Alexey Boubnov

Karlsruhe Institute of Technology

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Simon R. Bare

Stanford Synchrotron Radiation Lightsource

Adam S. Hoffman

SLAC National Accelerator Laboratory

Jan‐Dierk Grunwaldt

Karlsruhe Institute of Technology

Maria Casapu

Karlsruhe Institute of Technology

Matteo Cargnello

Stanford University

Arun S. Asundi

SLAC National Accelerator Laboratory

Erisa Saraçi

Karlsruhe Institute of Technology

Stacey F. Bent

Stanford University

Henning Lichtenberg

Hochschule Niederrhein

Andreas Gremminger

Karlsruhe Institute of Technology

Cooperative Institutions

Karlsruhe Institute of Technology

Stanford University

SLAC National Accelerator Laboratory

Interface (United States)

Technical University of Denmark

University of California, Berkeley

Lawrence Berkeley National Laboratory

Fritz Haber Institute of the Max Planck Society

Stanford Synchrotron Radiation Lightsource

Karlsruhe University of Education

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Operando spatially- and time-resolved XAS and valence-to-core XES to study the mechanism of the NH₃-SCR over Fe-zeolites

Dmitry E. Doronkin Hudson Wallace Pereira de Carvalho Alexey Boubnov Tobias Günter Maria Casapu

X-ray absorption spectroscopy

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Postshock Thermally Induced Transformations in Experimentally Shocked Magnetite

Geochemistry Geophysics Geosystems (2018)

Agnes Kontny Б. Резник Alexey Boubnov Jörg Göttlicher Ralph Steininger

Abstract We studied the effect of 973 K heating in argon atmosphere on the magnetic and structural properties of a magnetite‐bearing ore, which was previously exposed to laboratory shock waves between 5 and 30 GPa. For this purpose magnetic properties were studied using temperature‐dependent magnetic susceptibility, magnetic hysteresis and low‐temperature saturation isothermal remanent magnetization. Structural properties of magnetite were analyzed using X‐ray diffraction, high‐resolution scanning electron microscopy and synchrotron‐assisted X‐ray absorption spectroscopy. The shock‐induced changes include magnetic domain size reduction due to brittle and ductile deformation features and an increase in Verwey transition temperature due to lattice distortion. After heating, the crystal lattice is relaxed and apparent crystallite size is increased suggesting a recovery of lattice defects documented by a mosaic recrystallization texture. The structural changes correlate with modifications in magnetic domain state recorded by temperature‐dependent magnetic susceptibility, hysteresis properties and low‐temperature saturation isothermal remanent magnetization. These alterations in both, magnetic and structural properties of magnetite can be used to assess impact‐related magnetic anomalies in impact structures with a high temperature overprint.

10.1002/2017gc007331

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Increased Ir–Ir Interaction in Iridium Oxide during the Oxygen Evolution Reaction at High Potentials Probed by Operando Spectroscopy

ACS Catalysis (2021)

Steffen Czioska Alexey Boubnov Daniel Escalera‐López Janis Geppert Alexandra Zagalskaya

The structure of IrO2 during the oxygen evolution reaction (OER) was studied by operando X-ray absorption spectroscopy (XAS) at the Ir L3-edge to gain insight into the processes that occur during the electrocatalytic reaction at the anode during water electrolysis. For this purpose, calcined and uncalcined IrO2 nanoparticles were tested in an operando spectroelectrochemical cell. In situ XAS under different applied potentials uncovered strong structural changes when changing the potential. Modulation excitation spectroscopy combined with XAS enhanced the information on the dynamic changes significantly. Principal component analysis (PCA) of the resulting spectra as well as FEFF9 calculations uncovered that both the Ir L3-edge energy and the white line intensity changed due to the formation of oxygen vacancies and lower oxidation state of iridium at higher potentials, respectively. The deconvoluted spectra and their components lead to two different OER modes. It was observed that at higher OER potentials, the well-known OER mechanisms need to be modified, which is also associated with the stabilization of the catalyst, as confirmed by in situ inductively coupled plasma mass spectrometry (ICP-MS). At these elevated OER potentials above 1.5 V, stronger Ir–Ir interactions were observed. They were more dominant in the calcined IrO2 samples than in the uncalcined ones. The stronger Ir–Ir interaction upon vacancy formation is also supported by theoretical studies. We propose that this may be a crucial factor in the increased dissolution stability of the IrO2 catalyst after calcination. The results presented here provide additional insights into the OER in acid media and demonstrate a powerful technique for quantifying the differences in mechanisms on different OER electrocatalysts. Furthermore, insights into the OER at a fundamental level are provided, which will contribute to further understanding of the reaction mechanisms in water electrolysis.

