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.