LIQUID-PHASE HYDROGENATION OF CYCLOHEXENE OVER PT FOIL CATALYSTS

A liquid-phase reaction cell, coupled to an ultrahigh-vacuum surface a nalysis chamber, was built to study liquid-phase hydrogenation reactio ns on small area model catalyst surfaces. The hydrogenation of cyclohe xene to cyclohexane was studied at about 1.5 atm total pressure of H-2 and as a function of temperature in the 313-333 K range in liquid cyc lohexene. The hydrogenation rate of cyclohexene on a clean Pt surface increased with the increasing circulation velocity of the liquid, indi cating that the reaction rate was controlled by hydrogen diffusion to the surface. When the surface reaction rate was reduced by the deposit ion of hydrocarbon fragments on the platinum surface, the rate of cycl ohexene hydrogenation became independent of hydrogen diffusion and bec ame controlled by the kinetics of the surface reaction. The estimated activation energy of the reaction is 6 kcal/mol for cyclohexene hydrog enation on a platinum foil that was partly covered with carbonaceous d eposits. (C) 1996 Academic Press, Inc.