Characterization of Ni@Pt and Co@Pt overlayer catalysts using XAS studies

• Ni@Pt and Co@Pt alumina supported overlayer catalysts.
• White line demonstrates electronic effect of Ni or Co to lower Pt d-band.
• Coordination number and interatomic distance show Pt is on the surface of Ni or Co.
• XAS data correlate with ethylene hydrogenation reactivity results.

The use of XAS studies on Co@Pt and Ni@Pt pseudomorphic overlayer catalysts along with a ethylene hydrogenation descriptor reaction have shown that the d-band of Pt can be affected by the parent metal that it is overlayed on. Pt bond distances were found to be shorter than pure Pt when atop the base Ni and Co indicating that the base metal was exerting compressive strain on the Pt and, for two reasons, causing the Pt d-band to broaden and therefore shift downwards in energy. First, the compressive strain alone has been shown to broaden the d-band of larger atoms atop of smaller ones (i.e. Pt atop Ni) and in the case of the Co@Pt sample Co has one less valence electron than Ni and Pt. This allows for more, than Ni and Pt, of a synergistic interaction between Co and Pt in the overlayer samples resulting in even larger Pt d-bandwidth broadening and shifting. This XAS data was confirmed via reactivity studies as the overlayer samples of both Ni and Co based catalysts had lower reactivity than the pure Pt samples.

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