Vapor-phase transport synthesis of microfibrous-structured SS-fiber@ZSM-5 catalyst with improved selectivity and stability for methanol-to-propylene
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. Sinter-locked three-dimensional microfibrous-structure consisting 15 vol% stainless steel fibers (SS-fiber, 20 μm dia.) was dip-coated with synthesis gel containing silicalite-1 and subsequently steamed at 180 °C using ethylenediamine (EDA) solution. As-synthesized ZSM-5 shell contains fine coffin-shape crystals and small grains with remarkable intercrystalline mesopores derived from the initial aggregated aluminosilicate particles while the mesopore size is ever-changing with the crystallization progress. Catalyst lifetime for the MTP reaction shows a volcano-like evolution against the VPT time length, which is correlated well with the crystallization-time-dependent Brönsted acid amount and mesoporosity. The most promising SS-fiber@HZSM-5 catalyst is the one obtained via the 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.