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)acetylacetones in the gas phase under various reaction conditions. Powders were analyzed by XPS, HRTEM, XRD, and CO adsorption. XPS spectra were recorded in order to determine elementary composition of the powders and chemical states of the metals. The produced powders are contaminated with carbon and exhibit unusual electronic structures. The amount of carbon depends on the reaction conditions during powder production. From TEM and XRD analysis particle sizes and size distributions of metal clusters were obtained. The mean size ranged from 1.8 to 2.9 nm. HRTEM of bimetallic powders revealed the existence of bimetallic Pt/Pd clusters supported on carbon particles. While the results of CO adsorption studies for monometallic powders are in good agreement with TEM results, bimetallic dusters showed deviations. The catalytic activity of laser photolytic generated powders was determined by using the hydrogenolysis 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.