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首页> 外文期刊>The journal of physical chemistry, C. Nanomaterials and interfaces >Direct Synthesis and Structural Characteristics of Ordered SBA-15 Mesoporous Silica Containing Tungsten Oxides and Tungsten Carbides
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Direct Synthesis and Structural Characteristics of Ordered SBA-15 Mesoporous Silica Containing Tungsten Oxides and Tungsten Carbides

机译：含钨氧化物和碳化钨的有序SBA-15介孔二氧化硅的直接合成和结构特征

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摘要

A series of WO3-SBA-15 materials with different Si/W ratios have been hydrothermally synthesized using tetraethyl orthosilicate (TEOS) as silica precursor, ammonium paratungstate as tungsten precursor, and EO20-PO70EO20 (P123) as structure-directing reagent. After temperature-programmed carburization (TPC) in flowing CH4/H2 (20/80 v/v mixture), the materials were converted to the corresponding W_xC-SBA-15 materials. The structure of the oxide and carbide materials has been characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), nitrogen adsorption-desorption measurements, 29Si magic-angle spinning (MAS) NMR spectroscopy, Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), and thermogravimetric and differential scanning calorimetric analysis (TG-DSC) measurements. The results show that after hydrothermal synthesis using different amounts of tungsten and subsequent carburization, the materials retain the mesopore structure of SBA-15. When Si/W = 30-15, the majority of the tungsten is dispersed in the channels of SBA-15 with the remainder being incorporated into the framework of SBA-15 with the formation of Si-O-W bonds. The tungsten carbide exists as a single W2C phase after carburization. At higher tungsten content (Si/W = 7.5), the amount of tungsten in the framework of SBA-15 increases with the formation of both Si-O-W bonds and W-O-W bonds. The tungsten carbide formed after carburization exists as a mixture of W2C and WC phases. A model for the distribution of tungsten in SBA-15 is proposed involving three different tungsten species: alpha-W inside SBA-15 channels, beta-W embedded in the internal surfaces of the SBA-15 channels, and gamma-W inside the framework of SBA-15. After temperature-programmed carburization, alpha-W sites are transformed into W2C, whereas beta-W sites afford WC; in contrast, gamma-W sites show little change after carburization.
机译：以原硅酸四乙酯（TEOS）为二氧化硅前驱体，仲钨酸铵为钨前驱体和EO20-PO70EO20（P123）为结构导向剂，水热合成了一系列不同Si / W比的WO3-SBA-15材料。在流动的CH4 / H2（20/80 v / v混合物）中进行程序升温渗碳（TPC）后，将材料转换为相应的W_xC-SBA-15材料。使用X射线衍射（XRD），X射线荧光（XRF），氮吸附-脱附测量，29Si幻角旋转（MAS）NMR光谱，傅里叶变换红外（FTIR）对氧化物和碳化物材料的结构进行了表征光谱，透射电子显微镜（TEM）以及热重和差示扫描量热分析（TG-DSC）测量。结果表明，在使用不同量的钨进行水热合成并随后进行渗碳处理之后，该材料保留了SBA-15的中孔结构。当Si / W ＝ 30-15时，大部分钨分散在SBA-15的通道中，其余的钨结合到SBA-15的框架中，形成Si-O-W键。碳化钨在渗碳后以W2C单相形式存在。在较高的钨含量下（Si / W = 7.5），SBA-15框架中的钨含量随Si-O-W键和W-O-W键的形成而增加。渗碳后形成的碳化钨以W2C和WC相的混合物形式存在。提出了一种在SBA-15中分布钨的模型，该模型涉及三种不同的钨物质：SBA-15通道内的alpha-W，嵌入SBA-15通道内表面的beta-W和框架内的g-W SBA-15。经过程序升温的渗碳后，α-W位转变为W2C，而β-W位提供WC。相反，渗碳后，γ-W位几乎没有变化。

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