Altering the Atomic Order in Nanosized CHA Zeolites by Postsynthetic Silylation Treatment

In this work, a new post-synthetic hydrothermal approach leading to simultaneous dealumination and silylation of zeolite nanocrystals is presented. Starting from a nanosized chabazite (CHA) type zeolite with a Si/Al ratio equal to 2, a set of samples with Si/Al ratios up to 4 are obtained by altering the acidity and concentration of the added silica modifier during the post-synthesis treatment leading to concurrent dealumination and silylation. The effect of the acidity during the post-synthetic silylation treatment at different pH of 1.0-8.5 at a constant silicon concentration is investigated. The nanosized CHA samples are characterized in details by Fourier transform infrared spectroscopy and NMR spectroscopy (H-1, Si-29, Al-27), X-ray diffraction, and thermogravimetric analyses. The post-synthesis approach reported here can be applied to other zeolite types for fine-tuning of their structural features including type and location of T-atoms, silanol sites, and active sites.