Publications
2024
Haunold, Thomas; Anić, Krešimir; Genest, Alexander; Rameshan, Christoph; Roiaz, Matteo; Li, Hao; Wicht, Thomas; Knudsen, Jan; Rupprechter, Günther
Journal ArticleOpen AccessIn: Surface Science, 2024.
Abstract | Links | BibTeX | Tags: P08, P10
@article{Haunold_2024a,
title = {Hydroxylation of an ultrathin Co_{3}O_{4}(111) film on Ir(100) studied by in situ ambient pressure XPS and DFT},
author = {Thomas Haunold and Krešimir Anić and Alexander Genest and Christoph Rameshan and Matteo Roiaz and Hao Li and Thomas Wicht and Jan Knudsen and Günther Rupprechter},
url = {https://doi.org/10.1016/j.susc.2024.122618},
year = {2024},
date = {2024-09-26},
urldate = {2024-09-26},
journal = {Surface Science},
abstract = {In the present work, we have studied the interaction of water with spinel cobalt oxide (Co_{3}O_{4}), an effect which has been considered a major cause of its catalytic deactivation. Employing a Co_{3}O_{4}(111) model thin film grown on Ir(100) in (ultra)high vacuum, and ambient pressure X-ray photoelectron spectroscopy (APXPS), hydroxylation in 0.5 mbar H_{2}O vapor at room temperature was monitored in real time. The surface hydroxyl (OH) coverage was determined via two different models based (i) on the termination of a pristine and OH-covered Co_{3}O_{4}(111) surface as derived from density functional theory (DFT) calculations, and (ii) on a homogeneous cobalt oxyhydroxide (CoO(OH)) overlayer. Langmuir pseudo-second-order kinetics were applied to characterize the OH evolution with time, suggesting two regimes of chemisorption at the mosaic-like Co_{3}O_{4}(111) film: (i) plateaus, which were quickly saturated by OH, followed by (ii) slow hydroxylation in the “cracks” of the thin film. H_{2}O dissociation and OH formation, blocking exposed Co^{2+} ions and additionally consuming surface lattice oxygen, respectively, may thus account for catalyst deactivation by H_{2}O traces in reactive feeds.},
keywords = {P08, P10},
pubstate = {published},
tppubtype = {article}
}
In the present work, we have studied the interaction of water with spinel cobalt oxide (Co3O4), an effect which has been considered a major cause of its catalytic deactivation. Employing a Co3O4(111) model thin film grown on Ir(100) in (ultra)high vacuum, and ambient pressure X-ray photoelectron spectroscopy (APXPS), hydroxylation in 0.5 mbar H2O vapor at room temperature was monitored in real time. The surface hydroxyl (OH) coverage was determined via two different models based (i) on the termination of a pristine and OH-covered Co3O4(111) surface as derived from density functional theory (DFT) calculations, and (ii) on a homogeneous cobalt oxyhydroxide (CoO(OH)) overlayer. Langmuir pseudo-second-order kinetics were applied to characterize the OH evolution with time, suggesting two regimes of chemisorption at the mosaic-like Co3O4(111) film: (i) plateaus, which were quickly saturated by OH, followed by (ii) slow hydroxylation in the “cracks” of the thin film. H2O dissociation and OH formation, blocking exposed Co2+ ions and additionally consuming surface lattice oxygen, respectively, may thus account for catalyst deactivation by H2O traces in reactive feeds.
Birschitzky, Viktor C.; Leoni, Luca; Reticcioli, Michele; Franchini, Cesare
Machine Learning Small Polaron Dynamics
Journal ArticleOpen AccessSubmittedarXivIn: arXiv, 2024.
