Study on the adsorption and oxidation mechanism of mercury by HCl over γ-Fe2O3 catalyst
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摘要: 本研究采用密度泛函理论(DFT)研究了在γ-Fe2O3表面HCl对Hg0的吸附和催化氧化的作用机制。构建了Hg0、HCl、HgCl和HgCl2在γ-Fe2O3(001)表面的吸附模型,分析了HCl对γ-Fe2O3表面催化氧化Hg0的作用机理,并通过反应路径的能量分布测定,研究了γ-Fe2O3表面Hg0的氧化过程。结果表明,Hg0倾向于化学吸附在γ-Fe2O3(001)表面Feoct位。HCl在催化剂表面进行解离吸附,形成吸附态Cl和羟基,从而促进Hg0的吸附。HgCl以分子形式化学吸附在γ-Fe2O3(001)上,并作为Hg0氧化过程的中间体。HgCl2倾向在γ-Fe2O3表面上的平行吸附。同时,HCl在γ-Fe2O3(001)上氧化Hg0遵循L-H机理,即化学吸附的Hg0与解离吸附的HCl反应,且HCl对Hg0的非均相氧化通过两步反应途径进行,即Hg0 (ads)→HgCl(ads)→HgCl2(ads)。Abstract:
The mechanism of adsorption and oxidation of Hg0 by HCl on γ-Fe2O3 surface was investigated by density functional theory (DFT) calculation. The adsorption models of Hg0, HCl, HgCl and HgCl2 on γ-Fe2O3(001) surface were constructed, and the reaction mechanism of catalytic oxidation of Hg0 by HCl on γ-Fe2O3 surface was analyzed. The results illustrate that the Hg0 tends to be chemically adsorbed at Feoct site. HCl can be dissociated and adsorbed on the surface of the catalyst to form adsorbed Cl and hydroxyl groups, and promote the adsorption of Hg0. HgCl can be molecularly chemisorbed upon γ-Fe2O3(001) and act as an intermediate. HgCl2 tends to be adsorbed in parallel on the surface of γ-Fe2O3. HCl oxidizes Hg0 on γ-Fe2O3(001) following the L-H mechanism: chemically adsorbed Hg0 reacts with dissociatively adsorbed HCl. By measuring the energy distribution of the reaction path, the oxidation process of Hg0 on the surface of γ-Fe2O3 was studied. The heterogeneous oxidation of Hg0 by HCl proceeds on a two-step reaction pathway: Hg0(ads)→HgCl(ads)→HgCl2(ads). -
Key words:
- Hg0 /
- γ-Fe2O3 /
- HCl /
- catalytic oxidation mechanism /
- DFT
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表 1 键长的计算和文献值
Table 1 Bond length of calculated values and literature values
表 2 Hg0在γ-Fe2O3表面吸附的优化参数
Table 2 Optimized adsorption parameters of Hg0 adsorbed on γ-Fe2O3
Eads/(kJ·mol−1) RHg-X/Å ΔQ/e 1A −39.26 2.919 0.14 1B −24.47 3.194 0.05 1C −24.73 3.518/3.535 0.08 表 3 HCl在γ-Fe2O3表面吸附的优化参数
Table 3 Optimized adsorption parameters of HCl adsorbed on γ-Fe2O3
Eads/(kJ·mol−1) RCl−Fe/Å RH−O/Å ΔQ/e 2A −73.69 2.192 0.993 0.07 2B −106.66 2.169 0.983 0.15 表 4 HgCl在γ-Fe2O3表面吸附的优化参数
Table 4 Optimized adsorption parameters of HgCl adsorbed on γ-Fe2O3
Eads/(kJ·mol−1) RHg−Fe/Å RCl−Fe/Å RHg−Cl/Å ΔQ/e 3A −136.92 2.545 2.383 0.03 3B −141.25 2.165 3.041 −0.22 3C −174.54 2.885 2.167 3.236 −0.11 3D −180.67 2.926 2.166 3.290 −0.12 表 5 HgCl2在γ-Fe2O3表面吸附的优化参数
Table 5 Optimized adsorption parameters of HgCl2 adsorbed on γ-Fe2O3
Eads/(kJ·mol−1) RHg−Fe/Å RCl−Fe/Å ΔQ/e 4A −63.28 2.956 2.942/2.968 0.03 4B −58.43 2.881 2.159/2.161 −0.26 4C −27.13 2.749 0.05 -
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