Effects of synthesis methods on the physicochemical properties and Hg0 capture capability of MnO2-CeO2 mixed oxides

This study illustrated the effects of synthesis methods, namely, co-precipitation (CP), hydrothermal (HT), and ethylene glycol-assisted solvothermal method (EG), on the physicochemical properties and Hg-0 capture capability of MnO2-CeO2 mixed oxides. For the samples prepared using CP and EG methods, a downward trend in the Hg-0 removal efficiency from ca. 100% to lower than 40% was presented as the temperature increased. While for the adsorbent synthesized using EG method, Hg-0 removal efficiency first increased to the peak value of ca. 87% at 200 degrees C and then declined with the temperature increasing to 250 degrees C. A relatively strong oxidability facilitated the direct oxidation of the physically adsorbed Hg-0 to HgO, which, to some extent, explained the higher Hg-0 removal efficiency of the adsorbents synthesized using CP and HT methods at lower temperatures. Plentiful surface acid sites promoted the physisorption of Hg-0, which was beneficial for the next Hg-0 oxidation step and constituted an important reason for the elevated high-temperature Hg-0 adsorption capability of the adsorbent prepared via EG method. During the Hg-0 capture process, chemisorption dominated with Mn4+ acting as an active site to oxidize Hg-0 and Ce4+ functioning as a promoter to accelerate the regeneration of Mn4+.

Automated summary

This study investigated the effects of different synthesis methods on the physicochemical properties and Hg-0 capture capability of MnO2-CeO2 mixed oxides. Samples prepared using co-precipitation and ethylene glycol-assisted solvothermal method showed a decrease in Hg-0 removal efficiency with increasing temperature, while the adsorbent synthesized using hydrothermal method exhibited higher Hg-0 removal efficiency at lower temperatures. The presence of abundant surface acid sites promoted the physisorption of Hg-0 and facilitated the oxidation step, leading to enhanced high-temperature Hg-0 adsorption capability for the adsorbent prepared via ethylene glycol-assisted solvothermal method.