It is well known that particle size plays an important role in catalytic activity although the reason(s) why significant changes in activity are observed to occur with small changes in size are not well understood. The presence of particular facets, metal-support interactions, and redox state etc., are also capable of playing a role. The difficulty in realising which features are pertinent in a catalytic process stems from issues regarding sample complexity in typical heterogeneous catalysts, as well as technical challenges with instruments used to investigate samples in terms of their sensitivity and capability to distinguish between a specific vs. ensemble response in catalytically active vs. spectator species. We show here how the combination of using a synthesis method which achieves a discrete dispersion of metal Pd nanoparticles with a very narrow particle size distribution (σ ~ 1 nm) in combination with nano-beam X-ray spectroscopy allows us to follow the changes in redox state with time. Importantly, the data are obtained in one example, from an illuminating spot containing ca. 20 nanoparticles with an extremely small size distribution.