The seminal paper of Brunelle (1978) outlined the rational method of catalyst synthesis
whereby charged metal coordination complexes such as hexachloroplatinate ([PtCl6]-2)
or platinum tetraammine ([(NH3)4Pt]+2) can be electrostatically adsorbed onto oxide
surfaces which contain naturally occurring hydroxyl groups (-OH) that are either
protonated and positively charged (--OH2
+) or deprotonated or negatively charged (-O-),
depending on the solution pH.The method of “strong electrostatic adsorption” (SEA) can be extended to the rational
synthesis of bimetallic catalysts. In this study it is demonstrated that cationic ammine
complexes of palladium or platinum selectively adsorb onto the cobalt oxide particles of
a cobalt oxide/carbon surface. This done at an equilibrium pH of 11, where the carbon
surface is negligibly charged and the cobalt oxide surface is deprotonoated and
negatively charged. Reduction at high temperature leads to homogeneously alloyed
particles while lower temperature reduction leads to core-shell morphologies with a core
of cobalt.
We have employed this method to synthesize highly dispersed, highly loaded noble
and base metals on silica, alumina, and carbon supports (Regalbuto 2007). Electrostatic
control of metal complex adsorption might also be achieved at the nanoscale over
surfaces containing two oxides for a scientific method to prepare a wide range of
bimetallic catalysts and promoted catalysts. The idea is illustrated in Figure 1 in the
simulation of surface potential versus pH for a surface consisting of a carbon with