Pt/Al2O3 II. Activity and selectivity patterns for methylcyclopropane hydrogenolysis and cyclopentane exchange with deuterium: Comparison with Pt/SiO2

The activity and selectivity of a series of Pt/Al2O3 catalysts for the hydrogenolysis of methylcyclopropane and exchange between deuterium and cyclopentane have been determined. The series investigated included the range from 4.1 to 106 percentage exposed of platinum (Dh). Turnover frequencies, Nt, for methylcyclopropane hydrogenolysis at 0 °C determined after high-temperature pretreatment (H2, Tp > 350 °, 1) were independent of Dh as were the activation energies for i-butane and n-butane formation, 36.4 ± 2 and 42.3 ± 4 kJ mol−1, respectively. For cyclopentane-deuterium exchange at 81 °C the isotopic distribution patterns were clearly dependent upon Dh, particularly noted as a decrease in d 10 (d 2 -d 10 ) with increasing Dh. Activation energy for overall exchange was about 75 kJ mol−1 with some dependence on Dh for the individual distributions. Catalyst pretreatment conditions affect activity for both reactions. For methylcyclopropane a minimum is observed for Tp about 200 °C, with an inversion in ordering of Nt vs Dh at higher temperatures, as previously observed for Pt/SiO2. For cyclopentane, Nt decreases with increasing Dh at Tp = 450 °C. The method of catalyst preparation also showed some effect on Nt for methylcyclopropane, but not for cyclopentane. A summary discussion of the factors responsible for various pretreatment effects on Pt/SiO2 and Pt/Al2O3 is given for both reactions.