Deng Xingyi, Min Byoung Koun, Guloy Amado, Friend Cynthia M
Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, USA.
J Am Chem Soc. 2005 Jun 29;127(25):9267-70. doi: 10.1021/ja050144j.
We show that the dissociation probability of O2 on the reconstructed, Au111-herringbone surface is dramatically increased by the presence of some atomic oxygen on the surface. Specifically, at 400 K the dissociation probability of O2 on oxygen precovered Au111 is on the order of 10(-3), whereas there is no measurable dissociation on clean Au111, establishing an upper bound for the dissociation probability of 10(-6). Atomic oxygen was deposited on the clean reconstructed Au111-herringbone surface using electron bombardment of condensed NO2 at 100 K. The dissociation probability for dioxygen was measured by exposing the surface to 18O2. Temperature programmed desorption (TPD) was used to quantify the amount of oxygen dissociation and to study the stability of the oxygen in all cases. Oxygen desorbs as O2 in a peak centered at 550 K with pseudo-first-order kinetics; i.e., the desorption peak does not shift with coverage. Our interpretation is that the coverage dependence of the activation energy for dissociation (deltaE(dis)) and/or preexponential factor (nu(d)) may be responsible for the unusual desorption kinetics, implying a possible energy barrier for O2 dissociation on Au111. These results are discussed in the context of Au oxidation chemistry and the relationship to supported Au nanoparticles.
我们表明，表面上存在一些原子氧会显著提高O₂在重构的Au111人字形表面上的解离概率。具体而言，在400K时，O₂在氧预覆盖的Au111上的解离概率约为10⁻³，而在清洁的Au111上没有可测量的解离，确定了解离概率的上限为10⁻⁶。通过在100K下对冷凝的NO₂进行电子轰击，将原子氧沉积在清洁的重构Au111人字形表面上。通过将表面暴露于¹⁸O₂来测量双氧的解离概率。程序升温脱附（TPD）用于量化氧解离的量，并研究所有情况下氧的稳定性。氧以O₂的形式在以550K为中心的峰中脱附，具有准一级动力学；即，脱附峰不随覆盖度移动。我们的解释是，解离活化能（ΔE(dis)）和/或指前因子（ν(d)）的覆盖度依赖性可能是异常脱附动力学的原因，这意味着Au111上O₂解离可能存在能量障碍。在Au氧化化学的背景下以及与负载型Au纳米颗粒的关系中讨论了这些结果。
