Mechanistic study on the role of VOx in the acidity, oxidizability, and Hg0 capture capability of FeOx-VOx binary mixed oxides

Abstract

In this article, we have prepared a series of FeOx-VOx mixed oxides using the sol-gel method and evaluated their Hg0 removal performance. Virgin Fe showed poor activity, as evidenced by its low Hg0 capture capacity of ca. 6.7 μg/g. When VOx was introduced, abundant acid sites came out on the adsorbent surfaces, which facilitated the physisorption of Hg0 and overpowered the negative effects of the weakened oxidizability involved in the oxidation of Hg0. Consequently, improved Hg0 adsorption performance was observed as ca. 41.9 μg/g Hg0 capture capacity could be obtained as the molar ratio of V/Fe reached 1/9. Throughout the whole Hg0 capture process, chemisorption dominated with the initial adsorption stage constituting the rate-controlling step. V5+, together with chemical adsorbed oxygen, was directly involved in the oxidation of Hg0, whereas Fe3+ functioned as a promoter-like site to accelerate the regeneration of V5+. Finally, FeOx-VOx adsorbent exhibited elevated Hg0 capture capacity in NO- or SO2-containing flue gas as well as satisfactory recyclability, demonstrating its potential as an adsorbent for practical applications.