Efficient MnFeW/Ti catalyst for simultaneous removal of NO and Hg0 in flue gas at low temperature: Effect of NO on Hg0 oxidation and reaction mechanism

Abstract

The MnFeW/Ti catalyst was synthesized and used for simultaneously removing NO and Hg0 from flue gas at low temperature and its catalytic performance has been tested. The MnFeW/Ti catalyst showed over 80% NOx conversion and 88% Hg0 removal between 180 and 300 °C at a high GHSV of 100000 h−1. NO obviously enhanced the catalytic capability for Hg0 removal and NH3 had almost no effect on Hg0 removal because NH3 did not affect the adsorption of NO and Hg0. Hg balance results revealed that Hg0 removal over MnFeW/Ti catalyst proceeded via both chemisorption and catalytic oxidation, which is attributed to the different bonding strength between Hg0 and active sites. The Hg0 oxidation process was also investigated through transient reaction experiments along with Hg-TPD and XPS characterization. Hg0 oxidation over MnFeW/Ti catalyst obeys both Mars–Maessen mechanism in which active oxygen reacts with adsorbed Hg0 and Langmuir − Hinshelwood mechanism comprising the reaction of formed NO2 with adsorbed Hg0. HgO, resulted from the reaction between NO2 as an active intermediate and adsorbed Hg0, is liable to desorb from MnFeW/Ti catalyst.