AVS 45th International Symposium
    Surface Science Division Monday Sessions
       Session SS2-MoA

Paper SS2-MoA9
Dehydrogenation of Ethylbenzene Studied on Single Crystalline Iron Oxide Model Catalyst Films

Monday, November 2, 1998, 4:40 pm, Room 309

Session: Surface Chemistry on Model Catalysts
Presenter: W. Weiss, Fritz-Haber-Institut der MPG, Germany
Authors: W. Weiss, Fritz-Haber-Institut der MPG, Germany
D. Zscherpel, Fritz-Haber-Institut der MPG, Germany
M. Ritter, Fritz-Haber-Institut der MPG, Germany
R. Schloegl, Fritz-Haber-Institut der MPG, Germany
Correspondent: Click to Email
We study the dehydrogenation of ethylbenzene (EB) to styrene over single crystalline FeO(111), Fe@sub3@O@sub4@(111) and @alpha@-Fe@sub2@O@sub3@(0001) model catalyst films grown onto Pt(111) substrates. The epitaxial film growth and their atomic surface structures were studied by STM and LEED. 1-2 ML thick FeO(111) films form oxygen terminated surfaces structures. The Fe@sub3@O@sub4@(111) surface exposes iron atoms in the topmost layer, as determined by a dynamical LEED intensity analysis reveiling a Pendry r-factor of 0.2. The @alpha@-Fe@sub2@O@sub3@(0001) surface exposes two different terminations, iron and oxygen, depending on the ambient oxygen partial pressure. With TDS and UPS a stong chemisorption of EB is observed on the iron terminated Fe@sub3@O@sub4@ and @alpha@-Fe@sub2@O@sub3@ films, wheras only physisorption is observed on the oxygen terminated FeO(111) film. Surface defects on the films were imaged by atomic resolution STM measurements, and the role of the oxide stoichiometry and surface defect concentrations for the model catalyst activities was studied by combining batch reactor experiments at total gas pressures of 1 mbar with pre- and post reaction surface analysis in UHV. No styrene is formed over Fe@sub3@O@sub4@ films. Fe@sub2@O@sub3@ films are catalytically active, and the styrene formation rate increases with increasing surface defect concentration on these films. This reveals Fe@sub2@O@sub3@ as the active oxide phase and atomic surface defects as catalytically active sites thereon. These defects can be steps, vacancies or adatoms. The formation of carbonaceous surface deposits that deactivate the model catalyst films after about 30 min reaction time was monitored with a PEEM microscope. A pattern formation is observed which indicates that the catalyst deactivation is a site selective process, which presumably starts at extended surface defects.