Impact of individual flue gas components on mercury oxidation over a V2O5–MoO3/TiO2 catalyst

Abstract

A titanium–vanadium–molybdenum (V₂O₅–MoO₃/TiO₂) SCR (selective catalytic reduction) catalyst has been confirmed to be effective for mercury oxidation in 6% O₂/N₂ atmosphere, but the influence of the actual flue gas components on mercury oxidation over this catalyst has not been reported. The individual flue gas components can significantly influence the mercury oxidation ability of the SCR catalyst. In this study, the effect of individual flue gas components on V₂O₅–MoO₃/TiO₂ for mercury oxidation was evaluated. The results suggested that the mercury oxidation efficiency of V₂O₅–MoO₃/TiO₂ was over 95% in the presence of 20 ppm HCl. The process of mercury oxidization by HCl over V₂O₅–MoO₃/TiO₂ followed the Langmuir–Hinshelwood mechanism. O₂ was critical in this process, and we could continue catalytic recycling by re-oxidizing the reduced lattice oxygen. NH₃ and H₂O, especially H₂O, suppressed the mercury oxidation ability of the catalyst. The mercury oxidation ability of V₂O₅–MoO₃/TiO₂ was almost lost in the presence of 8% H₂O. Even after elimination of H₂O, the mercury oxidation efficiency only recovered to 55%. This was due to the competition of NH₃ or H₂O with Hg⁰ for the same active sites on the surface of the catalyst. Unfortunately, H₂O caused irreversible damage to the active sites. Additionally, the mercury oxidation efficiency was over 60% even with the existence of high SO₂ content. This indicated that this catalyst can display some degree of sulfur resistance.