In situ polymerization of poly(vinylimidazole) into the pores of ‎hierarchical MFI zeolite as an acid–base bifunctional catalyst for one-pot ‎C–C bond cascade reactions

Abstract

Poly(vinylimidazole)/hierarchical ZSM-5 has been prepared as a novel and efficient acid–base bifunctional catalyst by a simple method. First, the hierarchical ZSM-5 zeolite was synthesized by an indirect method from KIT-6 as a silica source. By this method, control of the zeolite crystallization was achieved due to the adjustment transformation processing of amorphous mesoporous silica to zeolite crystal. Then, vinylimidazole as a basic part was polymerized by an in situ method into the zeolite’s pores. This acid–base bifunctional heterogeneous catalyst was characterized by FT-IR, TG-DTG, N2 adsorption–desorption, TEM, SEM, NH3-TPD, and XRD. The catalyst has been applied to one-pot C–C bond formation tandem reactions including deacetalization–Henry reaction and deacetalization–Aldol condensation by the simple method at low temperature. Due to the uniform distribution of poly(vinylimidazole) in the micro-meso pores of the hierarchical zeolite reactants, the products easily pass through the catalytic active sites. The co-existence of acidic and basic sites in the structure of the catalyst has a crucial role in the superior activity of this catalyst. Moreover, the catalyst showed excellent recyclability and high activity even after 7 runs with ‎only a 10% reduction in activity being detected.‎