Postsynthesis, characterization, and catalytic properties of aluminosilicates analogous to MCM-56

Aluminosilicates with different Si/Al ratios and showing a structure similar to MCM-56 were postsynthesized from fully crystallized lamellar MWW-type precursors under controlled acid treatment. The effects of pretreatment conditions on the construction of MCM-56 analogue structure were investigated, and the physicochemical properties of the resulting materials were characterized by means of various techniques. When the precursors were treated in HNO ₃ solution with a concentration ≥2 M at temperatures lower than 353 K, a structure analogous to MCM-56 was formed favorably even after further calcination, whereas the treatment at higher temperatures or with 5 M HNO ₃ resulted in conventional three-dimensional MWW topology. The formation of MCM-56-like structure was closely related to the reorientation of the interlayer H-bond moieties as a result of a partial removal of occluded structure directing agent. Compared with MCM-22, the MCM-56 analogues possessed a structural disorder along the layer stacking direction but had a larger external surface, which mitigated effectively the steric restrictions imposed by the intracrystal micropores to bulky molecules. The MCM-56 zeolites, maintaining the basic structure units of the MWW zeolite, turned out to serve as promising solid acid catalysts for processing larger molecules.