Interaction of methanol with alkali metal exchanged molecular sieves. I. IR spectroscopy study

The adsorption of methanol over various alikali metal exchanged zeolites (Z SM5, MOR, and FAU) was studied by in situ IR spectroscopy and,gravimetry. L ower Si/Al ratios (increasing the polarity of the zeolite lattice) increase d the interaction between methanol hydrogens, i.e., hydroxy as well as the methyl hydrogens, and the lattice oxygen. Similarly, this interaction was s trengthened as the atomic weight of the alkali metal cation increased. This stronger hydrogen bonding did not lead to an overall higher heat of adsorp tion. This suggests that the most important interaction occurs between the electron lone-pair donor function of methanol (i.e., the oxygen) and the el ectron pair acceptor function of the zeolite (i.e., the alkali metal cation ). The methanol adsorption complexes in the zeolite pores are discussed.