Abstract | Links | BibTeX | Tags: P07
@article{Birschitzky_2024b,
title = {Machine Learning Small Polaron Dynamics},
author = {Viktor C. Birschitzky and Luca Leoni and Michele Reticcioli and Cesare Franchini},
url = {https://arxiv.org/abs/2409.16179},
year = {2024},
date = {2024-09-24},
journal = {arXiv},
abstract = {Polarons are crucial for charge transport in semiconductors, significantly impacting material properties and device performance. The dynamics of small polarons can be investigated using first-principles molecular dynamics. However, the limited timescale of these simulations presents a challenge for adequately sampling infrequent polaron hopping events. Here, we introduce a message-passing neural network that learns the polaronic potential energy surface by encoding the polaronic state, allowing for simulations of polaron hopping dynamics at the nanosecond scale. By leveraging the statistical significance of the long timescale, our framework can accurately estimate polaron (anisotropic) mobilities and activation barriers in prototypical polaronic oxides across different scenarios (hole polarons in rocksalt MgO and electron polarons in pristine and F-doped rutile TiO_{2}) in excellent agreement with experimental observations.},
keywords = {P07},
pubstate = {published},
tppubtype = {article}
}
Polarons are crucial for charge transport in semiconductors, significantly impacting material properties and device performance. The dynamics of small polarons can be investigated using first-principles molecular dynamics. However, the limited timescale of these simulations presents a challenge for adequately sampling infrequent polaron hopping events. Here, we introduce a message-passing neural network that learns the polaronic potential energy surface by encoding the polaronic state, allowing for simulations of polaron hopping dynamics at the nanosecond scale. By leveraging the statistical significance of the long timescale, our framework can accurately estimate polaron (anisotropic) mobilities and activation barriers in prototypical polaronic oxides across different scenarios (hole polarons in rocksalt MgO and electron polarons in pristine and F-doped rutile TiO2) in excellent agreement with experimental observations.
Kovács, Péter; Heid, Esther; Madsen, Georg K. H.
LoGAN: Local generative adversarial network for novel structure prediction
Journal ArticleOpen AccessIn: Machine Learning: Science and Technology, vol. 5, no. 3, pp. 035079, 2024.
Abstract | Links | BibTeX | Tags: P09
@article{Kovacs_2024a,
title = {LoGAN: Local generative adversarial network for novel structure prediction},
author = {Péter Kovács and Esther Heid and Georg K. H. Madsen},
url = {https://iopscience.iop.org/article/10.1088/2632-2153/ad7a4d},
doi = {10.1088/2632-2153/ad7a4d},
year = {2024},
date = {2024-09-23},
urldate = {2024-09-23},
journal = {Machine Learning: Science and Technology},
volume = {5},
number = {3},
pages = {035079},
abstract = {The efficient generation and filtering of candidate structures for new materials is becoming increasingly important as starting points for computational studies. In this work, we introduce an approach to Wasserstein generative adversarial networks for predicting unique crystal and molecular structures. Leveraging translation- and rotation-invariant atom-centered local descriptors address some of the major challenges faced by similar methods. Our models require only small sets of known structures as training data. Furthermore, the approach is able to generate both non-periodic and periodic structures based on local coordination. We showcase the data efficiency and versatility of the LoGAN approach by recovering all stable C_{5}H_{12}O isomers using only 39 C_{4}H_{10}O and C_{6}H_{14}O training examples, as well as all known low-energy SiO_{2} crystal structures utilizing only 167 training examples of other SiO_{2} crystal structures. We also introduce a filtration technique to reduce the computational cost of subsequent characterization steps by selecting samples from unique basins on the potential energy surface, which allows to minimize the number of geometry relaxations needed after structure generation. LoGAN thus represents a new, versatile approach to generative modeling of crystal and molecular structures in the low-data regime, and is available open-source.},
howpublished = {ChemRxiv},
keywords = {P09},
pubstate = {published},
tppubtype = {article}
}
The efficient generation and filtering of candidate structures for new materials is becoming increasingly important as starting points for computational studies. In this work, we introduce an approach to Wasserstein generative adversarial networks for predicting unique crystal and molecular structures. Leveraging translation- and rotation-invariant atom-centered local descriptors address some of the major challenges faced by similar methods. Our models require only small sets of known structures as training data. Furthermore, the approach is able to generate both non-periodic and periodic structures based on local coordination. We showcase the data efficiency and versatility of the LoGAN approach by recovering all stable C5H12O isomers using only 39 C4H10O and C6H14O training examples, as well as all known low-energy SiO2 crystal structures utilizing only 167 training examples of other SiO2 crystal structures. We also introduce a filtration technique to reduce the computational cost of subsequent characterization steps by selecting samples from unique basins on the potential energy surface, which allows to minimize the number of geometry relaxations needed after structure generation. LoGAN thus represents a new, versatile approach to generative modeling of crystal and molecular structures in the low-data regime, and is available open-source.
