Synthesis of zeolite Beta, MFI, and MTW using imidazole, piperidine, and pyridine based quaternary ammonium salts as structure directing agents

Abstract

The synthesis of zeolites is investigated using a variety of quaternary ammonium salts of imidazole, piperidine, and pyridine based structure directing agents. The materials were characterized by a complementary combination of X-ray diffraction, N 2-adsorption/desorption, scanning electron microscopy, and transmission electron microscopy. Only suitable quaternary ammonium salts were able to form zeolites Beta, MFI, and MTW. Zeolites (especially Beta) obtained using these quaternary ammonium salts are nanocrystalline in nature and exhibited high surface area and pore volume compared to conventional zeolites. Experimental evidence and density functional theory studies suggest that a limited conformational freedom, provided by the cyclic structure of the quaternary ammonium salts, is an important prerequisite and acts as a structure directing agent for the synthesis of zeolites.