Resolving Atomic Ordering Differences in Group 11 Nanosized Metals and Binary Alloy Catalysts by Resonant High-Energy X-ray Diffraction and Computer Simulations

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• 作者：Valeri Petkov ; Sarvjit Shastri ; Shiyao Shan ; Pharrah Joseph ; Jin Luo ; Chuan-Jian Zhong ; Takahiro Nakamura ; Yuliati Herbani ; Shunichi Sato
• 刊名：Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：October 24, 2013
• 年：2013
• 卷：117
• 期：42
• 页码：22131-22141
• 全文大小：688K
• 年卷期：v.117,no.42(October 24, 2013)
• ISSN：1932-7455

文摘

Resonant high-energy X-ray diffraction coupled to atomic pair distribution function analysis and computer simulations is used to study the atomic-scale structure of group 11 nanosized metals and binary alloy catalysts. We find that nanosized Cu is quite disordered structurally whereas nanosized Ag and especially Au exhibit a very good degree of crystallinity. We resolve Cu鈥揅u and Ag鈥揂g atomic correlations from Au-involving ones in Au鈥揅u and Au鈥揂g nanoalloys and show that depending on the synthetic route group 11 binary alloys may adopt structural states that obey or markedly violate Vegard鈥檚 law. In the latter case, Cu and Ag atoms undergo substantial size expansion and contraction by as much as 0.3 and 0.03 脜, respectively, while heavier Au atoms remain practically intact. The size change of Cu and Ag atoms does not follow Pauling鈥檚 rule of electronegativity predicting charge flow toward the more electronegative Au but occurs in a way such that Cu/Au and Ag/Au atomic size ratios in the nanoalloys become closer to one. Atomic size adjusting and the concurrent charge redistribution result in a synergistic effect of oxygen inactive Au and oxygen very active Cu and Ag leading to nanoalloys with very good activity for low-temperature oxidation of CO.