6 results on '"J. W. Hans Niemantsverdriet"'
Search Results
2. Mechanistic insight into carbon-carbon bond formation on cobalt under simulated Fischer-Tropsch synthesis conditions
- Author
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Hans Fredriksson, J. W. Hans Niemantsverdriet, Michael A. Gleeson, Devyani Sharma, C. J. Kees-Jan Weststrate, and Daniel Garcia Rodriguez
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Ethylene ,Reaction kinetics and dynamics ,Science ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,Heterogeneous catalysis ,Photochemistry ,01 natural sciences ,General Biochemistry, Genetics and Molecular Biology ,Article ,Catalysis ,chemistry.chemical_compound ,X-ray photoelectron spectroscopy ,lcsh:Science ,chemistry.chemical_classification ,Multidisciplinary ,Catalytic mechanisms ,Fischer–Tropsch process ,General Chemistry ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Hydrocarbon ,chemistry ,Carbon–carbon bond ,lcsh:Q ,0210 nano-technology ,Cobalt - Abstract
Facile C-C bond formation is essential to the formation of long hydrocarbon chains in Fischer-Tropsch synthesis. Various chain growth mechanisms have been proposed previously, but spectroscopic identification of surface intermediates involved in C-C bond formation is scarce. We here show that the high CO coverage typical of Fischer-Tropsch synthesis affects the reaction pathways of C2Hx adsorbates on a Co(0001) model catalyst and promote C-C bond formation. In-situ high resolution x-ray photoelectron spectroscopy shows that a high CO coverage promotes transformation of C2Hx adsorbates into the ethylidyne form, which subsequently dimerizes to 2-butyne. The observed reaction sequence provides a mechanistic explanation for CO-induced ethylene dimerization on supported cobalt catalysts. For Fischer-Tropsch synthesis we propose that C-C bond formation on the close-packed terraces of a cobalt nanoparticle occurs via methylidyne (CH) insertion into long chain alkylidyne intermediates, the latter being stabilized by the high surface coverage under reaction conditions., The mechanism by which C-C bonds form during Fischer-Tropsch synthesis remains debated while spectroscopic identification of reaction intermediates remains scarce. Here, the authors identify alkylidynes as reactive intermediates for C-C bond formation on cobalt terrace sites and moreover show that these intermediates are stabilized by the high surface coverage typical for Fischer-Tropsch synthesis.
- Published
- 2020
3. Photosystem II Acts as a Spin-Controlled Electron Gate during Oxygen Formation and Evolution
- Author
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Yunzhe Jiao, Jose Gracia, Tingbin Lim, Ryan Sharpe, and J. W. Hans Niemantsverdriet
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Spin states ,Photosystem II ,Chemistry ,Oxygen evolution ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,Biochemistry ,Acceptor ,Catalysis ,0104 chemical sciences ,Artificial photosynthesis ,Condensed Matter::Materials Science ,Electron transfer ,Colloid and Surface Chemistry ,Unpaired electron ,Physics::Chemical Physics ,0210 nano-technology ,Spin (physics) - Abstract
The oxygen evolution complex (OEC) of photosystem II (PSII) is intrinsically more active than any synthetic alternative for the oxygen evolution reaction (OER). A crucial question to solve for the progress of artificial photosynthesis is to understand the influential interactions during water oxidation in PSII. We study the principles of interatomic electron transfer steps in OER, with emphasis on exchange interactions, revealing the influence of delocalizing ferromagnetic spin potentials during the catalytic process. The OEC is found to be an exchange coupled mixed-valence electron-spin acceptor where its orbital physics determine the unique activity of PSII. The two unpaired electrons needed in the triplet O2 molecule interact with the high spin state of the catalyst via exchange interactions; the optimal ferromagnetic catalyst and the resulting radical intermediates are spin paired. As a result, the active center of the CaMn4O5 cofactor, stimulated by the driving potential provided by photons, works as...
