Mercury Oxidation over a Vanadia-based Selective Catalytic Reduction Catalyst

Abstract

The process of the reaction among elemental mercury (Hg 0 ) and reactive flue gas components across the selective catalytic reduction (SCR) catalyst was studied in a laboratory-scale reactor. Prepared vanadia-based SCR catalysts were characterized and analyzed to understand the potential reaction pathways. Mercury oxidation was observed when pro-exposure of the SCR catalyst to HCl, followed by passing through Hg 0 /N 2 in the absence of gas-phase HCl. At testing conditions, Hg 0 was found to desorb from the catalyst surface by adding HCl to the gas steam, which implies that HCl adsorption onto the SCR catalyst is strong relative to the mercury. Surface analysis verified the absorption of HCl onto the SCR catalysts, and the potential reaction pathways were proposed. Indeed, the monomeric vanadyl sites on the catalyst surface were found to be responsible for the adsorption of both Hg 0 and HCl, which means they are active for mercury oxidation. Furthermore, the detailed Langmuir-Hinshelwood mechanism was proposed to explain the mercury oxidation on the SCR catalyst, where reactive Cl generated from adsorbed HCl reacts with adjacent Hg 0 .

Analytical management of SCR catalyst lifetimes and multipollutant performance

“…The strong coupling between NO reduction and Hg 0 oxidation via competitive adsorption of NH 3 and HCl was also independently validated with an extensive series of lab tests (Kamata et al, 2008). He et al (2009) observed HCl adsorption on monomeric vanadyl sites on a typical SCR catalyst, and suggested that such adsorbates explain the apparent inhibition of Hg 0 oxidation in the presence of NH 3 .…”

Oxidation Catalysts for Elemental Mercury in Flue Gases—A Review

“…Hg el adsorption on the SCR catalyst surface was only observed in the absence of HCl [76,77]. When HCl or NH 3 was added to the simulated flue gas, a rapid mercury desorption was observed [23,76,77]. Eswaran and Stenger [76] also reported strong Hg adsorption in the presence of H 2 SO 4 .…”

“…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].…”

“…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.…”

Study on mechanism of mercury oxidation by fly ash from coal combustion

“…(6)). Previous studies have indicated inorganic metal oxides in fly ash have significant mercury oxidation capacity [16,17]. And the sorbent itself can be oxidized with the occurrence of oxygen in flue gas (eq.…”