Abstract
Despite
extensive efforts over the past several decades, the current
mechanistic understanding of zeolite crystallization is still far from
satisfactory, thus precluding the synthesis of designer zeolites. Here
we show that the nucleation and in situ transformation pathways during
the synthesis of medium-pore zeolite TNU-9 can be altered by
controlling the extent of cooperative structure direction between Na+ and Cs+ ions in the presence of 1,4-bis(N-methylpyrrolidinium)butane
cations as an organic structure-directing agent. The intermediate phase
selectivity was found to change from bikitaite to analcime to layered
MCM-22 precursor when the gel Na/Cs ratio was adjusted to 7, 15, and 20,
respectively. We also show that the transformation of bikitaite into
TNU-9 begins at the surface of intermediate crystals, unlike that of
analcime and MCM-22 precursor by a dissolution-recrystallization
process. The force field simulation results suggest that the nucleation
of different intermediate phases is not thermodynamically but
kinetically controlled. This study provides a new basis for advancing
the fundamental understanding of zeolite crystallization pathways.
J. Zeng, G. Sastre, S.B. Hong, Capturing different intermediate phases during zeolite synthesis, Journal of the American Chemical Society, 2024. DOI: 10.1021/jacs.4c07414.
