Temperature-dependent evolution of the oxidation states of cobalt and platinum in Co1-xPtx clusters under H2 and CO + H2 atmospheres

Bing Yang, Ghassan Khadra, Juliette Tuaillon-Combes, Eric C. Tyo, Michael J. Pellin, Benjamin Reinhart, Sönke Seifert, Xinqi Chen, Veronique Dupuis*, Stefan Vajda

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

10 Scopus citations


Co1-xPtx clusters of 2.9-nm size with a range of atomically precise Pt/Co atomic ratios (x = 0, 0.25, 0.5, 0.75, 1) were synthesized using the mass-selected low-energy cluster beam deposition (LECBD) technique and soft-landed onto an amorphous alumina thin film prepared by atomic layer deposition (ALD). Utilizing ex situ X-ray photoemission spectroscopy (XPS), the oxidation state of the as-made clusters supported on Al2O3 was determined after both a 1-h-long exposure to air and aging for several weeks while exposed to air. Next, the aged cluster samples were characterized by grazing-incidence X-ray absorption spectroscopy (GIXAS) and then pretreated with diluted hydrogen and further exposed to the mixture of diluted CO and H2 up to 225 °C at atmospheric pressure, and the temperature-dependent evolutions of the particle size/shape and the oxidation states of the individual metal components within the clusters were monitored using in situ grazing-incidence small-angle X-ray scattering and X-ray absorption spectroscopy (GISAXS/GIXAS). The changes in the oxidation states of Co and Pt exhibited a nonlinear dependence on the Pt/Co atomic ratio of the clusters. For example, a low Pt/Co ratio (x ≤ 0.5) facilitates the formation of Co(OH)2, whereas a high Pt/Co ratio (x = 0.75) stabilizes the Co3O4 composition instead through the formation of a Co-Pt core-shell structure where the platinum shell inhibits the reduction of cobalt in the core of the Co1-xPtx alloy clusters. The obtained results indicate methods for optimizing the composition and structure of binary alloy clusters for catalysis.

Original languageEnglish (US)
Pages (from-to)21496-21504
Number of pages9
JournalJournal of Physical Chemistry C
Issue number38
StatePublished - Sep 29 2016

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films


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