Deposition of Pd into mesoporous silica SBA-15 using supercritical carbon dioxide

Pd was deposited into mesoporous silica SBA-15 using supercritical CO₂ (scCO₂). Palladium hexafluoroacetylacetonate [Pd(hfac)₂] was dissolved in scCO₂ and impregnated into the support at very mild conditions, 40 °C and 85 bar. Then the organometallic precursor was reduced with H₂ in the CO₂ mixture or, after depressurization, in pure H₂. Materials were characterized by TGA, XRD, TEM, SEM, EDX, ICP-OES and N₂-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 H₂. 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.