Active Sites and Reactive Intermediates in Titanium Silicate Molecular Sieves
Active Sites and Reactive Intermediates in Titanium Silicate Molecular Sieves
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DOI：
10.1002/chin.200450212
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发表时间：
2004-12
期刊：
影响因子：
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通讯作者：
P. Ratnasamy;D. Srinivas;H. Knözinger
中科院分区：
文献类型：
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作者：
P. Ratnasamy;D. Srinivas;H. Knözinger
摘要：本文对以下方面的最新进展进行了总结和批判性分析：(a) 脱水硅酸钛分子筛上 Ti 离子和其他官能团（如 OH）的性质和配位状态，(b) 催化反应过程中这些活性位点与氧化剂/反应物分子相互作用产生的含氧中间体的类型和结构，以及 (c) 影响反应活性和选择性的因素 这些活性位点和反应中间体。在脱水状态下，大多数Ti 4+ 离子具有四足(Ti(OSi) 4 )或三足(Ti(OSi) 3 OH)结构。与H 2 O 2 接触时，分别形成钛氧物质Ti(O 2 H) 和Ti(O 2 - )。在与有机反应物反应时，这些钛氧物种中的 O-O 键断裂以异质或均质方式发生。产物选择性由这两种 O-O 裂解模式的相对重要性决定。钛的配位环境、O-O键上的取代基（H或烷基）、温度、溶剂、有机反应物的性质等因素都会影响O-O裂解的模式。还描述了钛位点和氧钛中间体的结构和催化活性之间的相关性。
Abstract This review is a summary and critical analysis of recent advances in the understanding of (a) the nature and coordination state of Ti ions and other functional groups (such as OH) on dehydrated titanium silicate molecular sieves, (b) the type and structure of the oxo intermediates generated by the interaction of these active sites with oxidant/reactant molecules during catalytic reactions, and (c) the factors that influence the reactivity and selectivity of these active sites and reaction intermediates. In the dehydrated state, most of the Ti 4+ ions have the tetrapodal (Ti(OSi) 4 ) or the tripodal (Ti(OSi) 3 OH) structure. On contact with H 2 O 2 , titanium oxo species, Ti(O 2 H) and Ti(O 2 − ), respectively, are formed. On reaction with organic reactants, O–O bond cleavage in these titanium oxo species occurs in a hetero- or homolytic manner. Product selectivity is determined by the relative importance of these two modes of O–O cleavage. Factors such as the coordinative environment of titanium, substituents on the O–O bond (H or alkyl), temperature, solvent, nature of the organic reactant, etc. influence the mode of O–O cleavage. Correlations between the structure and catalytic activity of titanium sites and oxo-titanium intermediates are also described.