DFT model development of V2O5-TiO2 catalyst for oxidation of mercury pollutants

Abstract

Mercury pollution in South Africa is a growing problem due to the country’s dependency on coal combustion for generating electricity. During coal combustion, mercury can be emitted as elemental mercury (Hg0), in its oxidized form (Hg2+) or as particle-bound mercury (Hg(p)). Hg2+ and Hg(p) are easier to remove from the flue gas than Hg0.[2, 3] However, Hg0 could be oxidized to Hg2+ in coal combustion power plants by using selective catalytic reduction (SCR) catalysts. Hg2+ can then be removed by conventional wet flue gas desulfurization processes, because Hg2+ is highly soluble in aqueous solutions. This provides an economic viable solution, since existing SCR systems promotes upstream mercury oxidation[2], already employed for the reduction of NOx to N2. However, SCR catalysts are not 100% effective. In order to be able to develop better SCR catalysts, more research is needed in ascertaining the mechanism of mercury oxidation on the catalyst surface. In this study, the focus was on investigating a possible mechanism for mercury oxidation on the surface of a V2O5-TiO2 catalyst. This investigation was achieved by developing a density functional theory (DFT) model for the TiO2 anatase support surface and subsequently the V2O5-TiO2 catalyst, and validating these through comparison with a study done by Wilcox[4]. A mechanism was then postulated and investigated for the oxidation of mercury over the V2O5-TiO2 catalyst. The postulated mechanism for mercury oxidation over this catalyst was proven to be plausible. This model can now be refined to fully understand oxidation of mercury over the V2O5-TiO2 catalyst.