Negative effect of SO2 on mercury removal over catalyst/sorbent from coal-fired flue gas and its coping strategies: A review

Adsorption and catalytic oxidation are presently considered to be the most cost-effective and feasible methods for Hg0 removal from coal-fired flue gas. For most of the catalysts/sorbents developed so far, SO2 poisoning remains a thorny issue for the long-term operation. This review comprehensively discusses the negative effect of SO2 on mercury removal over catalyst/sorbent from coal-fired flue gas and its coping strategies. Instructive conclusions are obtained, which can serve as a theoretical basis for the development of novel SO2-resistant catalyst/sorbent for efficient abatement of Hg0. Briefly, there are four main reasons for the negative effect of SO2 on Hg0 removal: Competitive adsorption, consumption of active species by SO2, SO2-induced Hg2+ reduction and sulfate for-mation. According to the inhibition mechanism of SO2 on Hg-0 removal, we think there are some feasible ap-proaches and strategies for coping with the SO2 poisoning problem: Increasing Hg-0 affinity, suppressing SO2 adsorption, inhibiting SO2 oxidation, introducing sacrificial agent, increasing active sites, promoting sulfate decomposition and designing the micro/macro catalyst/sorbent structure. In addition, the adverse effect of SO2 on Hg-0 removal can be also weakened by the adjustment of operating parameters and process. Finally, future works to be conducted focused on the SO2 resistance of catalyst/sorbent for mercury removal are proposed.