title: Structure and catalytic properties of nanosized alumina supported platinum and palladium particles synthesized by reaction in microemulsion.
abstract: Mixtures of nanosized platinum and palladium particles have been prepared by reduction of salt-containing microemulsion droplets using hydrazine as the reducing agent. To avoid possible negative effects of the presence of sulfur compounds during the preparation the microemulsion was made using the sulfur-free nonionic polyoxyethylene 4 lauryl ether surfactant. Transmission electron microscopy showed that the as-prepared mixtures contained crystalline platinum particles of fairly homogeneous size (20 to 40 nm) with adsorbed amorphous palladium particles 2 to 5 nm in size. Catalyst samples were prepared by depositing the nanoparticles on a gamma-Al(2)O(3) support followed by heating in air at 600 degrees C. Alloyed particles of platinum and palladium with sizes ranging from 5 to 80 nm were obtained during the heating. The majority of the particles had the fcc structure and their compositional range was dependent upon the Pt:Pd molar ratio of the microemulsion. A catalyst prepared from a microemulsion with a 20:80 Pt:Pd molar ratio showed the highest catalytic activity for CO oxidation, while pure platinum and palladium catalysts showed higher sulfur resistance. These results differ from the performance of conventional wet-impregnated catalysts, where a 50:50 Pt:Pd molar ratio resulted in the highest catalytic activity as well as the highest sulfur resistance.
authors.affiliation: Department of Applied Surface Chemistry, Chalmers University of Technology, SE-412 96, Göteborg, Sweden.
authors.forename: Masatomo
authors.initials: M
authors.lastname: Yashima
authors.forename: Lena K L
authors.initials: LK
authors.lastname: Falk
authors.forename: Anders E C
authors.initials: AE
authors.lastname: Palmqvist
authors.forename: Krister
authors.initials: K
authors.lastname: Holmberg