Revealing Insights into the Mechanism of Hg0 Removal over MnO2 Hollow Sphere Adsorbents: Effect of Calcination Temperatures

In this study, MnO2 hollow spherical adsorbents were synthesized using the template approach, and the impacts of calcination temperatures on their physicochemical parameters and Hg-0 removal ability were investigated. The adsorbent calcined at 300 degrees C (labeled as Mn300) demonstrated the highest performance; at 200 degrees C, the Hg-0 removal efficiency reached over 90%. The presence of surface acid sites promoted the physisorption of Hg-0 and compensated for the relatively weak oxidative ability, which made much of the Hg-0 susceptible to capture on the adsorbent surface and consequently explained Mn300's superior Hg-0 capture capacity. The Mars-Maessen mechanism helped to understand the Hg-0 capture pathways over Mn300, with Mn4+ and chemisorbed oxygen serving as the active species to oxidize Hg-0 to HgO. Finally, Mn300 demonstrated reasonable recyclability and a rather weak gas-component adaptability, indicating that additional modification is required to improve the practical use of the adsorbent.