Hollow silica nanospheres containing various precious metal clusters such as Rh, Ir and Ru were synthesized by solubilizing corresponding metal ammine complexes into NP-6/cyclohexane reversed micelle system. The condensation and nucleation of the metal ammine complex in the reversed micelles took place and the resulting nanocrystals of the ammine complexes acted as a structure-directing agent for the formation of hollow cavity in silica spheres. The nano-hollow spheres were stable for thermal treatment up to 1073 K. By this method, bimetallic nanoparticles, i.e. Rh-Co-SiO2 and Ir-Co-SiO2, were also easily synthesized and both metal elements containing in the hollows may be alloyed after thermal treatment. The Ir- and Rh-SiO2 nano-hollows exhibited excess hydrogen uptake. In particular, over Ir-SiO2 sample, the H/Ir ratios reached 3.3 under 200 Torr of hydrogen at room temperature. At higher pressure, the H/M value reached 11.6 at 2.6 MPa. (C) 2007 Elsevier B.V. All rights reserved.