Guest ordering in zeolite hosts

Microbalance thermal analysis (TA) experiments reveal that amine molecules adsorbed in zeolite hosts such as MFI, BEA, and MOR differ substantially depending on the guest-host interactions involved. Three groups of amine species that are observed in acidic zeolites are broadly defined as: (1) primary adsorbed species (PAS) anchored directly to the host active sites: (2) nearest-neighbor species (NNS) that are attached to PAS; and (3) weakly bound species (WBS) that are largely separated from proton sites and hence are only marginally affected by the active centers. This short-range ordering of amine adsorbates can be affected further by both host features, such as SiO 2 /Al 2 O 3 ratio and pore size, and guest features such as the size, branching, and number of alkyl groups attached to the amine. Thus, the population of a zeolite host with amine PAS, NNS, and WBS may be designed for a particular purpose. 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 process described above might be utilized in designing guest-host ensembles with zeolites and related materials. Nearest-neighbor effects, for example, could be considered and adjusted when strategies for long-range ordering of guest molecules in host matrices are developed.