Interactions of water and methanol with MeAPO-5: FTIR microspectroscopic study on single crystals

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

Equation of the Sorption Isotherm on Zeolite Y Including Heterogeneity of the Sorbent: A Novel Modification

The complex character of water vapour sorption on zeolite Y has been demonstrated. It has been found that the assumptions of the Dubinin theory of volume filling of micropores (TVFM) are applicable to the description of such water vapour sorption. An equation for the adsorption isotherm is given which describes the experimental data in a satisfactory manner and which includes both the heterogeneity of the zeolite surface and the size distribution of the micropores participating in the sorption process. The equation yields realistic values of the total micropore volume which are close to the experimental sorption capacities. A significant effect of the sodium counterions on the sorption of water vapour has been found