Synthesis of porous manganese oxides and carbon monoxide oxidation with them

Takanori Miyake ,  Eri Matsuda ,  Tarou Ishima ,  Makoto Sano 

Kansai University, Suita 3-3-35, Osaka 564-8680, Japan

Abstract

Manganese compound, todorokite, having one dimensional microporous structure is known. Todorokite is made up with MnO6 octahedra connected to each other by its corner and edge. The rectangular pore mouth consists of 3x3 array of the MnO6 unit and its pore size is 0.69 nm x 0.69 nm. Although todorokite is expected as a functional material for catalysts or battery materials, not many minute researches on the synthesis are reported so far. We studied the synthesis, characterization of todorokite and its catalytic performance for carbon monoxide (CO) oxidation.

Several todorokites were synthesized by changing the aging time during the synthesis of its precursor, birnessite, of layered structure. Then, the birnessite was ion-exchanged to buserite and the buserite was finally transformed to todorokite by the hydrothermal treatment. The products were analyzed by several methods such as XRD, Iodometry, FE-SEM and TEM. CO oxidation was studied using a conventional fixed bed reactor.

It was revealed from XRD that crystallinity of todorokite depended on the aging time of birnessite and high crystallinity necessitated aging for 3 to 7 days. Primary particle size of todorokite calculated by Sherrer equation increased with the aging time to about 25 nm. The valence of manganese in todorokite coincided with that in birnessite and was almost constant irrespective of aging time between 5 min and 7 days. The morphology of todorokite observed by FE-SEM changed from amorphous for shorter aging time to plate-like structure for longer aging time. On the other hand, TEM revealed that even in 5 min aging, small plate-like particles of birnessite were observed together with dominant amorphous particles. CO oxidation was studied as a model reaction. Higher CO oxidation activity was observed on the todorokite obtained by aging birnessite for 3 hrs. The relation between the activity and crucial properties of todorokite will be discussed.

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Presentation: Poster at E-MRS Fall Meeting 2006, Symposium B, by Takanori Miyake
See On-line Journal of E-MRS Fall Meeting 2006

Submitted: 2006-05-09 11:11
Revised:   2009-06-07 00:44
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