Location and conformation of n-alkanes in zeolites : an analysis of configurational-bias Monte Carlo calculations

Results from calculations using a novel Monte Carlo method to simulate the sorption of n-butane to n-decane in various all- silica zeolites are analyzed to obtain information on the location and the conformation of the sorbed molecules. In general, the framework topology determines the conformation of the sorbed molecules. In mordenite, we find that butane is able to adsorb relatively unhindered, whereas longer chains are oriented parallel to the main channel direction and become less kinked with increasing carbon number. In ferrierite, butane molecules are distributed over both the 8- and 10-ring channels, while pentane and longer molecules are restricted to an all-trans conformation in the larger 10-ring channel. Faujasite appears to only slightly perturb the distribution of alkane conformations, compared to those found for gas phase alkanes. In zeolites rho and A, all alkanes are sorbed in a highly coiled conformation inside the alpha-cages of these structures