No abstract

No abstract

Indium oxide (In 2 O 3 ) has emerged as a highly active catalyst for methanol synthesis by CO 2 hydrogenation. In this work we elucidate the reduction behavior and oxygen dynamics of cubic In 2 O 3 nanoparticles by in situ Raman and UV−vis spectra in combination with density functional theory (DFT) calculations. We demonstrate that application of UV and visible Raman spectroscopy enables, first, a complete description of the In 2 O 3 vibrational structure fully consistent with theory and, second, the first theoretical identification of the nature of defect-related bands in reduced In 2 O 3 . Combining these findings with quasi in situ XPS and in situ UV−vis measurements allows the temperature-dependent structural dynamics of In 2 O 3 to be unraveled. While the surface of a particle is not in equilibrium with its bulk at room temperature, oxygen exchange between the bulk and the surface occurs at elevated temperatures, leading to an oxidation of the surface and an increase in oxygen defects in the bulk. Our results demonstrate the potential of combining different in situ spectroscopic methods with DFT to elucidate the complex redox behavior of In 2 O 3 nanoparticles.

No abstract

The oxidative dehydrogenation (ODH) of propane over supported vanadia catalysts is an attractive route toward propene (propylene) with the potential of industrial application and has been extensively studied over decades. Despite numerous mechanistic studies, the active vanadyl site of the reaction has not been elucidated. In this work, we unravel the ODH reaction mechanism, including the nuclearity-dependent vanadyl and surface dynamics, over ceriasupported vanadia (VO x /CeO 2 ) catalysts by applying (isotopic) modulation excitation IR spectroscopy supported by operando Raman and UV−vis spectroscopies. Based on our loading-dependent analysis, we were able to identify two different mechanisms leading to propylene, which are characterized by isopropyland acrylate-like intermediates. The modulation excitation IR approach also allows for the determination of the time evolution of the vanadia, hydroxyl, and adsorbate dynamics, underlining the intimate interplay between the surface vanadia species and the ceria support. Our results highlight the potential of transient IR spectroscopy to provide a detailed understanding of reaction mechanisms in oxidation catalysis and the dynamics of surface catalytic processes in general.