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Polarization of electrostatic charge in neutral Ag-Au alloy clusters
Lim, Eunhak,Heo, Jiyoung,Bowen, Kit H.,Kim, Seong K. Elsevier 2018 Chemical physics letters Vol.709 No.-
<P><B>Abstract</B></P> <P>In our theoretical investigation for small Ag-Au alloy clusters, we found that pronounced polarization of their electrostatic charge occurs with some generic regularities. We propose a set of “rules” for the charge distribution, which may be extended to larger Ag-Au alloy clusters or even bulk solids: (1) atoms in lower-coordinated sites tend to be charged more negatively or less positively; (2) the charge of Au is affected by nearest neighbor atoms only, contrary to the case of Ag. The origins of these phenomenological rules may include site-dependent electronic polarization and the difference in s/p hybridization between Ag and Au.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Pronounced polarization of electrostatic charge is found in small Ag<I> <SUB>m</SUB> </I>, Au<I> <SUB>n</SUB> </I>, and Ag<I> <SUB>m</SUB> </I>Au<I> <SUB>n</SUB> </I> clusters. </LI> <LI> The charge is strongly affected by the mode of interactions with neighboring atoms. </LI> <LI> Two simple, phenomenological rules are derived regarding the charge distribution. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Tang, X.,Schneider, J.,Dollinger, A.,Luo, Y.,Wö,rz, A. S.,Judai, K.,Abbet, S.,Kim, Y. D.,Gantefö,r, G. F.,Fairbrother, D. H.,Heiz, U.,Bowen, K. H.,Proch, S. The Royal Society of Chemistry 2014 Physical chemistry chemical physics Vol.16 No.14
<P>Recent research in heterogeneous catalysis, especially on size-selected model systems under UHV conditions and also in realistic catalytic environments, has proved that it is necessary to think in terms of the exact number of atoms when it comes to catalyst design. This is of utmost importance if the amount of noble metal, gold in particular, is to be reduced for practical reactions like CO oxidation. Here it is shown that on TiO<SUB>2</SUB> only Au<SUB>6</SUB> and Au<SUB>7</SUB> clusters are active for CO oxidation which holds for the single crystal, thin films, and titania clusters deposited on HOPG. Size-selected cluster deposition and TPD methods have been employed to investigate the CO oxidation activity of Au<SUB><I>n</I></SUB>/TiO<SUB>2</SUB> systems which are compared to recent results reported by Lee <I>et al.</I> to form a consistent picture in which only two species can be regarded as “active”. The efficiency of investigated Au<SUB><I>n</I></SUB>/(TiO<SUB>2</SUB>)<SUB>93</SUB>/HOPG composite materials is attributed to carbon-assisted oxygen spillover from gold to support particles and across grain boundaries.</P> <P>Graphic Abstract</P><P>The probability of creating CO oxidation-active species on TiO<SUB>2</SUB> is very small since only Au<SUB>6</SUB> and Au<SUB>7</SUB> are catalytically active. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4cp00160e'> </P>