Quantum-chemical modeling of the hydrocarbon transformations in acid zeolite catalysts

Results of quantum-chemical modeling of a number of elementary steps involv ed in the acid zeolite-catalyzed conversion of hydrocarbons are collected t ogether and compared. The elementary steps considered are protolytic cracki ng, protolytic dehydrogenation, hydride transfer, skeletal isomerization, a nd beta-scission. The hydrocarbon parts of transition states (TS) for these steps represent carbocations specific for each reaction. Geometry paramete rs of the TS and activation energies depend on the relative stability of th ese carbocations. The reactions considered can proceed via several alternat ive routes dependent on the species involved and on the details of the inte raction of the hydrocarbon portion of the activated complex with the zeolit e oxygen atoms. Variation of the acid strength of zeolite cluster models ca n be employed for studies of the acid strength sensitivity of the activatio n energies and other quantities of interest as well as for extrapolation of these quantities computed on small clusters towards zeolitic values.