HYDROGENATIVE RING-OPENING OF PROPYLCYCLOPROPANE OVER SILICA-SUPPORTED PT AND PD CATALYSTS

The effects of temperature and hydrogen pressure on the hydrogenative ring opening of propylcyclopropane over Pt/SiO2 and Pd/SiO2 catalysts were studied. Temperature dependence in the 323-373 K temperature rang e in a pulse system was investigated, while a static recirculation rea ctor was used for hydrogen pressure dependence measurements. The ring- opening reactions took place exclusively at all temperatures and hydro gen pressures studied. Monotonous increase was observed for the reacti vity of propylcyclopropane as a function of temperature. At constant t emperature, the reaction rate vs. hydrogen pressure dependence curves passed through a maximum indicating dissociative adsorption over both Pt and Pd catalysts. The scission of the sterically less hindered dire ction (producing 2-methylpentane) was the major reaction pathway on bo th catalysts with practically identical regioselectivity values. On th e basis of these results a selective mechanism was proposed for the ri ng-opening reaction.