CO Oxidation on the Ag-Doped Au Nanoparticles
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CO Oxidation on the Ag-Doped Au Nanoparticles Wenqiang Ma • Fuyi Chen
Received: 4 September 2012 / Accepted: 2 October 2012 / Published online: 6 November 2012 Ó Springer Science+Business Media New York 2012
Abstract The CO oxidation reactivity of negatively and positively charged isolated cuboctahedron (c-Oh) Au13 and Au12Ag nanoparticles is investigated using density functional theory calculations. Charging the nanoparticles modifies the structural stability of the Au13 and Au12Ag nanoparticles as well as the electron distribution in the core and shell atoms. An Ag-doping in gold (Au) clusters improves CO or O2 adsorption on Au12Ag cluster. For Au13 cluster, CO preadsorption increases the capacity of CO and O2 coadsorption, but the result is opposite for Au12Ag cluster. The neutral Au13 and Au12Ag clusters exhibit relatively poor reactivity for CO oxidation, while the reactivity is enhanced significantly by excess electrons. In comparisons of the results of CO oxidation on Ag- and un-doped Au nanoparticles, we discover Ag-doping in Au cluster surely decreases first energy barrier (Ea), and increases slightly second energy barrier (Eb). This work provides a fundamental insight into how the excess charges affect the adsorption activity and how the Ag-doping in Au clusters adjusts the catalytic activity for Ag- or un-doped c-Oh Au clusters. Keywords Density functional theory (DFT) Clusters Nanoalloys Adsorption Catalyst W. Ma (&) F. Chen State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, People’s Republic of China e-mail: [email protected] F. Chen e-mail: [email protected] W. Ma College of Physics and Electronic Information, Yan’an University, Yan’an 716000, Shaanxi, People’s Republic of China
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1 Introduction The properties of nanoscale materials are usually very different from those of the corresponding bulk materials. The high surface to volume ratio of nanomaterials causes such materials to have frequent contact with the reactants of a targeted chemical reaction and to enhance the catalytic activity. Furthermore, nanoscale materials have a large number of low-coordinated atoms at the surface, which also leads to a high reactivity [1–3]. The catalytic performance of the nanocatalysts can not be explained by just one factor. A complicated combination of factors, such as the size, composition, and structure of a nanoparticle, is required to explain catalytic performance. However, the exact nature of their relationship and priority is still in debate. The calculations of CO and O2 adsorption on gold (Au) nanoparticle with different structures showed a different chemical inertness on different structures of Au nanoparticle [4–6]. Other some calculations of Au clusters also showed a size-dependent reactivity [7–10]. Furthermore, the charge effect and coadsorption of CO ? O2 on Au clusters also obtained detailed investigations [11–17]. These studies on the development and design of catalysts have highlighted how Au nanoparticles enhance the performanc
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