Rafsanjani-Abbasi, Ali; Buchner, Florian; Lewis, Faith J.; Puntscher, Lena; Kraushofer, Florian; Sombut, Panukorn; Eder, Moritz; Pavelec, Jiří; Rheinfrank, Erik; Franceschi, Giada; Birschitzky, Viktor; Riva, Michele; Franchini, Cesare; Schmid, Michael; Diebold, Ulrike; Meier, Matthias; Madsen, Georg K. H.; Parkinson, Gareth S.
Digging Its Own Site: Linear Coordination Stabilizes a Pt1/Fe2O3 Single-Atom Catalyst
Journal ArticleOpen AccessIn: ACS Nano, vol. 18, iss. 39, pp. 26920–26927, 2024.
Abstract | Links | BibTeX | Tags: P02, P04, P07, P09
@article{Rafsanjani_2024a,
title = {Digging Its Own Site: Linear Coordination Stabilizes a Pt_{1}/Fe_{2}O_{3} Single-Atom Catalyst},
author = {Ali Rafsanjani-Abbasi and Florian Buchner and Faith J. Lewis and Lena Puntscher and Florian Kraushofer and Panukorn Sombut and Moritz Eder and Jiří Pavelec and Erik Rheinfrank and Giada Franceschi and Viktor Birschitzky and Michele Riva and Cesare Franchini and Michael Schmid and Ulrike Diebold and Matthias Meier and Georg K. H. Madsen and Gareth S. Parkinson},
url = {https://doi.org/10.1021/acsnano.4c08781},
year = {2024},
date = {2024-09-18},
urldate = {2024-09-18},
journal = {ACS Nano},
volume = {18},
issue = {39},
pages = {26920–26927},
abstract = {Determining the local coordination of the active site is a prerequisite for the reliable modeling of single-atom catalysts (SACs). Obtaining such information is difficult on powder-based systems and much emphasis is placed on density functional theory computations based on idealized low-index surfaces of the support. In this work, we investigate how Pt atoms bind to the (11̅02) facet of α-Fe_{2}O_{3}; a common support material in SACs. Using a combination of scanning tunneling microscopy, X-ray photoelectron spectroscopy, and an extensive computational evolutionary search, we find that Pt atoms significantly reconfigure the support lattice to facilitate a pseudolinear coordination to surface oxygen atoms. Despite breaking three surface Fe–O bonds, this geometry is favored by 0.84 eV over the best configuration involving an unperturbed support. We suggest that the linear O–Pt–O configuration is common in reactive Pt-based SAC systems because it balances thermal stability with the ability to adsorb reactants from the gas phase. Moreover, we conclude that extensive structural searches are necessary to determine realistic active site geometries in single-atom catalysis.},
keywords = {P02, P04, P07, P09},
pubstate = {published},
tppubtype = {article}
}
Determining the local coordination of the active site is a prerequisite for the reliable modeling of single-atom catalysts (SACs). Obtaining such information is difficult on powder-based systems and much emphasis is placed on density functional theory computations based on idealized low-index surfaces of the support. In this work, we investigate how Pt atoms bind to the (11̅02) facet of α-Fe2O3; a common support material in SACs. Using a combination of scanning tunneling microscopy, X-ray photoelectron spectroscopy, and an extensive computational evolutionary search, we find that Pt atoms significantly reconfigure the support lattice to facilitate a pseudolinear coordination to surface oxygen atoms. Despite breaking three surface Fe–O bonds, this geometry is favored by 0.84 eV over the best configuration involving an unperturbed support. We suggest that the linear O–Pt–O configuration is common in reactive Pt-based SAC systems because it balances thermal stability with the ability to adsorb reactants from the gas phase. Moreover, we conclude that extensive structural searches are necessary to determine realistic active site geometries in single-atom catalysis.
