Abstract
The deposition of preformed nanocluster beams onto suitable supports represents a new paradigm for the precise preparation of heterogeneous catalysts. The performance of the new materials must be validated in model catalytic reactions. It is shown that gold/copper (Au/Cu) nanoalloy clusters (nanoparticles) of variable composition, created by sputtering and gas phase condensation before deposition onto magnesium oxide powders, are highly active for the catalytic reduction of 4-nitrophenol in solution at room temperature. Au/Cu bimetallic clusters offer decreased catalyst cost compared with pure Au and the prospect of beneficial synergistic effects. Energy-dispersive X-ray spectroscopy coupled with aberration-corrected scanning transmission electron microscopy imaging confirms that the Au/Cu bimetallic clusters have an alloy structure with Au and Cu atoms randomly located. Reaction rate analysis shows that catalysts with approximately equal amounts of Au and Cu are much more active than Au-rich or Cu-rich clusters. Thus, the interplay between the Au and Cu atoms at the cluster surface appears to enhance the catalytic activity substantially, consistent with model density functional theory calculations of molecular binding energies. Moreover, the physically deposited clusters with Au/Cu ratio close to 1 show a 25-fold higher activity than an Au/Cu reference sample made by chemical impregnation.
Highlights
The deposition of preformed nanocluster beams onto suitable supports clusters of tunable size typically below 10 nm are pre-assembled into represents a new paradigm for the precise preparation of heterogeneous a beam and deposited in a vacuum catalysts
If the cluster composition is assumed to be Au1Cu1 and the cluster has a spherical shape on the support, the diameter of a cluster with a mass of 65 000 amu should be ≈2.4 nm (≈3.0 nm for hemispherical clusters), which is much smaller than the average diameter, 4.6 nm, obtained from high-angle annular dark-field (HAADF) images
It should be noted that the surface agglomeration which happens during the deposition process occurs because the powder supports in the vibration cup cannot be agitated entirely evenly, especially when they are charged by the cluster ion beam, leading to uneven cluster coverage
Summary
The deposition of preformed nanocluster beams onto suitable supports clusters (nanoparticles) of tunable size typically below 10 nm are pre-assembled into represents a new paradigm for the precise preparation of heterogeneous a beam and deposited in a vacuum catalysts. The performance of the new materials must be validated in model catalytic reactions. The physically deposited clusters with Au/Cu ratio close to 1 show a 25-fold higher activity than an compare their behavior with catalysts prepared by more traditional and well-established routes. We report a first investigation of a solution phase transformation performed by nanoalloy catalysts prepared by cluster beam deposition. Cluster beam deposition is a new method to prepare heteroge- reaction[12,13,14] and selective oxidation of carbon–carbon double neous catalysts for research and development, in which atomic bonds[15,16] and carbon–oxygen bonds.[17,18] The 4-nitrophenol
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