Abstract
Abstract In a continuous-flow system in which the temperature is first increased and then decreased in a stepwise manner, EUROPT-1 (6.3% Pt/SiO2) loses ∼60% of its activity for the hydrogenolysis of n-butane during the first high-temperature excursion (to 655 K), and 80% of its activity for isomerization to isobutane. Selectivities for hydrogenolysis products are only slightly altered due to a small increase in the probability of central CC bond fission, which is close to statistical. In similar experiments, hydrogenolysis activity for propane falls less (∼33%) and for ethane hardly at all. Arrhenius plots for n-butane hydrogenolysis are distinctly nonlinear, showing somewhat higher activation energies (∼120 kJ mo−1) above 605 K than below it. Activation energies for reactions of propane and of ethane are ∼150 and ∼190 kJ molt-1, respectively. It appears that the species responsible for the loss of activity are highly dehydrogenated forms of the reactant alkane. These results for EUROPT-1 are contrasted to those recently published for EUROPT-3 (0.3% Pt/Al2O3); the later, although having a similar dispersion, is more active in hydrogenolysis but much less active in isomerization, and differs from the Pt/SiO2 catalysts in a number of other respects.
Published Version
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