Pittenauer, Michael; Rameshan, Raffael; Schrenk, Florian; Wang, Chunlei; Eder, Moritz; Parkinson, Gareth S.; Rameshan, Christoph; Föttinger, Karin
Journal ArticleSubmittedIn: ChemRxiv, 2024.
Abstract | Links | BibTeX | Tags: P04, P10
@article{Pittenauer_2024a,
title = {On the dependence of the catalytic activity of nickel-ferrite nanoparticles in the oxidative dehydrogenation of 2-propanol on the crystallite size},
author = {Michael Pittenauer and Raffael Rameshan and Florian Schrenk and Chunlei Wang and Moritz Eder and Gareth S. Parkinson and Christoph Rameshan and Karin Föttinger},
url = {https://chemrxiv.org/engage/chemrxiv/article-details/670d0de851558a15ef07c30d},
year = {2024},
date = {2024-09-18},
urldate = {2024-09-18},
journal = {ChemRxiv},
abstract = {Nickel ferrite spinel nanoparticles of different crystallite sizes were prepared in a glycine assisted sol-gel autocombustion reaction and characterised by powder x-ray diffraction, attenuated total reflection infrared spectroscopy, near ambient pressure x-ray photoelectron spectroscopy, nitrogen physisorption, hydrogen and carbon monoxide temperature programmed reduction and oxygen and carbon dioxide temperature programmed desorption. A different distribution of Ni^{2+} cations in the tetrahedrally and octahedrally coordinated sites of the spinel lattice and an increased reducibility of the smaller crystallite size sample were identified as the main impacts of different crystallite size. Their catalytic activity in the oxidative dehydrogenation of 2-propanol was investigated by temperature programmed reaction studies using different ratios of 2-propanol:O_{2} as well as of possible parallel and consecutive reactions at atmospheric pressure and maximum 400 °C. Operando-DRIFTS-MS studies at different 2-propanol:O_{2} ratios were carried out under continuous-flow conditions at atmospheric pressure as well. Thereby, the increased reducibility of the small crystallite size sample could be linked to an unselective activity for dehydrogenation yielding acetone and hydrogen, partial oxidation of 2-propanol and acetone, and total combustion leading to a complex network of reactions going on, being further pushed by an excess of oxygen. Ex-situ x-ray diffraction measurements were performed following the temperature programmed reaction experiments. The large crystallite size sample was found to be generally less active, but more selective towards non-oxidative dehydrogenation. Ex-situ x-ray diffraction measurements performed following the temperature programmed reaction experiments confirmed the increased reducibility of the smaller crystallite size sample. In the operando IR studies, 2-propoxide, adsorbed acetone, carbonates and acetates were identified as species occurring in the reaction. },
keywords = {P04, P10},
pubstate = {published},
tppubtype = {article}
}
Nickel ferrite spinel nanoparticles of different crystallite sizes were prepared in a glycine assisted sol-gel autocombustion reaction and characterised by powder x-ray diffraction, attenuated total reflection infrared spectroscopy, near ambient pressure x-ray photoelectron spectroscopy, nitrogen physisorption, hydrogen and carbon monoxide temperature programmed reduction and oxygen and carbon dioxide temperature programmed desorption. A different distribution of Ni2+ cations in the tetrahedrally and octahedrally coordinated sites of the spinel lattice and an increased reducibility of the smaller crystallite size sample were identified as the main impacts of different crystallite size. Their catalytic activity in the oxidative dehydrogenation of 2-propanol was investigated by temperature programmed reaction studies using different ratios of 2-propanol:O2 as well as of possible parallel and consecutive reactions at atmospheric pressure and maximum 400 °C. Operando-DRIFTS-MS studies at different 2-propanol:O2 ratios were carried out under continuous-flow conditions at atmospheric pressure as well. Thereby, the increased reducibility of the small crystallite size sample could be linked to an unselective activity for dehydrogenation yielding acetone and hydrogen, partial oxidation of 2-propanol and acetone, and total combustion leading to a complex network of reactions going on, being further pushed by an excess of oxygen. Ex-situ x-ray diffraction measurements were performed following the temperature programmed reaction experiments. The large crystallite size sample was found to be generally less active, but more selective towards non-oxidative dehydrogenation. Ex-situ x-ray diffraction measurements performed following the temperature programmed reaction experiments confirmed the increased reducibility of the smaller crystallite size sample. In the operando IR studies, 2-propoxide, adsorbed acetone, carbonates and acetates were identified as species occurring in the reaction.
