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.