(659h) Modifying the Electronic Environment of VOx Active Site By Altering the Support Structure to Improve Hg Oxidation Activity

The emission of mercury (Hg) during the combustion of fossil fuels represents a significant threat to the global climate due to its highly toxic nature and ability to accumulate in human organisms. To date, efficient removal of harmful Hg from flue gas of coal combustion facilities can be achieved through catalytic oxidation of elemental Hg using a highly active VO_x/TiO₂ catalyst. It has been reported that the activity of VO_x/TiO₂ catalysts can be enhanced in reactions such as NO_x reduction, N₂O decomposition, and Hg oxidation by introducing modifications to the catalyst. In addition to pre- or post-treatments that impact the catalyst status, the catalytic activity of VO_x/TiO₂ catalysts can be improved by modifying the composition of the catalytic active center. Particularly, support modification can enhance the reactivity by altering the electronic environment of VO_x active center, which is crucial for surface-reactant interaction.

In this study, density functional theory (DFT) calculations were employed to investigate the effects of support tuning methods (e.g., crystallographic phase control and reduction treatment) on Hg oxidation activity and elucidate the changes in the electronic environment of active site. As a result, the phase control to the TiO₂ support improved Hg oxidation activity, while reduction treatment decreased it due to changes in the charge density at the VO_x active center. In addition, the interaction between the V site and surface Cl played a critical role in balancing two key reaction steps of HCl dissociation and HgCl₂ desorption, thereby influencing Hg oxidation reactivity. These findings provide valuable guidance for enhancing the activity of the VO_x/TiO₂ catalyst in various reactions, such as Hg oxidation and selective catalytic reduction (SCR) of NO_x compounds.