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首页> 外文期刊>The journal of physical chemistry, C. Nanomaterials and interfaces >Ultraviolet-Visible Spectroscopy and Temperature-Programmed Techniques as Tools for Structural Characterization of Cu in CuMgAIO_x Mixed Metal Oxides
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Ultraviolet-Visible Spectroscopy and Temperature-Programmed Techniques as Tools for Structural Characterization of Cu in CuMgAIO_x Mixed Metal Oxides

机译：紫外可见光谱和温度编程技术作为CuMgAIO_x混合金属氧化物中Cu结构表征的工具

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Ultraviolet—visible (UV— vis) spectroscopy was used in combination with temperature-programmed reduction (TPR) methods to provide information about the Cu structure in CuMgAlO_x mixed oxides. UV—vis spectra revealed the presence of highly dispersed, isolated and oligomeric, CuO species in a distorted octahedral environment. From these spectra, optical absorption edge energies were determined and correlated with the number of nearest CuO neighbors (a measure of CuO domain size) and Cu content in the mixed oxides. Increasing the Cu content from 4 to 21 at. % increased the number of nearest CuO neighbors in oligomeric CuO from about 2 to 4 and produced materials that were more easily reducible, as inferred from TPR of untreated and N2O-passivated CuMgAlO_x. A further increase in Cu content to 38 at. % increased the number of nearest CuO neighbors to 4.5 but resulted in a decrease of reducibility because of the evolution of an amorphous CuO phase in the bulk of the mixed oxides. This work represents the first demonstration of combining UV—vis spectroscopy with TPR of untreated and N2O-passivated CuMgAlO_x as a relatively simple and inexpensive methodology for in-depth structural characterization of Cu in mixed metal oxides from which the composition, domain size, and relative fraction of total (surface + bulk) and surface oligomeric CuO species can be determined. A methodology that allows assessment of the extent of CuO bulk enrichment in CuMgAlO_x materials is also presented.
机译：紫外-可见（UV-vis）光谱与程序升温还原（TPR）方法结合使用，可提供有关CuMgAlO_x混合氧化物中Cu结构的信息。紫外可见光谱显示在扭曲的八面体环境中存在高度分散，分离和低聚的CuO物种。从这些光谱中，确定了光吸收边缘能，并将其与最近的CuO邻域的数量（CuO域尺寸的度量）和混合氧化物中的Cu含量相关。将铜含量从4 at增加到21 at。从未经处理的和N2O钝化的CuMgAlO_x的TPR推断，低聚CuO中最接近的CuO邻域的百分比将从约2增加到4，并且产生的材料更易于还原。铜含量进一步增加到38 at。 ％将最近的CuO邻域的数目增加到4.5，但是由于在大部分混合氧化物中无定形CuO相的析出而导致还原性降低。这项工作代表了将紫外-可见光谱与未经处理的和N2O钝化的CuMgAlO_x的TPR相结合的首次演示，这是一种相对简单且便宜的方法，可用于深入研究混合金属氧化物中的Cu的结构特征，从中可以了解其组成，畴尺寸和相对可以确定总（表面+本体）和表面低聚CuO种类的分数。还提出了一种方法，该方法可以评估CuMgAlO_x材料中CuO的体积富集程度。

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