How does ethylene hydrogenation transform supported Pt catalysts?
Hummingbird Rewind: As part of our three-part series featuring the new X-ray gas heating sample holder, we recall an early demonstration of the method from Yuanyuan Li and Anatoly Frenkel from Yeshiva University, along with their colleagues from Brookhaven National Laboratory, the University of Illinois at Urbana Champaign, and KTH Royal Institute of Technology. The gas flow X-ray sample holder was used to characterize the structural evolution of supported Pt nanocatalysts during ethylene hydrogenation. The team combined correlated synchrotron X-ray absorption spectroscopy (XAS) including X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) with scanning transmission electron microscopy (STEM) to demonstrate dynamic transformations across a broad range of cluster sizes.
a) XANES spectra, b) Fourier transform magnitudes of Pt L3edge EXAFS spectra, and c) STEM images as measured in operando mode. d) Combined EXAFS and STEM results. e) Relative numbers of clusters (normalized by # of particles counted in the STEM size distribution above the 1 nm cutoff) obtained by combining the results of XAFS and STEM. f) Combination of XAFS and STEM analyses accounts for the Pt species and for their evolution in reaction conditions. Copyright © 2015 Springer Nature Limited
By coupling these techniques to characterize metal species across a range of length scales (0-5 nm), substantial restructuring of Pt catalysts is demonstrated across a wide range of cluster sizes. Metal clusters are fragmented into smaller clusters in the sub-nm range followed by coalescence into larger particles. The results will inform future supported Pt nanocatalyst process optimization, while the method demonstrated can be applied to a broad range of mechanistic investigations into dynamic reactions across nanocatalyst systems and length scales.
Reference: Yuanyuan Li, Dmitri Zakharov, Shuang Zhao, Ryan Tappero, Ulrich Jung, Andreas Elsen, Philippe Baumann, Richard G. Nuzzo, Eric A. Stach, Anatoly I. Frenkel, Nature Communications 4 (2015) DOI: 10.1038/ncomms8583
Full paper Copyright © 2015 Springer Nature Limited
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