Mesoporus MCM-22 zeolites prepared through organic amine-assisted reversible structural change and protective desilication for catalysis of bulky molecules

Mesoporous MCM-22 zeolite (meso-MCM-22) has been prepared by treating MCM-22 with sodium hydroxide solution through an organic amine-assisted reversible structural change. The alkaline treatment conditions, such as temperature, time, organic amine type, and its amount, were examined in detail. The desilication with sole NaOH caused an easy collapse of the crystalline structure of MWW topology. In contrast, the NaOH treatment with the coexistence of piperidine introduced mesopores of ∼20 nm into the MCM-22 crystals. Meanwhile, the calcined MCM-22 with three-dimensional (3D) MWW crystalline structure was converted to a 2D layered precursor with a well retained framework. The acid sites related to framework aluminum cations were almost intact after mesopore creation, as evidenced by pyridine or ammonia adsorption-desorption and ²⁷Al NMR investigation. In comparison with MCM-22, meso-MCM-22 possessed a larger external surface, which mitigated effectively the steric restrictions to bulky molecules imposed by the intracrystal micropores. Meso-MCM-22 was superior to MCM-22 in the cracking of 1,3,5-triisopropyl benzene as well as the alkylation of benzene with isopropyl alcohol.