Theoretical Study of Host-Guest Interactions in the Large and Small Cavities of MOR Zeolite Models

Small probe molecules like CO and CH3CN are used to estimate the acid strength of Bronsted sites in mordenite (H-MOR) models, depending on their framework location, main channel (MC) or side pocket (SP). Adsorption strength on Bronsted sites has often been correlated with the concept of confinement, smaller cavities being considered as catalytically more active. In this work, we show that, at zero coverage (1 molecule per site, per cavity), the host guest energetic interactions do not depend on the cavity volumes, leading to similar adsorption energies for MC and SP sites. This unexpected result is in agreement with recent experimental studies which show that confinement is more related with higher concentration of host molecules in small rather than large cavities at high pressure.