期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 138, 期 48, 页码 15743-15750出版社
AMER CHEMICAL SOC
DOI: 10.1021/jacs.6b10169
关键词
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资金
- European Union [671093]
- Spanish Government [SEV 2012-0267, MAT2015-71261-R]
- DOE Office of Science [DE-AC02-06CH11357]
- European Research Council (ERC) [671093] Funding Source: European Research Council (ERC)
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 H-2, O-2, and H2O. Remarkably, temperatures in the range 650-750 degrees 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 similar to 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 (similar to 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.
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