Web Release Date: November 16,
3-D Structure of Nanosized Catalysts by High-Energy X-ray Diffraction and Reverse Monte Carlo Simulations: Study of Ru
and
Department of Physics, Central Michigan University, Mt. Pleasant, Michigan 48859, ITODYS, University Paris 7-Denis Diderot, UMR 7086, F 75251, Paris Cedex 05, France, and Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439
Received: July 4, 2007
In Final Form: September 20, 2007
Abstract:
Ruthenium exhibits a high catalytic activity that is further enhanced when the material is used as nanosized particles. The origin of the enhanced performance lies in the highly increased surface to volume ratio and, often, to the surface/environment-driven structural relaxation taking place at the nanoscale. In this paper, we show how high-energy X-ray diffraction, atomic pair distribution function analysis, and reverse Monte Carlo simulations may be used to determine the 3-D structure of nanoparticle catalysts such as Ru with sizes less than 5 nm. Ruthenium particles that are 4 nm in size are found to possess a hexagonal close packed-type structure, similar to that found in bulk Ru. Particles that are only 2 nm in size are heavily disordered and consist of a Ru core and a Ru-S skin due to the usage of thiol-based capping agents. This work is the first application of an approach for determining the atomic-scale structure of nanosized catalysts based entirely on experimental diffraction data. The new structural information is a starting point for a better understanding of the structure-property relationship and, hence, for the design of improved nanosized catalysts, including Ru.
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