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An experimental and theoretical study of furan decomposition on palladium(111) using scanning tunneling microscopy and density functional theory.

机译：利用扫描隧道显微镜和密度泛函理论对呋喃在钯（111）上分解的实验和理论研究。

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摘要

Furan (C4H4O) has been investigated as a prototypical model species in heterogeneous catalyst studies, under both ultrahigh vacuum and industrial conditions. The adsorption and decomposition of furan on Pd(111) has been previously studied with thermal desorption and vibrational spectroscopies; these studies support intact adsorption of the heterocycle below 280 K, with dissociation to H, CO, and a C3H3 species for temperatures between 280 to 320 K. The hydrocarbon moiety is adsorbed through ∼400 K, whereupon complete dehydrogenation to a carbidic overlayer is onset.; Using scanning tunneling microscopy (STM), I have imaged the intactly-adsorbed molecules in UHV at temperatures below 280 K; these experiments have revealed strikingly different adsorption behaviors on narrow and wide terraces of vicinal Pd(111). For higher temperatures (up to 415 K), STM has been used to probe C4H4O dissociation to form the C3H3 species. These data exhibit structure-specific properties, most prominently a preferential adsorption of furan at upper step edge sites and an apparent depletion of such sites after the reaction has gone to completion. Such observations are consistent with previous experimental and theoretical studies of molecular adsorption, diffusion, and reaction on vicinal, low-Miller-index transition metal surfaces.; The structure and energetics of furan chemisorption on Pd(111) are explored with surface electronic calculations based on ab initio density functional theory (DFT). These calculations reveal two types of stable adsorption configurations, located in positions of high symmetry relative to hollow sites on the close-packed surface. The chemisorption strengths in these geometries are closely correlated to the relaxed structures of both the adsorbate and the substrate, and involve a partial loss of aromaticity in the furan molecule.; Calculated STM images of the stable furan configurations on the Pd(111) surface are also presented; these plots are generated from computational methods based on DFT and the extended Huckel molecular orbital theory (EHT). Calculations of the C3H3 species have also been performed using the EHT-based method. Overall, the theoretical results show a good qualitative correspondence to the experimental data. This investigation indicates that the EHT-based approach can reproduce the key symmetries of the adsorbate electronic structure in spite of its simplicity.
机译：在超高真空和工业条件下，呋喃（C4H4O）已作为非均相催化剂研究中的典型模型物种进行了研究。以前已经通过热解吸和振动光谱研究了呋喃在Pd（111）上的吸附和分解。这些研究支持温度低于280 K的杂环的完整吸附，并在280至320 K的温度下分解为H，CO和C3H3物种。烃部分被吸附至约400 K，随后开始完全脱氢为碳化物覆盖层。;使用扫描隧道显微镜（STM），我在280 K以下的温度下对超高压中完整吸附的分子进行了成像；这些实验揭示了在邻域Pd（111）的狭窄和宽阶上的吸附行为截然不同。对于更高的温度（最高415 K），STM已用于探测C4H4O的解离形成C3H3物质。这些数据显示出特定于结构的特性，最突出的是呋喃在较高的台阶边缘位点上的优先吸附，并且在反应完成后这些位点的表观损耗。这些观察结果与先前在邻近，低米勒指数过渡金属表面上的分子吸附，扩散和反应的实验和理论研究一致。通过基于从头算密度泛函理论（DFT）的表面电子计算，探讨了呋喃化学吸附Pd（111）的结构和能量。这些计算揭示了两种类型的稳定吸附构型，它们相对于紧密堆积的表面上的中空位点处于高度对称的位置。在这些几何形状中，化学吸附强度与被吸附物和底物的松弛结构密切相关，并导致呋喃分子中芳香性的部分损失。还显示了在Pd（111）表面上稳定的呋喃构型的STM计算图像；这些图是基于DFT和扩展的Huckel分子轨道理论（EHT）的计算方法生成的。还使用基于EHT的方法进行了C3H3种类的计算。总体而言，理论结果显示出与实验数据良好的定性对应。这项研究表明，基于EHT的方法尽管简单，但却可以重现被吸附物电子结构的关键对称性。

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  • 作者

    Loui, Albert.;

  • 作者单位

    University of California, Davis.;

  • 授予单位 University of California, Davis.;
  • 学科 Physics Condensed Matter.
  • 学位 Ph.D.
  • 年度 2005
  • 页码 219 p.
  • 总页数 219
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 O49;
  • 关键词

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