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This paper discusses a recent study of mercury catalytic oxidation by chlorinating reagents. Gold was chosen as the catalyst because of its reluctance to chemisorb some gases such as O2, NO, H2O, and SO2. This property, as demonstrated in this study, is instrumental to mercury oxidation by circumventing some undesired inhibitory reactions such as OH + NO + M --> HONO + M and OH + SO2 + M --> HOSO2 + M, which were recognized under homogeneous situations at high temperatures. In comparison to Cl2, HCl showed weak oxidizing capability but appreciable inhibition in mercury oxidation by Cl2, probably through the competition of active sites with Cl2. Overall, the mercury catalytic oxidation by Cl2 on gold catalyst surfaces was viable, reaching 40-60% in this study under temperatures of 448-498 K, where the thermal decomposition of formed Hg2+ was effectively avoided.

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The sorption of mercury, as Hg 0 and HgCl 2 , in a synthetic flue gas (SFG) by three activated carbons has been examined by XAFS spectroscopy. The three carbons consisted of a sulfuractivated carbon, an iodine-activated carbon, and an activated carbon derived from lignite. In addition to mercury, the occurrence and behavior of sulfur, chlorine, calcium, and iodine were also examined by XAFS spectroscopy. These other elements were present either as activating species on the carbons or as reactive components (SO 2 , HCl) in the SFG. The XAFS results showed that each type of activated carbon behaves differently with respect to sorption of mercury and other species from the SFG. For the iodine-and sulfur-activated carbons, the XAFS data confirm that it is the activating element (I or S) that forms a sorption complex with mercury. However, the activated carbon from lignite exhibited a more variable behavior that reflected the conditions of the experiments, in particular whether HCl or HgCl 2 was present in the SFG. This study reveals some of the complexities that are involved in low-temperature sorption of mercury by activated carbons in that the sorption mechanism clearly involves acidic species of sulfur and chlorine in the gas phase, the affinity of the carbon for such species, and the nature of the active sites on the carbons, in addition to the mercury speciation.

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