Tampieri, Alberto; Romanelli, Federica; Pittenauer, Michael; Lederer, Thomas; Föttinger, Karin
Journal ArticleSubmittedIn: ChemRxiv, 2024.
Abstract | Links | BibTeX | Tags: P10
@article{Tampieri_2024a,
title = {Towards industrially-relevant liquid-phase flow oxidations of secondary alcohols over spinel cobaltites},
author = {Alberto Tampieri and Federica Romanelli and Michael Pittenauer and Thomas Lederer and Karin Föttinger},
url = {https://chemrxiv.org/engage/chemrxiv/article-details/670cd07d12ff75c3a15cea2d},
year = {2024},
date = {2024-09-17},
urldate = {2024-09-17},
journal = {ChemRxiv},
abstract = {Selective partial oxidation of alcohols is a straightforward synthetic pathway to access aldehydes and ketones, important building blocks for the chemical industry. The catalytic oxidation of higher secondary alcohols is challenging, which entails the need for low temperatures to preserve the selectivity or, in practice, the use of a liquid phase. In this work, we explored the applicability of Co-based spinel oxides as alternatives to noble metal-based supported catalysts for the oxidation of alcohols such as 2-butanol and 2-propanol. We developed a small-scale tri-phasic process in flow for consecutive weeks and using technical grade microporous catalysts, en route to more industrially-relevant systems, focussing on the practical aspects of the process. Co_{3}O_{4}, MnCo_{2}O_{4}, NiCo_{2}O_{4}, ZnCo_{2}O_{4}, and CoFe_{2}O_{4} were rapidly synthesised by combustion and characterised by XRD, SEM, EDX, XPS, N_{2}-physisorption and FT-IR. The same catalysts were tested in batch in the liquid phase to explore the impact of the reaction conditions on the reaction outcome and to rule out flow-specific effects. Gas phase reactions unveiled the different behaviour of the same catalysts in different environments, highlighting phase-specific effects such as the beneficial (liquid phase) vs inhibiting (gas phase) impact of Mn doping.},
keywords = {P10},
pubstate = {published},
tppubtype = {article}
}
Selective partial oxidation of alcohols is a straightforward synthetic pathway to access aldehydes and ketones, important building blocks for the chemical industry. The catalytic oxidation of higher secondary alcohols is challenging, which entails the need for low temperatures to preserve the selectivity or, in practice, the use of a liquid phase. In this work, we explored the applicability of Co-based spinel oxides as alternatives to noble metal-based supported catalysts for the oxidation of alcohols such as 2-butanol and 2-propanol. We developed a small-scale tri-phasic process in flow for consecutive weeks and using technical grade microporous catalysts, en route to more industrially-relevant systems, focussing on the practical aspects of the process. Co3O4, MnCo2O4, NiCo2O4, ZnCo2O4, and CoFe2O4 were rapidly synthesised by combustion and characterised by XRD, SEM, EDX, XPS, N2-physisorption and FT-IR. The same catalysts were tested in batch in the liquid phase to explore the impact of the reaction conditions on the reaction outcome and to rule out flow-specific effects. Gas phase reactions unveiled the different behaviour of the same catalysts in different environments, highlighting phase-specific effects such as the beneficial (liquid phase) vs inhibiting (gas phase) impact of Mn doping.
