| 1. |
- Chakraborty, Debasish, et al.
(författare)
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Reversible Atomization and Nano-Clustering of Pt as a Strategy for Designing Ultra-Low-Metal-Loading Catalysts
- 2022
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 126:38, s. 16194-16203
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Tidskriftsartikel (refereegranskat)abstract
- Noble metal-based catalysts have numerous industrial uses, and maximum utilization of the precious metals by lowering the metal loading is of significant interest in heterogeneous catalysis research. However, lowering the metal loading could lead to single-atom metal species formation, which may not be active for important reactions like propylene oxidation. We report a way to drastically reduce precious metal loading of catalysts by judiciously choosing an active metal/support pair and using the reversible atomization-nanoparticulate formation of transition metal on a high-surface area support. Here, Pt and MgAl2O4 are used as the transition metal and high-surface area support, respectively. Through catalytic testing and characterization using scanning transmission electron microscopy and synchrotron X-ray absorption spectroscopy, a reversible change between atomization and nano-cluster formation under oxidizing and reducing conditions has been found. Via density functional theory, favorable sites for reversible Pt adsorption are identified, including ionic Pt4+ sites that can serve to nucleate nanoclusters. Catalytic reaction modeling also rationalizes the catalytic inertness of atomic Pt sites. Finally, a re-activation mechanism for the atomized Pt based on gases present during reaction has been formulated and demonstrated.
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| 2. |
- Jeppesen, Henrik S., et al.
(författare)
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LiquidReactionCell - a versatile setup for in situ synchrotron studies of compounds in liquid suspension and solution
- 2022
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Ingår i: CrystEngComm. - : Royal Society of Chemistry (RSC). - 1466-8033. ; 25:5, s. 751-760
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Tidskriftsartikel (refereegranskat)abstract
- There is an increasing interest in understanding the atomic level formation of functional materials, e.g. through nucleation and growth from their precursors in solution or through chemically induced phase transitions. Such information is achievable though synchrotron-based in situ X-ray absorption spectroscopy (XAS) and total scattering (TS) experiments. In this study we present a new and versatile setup for in situ investigations of chemical reactions. Our setup, LiquidReactionCell (LRC), is constructed in borosilicate glass, i.e., it is chemically inert and transparent to visible light, and it resembles regular laboratory glassware. The setup is designed to handle homogenous solutions and fine powder suspensions at ambient conditions, and it can be used to follow chemically or light induced reactions, for example. Chemical precursors can be added during data collection, and inert conditions can be obtained in the cell. Herein, we demonstrate the versatility and use of the LRC in XAS and TS experiments. Specifically, we compare data collected on powder suspensions in the LRC with data measured on powders under ideal conditions. Bi24O31X10 (X = Cl, Br) are emerging materials for photocatalysis and are used as model compounds herein. Gratifyingly, only minor differences are observed between data collected on suspensions in the LRC and data collected on a pressed pellet (for XAS) or on a powder in a Kapton capillary (for TS). These results propose that the LRC has the potential to cover a broad range of chemical reactions.
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| 3. |
- Lützenkirchen-Hecht, Dirk, et al.
(författare)
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Time-Resolved Grazing Incidence X-Ray Absorption Spectroscopy for the In Situ Investigation of the Initial Stages of Sputter-Deposited Copper Thin Films
- 2022
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Ingår i: Physica Status Solidi (A) Applications and Materials Science. - : Wiley. - 1862-6300. ; 219:9
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Tidskriftsartikel (refereegranskat)abstract
- The sputter deposition and the growth of thin copper films on float glass substrates are in situ studied using grazing incidence, reflection mode X-ray absorption fine structure spectroscopy with subsecond time resolution. The experimental data are compared with model calculations, assuming the presence of crystalline, face-centered cubic metallic Cu nanostructures. From a detailed analysis of the measured spectra, the film thickness as well as the surface roughness is determined, leading to a detailed understanding of the films growth as a function of the sputter deposition time. In particular, different stages of film growth can clearly be distinguished from the fits of the experimental data. The results suggest the formation of isolated, approximately nm-sized copper clusters in the initial phase of the film deposition for the first few seconds, a coalescence phase with a nominal thickness of ≈1.5−2.8 nm, constant roughness of about 1.4 nm for the subsequent ≈5 s, and finally 3D growth of the Cu crystallites in the film for later stages of film growth. Further prospects of the methodology are given.
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