Modulation Excitation Spectroscopy: A Powerful Tool to Elucidate Active Species and Sites in Catalytic Reactions.

ConspectusA rational design of catalysts requires a knowledge of the active species and sites. Often, catalyst surfaces are dominated by spectators, which do not participate in the reaction, while the catalytically active species and sites are hidden. Modulation-excitation spectroscopy (MES) allows discrimination between active and spectator species by applying a concentration modulation, which is translated into the active (that is, actively responding) species by phase-sensitive detection (PSD).

Importance of Metal-Support Interactions for CO Hydrogenation: An Near-Ambient Pressure X-ray Photoelectron Spectroscopy Study on Gold-Loaded InO and CeO Catalysts.

Metal-support interactions, which are essential for the design of supported metal catalysts, used, e.g., for CO activation, are still only partially understood.

Elucidating CO Hydrogenation over In O Nanoparticles using Operando UV/Vis and Impedance Spectroscopies.

In O has emerged as a promising catalyst for CO activation, but a fundamental understanding of its mode of operation in CO hydrogenation is still missing, as the application of operando vibrational spectroscopy is challenging due to absorption effects. In this mechanistic study, we systematically address the redox processes related to the reverse water-gas shift reaction (rWGSR) over In O nanoparticles, both at the surface and in the bulk. Based on temperature-dependent operando UV/Vis spectra and a novel operando impedance approach for thermal powder catalysts, we propose oxidation by CO as the rate-determining step for the rWGSR.

Toward an Atomic-Level Understanding of Ceria-Based Catalysts: When Experiment and Theory Go Hand in Hand.

ConspectusBecause ceria (CeO) is a key ingredient in the formulation of many catalysts, its catalytic roles have received a great amount of attention from experiment and theory. Its primary function is to enhance the oxidation activity of catalysts, which is largely governed by the low activation barrier for creating lattice O vacancies. Such an important characteristic of ceria has been exploited in CO oxidation, methane partial oxidation, volatile organic compound oxidation, and the water-gas shift (WGS) reaction and in the context of automotive applications.

Reduction Behavior of Cubic InO Nanoparticles by Combined Multiple Spectroscopy and DFT.

Indium oxide (InO) has emerged as a highly active catalyst for methanol synthesis by CO hydrogenation. In this work we elucidate the reduction behavior and oxygen dynamics of cubic InO nanoparticles by 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 InO vibrational structure fully consistent with theory and, second, the first theoretical identification of the nature of defect-related bands in reduced InO.

Insight into the mechanism of the water-gas shift reaction over Au/CeO catalysts using combined operando spectroscopies.

The mechanism of the low-temperature water-gas shift (LT-WGS) reaction over Au/CeO catalysts with different ceria terminations, i.e., (111), (110), and (100) facets, was investigated.

Elucidating the Oxygen Storage-Release Dynamics in Ceria Nanorods by Combined Multi-Wavelength Raman Spectroscopy and DFT.

The oxygen storage-release dynamics in ceria nanorods is elucidated by using a combination of in situ multi-wavelength Raman spectroscopy and density functional theory calculations. Ceria nanorods exposing CeO(100) and CeO(110) facets are shown to be characterized by highly facet-dependent properties regarding molecular oxygen activation and decomposition as well as lattice oxygen dynamics. Temperature-dependent Raman results show that oxygen is stored in the form of peroxide species on the (100) facets, which are then released as gaseous oxygen, whereas lattice oxygen is involved with the (110) facets.