Highly Dispersed Mn–Ce Binary Metal Oxides Supported on Carbon Nanofibers for Hg0 Removal from Coal-Fired Flue Gas

Yongjun Xia,Zijian Zhou,Zhiqiang Liao,Yan Zheng

doi:10.3390/app8122501

Yongjun Xia, Zijian Zhou + Show 2 more

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https://doi.org/10.3390/app8122501

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Abstract

Highly dispersed Mn–Ce binary metal oxides supported on carbon nanofibers (MnOx–CeO2/CNFs(OX)) were prepared for Hg0 removal from coal-fired flue gas. The loading value of the well-dispersed MnOx–CeO2 was much higher than those of many other reported supports, indicating that more active sites were loaded on the carbon nanofibers. In the present study, 30 wt % metal oxides (15 wt % MnOx and 15 wt % CeO2) were successfully deposited on the carbon nanofibers, and the sorbent yielded the highest Hg0 removal efficiency (>90%) within 120–220 °C under a N2/O2 atmosphere. An increase in the amount of highly dispersed metal oxides provided abundant active species for efficient Hg0 removal, such as active oxygen species and Mn4+ cations. Meanwhile, the carbon nanofiber framework provides the pathway for charge transfer during the heterogeneous Hg0 capture reaction processes. Under a N2+6%O2 atmosphere, a majority of Hg0 was removed via chemisorption reactions. The effects of flue gas composition were also investigated. O2 replenished the active oxygen species on the surface and thus greatly promoted the Hg0 removal efficiency. SO2 had an inhibitory effect on Hg0 removal, but NO facilitated Hg0 capture performance. Overall, carbon nanofibers seems to be a good candidate for the support and MnOx–CeO2/CNFs(OX) may be promising for Hg0 removal from coal-fired flue gas.

Highlights

Mercury (Hg) pollution has attracted worldwide concern because Hg and its compounds cause serious damage to human health and the environment [1]
Of global anthropogenic mercury emissions, but mercury emitted from power plants has not been controlled efficiently until recent years [2,3]
We found that chemically adsorbed oxygen species were mainly responsible for the low-temperature activity of MnOx in the absence of HCl [17]

Summary

Introduction

Mercury (Hg) pollution has attracted worldwide concern because Hg and its compounds cause serious damage to human health and the environment [1]. 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 (Hg2+ ), particulate-bounded (HgP ), and elemental (Hg0 ) mercury [4,5]. HgP could be captured along with the fly ash by dust removal devices (electrostatic precipitators or fabric filters), and water-soluble Hg2+ could be removed by wet flue gas desulfurization devices [6,7]. Hg0 in the flue gas is difficult to control; Hg0 is the dominant species emitted to the atmosphere. To remove Hg0 , adsorption and catalytic oxidation technologies have been proposed

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