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首页> 外文期刊>Catalysis science & technology >Fully-occupied Keggin type polyoxometalate as solid base for catalyzing CO2 cycloaddition and Knoevenagel condensation
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Fully-occupied Keggin type polyoxometalate as solid base for catalyzing CO2 cycloaddition and Knoevenagel condensation

机译：忙于Keggin polyoxometalate作为类型固体二氧化碳催化环加成反应和基地诺文葛耳凝结

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摘要

The highly negatively charged alkaline Keggin type polyoxometalate (POM) Na-16[SiNb12O40]center dot xH(2)O (NaSiNb12) was synthesized and used as an efficient solid base catalyst for CO2 cycloaddition and Knoevenagel condensation reactions. This is the first report of the basicity of a fully-occupied POM with the Keggin type structure. Theoretical calculations by the density functional theory (DFT) method revealed the high negative NBO (natural bond orbital) charges (-0.919--1.029) of the oxygen atoms in [SiNb12O40](16-), suggesting the existence of basicity, which was confirmed by CO2-TPD and the in situ FTIR spectra of methanol absorbed on the POM solid. Catalysis tests indicated that the POM solid base was very efficient in catalyzing the heterogeneous Knoevenagel condensation, giving high conversion and selectivity for several substrates. The catalyst NaSiNb12 also presented high activity in the cycloaddition of CO2 to epichlorohydrin under relatively mild conditions (120 degrees C, 1 MPa) in the absence of any solvent or co-catalyst. This solid base catalyst could be reused five times without an obvious decrease in the conversion and selectivity.
机译：高度带负电荷的碱性Keggin类型polyoxometalate (POM) Na-16 SiNb12O40中心圆点xH (2) O (NaSiNb12)合成,用作高效的二氧化碳固体碱催化剂环加成作用和诺文葛耳凝结反应。碱度的忙于POM Keggin类型的结构。密度泛函理论(DFT)方法高负NBO(自然键轨道)费用(-0.919——1.029)的氧原子(SiNb12O40)(16),暗示的存在碱度,CO2-TPD和确认原位红外光谱上的甲醇吸收光谱POM固体。坚实的基础是非常有效的催化的异构诺文葛耳凝结,使高转化率和选择性数基板。高二氧化碳的环加成作用的活动在相对温和的条件下环氧氯丙烷(120摄氏度,1 MPa)没有任何溶剂或co-catalyst。没有一个明显的可以被再利用五次降低转化率和选择性。

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