Hydrothermal interconversion of FAU-type zeolite in the presence of sodium and tetramethylammonium ions

Hydrothermal interzeolite transformation is one of the well-known methods for synthesizing zeolites with novel structures and/or compositions. Since various crystallization factors can influence the interzeolite conversion process like in general hydrothermal synthesis, it is important to examine them. In this study, we explored the interconversion process of the FAU-type zeolite in the simplest interzeolite transformation system, containing tetramethylammonium (TMA+) and Na+ ions as structure-directing agents. The effects of various synthetic parameters, such as the concentration of OH−, Na+, and TMA+ ions, the Si/Al ratio, crystallization time and temperature, and types of inorganic and organic cations were investigated during the interzeolite crystallization. In the optimal synthetic condition, the initial structure of parent high silica zeolite Y was transformed in the order of X-ray amorphous → low silica FAU → MAZ → SOD. The solid products obtained under the various crystallization conditions were characterized by powder XRD, SEM, framework IR, 29Si MAS NMR, elemental and thermal analyses, etc. to investigate the prevailing factor in each transformation step. The proper concentration of OH− in the synthetic mother liquor was determined to be the governing factor necessary to initiate the interzeolite transformation, and to expect a certain zeolitic phase by the structure-directing of inorganic and/or organic cations. © 2021 Elsevier Inc.