SELECTIVE ION-EXCHANGE OF PALLADIUM ON ALUMINA SILICA COMPOSITE OXIDES

The selective ion exchange of palladium tetraamine with the negatively charged surface of silica or alumina components of an alumina over silica composite oxide was studied. Depending on solution pH, the ion exchange was directed either only on silica or on both silica and alumina. The partitioning of adsorbed palladium on the surface of silica and alumina components was estimated by a quantitative analysis of hydrogen consumption curves using temperature-programmed reduction. The significance of the results of this work arises from the potential use of composite alumina/silica as an alternative catalyst support for selective alkyne and alkadiene hydrogenation, a reaction that is extremely sensitive to support acidity. By aqueous impregnation, Al2O3 can be dispersed on SiO2 to form composite materials. Due to differences in their point of zero charges (pzc), active metals can be preferentially dispersed on either alumina or silica using different solution pH's. The support acidity can be easily moderated with different Al2O3 to SiO2 ratios for optimum catalyst performance.