Correlation between the electronic/local structure and CO-oxidation activity of PdxRu1−x alloy nanoparticles

Chulho Song; Akhil Tayal; Okkyun Seo; Jaemyung Kim; Yanna Chen; Satoshi Hiroi; L. S. R. Kumara; Kohei Kusada; Hirokazu Kobayashi; Hiroshi Kitagawa; Osami Sakata

doi:10.1039/C8NA00305J

Correlation between the electronic/local structure and CO-oxidation activity of Pd_xRu_1−x alloy nanoparticles†

Chulho Song,

‡^a Akhil Tayal,

§^a Okkyun Seo,^ba Jaemyung Kim,^a Yanna Chen,^ba Satoshi Hiroi,^b L. S. R. Kumara,

¶^a Kohei Kusada,^c Hirokazu Kobayashi,^c Hiroshi Kitagawa

^c and Osami Sakata

*^abd

Author affiliations

* Corresponding authors

^a Synchrotron X-ray Station at SPring-8, Research Network and Facility Services Division, National Institute for Materials Science (NIMS), 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan
E-mail: SAKATA.Osami@nims.go.jp
Tel: +81 791 58 1970

^b Synchrotron X-ray Group, Research Center for Advanced Measurement and Characterization, NIMS, 1-1-1 Kouto, Sayo, Hyogo 679-5148, Japan

^c Division of Chemistry, Graduate School of Science, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto 606-8502, Japan

^d Department of Materials Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, Nagatsuta, Midori, Yokohama 226-8502, Japan

Abstract

Pd_xRu_1−x nanoparticles (NPs) were observed to display enhanced CO oxidation activity with the maximum performance obtained at the composition x = 0.5. To unveil the origin of this superior CO oxidation activity, we investigated the local structure, valence state, and electronic properties of Pd_xRu_1−x NPs using synchrotron-based X-ray techniques. Site specific information obtained from X-ray absorption fine structure (XAFS) spectroscopy revealed that the local disorder around Pd and Ru atoms and their valence state can be systematically tuned by varying the Pd composition. Furthermore, the XAFS results indicated a strong correlation among the structural and valence state and the observed CO oxidation catalytic properties of Pd_xRu_1−x NPs. Hard X-ray photoelectron spectroscopy (HAXPES) analysis suggested that the capability of CO oxidation requires an optimum balance between the adsorption and desorption energy for CO adsorption and eventually conversion to CO₂. A comparison between the experimental valence band (VB) HAXPES spectra of Pd_xRu_1−x NPs and the linear combination of VB HAXPES spectra of Pd and Ru NPs revealed that the charge transfer from Pd to Ru occurs in the Pd_xRu_1−x alloy at intermediate compositions, causing electron enrichment of the Ru surface. In addition, the maximum red-shift in the edge-position relative to that of bulk Pd/Ru and high structural disorder were observed for the PdRu alloy at the intermediate composition. This coupled behavior of structure and electronic properties followed the experimental trend of CO oxidation activity in this system.

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Correlation between the electronic/local structure and CO-oxidation activity of Pd_xRu_1−x alloy nanoparticles†

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Nanoscale Advances

Correlation between the electronic/local structure and CO-oxidation activity of PdxRu1−x alloy nanoparticles†

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Correlation between the electronic/local structure and CO-oxidation activity of PdxRu1−x alloy nanoparticles

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Correlation between the electronic/local structure and CO-oxidation activity of Pd_xRu_1−x alloy nanoparticles†

Correlation between the electronic/local structure and CO-oxidation activity of Pd_xRu_1−x alloy nanoparticles