It has been well established that bimetallic systems can exhibit activity different than that of pure metals, and there are many examples in the catalysis literature illustrating the ability of a second metal to promote the desired catalytic activity and selectivity. 1À6 Consequently, there is much interest in basic understanding of the chemical activity on bimetallic surfaces in order to develop catalysts with properties that can be tuned by changing compositions. In some cases, reactions are promoted via a bifunctional mechanism, in which the reaction requires the different activities provided by each metal. 7À12 Furthermore, electronic effects associated with the formation of new me-talÀmetal bonds may alter surface chemical properties, such as CO adsorption strength, 6,13À16 hydrogenation activity, 3,17À19 dehydrogenation activity, 20,21 and reforming selectivity. 3,22,23 Bimetallic surfaces may also provide mixed-metal sites with activity different from that of the pure metal sites, such as on the SnÀPt alloy surfaces. 24À26 In addition, interactions between the metal clusters and the oxide support may also be used to control surface chemistry on the clusters, with lattice oxygen participating in reactions on the oxide-supported clusters. For example, atomic carbon on Ni clusters recombine with lattice oxygen from the titania support to produce gaseous CO, 27,28 and gaseous products containing lattice oxygen are observed in reactions on metal clusters supported on ceria. 29À34 Also for noble metals on ceria supports, ceria plays an important role in oxygen storage in the three-way catalysts for the conversion of CO, NO x , and hydrocarbons into CO 2 , water, and N 2 . 35À37 In other cases, it has been reported that chemical activity occurs at metal clusterÀoxide interfacial sites. 29,38À42 In order to probe the nature of metalÀmetal and metalÀsupport interactions, we have chosen to study a model system consisting of vapor-deposited NiÀAu bimetallic clusters supported on rutile TiO 2 (110). In this model system, the relationships between morphology, composition, and chemical activity can be explored on a fundamental level. The AuÀtitania system is one of chemical interest due to the unusual catalytic properties of

We report the development of a pattern recognition scheme that takes into account both fcc and hcp adsorption sites in performing self-learning kinetic Monte Carlo (SLKMC-II) simulations on the fcc(111) surface. In this scheme, the local environment of every under-coordinated atom in an island is uniquely identified by grouping fcc sites, hcp sites and top-layer substrate atoms around it into hexagonal rings. As the simulation progresses, all possible processes, including those such as shearing, reptation and concerted gliding, which may involve fcc-fcc, hcp-hcp and fcc-hcp moves are automatically found, and their energetics calculated on the fly. In this article we present the results of applying this new pattern recognition scheme to the self-diffusion of 9-atom islands (M(9)) on M(111), where M  =  Cu, Ag or Ni.

Fragmentation of mitochondrial network has been implicated in many neurodegenerative, renal, and metabolic diseases. However, a quantitative measure of the microscopic parameters resulting in the impaired balance between fission and fusion of mitochondria and consequently the fragmented networks in a wide range of pathological conditions does not exist. Here we present a comprehensive analysis of mitochondrial networks in cells with Alzheimer’s disease (AD), Huntington’s disease (HD), amyotrophic lateral sclerosis (ALS), Parkinson’s disease (PD), optic neuropathy (OPA), diabetes/cancer, acute kidney injury, Ca2+ overload, and Down Syndrome (DS) pathologies that indicates significant network fragmentation in all these conditions. Furthermore, we found key differences in the way the microscopic rates of fission and fusion are affected in different conditions. The observed fragmentation in cells with AD, HD, DS, kidney injury, Ca2+ overload, and diabetes/cancer pathologies results from the imbalance between the fission and fusion through lateral interactions, whereas that in OPA, PD, and ALS results from impaired balance between fission and fusion arising from longitudinal interactions of mitochondria. Such microscopic difference leads to major disparities in the fine structure and topology of the network that could have significant implications for the way fragmentation affects various cell functions in different diseases.

openAccessArticle: FalsePage Range: 3548-3548doi: 10.1016/j.jcp.2011.12.029Harvest Date: 2016-01-12 15:09:32issueName:cover date: 2012-05-01pubType

The reaction of methanol on Pt−Au bimetallic clusters on TiO 2 (110) with varying bulk Au fractions has been studied by temperature programmed desorption (TPD) experiments and density functional theory (DFT) calculations. The bimetallic clusters with bulk Au fractions greater than 50% have surfaces that are 100% Au, but these Pt−Au clusters exhibit activity for methanol decomposition that is characteristic of Pt rather than Au; while methanol reaction on pure Pt clusters forms CO as a major product, reaction on pure Au clusters produces formaldehyde. Furthermore, as the bulk Pt concentration is decreased from 100 to 50% in the Pt−Au clusters, the CO yield decreases by only ∼25%. This behavior is consistent with methoxy-induced diffusion of Pt to the surface of the clusters in order to form strong Pt− methoxy bonds. DFT studies indicate that it is thermodynamically favorable for Pt to diffuse to the surface and bind to the methoxy adsorbate. Specifically, DFT calculations show that the methoxy intermediate bound to a single Pt atom in a Au monolayer on Pt( 111) is more thermodynamically stable than methoxy bound to a Au monolayer modified by underlying Pt(111). Although extensive changes in activity due to bimetallic interactions are not observed, the peak temperature for CO desorption decreases by 25 K as the Pt fraction is decreased from 100% to 25%, and the selectivity for methane is higher on bimetallic clusters than on either of the pure metals.