PT PARTICLES FROM THE PT15(CO)302- CLUSTER COMPOUND

Highly dispersed platinum particles were prepared by the pyrolysis of Pt15(CO)302- on hydroxylated and dehydroxylated, high surface area γ-Al2O3 Metal carbonyl decomposition was monitored by infrared spectroscopy, transmission electron microscopy, and hydrogen and carbon monoxide chemisorption experiments. The catalytic properties of these materials were examined for isomerization and hydrogenolysis of neopentane at 523-623 K and 1 atm pressure. The metal carbonyl cluster is weakly adsorbed on initial contact with the alumina surface showing CO stretching bands characteristic of the original cluster molecule. After several days of contact, or upon heating, the cluster rearranges to a more bulk-like platinum form. The original cluster compound cannot subsequently be regenerated with exposure to CO or mild reduction treatment. Metal particles originating from the Pt15 cluster are highly dispersed. Preliminary neopentane reaction studies show high selectivity for hydrogenolysis, following treatment in hydrogen at 620 K, consistent with the selectivity of highly dispersed platinum catalysts. Following reduction at 1070 K, the selectivity shifted to favor isomerization. Since electron microscopy results indicated minor particle sintering, the selectivity change may be attributed to surface annealing of the defect crystallite structures from the initial cluster at the higher reduction temperature. © 1990.