Propylene oxide is an immensely important industrial building block. It is mostly used in production of polyurethane plastics. Current production methods are either expensive of environmentally taxing. Direct gas phase propylene oxidation using molecular oxygen would solve most of these problems. However, these processes also suffer from several drawbacks, namely low selectivity and catalyst deactivation. We designed catalysts that were similar in structure and showed very different selectivity in the propylene epoxidation. With these materials we performed several in situ and operando analysis and combined them with theoretical methods. The goal was to discern the underlying reasons for the observed differences in selectivity during propylene epoxidation reaction.