Bimetallic Ag-Pt Sub-nanometer Supported Clusters as Highly Efficient and Robust Oxidation Catalysts

A combined experimental and theoretical investigation of Ag-Pt sub-nanometer clusters as heterogeneous catalysts in the CO→CO_2 reaction (COox) is presented. Ag_9Pt_2 and Ag_9Pt_3 clusters are size-selected in the gas phase, deposited on an ultrathin amorphous alumina support, and tested as catalysts experimentally under realistic conditions and by first-principles simulations at realistic coverage. In situ GISAXS/TPRx demonstrates that the clusters do not sinter or deactivate even after prolonged exposure to reactants at high temperature, and present comparable, extremely high COox catalytic efficiency. Such high activity and stability are ascribed to a synergic role of Ag and Pt in ultranano-aggregates, in which Pt anchors the clusters to the support and binds and activates two CO molecules, while Ag binds and activates O_2, and Ag/Pt surface proximity disfavors poisoning by CO or oxidized species

Bimetallic Ag-Pt Sub-nanometer Supported Clusters as Highly Efficient and Robust Oxidation Catalysts

A combined experimental and theoretical investigation of Ag-Pt sub-nanometer clusters as heterogeneous catalysts in the CO→CO_2 reaction (COox) is presented. Ag_9Pt_2 and Ag_9Pt_3 clusters are size-selected in the gas phase, deposited on an ultrathin amorphous alumina support, and tested as catalysts experimentally under realistic conditions and by first-principles simulations at realistic coverage. In situ GISAXS/TPRx demonstrates that the clusters do not sinter or deactivate even after prolonged exposure to reactants at high temperature, and present comparable, extremely high COox catalytic efficiency. Such high activity and stability are ascribed to a synergic role of Ag and Pt in ultranano-aggregates, in which Pt anchors the clusters to the support and binds and activates two CO molecules, while Ag binds and activates O_2, and Ag/Pt surface proximity disfavors poisoning by CO or oxidized species

Thermal stability of uni-size Pt cluster disk constructed on silicon substrate

Thermal stability of a uni-size platinum cluster disk, Pt30, constructed on a silicon (111) surface was investigated in a temperature range from room temperature to 773 K by means of a scanning tunneling microscope (STM). The apparent height and diameter and the number density of the cluster disks were obtained from the STM images as a function of the heating temperature. According to the statistical analysis of these specific values, it has been concluded that both the cluster disk and the neighboring substrate surface are stable up to 673 K, then they start being decomposed at the higher temperatures

Size dependence of thermal stability of Pt clusters bound to Si substrate surface prepared by cluster impact deposition

Thermal behavior of Pt10 and Pt1 bound to a silicon substrate prepared by the impact of size-selected Pt cluster ions at 1 eV per Pt atom was investigated. Their height and diameter were obtained by statistical analysis of their images using scanning-tunneling microscopy. The Pt10 are stably bound to the Si surface as monatomic-layered Pt10Six disks with insertion of Si atoms into the clusters at the moment of the impact, and they start to be decomposed between 623 and 673 K under vacuum conditions. The thermal stability of the Pt10Six disks is comparable to that of a Pt thin film prepared on a Si substrate, but inferior to that of Pt30 disks on the Si substrate. Comparing with thermal behavior of Pt atoms and a PtSi thin film on the Si substrate, it has been concluded that more Si atoms start to diffuse into a Pt10Six disk between 623 and 673 K, while they do not into a Pt30 disk having a close-packed arrangement of the Pt atoms as high as 673 K, owing to a higher barrier for the Si insertion into the close-packed cluster disk than into the Pt10Six disk having a longer Pt-Pt internuclear distance

Inverted Vibrational and Rotational Excitation of CN(B 2 Σ + ) Produced through Superexcited Ion-Pair States of MCN (M = Na, K, Rb)

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Molecular Dynamics Simulation of Dynamic Solvation Effect in the Collision of I_2^-(CO_2)_n Cluster with Si Surface

Cluster-surface collision induced dissociation of an I_2^- molecule initially embedded in a I_2^-(CO_2)_n cluster was investigated. Molecular dynamics simulation which provides a microscopic description for energy acquisition in the cluster-surface impact. The trajectory calculations using a realistic Si surface model indicate that the collisions of I_2^-(CO_2)_n with a Si surface can be treated as perfectly elastic ones. The dissociation probability of I_2^- was computed for I_2^-(CO_2)_n with n=0-6 on the basis of a hard-wall model. The size dependence of the dissociation probability ascribable to the wedge effect by a CO_2 molecule located halfway between the I atoms, which is consistent with experimental result by Yasumatsu et al