Methane activation by platinum: critical role of edge and corner sites of metal nanoparticles.
Methane activation by platinum: critical role of edge and corner sites of metal nanoparticles.
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DOI：
10.1002/chem.201000296
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发表时间：
2010-06
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影响因子：
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通讯作者：
F. Viñes;Y. Lykhach;T. Staudt;M. Lorenz;C. Papp;H. Steinrück;J. Libuda;Konstantin M. Neyman;
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文献类型：
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作者：
F. Viñes;Y. Lykhach;T. Staudt;M. Lorenz;C. Papp;H. Steinrück;J. Libuda;Konstantin M. Neyman;
用最新的密度泛函方法和超声分子束与高分辨光电子能谱相结合的方法，在模型铂催化剂上研究了甲烷的完全脱氢反应。密度泛函计算结果表明，CH(3)和CH(2)等中间物种在颗粒边缘和转角的位置被特别稳定了50-80kJ·mol(-1)。这种稳定是由于低配位中心的活性增强，并伴随着它们适应吸附的特殊灵活性。甲烷完全脱氢的动力学根据从铂(111)扩展表面切换到铂纳米颗粒时的反应能量分布而得到很大程度的修正。CH(3)和CH(2)的生成步骤在铂(111)上是吸热的，在铂(79)上是明显放热的。在后一种情况下观察到反应势垒的显著降低，第一次C-H键断裂的反应势垒约为60kJ·mol(-1)，甲基分解的反应势垒约为40kJ·mol(-1)。甲烷在铜(111)表面有序的CeO(2)膜负载的铂纳米颗粒上的甲烷分解实验证实了密度泛函理论。结果表明，在铂纳米颗粒表面生成的CH(3)在100K时发生自发脱氢，这与以往在铂单晶表面生成的CH(3)在更高的温度下是稳定的结果形成鲜明对比。这一结果强调了颗粒边缘位置在甲烷活化和脱氢中的关键作用。
Complete dehydrogenation of methane is studied on model Pt catalysts by means of state-of-the-art DFT methods and by a combination of supersonic molecular beams with high-resolution photoelectron spectroscopy. The DFT results predict that intermediate species like CH(3) and CH(2) are specially stabilized at sites located at particles edges and corners by an amount of 50-80 kJ mol(-1). This stabilization is caused by an enhanced activity of low-coordinated sites accompanied by their special flexibility to accommodate adsorbates. The kinetics of the complete dehydrogenation of methane is substantially modified according to the reaction energy profiles when switching from Pt(111) extended surfaces to Pt nanoparticles. The CH(3) and CH(2) formation steps are endothermic on Pt(111) but markedly exothermic on Pt(79). An important decrease of the reaction barriers is observed in the latter case with values of approximately 60 kJ mol(-1) for first C-H bond scission and 40 kJ mol(-1) for methyl decomposition. DFT predictions are experimentally confirmed by methane decomposition on Pt nanoparticles supported on an ordered CeO(2) film on Cu(111). It is shown that CH(3) generated on the Pt nanoparticles undergoes spontaneous dehydrogenation at 100 K. This is in sharp contrast to previous results on Pt single-crystal surfaces in which CH(3) was stable up to much higher temperatures. This result underlines the critical role of particle edge sites in methane activation and dehydrogenation.