H-1, H-2, and C-13 solid-state NMR studies of methanol adsorbed on a series of acidic microporous zeotype materials

Adsorption of (CH3OH)-C-13, CH3OD, CD3OH, and CD3OD on well characterized H-ZSM-5, H-M, H-SAPO-5, FAU type H-Y, and EMT type H-Y microporous materials at various coverages has been studied by using H-1 and C-13 MASNMR. At low methanol coverages the more acidic molecular sieves are able to protonate methanol molecules producing adsorbed methoxonium ions. In less acidic materials hydrogen bonding occurs involving the Bronsted acid site. As the coverage increases methanol clusters form and the bonding within these clusters weakens as demonstrated by the H-1 MASNMR chemical shift trends. This bond weakening gives rise to an increase in mobility of methanol molecules adsorbed within H-ZSM-5 channels and is confirmed by H-2 static wide-line spectra of CH3OD adsorbed on D-ZSM-5.