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.
SAPO‐34 is an important member in the family of zeolites, which shows excellent catalytic activity in MTOreaction, but suffers from the diffusion bottleneck. To overcome the diffusion problem, porogen was added to generate meso/macro pores in SAPO‐34zeolite. In this work, amphipathic molecules were designed as CSDA to synthesize a tri‐level hierarchically porous SAPO‐34, and the introduction of CSDA
SAPO-34是分子筛家族中的重要成员,它在MTO反应中显示出出色的催化活性,但存在扩散瓶颈。为克服扩散问题,添加了致孔剂以在SAPO-34沸石中产生细孔/大孔。在这项工作中,将两亲性分子设计为CSDA,以合成三级层次多孔SAPO-34,并且CSDA的引入可以促进Si原子掺入AlPO 4骨架,改变颗粒的形态并降低所制备的酸度。 SAPO-34沸石。制备的SAPO-34催化剂对C 2 H 4和C 3 H 6的选择性更高在MTO反应中比传统的SAPO-34沸石要好。由于两亲分子与CHA的拓扑结构之间的匹配,所制备样品的形态和微观结构随两亲分子的碳链而变化。