Wanzenböck, Ralf; Heid, Esther; Riva, Michele; Franceschi, Giada; Imre, Alexander M.; Carrete, Jesús; Diebold, Ulrike; Madsen, Georg K. H.
Exploring Inhomogeneous Surfaces: Ti-rich SrTiO3(110) Reconstructions via Active Learning
Journal ArticleOpen AccessIn: Digital Discovery, vol. 3, pp. 2137-2145, 2024.
Abstract | Links | BibTeX | Tags: P02, P09
@article{Wanzenboeck2024b,
title = {Exploring Inhomogeneous Surfaces: Ti-rich SrTiO_{3}(110) Reconstructions via Active Learning},
author = {Ralf Wanzenböck and Esther Heid and Michele Riva and Giada Franceschi and Alexander M. Imre and Jesús Carrete and Ulrike Diebold and Georg K. H. Madsen},
url = {https://doi.org/10.1039/D4DD00231H},
year = {2024},
date = {2024-09-16},
urldate = {2024-09-16},
journal = {Digital Discovery},
volume = {3},
pages = {2137-2145},
abstract = {The investigation of inhomogeneous surfaces, where various local structures co-exist, is crucial for understanding interfaces of technological interest, yet it presents significant challenges. Here, we study the atomic configurations of the (2×m) Ti-rich surfaces at (110)-oriented SrTiO_{3} by bringing together scanning tunneling microscopy and transferable neural-network force fields combined with evolutionary exploration. We leverage an active learning methodology to iteratively extend the training data as needed for different configurations. Training on only small well-known reconstructions, we are able to extrapolate to the complicated and diverse overlayers encountered in different regions of the heterogeneous SrTiO_{3}(110)-(2×m) surface. Our machine-learning-backed approach generates several new candidate structures, in good agreement with experiment and verified using density functional theory. The approach could be extended to other complex metal oxides featuring large coexisting surface reconstructions.},
keywords = {P02, P09},
pubstate = {published},
tppubtype = {article}
}
The investigation of inhomogeneous surfaces, where various local structures co-exist, is crucial for understanding interfaces of technological interest, yet it presents significant challenges. Here, we study the atomic configurations of the (2×m) Ti-rich surfaces at (110)-oriented SrTiO3 by bringing together scanning tunneling microscopy and transferable neural-network force fields combined with evolutionary exploration. We leverage an active learning methodology to iteratively extend the training data as needed for different configurations. Training on only small well-known reconstructions, we are able to extrapolate to the complicated and diverse overlayers encountered in different regions of the heterogeneous SrTiO3(110)-(2×m) surface. Our machine-learning-backed approach generates several new candidate structures, in good agreement with experiment and verified using density functional theory. The approach could be extended to other complex metal oxides featuring large coexisting surface reconstructions.
Hütner, Johanna I.; Conti, Andrea; Kugler, David; Mittendorfer, Florian; Kresse, Georg; Schmid, Michael; Diebold, Ulrike; Balajka, Jan
Stoichiometric reconstruction of the Al2O3(0001) surface
Journal ArticleOpen AccessarXivIn: Science, vol. 385, pp. 1241–1244, 2024, ISSN: 1095-9203.
