Marked capability for hydrogen occlusion of hollow silica nanospheres containing group 8–10 metal clusters

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.