Microstructure of supported platinum-gold bimetallic catalysts

Abstract

Bimetallic supported catalysts comprised of a Group VIII metal, such as platinum, and a Group IB element, like gold, have been found to possess superior selectivities towards the formation of desired products as well as a decreased rate of deactivation. The correlation between the microstructure of these materials with their catalytic behavior is essential in understanding the reaction kinetics. Previous electron microscopic studies on bimetallic catalysts have primarily concentrated upon systems whose metallic components are immiscible in the bulk. In this project, the partially miscible Pt-Au and the completely miscible Pt-Sn systems were investigated. In Pt-Au catalysts the catalytically inactive Au component is known to dilute the ensembles of the Pt active sites, thereby favoring the production of compounds whose intermediates require fewer adsorption sites. The typical metal particle size distribution in Pt-Au catalysts ranges from 0.5 nm to 40 nm. The microanalysis of particles larger than 10 nm can be easily done by means of small probe microdiffraction and EDX. The structure and composition of the smaller particles, where most of the interesting catalysis takes place, was determined from the structure images of high resolution electron microscopy.