Operando XAS measurements in the near (XANES) and the extended (EXAFS) Au L_III edge as well as in situ diffuse reflectance FTIR (DRIFTS) spectroscopy were employed in combination with kinetic measurements in a further attempt to identify the nature of the active Au species responsible for the high activity of Au/CeO₂ catalyst in the low-temperature water gas shift (LT-WGS) reaction. The changes in the reaction behavior during the LT-WGS were followed at 180 °C for different initial states of the catalyst, prepared by either reducing or oxidizing pretreatments at different temperatures. Findings from kinetic and deactivation measurements were correlated with experimental data on the Au particle size, the Au oxidation state, and the CO-Au adsorption properties directly after different pretreatments and during the subsequent LT-WGS reaction obtained by operando/in situ spectroscopy measurements. The combined experimental results show that the use of different pretreatments can significantly influence the electronic state of the Au species (Au^δ-, Au⁰, Au^δ+). Exposure to the reaction atmosphere under the present reaction conditions, however, results in the rapid formation of extremely small, (sub)nanometer-sized Au⁰ nanoparticles, which are the dominant Au species and responsible for the high WGS activity. Small amounts of oxidic gold species (Au³⁺) persisting during reaction after the strongly oxidative O400 pretreatment, in the few percent range, are too little to be responsible for the catalytic activity of that catalyst and changes therein with time on stream.

中文翻译：

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Au / CeO ₂上低温水煤气变换反应中的活性金物种：时间分辨的Operando XAS和DRIFTS研究

将近（XANES）和扩展（EXAFS）Au L _III边缘的Operando XAS测量以及原位漫反射FTIR（DRIFTS）光谱与动力学测量结合使用，以进一步尝试确定活性Au的性质Au / CeO ₂高活性的物种催化剂在低温水煤气变换（LT-WGS）反应中。对于催化剂的不同初始状态，通过在不同温度下还原或氧化预处理制备的LT-WGS，反应行为在180°C下变化。动力学和失活测量的结果与在不同预处理之后以及在通过操作/原位光谱测量获得的后续LT-WGS反应过程中直接获得的Au粒径，Au氧化态和CO-Au吸附特性的实验数据相关。综合的实验结果表明，使用不同的预处理方法可以显着影响Au物种（^Auδ-，Au ⁰，Auδ ⁺）。然而，在当前反应条件下暴露于反应气氛导致快速形成非常小的（亚）纳米尺寸的Au ⁰纳米颗粒，其是主要的Au种类并且对高WGS活性负责。在强氧化性O400预处理后的反应过程中，残留的少量氧化金物质（Au ³⁺）处于百分之几的范围内，太少以至于不能对该催化剂的催化活性负责，并且随运行时间而变化。