Publications

@article{Schrenk_2024a,

title = {  How reduction temperature influences the structure of perovskite-oxide catalysts during the dry reforming of methane},

author = {Florian Schrenk and Lorenz Lindenthal and Hedda Drexler and Tobias Berger and Raffael Rameshan and Thomas Ruh and Karin Föttinger and Christoph Rameshan},

doi = {10.1039/d4su00483c},

year  = {2024},

date = {2024-10-04},

journal = {RSC Sustainability},

abstract = {Dry reforming of methane is a promising reaction to convert CO_{2} and combat climate change. However, the reaction is still not feasible in large-scale industrial applications. The thermodynamic need for high temperatures and the potential of carbon deposition leads to high requirements for potential catalyst materials. As shown in previous publications, the Ni-doped perovskite-oxide Nd_{0.6}Ca_{0.4}Fe_{0.97}Ni_{0.03}O_{3} is a potential candidate as it can exsolve highly active Ni nanoparticles on its surface. This study focused on controlling the particle size by varying the reduction temperature. We found the optimal temperature that allows the Ni nanoparticles to exsolve while not yet enabling the formation of deactivating CaCO_{3}. Furthermore, the exsolution process and the behaviour of the phases during the dry reforming of methane were investigated using in-situ XRD measurements at the DESY beamline P02.1 at PETRA III in Hamburg. They revealed that the formed deactivated phases would, at high temperatures, form a brownmillerite phase, thus hinting at a potential self-healing mechanism of these materials. },

keywords = {P10},

pubstate = {published},

tppubtype = {article}

}

@article{Montero-de-Hijes_2024b,

title = {Density isobar of water and melting temperature of ice: Assessing common density functionals},

author = {Pablo Montero de Hijes and Christoph Dellago and Ryosuke Jinnouchi and Georg Kresse},

url = {https://doi.org/10.1063/5.0227514},

year  = {2024},

date = {2024-10-03},

urldate = {2024-06-06},

journal = {The Journal of Chemical Physics},

volume = {161},

pages = {131102},

abstract = {We investigate the density isobar of water and the melting temperature of ice using six different density functionals. Machine-learning potentials are employed to ensure computational affordability. Our findings reveal significant discrepancies between various base functionals. Notably, even the choice of damping can result in substantial differences. Overall, the outcomes obtained through density functional theory are not entirely satisfactory across most utilized functionals. All functionals exhibit significant deviations either in the melting temperature or equilibrium volume, with most of them even predicting an incorrect volume difference between ice and water. Our heuristic analysis indicates that a hybrid functional with 25% exact exchange and van der Waals damping averaged between zero and Becke–Johnson dampings yields the closest agreement with experimental data. This study underscores the necessity for further enhancements in the treatment of van der Waals interactions and, more broadly, density functional theory to enable accurate quantitative predictions for molecular liquids.},

keywords = {P03, P12},

pubstate = {published},

tppubtype = {article}

}

@article{Ryan_2024a,

title = {Quantitative Measurement of Cooperative Binding in Partially Dissociated Water Dimers at the Hematite “R-Cut” Surface},

author = {Paul T. P. Ryan and Panukorn Sombut and Ali Rafsanjani-Abbasi and Chunlei Wang and Fulden Eratam and Francesco Goto and Ulrike Diebold and Matthias Meier and David A. Duncan and Gareth S. Parkinson},

url = {https://arxiv.org/abs/2406.18264

https://pubs.acs.org/doi/10.1021/acs.jpcc.4c04537},

year  = {2024},

date = {2024-09-30},

urldate = {2024-06-26},

journal = {The Journal of Physical Chemistry C},

abstract = {Water–solid interfaces pervade the natural environment and modern technology. On some surfaces, water–water interactions induce the formation of partially dissociated interfacial layers; understanding why is important to model processes in catalysis or mineralogy. The complexity of the partially dissociated structures often makes it difficult to probe them quantitatively. Here, we utilize normal incidence X-ray standing waves (NIXSW) to study the structure of partially dissociated water dimers (H_{2}O–OH) at the α-Fe_{2}O_{3}(012) surface (also called the (11̅02) or “R-cut” surface): a system simple enough to be tractable yet complex enough to capture the essential physics. We find the H_{2}O and terminal OH groups to be the same height above the surface within experimental error (1.45 ± 0.04 and 1.47 ± 0.02 Å, respectively), in line with DFT-based calculations that predict comparable Fe–O bond lengths for both water and OH species. This result is understood in the context of cooperative binding, where the formation of the H-bond between adsorbed H_{2}O and OH induces the H_{2}O to bind more strongly and the OH to bind more weakly compared to when these species are isolated on the surface. The surface OH formed by the liberated proton is found to be in plane with a bulk truncated (012) surface (−0.01 ± 0.02 Å). DFT calculations based on various functionals correctly model the cooperative effect but overestimate the water–surface interaction.},

keywords = {P02, P04, P07},

pubstate = {published},

tppubtype = {article}

}

@article{Redondo2024,

title = {Real-space investigation of polarons in hematite Fe2O3},

author = {Jesus Redondo and Michele Reticcioli and Vit Gabriel and Dominik Wrana and Florian Ellinger and Michele Riva and Giada Franceschi and Erik Rheinfrank and Igor Sokolovic and Zdenek Jakub and Florian Kraushofer and Aji Alexander and Laerte L. Patera and Jascha Repp and Michael Schmid and Ulrike Diebold and Gareth S. Parkinson and Cesare Franchini and Pavel Kocan and Martin Setvin},

url = {https://arxiv.org/abs/2303.17945},

year  = {2024},

date = {2024-09-27},

urldate = {2023-03-31},

journal = {Science Advances},

abstract = {In polarizable materials, electronic charge carriers interact with the surrounding ions, leading to quasiparticle behaviour. The resulting polarons play a central role in many materials properties including electrical transport, optical properties, surface reactivity and magnetoresistance, and polaron properties are typically investigated indirectly through such macroscopic characteristics. Here, noncontact atomic force microscopy (nc-AFM) is used to directly image polarons in Fe_{2}O_{3} at the single quasiparticle limit. A combination of Kelvin probe force microscopy (KPFM) and kinetic Monte Carlo (KMC) simulations shows that Ti doping dramatically enhances the mobility of electron polarons, and density functional theory (DFT) calculations indicate that a metallic transition state is responsible for the enhancement. In contrast, hole polarons are significantly less mobile and their hopping is hampered further by the introduction of trapping centres.},

keywords = {P02, P04, P07},

pubstate = {published},

tppubtype = {article}

}

@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}

}

@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}

}

@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}

}

@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},

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}

}

@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},

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}

}

@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},

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}

}