Change in the Electronic Environment of the VOx Active Center via Support Modification to Enhance Hg Oxidation Activity

Abstract

Oxidation of elemental Hg (Hg0) is catalytically and economically an efficient way to remove the harmful Hg contained in the flue gas from coal combustion facilities. Thus, the development of a highly active V2O5/TiO2 catalyst, which is active to the Hg oxidation, is very essential. Support modification can change the reactivity of V2O5/TiO2 by affecting the V2O5 active center which is critical to the surface–reactant interaction, so understanding the effects of support tuning methods, e.g., crystallographic phase control and reduction treatment, on the Hg oxidation activity is valuable. Herein, density functional theory calculations were performed to mechanistically investigate the change of Hg oxidation reactivity by the support tuning methods and to elucidate the change of the electronic environment at the active site. The phase control to the TiO2 support was found to improve the Hg oxidation activity, but the reduction treatment decreased the activity, which is attributed to the change of the charge density at V2O5. Furthermore, the origin of the reactivity change was elucidated within a Sabatier-like principle that the interaction between the V site and the surface Cl critically contributes to the change of the Hg oxidation reactivity by balancing the competition between two key reaction steps of HCl dissociation and HgCl2 desorption. Our results provide guidance to improve the activity of the VOx/TiO2 catalyst for various reactions such as Hg oxidation and selective catalytic reduction of NOx and so on.