Effect of calcination temperature on the activity and structure of MnOx/TiO2 adsorbent for Hg0 removal

The influence of calcination temperature (200-800 degrees C) on the activity and structure of MnOx/TiO2 adsorbent prepared by a deposition-precipitation method is investigated by using an elemental mercury (Hg-0) removal setup and a variety of techniques such as N-2 adsorption/desorption, SEM, XRD, H-2-TPR, FTIR, TG-DSC, and XPS. The results exhibit that the Hg-0 removal activity of MnOx/TiO2 adsorbent is closely related to the calcination temperature. The Hg-0 removal activity firstly increases below 400 degrees C and then decreases with the increase of calcination temperature. Calcination at various temperatures may cause several successive structural changes such as the evaporation of water, decomposition of manganese compounds, enhancement of MnOx crystallization, and the crystal phase transformation of MnOx and TiO2. Some agglomerations of MnOx/TiO2 occur at higher calcination temperature, resulting in the drastic decreases of BET surface area and pore volume. Meanwhile, the particle sizes greatly increase. With an increase in calcination temperature, the oxidation state of manganese would convert from Mn4+ to Mn3+, and the surface chemisorbed oxygen decreases due to the removal of surface chemisorbed oxygen. Excessively higher calcination temperature would lead to the deactivation of MnOx/TiO2. (C) 2014 Elsevier B.V. All rights reserved.