The overall mercury removal efficiency of commonly applied air pollution control devices (APCDs) mainly depend on the occurrence of mercury species and their properties. It is commonly agreed that oxidized mercury compounds especially HgCl{sub}2(g) favor the removal of mercury in electrostatic precipitators (ESP) and in wet desulfurization units (wet FGD). Contradictory statements exist about the oxidation of Hg{sup}0(g) to HgCl{sub}2(g) across SCR-DeNO{sub}x catalysts and their effect on the fate of mercury in downstream APCDs. This paper comprises results from parametric studies at a laboratory catalytic unit that are performed to investigate in detail the oxidation process in a model flue gas. In a first phase different catalyst types (customary honeycomb as well as plate-type) were screened towards their potential to oxidize Hg{sup}0(g) to HgCl{sub}2(g) in a model flue gas with a HCl concentration of 60 ppm typical at units firing bituminous coal. The contribution of homogenous gas-phase oxidation was determined in preliminary tests without the catalysts, showing mercury oxidation rates between 5 and 20%. The application of catalysts increased mercury oxidation rates to values between 70 and 95% in the temperature range between 280 and 420°C.
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