Defect Sites in Zeolites: Origin and Healing

This paper deals with the synthesis conditions-defect formation relationship in zeolites. Silicalite-1 (MFI-type) is used as a model material. Samples synthesized from a system with high basicity (at 100 degrees C), a system with moderate basicity (at 150 degrees C), and a fluoride-containing system in neutral medium (at 170 degrees C) are compared. Well-crystallized materials with sizes approximate to 0.1, 1-10, and 30-40 mu m are obtained. The samples are analyzed by complementary methods providing information on the short- and long-range order in the zeolite framework. A strong correlation between the number of point defects in the zeolite framework and preparation conditions is established. Silicalite-1 synthesized under mild synthesis conditions from a highly basic system exhibits a larger number of framework defects and thus low hydrophobicity. Further, the calcined samples are subjected to aluminum and silicon incorporation by postsynthesis treatment. The Al/Si incorporation in the zeolite framework and its impact on the physicochemical properties is studied by XRD, TEM/SEM, solid-state NMR, FTIR, and thermogravimetric analyses. The defects healing as a function of the number of point defects in the initial material and zeolite crystal size is evaluated. The results of this study will serve for fine-tuning zeolite properties by in situ and postsynthesis methods.

Automated summary

This study investigates the relationship between synthesis conditions and defect formation in zeolites, and explores the impact of defect healing on the physicochemical properties of zeolites. The results reveal that synthesis conditions have a significant influence on the hydrophobicity and defect quantity of zeolites.