Insights into the Site-Selective Adsorption of Methanol and Water in Mordenite Zeolite by 129Xe NMR Spectroscopy

Mordenite (MOR) zeolite is known to possess a 12-membered ring (12 MR) and 8 MR channels, which are interconnected by 8 MR side pockets. Hyperpolarization (HP) 129 Xe NMR reveals a new Xe adsorption site in addition to the usual 12 MR main channels and 8 MR side pockets. Different guest molecules exhibit explicitly site-selective adsorption on different sites of MOR, as demonstrated by in situ continuous-flow HP 129 Xe NMR studies. For example, methanol prefers to adsorb on 12 MR main channels while water prefers to adsorb on this new site connecting the 12 MR main channel and 8 MR pocket. Furthermore, the adsorption of methanol reduces the pore size of main channels and the free mean path of Xe there, while water reduces the interaction of Xe molecules with MOR.