Phase Selective Synthesis of SBT and FAU-SBT-SBS Intergrown Zeolites Using Asymmetric Organic Structure-Directing Agents for Upgrading of Polyethylene Pyrolysis Oil

Graphical SBT zeolites and FAU-SBT-SBS triple intergrowth zeolites were synthesized using three asymmetric di-quaternary ammonium salts as structure-directing agents. The FAU-SBT-SBS intergrowth exhibited higher selectivities for ethylene and propylene than that of Y zeolite in catalytic upgrading of polyethylene pyrolysis oil, owing to presence of more strong acid sites. Organic structure directing agents (OSDAs) based on asymmetric di-quaternary ammonia compounds have been rarely explored in crystallization of zeolites, owing to difficulties in structural control. Their use holds promise to regulate physicochemical properties of zeolitic materials toward enhancing the relevant catalytic performances. In this study, a stepwise alkylation of 1,4-diazabicyclo[2.2.2]octane (Dab) to generate asymmetric di-quaternary derivatives has been established, enabling their use as OSDAs in large pore zeolite synthesis. Through exploratory syntheses, we showed that small Me-Dab-Et can direct the formation of SBT zeolite in multiple inorganic cation (Cs + ─Na + ) crystallization, while the bulky Me-Dab- i Pr and Me-Dab- s Bu lead to the formation of FAU - SBT - SBS intergrowths. The obtained SBT zeolite exhibited higher olefin selectivity in catalytic upgrading of pyrolysis oil derived from polyethylene, with respect to alike cage-containing faujasite ( FAU ) zeolite. Our findings expand the library of asymmetric di-quaternary OSDAs and highlight their capability to achieve phase selective synthesis of large pore zeolites.