Electron Microscopic Study of Intergrowth of MFI and MEL: Crystal Faults in B-MEL

Recently, a pure MEL type silica zeolite was successfully synthesized by one of the authors. Boron atoms were incorporated into its framework structure by using similar synthesis conditions with gels containing boron in an effort to confer catalytic activity. The nature of crystal faults in the borosilicate-MEL zeolite (B-MEL) was studied using transmission and scanning electron microscopy (TEM and SEM). Electron diffraction (ED) patterns show characteristic diffuse streaks along the [100] and [010] directions. From the analyses of both the diffuse streaks in ED patterns and high-resolution electron microscopy (HREM) images, it was determined that the framework structure of the B-MEL crystal has many planar faults that are parallel to the (100) and (010) planes. The local structure of the planar faults can be interpreted by the intergrowth of the MFI type structure, and a model of the growth process for the B-MEL is speculated from the results.