Characterization and catalytic properties of MCM-56 and MCM-22 zeolites

We present an investigation of the structure and properties of MCM-56 and MCM-22. These materials have been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N-2 adsorption isotherms. DIFFaX was used to simulate pronounced peak broadening in the X-ray diffraction patterns of MCM-56. Toluene disproportionation is used as a test reaction to compare the catalytic activity of MCM-22 and MCM-56. We have found that MCM-56 is made of very thin MWW-type layers. The layers are typically one unit cell along the c direction (with a few of them having two or three unitcells). These very thin layers of MCM-56 become tightly curled upon calcination. The structures thus formed pack very efficiently, and this phenomenon prevents access of organic molecules like toluene to most of the 12 MR cups on the crystal exterior. Although MCM-56 is active for the disproportionation of toluene, its activity is lower than that of MCM-22. A calcination procedure that prevents the curling up of the MCM-56 layers is needed to make MCM-56 a useful catalyst for large organic molecules. (C) 2000 Elsevier Science B.V. All rights reserved.