Vapor-phase transport synthesis of microfibrous-structured SS-fiber@ZSM-5 catalyst with improved selectivity and stability for methanol-to-propylene
A microstructured SS-fiber@ZSM-5 core–shell catalyst engineered from micro- to macro-scale in one step is developed through a cost-effective and high-efficiency vapor-phase transport (VPT) synthesis. A sinter-locked three-dimensional microfibrous-structure consisting of 15 vol% stainless steel fibers (SS-fiber, 20 μm dia.) was dip-coated with a synthesis gel containing silicalite-1 and subsequently steamed at 180 °C using ethylenediamine (EDA) solution. The as-synthesized ZSM-5 shell contains fine coffin-shaped crystals and small grains with remarkable intercrystalline mesopores derived from the initial aggregated aluminosilicate particles while the mesopore size is ever-changing with the progression of the crystallization. The catalyst lifetime for the MTP reaction shows a volcano-like evolution against the VPT time length, which correlates well with the crystallization-time-dependent amount of Brønsted acid and mesoporosity. The most promising SS-fiber@HZSM-5 catalyst is the one obtained via VPT synthesis for 120 h, with a high shell diffusion coefficient of 1.6 × 10−14 m2 s−1, delivering a prolonged single-run lifetime of 45 h with a high propylene selectivity of ∼46.9% at 450 °C at a high methanol weight hourly space velocity (WHSV) of 10 h−1.