FT-IR Study of Dissociative Water Adsorption on 1-Butyl-3-methylimidazolium Exchanged Mordenite Zeolite

The H+ in the acidic OH groups on H-mordenite zeolite (HM20) was ion exchanged by using 1-butyl-3-methylimidazolium cation ([bmim](+)). No absorption band for the acidic OH groups on the zeolite could be observed in the [bmim] mordenite ([bmim]M20) by FT-IR. The CO adsorption on [bmim]M20 also showed the absence of acidic OH groups, indicating that the ion exchange reaction goes to completion. The bands attributed to the hydrogen bonded nu OH of the acidic OH groups on zeolites (so-called ABC triplet) appeared due to water adsorption on [bmim]M20, for which there are no acidic OH groups. This indicates the generation of acidic OH groups, which could be attributed to dissociative adsorption of water on [bmim]M20 and water adsorption to the acidic OH groups. The nu CH band for the CH on imidazolium is thought to interact with anions, which would lead to the generation of OH-.