Abstract
An atomic- and molecular-level understanding of heterogeneous catalysis is required to characterize the nature of active sites and improve the rational design of catalysts1,2,3. Achieving this level of characterization requires techniques that can correlate catalytic performances to specific surface structures, so as to avoid averaging effects1. Tip-enhanced Raman spectroscopy4,5,6,7 combines scanning probe microscopy with plasmon-enhanced Raman scattering and provides simultaneous topographical and chemical information at the nano/atomic scale from ambient8,9,10 to ultrahigh-vacuum11,12 and electrochemical environments13,14. Therefore, it has been used to monitor catalytic reactions15,16,17,18 and is proposed to correlate the local structure and function of heterogeneous catalysts19. Bimetallic catalysts, such as Pd–Au, show superior performance in various catalytic reactions20,21, but it has remained challenging to correlate structure and reactivity because of their structural complexity. Here, we show that TERS can chemically and spatially probe the site-specific chemical (electronic and catalytic) and physical (plasmonic) properties of an atomically well-defined Pd(sub-monolayer)/Au(111) bimetallic model catalyst at 3 nm resolution in real space using phenyl isocyanide as a probe molecule (Fig. 1a). We observe a weakened N≡C bond and enhanced reactivity of phenyl isocyanide adsorbed at the Pd step edge compared with that at the Pd terrace. Density functional theory corroborates these observations by revealing a higher d-band electronic profile for the low-coordinated Pd step edge atoms. The 3 nm spatial resolution we demonstrate here is the result of an enhanced electric field and distinct electronic properties at the step edges.
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Acknowledgements
The authors acknowledge support from MOST (2016YFA0200601, 2013CB933703 and 2011YQ03012400), NSFC (21633005, 21227004, 21321062 and J1310024) and MOE (IRT13036). The authors thank J.M. Feliu, N. Zheng, D.-Y. Wu, M. Zhang, X.-G. Zhang and A. Terfort for discussions, S. Mo for assistance with ICP-MS measurements and Y. Zheng for help with XPS measurements. The authors acknowledge the National Supercomputer Center in Guangzhou for Tianhe-2 CPU time and assistance. C.T.W. acknowledges support from the PCOSS fellowship programme.
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B.R. supervised the project. J.-H.Z. and B.R. conceived the ideas. J.-H.Z., X.W. and H.-S.S performed the experiments. X.J. performed electronic structure and vibrational frequency calculations. L.M. and Z.-L.Y. performed electromagnetic field simulations. C.T.W. helped with experiments and analysis. All authors contributed to data interpretation and writing of the manuscript.
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Zhong, JH., Jin, X., Meng, L. et al. Probing the electronic and catalytic properties of a bimetallic surface with 3 nm resolution. Nature Nanotech 12, 132–136 (2017). https://doi.org/10.1038/nnano.2016.241
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DOI: https://doi.org/10.1038/nnano.2016.241
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