Development of Novel Methods for Synthesizing Hydrophobic Metallosilicates

通过提高分子筛的疏水性，合成了对过氧化氢氧化有机物具有高活性和高选择性的分子筛催化剂。研究了TS-1、Ti-β和Ti-MWW的疏水性和酸性与催化性能的关系，发现Ti-β具有3D-12的磁共振通道，能够环氧化大环化合物，但环氧化物被水裂解生成二元醇，这可能与Ti-β的酸性有关。通过对煅烧后的β-Ti与季铵离子进行离子交换，成功地制备了具有高环氧化活性和选择性的β-Ti。铵离子交换的催化剂对环氧化反应没有选择性，因为铵离子在反应过程中被氧化，而与碱金属离子的离子交换导致氧化活性的抑制。在硼酸的存在下，采用哌啶或六亚甲基亚胺作为结构导向剂，成功地使Ti-MWW晶化为纯相。Ti-MWW中总是含有一部分八面体的Ti物种，这些Ti物种在煅烧时聚集形成八面体。然而，这些骨架外Ti物种连同一部分骨架硼一起通过用酸溶液处理合成的样品而容易地除去。Ti-MWW因此预处理的特点是含有主要四面体Ti物种的框架网站通过各种光谱技术。Ti-MWW对过氧化氢环氧化反应的催化活性高于TS-1。结果表明，以六亚甲基亚胺为模板的Ti-MWW具有更高的催化活性，前者为六方片状，晶粒尺寸较小，后者由针状颗粒凝聚而成。因此，我们开发了一种获得具有小晶粒尺寸、高疏水性和低酸性的钛硅酸盐催化剂的方法，其在液相氧化中显示出高活性。

By increasing hydrophobicity, zeolite catalysts showing high activity and selectivity for the oxidation of organic compounds with aqueous hydrogen peroxide were synthesized. The relationship between catalytic performance and either hydrophobicity or acidity was investigated for TS-1, Ti-β and Ti-MWW.Ti-β, which has 3D-12 MR channel, was able to epoxidize bulky cyclic compounds ; however, epoxides were cleaved by water to give diols, which should be due to the acidity of Ti-β. By ion-exchanging calcined Ti-β with quaternary ammonium ions, Ti-β showing high activity and selectivity for epoxidation was successfully prepared. Ammonium ion-exchanged catalyst was not selective for epoxidation because of the oxidation of ammonium ion during the reaction while ion-exchange with alkali metal ions resulted in suppression of oxidation activity. With the coexistence of boric acid, Ti-MWW was successfully crystallized to show pure phase by using either piperidine or hexamethyleneimine as a structure directing agent. Ti-MWW always contained a part of octahedral Ti species which aggregated upon the calcination to form anatase. Nevertheless, these extraframework Ti species together with a part of framework boron was removed readily by treating the as-synthesized samples with acid solutions. Ti-MWW thus pretreated was characterized as containing mainly tetrahedral Ti species in the framework sites by various spectroscopic techniques. Ti-MWW was more active for the epoxidation reactions with hydrogen peroxide than TS-1. Piperidine-directed Ti-MWW was more active than hexamethyleneimine-directed Ti-MWW.The former was hexagonal plate with small crystallite size in shape and the latter consisted of a coagulation of needle-like particles. Thus we have developed a method of obtaining titanosilicate catalysts having small crystallite size, high hydrophobicity and low acidity, which show high activity in liquid-phase oxidations.