ENERGETICS AND SITING OF SORBED MOLECULES IN ZEOLITES BY COMPUTER-SIMULATIONS - COMPARISON WITH CALORIMETRIC AND STRUCTURAL RESULTS .1. ALIPHATICS AND AROMATICS IN FAUJASITE AND MORDENITE

Sorbent/sorbate interactions corresponding to FAU(faujasite)/sorbate a nd MOR (mordenite)/sorbate systems have been investigated by using the theoretical exp-6-1 Buckingham model. In FAU/sorbate systems this sim ple molecular mechanics model correctly simulates the salient structur al and energetical features corresponding to known sorbate complexes; it is furthermore established that in case of saturated hydrocarbons t he coulombic interactions might be neglected, the correct sorption hea ts being calculated without considering any hypothetical local relaxat ion of the zeolitic framework. In the case of MOR/alkane systems, it i s shown that for methane and ethane, possible sorption sites exist in the side pockets, whereas longer n-alkanes essentially reside in the m ain 12-ring channel. In all cases the calculated sorption energies for the n-alkanes vary linearly versus the aliphatic carbon chain-length. It is found that hexane isomers have comparable sorption heats.