Protozeolite seed-assisted construction of hierarchical nano-ZSM-5 zeolites and their catalytic application in Meinwald rearrangement

Abstract

A facile strategy affording hierarchical nano-ZSM-5 zeolites with high yields (approaching 100%) and crystallinity using a seed-assisted dry-gel conversion (SA-DGC) method is developed. Only a small amount of tetrapropylammonium hydroxide (TPAOH) was used for the synthesis of protozeolite seeds without involving the use of any structure-directing agents (i.e., SiO₂/TPA⁺ = 30). A very small amount of water (i.e., 1.0 mL) was required for crystallization conditions. Protozeolite seeds with a size not exceeding 20 nm can provide a high-activity nucleus for zeolite crystallization, and the precursor is not in direct contact with water and freely migrates, resulting in the formation of nano-zeolites (100–200 nm) around the microregion of the seeds during steaming treatment. Owing to the high-quality nanosized crystals, the as-prepared hierarchical nano-ZSM-5 zeolites exhibit outstanding performance in the rearrangement of styrene oxide and its derivatives compared with conventional ZSM-5 zeolites.