X-ray absorption spectroscopies of Mg-Al-Ni hydrotalcite like compound for explaining the generation of surface acid sites
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- 作者：Hong Khanh Dieu Nguyen ; Toan Dang Nguyen…
- 关键词：EXAFS ; XAS ; XANES ; Hydrotalcite ; Brucite
- 刊名：Korean Journal of Chemical Engineering
- 出版年：2017
- 出版时间：February 2017
- 年：2017
- 卷：34
- 期：2
- 页码：314-319
- 全文大小：
- 刊物类别：Chemistry and Materials Science
- 刊物主题：Industrial Chemistry/Chemical Engineering; Catalysis; Materials Science, general; Biotechnology;
- 出版者：Springer US
- ISSN：1975-7220
- 卷排序：34
文摘
Hydrotalcite-like compound containing metal cations such as Mg2+, Al3+ and Ni2+ was characterized using Ni K-edge EXAFS and in situ Ni K-edge XANES techniques for clarifying its bonding environment around Ni2+ sites and structure changes during calcination from room temperature to 550 °C, respectively. At the fixed molar ratio of Mg/Ni/Al of 2/1/1, the results obtained from EXAFS analysis showed a slight blue shift before and after the calcination at 550 °C and a reduction in white line peak; the best fits of the two samples revealed tiny change in coordination number about 7 for Ni-O path but considerable difference for Ni-Mg(Al) path from about 4.5 to 9.5, confirming a modification from brucite like to mixed oxide structure. On the other hand, bond distances of the Ni-O and Ni-Mg paths nearly fixed at about 2.06 Å to 3.0 Å reflected stability of the cationic bond order on each plane, but partial collapse and decomposition of the interlayer formed by water molecules and anion CO32− after the calcination. Linear combination fit extracted from the in situ Ni K-edge XANES also confirmed the changes along with the calcination such as slow and fast decreases of brucite fraction at 150 °C and 330 °C, respectively, in corresponding to the mixed oxide fraction increases. The achieved bonding structures were also applied to explain acid-base occurrence of the hydrotalcite-like material, especially the acid sites generated by different static charges along with the bonds. The explanation was illustrated by NH3-TPD method.