Macroporous alumina with three-dimensionally interconnected pore structure: Synthesis, characterization and transformation mechanism
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摘要: 利用相分离技术制备了非晶三维贯穿大孔氧化铝初始材料，然后通过氨水水热改性处理，使其大孔形态发生了显著改变，孔壁边缘生长有尺寸为50-300 nm的片状聚集体，大孔尺寸由430 nm下降到250 nm，但仍然保持蠕虫状三维贯穿且空间分布均匀的特性。改性后的氧化铝材料经550℃焙烧转化为高结晶度γ氧化铝，比表面积达到331 m2/g，具有8.9 nm及250 nm两种集中的孔径分布，L酸度及抗压强度均有所提高。研究表明，无定形水合羟基铝离子聚合物与氨水发生再水合反应生成薄水铝石中间物，因此，可在较低的焙烧温度下转晶为γ态；大孔孔壁边缘的AlOOH晶粒受NH4+模板诱导作用从里向外重排形成片状聚集体，从而改变了大孔的形态。Abstract: Amorphous macroporous alumina with three-dimensionally interconnected pore structure was prepared by phase separation technique. The macroporous morphology was modified significantly by hydrothermal treatment with ammonia. There are many plate-like aggregates of alumina with a size of 50-300 nm at the edge of wall; the product is still characterized by the worm-like three-dimensional penetration and uniform spatial distribution, whereas the size of macropores decreases from 430 to 250 nm. The modified alumina material was converted into high crystallinity gamma alumina by calcination at 550℃, which displays a specific surface area of up to 331 m2/g and pore size distributions con-centrated at 8.9 and 250 nm; meanwhile, the Lewis acidity and crushing strength are also improved. It was speculated that the amorphous hydrated hydroxyaluminium ion polymer rehydrated to form boehmite intermediate and transformed into gamma state at low calcination temperature; the AlOOH particles at the edge of macropore wall were then rearranged from inside to outside with NH4+ as template, fabricated into plate-like aggregates.
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Key words:
- 3D-interconnected penetration /
- macropore /
- ammonia /
- hydrothermal treatment /
- γ-alumina
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图 1 样品的XRD谱图
Figure 1 XRD patterns of the as-synthesized products
a: primary sample; b: modified sample without calcination; c: reference sample; d: modified sample after calcination
图 2 改性与未改性处理所得样品的SEM照片
Figure 2 SEM images of the as-synthesized products
(a)-(c): primary sample; (d), (e): modified sample
图 3 样品的压汞法孔径分布
Figure 3 Pore size distribution curves measured by mercury porosimetry of samples
(a): primary sample; (b): modified sample
图 4 改性前后样品的吡啶吸附红外光谱谱图
Figure 4 FT-IR spectra of pyridine adsorptionon the primary and modified samples
图 5 三维贯穿大孔γ氧化铝的晶化及形态转化机制示意图
Figure 5 Schematic illustrationfor the crystallization and transformation of macroporous γ-aluminawith three-dimensional penetration
表 1 大孔氧化铝的抗压强度
Table 1 Crushing strength of the as-synthesized products
Sample Crushing strength /(N·mm-1) 550℃ 600℃ 650℃ 700℃ 750℃ 800℃ Primary sample 18.8 19.4 20.3 21.4 21.9 23.4 Modified sample 18.5 19.6 20.9 21.7 22.3 24.2 
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表 2 氨水处理前后样品的L酸分布
Table 2 Distribution of Lewis acidity on the primary and modified samples via ammonia treatment
Sample Acidity /(mmol·g-1) 160℃ 250℃ 350℃ Primary sample 0.409 0.276 0.128 Modified sample 0.413 0.189 0.089
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