Highly stable aluminosilicates with a dual pore system: Simultaneous formation of meso- and microporosities with zeolitic BEA building units

Abstract

Highly stable Al-MCM-48-type mesoporous materials with zeolitic secondary building units (SBUs) of BEA zeolite in the framework (hereafter denoted as Al-MCM-48-BEA) were synthesized by direct hydrothermal methods. The synthesis involves simultaneous introduction of two types of structure directing agents, namely, tetraethylammonium hydroxide (TEAOH) for controlling the fabrication of SBU of BEA and a mixture of cetyltrimethylammonium bromide (CTMABr) and Brij-30 for directing the formation of cubic mesophase. The results of X-ray diffraction (XRD) and fourier-transform infrared (FT-IR) spectroscopy revealed the coexistence of mesoporous Al-MCM-48-type arrays with Ia–3 d cubic structure zeolitic SBUs in the materials. In addition, two distinct types of pore systems with characteristics of meso- and micropores were identified in Al-MCM-48-BEA materials by using variable-temperature (VT)-hyperpolarized (HP) 129Xe NMR spectroscopy. Thus, Al-MCM-48-BEA materials possess SBUs of BEA in the walls of highly ordered cubic mesoporous arrays and therefore exhibit much higher thermal, hydrothermal, and mechanical stabilities in comparison to conventional Al-MCM-48 materials. Consequently, these novel materials were found to have strong acidic sites, rendering them highly active and selective catalysts for the formation of α-tocopherol (vitamin E) in the alkylation–condensation of isophytol with trimethylhydroquinone under supercritical CO 2 media.