Abstract

Gold surfaces and nanoparticles have commonly been investigated by IR spectroscopy using carbon monoxide as a molecular probe. An evolution of the IR spectra with time under CO was reported in some cases and tentatively assigned to geometrical effects (e.g. surface reconstruction or particle restructuring) or electronic effects, e.g. gold becoming negatively charged following support reduction. We report here an investigation of the evolution of the IR spectrum of CO adsorbed at 50 °C in the case of Au nanoparticles supported on non-reducible silica and alumina supports. The evolution of the carbonyl IR band signal, proposed to arise mostly from Au particle restructuring, was clearly observed. In addition, the formation of hydrogenocarbonates species on the alumina reemphasized that Au nanoparticles are somewhat active for CO dissociation via Boudouard reaction near room temperature, leading to some deposition of carbon. Water could not prevent restructuring, while O₂ prevented irreversibly the reconstruction, which could even be reversed when O₂ was introduced on an already restructured sample. It is hypothesized that the role of O₂ would be to remove the deposited elemental carbon that otherwise stabilize reconstructed Au. These results emphasize the complexity of the parameters affecting the restructuration of Au surfaces induced by CO and the difficulty in interpreting IR spectra of CO adsorption on Au-based materials.

Graphic Abstract

中文翻译：

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重新审视吸附在不可还原载体上的金纳米粒子上的CO的红外光谱的演变

摘要

通常通过使用一氧化碳作为分子探针的IR光谱研究金表面和纳米颗粒。在某些情况下，报告了在CO下红外光谱随时间的变化，并暂时归因于几何效应（例如表面重构或粒子重组）或电子效应，例如金在支持物减少后变成带负电荷。我们在此报告了在不可还原的二氧化硅和氧化铝载体上负载金纳米颗粒的情况下，在50°C吸附的CO的IR光谱演变的调查。可以清楚地观察到羰基IR波段信号的演化，这主要是由于金粒子的重组引起的。此外，氧化铝上碳酸氢盐类物质的形成再次强调了金纳米粒子在室温附近通过Boudouard反应对于CO分解具有一定活性，从而导致一些碳沉积。水不能阻止重组，而O₂不可逆地阻止了重建，当在已经重组的样品上引入O ₂时甚至可以逆转。假设O ₂的作用是去除沉积的元素碳，否则该元素碳会稳定重构的Au。这些结果强调了影响由CO诱导的Au表面的重构的参数的复杂性以及解释CO在Au基材料上的吸附的IR光谱的难度。

图形摘要