Synthesis of Mesophase Cerium(IV) Oxides via Surfactant Templating
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Synthesis of Mesophase Cerium(IV) Oxides via Surfactant Templating Masahiko Inagaki, Atsushi Hozumi, Yoshiyuki Yokogawa and Tetsuya Kameyama National Industrial Research Institute of Nagoya, 1-1 Hirate-cho, Kita-ku, Nagoya 462-8510, Japan. ABSTRACT Mesostructured cerium(IV) oxides were directly synthesized via the hexamethylenetetramine (HMT) homogeneous precipitation method. Cerium(III) nitrate, a templating agent, HMT and water were mixed in a molar ratio of 1 : 0.1-2 : 1-15 : 100-1000 and kept at 65 to 95°C for 10 to 40 hours. 1-Hexadecanesulfonic acid sodium salt was used as the templating agent. Lowangle XRD patterns showed that the as-prepared powders had a lamellar structure with d100=4.1 nm. Wide-range (2θ=10-70°) XRD patterns also exhibited reflection peaks of CeO2 with a fluorite structure. However, the low-angle reflection peaks disappeared in calcined specimens. INTRODUCTION Recently the study of mesoporous materials based on the supra-molecular templating method has progressed rapidly and the achievements have attracted much attention. This templating technique has also been extended to the synthesis of non-silicate mesoporous materials. Mesoporous Al2O3 [2], Nb2O5 [3], Ta2O5 [3], ZrO2 [4-8], TiO2 [9, 10], MnO2 [11], HfO2 [12], SnO2 [13] and rare-earth oxides [16] have been synthesized over the past years. Stucky and co-workers have also reported the synthesis of several mesoporous oxides and mesopoorous mixed oxides [1,14,15]. Mesoporous materials based on transition metal oxides are promising as highly functional electrical, magnetic or optical host materials, as well as catalysts and molecular sieves. Cerium(IV) oxide (ceria) and trivalent or divalent cation doped ceria have capabilities for redox chemistry, photocatalysis, UV absorption and oxygen ion conductivity. If such ceria can be synthesized as mesoporous solids, these materials might find application in gas sensors, fuel cells, dye-sensitized solar cells and high-surface-area redox catalysts. To our knowledge, no studies have been conducted on the synthesis of mesostructured cerium(IV) oxides. Here, we report on the direct synthesis of such a mesostructured ceria by a combination of the hexamethylenetetramine (HMT) homogeneous precipitation method [17] and supramolecular templating. EXPERIMENTAL PROCEDURE Cerium(III) nitrate (CeN), a templating agent, HMT and water were mixed in a molar ratio of 1 : 0.1-2 : 1-15 : 100-1000. 1-Hexadecanesulfonic acid sodium salt (HDSAS) was used as the templating agent. HDSAS was dissolved in H2O at 65°C. CeN and HMT were then added to the HDSAS solution and it was stirred for about 30 min at 65°C. The mixed solution was placed in a TeflonTM vessel, which was sealed with a cap and then heated in an oven maintained at a temperature 65-95°C. The vessel was kept at that temperature for 10-40 hours. The resulting dispersion was filtered through a 1 µm filter. The precipitates were GG6.14.1
washed with water several times and then lyophilized. In order to remove the template agent, the as-prepared powders were ca
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