Synthesis of Hierarchically Micro/Mesoporous ZSM-5 Nanozeolites and Their Superior Catalytic Performance for the Methanol-to-Propylene Reaction

Hierarchically structured high-silica ZSM-5 nanozeolites with an average particle size of about 115 nm and abundant inter/intra-crystal mesopores were successfully synthesized via a new combination of dry-gel crystallization (DGC) and subsequent alkali-etching treatment. The alkali-etching process effectively introduced auxiliary intracrystal mesopores into the nanozeolite precursors, significantly increasing the specific surface area and total pore volume while maintaining appropriate surface acidity, which had been confirmed by comprehensive characterizations, e.g., XRD, N2 sorption isotherms, SEM, TEM, NMR, ICP-OES, and NH3-TPD. Benefiting from the developed three-dimensional interconnected micro/mesoporous structure, the resultant nanoZSM-5(200)_D catalyst exhibited superior performance in the methanol-to-propylene (MTP) reaction. It achieved 46% propylene selectivity and an exceptionally prolonged catalyst lifetime for 90% methanol conversion of 224 h (t90), which is approximately 3 times and 16 times that of the nanoZSM-5(200) precursor and purely microporous ZSM-5(200) counterpart, respectively. Additionally, the universality of the here-reported two-step procedure has also been proven, which offers a new choice for preparation of high-performance hierarchically structured zeolite catalysts.