Highly active surfaces for CO oxidation on rh, pd, and pt
Highly active surfaces for CO oxidation on rh, pd, and pt
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DOI：
10.1016/j.susc.2007.08.019
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发表时间：
2007-12-01
期刊：
影响因子：
1.9
通讯作者：
Goodman, D. Wayne
中科院分区：
文献类型：
--
作者：
Chen, M. S.;Cal, Y.;Goodman, D. Wayne
研究表明，当温度在450 ~ 600 K之间，压力在1 ~ 300 Torr之间时，pt族金属的CO氧化速率随着O-2/CO比增加到0.5以上而显著增加。在离散的O-2/CO比>.5下形成的催化表面，比在化学计量反应条件下和类似的反应物压力下观察到的速率或之前在任何反应物条件下的超高真空研究中观察到的速率大2-3个数量级，并推断出在没有传质限制的情况下CO的碰撞极限。对于Rh、Pd和Pt，达到这些所谓的“超活跃”状态（CO的反应概率被认为接近于一）所需的O-2/CO比率与氧的吸附能、大块氧化物的形成热和金属颗粒大小直接相关。俄歇光谱和x射线光发射光谱显示，超活性表面由大约1ml的表面氧组成。在原位偏振调制反射吸收红外光谱测量中，没有检测到CO的吸附。相比之下，在化学计量的O-2/CO条件下，相似的温度和压力下，Rh、Pd和Pt基本上被化学吸附的CO饱和，CO氧化活性低得多。(C) 2007 Elsevier B.V.版权所有
Studies show that the rate of CO oxidation on Pt-group metals at temperatures between 450 and 600 K and pressures between 1 and 300 Torr increases markedly with an increase in the O-2/CO ratio above 0.5. The catalytic surfaces, formed at discrete O-2/CO ratios >0.5, exhibit rates 2-3 orders of magnitude greater than those rates observed for stoichiometric reaction conditions and similar reactant pressures or previously in ultrahigh vacuum studies at any reactant conditions and extrapolate to the collision limit of CO in the absence of mass transfer limitations. The O-2/CO ratios required to achieve these so-called "hyperactive" states (where the reaction probabilities of CO are thought to approach unity) for Rh, Pd, and Pt relate directly to the adsorption energies of oxygen, the heats of formation of the bulk oxides, and the metal particle sizes. Auger spectroscopy and X-ray photoemission spectroscopy reveal that the hyperactive surfaces consist of approximate 1 ML of surface oxygen. In situ polarization modulation reflectance absorption infrared spectroscopy measurements coupled with no detectable adsorbed CO. In contrast, under stoichiometric O-2/CO conditions and similar temperatures and pressures, Rh, Pd, and Pt are essentially saturated with chemisorbed CO and exhibit far less activity for CO oxidation. (C) 2007 Elsevier B.V. All rights reserved.