Synergetic removal of elemental mercury and NO over TiCe0.25Sn0.25Ox catalysts from flue gas: Performance and mechanism study

Abstract

A novel TiCe0.25Sn0.25Ox catalyst was designed and prepared by a sol-gel method for synergetic removal of NO and elemental mercury (Hg0) from flue gas. The as-designed TiCe0.25Sn0.25Ox catalyst achieved a synergetic removal efficiency of NO (NH3-SCR) and Hg0 (Hg0 oxidation) of 95%, 85% and 70%, 65% (after 300 ppm SO2 and 6 vol% H2O were injected) at 200 °C under simulated flue gases conditions, respectively. Moreover, the mercury, which gathered on the surface of TiCe0.25Sn0.25Ox after adsorption and oxidation, could be released and collected by the thermal decomposition method, avoiding the secondary pollution by mercury. The mechanism underlying the synergetic removal of NO and Hg0 was also investigated using various characterization techniques. The synergistic catalysis between redox and solid acid contributed to the synergetic removal of NO and Hg0 over TiCe0.25Sn0.25Ox. The results of XRD and XPS revealed that the lattice oxygen was a key factor for Hg0 oxidation reaction. The results of N2-physisorption, NH3-TPD, H2-TPR and Py-IR illustrated that TiCe0.25Sn0.25Ox possessed the mesopores structure, suitable particle sizes, the excellent redox and weak acid (Lewis sites) properties, contributing to its high NO and Hg0 removal efficiency. Furthermore, the removal of NO and Hg0 showed a synergetic effect. The analysis of Hg-TPD and (NO + O2)-TPD had confirmed that the mid-product NO2 of NH3-SCR reaction was favorable for Hg0 oxidation. In summary, the TiCe0.25Sn0.25Ox possesses not only good synergetic removal performance for NO and Hg0 but also satisfactory anti-sulfur performance, which is a promising candidate for the effective and economical removal of NO and Hg0 in the cement and steel industries.