Surface chemistry, structure, and reactivity
of multi-component spinel nanoparticles

@article{Yigit_2024a,

title = {Preferential CO oxidation (PROX) on LaCoO_{3}–based catalysts: Effect of cobalt oxidation state on selectivity},

author = {Nevzat Yigit and Karin Föttinger and Johannes Bernardi and Günther Rupprechter},

url = {https://doi.org/10.1016/j.jcat.2025.115973},

year  = {2025},

date = {2025-01-20},

urldate = {2025-01-20},

journal = {Journal of Catalysis},

issue = {0021-9517},

pages = {115973},

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_{2–} and H_{2–} temperature programmed reduction (TPR). Different reductive and oxidative pretreatments were applied to systematically vary the Co oxidation state in order to examine its effect on catalytic performance and to single out active site requirements. Upon reduction at increasing temperature, 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}. The Co oxidation state of the various catalysts correlated with their CO_{2} 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 and stable CO_{2} selectivity over a temperature range of 100 °C–220 °C. Higher oxygen concentration further broadens the PROX window.},

keywords = {P08, P10},

pubstate = {published},

tppubtype = {article}

}

@article{Rakngama_2024a,

title = {Hydrothermal synthesis of ZnZrO_{x} catalysts for CO_{2} hydrogenation to methanol: the effect of pH on structure and activity},

author = {Issaraporn Rakngam and Gustavo A. S. Alves and Nattawut Osakoo and Jatuporn Wittayakun and Thomas Konegger and Karin Föttinger},

doi = {10.1039/D4SU00522H},

year  = {2024},

date = {2024-10-11},

urldate = {2024-10-11},

journal = {RSC Sustainability},

abstract = {With the growing necessity of achieving carbon neutrality in the industrial sector, the catalytic hydrogenation of carbon dioxide into methanol has been widely considered one of the key strategies for the utilization of captured CO_{2}. For this reason, the development of alternative catalysts such as ZnZrO_{x} has attracted considerable interest, given its superior stability and versatility in comparison to the conventional Cu-based materials. In this work, ZnZrO_{x} has been produced by a hydrothermal synthesis method at varied synthesis pH between 7 and 10 and a positive association between pH and catalytic CO_{2} conversion is observed. At 2.0 MPa and 250 °C, ZnZrO_{x} produced at pH 10 shows a methanol selectivity of 95% at a CO_{2} conversion of 3.4%. According to characterization, basic pH conditions enable the formation of abundant t-ZrO_{2} and the subsequent incorporation of Zn^{2+} into this phase, although the content of surface Zn does not increase between pH 8 and 10. Nevertheless, synthesis pH values can be correlated with surface oxygen content and CO_{2} adsorption capacity, which could be important contributors to the higher catalytic activity observed as a result of higher synthesis pH values. Finally, the comparison between NaOH and NH_{4}OH as additives to adjust pH 10 indicate similar catalytic activities and surface properties, which emphasizes the proposed trend between hydrothermal synthesis pH and catalytic activity for CO_{2} hydrogenation.},

keywords = {P10},

pubstate = {published},

tppubtype = {article}

}

@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},

urldate = {2024-10-04},

journal = {RSC Sustainability},

volume = {2},

issue = {11},

pages = {3334-3344},

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{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{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}

}

@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}

}

@article{berger2024,

title = {Cu-doped perovskite-type oxides: A structural deep dive and examination of their exsolution behaviour influenced by B-site doping},

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

doi = {10.1016/j.cattod.2024.114787},

year  = {2024},

date = {2024-07-01},

urldate = {2024-07-01},

journal = {Catalysis Today},

volume = {437},

number = {114787},

abstract = {Perovskite-type oxides have gained significant attention in the scientific community due to their unique properties and potential applications. Their ability to exsolve reducible B-site cations (e.g. Co, Ni, Cu) combined with their flexibility regarding A-site and B-site composition allows for the tailoring of novel catalytic materials. This study focuses on B-site doped perovskite-type oxides with a general formula of Nd_{0.6}Ca_{0.4}Fe_{1-x}Cu_{x}O_{3} and Pr_{0.6}Ca_{0.4}Fe_{1-x}Cu_{x}O_{3} (x = 0.0, 0.03, 0.05, 0.10) for potential use as a catalyst for Methanol Steam Reforming via the exsolution of catalytically active Cu nanoparticles. The atomic and electronic structure, morphology, and exsolution behaviour of these materials were investigated experimentally and with density functional theory, with a specific emphasis on the impact of B-site doping with varying Cu content as well as choice of A-site element. Both parameters influenced the crystal structure, surface area, and morphology of the materials. The exsolution behaviour of the materials was observed using in-situ XRD at DESY beamline P02.1 at PETRA III, with nanoparticles forming after reductive treatments on the host oxide surface. The quantity and size of the nanoparticles were found to be adjustable by selecting the A-site ion, doping content at the B-site, and the choice of reducing agent. Materials with higher Cu content on the B-site exhibited facilitated exsolution. Furthermore, exsolution was promoted with Nd as the A-site element compared to Pr. In conclusion, the controlled exsolution of Cu nanoparticles introduces Cu-doped perovskite-type oxides as promising candidates for developing novel catalytic systems. The findings underscore the importance of fine-tuning the oxide composition (A-site element, amount of B-site dopant) to achieve tailored exsolution of nanoparticles, which is crucial for rational material design. By leveraging this knowledge, catalysts with finely tuned properties can be created for specific applications and operational environments.},

