Structural and compositional studies of crystalline MAPO molecular sieves formed in ionothermal synthesis using imidazolium bromides

摘要

In this contribution, we extend some of the explorations in using ionic liquids as both solution media and organic-guest contributors to the eventual crystallizing structure, when attempts are made synthesize MAPO molecular sieves. We synthesize a family of imidazolium bromides for this purpose and demonstrated a trend toward increasing substituent length on the nitrogen sites. These materials are run as reaction systems using 5 inorganic situations: metals Ni, Zn, Co and Mg substituting in part for Al, and then a 5th reaction where there is no metal added. A variety of MAPO products are made and there are some correlations for the size of the imidazolium guest and the internal void space of the microporous material. Further analysis of some of the details of the products was carried out using solid state MAS NMR and focusing on Al, P and F nuclei in the products. There are some interesting observations found as to deviation from simple tetrahedral coordination for the Al and P, depending upon the imidazolium guest and the metal incorporated. Then, more attention was also focused on the reactions for Ni where once the guests became large enough the products seemed to be the 12-ring structure AFI which has parallel one dimensional pores. It seemed to be that the Ni is not able to be part of the lattice in these instances, and in fact, AFI is the product for a variety of the larger imidazolium guest molecules in the reaction run without any metal added for substitution.