Heterogeneous catalysis takes place through interaction of molecules with active sites at solid surfaces. Defects may be (part of) the active site. The surface is the largest, unavoidable but desirable defect in catalytically active nanoparticles with a large surface to volume ratio. Surfaces terminate the translational symmetry in nanocrystals generating an inevitable boundary layer residing on a crystalline core. Active sites in heterogeneous oxidation catalysis are supposedly redox active transition metal cation-centered ensembles at the surface. Therefore, the structure of active sites is not accessible through conventional diffraction. However, spectroscopic methods provide information about the molecular, local (molecular) structure. S, although structure determination is very challenging for complex oxides especially due to the distribution of local geometries in high surface area catalysts. We want to address this challenge by generating highly crystalline, nanoscaled model materials via chemical vapor synthesis (CVS). These will be characterized focusing with a focus on crystal structure including defects using X-ray scattering and diffraction (XRD), neutron and electron scattering and local structure using X-ray absorption spectroscopy (XAFS). Emphasis is placed on quantitative information like defect densities or moments of partial pair distribution functions (PDF). Our goal is to contribute quantitative indicators of the real structure to structure-activity-relationships and further the understanding of oxidation catalysis based onstarting from the hypotheses that (i) protons / surface hydroxyl groups play an important role for proton-coupled electron transfer reactions (PCET), (ii) redox active (transition metal) cations are (part of the) the active sites, and (iii) complex local structures (e.g., defects) increase catalytic activity.