Catalysis research is complex and multidisciplinary in its nature. The performance of an industrially used catalyst is determined by a multitude of factors, from material composition to oxidation state, support porosity, reactant and product distribution in the reactor as well as temperature gradients and local hot spots. Therefore, under “real” conditions, it is nearly impossible to learn which are the most important properties of a catalyst. By preparing simplified model systems, it is possible to eliminate some of the variables during catalyst testing and learn about the materials fundamental properties. We prepare flat model catalysts, consisting of merely a few µg of catalytically active material and test them in a custom made micro reactor with in-situ mass spectrometry and UV-vis spectroscopy. The flat model catalysts have the advantage that there are no hot spots or diffusion limitations in the gas phase that can obscure the findings and that all catalyst material is accessible to in-situ characterization. A few examples will be presented, where we the importance of the oxidation state of the active material and the interaction between catalyst, support and promoter is elucidated.