Synthesis and Characterization of Mn-Containing Cubic Mesoporous MCM-48 and AlMCM-48 Molecular Sieves
1999; American Chemical Society; Volume: 11; Issue: 10 Linguagem: Inglês
10.1021/cm990300j
ISSN1520-5002
AutoresJie Xu, Zhaohua Luan, Martin Hartmann, Larry Kevan,
Tópico(s)Mesoporous Materials and Catalysis
ResumoEmploying electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopy, five Mn(II) species are found in three kinds of Mn-containing MCM-48 materials: 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 centered at g = 2.00 has distorted octahedral symmetry and is observed in hydrated ion-exchanged Mn−MCM-48 and in synthesized calcined MnMCM-48. Mn(II) species II with a group of single peaks between g = 11.32 and 2.62 with possible distorted tetrahedral symmetry and a 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 is assigned 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 octahedral symmetry 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 in dehydrated or hydrogen reduced MnMCM-48. Mn(II) species I, II and IV correspond to extraframework 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 accessible to water, but framework Mn(II) species III coordinates with only three D2O molecules and is less accessible to water. Similar results are also obtained for Mn-containing AlMCM-48 materials.
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