The structural-dynamic behaviour of gamma-Al2O3 supported Rh nanoparticles under He, H-2/He, and NO/He has been investigated using a newly developed methodology that permits dispersive EXAFS (EDE), diffuse reflectance infra red spectroscopy (DRIFTS), and mass spectrometry (MS) to be applied simultaneously to the study of gas-solid interactions. This reveals a considerably variability in nanoparticle habit (for 11 angstrom diameter nanoparticles as a function of temperature), and between 8 angstrom and 11 angstrom particles in their response to NO. The selectivity (N-2/(N-2 + N2O)) of the reactive interaction between NO and the supported Rh shows essentially no particle size dependence above 473 K: it is apparent, however, that considerable differences in some aspects of the structural behaviour of the 8 angstrom and 11 angstrom Rh particles do nonetheless, exist. At 373 < T < 473 K a clear divergence in structural, functional, and reactive response of the different sized supported Rh nanoparticles toward NO is observed. These observations are discussed in terms of the ability of different sized Rh particles to change structure in response to the reactive environment, the subsequent effect this has on the nitrosyl functionality that different phases may support, and the reactive pathways for NO conversion that may therefore arise.