Reversible Redox Property of Co(III) in Amorphous Co-Doped SiO2/γ-Al2O3 Layered Composites |
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| Authors: | Shotaro Tada Shota Saito Akito Mori Hideki Mizuno Shiori Ando Toru Asaka Yusuke Daiko Sawao Honda Samuel Bernard Yuji Iwamoto |
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| Affiliation: | 1.Department of Life Science and Applied Chemistry, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan; (S.T.); (S.S.); (A.M.); (H.M.); (S.A.); (T.A.); (Y.D.); (S.H.);2.Centre Européen de la Céramique, University of Limoges, 12 Rue Atlantis, 87068 Limoges, France; |
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| Abstract: | This paper reports on a unique reversible reducing and oxidizing (redox) property of Co(III) in Co-doped amorphous SiO2/γ-Al2O3 composites. The Fenton reaction during the H2O2-catalyzed sol–gel synthesis utilized in this study lead to the partial formation of Co(III) in addition to Co(II) within the composites. High-resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) analyses for the composite powder sample with a composition of Al:Si:Co = 85:10:5 showed the amorphous state of the Co-doped SiO2 that modified γ-Al2O3 nanocrystalline surfaces. In situ X-ray absorption fine structure (XAFS) spectroscopic analysis suggested reversible redox reactions of Co species in the composite powder sample during heat-treatment under H2 at 500 °C followed by subsequent cooling to RT under Ar. Further analyses by in situ IR spectroscopy combined with cyclic temperature programmed reduction/desorption (TPR/TPD) measurements and X-ray photoelectron spectroscopic (XPS) analysis revealed that the alternating Co(III)/(II) redox reactions were associated with OH formation (hydrogenation)-deformation (dehydrogenation) of the amorphous aluminosilicate matrix formed in situ at the SiO2/γ-Al2O3 hetero interface, and the redox reactions were governed by the H2 partial pressure at 250–500 °C. As a result, a supported mesoporous γ-Al2O3/Co-doped amorphous SiO2/mesoporous γ-Al2O3 three-layered composite membrane exhibited an H2-triggered chemical valve property: mesopores under H2 flow (open) and micropores under He flow (closure) at 300–500 °C. |
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| Keywords: | Co(III) aluminosilicate reversible Co(III)/(II) redox property membrane H2-triggered chemical valve property |
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