Krishna Nunna V, Selvam Parasuraman
National Centre for Catalysis Research and Department of Chemistry, Indian Institute of Technology-Madras, Chennai, 600 036, India.
New Industry Creation Hatchery Center, Tohoku University, 6-6-10, Aoba, Aramaki, Sendai, 980 8579, Japan.
Chemistry. 2017 Jan 31;23(7):1604-1612. doi: 10.1002/chem.201604368. Epub 2017 Jan 6.
A new intrinsic hydrolysis method was employed, for the first-time, to synthesize well-ordered H-AlSBA-15 with trivalent aluminium exclusively in the tetrahedral framework structure of SBA-15. Unlike other methods, which involve incorporation of aluminium ions in both the framework (Brønsted) and non-framework (Lewis) sites of the silicate matrix, the intrinsic hydrolysis method isomorphously substitutes aluminium ions in the tetrahedral network even at high aluminium content. This unique approach relies mainly on the hydrolysis rates of the inorganic (silicon and aluminium) precursors used for the preparation in such a way that the condensation occurs simultaneously so as to overcome the usually encountered difficulties in stabilizing aluminium ions in the silicate matrix. In this way, we could successfully synthesize high quality Brønsted acidic H-AlSBA-15, hitherto not reported. The synthesized materials were systematically characterized by various analytical, spectroscopic, and imaging techniques, including XRD, Brunauer-Emmett-Teller (BET) surface area measurements, TEM, SEM, Si and Al magic angle spinning NMR spectroscopy, X-ray fluorescence (XRF), and NH temperature-programmed desorption (TPD). The characterization results reveal the presence of a highly porous structure (with narrow pores) and tetrahedrally coordinated trivalent aluminium in the silicate matrix with more medium to strong Brønsted acid sites. The resulting high quality catalysts exhibit excellent activity for tert-butylation of phenol with high selectivity towards para-tert-butyl phenol and 2,4-di-tert-butyl phenol.
首次采用一种新的本征水解方法，合成了在SBA - 15的四面体骨架结构中仅含有三价铝的有序H - AlSBA - 15。与其他方法不同，其他方法涉及在硅酸盐基体的骨架（布朗斯特）和非骨架（路易斯）位点都引入铝离子，而本征水解方法即使在高铝含量下也能在四面体网络中同晶取代铝离子。这种独特的方法主要依赖于用于制备的无机（硅和铝）前驱体的水解速率，使得缩合同时发生，从而克服了在硅酸盐基体中稳定铝离子时通常遇到的困难。通过这种方式，我们成功合成了高质量的布朗斯特酸性H - AlSBA - 15，这在以前尚未见报道。采用各种分析、光谱和成像技术对合成材料进行了系统表征，包括XRD、布鲁诺尔 - 埃米特 - 泰勒（BET）比表面积测量、TEM、SEM、硅和铝的魔角旋转核磁共振光谱、X射线荧光（XRF）以及NH程序升温脱附（TPD）。表征结果表明，在硅酸盐基体中存在高度多孔结构（具有窄孔）和四面体配位的三价铝，且有更多中强布朗斯特酸位点。所得的高质量催化剂对苯酚叔丁基化反应表现出优异的活性，对叔丁基苯酚和2,4 - 二叔丁基苯酚具有高选择性。
