Quinuclidine derivatives as structure directing agents for the synthesis of boron containing zeolites

Abstract

n-Alkylquinuclidinium ions with alkyl groups in the range from C ₁ to C ₆ were synthesized with the purpose of studying their influence as structure directing agents (SDAs) in zeolite synthesis, in particular on the structure type formed. Syntheses were performed in the system SiO ₂ –B ₂ O ₃ –SDA–H ₂ O–CH ₃ OH under hydrothermal conditions at 160, 180, and 200 °C. B ₂ O ₃ was added in order to allow for charge balance through partial replacement of silicon atoms by the trivalent atom as established by ¹¹ B MAS NMR spectroscopy. The synthesis experiments led to the formation of seven different structure types: dodecasil 1H (DOH); decadodecasil 3R (DDR), sigma-2 (SGT), RUB-1 (LEV), ZSM-5 (MFI), EU-1 (EUO) and ZSM-12 (MTW) all containing n-alkylquinuclidinium ions as templates. In one case (SGT-type material) the active templating ion, methylquinuclidinium, was formed in situ from quinuclidine and methanol present in the reaction mixture. In order to identify the templating molecules (SDA) in the zeolite host framework solid-state ¹ H– ¹³ C CP MAS NMR was used. A single crystal structure refinement of quinuclidinium–DDR clearly shows the host–guest arrangement inside the zeolite pores.