Probing the Spatial Proximities among Acid Sites in Dealuminated H-Y Zeolite by Solid-State NMR Spectroscopy

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• 作者：Shenhui Li ; Shing-Jong Huang ; Wanling Shen ; Hailu Zhang ; Hanjun Fang ; Anmin Zheng ; Shang-Bin Liu ; Feng Deng
• 刊名：Journal of Physical Chemistry C
• 出版年：2008
• 出版时间：September 18, 2008
• 年：2008
• 卷：112
• 期：37
• 页码：14486-14494
• 全文大小：268K
• 年卷期：v.112,no.37(September 18, 2008)
• ISSN：1932-7455

文摘

A comprehensive study has been made to probe the spatial proximities among different acid sites in dealuminated H-Y zeolites modified with various degrees of calcination, steam, and acid treatments by using a variety of different solid-state NMR techniques, including multinuclear MAS NMR and two-dimensional ¹H double-quantum (DQ) MAS NMR spectroscopy. The effects of dealumination treatments on the nature, concentration, and location of extraframework Al species in H-Y zeolites were followed by ¹H DQ MAS NMR of hydroxyl protons in conjunction with ¹H, ²⁷Al, and ²⁹Si MAS NMR results. It was found that the extraframework AlOH species (Lewis acid sites) are always in close proximity to the bridging AlOHSi hydroxyls (Brønsted acid sites) on the framework of dealuminated H-Y zeolites prepared by thermal and hydrothermal treatments, indicating the presence of a Brønsted/Lewis acid synergy effect. However, such an effect is absent in acid-treated H-Y zeolites, as also confirmed by ¹³C CP/MAS NMR of adsorbed 2-¹³C-acetone.