Temperature-dependent lineshape of 1H magic-angle spinning nuclear magnetic resonance spectra of acidic hydroxyl groups in zeolites

Abstract

The 1H magic-angle spinning nuclear magnetic resonance ( 1H MAS NMR) spectra of acidic (bridging) hydroxyl (OH) groups on H-ZSM-5 zeolites were measured from room temperature to 373 K. The signal broadens with increasing temperature, indicating that the delocalization of the protons occurs at a temperature as low as 313 K. The broadening phenomena are less pronounced for H-ZSM-5 with higher Si Al ratios, indicating that the proton migration occurs more easily in H-ZSM-5 with higher aluminium concentrations. On the other hand, the linewidth of the signal due to protons of the non-acidic silanol groups does not depend on the temperature. The temperature dependence of the linewidths was also observed for 1H MAS NMR spectra of mordenite and Y zeolite.