Penta-coordinated Al³⁺ ions as preferential nucleation sites for BaO on γ-Al₂O₃: An ultra-high-magnetic field ²⁷Al MAS NMR study

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• 作者：Ja Hun Kwak ; Jian Zhi Hu ; Do Heui Kim ; Janos Szanyi ; Charles H.F. Peden
• 关键词：BaO ; Al₂O₃ ; ²⁷Al MAS NMR ; none ; color ; black" href="/science?_ob=MathURL&_method=retrieve&_udi=B6WHJ-4PHSFMG-1&_mathId=mml1&_user=10&_cdi=6852&_rdoc=21&_acct=C000050221&_version=
• 刊名：Journal of Catalysis
• 出版年：2007
• 期刊代码：97_00219517
• 类别：ce
• 出版时间：1 October 2007
• 卷：251
• 期：1
• 页码：189-194
• 文件大小：202 K

摘要

We report the first observation of preferential anchoring of an impregnated catalytic phase onto penta-coordinated Al³⁺ sites on the surface of γ-Al₂O₃. The interaction of barium oxide with a γ-alumina support was investigated by high resolution solid state ²⁷Al magic angle spinning NMR at an ultra-high magnetic field of 21.1 T and at sample spinning rates of up to 23 kHz. Under these experimental conditions, a peak in the NMR spectrum at f" alt="not, vert, similar" border=0>23 ppm with relatively low intensity, assigned to 5-coordinated Al³⁺ ions, is clearly distinguished from the two other peaks representing Al³⁺ ions in tetra-, and octahedral coordination. Spin-lattice ²⁷Al relaxation time measurements clearly show that these penta-coordinated Al³⁺ sites are located on the surface of the γ-alumina support. BaO deposition onto this γ-alumina sample resulted in the loss of intensity of the 23 ppm peak. The intensity loss observed was linearly proportional to the amount of BaO deposited. The results of this study strongly suggest that, at least for BaO, these penta-coordinated Al³⁺ ions are the nucleation sites.