【摘要】 采用量子力学方法研究了具有不同Brnsted酸强度的Y分子筛酸中心的结构特性,计算了O—H键长(dO—H)、H的Mulliken电荷(qH)、O—H伸缩振动频率(νO—H)、∠Si—O—Al、分子轨道能量等结构参数,并探讨了这些结构参数与分子筛酸强度的对应关系。研究表明,dO—H、qH、νO—H、∠Si—O—Al与分子筛Brnsted酸强度并不呈严格的对应关系,而酸性羟基O—H的反键轨道能量(EO—H*)与酸强度存在良好的对应关系,EO—H*越低,Brnsted酸性越强。因为EO—H*越低,O—H反键轨道越容易被电子填充;反键轨道被电子填充后,体系能量升高,O—H键越容易被破坏,越容易给出H+,从而Brnsted酸性越强。因此,提出可以用EO—H*表征Y分子筛Brnsted酸强度,补充和完善了表征分子筛酸强度的结构参数。更多还原

【Abstract】 The quantum mechanics method was applied to investigate the structure characteristics of Y zeolite with different Brnsted acid strength.The structural parameters,such as O—H bond distance(dO—H),H Mulliken charge(qH),O—H stretching vibration frequency(νO—H),Si—O—Al angle and molecular orbital energy,were calculated.The relationship between these structural parameters and Brnsted acid strength was discussed.The results showed that there were poor correlations between qH,dO—H,νO—Hor Si—O—Al angle and B-acidity,however,there was a better correlation between anti-bonding orbita energy(EO—H*)and B-acidity.The lower the EO—H*,the stronger the B-acidity.An anti-bonding orbit with lower EO—H*was more easily filled with electron,due to which the energy of the system would rise up to cause the O—H bond broken to give H+,thus the B-acidity would be stronger.On this basis,EO—H*was put forward to characterize Brnsted acid strength of Y zeolite,which would be a good complement to the structure parameters for acid site strength of Y zeolite.更多还原