Highly ordered supermicroporous aluminosilicates with cubic Pm3n symmetry were prepared for the first time in weakly acidic solutions of succinic acid and malonic acid using dodecyltriethylammonium bromide as a template. The polycarboxylic acids acted as auxiliaries for fabricating the cubic Pm3n structure as well as weak acids. Thermally stable aluminosilicates with a high utilization ratio of Al could be obtained in the presence of succinic acid by either facilely adding aluminum source into the initial synthesis gel or by grinding the as-made silica-surfactant composite with aluminum nitrate. In contrast, thermally stable aluminosilicates could only be prepared via a post-synthesis approach in the presence of malonic acid, probably because of the powerful coordination tendency between malonic acid and Al cations. The thermal stability of the aluminosilicates was enhanced because of the incorporation of Al into the framework or grafting of Al onto the pore walls. Aluminosilicates prepared via the post-synthesis approach preserved the cubic Pm3n structure better than the directly-synthesized ones. In spite of the kind of polycarboxylic acids or the preparation methods, Al was predominantly tetrahedrally coordinated. The aluminosilicates showed a high specific area and pore volume, especially for the post-synthesized ones. The pore size was in the supermicroporous range evidenced by N2 physisorption, though that of the aluminosilicates prepared via the post-synthesis approach was larger. TEM images verified the Pm3n symmetry of the materials herein. The cubic Pm3n aluminosilicates prepared in our research exhibited equal reactivity but a much pronounced deactivation resistance property in the acetalization of cyclohexanone with pentaerythritol.
在弱酸性
琥珀酸和美克酸溶液中,首次使用
十二烷基三乙基
铵溴化物作为模板制备了具有立方Pm3n对称性的高度排布超微孔铝
硅酸盐。这些多
羧酸作为辅助剂,不仅用于构建立方Pm3n结构,同时也作为弱酸。在
琥珀酸存在的情况下,通过轻易地将铝源添加到初始合成凝胶中或将所制得的
二氧化硅-表面活性剂复合物与铝
硝酸盐研磨,可以获得热稳定性高、铝利用率高的铝
硅酸盐。相比之下,在美克酸存在下,热稳定性较好的铝
硅酸盐只能通过后合成方法制备,这可能是由于美克酸与铝阳离子之间存在强大的配位倾向。铝的加入或铝在孔壁上的接枝增强了铝
硅酸盐的热稳定性。通过后合成方法制备的铝
硅酸盐比直接合成的铝
硅酸盐更好地保持了立方Pm3n结构。无论是多
羧酸的种类还是制备方法,铝主要以四面体配位的形式存在。这些铝
硅酸盐表现出高比表面积和孔容积,尤其是后合成的铝
硅酸盐。通过氮气物理吸附证实,其孔径位于超微孔范围,尽管通过后合成方法制备的铝
硅酸盐孔径更大。透射电子显微镜(
TEM)图像证实了材料的Pm3n对称性。我们研究中制备的立方Pm3n铝
硅酸盐在
环己酮与五羟基醇的
缩醛化反应中表现出相同的活性,但具有明显更强的失活抗性。