QUANTUM CHEMICAL STUDY OF THE ELECTRONIC-STRUCTURE AND GEOMETRY OF SURFACE ALKOXY GROUPS AS PROBABLE ACTIVE INTERMEDIATES OF HETEROGENEOUS ACIDIC CATALYSTS - WHAT ARE THE ADSORBED CARBENIUM IONS
QUANTUM CHEMICAL STUDY OF THE ELECTRONIC-STRUCTURE AND GEOMETRY OF SURFACE ALKOXY GROUPS AS PROBABLE ACTIVE INTERMEDIATES OF HETEROGENEOUS ACIDIC CATALYSTS - WHAT ARE THE ADSORBED CARBENIUM IONS
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DOI：
10.1016/0021-9517(89)90139-5
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发表时间：
1989-09-01
影响因子：
7.3
通讯作者：
SENCHENYA, IN
中科院分区：
文献类型：
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作者：
KAZANSKY, VB;SENCHENYA, IN
采用半经验（修正的忽略微分重叠）和从头算（STO-3G基组）量子化学方法对高硅沸石表面烷氧基的电子结构和几何构型进行了计算.的烷基片段的净正电荷被发现是低的，几乎恒定的，当通过从甲氧基到异丙氧基取代基。得出的结论是，碳正离子的性质是一个特点，而不是地面状态的表面酯，但过渡态与延长的C O键，这是形成之前很久，他们完全解离。这种活化配合物还具有吸附卡宾或叶立德的某些特征。在此框架内讨论了一些酸性催化反应在沸石上的机理。
Semiempirical (modified neglect of differential overlap) and ab initio (in STO-3G basis set) quantum chemical calculations were carried out on the electronic structure and geometry of alkoxy groups on the surface of zeolites with a high silica content. The net positive charge of the alkyl fragments was found to be low and almost constant when passing from methoxyl to isopropoxyl substituents. It was concluded that carbenium ion properties are a characteristic not of the ground states of surface esters, but of the transition states with elongated CO bonds, which are formed long before their full dissociation. Such activated complexes also possess some features of adsorbed carbenes or ylides. The mechanisms of some acidic catalytic reactions on zeolites are discussed within this framework.