Reaction fronts in the oxidation of hydrogen on Pt(111):: Scanning tunneling microscopy experiments and reaction-diffusion modeling
Reaction fronts in the oxidation of hydrogen on Pt(111):: Scanning tunneling microscopy experiments and reaction-diffusion modeling
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DOI：
10.1063/1.1453964
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发表时间：
2002-04-01
影响因子：
4.4
通讯作者：
Ertl, G
中科院分区：
文献类型：
--
作者：
Sachs, C;Hildebrand, M;Ertl, G
用扫描隧道显微镜(STM)研究了氢在铂(111)表面氧化过程中的行进反应前沿。在170K以下的温度下，用氢气给氧覆盖的表面观察到了前锋，前锋代表了10到100 nm宽的OH覆盖区域，将未反应的O原子从反应产物H2O中分离出来。O原子通过OH区的运动转化为H2O。小规模的STM数据在原子尺度上显示了前锋内的过程。更大规模的实验揭示了锋面的速度和宽度是温度的函数。建立了一个简单的反应-扩散模型，该模型包含两个反应步骤和水分子的表面扩散，定性地再现了实验观测结果。文中还解析地推导出了前缘速度的下限。通过STM和低能电子衍射实验测定了两个反应步骤的速率常数和H2O的扩散系数，使实验和理论进行了定量比较。有了这些参数，模型预测的前锋速度大约比STM测得的速度小一个数量级。根据温度的不同，预测的锋面宽度比实验值大两到三个数量级。我们的结论是，这些偏差是由于反应扩散系统不能描述前锋内部复杂的化学过程和结构变化造成的。原子分辨的STM数据表明，颗粒之间的相互作用特别影响H2O分子的扩散。(C)2002年美国物理研究所。
Traveling reaction fronts in the oxidation of hydrogen on a Pt(111) surface were investigated by means of scanning tunneling microscopy (STM). The fronts were observed during dosing of the oxygen covered surface with hydrogen at temperatures below 170 K. The fronts represented 10 to 100 nm wide OH-covered regions, separating unreacted O atoms from the reaction product H2O. O atoms were transformed into H2O by the motion of the OH zone. Small scale STM data showed the processes within the fronts on the atomic scale. Experiments on larger scale revealed the velocity and the width of the fronts as a function of temperature. A simple reaction-diffusion model has been constructed, which contains two reaction steps and the surface diffusion of water molecules, and qualitatively reproduces the experimental observations. A lower bound for the front velocity was also derived analytically. For a quantitative comparison between experiment and theory the rate constants of the two reaction steps and the diffusion coefficient of H2O were determined by STM and low energy electron diffraction experiments. With these parameters, the front velocities predicted by the model are approximately one order of magnitude smaller than those determined by STM. The predicted front widths are, depending on the temperature, between two and three orders of magnitude larger than the experimental values. We conclude that these deviations result from the inability of the reaction-diffusion system to describe the complex chemical processes and structure changes within the fronts. The atomically resolved STM data indicate attractive interactions between the particles that in particular affect the diffusion of the H2O molecules. (C) 2002 American Institute of Physics.