Investigation on specific adsorption of hydrogen on lithium-doped mesoporous silica |
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Authors: | Masaru Kubo Hiroshi Ushiyama Atsushi Shimojima Tatsuya Okubo |
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Affiliation: | (1) Instituto de Tecnologia Quimica U.P.V.-C.S.I.C., Universidad Politecnica de Valencia, Av. Los Naranjos s/n, 46022 Valencia, Spain |
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Abstract: | This paper reports the synthesis, structure, and hydrogen adsorption property of Li-doped mesoporous silica (MPS) with a 2D hexagonal structure. The Li-doping is achieved by impregnation of the cylindrical mesopores with an ethanol solution of lithium chloride followed by heat treatment. Detailed characterization by solid-state NMR, TG-MS, and FT-IR suggests that, during the heat treatment, lithium chloride reacts with surface ethoxy groups (≡Si-OEt) to form ≡SiOLi groups, while ethyl chloride is released into the gas phase. The hydrogen uptake at 77 K and 1 atm increases from 0.68 wt% for the undoped MPS to 0.81 wt% for Li-doped MPS (Li-MPS). The isosteric heat of adsorption is 4.8 kJ mol−1, which is consistent with the quantum chemistry calculation result (5.12 kJ mol−1). The specific hydrogen adsorption on Li-MPS would be explained by the frontier orbital interaction between HOMO of hydrogen molecules and LUMO of ≡SiOLi. These findings provide an important insight into the development of hydrogen storage materials with specific adsorption sites. |
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