10 results on '"Ivan, Khalakhan"'
Search Results
2. Metal–Support Interaction and Charge Distribution in Ceria-Supported Au Particles Exposed to CO
- Author
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Oleksii Bezkrovnyi, Albert Bruix, Dominik Blaumeiser, Lesia Piliai, Simon Schötz, Tanja Bauer, Ivan Khalakhan, Tomáš Skála, Peter Matvija, Piotr Kraszkiewicz, Mirosława Pawlyta, Mykhailo Vorokhta, Iva Matolínová, Jörg Libuda, Konstantin M. Neyman, and Leszek Kȩpiński
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Catalysts ,General Chemical Engineering ,Catalitzadors ,Materials Chemistry ,Or ,Oxides ,Gold ,General Chemistry ,Òxids - Abstract
Understanding how reaction conditions affect metal-support interactions in catalytic materials is one of the most challenging tasks in heterogeneous catalysis research. Metal nanoparticles and their supports often undergo changes in structure and oxidation state when exposed to reactants, hindering a straightforward understanding of the structure-activity relations using only ex situ or ultrahigh vacuum techniques. Overcoming these limitations, we explored the metal-support interaction between gold nanoparticles and ceria supports in ultrahigh vacuum and after exposure to CO. A combination of in situ methods (on powder and model Au/CeO2 samples) and theoretical calculations was applied to investigate the gold/ceria interface and its reactivity toward CO exposure. X-ray photoelectron spectroscopy measurements rationalized by first-principles calculations reveal a distinctly inhomogeneous charge distribution, with Au+ atoms in contact with the ceria substrate and neutral Au0 atoms at the surface of the Au nanoparticles. Exposure to CO partially reduces the ceria substrate, leading to electron transfer to the supported Au nanoparticles. Transferred electrons can delocalize among the neutral Au atoms of the particle or contribute to forming inert Auδ− atoms near oxygen vacancies at the ceria surface. This charge redistribution is consistent with the evolution of the vibrational frequencies of CO adsorbed on Au particles obtained using diffuse reflectance infrared Fourier transform spectroscopy.
- Published
- 2022
3. Successive Vapor-Phase Guerbet Condensation of Ethanol and 1-Butanol to 2-Ethyl-1-hexanol over Hydroxyapatite Catalysts in a Flow Reactor
- Author
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Oksana V. Zikrata, Olga V. Larina, Karina V. Valihura, Pavlo I. Kyriienko, Dmytro Yu. Balakin, Ivan Khalakhan, Katerina Veltruská, Andraž Krajnc, Gregor Mali, Sergiy O. Soloviev, and Svitlana M. Orlyk
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Renewable Energy, Sustainability and the Environment ,General Chemical Engineering ,Environmental Chemistry ,General Chemistry - Published
- 2021
4. Interplay Among Dealloying, Ostwald Ripening, and Coalescence in PtXNi100–X Bimetallic Alloys under Fuel-Cell-Related Conditions
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Daniel J. S. Sandbeck, Heinz Amenitsch, Ivan Khalakhan, Serhiy Cherevko, Marco Bogar, Yurii Yakovlev, Iva Matolínová, Bogar, Marco, Yakovlev, Yurii, John Seale Sandbeck, Daniel, Cherevko, Serhiy, Matolínová, Iva, Amenitsch, Heinz, and Khalakhan, Ivan
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Ostwald ripening ,particle coalescence ,Materials science ,General Chemistry ,in situ grazing-incidence small-angle X-ray scattering ,Catalysis ,fuel cell ,symbols.namesake ,Chemical engineering ,symbols ,Fuel cells ,Coalescence (chemistry) ,bimetallic catalyst dealloying ,Bimetallic strip ,degradation - Abstract
Platinum-based bimetallic alloys have been largely investigated during the last few years as a valid alternative to bare Pt cathode catalysts for proton-exchange membrane fuel cells (PEMFCs) to improve their cost-efficiency. Nonetheless, Pt bimetallic alloys are characterized by a reduced stability, which is poorly understood at a fundamental level. It is thus essential to describe the entire chain of interconnected degradation mechanisms to formulate a comprehensive model of catalyst degradation that will help interpret bimetallic alloy behavior in real complex fuel cell systems. By combining in situ inductively coupled plasma mass spectroscopy, in situ grazing-incidence small-angle X-ray scattering, and ex situ scanning electron microscopy, we have studied the morphological evolution of PtXNi100–X model catalysts with different Ni contents (ranging from 0 to 75%) undergoing potentiodynamic cycling to two different upper potentials mimicking the different operational conditions of a PEMFC: 1.0 and 1.3 VRHE. Data analysis allowed us to develop a methodology to distinguish the influence of Ni dissolution, particle coalescence, and Ostwald ripening on particle size distribution and interparticle distance and to realize time-dependent interplay maps to highlight the timeframe in which the aforementioned phenomena are prevailing or coexisting. Results show that Ni dissolution is the only phenomenon inducing morphological evolution when the lower upper potential is chosen. On the contrary, at 1.3 VRHE, Ni dissolution is rapidly overcome by particle coalescence at first and by Ostwald ripening in the later stages of the investigated time range. The onset of every phenomenon was found to occur earlier in time for larger values of Ni concentrations.
