Interaction of ethylbenzene and styrene with iron oxide model catalyst films at low coverages: A NEXAFS study

Abstract

The adsorption of ethylbenzene and styrene on well ordered epitaxial iron oxide model catalyst films with different stoichiometries was investigated using near-edge X-ray absorption fine structure spectroscopy (NEXAFS). On the iron-terminated Fe₃O₄(111) and α-Fe₂O₃(0001) surfaces chemisorption of ethylbenzene and styrene is observed occurring initially on the iron sites ia the π-electron system of the phenyl ring. This forces the molecules into an almost flat configuration (η⁶-like ring adsorption geometry). In the case of ethylbenzene this adsorption complex is supposed to lead to an activation of the C–H bonds, thus facilitating the dehydrogenation to styrene. The tilt angle of the aromatic ring systems increases to about 40° when approaching monolayer saturation. In contrast, the interaction with the oxygen-terminated FeO(111) surface is weak and of the physisorption type. The adsorbate–adsorbate interaction dominates and causes a tilted adsorption of the molecules from the beginning.