Tang Hongjian, Duan Yufeng, Zhu Chun, Cai Tianyi, Li Chunfeng, Cai Liang
Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University, Nanjing, Jiangsu 210096, China.
Key Laboratory of Energy Thermal Conversion and Control of Ministry of Education, School of Energy and Environment, Southeast University, Nanjing, Jiangsu 210096, China.
Chemosphere. 2017 Oct;184:711-719. doi: 10.1016/j.chemosphere.2017.06.039. Epub 2017 Jun 12.
Alkali metal-based sorbents are potential for oxidized mercury (Hg) selective adsorption but show hardly effect to elemental mercury (Hg) in flue gas. Density functional theory (DFT) was employed to investigate the Hg and HgCl adsorption mechanism over alkali metal-based sorbents, including calcium oxide (CaO), magnesium oxide (MgO), potassium chloride (KCl) and sodium chloride (NaCl). Hg was found to weakly interact with CaO (001), MgO (001), KCl (001) and NaCl (001) surfaces while HgCl was effectively adsorbed on top-O and top-Cl sites. Charge transfer and bond population were calculated to discuss the covalency and ionicity of HgCl bonding with the adsorption sites. The partial density of states (PDOS) analysis manifests that HgCl strongly interacts with surface sites through the orbital hybridizations between Hg and top O or Cl. Frontier molecular orbital (FMO) energy and Mulliken electronegativity are introduced as the quantitative criteria to evaluate the reactivity of mercury species and alkali metal-based sorbents. HgCl is identified as a Lewis acid and more reactive than Hg. The Lewis basicity of the four alkali metal-based sorbents is predicted as the increasing order: NaCl < MgO < KCl < CaO, in consistence with the trend of HgCl adsorption energies.
碱基金属吸附剂具有选择性吸附氧化态汞（Hg）的潜力，但对烟气中的元素汞（Hg）几乎没有作用。采用密度泛函理论（DFT）研究了碱基金属吸附剂（包括氧化钙（CaO）、氧化镁（MgO）、氯化钾（KCl）和氯化钠（NaCl））对Hg和HgCl的吸附机理。发现Hg与CaO（001）、MgO（001）、KCl（001）和NaCl（001）表面的相互作用较弱，而HgCl有效地吸附在顶部O和顶部Cl位点上。计算了电荷转移和键布居，以讨论HgCl与吸附位点键合的共价性和离子性。态密度（PDOS）分析表明，HgCl通过Hg与顶部O或Cl之间的轨道杂化与表面位点强烈相互作用。引入前线分子轨道（FMO）能量和穆利肯电负性作为评估汞物种和碱基金属吸附剂反应活性的定量标准。HgCl被确定为路易斯酸，比Hg更具反应活性。预测四种碱基金属吸附剂的路易斯碱性按递增顺序排列为：NaCl < MgO < KCl < CaO，这与HgCl吸附能的趋势一致。
