Performance and Mechanism of MnO2/γ-Al2O3 for Gaseous Thallium Capture from Cement Kiln Flue Gas
Thallium (Tl) is a highly toxic trace heavy metal, posing severe risks to human health and the environment. Cement kilns are significant sources of gaseous Tl emissions, with concentrations up to 25 μg·m−3, which can poison SCR catalysts and cause environmental contamination. This study developed MnO2/γ-Al2O3 adsorbents via wet impregnation with varying Mn loadings (0–15 wt%) to capture gaseous TlCl. Fixed-bed adsorption experiments at 300 °C with 20% O2 revealed that capture capacity initially increased with Mn loading, peaking at 10 wt% MnO2 (10MnO2/γ-Al2O3), then declined at 15 wt%. Characterization (XRD, O2-TPD, H2-TPR) indicated that Mn species enhanced redox properties, oxidizing Tl+ to Tl3+ and immobilizing it on the surface. DFT calculations showed that TlCl forms stronger Al–Cl and Mn–Cl bonds on MnO2/γ-Al2O3 than on γ-Al2O3, with higher adsorption energy and greater charge transfer, corroborating experimental results. The optimal adsorbent, 10MnO2/γ-Al2O3, demonstrates superior Tl capture performance, offering a promising upstream solution for protecting SCR catalysts and reducing atmospheric Tl emissions from cement kilns.