Water and methanol were chosen as small polar probe molecules. Their interactions with the framework of AFI type molecular sieves in the form of single large crystals were investigated with FTIR microspectroscopy. Water molecules interact with framework Al cations of AlPO4-5. Hydrogen bonds between water molecules themselves as well as between water and framework oxygen have been inferred from the absence of free stretching OH vibrations. Methanol exhibited weaker interactions with AlPO4-5 than water. The both polar molecules on MeAPO-5 materials interacted primarily with the bridging OH groups. Strongly polar molecules revealed a bimodal distribution of acid strength of the bridging OH groups. Two adsorbate species have been found to occur, both bound via hydrogen bonds of different strength dependent on the adsorption site. The interactions between the probe molecules and the framework are stronger in the confined environment of the narrow channels than in the wide channels. All these interactions are weak and do not lead to structure changes as, e.g., in ZSM-5.
- Water probe
- Acid sites
- IR microspectroscopy
- Methanol probe
Müller, G., Bodis, J., & Kornatowski, J. (2004). Interactions of water and methanol with MeAPO-5: FTIR microspectroscopic study on single crystals. Microporous and mesoporous materials, 69(1-2), 1-7. https://doi.org/10.1016/j.micromeso.2003.12.025