Abstract | Links | BibTeX | Tags: P02, P03
@article{Huetner2024,
title = {Stoichiometric reconstruction of the Al_{2}O_{3}(0001) surface},
author = {Johanna I. Hütner and Andrea Conti and David Kugler and Florian Mittendorfer and Georg Kresse and Michael Schmid and Ulrike Diebold and Jan Balajka},
url = {https://www.science.org/doi/10.1126/science.adq4744
https://arxiv.org/abs/2405.19263},
issn = {1095-9203},
year = {2024},
date = {2024-09-12},
urldate = {2024-09-12},
journal = {Science},
volume = {385},
pages = {1241--1244},
publisher = {American Association for the Advancement of Science (AAAS)},
abstract = {Macroscopic properties of materials stem from fundamental atomic-scale details, yet for insulators, resolving surface structures remains a challenge. We imaged the basal (0001) plane of α–aluminum oxide (α-Al_{2}O_{3}) using noncontact atomic force microscopy with an atomically defined tip apex. The surface formed a complex (√31 × √31)R±9° reconstruction. The lateral positions of the individual oxygen and aluminum surface atoms come directly from experiment; we determined with computational modeling how these connect to the underlying crystal bulk. Before the restructuring, the surface Al atoms assume an unfavorable, threefold planar coordination; the reconstruction allows a rehybridization with subsurface O that leads to a substantial energy gain. The reconstructed surface remains stoichiometric, Al_{2}O_{3}.},
keywords = {P02, P03},
pubstate = {published},
tppubtype = {article}
}
Macroscopic properties of materials stem from fundamental atomic-scale details, yet for insulators, resolving surface structures remains a challenge. We imaged the basal (0001) plane of α–aluminum oxide (α-Al2O3) using noncontact atomic force microscopy with an atomically defined tip apex. The surface formed a complex (√31 × √31)R±9° reconstruction. The lateral positions of the individual oxygen and aluminum surface atoms come directly from experiment; we determined with computational modeling how these connect to the underlying crystal bulk. Before the restructuring, the surface Al atoms assume an unfavorable, threefold planar coordination; the reconstruction allows a rehybridization with subsurface O that leads to a substantial energy gain. The reconstructed surface remains stoichiometric, Al2O3.
Yigit, Nevzat; Föttinger, Karin; Bernardi, Johannes; Rupprechter, Günther
Preferential CO oxidation (PROX) on LaCoO3–based perovskites: Effect of pretreatment on structure and selectivity
Journal ArticleSubmittedIn: Journal of Catalysis, 2024.
Abstract | BibTeX | Tags: P08, P10
@article{Yigit_2024a,
title = {Preferential CO oxidation (PROX) on LaCoO_{3}–based perovskites: Effect of pretreatment on structure and selectivity},
author = {Nevzat Yigit and Karin Föttinger and Johannes Bernardi and Günther Rupprechter},
year = {2024},
date = {2024-09-11},
urldate = {2024-09-11},
journal = {Journal of Catalysis},
abstract = {The perovskite LaCoO_{3} (LCO) was used as catalyst for preferential oxidation of CO (PROX). LCO was synthesized via the modified Pechini method and characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and CO- and H_{2}- temperature programmed reduction (TPR), before and after different reductive and oxidative pretreatments. Depending on the reduction conditions, LaCoO_{3} transformed to brownmillerite-type La_{2}Co_{2}O_{5}, exsolved Co^{0} nanoparticles supported on La_{2}O_{3} and, upon reoxidation, to Co_{3}O_{4}/La}2}O_{3}, paralleled by corresponding changes in the PROX performance. The Co oxidation state of the various catalysts correlated with their selectivity: LCO containing only Co^{3+} exhibited 100% CO_{2} selectivity in a wide temperature window, whereas La_{2}Co_{2}O_{5}, Co/La_{2}O_{3} and Co_{3}O_{4}/La_{2}O_{3} had markedly lower selectivity. It is suggested that Co^{3+} is crucial and that the strong resistivity of LaCoO_{3} towards reduction is responsible for the high CO_{2} selectivity over a temperature range of 100 °C-220 °C.},
keywords = {P08, P10},
pubstate = {published},
tppubtype = {article}
}
The perovskite LaCoO3 (LCO) was used as catalyst for preferential oxidation of CO (PROX). LCO was synthesized via the modified Pechini method and characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and CO- and H2- temperature programmed reduction (TPR), before and after different reductive and oxidative pretreatments. Depending on the reduction conditions, LaCoO3 transformed to brownmillerite-type La2Co2O5, exsolved Co0 nanoparticles supported on La2O3 and, upon reoxidation, to Co3O4/La2O3, paralleled by corresponding changes in the PROX performance. The Co oxidation state of the various catalysts correlated with their selectivity: LCO containing only Co3+ exhibited 100% CO2 selectivity in a wide temperature window, whereas La2Co2O5, Co/La2O3 and Co3O4/La2O3 had markedly lower selectivity. It is suggested that Co3+ is crucial and that the strong resistivity of LaCoO3 towards reduction is responsible for the high CO2 selectivity over a temperature range of 100 °C-220 °C.
