【摘要】 应用密度泛函理论计算,研究了Ti-MWW分子筛10元环正弦孔道内骨架钛物种的结构和振动光谱。计算采用基于36T簇模型的B3LYP/6-31G(d,p)方法,确定了[Ti(OSi)4]物种优先落位于T3位,在924~987 cm-1区域内存在3个振动峰,都属于以Ti为正四面体中心分布的4个Ti-O-Si键的协同伸缩振动,其中958 cm-1的振动强度较大,属于[Ti(OSi)4]的特征频率。T2和T8位上钛物种不出现该特征峰。Ti髧中心上吸附一个水分子形成五配位配合物,其特征振动频率没有变化。[Ti(OSi)4]物种进一步水解形成[Ti(OSi)3OH]物种,其Ti-O-Si的特征振动蓝移到969 cm-1。此外,还考察了Ti-MWW分子筛中可能存在的骨架硼以及羟基巢的结构和振动光谱,计算频率与已有文献数据相符。更多还原

【Abstract】 Density functional theory was applied to study the structure and vibratioanl spectra of framework titanium located in the 10-membered ring channel of Ti-MWW. The calculations were carried out at B3LYP/6-31G(d,p) level of theory based on the 36 T cluster models, leading to the results that the [Ti(OSi)4] species prefer to locate at the T3 site. The stretching vibrations correlated to [Ti(OSi)4] occur between 924~987 cm-1, including three vibrational modes as the collection of asymmetric stretching motions of four Ti-O-Si centred on tetrahedral Ti髧 center, in which the strongest band at 958 cm-1is attributed to the Ti-specific vibrational frequency. The960 cm-1band is absent from the Ti-species at the T2 and T8 sites. Adsorption of H2 O on Ti(OSi)4has no influence on the 960 cm-1band. The hydrolysis of [Ti(OSi)4] resulted in [Ti(OSi)3OH], showing the Ti-specific vibrational frequency shifted to 969 cm-1. In addition, we also explored the structures and vibrational spetra of framework boron and hydroxyl nest. The calculated frequencies are in good agreement with the reported experimental values.更多还原