Synthesis of Zeolites via Interzeolite Transformations without Organic Structure-Directing Agents

We report synthetic protocols and guiding principles inspired by mechanistic considerations for the synthesis of crystalline microporous solids via interzeolite transformations that avoid direct intervention by organic structure-directing agents. These protocols are specifically implemented to synthesize high-silica MFI (ZSM-5), CHA (chabazite), STF (SSZ-35), and MTW (ZSM-12) zeolites from FAU (faujasite) or BEA (beta) parent materials. These transformations succeed when they lead to daughter structures with higher framework densities, and their nucleation and growth become possible by the presence of seeds or of structural building units common to the parent and target structures, leading, in the latter case, to spontaneous transformations by choosing appropriate synthesis conditions. These protocols allow the synthesis of high-silica frameworks without the use of organic templates otherwise required. The NaOH/SiO₂ ratio and Al content in reagents are used to enforce synchronization between the swelling and local restructuring within parent zeolite domains with the spalling of fragments or building units from seeds of the target structure. Seed-mediated interconversions preserve the habit and volume of the parent crystals because of the incipient nucleation of the target structure at the outer regions of the parent domains. The pseudomorphic nature of these transformations requires the concurrent nucleation of mesopores within daughter zeolite crystals because their framework density is larger than that for the parent zeolites. The approach and evidence described shows, for the first time, that a broad range of zeolites rich in silica, and thus more useful as catalysts, can be made without the organic templates originally used to discover them.