HYDROGEN-TRANSFER CATALYSIS BY PLATINUM ON ZEOLITES

Platinum catalysts supported on gamma-alumina and on a variety of zeol ites have been characterized and evaluated for activity in the transfe r hydrogenation of propylene using butanes as the hydrogen source. Zeo lite supports evaluated include both aluminosilicates and borosilicate s having the ZSM-5 and beta structures. Platinum on acid zeolites show s enhanced activity for the hydrogen transfer, compared to platinum su pported on alumina. However, with platinum on acidic zeolites, propyle ne hydrogenation is accompanied by a number of competing, acid-catalyz ed reactions which lower the selectivity to propane and butenes. Of th e acid zeolites studied, low aluminum, borosilicates were found to be more selective than the corresponding aluminosilicates of similar stru cture. Partial neutralization of the zeolitic acidity with alkali cati ons lowered the nonselective acid catalysis. Metal-catalyzed hydrogen transfer activity was not diminished by this partial neutralization so that hydrogen transfer selectivity increased. In the case of the boro silicate-supported catalysts, maximum activity near 90% conversion of propylene to propane and selectivity for hydrogen transfer greater tha n 95% were obtained when sufficient alkali was added to neutralize the acidity associated with framework aluminum while maintaining the acid ity associated with boron. Feed studies with an optimized catalyst pro vide additional mechanistic insights. (C) 1998 Academic Press.