Within the scope of TACO, my research focuses on the elucidation of structure-performance relationships of ideal water-gas shift catalysts. Due to the structural complexity of nanoparticles, this relation often remains unclear, making the rational design of tailored catalysts difficult. By using magnetite single crystals with well-defined surface structures on the atomic level, we identify the role of individual surface sites and the role of metal co-catalysts in the reaction. Specifically, we use STM in combination with XPS to take a direct look at the surface and into the chemical surrounding of its components. In combination with TPD, we link these properties to the reactivity. Evaporating different metals onto the iron oxide crystal allows the comparison of their behavior and performance in the water-gas shift reaction. This way, we can understand the industrially applied chromium-based system at the atomic level and replace it with non-toxic materials.