SPECTROSCOPY OF PRISMATIC AND CUBESHAPED ZSM-5 CRYSTALS

Cubic and prismatic single crystals of ZSM-5 were prepared according to the method of Jansen et al. (ACS Symp. Ser. 398, 1989, p. 257) and compared with microcrystalline ZSM-5. From the viewpoint of XRD and i.r. spectroscopy, all the materials are well crystallized. Si-29 MAS n.m.r. shows, however, that the cubic crystals have superior crystallinity. The cubes are composed of oriented prismatic crystals. The Si/Al ratio is 500; most of the Al of the synthesis mixture is incorporated into analcime crystals. The same holds for the prismatic crystals, but not for the microcrystalline material. For the three materials, the number of silanol groups is 3-7%, which is small compared to the numbers given in the literature or theoretically predicted. Cu2+ is ion-exchanged via a solid-state reaction with Cu or CuCl2.2 H2O. The Cu2+ coordinates at two distinct sites in prismatic and cubic crystals and three sites in the microcrystalline material. The sites have e.s.r. parameters, which are similar to those for Cu2+ in mordenite.