A Combined MQMAS NMR And Quantum Chemical Calculation Study Of Microporous Molecular Sieves

In this dissertation, principles and some common methods in solid state nuclear magnetic resonance spectroscopy of half-integer quadrupolar nuclei were first reviewed. Then, experimental and theoretical aspects of the multiple-quantum magic-angle spinning technique (MQMAS) were discussed in detail. MQMAS combined with quantum chemical calculations were used to study coordination states and distribution of Al species in zeolite HZSM-5, MCM-22 and to investigate the structure of boron-modified mordenite. In addition, the influence of Al, Ga isomorphous substitution on the 29Si NMR spectra of zeolite was investigated by ab initio method.The coordination states of Al species in calcined HZSM-5 were investigated using 29Si, 27Al MAS NMR and 2D MQMAS. In the 27Al 3QMAS spectra, the existence of the distorted tetrahedral Al (δiso=59.2ppm, Cqcc = 5.2 MHz) was confirmed and the signal due to 5- coordinated non-framework Al in the sample calcined at 750℃was directly observed.The distribution of Al in the zeolite MCM-22 lattice was studied by 27Al MQMAS NMR and quantum chemical calculation. Three different framework Al species in tetrahedral coordination were clearly observed in the 5QMAS spectra. According to the simulation and analysis of 27Al 5QMAS spectra, it could be concluded that the Al was randomly distributed in the framework of MCM-22 zeolite when the Si/Al ratio was varied from 10 to 15...