Tailoring nanosized ZSM-5 through seed-induced solvent-free crystallization for methanol-to-olefins conversion

Abstract

ZSM-5 catalysts are central to the methanol-to-olefins (MTO) process, yet their conventional hydrothermal synthesis requires excessive solvents and organic templates, hindering sustainability and economic feasibility. Here, we develop a seed-assisted, solvent-free synthesis strategy that precisely controls nucleation to produce nanosized ZSM-5 with hierarchical porosity and tunable acidity. Introducing 5–20 wt% of preformed seeds significantly accelerates nucleation, reduces crystal size from 15 μm to submicron scale of 0.4 μm, and enhances both crystallinity and mesoporosity while preserving phase purity. Among these, the 10 wt% seeded sample (ZA-10) achieves the optimal balance between crystal refinement and textural improvement. Systematic aluminum tuning at a Si/Al ratio of 30 further optimizes acid site distribution and pore structure, yielding a catalyst with the highest density of weak acid sites and largest mesopore volume. Consequently, ZA-10 demonstrates outstanding catalytic stability, maintaining over 90 % methanol conversion for 94 h and delivering 32.6 % propylene selectivity. In contrast, unseeded catalysts rapidly deactivate due to their larger crystal size and limited porosity. These findings confirm that integrating seed-assisted nucleation with controlled aluminum incorporation effectively overcomes key limitations of solvent-free ZSM-5 synthesis, providing a eco-friendly pathway toward high-performance MTO catalysts.