OSDA-free synthesis of zeolite beta: Broadening the methodology for a successful use of the product as a seed

Abstract

The synthesis of zeolite beta without any organic structure directing agents (OSDAs) is achieved by the addition of seed crystals. Applying the obtained OSDA-free synthesized zeolite beta as seed crystals for this purpose was quite tricky and subsequently leads to the formation of mordenite zeolite as a contaminant. Herein, we show a successful post-synthetic powder technology for retrieving the micrometer-sized pure zeolite beta seed particles that were originally blend with mordenite impurity. Taking advantage of the particle size variation, this new technique (involving a specially designed centrifugation unit) allowed us to segregate up to 35% of pure beta microparticles and use them as OSDA-free beta seeds. The recyclability of this technique is successful up to three generations after which the size variation window between the blend beta and mordenite particles become inseparably narrow. It was also clarified that controlling the silicon to aluminum (Si/Al) ratio and dissolution of the segregated microparticles using acid and alkali treatments respectively aid the formation of pure phase of zeolite beta.