Surface chemistry and stability of metastable corundum-type In₂O₃

Abstract

To account for the explanation of an eventual sensing and catalytic behavior of rhombohedral In 2 O 3 (rh-In 2 O 3 ) 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 In 2 O 3 . In particular, for highly reducible oxides such as In 2 O 3 , 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-In 2 O 3 proceeds to a large extent indirectly via rh-In 2 O 3 -c-In 2 O 3 -In metal. As deduced from the CO and CO 2 adsorption experiments, rhombohedral In 2 O 3 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 2 selectivity in methanol steam reforming.

Metal–Organic Framework-Derived Synthesis of Cobalt Indium Catalysts for the Hydrogenation of CO2 to Methanol

“…59,60 Additionally, it is known that in strongly reductive atmospheres, such as CO and H 2 , the allotrope transformation proceeds following the same pathwayrh-In 2 O 3 → c-In 2 O 3 , meanwhile the reverse transformation happens only at high energy input. 61 Extrapolating the observation, one of the processes occurred during the catalytic run is recrystallization of amorphous S13B). Finally, the third and more peculiar component found to be formed is a mixed metal carbide, Co 3 InC 0.75 (Figure 3D).…”

Joint Theoretical and Experimental Study on the La Doping Process in In2O3: Phase Transition and Electrocatalytic Activity

“…24 The process of phase trans- formation in In 2 O 3 has been a focus of attention, since the different polymorphs show specific properties that directly affect the performance of the desired applications. 25 Koch et al 26 observed from adsorption measurements that rh-In 2 O 3 exhibits predominantly Lewis acidic surface sites compared to bcc-In 2 O 3 ; thus, the cubic structure presented a superior CO 2 selectivity in methanol steam reforming. Wu et al 27 investigated the photocatalytic activities of rh-In 2 O 3 and bcc-In 2 O 3 nanostructures and obtained the highest efficiency for degradation of tetracycline using rh-In 2 O 3 .…”

X-Ray Diffraction under Extreme Conditions at the Advanced Light Source

“…The capillaries containing the sample powder can be connected to a mass-flow controlled gas atmosphere, which allows for time varying, well-controlled gas-atmospheres. This set-up creates excellent data in the realm of catalysis and solid state chemistry (e.g., Mattox et al [48], Köck et al [49]). Figure 10.…”