Wang, Chunlei; Sombut, Panukorn; Puntscher, Lena; Ulreich, Manuel; Pavelec, Jiri; Rath, David; Balajka, Jan; Meier, Matthias; Schmid, Michael; Diebold, Ulrike; Franchini, Cesare; Parkinson, Gareth S.
A Multitechnique Study of C2H4 Adsorption on a Model Single-Atom Rh1 Catalyst
Journal ArticleOpen AccessIn: The Journal of Physical Chemistry C, vol. 128, iss. 37, pp. 15404–15411, 2024.
Abstract | Links | BibTeX | Tags: P02, P04, P07
@article{Wang_2024b,
title = {A Multitechnique Study of C_{2}H_{4} Adsorption on a Model Single-Atom Rh_{1} Catalyst},
author = {Chunlei Wang and Panukorn Sombut and Lena Puntscher and Manuel Ulreich and Jiri Pavelec and David Rath and Jan Balajka and Matthias Meier and Michael Schmid and Ulrike Diebold and Cesare Franchini and Gareth S. Parkinson},
url = {https://doi.org/10.1021/acs.jpcc.4c03588},
year = {2024},
date = {2024-09-05},
journal = {The Journal of Physical Chemistry C},
volume = {128},
issue = {37},
pages = {15404–15411},
abstract = {Single-atom catalysts are potentially ideal model systems to investigate structure–function relationships in catalysis if the active sites can be uniquely determined. In this work, we study the interaction of C_{2}H_{4} with a model Rh/Fe_{3}O_{4}(001) catalyst that features 2-, 5-, and 6-fold coordinated Rh adatoms, as well as Rh clusters. Using multiple surface-sensitive techniques in combination with calculations of density functional theory (DFT), we follow the thermal evolution of the system and disentangle the behavior of the different species. C_{2}H_{4} adsorption is strongest at the 2-fold coordinated Rh_{1} with a DFT-determined adsorption energy of −2.26 eV. However, desorption occurs at lower temperatures than expected because the Rh migrates into substitutional sites within the support, where the molecule is more weakly bound. The adsorption energy at the 5-fold coordinated Rh sites is predicated to be −1.49 eV, but the superposition of this signal with that from small Rh clusters and additional heterogeneity leads to a broad C_{2}H_{4} desorption shoulder in TPD above room temperature.},
keywords = {P02, P04, P07},
pubstate = {published},
tppubtype = {article}
}
Single-atom catalysts are potentially ideal model systems to investigate structure–function relationships in catalysis if the active sites can be uniquely determined. In this work, we study the interaction of C2H4 with a model Rh/Fe3O4(001) catalyst that features 2-, 5-, and 6-fold coordinated Rh adatoms, as well as Rh clusters. Using multiple surface-sensitive techniques in combination with calculations of density functional theory (DFT), we follow the thermal evolution of the system and disentangle the behavior of the different species. C2H4 adsorption is strongest at the 2-fold coordinated Rh1 with a DFT-determined adsorption energy of −2.26 eV. However, desorption occurs at lower temperatures than expected because the Rh migrates into substitutional sites within the support, where the molecule is more weakly bound. The adsorption energy at the 5-fold coordinated Rh sites is predicated to be −1.49 eV, but the superposition of this signal with that from small Rh clusters and additional heterogeneity leads to a broad C2H4 desorption shoulder in TPD above room temperature.