State of gold on an Au/Al2O3 catalyst subjected to different pre-treatments: An FTIR study
State of gold on an Au/Al2O3 catalyst subjected to different pre-treatments: An FTIR study
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DOI：
10.1016/j.catcom.2005.11.018
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发表时间：
2006-05
影响因子：
3.7
通讯作者：
T. Venkov;H. Klimev;M. Centeno;J. Odriozola;K. Hadjiivanov
中科院分区：
文献类型：
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作者：
T. Venkov;H. Klimev;M. Centeno;J. Odriozola;K. Hadjiivanov
采用沉积-沉淀法制备了Au/Al 2 O3催化剂，并对其进行了XRD、TEM、吸附CO的FTIR光谱和催化性能测试。在室温下抽真空的样品上吸附的CO的IR光谱显示没有金位点。该结果由以下事实解释：该样品上的金以Au 3+阳离子存在，并且这些位点（以及Al 3+位点）被水阻断。当样品在473 K下活化时，在100 K下的CO吸附产生：（i）与载体相关的羰基带和（ii）在2167 cm −1处的带，该带在抽真空时稳定，并归属于Au+-CO物种。在573 K抽真空的样品导致自动还原的Au+网站。随后的CO吸附导致形成两种类型的Au 0-CO物种（在2112和2105 cm −1处的谱带）。在673 K活化的样品中只检测到一种Au 0位（2105 cm-1处的羰基带）。样品在673 K下在O2气氛中的再氧化导致所有可接近的金属金的氧化，并出现（i）少量孤立的Au+位点（在2175 cm-1处的相应羰基带）和（ii）与金属颗粒表面上的Au+阳离子相关的另一种位点（在2139 cm-1处的相应羰基带，在抽空期间消失）。这两种阳离子在573 K下都是稳定的，但金阳离子在673 K下自动还原。比较的FTIR结果与催化研究允许在CO氧化反应的活性位点的性质上的一些结论。
An Au/Al2O3sample was prepared by deposition–precipitation and characterized by different techniques (XRD, TEM, FTIR spectroscopy of adsorbed CO and catalytic test). IR spectroscopy of adsorbed CO on a sample evacuated at ambient temperature reveals no gold sites. The results were explained by the fact that gold on this sample was present as Au3+cations and these sites (as well as the Al3+sites) were blocked by water. When the sample was activated at 473K, CO adsorption at 100K produced: (i) carbonyl bands associated with the support and (ii) a band at 2167cm−1, stable towards evacuation and assigned to Au+–CO species. Evacuation of the sample at 573K led to auto-reduction of the Au+sites. Subsequent CO adsorption resulted in formation of two types of Au0–CO species (bands at 2112 and 2105cm−1). Only one kind of Au0sites (respective carbonyl band at 2105cm−1) were detected with samples activated at 673K. Re-oxidation of the sample at 673K in O2atmosphere resulted in oxidation of all accessible metallic gold and appearance of (i) a small amount of isolated Au+sites (respective carbonyl band at 2175cm−1) and (ii) another kind of sites (respective carbonyl band at 2139cm−1, disappearing during evacuation) associated with Au+cations on the surface of the metal particles. Both kinds of cations were stable at 573K but gold cations were auto-reduced at 673K. Comparison of the FTIR results with catalytic studies allowed some conclusions on the nature of the active sites in the CO oxidation reaction.