Mechanism of Mercury Adsorption and Oxidation by Oxygen over the CeO₂ (111) Surface: A DFT Study.

Li Zhao,Yangwen Wu,Qiang Lu,Laibao Zhang,Yongping Yang,Jian Han

doi:10.3390/ma11040485

Abstract

CeO2 is a promising catalytic oxidation material for flue gas mercury removal. Density functional theory (DFT) calculations and periodic slab models are employed to investigate mercury adsorption and oxidation by oxygen over the CeO2 (111) surface. DFT calculations indicate that Hg0 is physically adsorbed on the CeO2 (111) surface and the Hg atom interacts strongly with the surface Ce atom according to the partial density of states (PDOS) analysis, whereas, HgO is adsorbed on the CeO2 (111) surface in a chemisorption manner, with its adsorption energy in the range of 69.9–198.37 kJ/mol. Depending on the adsorption methods of Hg0 and HgO, three reaction pathways (pathways I, II, and III) of Hg0 oxidation by oxygen are proposed. Pathway I is the most likely oxidation route on the CeO2 (111) surface due to it having the lowest energy barrier of 20.7 kJ/mol. The formation of the HgO molecule is the rate-determining step, which is also the only energy barrier of the entire process. Compared with energy barriers of Hg0 oxidation on the other catalytic materials, CeO2 is more efficient at mercury removal in flue gas owing to its low energy barrier.

Highlights

Mercury, a pollutant harmful to human health and the environment, has become a global concern due to its toxicity, high volatility, and bioaccumulation [1,2,3,4]
Experimental results from Li et al and Fan et al showed that CeO2 had a satisfactory catalytic performance in the oxidation of Hg0 and maintains over 90% oxidation efficiency under simulated flue gas conditions [16,18]
Zhao et al investigated the modification of a commercial SCR catalyst with a series of metal oxides and found that the SCR catalyst doped with CeO2 exhibited the highest

Summary

Introduction

A pollutant harmful to human health and the environment, has become a global concern due to its toxicity, high volatility, and bioaccumulation [1,2,3,4]. In October 2013, the first legally-binding international treaty, called the Minamata Convention, was concluded to limit global emissions of mercury [5,6]. Coal-fired power plants are regarded as major sources of atmospheric mercury emissions [7,8]. Standard of Air Pollutants for Thermal Power Plant (GB13223-2011), released by the Ministry of Environmental Protection of China, set the limit for the emission of mercury and its compounds from coal-fired boilers to 0.03 mg/m3. Mercury removal technology for coal-fired flue gas is urgently needed

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