AVS 53rd International Symposium
    Surface Science Wednesday Sessions
       Session SS1-WeM

Paper SS1-WeM4
Interaction of O@sub 2@, CO, and Methanol with Bimetallic Model Catalysts

Wednesday, November 15, 2006, 9:00 am, Room 2002

Session: Reactions on Metal & Bimetallic Surfaces
Presenter: V. Zielasek, University of Bremen, Germany
Authors: T. Nowitzki, University of Bremen, Germany
B. Juergens, University of Bremen, Germany
H. Borchert, University of Bremen, Germany
S. Giorgio, CRMCN-CNRS, France
T. Risse, Fritz-Haber-Institut, Germany
V. Zielasek, University of Bremen, Germany
C. Henry, CRMCN-CNRS, France
H.-J. Freund, Fritz-Haber-Institut, Germany
M. Baeumer, University of Bremen, Germany
Correspondent: Click to Email
Bimetallic particles may exhibit catalytic activities which reach far beyond those of the monometallic components. For the Co/Pd combination which is, e.g., of technological relevance for the hydrogenation of CO on the route from natural gas to liquid fuel, we have studied the interaction with CO, O@sub 2@ and methanol on the molecular scale. As a model system, mono- and bimetallic nanoparticles were prepared under UHV conditions by physical vapour deposition on a thin alumina film grown on a NiAl(110) single crystal. Bimetallic particles were obtained by sequential deposition of the two metals. The composition of these particles depends on the succession of metal depositions: depositing Co first leads to Co-core Pd-shell particles, whereas depositing Pd first results in separated Pd crystallites with a Co shell and Co nanoparticles in between. Upon O@sub 2@ deposition at room temperature, monometallic Co clusters completely oxidize as revealed by XPS and TPD. Yet, the particles can be reduced by heating to temperatures above 550K. While XPS indicates mostly metallic Co, both, metallic and oxidic components are detected in TPD, pointing to a thin persistent surface oxide layer. Upon CO deposition on metallic Co particles we find significant CO dissociation above room temperature, which may be relevant for the CO hydrogenation. Methanol, which is known to dissociate at Pd nanoparticles, was exposed to monometallic Co and bimetallic Co-Pd particles to determine if and how the composition of the particles influences methanol decomposition and oxidation. In order to relate the investigation of the UHV model systems to technologically relevant catalytic processes, we have performed turn-over experiments for CO oxidation and methanol decomposition in ambient conditions at bimetallic particles of well-defined atomic structure. Surface adsorbate species were analyzed by IR spectroscopy.