As compared to bulk state, metal nanoparticles stabilized on supports offer larger surface to volume ratios, faster transport properties, altered physical properties and interesting confinement effects that are consequences of combination of their nanoscale dimensions and interaction with the supports. Due to these exciting properties, these nanomaterials are currently studied in the fields of heterogeneous catalysis and energy storage. [1,2] We report here in situ EXAFS results on three noble metal nanoparticles supported on different scaffolds (porous carbon, oxide). This experiment was carried out on the ROCK beam line by the help of the Lytle-type cell furnace. [3] The thermal behavior of Rh (~1.3 nm), Pd (~4.5 nm) and Ir (~1.5 nm) nanoparticles was studied under hydrogen and inert atmosphere up to 250-300 °C. The Figure below shows the thermal evolution of 1st neighbor distance (R) for Pd, Ir and Rh nanoparticles under different gaseous environments. The R distance is decreasing during heating whereas, the Debye-Waller factor (σ2) is increasing with temperature, irrespective of the environment gas and the nature of element. The differences between nanoparticles below 150 °C can be understood in terms of hydrogen interaction (hydrogen desorption from a hydride phase, formation of solid solution). This unexpected behavior is believe to originate from a nanosize effect increasingly important with decreasing the nanoparticle size. Moreover, this seems to be a more general trend, since similar behavior was already reported for supported Pt nanoparticles. [4] [1]L. Piccolo, in Nanoalloys Synth. Struct. Prop., Springer-Verlag (London, 2012). [2]C. Zlotea and M. Latroche, Colloids Surf. Physicochem. Eng. Asp. 439, 117 (2013). [3]C. La Fontaine, L. Barthe, A. Rochet, and V. Briois, Operando IV 4th Int. Congr. Operando Spectrosc. 205, 148 (2013). [4]J. H. Kang, L. D. Menard, R. G. Nuzzo, and A. I. Frenkel, J. Am. Chem. Soc. 128, 12068 (2006).