Computational Differentiation of Br酶nsted Acidity Induced by Alkaline Earth or Rare Earth Cations in Zeolites

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• 作者：Andrey A. Rybakov ; Alexander V. Larin ; Georgy M. Zhidomirov
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：November 19, 2012
• 年：2012
• 卷：51
• 期：22
• 页码：12165-12175
• 全文大小：526K
• 年卷期：v.51,no.22(November 19, 2012)
• ISSN：1520-510X

文摘

For bi- and trivalent Me^q+ (Me = metal) cations of alkaline earth (AE) and rare earth (RE) metals, respectively, the formation of the nonacid MeOH^(q-1)+ species and acid H鈥揙_zeo group, where O_zeo is the framework atom, from water adsorbed at the multivalent Me^q+(H₂O) cation in cationic form zeolites was checked at both isolated cluster (8R or 6R + 4R) and periodic (the mordenite framework) levels. Both approaches demonstrate qualitative differences for the stability of the dissociated water between the two classes of industrial cationic forms if two Al atoms are closely located. The RE forms split water while the AE ones do not, that can be a basis of different proton transfer in the RE zeolites (thermodynamic control) than in the AE forms (kinetic control). The cluster models allow quantitatively explaining nearly equal intensities I_HF I_LF of the high frequency (HF) and low frequency (LF) OH vibrations in the RE forms and lowered I_HF I_LF in the AE forms, where HF bands are assigned to the Me鈥揙H groups in the RE and AE forms, respectively, while LF bands are assigned to the Si鈥揙(H)鈥揂l groups. The role of electrostatic terms for water dissociation in the RE and AE forms is discussed.