CeO 2-TiO 2 catalysts for catalytic oxidation of elemental mercury in low-rank coal combustion flue gas

Abstract

CeO 2-TiO 2 (CeTi) catalysts synthesized by an ultrasound-assisted impregnation method were employed to oxidize elemental mercury (Hg 0) in simulated low-rank (sub-bituminous and lignite) coal combustion flue gas. The CeTi catalysts with a CeO 2/TiO 2 weight ratio of 1-2 exhibited high Hg 0 oxidation activity from 150 to 250 °C. The high concentrations of surface cerium and oxygen were responsible for their superior performance. Hg 0 oxidation over CeTi catalysts was proposed to follow the Langmuir-Hinshelwood mechanism whereby reactive species from adsorbed flue gas components react with adjacently adsorbed Hg 0. In the presence of O 2, a promotional effect of HCl, NO, and SO 2 on Hg 0 oxidation was observed. Without O 2, HCl and NO still promoted Hg 0 oxidation due to the surface oxygen, while SO 2 inhibited Hg 0 adsorption and subsequent oxidation. Water vapor also inhibited Hg 0 oxidation. HCl was the most effective flue gas component responsible for Hg 0 oxidation. However, the combination of SO 2 and NO without HCl also resulted in high Hg 0 oxidation efficiency. This superior oxidation capability is advantageous to Hg 0 oxidation in low-rank coal combustion flue gas with low HCl concentration. © 2011 American Chemical Society.