Hierarchization of USY Zeolite by NH4OH. A Postsynthetic Process Investigated by NMR and XRD

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• 作者：Joost Van Aelst ; Mohamed Haouas ; Elena Gobechiya ; Kristof Houthoofd ; An Philippaerts ; Sreeprasanth Pulinthanathu Sree ; Christine E. A. Kirschhock ; Pierre Jacobs ; Johan A. Martens ; Bert F. Sels ; Francis Taulelle
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：October 2, 2014
• 年：2014
• 卷：118
• 期：39
• 页码：22573-22582
• 全文大小：448K
• ISSN：1932-7455

文摘

Ammonia treatment of USY zeolite has led to a new hierarchical material. The local and global structural changes during the transformation have been monitored by XRD and by ¹H, ²⁹Si, and ²⁷Al solid-state NMR. A wealth of 1D and 2D NMR protocols were applied, including ¹H DQ鈥揝Q (double-quantum鈥搒ingle-quantum), ²⁷Al MQMAS (multiple-quantum magic angle spinning), ²⁹Si MAS (magic angle spinning) and CPMAS (cross-polarization magic angle spinning), and ¹H鈥?sup>29Si HETCOR (heteronuclear correlation). The effects of aqueous ammonia treatment, different thermal post-treatments, and rehydration were studied. An increasing loss of crystallinity was observed upon increasing duration of ammonia treatment. Under the experimental conditions, a few percent of silica was lost into solution and no loss of aluminum was observed. However, increasing numbers of silanol groups were detected. The progressive transformation induces formation of mesopores, reduction of the fraction of the sample exhibiting Bragg crystallinity, and apparition of a dense, amorphous aluminosilicate phase. The latter contains ammonium ions and strongly bound water, both of which are resistant to thermal decomposition up to 350 掳C. After about 24 h of treatment, the zeolite fraction is completely transformed into the amorphous phase. At intermediate stages, a complex hierarchical material is obtained with mesopores and zeolitic micropores next to a dense amorphous aluminosilicate, containing ammonium ions, highly structured water, and silanol nests.