Reinvestigation of Dehydration and Dehydroxylation of Hydrotalcite-like Compounds through Combined TG-DTA-MS Analyses

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• 作者：Jia Zhang ; Yun Feng Xu ; Guangren Qian ; Zhi Ping Xu ; Chun Chen ; Qiang Liu
• 刊名：Journal of Physical Chemistry C
• 出版年：2010
• 出版时间：June 24, 2010
• 年：2010
• 卷：114
• 期：24
• 页码：10768-10774
• 全文大小：286K
• 年卷期：v.114,no.24(June 24, 2010)
• ISSN：1932-7455

文摘

We reinvestigated dehydration and dehydroxylation of hydrotalcite and four other hydrotalcite-like compounds (HTlcs) with the combined thermogravimetry/differential thermal analysis/mass spectrometry (TG-DTA-MS) technique. The observations indicate that HTlcs undergo dehydration first and then dehydroxylation, followed by or overlapping with decomposition of interlayer anions. The detail deconvolution of MS curves of m/z = 18 reveals that both dehydration and dehydroxylation occurs in two consecutive steps. Dehydration of crystalline water molecules starts on the surface and edge in the first step, and then continues to the interlayer water. Both steps are influenced by the nature of the interlayer anions and layer cations. For the first time, we have assigned two dehydroxylation steps to two types of hydroxyl groups in the HT lattice, i.e. OH−(M(II)₃) and OH−(M(II)₂M(III)). The thermal stability of these two hydroxyl groups is principally determined by the nature of the cations. According to this research, the thermal stability of hydroxyl groups in HTlcs is OH-(Ca₃) (480 °C) > OH−(Mg₂Al) (410 °C) > OH−(Mg₂Fe) (350 °C) ≈ OH−(Mg₃) (300−370 °C) ≈ OH−(Ca₂Al) (330 °C) > OH−(Ca₂Fe) (290 °C) at a ramping rate of 2 °C/min.