H, 2H, and 13C Solid-State NMR Studies of Methanol Adsorbed on a Series of Acidic Microporous Zeotype Materials

Abstract

Adsorption of 13CH3OH, 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 1H and 13C 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 Brønsted acid site. As the coverage increases methanol clusters form and the bonding within these clusters weakens as demonstrated by the 1H 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 2H static wide-line spectra of CH3OD adsorbed on D-ZSM-5.