Control of Acid-Base Properties of New Nanocomposite Derivatives of MCM-36 by Mixed Oxide Pillaring

The layered precursor of zeolite MCM-22 was pillared with SiO2, Al2O3, MgO-Al2O3, BaO-Al2O3, Al2O3-SiO2, MgO-Al2O3-SiO2, and BaO-Al2O3-SiO2 to generate new derivatives of MCM-36. These nanocomposite materials are characterized by a layered structure consisting of microporous zeolite layers and mesoporous slit-shaped galleries formed by the incorporation of pure and mixed oxides between the zeolitic sheets. Enhanced Lewis acidity is generated by pillaring with (mixed) aluminum oxides. The adsorption of 2.6-di-tert-butylpyridine (2.6-DTBPy) demonstrated for all materials an increased accessibility to acid sites at the pore mouth or the outer surface of the zeolite layers compared to MCM-22. For (MgO\BaO)-Al2O3-SiO2-MCM-36 additional Brnsted acid sites of higher strength than the sites in the zeolitic sheets are observed, which are assigned to the silica-alumina clusters in the interlayer galleries. Basic properties were introduced by the incorporation of alkaline earth oxide aluminates (MgO\BaO-Al2O3) into the interlayer space. Two basic hydroxyl functions were detected by CO2 adsorption: (i) Mg(Ba)-OH and (ii) AlIV-OH groups on the spinel-type oxide clusters. The latter basic sites are attributed to hydroxyl groups on aluminum ions in a tetrahedral coordination sphere of the defect spinel-type oxide pillaring clusters.