RATES OF HYDROGENATION OF CYCLOALKENES FROM LIQUID PHASE ON PLATINUM-ALUMINA CATALYSTS

Reaction rates for the hydrogenationof 18 cycloalkenes from solution in cyclohexane on alumina-supported platinum catalysts at 25.0° near 1 atm of hydrogen are reported. These reactions are first order in hydrogen pressure and in the amount of catalystand zero order in cycloalkene. The temperature coefficients for cyclohexene and cycloheptene are 5.7 and 6.5kcal mole-1. The data are discussed in terms of the Horiuti-Polanyi mechanism. The nonintervention of isomerization under conditions inwhich olefin exchange is known to be extensive, and the product to be still more extensively isotopically exchanged, leads to the proposal that platinum surfaces present two types of catalytic sites. One of these types is involved in the hydrogen addition reaction; the other with olefin exchange. The Horiuti-Polanyi mechanism for the hydrogenation of alkenes on platinum is modified to correspond. © 1968, American Chemical Society. All rights reserved.