Study on Shape Selectivity in Hydrocarbon Oxidation catalyzed by Zedites

沸石催化烃氧化的择形研究

基本信息

批准号：
03453081
负责人：
TATSUMI Takashi
金额：
$ 3.97万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1991
资助国家：
日本
起止时间：
1991 至 1992
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-03453081/
关键词：
Zeolitc Shape selectivity Hydroxylation Hydrogen perotide Titanium Epoxidation 酸化

项目摘要

We have found remarkable shape selectivity in the epoxidation of alkenes and oxygenation of alkanes. Here we have investigated the factors determining the rates of oxidation of various substrates which have different steric and electronic characters over titanium silicalites TS-1 and TS-2.The catalytic reaction system is rather complicated. The liquid phase is separated into an organic phase and an aqucous phase. Since the solid catalyst exists almost exclusively in the aqueous phase, the substrates must transfer to the aqueous phase, where the catalyst and H_2O_2 are present. This accounts for the promoting effect of organic cosolvents in the oxidation of hydrophobic hydrocarbons.The next step is diffusion into zeolite pores. We have found that cyclic alkanes and alkenes are much more difficult to oxidize than linear ones. Thus the diffusion of molecules which have similar dimensions to the zeolites is affected by the coexisting molecules including water. The polarity of substrates an … More d hydrophobicity/- philicity of zeolites might also be taken into account.Even if the substrate is in the zeolite pores, the group to be oxidized must approach the active site. In the oxidation of unsaturated alcohols the influence on the chemoselectivity between terminal and internal double bonds was found quite different and interpreted in terms of their coordination ability to the Ti active site. The terminal CH_2=CH- double bonds, being less sterically demanding, appear to be able to interact strongly with the Ti active site, preventing the alcoholic group from approaching the active site.It has been revealed that the hydroxylation activity is proportional to the intensity of IR Ti=O stretching intensity. Therefore titanyl species might consist of active site. On the other hand, there is no relationship between the epoxidation activity and the intensity of the Ti=O stretching band.However, access to the active site is not the sufficient condition for the reaction. For the oxidation of unsaturated alcohols reactivity toward epoxidation was opposite to the coordination ability; higher turnover of epoxidation of the internal double bond than that of the terminal double bond would result from an electrophilic nature of the attack of active oxygen species against C=C double bonds.The final stage is the diffusion of products into the outside of the pores. We have found this process some- times limits the rate of the oxidation; the diffusion of reactants into the pore filled with products must be retard- ed. Thus it has been revealed that there are several prerequisite conditions to the completion of the H_2O_2 oxidation of organic substrates on titanium silicalites. Less

我们发现在烯烃的环氧化和烷烃的氧化中具有显着的形状选择性，在此我们研究了与钛硅沸石 TS-1 和 TS-2 相比具有不同空间和电子特征的各种底物的氧化速率的决定因素。反应体系相当复杂，由于固体催化剂几乎全部存在于水相中，因此液相分为有机相和水相。转移到存在催化剂和H_2O_2的水相，这解释了有机助溶剂对疏水性烃氧化的促进作用。下一步是扩散到沸石孔隙中。因此，与沸石具有相似尺寸的分子的扩散受到包括水在内的共存分子的影响。 ... 更多 d 沸石的疏水性/亲和性也可能被考虑在内。即使底物位于沸石孔中，待氧化的基团也必须接近活性位点。在不饱和醇的氧化中，末端之间的化学选择性受到影响。发现内部双键完全不同，并根据它们与 Ti 活性位点的配位能力进行解释。末端 CH_2=CH- 双键，空间要求较低，似乎是。能够与Ti活性位点强烈相互作用，阻止醇基接近活性位点。研究表明，羟基化活性与IR Ti=O拉伸强度成正比，因此钛氧基物质可能由活性位点组成。另一方面，环氧化活性与Ti=O伸缩带的强度之间没有关系。然而，对于不饱和醇的氧化反应活性而言，进入活性位点并不是反应的充分条件。环氧化与配位能力相反；内部双键的环氧化周转率高于末端双键，这是由于活性氧对C=C双键的攻击具有亲电子性质。最后阶段是扩散我们发现这个过程有时会限制反应物扩散到充满产物的孔中。钛硅沸石上有机底物完成H_2O_2氧化的几个先决条件较少。