- Published
- 2017
4. Efficient Solar-Driven Hydrogen Transfer by Bismuth-Based Photocatalyst with Engineered Basic Sites
- Author
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Ren Su, Shujie Zhu, Lai Chin Wu, Mathias S. Hvid, Jørgen Skibsted, Nina Lock, Chao Li, Yongwang Li, J. W. Hans Niemantsverdriet, Flemming Besenbacher, Yanbin Shen, and Yitao Dai
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Hydrogen transfer ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,Biochemistry ,Redox ,Catalysis ,0104 chemical sciences ,Bismuth ,Nitrobenzene ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,chemistry ,Photocatalysis ,Irradiation ,0210 nano-technology ,Selectivity ,Visible spectrum - Abstract
Photocatalytic organic conversions involving a hydrogen transfer (HT) step have attracted much attention, but the efficiency and selectivity under visible light irradiation still needs to be significantly enhanced. Here we have developed a noble metal-free, basic-site engineered bismuth oxybromide [Bi24O31Br10(OH)] that can accelerate the photocatalytic HT step in both reduction and oxidation reactions, i.e., nitrobenzene to azo/azoxybenzene, quinones to quinols, thiones to thiols, and alcohols to ketones under visible light irradiation and ambient conditions. Remarkably, quantum efficiencies of 42% and 32% for the nitrobenzene reduction can be reached under 410 and 450 nm irradiation, respectively. The Bi24O31Br10(OH) photocatalyst also exhibits excellent performance in up-scaling and stability under visible light and even solar irradiation, revealing economic potential for industrial applications.
- Published
- 2018
5. Cu model catalyst dynamics and CO oxidation kinetics studied by simultaneous in situ UV-Vis and mass spectroscopy
- Author
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Hans Fredriksson, J. W. Hans Niemantsverdriet, Yibin Bu, and Control Systems
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in situ UV-vis and mass spectroscopy ,Chemistry ,Cu model catalyst ,Analytical chemistry ,02 engineering and technology ,General Chemistry ,Activation energy ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,CO oxidation ,Catalysis ,0104 chemical sciences ,oxidation state of Cu catalyst ,Metal ,Ultraviolet visible spectroscopy ,Oxidation state ,visual_art ,visual_art.visual_art_medium ,Reactivity (chemistry) ,Microreactor ,kinetic measurements ,0210 nano-technology ,Localized surface plasmon - Abstract
The oxidation state of Cu nanoparticles during CO oxidation in CO + O2 gas mixtures was sensitively monitored via localized surface plasmon resonances. A microreactor, equipped with in situ UV-vis and mass spectrometry, was developed and used for the measurements. Cu nanoparticles of ∼30 nm average diameter were supported on optically transparent, planar quartz wafers. The aim of the study is 2-fold: (i) to demonstrate the performance and usefulness of the setup and (ii) to use the combined strength of model catalysts and in situ measurements to investigate the correlation between the catalyst oxidation state and its reactivity. Metallic Cu is significantly more active than both Cu(I) and Cu(II) oxides. The metallic Cu phase is only maintained under conditions where close to full oxygen conversion is achieved. This implies that kinetic measurements, aimed at determining the apparent activation energy for metallic Cu under realistic steady-state conditions, are difficult or impossible to perform.
- Published
- 2016
6. Detangling catalyst modification reactions from the oxygen evolution reaction by online mass spectrometry
- Author
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Tiny Verhoeven, M. Pilar del Río, Paula Abril, Dennis G. H. Hetterscheid, Konstantin G. Kottrup, J. W. Hans Niemantsverdriet, Cristina Tejel, Cornelis J. M. van der Ham, Inorganic Materials & Catalysis, Gobierno de Aragón, European Commission, and Ministerio de Economía y Competitividad (España)
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Evolution ,Reaction ,010405 organic chemistry ,Inorganic chemistry ,Oxygen evolution ,chemistry.chemical_element ,General Chemistry ,Iridium oxide ,010402 general chemistry ,Electrochemistry ,Mass spectrometry ,01 natural sciences ,Oxygen ,Catalysis ,0104 chemical sciences ,chemistry ,X-ray photoelectron spectroscopy ,oxygen evolution reaction ,Iridium - Abstract
Here we showcase the synthesis and catalytic response of the anionic iridium(III) complex [IrCl(pic)(MeOH)] ([1], pic = picolinate) toward the evolution of oxygen. Online electrochemical mass spectrometry experiments illustrate that an initial burst of CO due to catalyst degradation is expelled before the oxygen evolution reaction commences. Electrochemical features and XPS analysis illustrate the presence of iridium oxide, which is the true active species., Generous financial support from the MINECO/FEDER (CTQ2014-53033-P; C.T.) and Gobierno de Aragon/FSE (GA/FSE, Inorganic Molecular Architecture Group, E70; C.T.) is gratefully acknowledged. P.A. and M.P.d.R. thank the MINECO/FEDER for a fellowship and a JdC contract, respectively.
- Published
- 2016
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