Heterogeneous Mercury Reaction on a Selective Catalytic Reduction (SCR) Catalyst

Abstract

The heterogeneous mercury reaction mechanism, reactions among elemental mercury (Hg 0 ) and simulated flue gas across laboratory-scale selective catalytic reduction (SCR) reactor system was studied. The surface of SCR catalysts used in this study was analyzed to verify the proposed reaction pathways using transmission electron microscopy with energy dispersive X-ray analyses (TEM-EDX) and X-ray photoelectron spectroscopy (XPS). The Langmuir-Hinshelwood mechanism was proven to be most suitable explaining first-layer reaction of Hg 0 and HCl on the SCR catalyst. Once the first layer is formed, successive layers of oxidized mercury (HgCl 2 ) are formed, making a multi-layer structure.

Transformations of mercury in processes of solid fuel combustion – review

“…Wu and co-authors also highlighted oxidation effi ciency reaching 71% in the SCR systems. By means of the wet FGD without SCR, it was possible to capture 54.9-68.8% of total mercury, while with the SCR system the mercury removal effi ciencies ranged from 78% to 90.2% (Winberg et al 2004, Eom et al 2008, Strege 2008.…”

Oxidation Catalysts for Elemental Mercury in Flue Gases—A Review

“…Evidence of HCl adsorption on the catalyst surface was obtained by employing different surface analysis methods [23][24][25]. Following the reaction between HCl and the V 2 O 5 active sites on the catalyst surface, several vanadyl oxychloride complexes such as VOCl 2 , V 2 O 3 (OH) 2 Cl 2 , VO 2 Cl 2 are formed [23,24].…”

“…They explained the decrease of Hg el oxidation efficiency at temperatures above 250 °C with the decreasing adsorption of Hg el : therefore availability of one of the reaction partners. Eom et al [25] formulated the rate limiting reaction of the adsorbed mercury and the absorbed chlorine species on a commercial SCR-DeNOx catalyst as:…”

“…Besides NO x reduction, SCR catalysts are also active in the oxidation of volatile organic compounds [69,70]. In an additional side reaction, SCR catalysts also convert gaseous Hg el to Hg ox , particularly in the presence of HCl [21,23,25,71]. Currently, SCR catalysts are being developed as multi-pollutant control devices.…”

“…Hg adsorption on catalyst surfaces has been mentioned in a number of studies [25,72,73]. Hg el adsorption on the SCR catalyst surface was only observed in the absence of HCl [76,77].…”