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

Wei He; Jingyu Ran; Juntian Niu; Guangpeng Yang; Zhiliang Ou; Zhi He

doi:10.1016/j.jhazmat.2020.122646

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

J Hazard Mater. 2020 Oct 5:397:122646. doi: 10.1016/j.jhazmat.2020.122646. Epub 2020 Apr 13.

Authors

Wei He¹, Jingyu Ran², Juntian Niu³, Guangpeng Yang¹, Zhiliang Ou¹, Zhi He¹

Affiliations

¹ Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Ministry of Education of PRC, Chongqing University, Chongqing, 400044, China; School of Energy and Power Engineering, Chongqing University, Chongqing, 400044, China.
² Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Ministry of Education of PRC, Chongqing University, Chongqing, 400044, China; School of Energy and Power Engineering, Chongqing University, Chongqing, 400044, China. Electronic address: ranjy@cqu.edu.cn.
³ Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Ministry of Education of PRC, Chongqing University, Chongqing, 400044, China; School of Energy and Power Engineering, Chongqing University, Chongqing, 400044, China. Electronic address: juntianniu@cqu.edu.cn.

PMID: 32353782
DOI: 10.1016/j.jhazmat.2020.122646

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.

Keywords: CeO2; DFT; HCl; Mercury oxidation; Oxygen vacancy.