Adsorption energies of mercury-containing species on CaO and temperature effects on equilibrium constants predicted by density functional theory calculations

Bo Gyeong Kim, Xinxin Li, Paul Blowers

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Abstract

The adsorption of Hg, HgCl, and HgCl 2 on the CaO surface was investigated theoretically so the fundamental interactions between Hg species and this potential sorbent can be explored. Surface models of a 4 × 4 × 2 cluster, a 5 × 5 × 2 cluster, and a periodic structure using density functional theory calculations with LDA/PWC and GGA/BLYP functional, as employed in the present work, offer a useful description for the thermodynamic properties of adsorption on metal oxides. The effect of temperature on the equilibrium constant for the adsorption of mercury-containing species on the CaO (0 0 1) surface was investigated with GGA/BLYP calculations in the temperature range of 250-600 K. Results show that, at low coverage of elemental mercury, adsorption on the surface is physisorption while the two forms of oxidized mercury adsorption undergo stronger adsorption. The adsorption energies decrease with increasing coverage for elemental mercury on the surfaces. The chlorine atom enhances the adsorption capacity and adsorbs mercury to the CaO surface more strongly. The adsorption energy is changed as the oxidation state varies, and the equilibrium constant decreases as the temperature increases, in good agreement with data for exothermic adsorption systems.

Original languageEnglish (US)
Pages (from-to)2781-2789
Number of pages9
JournalLangmuir
Volume25
Issue number5
DOIs
Publication statusPublished - Mar 3 2009

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ASJC Scopus subject areas

  • Electrochemistry
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Materials Science(all)
  • Spectroscopy

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