大比表面积γ-Al_2O_3的制备及辅助剂蔗糖的用量对γ-Al_2O_3织构的影响

Sucrose-Assisted Preparation of High Surface Area γ-Alumina and Influence of Sucrose Content on Its Textural Properties

在由硝酸铝经氨水沉淀制备氧化铝的过程中,用蔗糖作为辅助剂制得了具有大比表面积的γ-Al2O3,并考察了蔗糖加入量对γ-Al2O3织构的影响.将硝酸铝和蔗糖共溶于水,滴加氨水至Al3+全部沉淀(pH=5·2),所得沉淀连同母液一起在80℃水浴中搅拌得到溶胶,将溶胶于110℃失水后即得凝胶.凝胶进一步失水后发生燃烧得到含碳的前体,再经600℃焙烧即得到γ-Al2O3(比表面积可达350m2/g左右).利用差热-热重分析、元素分析、氮吸附-脱附等温线、X射线粉末衍射和透射电子显微镜对前体及γ-Al2O3样品进行了表征.结果表明,γ-Al2O3不但具有大的比表面积,而且孔径较小,分布较为集中.通过改变蔗糖的用量,还可在一定程度上对γ-Al2O3的比表面积和孔结构等进行调控.

A novel and simple method using sucrose as assistant agent was developed to prepare γ-Al2O3 with high surface area and narrow pore size distribution. Firstly, ammonium hydroxide was dropped to mixed aqueous solution of aluminum nitrate and sucrose. The resulted precipitate in suspension was heated in a water bath at 80 ℃ with stirring until homogeneous sol was obtained. Then the sol was dried at 110 ℃ and turned into gel as for losing water. Then combustion occurred with a carbon-containing fluffy precursor left. Finally, the γ-Al2O3 was obtained by calcining the precursor at 600 ℃ with a slow air flow. By varying the sucrose amount, a series of γ-Al2O3 with different textural properties were prepared. The precursor and the γ-Al2O3 were characterized by DTA-TG, elemental analysis, N2 adsorption-desorption isotherms, XRD and TEM. The prepared γ-Al2O3 had specific surface area of 300--400 m^2/g and pore size distribution with most probable pore size of about 3.7 nm. According to the dispersion behavior of organic compound on γ-Al2O3, the related mechanism was discussed.