Synthesis and characterization of hierarchically porous alumina with three-dimensional interconnected pore structure
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摘要: 采用铝溶胶晶种引入、结合相分离的方法制备了具有三维贯通多级孔道结构的大孔氧化铝材料。采用扫描电镜（SEM）、X射线衍射（XRD）、N2吸附-脱附、压汞、核磁共振波谱（NMR）等测试方法对所得材料进行了表征。结果表明，该氧化铝材料具有200-600 nm的均匀分布且贯通的连续大孔孔道，经550℃焙烧即可得到结晶态γ-氧化铝。大孔氧化铝比表面积达到366 m2/g，具有以5 nm及400 nm为中心的较为集中的介孔-大孔多级孔道分布。焙烧后的样品中，铝具有四、六两种配位状态。制备过程中，聚环氧乙烷（PEO）作为诱导剂引发固-液两相分离，形成具有三维贯通多级孔道结构大孔氧化铝，而凝胶中引入铝溶胶时，AlOOH晶粒与铝交联水合物均相伴生，在凝胶过程诱导铝交联水合物转变为AlOOH，最终使大孔氧化铝在较低的焙烧温度即可转化为γ-氧化铝。Abstract: Hierarchically porous alumina with three-dimensional interconnected pore structure was prepared by phase separation method with alumina sol as the seed crystals; the alumina material was then characterized by SEM, XRD, N2 sorption, mercury porosimetry and NMR. The results reveal that the ierarchically porous alumina is provided with macropores of 200-600 nm in gamma phase; it has a high surface area of 366 m2/g and narrow double pore size distributions at about 5 and 400 nm. As revealed by NMR, AlO4, and AlO6 are formed in the calcined alumina sample. It is then suggested that during the synthesis, PEO acted as a seed can inspire phase separation, generating the interconnected three-dimensional macropores, while the crystalline grain in the sol may induce the aluminum hydrates to form active AlOOH, which is then transformed to gamma crystalline phase by calcination even at mild temperature.
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图 1 添加及未添加晶种所得样品的SEM照片
Figure 1 SEM images of the as-synthesized products
(a), (b): with seed crystals; (c), (d): without seed crystals
图 3 样品的N2吸附-脱附等温线及孔径分布
Figure 3 N2 adsorption isotherms and pore size distributions of the as-synthesized products
图 4 样品的压汞法孔径分布曲线
Figure 4 Pore width distribution curves measured by mercury porosimetry
图 5 550 ℃焙烧样品的27Al MAS NMR谱图
Figure 5 27Al MAS NMR spectra of the as-synthesized products calcined at 550 ℃
图 6 三维贯通多级大孔氧化铝形成示意图
Figure 6 Proposed synthesis mechanism for the hierarchically porous alumina with three-dimensional interconnected pores
表 1 多级大孔氧化铝的压碎强度
Table 1 Crushing strength of the as-synthesized products
Calcination temperature t/℃ 550 650 750 850 Crushing strength /(N·mm-1) 19.2 20.5 21.8 24.4 
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