Preparation of nanosized micro/mesoporous composites via simultaneous synthesis of Beta/MCM-48 phases

Abstract

Micro/mesoporous composites with nanoscale domains were prepared via simultaneous hydrothermal (HT) treatment of a MCM-48 precursor solution and a colloidal solution containing X-ray amorphous aluminosilicate precursors. Regardless of the composite materials, the method involved two steps: (i) preparation of two separate precursor solutions, one for nanosized aluminosilicate seeds via HT treatment of colloidal precursors resulting in zeolite Beta (100 °C, 3–7 days), the other one being freshly prepared precursor for synthesis of MCM-48 mesoporous materials, and (ii) HT treatment of a mixture containing the two solutions at 100 °C for various crystallization times. The composite materials were obtained by optimizing the silica source used for the preparation of the two precursor solutions, the Si/Al ratios, and the amount of the surfactant used for MCM-48 mesophase. Micro/mesoporous composites were characterized by various techniques and compared with the pure MCM-48 and pure zeolite Beta phases. Particle size distributions in the amorphous and crystalline solutions with the original concentrations were determined by dynamic light scattering. The mean radii for pure Beta nanocrystals, micro/mesoporous composites and pure MCM-48 were 68, 140 and 460 nm, respectively. The formation of composites containing both micro- and mesoporous phases was confirmed with XRD, IR spectroscopy, TG measurements and nitrogen sorption data.