Insight into the effect of facet-dependent surface and oxygen vacancies of CeO2 for Hg removal: From theoretical and experimental studies

Abstract

The reaction mechanisms of Hg oxidation on CeO2(111) and (110) surface are clarified by a group of designed experiments and density functional theory (DFT) calculations. CeO2 nanorods and nanoparticles with exposure (110) and (111) faces were prepared by hydrothermal methods, and their morphological properties were investigated using XRD, XPS and HRTEM. Combined experimental and DFT results, the nanorods show better activity than nanoparticles. The total oxidation of Hg can be partially prohibited by the high barriers for the incorporated chlorine activation at reduced surfaces, due to the strong electronic repulsion of heavily accumulated charges. The energy barrier profiles suggest Hg oxidation is much more favorable on CeO2(110) surface than that on CeO2(111) surface. In the Hg oxidation via HCl and O2, the role of O2 is not only replenishment of lattice oxygen, but also could generate surface oxygen as active center for HCl active. The complete catalytic cycle can be identified as four parts: (i) HCl activated by lattice oxygen, (ii) Hg oxidation on defect surface, (iii) HCl activated by adsorbed oxygen and (iv) Hg oxidation on stoichiometric surface. The results of this study provide deep insights into the effects of CeO2 nanocatalyst morphology on the Hg oxidation.