Bimetallic nanoparticles (NPs) are a new class of catalyst which displays improved catalytic properties different from the individual comprising elements.1 In general, the thermodynamically most favorable structure of bimetallic catalysts has been employed for computational catalysis studies that targeting the rational design of better catalytic systems.2 However, under the reaction condition, the thermodynamically most stable configuration of bimetallic NPs can be break down.3-4 Here, we use density functional theory calculations to study the structural stability and dynamic structural evolution of Au-Pd bimetallic NPs under CO oxidation condition to clarify the chemical nature of the reactive species of Au-Pd NPs for CO oxidation. Consistent with the case of Au-Pd bimetallic surfaces,3 the strong CO-philic nature of Pd drives preferential surface segregation of Pd which is prevented in the thermodynamically stable structure, Pd-core@Au-shell NP. Interestingly, Pd prefers to be located at the vertex of Au-Pd NPs as the following process: 1) the vertex Au atom of Au-Pd NP binds multiple CO molecule (up to four), 2) two CO molecules cooperatively form a staple-like motif of CO*-Au-CO*, 3) the CO*-Au-CO* creates a space under the central Au atom which can be utilized as a cannel for facile Au-Pd swapping, and 4) the strong CO-philic nature of Pd drives the Au-Pd swapping. Moreover, the results show that once the Pd is located at the vertex, the Au-Pd motif is kinetically stable under CO oxidation condition. Our findings show that the local catalytically active motifs of bimetallic NPs can be different from the thermodynamically most stable confinements and that dynamic effects should be considered in the function of bimetallic NPs whose components asymmetrically interact with reacting molecules. 1. Ferrando, R.; Jellinek, J.; Johnston, R. L. Chemical Reviews 2008, 108, 845-910. 2. Kim, H. Y.; Han, S. S.; Ryu, J. H.; Lee, H. M. The Journal of Physical Chemistry C 2010, 114, 3156-3160. 3. Kim, H. Y.; Henkelman, G. ACS Catalysis 2013. 4. Tao, F.; Grass, M. E.; Zhang, Y. W.; Butcher, D. R.; Renzas, J. R.; Liu, Z.; Chung, J. Y.; Mun, B. S.; Salmeron, M.; Somorjai, G. A. Science 2008, 322, 932-934.

Dynamic structural evolution of Au-Pd nanoparticles under CO oxidation condition

251st National Meeting (2016)

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