Synthesis of supported palladium catalysts

The synthesis of supported palladium catalysts is reviewed with emphasis on a summary of the chemistry of catalyst synthesis, oxide and carbon support properties and case studies from the period 1990-2000. With oxide supports aqueous precursor solutions are often used. The charge of the complex in combination with the iso-electric point (IEP) of the support is an important property to consider during synthesis affecting both dispersion and distribution over large support bodies. With carbon supports direct reduction of palladium precursor may occur that leads to large metallic Pd particles. With the latter support lyophilicity can largely affect Pd emplacement. With oxide and carbon supports sol-gel, deposition-precipitation, deposition-reduction, ion-exchange and impregnation methods have been applied. In general it turns out that the thermal treatment often dominates the primary application of the Pd-precursor in establishing the ultimate metal dispersion. Thermal treatment in an inert atmosphere at temperatures not exceeding 773 K prior to reduction is beneficial for the Pd dispersion. Gas-phase reduction leads to smaller Pd particles than does liquid-phase reduction. In our opinion large progress can be made to develop highly loaded thermostable Pd catalysts by utilizing deposition-precipitation techniques in combination with anchoring sites on the support. (C) 2001 Elsevier Science B.V. All rights reserved.