GUEST ORDERING IN ZEOLITE HOSTS

Microbalance thermal analysis (TA) experiments reveal that amine molec ules adsorbed in zeolite hosts such as MFI, BEA, and MOR differ substa ntially depending on the guest-host interactions involved. Three group s of amine species that are observed in acidic zeolites are broadly de fined as: (1) primary adsorbed species (PAS) anchored directly to the host active sites: (2) nearest-neighbor species (NNS) that are attache d to PAS; and (3) weakly bound species (WBS) that are largely separate d from proton sites and hence are only marginally affected by the acti ve centers. This short-range ordering of amine adsorbates can be affec ted further by both host features, such as SiO2/Al2O3 ratio and pore s ize, and guest features such as the size, branching, and number of alk yl groups attached to the amine. Thus, the population of a zeolite hos t with amine PAS, NNS, and WBS may be designed for a particular purpos e. Furthermore, amine PAS and NNS exhibit specific chemical reactivity typified by the formation of a polymeric product in both MFI and BEA host zeolites when heated in the presence of O-2. The basics of the pr ocess described above might be utilized in designing guest-host ensemb les with zeolites and related materials. Nearest-neighbor effects, for example, could be considered and adjusted when strategies for long-ra nge ordering of guest molecules in host matrices are developed. (C) El sevier Science Inc. 1997