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19: Iron oxide model catalysts: adsorption and catalysis
Abstract:
Hematite Fe2O3 is used as catalyst in the dehydrogenation of ethylbenzene to styrene. The formed hydrogen reduces the oxide but little is known about the the mechanism. Therefore, the interaction with molecular and atomic hydrogen and its desorption was studied on epitaxial iron oxide films of different phases using LEED, XPS and TDS. Room temperature exposure to atomic H causes partial disordering. Both OH groups and reduced (but not yet metallic) iron appear in XPS. FeO domains react very quickly and TDS shows only water desorption explaining the observed reduction. Fe2O3 domains react more slowly. Even at RT, Fe3O4 domains are formed. TDS shows desorption of both H2O and H2. Upon flashing, reduced iron and OH remain but the oxide reorders and separates into Fe2O3 and Fe3O4. Oxidation restores the original surface. The implications for the behavior of the catalyst will be discussed.
