Post-transformation of MWW-type lamellar precursors into MCM-56 analogues

A postsynthesis method has been developed to prepare various metallosilicates structurally analogous to MCM-56 from corresponding lamellar precursors made up of MWW sheets. The precursors were converted into high crystalline MCM-56 analogues readily by a controlled acid treatment. Acid-treating the MWW precursors at lower temperatures (<353 K) led to MCM-56 analogues even after further calcination, whereas the acid treatment at higher temperatures such as refluxing only resulted in conventional three dimensional (3D) MWW structure. In addition, the construction of MCM-56 structure depended greatly on the crystal size of the precursors, that is, the structural transformation of MCM-56 was achieved only for the precursors with a relatively smaller crystal size. The formation of MCM-56 analogues was however neither dependent of the types of metallosilicates (containing B, Al, Ti, Ga or Fe ions) nor the amount of framework metal ions. Compared with 3D Ti-MWW, the Ti-MCM-56 analogue had a larger external surface, which mitigated effectively the steric restrictions to bulky molecules imposed by the intracrystal micropores. The Ti-MCM-56 analogue was then superior to Ti-Beta, 3D Ti-MWW and TS-1 in the epoxidation of a wide range of bulky alkenes with tert-butyl hydroperoxide as well as in the oxidative desulfurization of dibenzothiophene with hydrogen peroxide.