Understanding mercury binding on activated carbon

Padak, Bihter; Wilcox, Jennifer

doi:10.1016/j.carbon.2009.06.029

Cited by 160 publications

(107 citation statements)

References 23 publications

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“…5, a linear C-Hg-Br molecule forms on the graphene edge site with Hg-Br and Hg-C bond distances of 2.45 Å and 2.1 Å, respectively. A similar interaction was also observed in a previous study where Padak and Wilcox carried out a Mulliken bond population analysis of Hg and chlorine (Cl) structures bound on four-ring graphene clusters using DFT [22]. They reported that the C-Hg bond was stronger when Hg was bound to the graphene edge site interacting with the Cl atom bound atop of Hg, which is in agreement with the current work.…”

Section: Chemical Nature Of Bound Mercury Species From Dftsupporting

confidence: 92%

“…Radovic showed that the reactivity of AC can be studied using a simplified graphene model in which a single graphene sheet mimics the AC surface [21]. Many studies have used graphene zigzag edge sites with unsaturated edge atoms to simulate the active sites on carbonaceous surfaces [22][23][24][25][26]. Using a 9-ring deep graphene ribbon model, electronic structure calculations have been carried out to determine the most stable concentrations and configurations of hydrogen (H), bromine (Br), and Hg atoms on the edge sites.…”

Section: Computational Detailsmentioning

confidence: 99%

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Mercury chemistry on brominated activated carbon

Sasmaz

Kirchofer

Jew

et al. 2012

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132

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Section: Chemical Nature Of Bound Mercury Species From Dftsupporting

confidence: 92%

Section: Computational Detailsmentioning

confidence: 99%

Mercury chemistry on brominated activated carbon

Sasmaz

Kirchofer

Jew

et al. 2012

Fuel

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132

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“…Mercury acts as a Lewis base prior to oxidation, thereby is likely to react with electrondeficient species. 67 As the Bader analysis revealed, all of the surface oxygen atoms are negatively charged and therefore have a low affinity for Hg atoms.…”

Section: ■ Computational Methodologymentioning

confidence: 99%

DFT Study of Hg Oxidation across Vanadia-Titania SCR Catalyst under Flue Gas Conditions

2013

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The density functional theory was used to analyze the thermodynamic stability and reactivity of the vanadia-titania catalyst below monolayer regime with the purpose of having a good representation of a commercial SCR catalyst (V 2 O 5 (<2 wt %)−TiO 2 ). The objective of this paper is to understand the reactivity of this catalyst in Hg oxidation. The SCR catalyst is modeled as a tetrahedrally coordinated divanadate unit supported on a 3-layer TiO 2 (001) slab to represent a catalyst with low vanadia loadings. Under flue gas conditions, the interaction of water with this surface has been studied as a function of pressure and temperature using ab initio thermodynamic calculations, showing that water coverage is temperature-dependent. Adsorbed water acts as a Lewis base, donating electrons to the TiO 2 (001) surface support, which increases the negative charge and reactivity of the oxygen atoms of the vanadia dimer. The reactivity of the vanadia dimer toward Hg oxidation is analyzed through the adsorption energies of Hg, HgCl, HCl, and H 2 O. Surfaces with high water coverage showed higher reactivity toward HgCl, which has the highest adsorption energy, followed by HCl. The adsorption energies of Hg suggest a negligible interaction with the vanadia dimer. Lateral interactions between neighboring adsorbed flue gas components on the vanadia dimer were studied, suggesting that having H 2 O or HgCl adsorbed on a neighboring oxygen atom increases the adsorption energies of Hg and HCl respectively. Temperature, pressure, and entropic effects were taken into account to study the reactivity of these surface interactions under flue gas conditions. Based on these results, it is proposed that the oxidation of Hg to HgCl 2 follows a Langmuir−Hinshelwood mechanism, represented as a cycle where HgCl and HCl interact without poisoning the surface. The proposed steps during the formation of HgCl 2 are the adsorption and dissociation of HCl, adsorption of HgCl, formation of HgCl 2 , and its desorption from the surface. ■ INTRODUCTIONThe U.S. Environmental Protection Agency (EPA) proposed the Mercury and Air Toxics Standards (MATS) in December 2011, which require U.S. natural gas and coal-fired power plants to install air pollution control devices to prevent 91% of the Hg present in flue gas from being released.1 Rising atmospheric levels of gaseous Hg have caused public concern because Hg has been shown to have negative neurological effects, affecting memory, attention, language, and visual skills.2 In the U.S., 40% of the total coal-fired generating capacity is generated in power plants equipped with selective catalytic reduction (SCR) units . Oxidized Hg is highly soluble in aqueous solutions, making its removal by conventional wet flue gas desulfurization processes possible. 5−7A widely employed material in commercial SCR units is titaniasupported vanadium and tungsten oxides, that is, V 2 O 5 −WO 3 / TiO 2 . 8,9 The active vanadia phase, V 2 O 5 , is responsible for NO x reduction 10 and can also catalyze Hg 0 oxidatio...

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“…Although several studies have been carried out to understand the mechanism of mercury retention (Padak and Wilcox, 2009), the effect of the inorganic ash constituents and organic matter on the retention of mercury has still not been fully assessed. Some inorganic components of fly ashes, such as iron oxide, aluminosilicates, and calcium oxide promote mercury oxidation and hence a better capture (Norton et al, 2001;Norton et al, 2003;Ghorishi et al, 2000).…”

Section: Influence Of the Composition And Characteristics Of The Sorbmentioning

confidence: 99%

Evaluation of the Variables that Influence Mercury Capture in Solid Sorbents

Antón¹,

Valle²,

Somoano³

et al. 2009

CCGP

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A B S T R A C TNewly obtained results on mercury retention in fly ashes and activated carbons during coal combustion are compared with previous findings. The influence of different variables on mercury capture, including the composition and nature of the sorbents, the composition of the flue gas and the mercury species in gas phase is investigated.Coal-fired utility boilers are currently the largest single-known source of mercury emissions. According to the USEPA's Information Collection Request (ICR), on average, only 40% of the mercury entering a coal-fired power plant is captured, while 60% is emitted into the atmosphere. Several solid materials, including activated carbons, are considered to be effective sorbents for Hg control in flue gases from coal combustion. However, more economical alternatives to retain mercury such as the optimization of conditions for improving mercury capture in fly ashes in the installation also need to be studied.In this work, the mercury retention capacity of different fly ashes was compared with retention by commercial activated carbons in different experimental conditions. As might be expected, the results obtained indicate that the quantity of mercury captured depends on the characteristics of the fly ashes and on the mode of occurrence of mercury in gas phase. The retention of elemental mercury in the fly ashes, unlike activate carbons, was greatly influenced by the gas composition. Although the efficiency of the mercury retention was higher in activated carbons than in fly ashes, some activated carbon showed a lower retention capacity for elemental mercury than some fly ashes in the simulated flue gas.

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Understanding mercury binding on activated carbon

Cited by 160 publications

References 23 publications

Mercury chemistry on brominated activated carbon

Mercury chemistry on brominated activated carbon

DFT Study of Hg Oxidation across Vanadia-Titania SCR Catalyst under Flue Gas Conditions

Evaluation of the Variables that Influence Mercury Capture in Solid Sorbents

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