Due to their very large surface area and ordered crystalline structure, Metal-Organic Framework (MOF) are of great interest in various fields, such as catalysis, drug transport and hydrogen storage. In addition, the pores of MOFs have an important role in the nanoconfinement of metal particles. Indeed, the ordered porosity ensures the monodispersion of the nanoparticles and the control of their size, their stabilization against coalescence and the change of the kinetic and thermodynamic properties of hydrogen absorption. The purpose of this PhD project is to determine the effect of nanoparticle size on physicochemical and hydrogenation properties. Indeed, 1 nm palladium, rhodium and bimetallic (Pd-Rh, Pd-Pt and Rh-Ir) clusters have been homogeneously dispersed within the pores of MIL-101(Cr). The insertion of the nanoparticles was carried out by double solvent impregnation technique followed by a reduction under H2/Ar flow. The obtained composites were characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption to determine physicochemical properties, and by in-situ X-ray absorption, thermal desorption spectroscopy and absorption measurements of hydrogen to determine the sorption properties of H2. Interestingly, 1 nm Pd clusters form solid solutions with hydrogen at room temperature and atmospheric pressure instead of a hydride phase, as observed for bulk Pd. This can be explained by a decrease in the critical temperature of the bi-phasic region (α-β) in the Pd-H phase diagram. However, under the same conditions, rhodium absorbs hydrogen and forms solid solutions, in contrary to bulk Rh. These results may open the route to a new material design strategy not only for solid-state hydrogen storage but also for heterogeneous catalysis field, given that Pd and Rh-based catalysts are widely used for many chemical reactions involving hydrogen.