Adsorption of Pd(hfac)2 on mesoporous silica SBA-15 using supercritical CO2 and its role in the performance of Pd–SiO2 catalyst
Journal of Supercritical Fluids
The adsorption of Palladium hexafluoroacetylacetonate [Pd(hfac) 2 ] dissolved in supercritical CO 2 (scCO 2 ) onto mesoporous silica SBA-15 has been studied by measuring the adsorption isotherms. At 40 • C and 8.5 MPa, the adsorption increases up to saturation at ca. 0.55 mol Pd(hfac) 2 /kg SiO 2 SBA-15. The influence of temperature, pressure and density of CO 2 on the adsorption equilibrium has been also examined. At constant temperatures of 40 and 60 • C, the amount adsorbed on the support
... d on the support decreases as pressure and density increase. At 8.5 MPa, the amount adsorbed increases as the temperature increases from 40 to 80 • C. At CO 2 constant density (350 kg/m 3 ), adsorption decreases as the temperature increased from 40 to 80 • C. For the assayed conditions, the maximum adsorption was achieved at 80 • C and 8.5 MPa. Data were successfully correlated to the Langmuir, modified Langmuir and Freundlich adsorption models. Adsorption of Pd(hfac) 2 on silica SBA-15 seems to be weak and it is mainly dominated by the large solubility of Pd(hfac) 2 in the supercritical fluid. Impregnated samples were reduced in pure H 2 at 40 • C and 6.0 MPa and their catalytic activity was evaluated for the hydrogenation of isophorone in supercritical CO 2 . Adsorption data were used to control the load of Pd in the catalyst and to tune the catalytic activity of these materials. Catalytic tests showed the importance of choosing the right impregnation conditions.