Sorption of alkanes on novel pillared zeolites; comparison between MCM-22 and MCM-36

MCM-22 was synthesized and modified by swelling and pillaring to obtain MCM-36. These two structures were characterized by means of XRD, SEM, XRF, nitrogen adsorption, NH₃ adsorption/desorption and IR spectroscopy. The sorption of light alkanes on the protonic form of MCM-22 and MCM-36 was investigated using gravimetry, calorimetry and in situ IR spectroscopy. Distinct differences in the properties of the two materials are observed. Swelling and pillaring of MCM-22 leads to an increase in crystal size and mesopore volume, while the micropore volume and the concentration of the Brønsted acid sites decreases. The acid sites are found to be sited to a large extent in the 10-membered-ring channels of MCM-22. This channel system is present in MCM-22 and MCM-36. As alkanes are sorbed in the same local environment in both samples, identical enthalpies of adsorption are observed. The enthalpy of adsorption varies with the entropy of sorption in a manner typical for structures consisting of 10-membered-ring channels. This indicates that the localized part of the alkane sorption properties on MCM-22 and MCM-36 is dominated by the 10-membered-ring channel system.