Reversible Transformation of Pt Nanoparticles into Single Atoms inside High-Silica Chabazite Zeolite

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• 作者：Manuel Moliner ; Jadeene E. Gabay ; Chris E. Kliewer ; Robert T. Carr ; Javier Guzman ; Gary L. Casty ; Pedro Serna ; Avelino Corma
• 刊名：Journal of the American Chemical Society
• 出版年：2016
• 出版时间：December 7, 2016
• 年：2016
• 卷：138
• 期：48
• 页码：15743-15750
• 全文大小：483K
• ISSN：1520-5126

文摘

We report the encapsulation of platinum species in highly siliceous chabazite (CHA) crystallized in the presence of N,N,N-trimethyl-1-adamantammonium and a thiol-stabilized Pt complex. When compared to Pt/SiO₂ or Pt-containing Al-rich zeolites, the materials in this work show enhanced stability toward metal sintering in a variety of industrial conditions, including H₂, O₂, and H₂O. Remarkably, temperatures in the range 650–750 °C can be reached without significant sintering of the noble metal. Detailed structural determinations by X-ray absorption spectroscopy and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy demonstrate subtle control of the supported metal structures from ∼1 nm nanoparticles to site-isolated single Pt atoms via reversible interconversion of one species into another in reducing and oxidizing atmospheres. The combined used of microscopy and spectroscopy is critical to understand these surface-mediated transformations. When tested in hydrogenation reactions, Pt/CHA converts ethylene (∼80%) but not propylene under identical conditions, in contrast to Pt/SiO₂, which converts both at similar rates. These differences are attributed to the negligible diffusivity of propylene through the small-pore zeolite and provide final evidence of the metal encapsulation.