In order to facilitate the removal of elemental mercury (Hg(0)) from coal-fired flue gas, catalytic oxidation of Hg(0) with manganese oxides supported on inert alumina (alpha-Al2O3) was investigated at lower temperatures (373-473 K). To improve the catalytic activity and the sulfur-tolerance of the catalysts at lower temperatures, several metal elements were employed as dopants to modify the catalyst of Mn/alpha-Al2O3. The best performance among the tested elements was achieved with molybdenum (Mo) as the dopant in the catalysts. It can work even better than the noble metal catalyst Pd/alpha-Al2O3. Additionally, the Mo doped catalyst displayed excellent sulfur-tolerance performance at lower temperatures, and the catalytic oxidation efficiency for Mo(0.03)-Mn/alpha-Al2O3 was over 95% in the presence of 500 ppm SO2 versus only about 48% for the unmodified catalyst. The apparent catalytic reaction rate constant increased by approximately 5.5 times at 423 K. In addition, the possible mechanisms involved in Hg(0) oxidation and the reaction with the Mo modified catalyst have been discussed.

MnO x /Al 2 O 3 catalysts (i.e., impregnating manganese oxide on alumina) were employed to remove elemental mercury (Hg 0 ) from flue gas. MnO x /Al 2 O 3 was found to have significant adsorption performance on capturing Hg 0 in the absence of hydrogen chloride (HCl), and its favorable adsorption temperature was about 600 K. However, the catalytic oxidation of Hg 0 became dominant when HCl or chlorine (Cl 2 ) was present in flue gas, and the removal efficiency of Hg 0 was up to 90% with 20 ppm of HCl or 2 ppm of Cl 2 . In addition, the catalysts with adsorbed mercury could be chemically regenerated by rinsing with HCl gas to strip off the adsorbed mercury in the form of HgCl 2 . Sulfur dioxide displayed inhibition to the adsorption of Hg 0 on the catalysts, but the inhibition was less to the catalytic oxidation of Hg 0 , especially in the presence of Cl 2 . The analysis results of XPS and pyrolysis-AAS indicated that the adsorbed mercury was mainly in the forms of mercuric oxide (HgO) and the weakly bonded speciation, and the ratio of them varied with the adsorption amount and manganese content on catalysts. The multifunctional performances of MnO x /Al 2 O 3 on the removal of Hg 0 appeared to be promising in the industrial applications.

Oxidation of Hg 0 with any oxidant or converting it to a particle-bound form can facilitate its removal. Two sulfur-chlorine compounds, sulfur dichloride (SCl 2 ) and sulfur monochloride (S 2 Cl 2 ), were investigated as oxidants for Hg 0 by gas phase reaction and by surface-involved reactions in the presence of flyash or activated carbon. The gas phase reaction rate constants between Hg 0 and the sulfur/chlorine compounds were determined, and the effects of temperature and the main components in flue gases were studied. The gas phase reaction between Hg 0 and SCl 2 is shown to be more rapid than the gas phase reaction with chlorine, and the second order rate constant was 9.1(±0.5) x 10 -18 mL-molecules -1 •s -1 at 373ºK. Nitric oxide (NO) inhibited the gas phase reaction of Hg 0 with sulfur-chlorine compounds. The presence of flyash or powdered activated carbon in flue gas can substantially accelerate the reaction. The predicted Hg 0 removal is about 90% with 5 ppm SCl 2 or S 2 Cl 2 and 40 g/m 3 of flyash in flue gas. The combination of activated carbon and sulfur-chlorine compounds is an effective alternative. We estimate that coinjection of 3-5 ppm of SCl 2 (or S 2 Cl 2 ) with 2-3 Lb/MMacf of untreated Darco-KB is comparable in efficiency to the injection of 2-3 Lb/MMacf Darco-Hg-LH. Extrapolation of kinetic results