The rational synthesis of Pt-Pd bimetallic catalysts by electrostatic adsorption

To improve the often poor metal dispersion and poor metall -metal2 contact of bimetallic catalysts prepared by dry impregnation (incipient wetness), we demonstrate several ways to employ strong electrostatic adsorption using Pt and Pd over silica, alumina, carbon, and oxidized carbon. Metal uptake versus pH was monitored for single metal solutions and mixtures of metal precursors. Catalysts were characterized by powder XRD, aberration-corrected STEM imaging, and EDXS line scans and mapping of individual nanoparticles. Electrostatic adsorption of mixed metal precursors (co-SEA) results in well dispersed, homogeneously alloyed nanoparticles, while sequential SEA gives well dispersed nanoparticles with core-shell morphologies. Shell metal loading can be increased by additional cycles of SEA, which gives some flexibility at catalyst composition in exchange for more synthesis steps. Dry impregnation yields larger, agglomerated, inhomogeneously alloyed particles. (C) 2014 Elsevier B.V. All rights reserved.