Optimal separation of 3 Å minimizes V=O dissociation energy to 36 kcal/mol.

Dissociation energy varies with particle separation, reaching up to 143 kcal/mol at 4 Å.

Oxygen mobility is driven by a compensation effect in chain-like bonding on the support surface.

Abstract

Supported vanadia catalysts are modeled within the cluster DFT approach to get an insight into the mechanism in which the support affects the activity of vanadia in the oxidation processes. The energy of the V=O group dissociation chosen as a descriptor of the oxidation activity is estimated using two aligned divanadate V2O3(OH)4 particles at various distances. Separation between particles allows to imitate (i) the various supporting materials (e.g. TiO2, SiO2, etc.), and (ii) the coverage of vanadia on a particular support. A substantial compensation of the energy loss upon the vanadyl oxygen abstraction via bonding to the vanadyl oxygen of neighboring vanadate particle has been predicted. On account of such compensation the overall energy of the V=O dissociation reaches its minimal value of 36 kcal/mol (dropping from maximum of 142 kcal/mol) at small separation of 3 {\AA} between dimers when the nearest vanadyl oxygen occupies a bridge V-O-V position. For dimers separated by about 4 {\AA}, the dissociation energy achieves its maximal value for isolated dimers of about 143 kcal/mol. Thus, these findings allows one to conclude that the oxygen mobility is a result of a compensation effect in a chain-like bonding between neighboring vanadyl groups on the surface of support.