| Abstract
| - The sorption of (methyl-substituted) pyridines and 2,2-dimethylalkanes on the medium-pore zeolites FERand TON has been studied by in situ IR spectroscopy, calorimetry, and gravimetry in order to describe sorptionat the outer surface and the pore mouths of the zeolite crystals. Six percent and 3% of the Brønsted acid sites(determined by adsorption of 2,4,6-trimethylpyridine) were found to be on the outer surface and the poremouth of TON and FER, respectively. This result agrees fairly well with the fraction of sites that are availablefor the 2,2-dimethylalkanes, which are unable to fully enter the pores of the zeolites studied. Remarkably, atlow coverage, all three dimethylalkanes adsorb in parallel to the outer surface. As the coverage increases,additional 2,2-dimethylpentane and 2,2-dimethylhexane molecules sorb in such a manner that the propyl andbutyl groups point into the pore. Also, approximately 80% of the 2,2-dimethylpentane and 2,2-dimethylhexanemolecules that initially sorbed parallel to the outer surface rearrange to this sorption structure. This orderingis well documented by the marked increase in the heat of adsorption as the equilibrium pressure increasesand by the IR spectra of hydroxyl groups in interaction with the alkane during this process.
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