Structure-activity relationship of VOx/TiO2 catalysts for mercury oxidation: A DFT study

Elemental mercury (Hg-0), mostly from coal combustion, poses a critical threat to ecosystems and the health of human beings, as it causes several fatal human diseases. Thus, there has been an effort to strengthen regulations around the world. Catalytic oxidation of Hg-0 into HgCl2 is considered an economical and practical option, and selective catalytic reduction catalysts such as titania-supported vanadia (VOx/TiO2) have been shown to also oxidize Hg-0 to Hg2+. Herein, based on density functional theory (DFT) calculations, we demonstrate the relationship between the coordinative environment of V in the VOx/TiO2 catalyst and the catalytic activity towards Hg-0 oxidation, as well as the effect of hydroxylation. We mechanistically estimate the Hg-0 oxidation activity of several VOx/TiO2 models using previously reported mechanisms. We also explore the temperature (T)- and pressure (p)-dependent thermodynamic stabilities of the VOx/TiO2 catalyst models by calculating the Gibbs free energy of formation (Delta G(form)). Finally, the thermodynamic (T, p) conditions that favor high activity of the VOx/TiO2 catalyst are suggested.

Automated summary

By utilizing density functional theory calculations, the study demonstrates the relationship between the coordinative environment of V in the VOx/TiO2 catalyst and the catalytic activity towards Hg-0 oxidation, as well as the effect of hydroxylation. Mechanistic estimation of the Hg-0 oxidation activity and calculation of the thermodynamic stabilities of the catalyst models suggest thermodynamic conditions that favor high catalytic activity.