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Density Functional Theory Study of Chemical Composition Influence on the Acidity of H−MCM-22 Zeolite

“…For single substitution, there is only one acidic site per model. The calculated PA for isomorphously MCM-22 zeolites by B, Al, and Fe showed the same sequence as in H-ZSM-5: [7][8][9][10][11][12][13][14] Al-MCM-22 < Fe-MCM-22 < B-MCM-22. The result was consistent with our previous calculation of isomorphously substituted MCM-22 zeolites by B, Al, Ga, and Fe, although the model was smaller than the present one and the center was another most probable substitution site T4.…”

“…Considering the effect of the substitution species, density functional theoretical calculations on isomorphously substituted ZSM-5 clusters by B, Al, Ga, and Fe have been reported, and the calculated acidity agreed well with the experimental results. [7][8][9][10][11][12][13][14] Recently, our group also compared the properties of isomorphously substituted MCM-22 zeolites with a small cluster model into which only one substitution atom was introduced and has correctly predicted their acidity. 15 In studying the influence of the number of trivalent substitution atoms by using four-membered-ring models for the substitution from Si to Al at the NNN site, Schroeder and Sauer 16 pointed out that a structure with Al-O-Si-O-Al linkage (the NNN model) was more stable than a structure where two aluminum atoms were separated as far as possible.…”

Characterization of Iron Atoms in the Framework of MFI-Type Zeolites by UV Resonance Raman Spectroscopy

“…Therefore, the characterization of a trace of heteroatoms in ZSM-5 is of great importance. However, it is often difficult to obtain the information on framework heteratoms in zeolites by the usual spectroscopic techniques when the concentration of the transition metal atom is low (8).…”

Strong Acidity of MFI-Type Ferrisilicate Determined by Temperature-Programmed Desorption of Ammonia

“…The sequence of acid strength is interesting from the viewpoint of theoretical chemistry, and therefore quantum chemical calculations according to this sequence have been published. [5][6][7][8][9] However, there appears some controversy. Careful measurements of calorimetry showed that the adsorption heat of ammonia was too similar to distinguish the acid strength of the MFI type ferri-, gallo-, and aluminosilicates.…”

“…Many researchers have accepted the acid strength sequence B < Fe < Ga < Al in corresponding metallosilicates because this order agrees well with the catalytic activity for a reaction that is believed to be a typical acid-catalyzed one such as cracking of alkane. The sequence of acid strength is interesting from the viewpoint of theoretical chemistry, and therefore quantum chemical calculations according to this sequence have been published. − …”