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

To effectively reduce the emission of Hg-0, developing an adsorbent with a superior Hg-0 removal performance constituted an important step. As a typical rare earth metal oxide, CeO2 was always used for Hg-0 capture because of its tunable physicochemical properties. However, the weak acidity and the intermediate oxidative ability restrained its effective removal of Hg-0, especially from the flue gas with a high Hg-0 content. Thanks to the superior acidity and oxidability, CrOx addition could ensure the sufficient physisorption of Hg-0 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 % Hg-0 removal efficiency could be reached at 150 degrees 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 Hg-0 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 Hg-0 removal efficiency of CeO2-CrOx mixed oxides. During the Hg-0 adsorption cycles, Mars-Maessen route dominated; Cr6+ played the role of an active site to oxidize Hg-0, 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.

Automated summary

By adding CrOx to CeO2, the removal performance of Hg-0 can be improved. The sample with a Ce/Cr molar ratio of 3/1 exhibited the best performance, with approximately 90% Hg-0 removal efficiency achieved at 150 degrees C. CeO2-CrOx mixed oxide has a larger specific surface area and abundant acid sites and reactive oxygen species, which facilitate the physisorption and oxidation of Hg0.