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- 2021
5. Carbon-Supported Mg–Al Oxide Hybrid Catalysts for Aqueous Ethanol Conversion into 1-Butanol in a Flow Reactor
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P. S. Yaremov, Dmytro Yu. Balakin, S. M. Orlyk, Olga V. Larina, Katerina Veltruska, Ivan Khalakhan, Nataliya D. Shcherban, Pavlo I. Kyriienko, and Sergiy O. Soloviev
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chemistry.chemical_compound ,chemistry ,Chemical engineering ,General Chemical Engineering ,Butanol ,Oxide ,chemistry.chemical_element ,General Chemistry ,Aqueous ethanol ,Carbon ,Industrial and Manufacturing Engineering ,Catalysis - Published
- 2021
6. Evolution of the PtNi Bimetallic Alloy Fuel Cell Catalyst under Simulated Operational Conditions
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Daniel J. S. Sandbeck, Milan Dopita, Marco Bogar, Ivan Khalakhan, Yurii Yakovlev, Mykhailo Vorokhta, Heinz Amenitsch, Serhiy Cherevko, Peter Kúš, and Iva Matolínová
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Ostwald ripening ,Materials science ,Alloy ,02 engineering and technology ,Electrolyte ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,0104 chemical sciences ,Corrosion ,Catalysis ,symbols.namesake ,Chemical engineering ,engineering ,symbols ,General Materials Science ,Thin film ,0210 nano-technology ,Bimetallic strip - Abstract
Comprehensive understanding of the catalyst corrosion dynamics is a prerequisite for the development of an efficient cathode catalyst in proton-exchange membrane fuel cells. To reach this aim, the behavior of fuel cell catalysts must be investigated directly under reaction conditions. Herein, we applied a strategic combination of in situ/online techniques: in situ electrochemical atomic force microscopy, in situ grazing incidence small angle X-ray scattering, and electrochemical scanning flow cell with online detection by inductively coupled plasma mass spectrometry. This combination of techniques allows in-depth investigation of the potential-dependent surface restructuring of a PtNi model thin film catalyst during potentiodynamic cycling in an aqueous acidic electrolyte. The study reveals a clear correlation between the upper potential limit and structural behavior of the PtNi catalyst, namely, its dealloying and coarsening. The results show that at 0.6 and 1.0 VRHE upper potentials, the PtNi catalyst essentially preserves its structure during the entire cycling procedure. The crucial changes in the morphology of PtNi layers are found to occur at 1.3 and 1.5 VRHE cycling potentials. Strong dealloying at the early stage of cycling is substituted with strong coarsening of catalyst particles at the later stage. The coarsening at the later stage of cycling is assigned to the electrochemical Ostwald ripening process.
- Published
- 2020
7. Unraveling the Surface Chemistry and Structure in Highly Active Sputtered Pt3Y Catalyst Films for the Oxygen Reduction Reaction
- Author
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Milan Dopita, Tomáš Skála, Rosemary Brown, Konstantin M. Neyman, Ivan Khalakhan, Thomas Vonderach, Iva Matolínová, Henrik Grönbeck, Niklas Lindahl, Vladimír Matolín, Mykhailo Vorokhta, and Björn Wickman
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Materials science ,Oxide ,chemistry.chemical_element ,Proton exchange membrane fuel cell ,02 engineering and technology ,Yttrium ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Overlayer ,Catalysis ,chemistry.chemical_compound ,chemistry ,X-ray photoelectron spectroscopy ,Chemical engineering ,General Materials Science ,Thin film ,0210 nano-technology ,Platinum - Abstract
Platinum is the most widely used and best performing sole element for catalyzing the oxygen reduction reaction (ORR) in low-temperature fuel cells. Although recyclable, there is a need to reduce the amount used in current fuel cells for their extensive uptake in society. Alloying platinum with rare-earth elements such as yttrium can provide an increase in activity of more than seven times, reducing the amount of platinum and the total amount of catalyst material required for the ORR. As yttrium is easily oxidized, exposure of the Pt-Y catalyst layer to air causes the formation of an oxide layer that can be removed during acid treatment, leaving behind a highly active pure platinum overlayer. This paper presents an investigation of the overlayer composition and quality of Pt3Y films sputtered from an alloy target. The Pt3Y catalyst surface is investigated using synchrotron radiation X-ray photoelectron spectroscopy before and after acid treatment. A new substoichiometric oxide component is identified. The oxide layer extends into the alloy surface, and although it is not completely removed with acid treatment, the catalyst still achieves the expected high ORR activity. Other surface-sensitive techniques show that the sputtered films are smooth and bulk X-ray diffraction reveals many defects and high microstrain. Nevertheless, sputtered Pt3Y exhibits a very high activity regardless of the film's oxide content and imperfections, highlighting Pt3Y as a promising catalyst. The obtained results will help to support its integration into fuel cell systems.
