Synthesis of nano-sized H-ZSM-5 zeolite aggregates by modified seed-induced method and their catalytic performance in methanol to propylene reaction

Abstract

Long chain quaternary ammonium salts such as cetyltrimethyl ammonium bromide, as one of important amphiphilic reagents, were preferred as mesoporous reagents for synthesizing hierarchical or nano-sized ZSM-5 zeolites in literatures of recent years. However, the inconvenient operation caused by foam restricted its practical application. In this work, Nano-sized ZSM-5 zeolites were successfully synthesized with a modified seed-induced method by using a short-chain tetrabutylammonium fluoride (TBAF) as a crystal inhibitor. The effects of TBAF/SiO₂ molar ratios and SiO₂/Al₂O₃ ratios on morphologies, textural properties, acidity and catalytic performance in MTP reaction were systematically investigated. The results confirmed that highly crystalline ZSM-5 nanocrystals with abundant mesopores were synthesized because of the amphipathy of TBAF. More interestingly, weak acidity could be tuned efficiently via varying TBAF/SiO₂ ratio at the similar strong acidity, while both the weak and strong acidity were changed by adjusting SiO₂/Al₂O₃ ratio. Moreover, the prepared nano-sized ZSM-5 catalyst (Z5-167-10) showed an excellent MTP reaction performance with long catalytic lifetime (120 h) and high propylene selectivity (44.9%) benefiting from the unique mesoporous structure and acid properties, which delayed the coke formation.