Synthesis and Characterization of Mn-Containing Cubic Mesoporous MCM-48 and AlMCM-48 Molecular Sieves
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- 作者：Jie Xu ; Zhaohua Luan ; Martin Hartmann ; and Larry Kevan
- 刊名：Chemistry of Materials
- 出版年：1999
- 出版时间：October 1999
- 年：1999
- 卷：11
- 期：10
- 页码：2928 - 2936
- 全文大小：119K
- 年卷期：v.11,no.10(October 1999)
- ISSN：1520-5002
文摘
Employing electron spin resonance (ESR) and electron spin echo modulation (ESEM)spectroscopy, five Mn(II) species are found in three kinds of Mn-containing MCM-48materials: ion-exchanged Mn-MCM-48, synthesized MnMCM-48, and synthesized MnMCM-48(Ca) with subsequent CaCl2 exchange. Mn(II) species I with a well-resolved sextet centeredat g = 2.00 has distorted octahedral symmetry and is observed in hydrated ion-exchangedMn-MCM-48 and in synthesized calcined MnMCM-48. Mn(II) species II with a group ofsingle peaks between g = 11.32 and 2.62 with possible distorted tetrahedral symmetry anda significant zero field contribution is observed in dehydrated Mn-MCM-48 and in MnMCM-48. Mn(II) species III with a symmetric line at g = 2.00 and a line width around 410 G isassigned to tetrahedral symmetry and is observed in MnMCM-48(Ca) and in MnAlMCM-48(Ca). Mn(II) species IV with a sextet centered from 4.11 to 4.34 also has distorted octahedralsymmetry and is obtained in partially dehydrated Mn-MCM-48 and Mn-AlMCM-48. Mn(II)species V with a peak at g = 5.70 has distorted tetrahedral symmetry and is produced indehydrated or hydrogen reduced MnMCM-48. Mn(II) species I, II and IV correspond toextraframework Mn(II), and Mn(II) species III and V are assigned to framework sites.Extraframework Mn(II) species I and II coordinate with four D2O molecules and are accessibleto water, but framework Mn(II) species III coordinates with only three D2O molecules andis less accessible to water. Similar results are also obtained for Mn-containing AlMCM-48materials.