Our proposed COAP (Cold Oxidation Adsorption Process) technology has shown effective adsorption of SO2 and NOx in flue gas (emission <1 ppmv), making it a potential future flue gas treatment technology. The core component of this technology, the adsorption tower, aims to adsorb SO2 and NOx at low temperatures (-40–0°C). Interestingly, we found it has synergetic effects on mercury removal and its mechanism still remains uncertain in the existing literature. Therefore, this research investigated the behavior of mercury oxidation by activated coke adsorbents modified with typical active components (Cl/Br/I/O) at ultra-low temperatures. The effects of common modification methods on the adsorption of activated coke at low temperatures were investigated using a low-temperature adsorption test benches. The oxidation mechanism of mercury on the adsorbent surface at low temperatures was revealed by BET and XPS characterization, showing that O* and C-X (where X = Cl, Br, I) play key roles in mercury adsorption at low temperatures. In addition, the promotion effect of SO2 and NO on mercury removal in O2 environment is more obvious at low temperature than at high temperature. This may be due to the oxidation reaction as an exothermic reaction, low temperature is conducive to the oxidation reaction. In order to clarify the distribution characteristics of mercury at low temperatures, the used activated cokewas used for Hg-TPD analysis. The experimental results indicate that low temperature does not alter the reaction pathway and reaction products. Overall, halogen and oxygen modified activated coke adsorbent showed superior Hg removal performance at low temperatures and this study is expected to provide deep understanding of mercury reaction mechanism at low temperature.
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