Fluoride-free Synthesis of Germanosilicate CIT-13 and Its Inverse Sigma Transformation To Form CIT-14

Abstract

Germanium-containing, extra-large pore molecular sieve CIT-13 is synthesized without the use of fluoride. After the removal of occluded organics, CIT-13 obtained from fluoride-free preparation shows significant differences from CIT-13 samples prepared in the presence of fluoride. CIT-13 prepared using a fluoride-free method is able to undergo inverse sigma transformation to yield CIT-14 and transforms into a CIT-5-type germanosilicate much faster than Ge-CIT-13 of similar Si/Ge ratios from a fluoride-containing synthesis. A Rietveld-refined structure solution for CIT-14 reveals that this new molecular sieve possesses 12- and 8-membered ring channels. Results from ¹⁹F magic-angle spinning (MAS) and ¹H–²⁹Si cross-polarized MAS nuclear magnetic resonance spectroscopy reveal that CIT-13 crystallized without fluoride has germanium siting which is different from CIT-13 synthesized in the presence of fluoride.

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