Oxygen evolution

X-ray absorption spectroscopy

XANES

10.1021/acscatal.1c02074

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Citations (104)

Effect of annealing on intrinsic magnetic properties in experimentally shocked magnetite

EGU General Assembly Conference Abstracts (2017)

Agnes Kontny Б. Резник Alexey Boubnov Jörg Göttlicher Ralph Steininger

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The SCR of NOx with NH3 Examined by Novel X-ray Emission and X-ray Absorption Methods

Topics in Catalysis (2016)

Tobias Günter Dmitry E. Doronkin Alexey Boubnov Hudson Wallace Pereira de Carvalho Maria Casapu

X-ray absorption spectroscopy

XANES

10.1007/s11244-016-0561-7

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Citations (26)

Understanding Support Effects of ZnO‐Promoted Co Catalysts for Syngas Conversion to Alcohols Using Atomic Layer Deposition

ChemCatChem (2020)

Sindhu S. Nathan Arun S. Asundi Joseph A. Singh Adam S. Hoffman Alexey Boubnov

Abstract Co 2 C, an emerging catalyst for the conversion of syngas to oxygenates, shows support‐sensitive behavior that has not yet been fully explained. Here, we characterize Co catalysts modified with ZnO atomic layer deposition on SiO 2 , carbon, CeO 2 , and Al 2 O 3 supports. We find that under syngas conditions, ZnO‐promoted Co transforms into Co 2 C on SiO 2 , carbon, and CeO 2 , but not on Al 2 O 3 . Moreover, the support affects the extent of carburization: while the SiO 2 ‐supported catalyst carburizes completely, carbon‐ and CeO 2 ‐supported catalysts show incomplete conversion of Co to Co 2 C. These three catalysts also exhibit different oxygenate selectivities. In contrast, the modified Al 2 O 3 ‐supported catalyst retains the Fischer‐Tropsch catalytic properties of metallic Co. By depositing increasing amounts of Al 2 O 3 by ALD on the SiO 2 support, decreasing Co 2 C formation and oxygenate selectivity occurs. In‐situ XANES reveals that Al 2 O 3 prevents Co 2 C formation by enabling the ZnO to restructure into ZnAl 2 O 4 during reduction. Thus, in addition to modifying the active catalyst phase, the promoter can also strongly interact with the support, significantly impacting catalyst performance.

Oxygenate

Fischer–Tropsch process

Carbon fibers

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Deposition

10.1002/cctc.202001630

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Investigation of the active sites of MoS2 based hydrotreating catalysts by modulated excitation X-ray absorption spectroscopy

Abhijeet Gaur T. Da̧broś Martin Høj Alexey Boubnov T. Prüßmann

X-ray absorption spectroscopy

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Catalysis by Single Metal Atoms: What is All the Fuss About?

Synchrotron Radiation News (2019)

Simon R. Bare Adam S. Hoffman Alexey Boubnov

"Catalysis by Single Metal Atoms: What is All the Fuss About?." Synchrotron Radiation News, 32(1), pp. 22–23

10.1080/08940886.2019.1559598

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Atomically Dispersed Reduced Graphene Aerogel-Supported Iridium Catalyst with an Iridium Loading of 14.8 wt %

ACS Catalysis (2019)

Melike Babucci F. Eylul Sarac Oztuna Louise M. Debefve Alexey Boubnov Simon R. Bare

Atomically dispersed iridium complexes were anchored on a reduced graphene aerogel (rGA) by the reaction of Ir(CO)2(acac) [acac = acetonylacetonato] with oxygen-containing groups on the rGA. Characterization by X-ray absorption, infrared, and X-ray photoelectron spectroscopies and atomic resolution aberration-corrected scanning transmission electron microscopy demonstrates atomically dispersed iridium, at the remarkably high loading of 14.8 wt %. The rGA support offers sites for metal bonding comparable to those of metal oxides, but with the advantages of high density and a relatively high degree of uniformity, as indicated by the same turnover frequencies for catalytic hydrogenation of ethylene at low and high iridium loadings. The atomic dispersion at a high metal loading—and the high density of catalytic sites per unit of reactor volume, a key criterion for practical catalysts—set this catalyst apart from those reported.

10.1021/acscatal.9b02231

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Citations (62)

Controlling catalytic activity and selectivity for partial hydrogenation by tuning the environment around active sites in iridium complexes bonded to supports

Chemical Science (2019)

Melike Babucci Chia‐Yu Fang Jorge E. Perez-Aguilar Adam S. Hoffman Alexey Boubnov

Enveloping atomically dispersed supported iridium with the choice of ionic liquid molecular sheaths and supports controls the catalytic performance.

10.1039/c8sc05287e

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Citations (44)