NaAlH4 表面Ti催化空间构型和X射线吸收光谱: Car-Parrinello分子动力学和密度泛函理论研究

通过采用Car-Parrinello分子动力学方法对掺杂Ti前后的NaAlH₄(001)2×2×1超晶胞表面晶体在333 K(60 ℃)温度条件催化脱氢的空间构型做了理论研究,发现掺杂Ti的合金中AlH₄团的其中两个Al—H键长分别从约1.64 (1 =0.1 nm)增大至1.74和1.93 ,而未掺杂合金表面中AlH₄团的4个Al—H键长基本不变,这意味着掺杂Ti相对未掺杂的合金更易于放氢.但在模拟温度条件下并未发现Ti-Al成键趋

Spatial configurations and x ray absorption of Ti catalyzing on NaAlH4 surfaces: Car-Parrinello molecular dynamics and density functional theory study

A theoretical study on the spatial configurations of the catalytic dehydrogenation of the pre- and post- Ti-doped NaAlH₄(001)2×2×1 supercell surface crystals was performed by using the Car-Parrinello molecular dynamics (CPMD) method at 333 K (60 ℃). It was be found that two of the Al—H bond lengths increased from approximately 1.64 to 1.74 and 1.93  respectively in the AlH₄ groups of the Ti-doped alloy. Compared with this change, the four Al—H bond lengths almost kept invariant in the AlH₄ group of un-doped alloy, which means that it was easier to dehydrogenate for the Ti-doped alloy than un-doped alloy. There was no bonding tendency between atom Ti and Al observed, which is probably because the temperature in the simulation process is not high enough. Based on the obtained surface crystal configuration, the Ti K-edge x ray absorption near-edge structure (XANES) spectra of the TiAl₃, TiH₂ crystals and Na₈Ti₈Al₁₆H₆₄(001) surface crystal have been calculated by using the full-potential linearized augmented plane wave method (FPLAPW). It was also found that the atom Ti may not only exist in the mixture of TiAl₃ and TiH₂ but also probably partially substitute for the Na atoms in NaAlH₄ surface crystal, by comparing the experimental XANES and edge x ray absorption fine structure (EXAFS) spectra.