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 formation. According to the inhibition mechanism of SO2 on Hg0 removal, we think there are some feasible approaches and strategies for coping with the SO2 poisoning problem: Increasing Hg0 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 Hg0 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.