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Model catalysts of supported Au nanoparticles and mass-selected clusters
Lim, Dong-Chan,Hwang, Chan-Cuk,Gantefö,r, Gerd,Kim, Young Dok Royal Society of Chemistry 2010 Physical chemistry chemical physics Vol.12 No.46
<P>In surface science, much effort has gone into obtaining a deeper understanding of the size-selectivity of nanocatalysts. In this article, electronic and chemical properties of various model catalysts consisting of Au are reported. Au supported by oxide surfaces becomes inert towards chemisorption and oxidation as the particle size became smaller than a critical size (2–3 nm). The inertness of these small Au nanoparticles is due to the electron-deficient nature of smaller Au nanoparticles, which is a result of metal-substrate charge transfer. Properties of Au clusters smaller than ∼20 atoms were shown to be non-scalable, <I>i.e.</I>, every atom can drastically change the chemical properties of the clusters. Moreover, clusters with the same size can show dissimilar properties on various substrates. These recent endeavours show that the activity of a catalyst can be tuned by varying the substrate or by varying the cluster size on an atom-by-atom basis.</P> <P>Graphic Abstract</P><P>The origin of size-selectivity in the chemical properties of nanoparticles and mass-selected clusters consisting of Au has been tackled. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c0cp00467g'> </P>
Lisinetskaya, Polina G.,Braun, Christian,Proch, Sebastian,Kim, Young Dok,Gantefö,r, Gerd,Mitrić,, Roland The Royal Society of Chemistry 2016 Physical chemistry chemical physics Vol.18 No.9
<P>We present a joint theoretical and experimental study of excited state dynamics in pure and hydrated anionic gold clusters Au-3(-)[H2O](n) (n = 0-2). We employ mixed quantum-classical dynamics combined with femtosecond time-resolved photoelectron spectroscopy in order to investigate the influence of hydration on excited state lifetimes and photo-dissociation dynamics. A gradual decrease of the excited state lifetime with the number of adsorbed water molecules as well as gold cluster fragmentation quenching by two or more water molecules are observed both in experiment and in simulations. Non-radiative relaxation and dissociation in excited states are found to be responsible for the excited state population depletion. Time constants of these two processes strongly depend on the number of water molecules leading to the possibility to modulate excited state dynamics and fragmentation of the anionic cluster by adsorption of water molecules.</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>
Thin films of size-selected Mo clusters: growth modes and structures
Dollinger, Andreas,Park, Eun Ji,Strobel, Christoph H.,Bleuel, Hannes,Marsteller, Alexander,Seo, Hyun Ook,Kim, Young Dok,Gantefö,r, Gerd The Royal Society of Chemistry 2015 Physical chemistry chemical physics Vol.17 No.32
<P>Thin films of MoO<SUB>3</SUB> were prepared by deposition of size-selected ligand-free Mo clusters under high vacuum conditions and subsequent exposure to air. The growth pattern is highly dependent on the cluster size. At low coverage, small clusters (Mo<SUB>51</SUB>) form a continuous monolayer of fused particles. On top of this monolayer, additional clusters survive as individual entities. Medium sized clusters (Mo<SUB>251</SUB> and Mo<SUB>1253</SUB>) do not coalesce and form a monolayer of clusters. Close examination using <I>in situ</I> scanning tunneling microscopy reveals a local order of the particles. At higher coverage a new pattern of large 3-dimensional aggregations of clusters (pylons) appears. The pylons are not formed under high vacuum conditions. Their formation is most likely caused by the air exposure. For the largest clusters (Mo<SUB>3349</SUB>) studied here, no monolayer is formed. Instead, the clusters are randomly distributed as expected for particles with zero mobility. These results demonstrate the high potential of cluster deposition for the production of new types of nanostructured surfaces, thin films and nanomaterials.</P> <P>Graphic Abstract</P><P>The growth pattern of film highly depends on cluster size. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5cp03147h'> </P>