Wieslaw J. Roth

MCM-36: The first pillared molecular sieve with zeoliteproperties

Publisher Summary This chapter describes the physical characterization of MCM-36, which unequivocally establishes its existence as a novel large pore pillared material with zeolite properties. MCM-36 is a pillared material obtained from MCM-22 layers. The preparation of MCM-36 involves a lamellar intermediate, designated MCM-22 precursor, produced in a hydrothermal process. The structural information concerning pore system of MCM-36 is revealed by adsorption methods. The layers in MCM-22 posses two kinds of pore systems. One consists of 10-ring interconnected channels within the layers. The second are isolated 12-ring cages on the surface, which result in pockets on the outside of MCM-22 crystal and internal supercages, accessible through 10-ring apertures, inside the crystal. Accordingly, the pore size distribution plot obtained for MCM-22 by Ar physisorption shows two distinct peak in the 6–7 A region. The complex pore structure of MCM-22 is also reflected in the unique three step uptake profile of bulky 2,2-dimethylbutane (DMB) observed in the dynamic sorption experiment.

Characterization of mesoporous molecular sieves: differences between M41s and pillared layered zeolites

Abstract Two major classes of mesoporous molecular sieves are currently of great interest: M41S materials prepared by direct synthesis and pillared materials synthesized by swelling and/or pillaring of layered solids. The pillared sieves derived from layered zeolite precursors and represented by MCM-36 complement the extensively studied M41S class and are of interest due to their much stronger acid activity. Both types are prepared under similar conditions (high pH, presence of surfactants) and share some common characteristics. This presents a problem of differentiating between them, especially because of possible contamination of the pillared product with M41S and the parent zeolite. The pillared zeolite case is particularly critical and requires proof that mesoporosity is not the result of M41S impurity. The typical methods employed to characterize both classes of mesoporous materials are X-ray diffraction, microscopy, static and dynamic adsorption/desorption techniques and catalytic testing. No single determination appears to provide an unambiguous answer concerning purity of the pillared phase. The absence of significant contaminants and identity of the product can be determined by combining results from all the mentioned techniques. The evidence of mesoporosity and pillaring are found by static sorption measurements and X-ray diffraction, respectively. Sorption isotherms and dynamic sorption in conjunction with microscopic images provide further indications of successful exfoliation of the layered zeolite precursor.

Method for preparing a pillared layered oxide material

There is provided a method for preparing a pillared layered material, designated MCM-36, with a characteristic X-ray diffraction pattern. Upon calcination of the swollen, non-pillared form of this material, the layers collapse and condense upon one another in a somewhat disordered fashion to form a non-swellable material. However, when the swollen layered material is intercalated with polymeric oxide pillars, the layer separation is maintained, even after calcination. A quaternary ammonium silicate, such as tetramethylammonium silicate, is used as a pillaring agent for treating the swollen material.

The Synthesis and Properties of M41S and Related Mesoporous Materials

Microporous and mesoporous inorganic materials form the backbone of many heterogeneous catalysts and separations media. Because of the extensive commercial applications of these classes of materials, substantial efforts on the part of both academic and industrial researchers have been made to unlock the hidden secrets of the mechanisms of their formation and, through the exploitation of this understanding, to synthesize novel materials with important properties. Much of the mechanistic work has focused on understanding the role of organic directing or templating agents which play a complex, cooperative role of spatial ordering through the filling of void space, balancing charge, and stabilizing structural units.