TY - JOUR
T1 - Temperature-dependent evolution of the oxidation states of cobalt and platinum in Co1-xPtx clusters under H2 and CO + H2 atmospheres
AU - Yang, Bing
AU - Khadra, Ghassan
AU - Tuaillon-Combes, Juliette
AU - Tyo, Eric C.
AU - Pellin, Michael J.
AU - Reinhart, Benjamin
AU - Seifert, Sönke
AU - Chen, Xinqi
AU - Dupuis, Veronique
AU - Vajda, Stefan
N1 - Funding Information:
The work at the Argonne National Laboratory was supported by the U.S. Department of Energy, BES-Materials Science and Engineering, under Contract DE-AC-02-06CH11357, with UChicago Argonne, LLC, the operator of Argonne National Laboratory. The use of the 12-ID-C and 12-BM beamlines of the Advanced Photon Source, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Argonne National Laboratory, was supported by the U.S. DOE under Contract No. DE-AC02-06CH11357. The Lyon authors acknowledge the use of PLYRA for cluster synthesis. The authors thank E. Bernstein and F. Tournus for their assistance with TEM characterization.
Publisher Copyright:
© 2016 American Chemical Society.
PY - 2016/9/29
Y1 - 2016/9/29
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=84989929851&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84989929851&partnerID=8YFLogxK
U2 - 10.1021/acs.jpcc.6b06483
DO - 10.1021/acs.jpcc.6b06483
M3 - Article
AN - SCOPUS:84989929851
SN - 1932-7447
VL - 120
SP - 21496
EP - 21504
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 38
ER -