Our research focusses on the investigation of the dynamic restructuring of functional nanomaterials under realistic conditions, e.g. model catalysts under a reactive gas atmosphere. To this purpose, we place a scanning tunneling microscope (STM) with high temporal and spatial resolution directly into gas mixtures at near ambient pressures (also called NAP-STM) and thus investigate how the structure of particles (metal clusters) and oxide supports changes under these conditions. By using size-selected clusters (i.e. small particles with a precisely defined number of atoms), it is possible to investigate how the formation and decay of highly reactive particle structures occurs, can be controlled and how such structural changes influence the function of a material. X-ray photoelectron spectroscopy under identical conditions (NAP-XPS) provides complementary information about the chemical and charge state of the materials, which we correlate with the structural and dynamic information from NAP-STM.