Fabrication of hierarchical Lewis acid Sn-BEA with tunable hydrophobicity for cellulosic sugar isomerization

Abstract

Lewis acid Sn-BEA catalysts with tunable morphology and hydrophobicity were successfully synthesized by the recrystallization of post-synthetic Sn-BEA in the presence of ammonium fluoride (NH4F) and tetraethylammonium bromide (TEABr). Three-dimensionally ordered mesoporous imprinted (3DOm-i) and nanocrystalline Sn-BEA catalysts with hydrophobic surface were synthesized for the first time by the method. This recrystallization method includes the dissolution of crystalline zeolite BEA by fluoride ions and the rearrangement of different types of silanol defects in the presence of TEABr. The method allows the final products to simultaneously inherit the morphology of their parent Al-BEA zeolites, and significantly reduce silanol defects within the catalysts. The Sn-BEA catalysts synthesized from the recrystallization method show largely enhanced catalytic performance for both glucose isomerization and bulky lactose isomerization in different solvents, which is presumably due to the hydrophobic surface and improved molecular transport property in the hierarchical zeolites. The recrystallization approach is a facile and reliable strategy to improve the hydrophobicity of zeolite catalysts with tunable morphologies ranging from nanocrystals to hierarchical structures.