Synthesis and Physicochemical Properties of Hierarchical MWW Zeolites

Features of the synthesis and physicochemical properties of a new class of materials— hierarchical MWW zeolites (HZ-MWW), prepared via recrystallization—are studied. Recrystallization is done in two stages in an alkaline solution containing cetyltrimethylammonium bromide. The effect the type of precursor and the concentration of alkali have on the morphological, textural, and acidic properties of HZ-MWW is studied. It is shown the recrystallization of a layered precursor under mild conditions in a 0.5 M NaOH solution slightly alters the porous structure while preserving the morphology of the zeolite crystal. It is established that an increase in the degree of recrystallization in 1 and 2 M NaOH solutions is accompanied by the fragmentation of crystals, growth of the external surfaces of materials, and the formation of a mesoporous phase formed by ordered pores around 3 nm in size. The evolution of the HZ-MWW porous structure is traced during the preparation of the hydrogen form with acidic properties. It is concluded that the ion exchange of HZ-MWW in ammonium nitrate solution washes out the amorphous phase and changes the texture of the H-forms of HZ-MWW, compared to the detemplated Na-forms. The acidic properties of HZ-MWW correlate with the Si/Al ratio and samples of the micropore volume.