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Abstract

Metal-oxide based catalysts are used for many important synthesis reactions in the chemical industry.
A better understanding of the catalyst operation can be achieved by studying elemantary reaction steps
on well-defined model catalyst systems. For the dehydrogenation of ethylbenzene to styrene in the
presence of steam both unpromoted and potassium promoted iron-oxide catalysts are active. Here we
review the work done over unpromoted single-crystalline FeO(111), Fe3O4(111) and a-Fe2O3(0001)
films grown epitaxially on Pt(111) substrates. Their geometric and electronic surface structures were
characterized by STM, LEED, electron microscopy and electron spectroscopic techniques. In an
integrative approach, the interaction of water, ethylbenzene and styrene with these films was
investigated mainly by thermal desorption and photoelectron emission spectroscopy. The
adsorption-desorption energetics and kinetics depend on the oxide surface terminations and are
correlated to the electronic structures and acid-base properties of the corresponding oxide phases,
which reveal insight into the nature of the active sites and into the catalytic function of semiconducting
oxides in general. Catalytic studies, using a batch reactor arrangement at high gas pressures and post
reaction surface analysis, showed that only a-Fe2O3(0001) containing surface defects is catalytically
active, whereas Fe3O4(111) is always inactive. This can be related to the elementary adsorption and
desorption properties observed in ultrahigh vacuum, which indicates that the surface chemical properties
of the iron-oxide films do not change significantly across the "pressure-gap". A model is proposed
according to which the active site involves a regular acidic surface sites and a defect site next to it.
The results on metal-oxide surface chemistry also have implications for other fields, such as
environmental science, biophysics and chemical sensor