Köck Eva-Maria, Kogler Michaela, Zhuo Chen, Schlicker Lukas, Bekheet Maged F, Doran Andrew, Gurlo Aleksander, Penner Simon
Institut für Physikalische Chemie, Universität Innsbruck, Innrain 52c, A-6020 Innsbruck, Austria.
Fachgebiet Keramische Werkstoffe/Chair of Advanced Ceramic Materials, Institut für Werkstoffwissenschaften und-technologien, Technische Universität Berlin, Hardenbergstr. 40, D-10623 Berlin, Germany.
Phys Chem Chem Phys. 2017 Jul 26;19(29):19407-19419. doi: 10.1039/c7cp03632a.
To account for the explanation of an eventual sensing and catalytic behavior of rhombohedral InO (rh-InO) and the dependence of the metastability of the latter on gas atmospheres, in situ electrochemical impedance spectroscopic (EIS), Fourier-transform infrared spectroscopic (FT-IR), in situ X-ray diffraction and in situ thermogravimetric analyses in inert (helium) and reactive gases (hydrogen, carbon monoxide and carbon dioxide) have been conducted to link the gas-dependent electrical conductivity features and the surface chemical properties to its metastability towards cubic InO. In particular, for highly reducible oxides such as InO, for which not only the formation of oxygen vacancies, but deep reduction to the metallic state (i.e. metallic indium) also has to be taken into account, this approach is imperative. Temperature-dependent impedance features are strongly dependent on the respective gas composition and are assigned to distinct changes in either surface adsorbates or free charge carrier absorbance, allowing for differentiating and distinguishing between bulk reduction-related features from those directly arising from surface chemical alterations. For the measurements in an inert gas atmosphere, this analysis specifically also included monitoring the fate of differently bonded, and hence, differently reactive, hydroxyl groups. Reduction of rh-InO proceeds to a large extent indirectly via rh-InO → c-InO → In metal. As deduced from the CO and CO adsorption experiments, rhombohedral InO exhibits predominantly Lewis acidic surface sites. The basic character is less pronounced, directly explaining the previously observed high (inverse) water-gas shift activity and the low CO selectivity in methanol steam reforming.
为了解释菱面体氧化铟（rh-InO）最终的传感和催化行为，以及后者的亚稳性对气体气氛的依赖性，我们进行了原位电化学阻抗谱（EIS）、傅里叶变换红外光谱（FT-IR）、原位X射线衍射和原位热重分析，实验在惰性（氦气）和反应性气体（氢气、一氧化碳和二氧化碳）中进行，以将与气体相关的电导率特征和表面化学性质与其对立方氧化铟的亚稳性联系起来。特别是对于像氧化铟这样的高还原性氧化物，不仅要考虑氧空位的形成，还要考虑深度还原到金属态（即金属铟），这种方法是必不可少的。与温度相关的阻抗特征强烈依赖于各自的气体组成，并归因于表面吸附物或自由电荷载流子吸光度的明显变化，从而能够区分与体相还原相关的特征和直接由表面化学变化引起的特征。对于在惰性气体气氛中的测量，该分析特别还包括监测不同键合、因而具有不同反应性的羟基的命运。rh-InO的还原在很大程度上间接通过rh-InO→c-InO→金属铟进行。从一氧化碳和二氧化碳吸附实验推断，菱面体氧化铟主要表现出路易斯酸性表面位点。碱性特征不太明显，这直接解释了先前观察到的高（逆）水煤气变换活性和甲醇蒸汽重整中低一氧化碳选择性。
