(720f) The Rational Synthesis of Pt/Pd Bimetallic Catalysts by Co-Sea

The Rational Synthesis of Pt/Pd Bimetallic Catalysts by co-SEA

Hye-Ran
Cho, John R. Regalbuto

Abstract

The most common method of preparing supported
metal catalysts begins by impregnating a porous oxide or carbon with an aqueous
solution of dissolved metal complexes. The goal of most preparations is to
convert the deposited precursor, often a coordination complex, into small metal
particles firmly anchored onto the high surface area support. For a given
amount of metal, the smaller the metal particles, the more catalytically active
sites are created. In promoted or bimetallic catalysts, the goal is normally to
maximize contact of the metal and promoter, or the two metals.

A simple "strong electrostatic adsorption"
(SEA) approach to create the smallest possible metal particles is, first, to
find the optimal pH at which the interaction between support and precursor is
strongest, and second, to reduce the precursor in a manner which preserves the
high dispersion.

In this work we demonstrate a particular
application of SEA for the rational synthesis of bimetallic catalysts.  We call this method co-SEA; two metal
precursors are simultaneously placed in solution and electrostatically adsorbed.  We hypothesize that a well mixed monolayer of precursors will form and after a
low temperature reduction, the closely associated metal precursors will
assemble into well dispersed, homogeneously alloyed particles.  

Co-SEA has been used to synthesize Pt/Pd bimetallic alloy catalysts
supported by oxidized and unoxidized carbon, alumina
and silica. The materials were characterized by X-ray diffraction, scattering
transmission electron microscopy, energy dispersive x-ray spectroscopy, and
temperature programmed reduction.