吡啶在H-MOR分子筛孔道中吸附的量子化学研究

Study on Pyridine Adsorption in H-MOR by Quantum Chemistry

用24T模型和两种ONIOM2方法(QM/QM和QM/MM)研究了杂原子H-AlMOR和H-BMOR分子筛的结构、酸性及其对吡啶的吸附性能.吸附热以及分子筛的几何结构和电子结构数据表明,H-BMOR的B酸性远远弱于H-AlMOR,因此二者可分别应用于对酸性要求不同的催化反应.采用QM/QM计算得到的吡啶在H-AlMOR上的吸附热(219.3 kJ/mol)与实验结果(200 kJ/mol)比较接近.QM/QM方法尽管耗时较多,但能得到更精确的结果,而QM/MM方法可用于定性研究及对模型结构的初步预测.吸附复合物的结构参数及红外振动频率等数据表明,吡啶在两种分子筛上吸附时均发生了质子转移,生成PyH+…ZeO-离子对.此外,吸附复合物中还存在多重氢键作用.

The structure and Bronsted acidity of H-AIMOR and H-BMOR as well as their adsorption for pyridine probe molecule were investigated by using a 24T cluster containing a two-layered 12-membered ring and ONIOM2 （QM/QM and QM/MM） hybride methods. The Bronsted acidity of H-AIMOR is stronger than that of H-BMOR. Pyridine adsorption energy on H-AIMOR of 219.3 kJ/mol calculated by ON IOM2 （QM/QM） method compares well with the experimental result of 200 kJ/mol. In addition, the structure and IR stretching frequencies of the adsorption complexes shows that proton transfer occurrs during the pyridine adsorption, and the PyH^＋ …ZeO^- ion pairs are further stabilized by multiple hydrogen bonding between the hydrogen atoms of pyridine and the framework oxygen atoms of the zeolite.