Theoretical Investigations On Properties And Modification Of Two Material Molecules

Material is the base to the existence and development of human beings, which is closely related with national economy and people's lives, and is named as one of three civilized mainstays of the day. In addition to its importance and universality, material is variety. Therefore, in this thesis we mainly focus on two material molecules: zeolites and dinuclear sandwich complex. Zeolites are crystalline aluminosilicates with periodic microporous systems, giving rise to regular three-dimensional networks of channels, cages, and rings. Due mainly to their high activity, shape-selectivity and thermal stability, zeolites are widely used in petroleum and natural gas processing, fine chemical industries, environmental protection and nuclear waste handling, etc., and are becoming important functional materials in modern industry. In this thesis, quantum chemical investigations on the acidity of IM-5 zeolite (its detailed structure was recently determined), location of transition metal and stability have been carried on. The results are helpful to further understand the functioning of IM-5 and to expand the potential applications in various areas. Through the theoretical calculations on the adsorption of guest molecule (Na2Al4 and CpNa) on zeolite, it provides a feasible hint to improve the acidity or catalyst activity of zeolite. Stimulated by the synthesis and isolation of the first bis-metallic sandwich compound Cp*ZnZnCp*, donor-acceptor bonded dinuclear metallocenes CpM'-MCp were reported. In the present thesis the isomerization stability of CpM'-MCp has been studied by using theoretically calculational method, and a new type dinuclear sandwich complexes DBe-LiCp associated by an one electron metal-metal single bond. The calculated results would be useful to further understand the metallocene chemistry, and may be expand this area. The main results are summarized as follows: 1. A detailed theoretical investigation is performed on the distribution of Al atom, the location of proton H and the strength of acidity of IM-5 zeolite. In IM-5 zeolite there are about 40 preferable Al, H locations with relatively high acidity, including the nine strongest acid sites of Al19H43 > Al14-H18 > Al5H13 > Al4H8 > Al10H26, Al15H26, Al15H37, Al22H45 and Al24H47. This may be one of the reasons why IM-5 as solid catalyst has high activity in industries, and in some case even more active than ZSM-5 zeolite.2. A detailed theoretical investigation is performed on the location of Cu2+ cation, stability and the adsorption of NO molecule. Cu2+ cation is most favorably located in the 6-membered ring in the wall of unusual two-dimensional medium-pore channel of IM-5. Compared with the stability of Cu2+ located in the most favorable site of ZSM-5, 78% (Al, Cu) location in IM-5 were more stable. Two reasons can explain the experimental fact that Cu-IM-5 is more active than Cu-ZSM5 in NO reduction: a) the adsorption ability of NO on Cu-IM5 is relatively higher than that on Cu-ZSM5, especially in 5-membered ring; b) the number of active centers in Cu-IM5 was obviously more than that in Cu-ZSM5.3. A detailed theoretical investigation is performed on the adsorption of all-metal aromatic molecule Na2Al4 on MCM-22 zeolite. The molecule Na2Al4 favorably locates in the supercage of MCM-22 within the 12-membered ring. During the adsorption, the all-metal aromaticity can be structurally and electronically retained within the zeolite-supported Na2Al4. And the adsorption of molecule Na2Al4 can effectively increase the local mobility of proton and improve the acidity of zeolite. The calculated results not only provide a new and feasible way to attain the stable Na2Al4 molecule, but also provide a clue to improve the acidity of zeolites and the ability of proton transferring.4. A detailed theoretical investigation is performed on the acidity and ethene protonation in CpNa-modified HMCM-22. Compared with the traditional HMCM-22, the CpNa-modified HMCM-22 zeolite possesses higher catalytic activity in ethene protonation, while, with lower acidity. The seeming violation from the traditional"acidity-activity"correlation can be ascribed to the dual factor of the guest molecule CpNa, i.e., Na+ moiety can"activate"the proton, whereas Cp? moiety can"restrict"the leaving of proton from the zeolite. It provides a hint that in some case enhanced"activity"is not necessarily correlated with enhanced"acidity", especially for modified zeolites.5. A detailed theoretical investigation is performed on the stability toward isomerization of a series of donor–acceptor bonded dinuclear metallocenes CpM'-MCp (M'=B, Al, Ga, In, Tl; M=Li, Na, K). The knownσ-type D–A sandwich form CpM'-MCp can be the ground-state isomer only for the donor M'=B. For M'=Al, Ga, In, Tl donors, the most stable isomer is of the previously unconsideredπ-type D–A sandwich form M'Cp-MCp.6. A detailed theoretical investigation is performed on the stability and the existence of one electron metal-metal bond of dinuclear sandwich complexes DBe-LiCp (D=Cp or Cp*). Through the calculations about the reaction energies for decomposition processes and the stability relative to other isomers, it is optimistically predicted that this new compounds may be detected in the gaseous phase below 326 K under appropriate experimental conditions.