TRANSFORMATION OF PLATINUM INTO A STABLE, HIGH-TEMPERATURE, DEHYDROGENATION-HYDROGENATION CATALYST BY ENSEMBLE SIZE-REDUCTION WITH RHENIUM AND SULFUR

The effect of the addition of rhenium and sulfur on the catalytic properties of platinum and on its ability to resist deactivation by carbonaceous deposits was studied. The reactions of neopentane (2,2-dimethylpropane), n-hexane, and cyclohexane in excess HL were studied on model bimetallic catalysts prepared by the deposition of platinum on a rhenium foil or vice versa. The rates were measured in a batch reactor with a ratio of H-2 to hydrocarbon of 30 or 60, a H-2 pressure of 450 kPa, and a reaction temperature in the range of 570 to 800 K. Rhenium-sulfur is catalytically inactive and acted only as a diluent to platinum. As the platinum ensembles on the surface became smaller by dilution with rhenium-sulfur, the rates of the structure-sensitive reactions decreased rapidly and eventually only hydrogenation-dehydrogenation reactions were observed. Most importantly, as the size of the platinum ensembles decreased, they became more resistant to poisoning than the larger ones. (C) 1994 Academic Press, Inc.