“Desert Rose” MCM-22 microsphere: Synthesis, formation mechanism and alkylation performance

Abstract A “Desert Rose” MCM-22 microsphere is achieved by combination of a gemini quaternary ammonium (C18-6-6 or C6-6-6) surfactant in HMI growth mixture. This specific MCM-22 microsphere appears about 2 μm in diameter, which is vortically assembled by hexagonal nanosheets with 200 nm long and 5–20 nm thick. The synergistic effect between C6-6-6/C18-6-6 and HMI is significant for controlling the flakelet crystal growth and forming the desert rose-like shaped morphology. This work focuses on fundamental nucleation and crystallization of zeolites, especially, the effect of C18-6-6/C6-6-6 on the structural morphology and properties. Typically, C6-6-6 preferentially interacts with aluminosilicate species, allowing slow depolymerization of silicon species and crystal nucleation, and promoting exfoliation of the interlayer by connecting with Al site on the surface. This rose-like shaped MCM-22 zeolite exhibits high benzene conversion (30–32%) and ethylbenzene selectivity (~90%) in the reaction of benzene and ethylene, which should be attributed to its lamellar structure with large surface area and mesoporous property, exposing more accessible acid sites than conventional MCM-22. Above all, our findings demonstrate a facile and effective route to directly synthesize thinner MWW-type materials, which may prove to be more broadly applicable to other layered zeolites.