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首页> 外文期刊>Chemistry of Materials >Vanadia-Silica Low-Temperature Aerogels: Influence of Aging and Vanadia Loading on Structural and Chemical Properties
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Vanadia-Silica Low-Temperature Aerogels: Influence of Aging and Vanadia Loading on Structural and Chemical Properties

机译：Vanadia-Silica低温气凝胶：老化和Vanadia负载对结构和化学性质的影响

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Vanadia-silica mixed oxides were prepared via the sol-gel method involving acid catalysis together with prehydrolysis in order to achieve matching of the reactivities of vanadium(Ⅴ) oxide triisopropoxide and tetraethoxysilicon(Ⅳ) precursors. Gelation was forced by the addition of basic solution. The as-received gels were supercritically dried by semicontinuous extraction with supercritical CO_2 at 313 K (low-temperature aerogels). The effects of composition, aging, and calcination temperature on the chemical, structural, and textural properties of the solids were investigated. The oxides were characterized by N_2 physisorption, XRD, vibrational spectroscopy, thermal analysis, UV-vis, and ~(51)V NMR. The low-temperature vanadia-silica aerogels were mesoporous and highly disperse. The increasing V content from 5 to 20 wt % nominal V_2O_5 caused a gradual decline in V dispersion. For 30 wt % "V_2O_5" the continuous formation of V-O-V connectivity resulted in crystallization of V_2O_5. The effect of aging in basic medium confined to the textural properties, significantly increasing BET surface area and especially pore volume. The prepared aerogels revealed a marked lack of stability against both apolar solvents in the presence of peroxides and polar solvents. The marked thermal stability in air at ≤873 K, however, combined with mesoporosity and high V dispersion, render these solids promising catalysts for gas-phase reactions.
机译：钒硅混合氧化物通过溶胶-凝胶法制备，该方法包括酸催化和预水解反应，以使三异丙氧基钒（Ⅴ）和四乙氧基硅（Ⅳ）前体的反应性匹配。通过添加碱性溶液来强制胶凝。所接收的凝胶通过在313 K下用超临界CO_2半连续萃取进行超临界干燥（低温气凝胶）。研究了组成，老化和煅烧温度对固体的化学，结构和质构性质的影响。通过N_2物理吸附，XRD，振动光谱，热分析，UV-vis和〜（51）V NMR对氧化物进行了表征。低温钒硅气凝胶是中孔且高度分散的。 V含量从标称V_2O_5的5wt％增加到20wt％引起了V分散度的逐渐下降。对于30重量％的“ V_2O_5”，V-O-V连接性的连续形成导致V_2O_5的结晶。在碱性介质中老化的影响仅限于组织性质，显着增加BET表面积，尤其是孔体积。制备的气凝胶在过氧化物和极性溶剂的存在下显示出对非极性溶剂的明显缺乏稳定性。然而，在≤873K的空气中，明显的热稳定性与介孔性和高V分散性相结合，使这些固体有望成为气相反应的催化剂。

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