Single-event rate parameters for the hydrocracking of cycloalkanes on Pt/US-Y zeolites

A single-event kinetic model is applied to the hydrocracking of cycloalkane model components on two bifunctional Pt/US-Y zeolites over a wide range of experimental conditions (T = 493-573 K, P = 10-50 bar, molar Hz-to-hydroca rbon ratio = 50-300),. Values for tile standard activation entropies of the , elementary steps were obtained from transition state theory, while indepe ndently determined Henry coefficients were used to describe the physisorpti on. Values for the composite activation energies, i.e., the sums of the pro tonation enthalpies of the alkene intermediates and the activation energies of the elementary carbenium ion transformations, were obtained from a regr ession of the experimental data. The composite activation energies for intr a-ring alkyl shifts vary from 21 to 25 kJ/mol, which is higher than these f or the corresponding acyclic alkyl shifts, which vary from 10 to 16 kJ/mol. The composite activation energies for cyclic protonated cyclopropane branc hing reactions range between 27 and 40 KJ/mol and are comparable to those o f the corresponding acyclic reactions. The same holds for exo-and acyclic b eta -scission, with Values from 22 to 76 kJ/mol. Endocyclic beta -seissions , in general, have lower composite activation energies, varying from 31 to 56 kJ/mol, than acyclic beta -scissions. Hom ever, because of a much lower preexponential factor, they proceed at a lower rate than acyclic beta -scis sions.