Promotional effect of Mo addition on CoOX/Ti-Ce catalyst for oxidation removal of elemental mercury in flue gas

Abstract

To enhance the catalytic activity for elemental mercury (Hg0) oxidation and SO2 resistance of catalyst, Mo was applied to modify the CoOX/Ti-Ce (Co/TiCe) catalyst for better performance. The results showed that CoMo5/TiCe had the highest activity for Hg0 oxidation in the wide temperature window of 100–400 °C in the presence of 10 ppm HCl and 6% O2. NO exhibited insignificant effect on Hg0 oxidation. SO2 and H2O were found to inhibit Hg0 oxidation. Hg0 oxidation by HCl over CoMo5/TiCe catalyst mainly occurred through the Eley-Rideal mechanism, where gas-phase or weakly-bonded Hg0 reacted with surface chlorine species originated from adsorbed HCl to form Hg2+. SO2 could obstruct the generation of surface active chlorine species, thus inhibiting Hg0 oxidation. Compared with Co/TiCe, CoMo5/TiCe showed better resistance to SO2 and H2O for Hg0 oxidation. In the presence of 200 ppm SO2, CoMo5/TiCe achieved Hg0 oxidation efficiency of 96.1% and a simultaneous NO conversion efficiency of 42.9% at 300 °C, showing better performance than Co/TiCe. The physicochemical properties of the catalysts were examined by BET, XRD, Ranman spectroscopy, H2-TPR, XPS and EDS techniques to reveal the effect of Mo addition on the catalytic performances. It was found that an interaction of Mo with Co promoted the dispersion of Co3O4, increased the Co2+ and Oα concentration and enhanced the reducibility of catalyst, which contributed to the improvement of Hg0 oxidation activity. Moreover, the SO2 resistance of catalyst was enhanced by suppressing the reaction between the catalyst and SO2 due to Mo addition.