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Adsorption on gold: Effects on surface morphology and reactivity.

机译：在金上的吸附：对表面形态和反应性的影响。

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摘要

Computational tools are used in conjunction with experiments to understand adsorption and reactions on gold surfaces. We focus on systems important for oxidation, a class of reactions gold can perform quite readily. Experimental results have illustrated that the structure of gold is sensitive to adsorbate type and coverage, temperature, and many other factors. We find the adsorption of atomic oxygen and chlorine can significantly affect the morphology of the surface, either by favorably interacting with defects on the surface or by incorporating gold into the adsorbate layer, a process that is energetically favorable at higher coverages. The adsorbate-gold interaction becomes more covalent upon gold incorporation, which lowers the partial negative charge on the adsorbate, allowing for closer packing on the surface. The temperature dependence on the oxygen-gold interaction motivated the use of ab-initio molecular dynamics to model the dynamic surface modification during adsorption of atomic oxygen. We successfully match calculated vibrational spectra with experimental high-resolution electron energy loss spectroscopy results and suggest chemisorbed oxygen (oxygen bound in a locally flat three-fold coordination site) as the reactive species for oxidation on the surface. Since reactivity is closely related to surface morphology we studied the reaction of propene with atomic oxygen on different defect covered gold surfaces. Reaction barriers for allylic hydrogen abstraction and oxametallacycle formation can differ by at least a factor of two and different pathways can be selected by modifying the surface structure. Furthermore, we find the correct pathway for phenol formation on cyclohexene and use ab-initio molecular dynamics to model the oxygen-covered gold surface for the oxidation of CO. We qualitatively reproduce experimental trends in reactivity and gain insight into the mechanism of CO oxidation on the oxygen-covered gold surface, confirming our previous result that chemisorbed oxygen is the reactive species on the surface.
机译：计算工具与实验结合使用以了解金表面的吸附和反应。我们专注于对氧化很重要的系统，金可以很容易地执行一类反应。实验结果表明，金的结构对吸附物的类型和覆盖率，温度以及许多其他因素敏感。我们发现原子氧和氯的吸附可通过与表面上的缺陷进行有利的相互作用或将金掺入吸附剂层中，从而显着影响表面形态，这一过程在更高的覆盖率下非常有利。掺入金后，吸附物与金的相互作用变得更共价，这降低了吸附物上的部分负电荷，从而使表面上的堆积更紧密。温度对氧-金相互作用的依赖性促使使用从头算分子动力学来模拟原子氧吸附过程中的动态表面改性。我们成功地将计算的振动光谱与高分辨率的电子能量损失光谱实验结果进行了匹配，并建议化学吸附的氧（结合在局部平坦的三重配位点中的氧）作为表面氧化的反应性物质。由于反应性与表面形态密切相关，我们研究了丙烯与原子氧在不同缺陷覆盖的金表面上的反应。烯丙基氢提取和氧杂金属环化合物形成的反应势垒可以相差至少两倍，并且可以通过修饰表面结构来选择不同的途径。此外，我们找到了在环己烯上形成苯酚的正确途径，并使用从头算分子动力学模型来模拟覆盖氧气的金表面，以氧化CO。我们定性地再现了反应性的实验趋势，并深入了解了CO在氧化反应中的氧化机理。氧覆盖的金表面，证实了我们先前的结果，化学吸附的氧是表面上的反应性物质。

著录项

  • 作者

    Baker, Thomas A.;

  • 作者单位

    Harvard University.;

  • 授予单位 Harvard University.;
  • 学科 Chemistry Physical.;Physics Condensed Matter.;Physics Theory.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 234 p.
  • 总页数 234
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 物理化学（理论化学）、化学物理学;
  • 关键词

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