水熱・ゾル-ゲル法を用いたHMoOと過剰のケイ酸エチルから生成するケイモリブデン酸のラマンスペクトル観察

概要

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In order to develop the preparation procedure for silicomolybdic acid (H4SiMo12O40, SMA) on silica catalysts, H2MoO4 and excess tetraethylorthosilicate (TEOS) are employed as starting reagents and three catalysts with different loadings are prepared by a hydrothermal sol-gel method. From Raman measurements in the course of the preparation steps, Raman spectra imply the formation of beta type silicomolybdic acid (β-SMA) reported by M. A. Bañares et al.; Raman spectroscopy suggests that the SMA species are formed in the precursor solution and is stable on 14.6 and 20 wt% MoO3/SiO2 even in the drying process (110 °C). When the loading is 7.9 wt%, Raman peaks of SMA disappear after the hydrothermal treatment at 100 °C. The structural distortion of the SMA due to hydrogen interaction between OH groups and Mo=O bonds is also observed. Raman measurement indicates the transformation to β- and α-MoO3 in 20 wt% MoO3/SiO2 after the calcination at 500 °C, but only surface molybdates are observed at the loadings of 7.9 and 14.6 wt%. The results indicate that H2MoO4 is also effective for the simple preparation of SMA. In addition, as no XRD patterns of all Mo species are observed, Raman spectroscopy is an effective method to structural analysis of Mo species, even in liquid and wet samples.
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