Pd was deposited into mesoporous silica SBA-15 using supercritical CO2 (scCO(2)). Palladium hexafluoroacetylacetonate [Pd(hfac)(2)] was dissolved in scCO(2) and impregnated into the support at very mild conditions, 40 degrees C and 85 bar. Then the organometallic precursor was reduced with H-2 in the CO2 mixture or, after depressurization, in pure H-2. Materials were characterized by TGA, XRD, TEM, SEM, EDX, ICP-OES and N-2-adsorption experiments. Pd nanoparticles evenly distributed into the support (1-3 mol% Pd by ICP-OES) are only obtained when the reduction is performed in pure H-2. Cluster size is limited in two dimensions by the pore size of the support but clusters grow larger with increasing impregnation time and turn into small nanowires. The catalytic activity of the Pd/SiO2 composite material was confirmed following the reduction of 4-nitrophenol to 4-aminophenol in water by UV-vis spectroscopy. (C) 2010 Elsevier B.V. All rights reserved.