Ethane oxidation was examined over silica supported silicomolybdic acid (SMA) catalysts under conditions described as excellent for partial oxidation to investigate the catalytic activities in the presence of non-catalytic ethane oxidation. When water vapor was absent or limited, SMA was transformed to the α-MoO3 phase, C2H6 conversion was enhanced, and the major products were C2H4 and CO, whereas little HCHO was formed. However, the selectivity for HCHO was improved by the addition of excess water vapor. The acidity of SMA, which was stabilized by water vapor as β-MoO3, might catalyze the scission of the C _ C bond, so partial oxidation to HCHO could be promoted in preference to oxidation to CH3CHO. In addition, the formation of the MoO2 phase, which was observed in the co-presence of C2H6 and water vapor, suggested that the lattice oxygen participated in the activation and oxidation of C2H6.
Mo-SBA-15 (mesoporous silica SBA-15 containing molybdenum oxides) was hydrothemally synthesized with H2MoO4, P123 as the template and tetraethylorthosilicate (TEOS). Mo species of precursor solutions and final products were characterized by Raman spectroscopy. Mo-P123 complexes are formed in solution by reaction of MoO2Cl2 dissolved in concentrated HCl and P123, but MoO2Cl2 does not react with TEOS. N2 adsorptiondesorption analysis and small angle X-ray diffraction reveal that the SBA-15 framework is formed in Mo-SBA-15 synthesized. This is explained that the Mo-P123 complexes act to form the SBA-15 framework as an effective template in the hydrothermal aging. The formed molybdenum oxides are expected to be dispersed in the SBA-15 channels and their structures are affected by the volume of concentrated HCl. UV-Vis spectroscopy indicates that the tetrahedrally coordinated mono-molybdates dominate in Mo-SBA-15 when 20 mL of concentrated HCl (HCl/H2MoO4 weight ratio 16.0) is added.
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