New description of the disorder in zeolite ZSM-48.

A new description of the disorder in ZSM-48 is given. It is shown that ZSM-48 is not a code for one material but for a family of materials consisting of tubular pores. The pores are formed of rolled up honeycomb-like sheets of fused T6-rings (T= tetrahedral), and the pore aperture contains 10 T-atoms. Neighboring pores are related by a zero shift along the pore direction or by a shift of half the repeat distance along the pore direction ( approximately 0.5 x 8.40 A). Additional T-T dimers fill spaces between the tubes. Using different degrees of disorder, the X-ray diffraction patterns of a variety of samples of ZSM-48 can be simulated. The present description of the disorder yields calculated diffraction patterns that are in better agreement with experimental patterns than previous descriptions. Unlike previous reports on ZSM-48, it is found that some materials can be highly ordered, others present mostly planar faults, and others still are better described by a two-dimensional (disordered) stacking of tubular pores. The local pore topology is the same in all (disordered) models, and the disorder does not block the pores. Differences in catalytic properties are probably due to differences in crystal morphology and size and to differences in the distribution of aluminum in the framework.