Adsorption and Activation of CO on Co3O4(111) Thin Films
Adsorption and Activation of CO on Co3O4(111) Thin Films
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DOI：
10.1021/acs.jpcc.5b04145
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发表时间：
2015-07-23
影响因子：
3.7
通讯作者：
Libuda, J.
中科院分区：
文献类型：
--
作者：
Ferstl, P.;Mehl, S.;Libuda, J.
为了探索钴氧化物在原子水平上的催化性能，我们在超高真空（UHV）条件下利用扫描隧道显微镜（STM）、高分辨X射线光电子能谱（HR-XPS）、红外反射吸收谱（IRAS）和程序升温脱附谱（TPD）研究了CO和O-2与有序Co 3 O 4（111）薄膜的相互作用.在低覆盖度和温度下，CO与（111）面上的表面Co 2+离子结合。在较大的曝光量下，形成压缩相，其中额外的CO位于Co2+离子之间的位点。此外，形成与缺陷相关的桥接碳酸盐物质，例如Co 3 O 4（111）阶地的台阶边缘或（111）取向晶粒的侧刻面。预吸附氧既不影响CO吸附在低覆盖度，也不形成表面碳酸盐，但它阻止形成高覆盖度的CO相。解吸的分子结合的CO发生高达180 K，而表面碳酸盐分解在一个广泛的温度范围高达400 K下释放的CO和，在较小程度上，CO2。当晶体氧大量流失时，Co 3 O 4晶粒最终转变为CoO岩盐结构。
To explore the catalytic properties of cobalt oxide at the atomic level, we have studied the interaction of CO and O-2 with well-ordered Co3O4(111) thin films using scanning tunneling microscopy (STM), high-resolution X-ray photoelectron spectroscopy (HR-XPS), infrared reflection absorption spectroscopy (IRAS), and temperature-programmed desorption spectroscopy (TPD) under ultrahigh vacuum (UHV) conditions. At low coverage and temperature, CO binds to surface Co2+ ions on the (111) facets. At larger exposure, a compressed phase is formed in which additional CO is located at sites in between the Co2+ ions. In addition, a bridging carbonate species forms that is associated with defects such as step edges of Co3O4(111) terraces or the side facets of the (111) oriented grains. Preadsorbed oxygen neither affects CO adsorption at low coverage nor the formation of the surface carbonate, but it blocks formation of the high coverage CO phase. Desorption of the molecularly bound CO occurs up to 180 K, whereas the surface carbonate decomposes in a broad temperature range up to 400 K under the release of CO and, to a lesser extent, of CO2. Upon strong loss of crystalline oxygen, the Co3O4 grains eventually switch to the CoO rocksalt structure.