Styrene synthesis over iron oxide model catalysts was studied by combining UHV characterization methods with in situ conversion measurements in a microflow reactor under realistic reaction conditions. Both unpromoted Fe2O3 and K-promoted model catalysts show a similar high starting activity while that of Fe3O4 is clearly lower. Water limits and K promotion slows down deactivation by coking and oxide reduction. The deactivation can be prevented and the high initial yield preserved by adding a small amount of oxygen to the feed. Both the presence of Fe3+ and intermediate adsorption strength for ethylbenzene and styrene are essential for high conversion yields. (C) 2004 Elsevier Inc. All rights reserved.