Iñiguez Jorge, Yildirim Taner
Institut de Ciència de Materials de Barcelona (CSIC), Campus UAB, 08193 Bellaterra, Spain.
J Phys Condens Matter. 2007 Apr 30;19(17):176007. doi: 10.1088/0953-8984/19/17/176007. Epub 2007 Apr 10.
We report a first-principles study of sodium alanate (NaAlH(4)) surfaces, both pure and with Ti atoms on them, focusing on their stability and reactivity with hydrogen. We find Ti causes the dissociation of H(2) molecules and contributes to the stability of the surface exposed to hydrogen. The Ti catalysts should thus facilitate the reaction by which NaAlH(4) (7.4 wt% of H) forms from Na(3)AlH(6) (5.9 wt% of H), which occurs under hydrogen pressure and requires H(2) dissociation to proceed. The presence of Ti also results in lower defect-formation energies, which should favour the NaAlH(4) decomposition reaction. Indeed, our calculations show that the chemical versatility of Ti brings close in energy a number of steps that presumably are relevant in the formation and decomposition of NaAlH(4), which suggests that the catalyst facilitates both processes. We also discuss the possibility of using other light transition metals (Sc, V, and Cr) as catalysts, and conclude that Ti is the best choice overall.
我们报道了对纯的以及表面带有钛原子的铝氢化钠（NaAlH₄）表面的第一性原理研究，重点关注其稳定性以及与氢的反应活性。我们发现钛会导致氢分子解离，并有助于提高暴露于氢的表面的稳定性。因此，钛催化剂应能促进由Na₃AlH₆（含氢5.9 wt%）形成NaAlH₄（含氢7.4 wt%）的反应，该反应在氢气压力下发生，且需要氢分子解离才能进行。钛的存在还会导致更低的缺陷形成能，这应有利于NaAlH₄的分解反应。实际上，我们的计算表明，钛的化学多功能性使一些可能与NaAlH₄形成和分解相关的步骤在能量上相近，这表明该催化剂对这两个过程都有促进作用。我们还讨论了使用其他轻过渡金属（钪、钒和铬）作为催化剂的可能性，并得出结论，总体而言钛是最佳选择。