keywords = {P10},

pubstate = {published},

tppubtype = {article}

}

@article{Latschka2023,

title = {Influence of hot liquid flowing water on Zeolite Y stability},

author = {Markus Latschka and Björn Wellscheid and Raffael Rameshan and Tobias Schöberl and Johannes Essmeister and Gernot Pacholik and Francesco Valentini and Laura Balta and Andreas Limbeck and Hanspeter Kählig and Karin Föttinger},

doi = {10.1016/j.micromeso.2023.112557},

year  = {2023},

date = {2023-04-15},

urldate = {2023-04-15},

journal = {Microporous and Mesoporous Materials},

volume = {354},

number = {112557},

abstract = {Zeolite Y is used in a wide field of catalysis because of its high surface area and strong acidity. Since flowing water is present in many catalytic liquid phase reactions, its impact was investigated. For that, the zeolite Y was treated with water at 200 °C and 42 bar in a flow reactor. The resulting characterization showed strong structural changes at high water flows. The typical zeolite structure was almost completely lost, but an amorphous phase similar to the faujasite framework was formed. Due to this, the characteristic micropores were destroyed (d = 0.7 nm, volume was reduced from 0.18 to 0.01 cm³/g) and small mesopores were created (d = 2–3 nm, volume was increased from 0.25 to 0.51 cm³/g). As a result, the specific surface area was not greatly reduced and was still at around 250 m²/g. In addition, the amount of octahedrally coordinated EFAl increased from 54 to 70% and a γ-Al_{2}O_{3} as well as a kaolinite phase was observed. The formed tetrahedrally coordinated EFAl is responsible for EFAl-OH groups, which are strong Brønsted acid sites. In general, the total acid sites of the zeolite Y were not strongly reduced and the ratio of Lewis to Brønsted acid sites slightly increased from 70:30% to 80:20%. For all Al species, the oxygen coordination was strongly distorted. After water treatment, on Si a large number of coordinated OSi and OAl groups were substituted with OH groups. The ratio of Si to Al decreased from 1 to 0.7, because Si was dissolved out of the zeolite by the water. On the surface, it was vice versa, there the Si accumulated (the Si/Al ratio increased from 0.2 to 0.8), presumably as silica gel.},

keywords = {P10},

pubstate = {published},

tppubtype = {article}

}

@article{TAMPIERI2022121889,

title = {Catalytic aldol condensation of bio-derived furanic aldehydes and acetone: Challenges and opportunities},

author = {Alberto Tampieri and Karin Föttinger and Noelia Barrabés and Francesc Medina},

url = {https://doi.org/10.1016/j.apcatb.2022.121889

https://www.sciencedirect.com/science/article/pii/S092633732200830X},

doi = {10.1016/j.apcatb.2022.121889},

year  = {2022},

date = {2022-08-24},

urldate = {2022-08-24},

journal = {Applied Catalysis B: Environmental},

volume = {319},

number = {121889},

abstract = {Bio-derived furfural and 5-hydroxymethylfurfural can be combined with acetone to yield aldol condensation products that may serve as biofuel and polymer precursors. We have explored different catalytic systems to obtain and purify each product in the most efficient way. The results of the catalytic tests of the cross-condensations and of the self-condensation of acetone allowed the comparison of the different reactivity of the two aldehydes. Online and in situ/operando ATR-IR was used to monitor the reaction over time and to study the interaction of the reaction species with the solid catalyst, especially the formation of deactivating organic matter that covers the surface, which is a major issue in heterogeneous condensation processes. In situ NMR was used to study the ongoing reaction, assessing its stereoselectivity, and to study the behavior of deuterated species in the catalytic system. Finally, the preparation of C14, a hetero-double-condensation product, was also explored.},

keywords = {P10},

pubstate = {published},

tppubtype = {article}

}