Oxidation Products of NaAlH4 Studied by Solid-State NMR and X-ray Diffraction

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• 作者：Margriet H. W. Verkuijlen ; Rene虂 de Gelder ; P. Jan M. van Bentum ; Arno P. M. Kentgens
• 刊名：Journal of Physical Chemistry C
• 出版年：2011
• 出版时间：April 14, 2011
• 年：2011
• 卷：115
• 期：14
• 页码：7002-7011
• 全文大小：1064K
• 年卷期：v.115,no.14(April 14, 2011)
• ISSN：1932-7455

文摘

The oxidation products of NaAlH₄ were studied using solid-state nuclear magnetic resonance experiments combined with X-ray diffraction (XRD) experiments. We studied the coordination of aluminum with oxygen using single-pulse ²⁷Al experiments. ²⁷Al鈭抺¹H} rotational echo double-resonance, ²³Na鈭抺²⁷Al}/²⁷Al鈭抺²³Na} transfer of population in double-resonance (TRAPDOR), and combined ²⁷Al鈭?sup>23Na TRAPDOR鈭抦ultiple-quantum magic-angle spinning (MQMAS) experiments were used to get qualitative information about Al鈭扝 and Al鈭扤a proximities. These NMR experiments show that the intermediate oxidation product is an amorphous sodium aluminum hydroxide with Al in a tetrahedral coordinated site. A ²⁷Al MQMAS experiment shows distributions of chemical shift and quadrupolar coupling parameters. Therefore, the material is probably highly disordered, and multiple compounds may be present. XRD measurements show that this phase indeed lacks long-range order. The end product contains mainly octahedral coordinated aluminum hydroxide. Crystalline aluminum hydroxides, consisting of gibbsite and bayerite, and sodium carbonate hydrates, Na₂CO₃路H₂O and Na₃(CO₃)₂路2H₂O, are observed by XRD measurements. Our results show that relatively harmless and nontoxic compounds are formed. However, the materials should handled carefully because of the strong basicity of compounds like sodium carbonate.