Finely divided, supported palladium particles are used as catalysts in many technical processes. However, there is still considerable potential to improve catalyst performance and selectivity. Important parameters that can be fine-tuned are the size, distribution and shape of the primary particles as appropriate for the particular application or process. We propose to measure nano-scale palladium particles supported on special grades of activated carbon. The samples are three Pd(5 wt%) on activated carbon catalysts of different average primary particle size (2, 3, 5 nm). Comparison between the samples should reveal: different site occupation (100)/(111) by hydrogen and changes of long range phase coherence in the 2-5 nm particle regime and, therefore, incomplete formation of the beta-phase PdH. The tenfold sensitivity advantage of MAPS over TOSCA is essential to these measurements.