- Published
- 2019
8. New Insight into the Gas-Sensing Properties of CuOx Nanowires by Near-Ambient Pressure XPS
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Ján Lančok, Jan Vlček, Kateřina Jarkovská, Pavel Hozák, Přemysl Fitl, Jana Cibulková, Iva Matolínová, Maryna Vorokhta, Mykhailo Vorokhta, David Tomeček, Martin Vrňata, Michal Novotný, Ivan Khalakhan, and Jan Fara
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Materials science ,Nanowire ,Heterojunction ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,General Energy ,X-ray photoelectron spectroscopy ,Chemical engineering ,Physical and Theoretical Chemistry ,0210 nano-technology ,Ambient pressure - Abstract
This article presents an investigation of the sensing properties of chemiresistors based on Cu2O/CuO core–shell nanowires containing p–p′ heterojunctions. The nanowires were synthesized by a conven...
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- 2019
9. Nanoscale Morphological and Structural Transformations of PtCu Alloy Electrocatalysts during Potentiodynamic Cycling
- Author
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Ivan Khalakhan, Milan Dopita, Mykhailo Vorokhta, Olaf Brummel, Manon Bertram, Iva Matolínová, Vladimír Matolín, Peter Kúš, Yurii Yakovlev, Jörg Libuda, and Fabian Waidhas
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Materials science ,Absorption spectroscopy ,Alloy ,Proton exchange membrane fuel cell ,chemistry.chemical_element ,02 engineering and technology ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Electrochemistry ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Catalysis ,General Energy ,Chemical engineering ,chemistry ,engineering ,Physical and Theoretical Chemistry ,Thin film ,0210 nano-technology ,Platinum ,Bimetallic strip - Abstract
PtCu bimetallic alloys are known to provide better activity than pure platinum in proton exchange membrane fuel cells. However, such catalysts undergo complex degradation processes during fuel cell operation, resulting in deterioration of their activity. By using in situ electrochemical (EC) atomic force microscopy combined with in situ EC infrared reflection absorption spectroscopy, we provide a comprehensive investigation of morphological and structural transformations of PtCu model thin film catalysts during accelerated degradation tests (ADTs). The ADTs consist of potentiodynamic cycling to three different upper potentials relevant for different modes of fuel cell operation. The results show that, depending on the upper potential limit, PtCu alloy electrocatalysts are subject to drastic changes in the surface composition, morphology, and structure.
- Published
- 2018
10. Stabilization of Small Platinum Nanoparticles on Pt–CeO2 Thin Film Electrocatalysts During Methanol Oxidation
- Author
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Roman Fiala, Mykhailo Vorokhta, Olaf Brummel, Georgi N. Vayssilov, Konstantin M. Neyman, Firas Faisal, Jörg Libuda, Hristiyan A. Aleksandrov, Sergey M. Kozlov, Gábor Kovács, Alberto Figueroba, Martin Dubau, Fabian Waidhas, Vladimír Matolín, and Ivan Khalakhan
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Materials science ,Inorganic chemistry ,Proton exchange membrane fuel cell ,Infrared spectroscopy ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Platinum nanoparticles ,Electrochemistry ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Catalysis ,General Energy ,X-ray photoelectron spectroscopy ,Physical and Theoretical Chemistry ,Thin film ,0210 nano-technology ,Spectroscopy - Abstract
Pt-doped CeOx thin film electrocatalysts have recently been shown to exhibit high activity and stability at the anode of proton exchange membrane fuel cells (PEM-FC). To identify the role of the Pt dopant and the origin of the high stability of Pt–CeOx films, we applied electrochemical in situ IR spectroscopy on Pt–CeOx model thin film catalysts during methanol (1 M methanol) oxidation. The model catalysts were prepared by magnetron cosputtering of Pt (9–21 atom %) and CeO2 onto clean and carbon-coated Au supports. All samples were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS) before and after reaction. At pH 1 (0.1 M HClO4) the Pt–CeOx dissolves partially during potential cycling, whereas the films are largely stable at pH 6 (0.1 M phosphate buffer). Electrochemical IR spectroscopy of the adsorbed CO shows that metallic Pt is formed on all Pt–CeOx samples during methanol oxidation. In comparison to Pt(111), Pt a...
- Published
- 2016
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