PRODUCTION AND CHARACTERIZATION OF HIGHLY DISPERSED CATALYTIC ACTIVE PLATINUM AND PALLADIUM POWDERS BY EXCIMER-LASER PHOTOLYSIS

Highly dispersed Pt, Pd, and bimetallic Pt/Pd powders were produced by excimer laser photolysis of their bis(1,1,1,5,5,5-hexafluoro)acetylac etones in the gas phase under various reaction conditions. Powders wer e analyzed by XPS, HRTEM, XRD, and CO adsorption. XPS spectra were rec orded in order to determine elementary composition of the powders and chemical states of the metals. The produced powders are contaminated w ith carbon and exhibit unusual electronic structures. The amount of ca rbon depends on the reaction conditions during powder production. From TEM and XRD analysis particle sizes and size distributions of metal c lusters were obtained. The mean size ranged from 1.8 to 2.9 nm. HRTEM of bimetallic powders revealed the existence of bimetallic Pt/Pd clust ers supported on carbon particles. While the results of CO adsorption studies for monometallic powders are in good agreement with TEM result s, bimetallic dusters showed deviations. The catalytic activity of las er photolytic generated powders was determined by using the hydrogenol ysis of ethane as a model reaction. The catalytic activity depends on reaction conditions during the powder production and is up to a factor of 60 higher compared to conventional supported catalysts.