Royal Society of Chemistry, RSC Advances, 89(4), p. 47906-47920, 2014
DOI: 10.1039/c4ra06114d
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The B, Al and Ga incorporated H-, NH4-, Li-, Na- and K-forms MTW zeolites were comparatively studied to understand the crystallization thermochemistry, structure stabilities and acid properties using dispersion corrected density functional theory method. Substitution energies were introduced to evaluate the synthesis prescriptions for MTW zeolites. The calculated results show that the trivalent and alkaline metal ions for the synthesis of the MTW zeolites are favored following the order: Al > Ga > B and Li > K ≈ Na > NH4 > H. The B–O, Si–O and O–H bonds show covalent property whereas the Al–O bonds show obvious ionic property. However, the Ga–O bonds show the property between the Al–O and B–O bonds. The introducing of alkaline metal ions significantly changes the cell volumes. As a result, the cell volumes of the H-form B, Al and Ga incorporated MTW zeolites are larger than Li-form while smaller than K-form MTW zeolites. Further property studies show that the Brønsted acid sites of the zeolites follow the order of HAl-MTW > HGa-MTW > HB-MTW. The Lewis acidity of HB-MTW is similar to that of HAl-MTW, while weaker than the HGa-MTW. These results are in well agreement with the previous experiments and provide new insight for the MTW zeolite.