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) Xe-129 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 Xe-129 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.