Hydrogen fluoride adsorption and reaction on the α-Al2O3(0001) surface: a density functional theory study.
Hydrogen fluoride adsorption and reaction on the α-Al2O3(0001) surface: a density functional theory study.
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DOI：
10.1063/1.3694102
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发表时间：
2012-03
期刊：
影响因子：
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通讯作者：
Jie Quan;Botao Teng;X. Wen;Yue Zhao;Rui Liu;M. Luo
中科院分区：
文献类型：
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作者：
Jie Quan;Botao Teng;X. Wen;Yue Zhao;Rui Liu;M. Luo
用密度泛函理论方法系统地研究了HF在α-Al(2)O(3)(0 0 0 1)表面的吸附和反应行为。通过增加p(2×1)α-Al(2)O(3)(0001)中HF分子的数目，我们发现HF在低覆盖度下发生化学解离，而物理吸附和解离吸附都发生在3/2单分子层覆盖度(ML)。在相同覆盖率(1.0ML)下，在p(2×1)模型中得到了不同构型的离解Hf，而在p(1×1)模型中只观察到了一种构型，这是因为p(1×1)比表面积小。初步的氟化反应研究表明，p(2×1)板中两个解离的Hf的总能量分别增加了1.00 eV和0.72 eV，用于水中间体的形成和脱附。HF和H(2O)O的共吸附行为表明，预吸附水不利于Al(2O)O(3)的氟化，这与实验结果吻合较好。计算的态密度表明，σ(H-F)峰消失，而σ(H-O)和σ(Al-F)峰出现在-8.4eV和-5~-3 eV。电荷密度差分析表明，解离后的F原子吸引电子，而表面Al原子的电子没有明显变化。
The adsorption and reaction behaviors of HF on the α-Al(2)O(3)(0001) surface are systematically investigated using density functional theory method. By increasing the number of HF molecules in a p(2 × 1) α-Al(2)O(3)(0001) slab, we find that HF is chemically dissociated at low coverage; while both physical and dissociative adsorption occurs at a 3/2 monolayer (ML) coverage. At the same coverage (1.0 ML), diverse configurations of the dissociated HF are obtained in the p(2 × 1) model; while only one is observed in the p(1 × 1) slab due to its smaller surface area compared with the former one. Preliminary fluorination reaction study suggests that the total energy of two dissociated HF in the p(2 × 1) slab increases by 1.00 and 0.72 eV for the formation and desorption of water intermediate, respectively. The coadsorption behaviors of HF and H(2)O indicate that the pre-adsorbed water is unfavorable for the fluorination of Al(2)O(3), which is well consistent with the experimental results. The calculated density of states show that the peak of σ(H-F) disappears, while the peaks of σ(H-O) and σ(Al-F) are observed at -8.4 and -5 to -3 eV for the dissociated HF. Charge density difference analysis indicates that the dissociated F atom attracts electrons, while no obvious changes on electrons are observed for the surface Al atoms.