An anion-promoted increase of the SiO₂/Al₂O₃ ratio of zeolites

Abstract

Increasing the SiO2/Al2O3 ratio (SAR) of zeolites is crucial for enhancing their acidic catalysis performance and thermal/hydrothermal stability. In this work, we reported a facile strategy to improve the SAR...

Crystallization of zeolite Beta in the presence of an anionic surfactant AESA

“…34 Fluoride anions are not only recognized as mineralizing agents and/or as catalysts for the breaking and formation of Si–O–Si bonds during gelation and/or crystallization, but also as structure directing agents and even “templates” in the formation of the zeolite structure, 35 being found inside the double four-membered ring (D4R) cages, 36 as well as zeolite building unit stabilizing agents via electron density transfer into framework Si atoms. 37,38 Sun et al reported that the addition of I − anions into the synthesis could increase the Si/Al ratio of the MOR zeolite by 0.43, 16 which is much lower than the increase in our work. They applied density functional theory calculations (DFT) to calculate the change of free energy barriers.…”

“…From both academic and industrial interest point of view, it is highly desired to synthesize zeolite Beta with a tunable Si/Al ratio as designed, which is crucial to make it achieve the optimized catalytic performance in acid-catalyzed chemical reactions. 16 However, it is still a challenge to synthesize zeolite Beta with a high Si/Al framework ratio and correspondingly increased yield in the traditional TEA + templated hydrothermal synthesis system. Camblor et al reported that the obstacle of improving the yield of zeolite Beta with a high Si/Al ratio is the low efficiency of Si incorporation from the gel to the zeolite structure, and the high efficiency of Al incorporation into the zeolite structure.…”

Regulation of the Si/Al ratios and Al distributions of zeolites and their impact on properties

“…166 The Si/Al ratios determined by solid state 29 Si MAS NMR is consistent with that measured by the elemental analysis. 24,72,141 By comparing the values with those obtained by chemical analyses, the (Si/Al) 𝑁𝑀𝑅 amount of extra-framework aluminium can be calculated. However, Equation 1 works well with materials that have framework Si/AI ratios less than about 10.…”

“…Guiding by this principle, Yu and co-workers reported a general and facile strategy to improve the Si/Al ratios of MOR, FAU, and MFI zeolites by adding iodide ions into the initial mixture, which promoted the formation of Si-O-Si bonds and thus provided the high-silica oligomer. 72,73 Shen and co-workers introduced the Co 2+ into the initial mixture for the OSDA-free crystallization of zeolite Y. 44 The introduced Co Please do not adjust margins Please do not adjust margins remaking of Si-O-Si bonds.…”