Density Functional Theory Study On MCM-22 Zeolite

In this thesis, the acidity and the active center of MCM-22 zeolite wereinvestigated by theoretical calculation. The main results are summarized as follows:1. It was found that the T1 and T4 sites, locating on the pocket mouth of the 12MR supercages, were easier for Al substitution and displayed stronger acidity.2. The acidity on the external surface of MCM-22 zeolite was studied by theoretical calculations combined with MAS NMR experiment. It was found that the probe molecule preferred to adsorbing on the opening of 12 MR external surface pockets, and formed a "ionic"structure (Z-…HP+)after interaction with zeolite.3. Proton hopping between O-sites among different T sites of the MCM-22 zeolite has been studied for the first time by DFT. It is found that the acidity of proton, channel system and the geometric parameters of the equilibrium state affected the hopping barriers4. DFT has been used to study the isomorphously substituted MCM-22 zeolite for the first time. It was found that the acidity of T-MCM-22 increased in the sequence of B < Fe < Ga < Al. The effect of the B element in the synthesis of the Ti-MCM22 was also discussed.5. The influence of the chemical composition on the acidity of the isomorphously substituted MCM-22 zeolite was investigated by DFT. It was found that the acidity of the MCM-22 zeolite decreased with increasing number of the trivalent substitution atoms. Moreover, the acidity increased in the sequence of B < [Al, B] < Fe < [Al, Fe] < Al.6. DFT has been used to study the location of Cu2+ ion in Cu exchanged MCM-22 zeolite. It was found that the most occupied sits are II and IV sites. And there is a stronger interaction between NO molecule and Cu-MCM-22 zeolite.