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Development of Novel Methods for Synthesizing Hydrophobic Metallosilicates

疏水性金属硅酸盐合成新方法的开发

基本信息

批准号：
11555212
负责人：
TATSUMI Takashi
金额：
$ 7.94万
依托单位：
Yokohama National University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B).
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

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.

通过提高分子筛的疏水性，合成了对过氧化氢氧化有机化合物具有高活性和高选择性的沸石催化剂。考察了TS-1、Ti-β和Ti-β的疏水性和酸性与催化性能的关系。具有3D-12 MR通道的Ti-β能够环氧化大体积环状化合物，而环氧化物被水裂解生成二醇，这应该是由于Ti-MW的酸性所致。将焙烧后的Ti-β与季铵离子进行离子交换，成功地制备了具有高活性和选择性的环氧化催化剂Ti-β。氨离子交换催化剂在环氧化反应中不具有选择性，与碱金属离子的离子交换抑制了环氧化反应的活性。在硼酸存在下，以哌啶或六亚甲基亚胺为结构导向剂，成功地将Ti-MWW晶化成纯相。Ti-MWW中总是含有一部分八面体的钛物种，这些物种在焙烧过程中聚集形成锐钛矿。然而，用酸性溶液处理合成的样品，这些骨架外的钛物种和部分骨架硼很容易被去除。用不同的光谱技术表征了这样处理过的Ti-MWW的骨架位置主要含有四面体的钛物种。与TS-1相比，Ti-MWW对过氧化氢的环氧化反应具有更高的活性。与六亚甲基亚胺导向的钛分子筛相比，哌啶导向的钛分子筛具有更高的活性，前者为六方片状，晶体尺寸较小，后者由针状颗粒凝聚而成。因此，我们开发了一种获得微晶尺寸小、疏水性强、酸性低的钛硅酸盐催化剂的方法，这些催化剂在液相氧化中表现出高活性。