title: Reversible Transformation of Pt Nanoparticles into Single Atoms inside High-Silica Chabazite Zeolite.
abstract: 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/SiO2or 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.
authors.affiliation: Instituto de Tecnología Química, Universitat Politècnica de València-Consejo Superior de Investigaciones Científicas , Avenida de los Naranjos s/n, 46022 Valencia, Spain.
authors.forename: Manuel
authors.initials: M
authors.lastname: Moliner
authors.affiliation: Astrix Technology Group , 125 Half Mile Road, Suite 200, Red Bank, New Jersey 07701, United States.
authors.forename: Jadeene E
authors.initials: JE
authors.lastname: Gabay
authors.affiliation: ExxonMobil Research and Engineering Co. , Annandale, New Jersey 08801, United States.
authors.forename: Chris E
authors.initials: CE
authors.lastname: Kliewer
authors.affiliation: ExxonMobil Research and Engineering Co. , Annandale, New Jersey 08801, United States.
authors.forename: Robert T
authors.initials: RT
authors.lastname: Carr
authors.affiliation: ExxonMobil Chemical Company , 4500 Bayway Drive, Baytown, Texas 77520, United States.
authors.forename: Javier
authors.initials: J
authors.lastname: Guzman
authors.affiliation: ExxonMobil Research and Engineering Co. , Annandale, New Jersey 08801, United States.
authors.forename: Gary L
authors.initials: GL
authors.lastname: Casty
authors.affiliation: ExxonMobil Research and Engineering Co. , Annandale, New Jersey 08801, United States.
authors.forename: Pedro
authors.initials: P
authors.lastname: Serna
authors.affiliation: Instituto de Tecnología Química, Universitat Politècnica de València-Consejo Superior de Investigaciones Científicas , Avenida de los Naranjos s/n, 46022 Valencia, Spain.
authors.forename: Avelino
authors.initials: A
authors.lastname: Corma