Designing the synthesis of catalytically active Ti-β by using various new templates in the presence of fluoride anion
作者:Manickam Sasidharan、Asim Bhaumik
DOI:10.1039/c1cp21013k
日期:——
Crystallization of large-pore Ti-β by using a variety of diquaternary ammonium derivatives of dibromoalkane and amines such as triethylamine, 1,4-diazabicyclo[2,2,2]octane (DABCO), and quinuclidine as structure-directing agents (SDA) is described. The size of hydrophobic bridging alkyl-chain length of the template [R3N+â(CH2)xâN+R3](OHâ)2 directs the final crystalline product: Ti-β, Ti-ZSM-12, Ti-nonasil or Ti-ZSM-5, as x gradually changes from 6 to 1, in the fluoride medium under hydrothermal conditions. A dense phase such as Ti-nonasil (clathrasil type) is crystallized as the size of hydrophobic bridging alkyl-chain length decreases. The use of Fâ anions as a mineralizer and Ti4+ as a heteroatom in the synthesis gel also influences the selectivity of final crystalline product. The phase purity and incorporation of Ti4+ into the lattice of β (BEA) and ZSM-12 frameworks are confirmed using XRD, UV-visible, FT-IR, 29Si NMR spectroscopes, elemental analysis (ICP), surface area measurements and catalytic test reactions. The morphology of Ti-β samples is dependent on the nature of the structure-directing agent as revealed by the scanning electron microscopic (SEM) observations. The catalytic activity in the epoxidation of 4-vinyl-1-cyclohexene is increased with the amount of tetrahedral Ti4+ atoms in the framework. The new templates can be effectively used for preparation of catalytically active Ti-β with the minimum number of framework defect sites.
使用多种二溴烷烃和胺类(如三乙胺、1,4-二氮杂双环[2,2,2]辛烷(DABCO)及奎宁环)的双四级铵衍生物作为结构导向剂(SDA),可以在氟化物介质中通过水热条件下的晶化过程,合成大孔Ti-β。模板中的疏水性桥连烷基链的长度[R₃N⁺–(CH₂)ₓ–N⁺R₃](OH⁻)₂决定了最终晶体的种类:随x从6逐渐变为1,依次形成Ti-β、Ti-ZSM-12、Ti-nonasil或Ti-ZSM-5。随着疏水性桥连烷基链长度的减小,结晶出了如Ti-nonasil(笼型)的致密相。在合成凝胶中,使用F⁻作为矿化剂和Ti⁴⁺作为杂原子也会影响最终晶体的选择性。通过XRD、UV-可见光、FT-IR、²⁹Si NMR光谱、元素分析(ICP)、比表面积测量及催化测试反应,确认了相纯度和Ti⁴⁺在β(BEA)及ZSM-12框架中的掺入。扫描电子显微镜(SEM)观察显示,Ti-β样品的形貌取决于结构导向剂的性质。在4-乙烯基-1-环己烯的环氧化反应中,随着框架中四面体Ti⁴⁺原子数量的增加,催化活性也增强。新的模板能有效用于制备具有最低框架缺陷位的催化活性Ti-β。