AVS 57th International Symposium & Exhibition
    In Situ Microscopy and Spectroscopy Topical Conference Tuesday Sessions
       Session IS+SS-TuM

Paper IS+SS-TuM1
Oxidation and Reduction of Pd(100) and Supported Pd Nanoparticle Model Catalysts

Tuesday, October 19, 2010, 8:00 am, Room Acoma

Session: In Situ Spectroscopy – Interfacial Chemistry/Catalysis
Presenter: J.N. Andersen, Lund University, Sweden
Authors: R. Westerstrom, Lund University, Sweden
S. Blomberg, Lund University, Sweden
N. Martin, Lund University, Sweden
J. Gustafson, Lund University, Sweden
E. Lundgren, Lund University, Sweden
J.N. Andersen, Lund University, Sweden
M.E. Messing, Lund University, Sweden
K. Deppert, Lund University, Sweden
H. Bluhm, Lawrence Berkeley National Laboratory
O. Balmes, ESRF Grenoble, France
R. van Rijn, ESRF Grenoble, France
Correspondent: Click to Email
Using in situ high pressure X-ray photoelectron spectroscopy, we study the oxidation and reduction by O2 and CO in the mbar pressure regime of Pd(100) and Pd nanoparticles of 15 or 35 nm diameter supported on a SiOx substrate. We find the oxidation behavior of these model catalysts to be qualitatively similar, with an ultra-thin surface oxide forming prior to the onset of bulk PdO formation. However, the Pd nano particles are observed to bulk oxidize at sample temperatures 40 degrees lower than Pd(100). For the PdO surface, we identify a core level shift of the Pd 3d and O 1s levels of -0.3 and -1.3 eV, respectively, relative to the corresponding levels in bulk PdO. In a CO atmosphere, the Pd 3d shift changes by +0.55 eV due to CO adsorption, and CO adsorbed on the oxide can be identified in the C1s. Also the reduction by CO is similar between the single crystal and the nanoparticle samples, but after the complete removal of the oxide, the nanoparticles incorporate carbon to form a Pd carbide. This is not observed for the single crystal sample.