Effects of Cu[sup 2+] ions on the structure and reactivity of todorokite- and cryptomelane-type manganese oxide octahedral molecular sieves

Journal Article · Thu Jul 01 04:00:00 EDT 1999 · Chemistry of Materials

DOI:https://doi.org/10.1021/cm9811040· OSTI ID:6444145

Nicolas-Tolentino, E; Tian, Z R; Zhou, H; Xia, G; Suib, S L ^[1]

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1. Univ. of Connecticut, Storrs, CT (United States). Dept. of Chemistry

The concentration effects on Cu uptake into the structures and reactivity of manganese oxide octahedral molecular sieves (OMS) were investigated. Two sets of 3 x 3-tunnel structure OMS designated as OMS-1 were synthesized by hydrothermal treatment at 160 C for 48 h. The Cu-OMS-1 series of materials (tunnel substituted) were prepared by incorporating Cu[sup 2+] ions into OL-1, which has a layered structure, at 60 C for 24 h. [Cu]-OMS-1 materials (framework substituted) were prepared by ion exchanging Cu[sup 2+] ions into the tunnels of OMS-1 under similar conditions. Cu-OMS-2 materials characterized by 2 x 2 tunnels were prepared by the reflux method. ICP analysis shows a Cu/Mn molar ratio of 0.278 for Cu-OMS-1 labeled C as the substitution limit for a pure sample based on its XRD pattern. The copper ions that substitute for Mn[sup 2+] in the framework are considered as defects in the structure of the crystallites which make them less stable than OMS-1 containing Mg[sup 2+] in the framework where it exhibits a stabilizing effect. Resistivity measurements show a decrease and leveling off as the concentration of Cu increases in the Cu-OMS-1 series, which is a trend consistent with doping. The resistivity of the OMS-2 structure increases with the amount of copper incorporated. Cu(II) ions replacing the divalent cations in the framework during hydrothermal synthesis possibly account for the properties observed in the Cu-OMS-1 materials. An increased catalytic activity was observed for this set of materials as the Cu/Mn ratio increased for the oxidative dehydrogenation of ethylbenzene to styrene at 300 C at 1 atm.

• Sponsoring Organization: DOE; USDOE, Washington, DC (United States)
• OSTI ID: 6444145
• Journal Information: Chemistry of Materials, Journal Name: Chemistry of Materials Vol. 11:7; ISSN CMATEX; ISSN 0897-4756
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
ADSORBENTS
ALLOYS
CATALYTIC EFFECTS
CHALCOGENIDES
COHERENT SCATTERING
CONCENTRATION RATIO
COPPER ADDITIONS
COPPER ALLOYS
DIFFRACTION
MANGANESE COMPOUNDS
MANGANESE OXIDES
MICROSTRUCTURE
MOLECULAR SIEVES
OXIDES
OXYGEN COMPOUNDS
SCATTERING
THERMODYNAMIC ACTIVITY
TRANSITION ELEMENT COMPOUNDS
X-RAY DIFFRACTION