Adsorption sites, metal-support interactions, and oxygen spillover identified by vibrational spectroscopy of adsorbed CO: A model study on Pt/ceria catalysts
Adsorption sites, metal-support interactions, and oxygen spillover identified by vibrational spectroscopy of adsorbed CO: A model study on Pt/ceria catalysts
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DOI：
10.1016/j.jcat.2012.01.022
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发表时间：
2012-05-01
影响因子：
7.3
通讯作者：
Libuda, J.
中科院分区：
文献类型：
--
作者：
Happel, M.;Myslivecek, J.;Libuda, J.
吸附CO的振动光谱通常用于氧化物负载的金属催化剂的表征，尽管关于频带分配的持续的模糊性。在这里，我们提出了明确定义的Pt/CeO 2（1 1 1）/Cu（1 1 1）模型催化剂的参考数据，旨在明确识别相关功能。用扫描隧道显微镜（STM）研究了Pt粒子的生长和形貌，用程序升温脱附（TPD）研究了Pt粒子的吸附性能，并用光电子能谱（PES）和共振光电子能谱（RPES）研究了Pt粒子的电子结构.结合分子束（MB）方法和红外反射吸收光谱（IRAS），我们将这些信息与CO的相互作用联系起来。在氧化铈载体上识别出两种类型的缺陷吸附位（2097 cm（-1），2120 cm（-1）），它们被归属为结构缺陷和还原的Ce 3+中心。这些位点的相对丰度在热处理后发生变化。在Pt纳米颗粒上，CO首先在台阶和边缘位点（2066 cm（-1））处吸附在顶部上，然后在桥接（1875 cm（-1））和顶部（2080-2097 cm（-1））几何形状中发生在（111）面上的吸附。首次，我们确定振动CO功能，这是由电子金属支持相互作用和氧反向溢出。在还原的CeO 2-x（111）上，出现了2053 cm（-1）的红移带，这是由于金属氧化物电子相互作用的改变，增加了Pt到CO的π-背键.热处理还激活氧从载体反向溢出到Pt纳米颗粒，由于CO位点旁边的共吸附氧，导致CO光谱（2090-2105 cm（-1））出现蓝移特征。(C)2012 Elsevier Inc. All rights reserved.
Vibrational spectroscopy of adsorbed CO is commonly used for the characterization of oxide-supported metal catalysts, in spite of persisting ambiguities concerning the band assignment. Here, we present reference data on well-defined Pt/CeO2(1 1 1)/Cu(1 1 1) model catalysts aiming at clear identification of the related features. Growth and morphology of the Pt particles are investigated by scanning tunneling microscopy (STM), the adsorption properties are probed by temperature programmed desorption (TPD), and the electronic structure has previously been studied by photoelectron spectroscopy (PES) and resonant photoelectron spectroscopy (RPES). Combining molecular beam (MB) methods and infrared reflection absorption spectroscopy (IRAS), we correlate this information to the interaction with CO.Two types of defect adsorption sites are identified on the ceria support (2097 cm(-1), 2120 cm(-1)), which are assigned to structural defects and reduced Ce3+ centers. The relative abundance of these sites changes upon thermal treatment. On the Pt nanoparticles, CO first adsorbs on-top at step and edge sites (2066 cm(-1)), before adsorption on the (1 1 1) facets occurs in bridging (1875 cm(-1)) and on-top (2080-2097 cm(-1)) geometry. For the first time, we identify vibrational CO features, which arise from electronic metal-support interactions and from oxygen reverse spillover. On reduced CeO2-x(1 1 1), a red-shifted band at 2053 cm(-1) appears, which is attributed to increased pi-backbonding from Pt to CO, as a result of a change in electronic metal-oxide interaction. Thermal treatment also activates oxygen reverse spillover from the support to the Pt nanoparticle, which gives rise to a blue-shifted feature in the CO spectrum (2090-2105 cm(-1)) due to coadsorbed oxygen next to CO sites. (C) 2012 Elsevier Inc. All rights reserved.