Morphology-dependent phase transformation of γ-Al2O3
Morphology-dependent phase transformation of γ-Al2O3
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DOI：
10.1016/j.apcata.2015.03.040
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发表时间：
2015-07-05
影响因子：
5.5
通讯作者：
Kwak, Ja Hun
中科院分区：
文献类型：
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作者：
Lee, Jaekyoung;Jeon, Himchan;Kwak, Ja Hun
通过XRD、BET比表面积测量、透射电子显微镜（TEM）、固态Al-27-NMR和乙醇程序升温脱附（TPD）研究了片状和棒状γ-Al 2 O3在空气中连续退火至1100 ℃后的相变，并与商业样品进行了比较。在1100 ℃退火后，商业γ-Al 2 O3大部分转化为α-Al 2 O3，表面积急剧减少（从200 m2/g减少到25 m2/g）。有趣的是，片状和棒状的γ-Al 2 O3，显示出完全相同的XRD图案转化为不同的相高温煅烧。片状γ-Al_2 O_3转变为θ相，而棒状γ-Al_2 O_3转变为δ相，而不是α-多晶型。在1100 ℃下进行相同处理后，片状和棒状氧化铝的表面积（类似于60 m2/g）明显高于商业氧化铝。这些结果表明，在γ-Al 2 O3的相变是强烈的影响，不仅由起始材料的晶体结构，但它的形态以及。在1100 ℃退火后，来自片状和棒状氧化铝的乙醇TPD显示出显著不同的解吸曲线，这表明不同的表面特征，即使它们具有几乎相同的表面积。这些不同的相变也支持固态Al-27-NMR。在1100 ℃退火后，商业氧化铝显示出主要存在八面体Al 3+离子，但其它两个样品显示出比初始γ-Al 2 O3更高数量的四面体Al 3+离子。TEM也证实了形态学变化。所有这些结果一致地表明γ-Al 2 O3的形态依赖性相变和与商业γ-Al 2 O3相比的片状和棒状γ-Al 2 O3的改进的热稳定性。(C)2015 Elsevier B. V.版权所有。
The phase transformations of platelet- and rod-shaped gamma-Al2O3 were investigated and compared to that of a commercial sample by XRD, BET surface area measurements, transmission electron microscopy (TEM), solid state Al-27-NMR, and ethanol temperature programmed desorption (TPD) after sequential annealing in air up to 1100 degrees C. After annealing at 1100 degrees C, commercial gamma-Al2O3 mostly transformed into alpha-Al2O3 with drastic surface area reduction (from 200 m(2)/g to 25 m(2)/g). Interestingly, platelet- and rod-shaped gamma-Al2O3 which showed exactly the same XRD patterns transformed into different phases upon the high temperature calcinations. Platelet-shaped gamma-Al2O3 transformed into theta-phase while the rod-shaped gamma-Al2O3 transformed into the delta-phase and not to the alpha-polymorph. Both platelet- and rod-shaped aluminas retained significantly higher surface area (similar to 60 m(2)/g) than the commercial one after the same treatment at 1100 degrees C. These results suggest that the phase transformation in gamma-Al2O3 is strongly affected by not only the crystal structure of the starting material, but its morphology as well. Ethanol TPD from platelet- and rod-shaped alumina after 1100 degrees C annealing, showed significantly different desorption profiles which suggest different surface characteristics even though they had almost the same surface areas. These different phase transformations were also supported by solid state Al-27-NMR. After 1100 degrees C annealing commercial alumina showed the presence of mostly octahedral Al3+ ions, but the other two samples displayed even higher number of tetrahedral Al3+ ions than the initial gamma-Al2O3. Morphological changes were also confirmed by TEM. All these results consistently suggest the morphology-dependent phase transformations of gamma-Al2O3 and the improved thermal stability of platelet- and rod-shaped gamma-Al2O3 in comparison to a commercial gamma-Al2O3. (C) 2015 Elsevier B.V. All rights reserved.