Interaction mechanism between heavy metals and Ce-doped CaO in flue gas of coal combustion
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摘要: 氧化钙(CaO)作为一种吸附剂广泛应用于燃煤烟气重金属的净化,但其吸附效率有限,需要进一步改性提升。金属铈(Ce)改性可调整其表面电子分布,增强化学活性。基于此,本研究建立了Ce-CaO (100)周期性模型,研究了燃煤烟气中汞、硒、铅三类重金属污染物的吸附机理。结果表明,除Hg0在Ce-CaO (100)表面上的吸附为物理吸附外,其余重金属污染物均为化学吸附,Ce位点和O位点为重金属污染物的主要活性吸附位点,吸附分子与Ce-CaO (100)表面之间存在明显的电荷转移与强烈的相互作用。Ce掺杂改性提升了CaO (100)表面对重金属污染物的吸附能力,尤其对Se0、SeO2和HgCl2的捕集能力显著提高。Abstract: Calcium oxide (CaO) has been widely used as an adsorbent in the purification of heavy metals in coal-fired flue gas. However, the adsorption efficiency is limited and a further modification is needed. The cerium (Ce) modification can redistribute the surface electrons and enhance the chemical activity of CaO. Therefore, the Ce-CaO (100) periodic model was established to study the adsorption mechanism of mercury, selenium, and lead pollutants in the coal-fired flue gas. The results show that, except for the physical adsorption of Hg0 on the Ce-CaO (100) surface, the other heavy metal pollutants are chemically adsorbed on the surface. The Ce-site and O-site are the main active adsorption sites of heavy metal pollutants. Intense charge transfer and strong interaction are observed between adsorption molecules and Ce-CaO (100). Moreover, the adsorption capacity of Ce-doped CaO (100) surface for heavy metal pollutants has been improved, especially the significantly increased capture capacity on Se0, SeO2 and HgCl2.
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Key words:
- coal-fired flue gas /
- heavy metals /
- modified CaO /
- adsorption mechanism /
- density functional theory
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表 1 Hg0、HgCl2和HgO在Ce-CaO (100)表面吸附构型的几何参数和吸附能
Table 1 Geometry parameters and adsorption energies of Hg0, HgCl2 and HgO on Ce-CaO (100) surface
RHg-surface1 /Å RHg-Cl2 /Å RHg-O3 /Å Ead /(kJ·mol-1) Hg0-Ce-CaO (100) 1A 3.315 - - -17.16 1B 3.048 - - -26.85 1C 3.433 - - -26.24 1D 3.378 - - -19.52 1E 3.497 - - -21.28 1F 3.161 - - -28.03 HgCl2-Ce-CaO (100) 1G 4.986 3.812 - -461.50 1H 3.448 3.535 - -452.30 1I 3.456 4.049 - -447.78 1J 4.835 3.596 - -441.30 HgO-Ce-CaO (100) 1K 3.286 - 2.799 -650.84 1L 3.548 - 2.778 -652.15 1M 3.257 - 2.82 -648.98 1N 4.646 - 4.646 -647.92 1: RHg-surface represents the distance between Hg atom and Ce-CaO surface; 2: RHg-Cl is the furthest distance between Hg atom and Cl atom in HgCl2 molecule; 3: RHg-O symbolizes the distance of Hg atom and O atom in HgO molecule 表 2 Se0和SeO2在Ce-CaO (100)表面吸附构型的几何参数和吸附能
Table 2 Geometry parameters and adsorption energies of Se0 and SeO2 on Ce-CaO (100) surface
RSe-surface5 /Å Ead /(kJ·mol-1) Se0-Ce-CaO (100) 2A 2.634 -525.91 2B 2.774 -529.18 2C 2.896 -515.84 2D 2.876 -465.89 2E 2.716 -429.69 SeO2-Ce-CaO (100) 2F 2.910 -437.93 2G 3.168 -392.45 2H 2.851 -398.34 2I 3.185 -437.81 5: RSe-surface represents the distance between Se atom and Ce-CaO surface 表 3 Pb0和PbCl2在Ce-CaO (100)表面吸附构型的几何参数和吸附能
Table 3 Geometry parameters and adsorption energies of Pb0 and PbCl2 on Ce-CaO (100) surface
RPb-surface7 /Å Ead /(kJ·mol-1) Pb0-Ce-CaO (100) 3A 2.500 -276.73 3B 3.339 -194.76 3C 3.412 -199.82 PbCl2-Ce-CaO (100) 3D 3.669 -282.08 3E 2.396 -263.13 7: RPb-surface represents the distance between Pb atom and Ce-CaO surface -
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