Heterogeneous Surfaces as Structure and Particle Size Libraries of Model Catalysts

Different types of model catalysts and their characterization by a wide range of surface analysis techniques have been a successful approach to determine the activity and/or selectivity of catalytic processes, with the effects of surface structure and particle size being key aspects. In recent years, new types of model systems, exhibiting regions of different crystallographic orientations or different particle sizes within one sample have been established: polycrystalline foils of precious metals, consisting of many mu m-sized domains of different structures, differently sized (from nm to mm) curved crystals with differently oriented facets and metal powder aggregates supported on thin oxide films. The signature property of such model systems is the possibility to examine the inherent catalytic properties of different crystallographic orientations/particle sizes simultaneously under identical reaction conditions by spatially-resolved kinetic experiments. Such heterogeneous model systems can be considered as surface structure libraries from which the desired surface structure can be chosen from dozens or even hundreds present on the specimen surface. Here, we review some new insights into catalytic ignition, reaction front propagation, oscillating surface reactions and long-ranging metal/oxide interface effects, gained by this approach. [GRAPHICS] .