## 1 Introduction  
Mercury (Hg) pollution has attracted worldwide concern because Hg and its compounds cause serious damage to human health and the environment [1]. Coal-fired power plants account for 24% of global anthropogenic mercury emissions, but mercury emitted from power plants has not been controlled efficiently until recent years [2; 3]. In coal-fired flue gas, Hg always exists in three forms: oxidized (Hg\({}^{2+}\)), particulate-bounded (Hg\({}^{\mathrm{P}}\)), and elemental (Hg\({}^{0}\)) mercury [4; 5]. Among them, Hg\({}^{\mathrm{P}}\) could be captured along with the fly ash by dust removal devices (electrostatic precipitators or fabric filters), and water-soluble Hg\({}^{2+}\) could be removed by wet flue gas desulfurization devices [6; 7]. However, Hg\({}^{0}\) in the flue gas is difficult to control; thus, Hg\({}^{0}\) is the dominant species emitted to the atmosphere. To remove Hg\({}^{0}\), adsorption and catalytic oxidation technologies have been proposed. Many materials, such as activated carbon [8; 9], have been used for Hg\({}^{0}\) adsorption, but the poor selectivity and high cost have limited large-scale application. In recent years, much attention has been paid to sorbents based on transition metal oxides. The transition metal oxides exhibit excellent performances for Hg\({}^{0}\) capture due to their extraordinary properties of multiple valence states and high chemical stability. VO\({}_{\rm x}\)[10; 11], CoO\({}_{\rm x}\)[12], CuO\({}_{\rm x}\)[13], and FeO\({}_{\rm x}\)[14], etc., have been investigated for Hg\({}^{0}\) removal in simulated coal-fired flue gas. However, the Hg\({}^{0}\) removal efficiencies of these transition metal oxides greatly rely on the concentration of HCl in the flue gas [5; 14]. When there is little HCl in the flue gas, the Hg\({}^{0}\) removal activity of the above sorbents will be limited [15]. Therefore, it is essential to develop transition-metal-oxide-based sorbents for efficient Hg\({}^{0}\) removal in flue gas with a low HCl concentration or in the absence of HCl. MnOx-supported sorbents may be a promising candidate for Hg\({}^{0}\) removal even in the absence of HCl [16]. In our previous study, we found that chemically adsorbed oxygen species were mainly responsible for the low-temperature activity of MnO\({}_{\rm x}\) in the absence of HCl [17]. O\({}_{2}\) in the flue gas is an important component to promote the Hg\({}^{0}\) removal activity because it can replenish the active oxygen species of the sorbents which are consumed in the Hg\({}^{0}\) adsorption reactions [18]. In addition, the O\({}_{2}\) concentration in flue gas is much higher than that of HCl, so making full use of O\({}_{2}\) to remove Hg\({}^{0}\) is of significance. Hence, CeO\({}_{2}\) has been widely used to modify the metal oxides to enhance their Hg\({}^{0}\) removal activity due to its large oxygen storage capacity [18]. Ce\({}^{3+}\) cations could yield charge imbalance, vacancies, and unsaturated chemical bonds, which lead to an increase of the chemisorbed oxygen concentration on its surface [19; 20]. In the Ce\({}^{4+}\)/Ce\({}^{3+}\) redox couple, CeO\({}_{2}\) loses the active oxygen to oxidize the cations with low valence and/or Hg\({}^{0}\), which then turn into Ce\({}_{2}\)O\({}_{3}\). Meanwhile, Ce\({}_{2}\)O\({}_{3}\) adsorbs O\({}_{2}\) and turns into CeO\({}_{2}\), which achieves the use of O\({}_{2}\) in flue gas [19]. Up to today, MnO\(\times\)-CeO\({}_{2}\) binary metal oxides have been used for Hg\({}^{0}\) removal in a few investigations. As far as is known, MnO\({}_{\rm x}\)-CeO\({}_{2}\) mixed oxides supported on TiO\({}_{2}\)[19; 21], Ti-PILCs [16], activated coke [22], and \(\gamma\)-Al\({}_{2}\)O\({}_{3}\)[23] for Hg\({}^{0}\) removal have been reported. These sorbents exhibited good Hg\({}^{0}\) removal performance. However, the results also showed that with increasing active metal oxide loading, the metal oxides tend to agglomerate, leading to an insufficient use of active metal oxides.