Starch coated silica nanospheres parenting the growth of trimodal porous zeolites for catalysis involving large molecules

Abstract

A simple method for the synthesis of nanocrystalline ZSM-5 and Beta zeolites with trimodal porosity was developed using starch coated silica nanospheres (as silica precursor) for generating interparticle porosity (50−200 nm); propyltriethoxysilane was used as an additive for generating intercrystalline mesopores (2−50 nm) in the presence of microporous zeolite porogen. Loading of starch and propyltriethoxysilane additive played a pivotal role in obtaining trimodal porosity with very small size zeolite nanoparticles having high surface area and pore volume. The possible growth mechanism for the fabrication of trimodal porous zeolite is presented. The resultant zeolite demonstrated excellent acidity and activity in the liquid phase acid catalyzed reactions such as esterification of hexanoic/oleic acid with benzyl alcohol, condensation of benzaldehyde and 2-hydroxyacetophenone, and Friedel−Crafts alkylation followed by ring closure reaction for the synthesis of vitamin E when compared to conventional zeolite with excellent recyclability. Such an economical starch mediated synthesis strategy can be extended to other zeolite frameworks and similar heterogeneous catalytic materials.