Relationship between Hg0 capture performance and physicochemical properties of CeO2-CrOx mixed oxides

Abstract

To effectively reduce the emission of Hg0, developing an adsorbent with a superior Hg0 removal performance constituted an important step. As a typical rare earth metal oxide, CeO2 was always used for Hg0 capture because of its tunable physicochemical properties. However, the weak acidity and the intermediate oxidative ability restrained its effective removal of Hg0, especially from the flue gas with a high Hg0 content. Thanks to the superior acidity and oxidability, CrOx addition could ensure the sufficient physisorption of Hg0 and accelerate its oxidation to HgO. Thus in this study, a serial CeO2-CrOx mixed oxides were prepared. The sample with Ce/Cr molar ratio of 3/1 exhibited the best performance; ca. 90 % Hg0 removal efficiency could be reached at 150 °C. Compared with virgin CeO2 and CrOx, the combination of these two metal oxides brought out a larger specific surface area, which would provide an increased number of active sites for Hg0 removal. Meanwhile, the presence of plentiful acid sites and reactive oxygen species favored the physisorption and oxidation of Hg0, hence contributing to a relatively high Hg0 removal efficiency of CeO2-CrOx mixed oxides. During the Hg0 adsorption cycles, Mars-Maessen route dominated; Cr6+ played the role of an active site to oxidize Hg0, while Ce4+ acted as a promoter-like site to boost the regeneration of Cr6+. Finally, CeO2-CrOx mixed oxide exhibited a satisfactory recyclability and a relatively weak gas component adaptability, suggesting that further modification should be conducted to improve the practicality of CeO2-CrOx mixed oxide.