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Effects of Multiple Platinum Species on Catalytic Reactivity Distinguished by Electron Microscopy and X‑ray Absorption Spectroscopy Techniques

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journal contribution
posted on 24.10.2017, 00:00 by Bing Nan, Xiu-Cui Hu, Xu Wang, Chun-Jiang Jia, Chao Ma, Ming-Xing Li, Rui Si
Supported platinum species in the forms of single atoms, ultrafine clusters, and metallic particles have been widely investigated because of their unique catalytic properties in diverse redox reactions. In this work, we used thermally stable ceria–zirconia–lanthana (Ce0.5Zr0.42La0.08Ox) as an active oxide support to deposit platinum with different loading amounts from 0.5 to 2 at. % via an incipient wetness impregnation. The as-obtained samples were measured under the methane oxidation reaction conditions with high space velocities up to 100,000 mL·g–1·h–1. Here, 1 at. % Pt sample showed the best catalytic performance with a total reaction rate of 1.93 μmolCH4·gcat–1·s–1 and exclusive platinum rate of 24.4 mmolCH4·molPt–1·s–1 at 450 °C. Multiple characterization means, especially aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray absorption fine structure (XAFS) with the related profile fittings, were carried out to determine the electronic and local coordination structures of platinum. On the basis of these experimental evidence, we have distinguished the effects of different components and found that platinum oxide clusters (PtxOy) with averaged sizes from subnanometer to 2–3 nm play an essential role for the oxidation of methane. Metallic Pt particles are probably active species, but their large-size characteristics impair the reactivity. However, ionic platinum single atoms may not be appropriate for this catalytic process.