Robust CON-type zeolite nanocatalyst in methanol-to-olefins reaction: downsizing, recrystallisation and defect-healing treatments toward prolonged lifetime

Abstract

CON-type zeolites have great potential as highly propene-selective catalysts in methanol-to-olefins reactions; however, their insufficient lifetime is a major limitation. This study demonstrates the remarkably prolonged lifetime of a CON-type zeolite in methanol-to-olefins reaction via a multistep strategy including post-milling recrystallisation and liquid-mediated healing of residual defects. Wet bead-milling for parent CON-type zeolite allows to yield nano-sized zeolite, partially composed of damaged parts. To remedy this, the milled zeolite undergoes a two-step hydrothermal treatment, where temperature and concentration of silicate species contained in alkaline solutions are carefully optimised. Furthermore, residual silanol defects in the recrystallised zeolite are healed via a liquid-mediated treatment using NH₄F/TEAOH solution. The defect-healed zeolite nanoparticles showed a lifetime more than twice that of the parent zeolite owing to the increased external surface area and the reduced subnano-scale defects. This protocol could play a significant role in designing robust catalysts with controlled particle sizes and reduced subnano-scale defects.