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Development of a compact laser-based heating stage for in situ spectroscopic characterizations
(2024)Surface and Interface AnalysisIn this work, we present a recent advancement in high-temperature instrumentation in the form of a heating stage that enables studies to be performed in the temperature range of 20–1250°C under high-vacuum, millibar, and atmospheric pressure conditions (10⁻⁷–1000 mbar). The newly developed laser-based heating solution is described in detail. Its functionality is highlighted in this study in the form of a heating stage compatible with in ...Journal Article -
Identifying and avoiding dead ends in the characterization of heterogeneous catalysts at the gas–solid interface
(2023)Nature CatalysisThe goal of catalyst characterization is to understand the structure and properties of a catalytic material and how they ultimately affect catalytic performance. However, pitfalls in the design of characterization experiments can impede their successful interpretation and the acquisition of relevant insights. Reducing the complexity of characterization experiments through simplified model conditions and samples causes gaps between the ...Journal Article -
Structural Evolution of Copper-Oxo Sites in Zeolites upon the Reaction with Methane Investigated by Means of Cu K-edge X-ray Absorption Spectroscopy
(2023)The Journal of Physical Chemistry CThe structure of copper sites formedunder an oxidative environmentand their evolution in the course of the reaction with methane atelevated temperature was investigated by means of Cu K-edge X-rayabsorption spectroscopy for a series of copper-containing MFI, MOR,and FAU zeolites. The pretreatment in oxygen at 723 K leads to theformation of copper-(II)-oxo sites, whose nature depends on the frameworktype. Dimeric species are formed in CuMFI ...Journal Article -
Mechanism of Hydrocarbon Formation in Methane and Methanol Conversion over Copper-Containing Mordenite
(2023)ACS CatalysisMethane conversion over copper-containing zeolites can lead to the formation of C-C bonds, yielding hydrocarbons. By employing in situ MAS NMR spectroscopy, we elucidated the pathways of the transformation of methane and its partial oxidation and coupling products over copper-containing mordenite. Below 773 K, the direct coupling of methane is not possible, while the transformation of methanol, methoxy species, and dimethyl ether takes ...Journal Article -
Colloidally Engineered Pd and Pt Catalysts Distinguish Surface- and Vapor-Mediated Deactivation Mechanisms
(2023)ACS CatalysisNoble metal-based catalysts are ubiquitous because of their high activity and stability. However, they irreversibly deteriorate over time especially in high-temperature applications. In these conditions, sintering is the main reason for deactivation, and understanding how sintering occurs gives the opportunity to mitigate these detrimental processes. Previous studies successfully distinguished between two fundamental sintering modes, ...Journal Article -
The Extent of Platinum-Induced Hydrogen Spillover on Cerium Dioxide
(2023)ACS NanoHydrogen spillover from metal nanoparticles to oxides is an essential process in hydrogenation catalysis and other applications such as hydrogen storage. It is important to understand how far this process is reaching over the surface of the oxide. Here, we present a combination of advanced sample fabrication of a model system and in situ X-ray photoelectron spectroscopy to disentangle local and far-reaching effects of hydrogen spillover ...Journal Article -
Platinum-Iron(II) Oxide Sites Directly Responsible for Preferential Carbon Monoxide Oxidation at Ambient Temperature: An Operando X-ray Absorption Spectroscopy Study**
(2023)Angewandte Chemie. International EditionOperando X-ray absorption spectroscopy identified that the concentration of Fe2+ species in the working state-of-the-art Pt−FeOx catalysts quantitatively correlates to their preferential carbon monoxide oxidation steady-state reaction rate at ambient temperature. Deactivation of such catalysts with time on stream originates from irreversible oxidation of active Fe2+ sites. The active Fe2+ species are presumably Fe+2O−2 clusters in contact ...Journal Article -
Structure of Selective and Nonselective Dicopper (II) Sites in CuMFI for Methane Oxidation to Methanol
(2022)ACS CatalysisThe one-step valorization of natural gas remains a challenge. Methane conversion to methanol via chemical looping over copper-containing zeolites is a promising route, and CuMFI is among the earliest successfully applied. However, the structure of the active sites in CuMFI, as well as the effect of copper loading and Si/Al ratio on the copper speciation, are yet to be understood. We found that for CuMFI, the Cu/Al ratio determines the ...Journal Article -
In situ Study of Low-temperature Dry Reforming of Methane Over La2Ce2O7 and LaNiO3 Mixed Oxides
(2022)Applied Catalysis B: EnvironmentalDry reforming of methane (DRM) is a promising process to generate synthetic gas with a low H2/CO ratio. The main issues in DRM are the deposition of carbon over the catalyst and active metal sintering. Pyrochlores and perovskites are stable materials with properties that can overcome these challenges due to the presence of well dispersed active metal and oxygen vacancies. La2Ce2O7 and LaNiO3 mixed oxides containing 5 wt% of nickel were ...Journal Article -
Dynamic Structural Changes due to Metal-Support Interaction under Reactive Conditions
(2022)Microscopy and MicroanalysisJournal Article