Catalysis by ultrathin
LaBO₃ (B=Co, Fe) perovskite films

@article{Li_2025a,

title = {Probing the Structure of D_{2}O Ice Layers on ALD-grown ZrO_{2}, Al_{2}O_{3} and TiO_{2} Thin Films by Sum Frequency Generation (SFG) Spectroscopy},

author = {Xia Li and Susanne Gross and Thomas Haunold and Moon-Hyung Jang and Markéta Zukalová and Martin Jindra and Joanna Elzbieta Olszówka and Yu Lei and Stefan Vajda and Günther Rupprechter},

doi = {10.1039/D5FD00152H},

year  = {2025},

date = {2025-12-16},

journal = {Faraday Discussions},

abstract = {Sum frequency generation (SFG) spectroscopy was applied to investigate D_{2}O adsorption on atomic layer deposition (ALD)–grown Al_{2}O_{3}, ZrO_{2}, and TiO_{2} films at 94 ± 1 K. Film composition and thickness were characterized by ellipsometry and X-ray photoelectron spectroscopy (XPS). Additional SFG measurements were conducted on the SiO_{2}/Si wafer and on a CoO film prepared by oxidizing Co foil. At D_{2}O exposure below 3 000 L, the spectra were dominated by interfacial features originating from the ice-oxide interface. These spectra exhibited a weak, broad O–D stretching band (OD_{3}) centered at 2650 cm^{-1}, attributed to water molecules hydrogen-bonded to the oxide surface; this assignment was supported by the absence of the OD_{3} feature on the SiO_{2}/Si substrate. A sharp peak at 2730 cm^{-1} was also observed and assigned to the “free” O–D stretch (non-hydrogen-bonded with any neighboring molecule) of surface D_{2}O molecules pointing into the vapor phase. Upon increasing D_{2}O exposure, both the OD_{3} and “free” OD bands decreased in intensity and were replaced by weakly hydrogen-bonded OD_{2} and strongly hydrogen-bonded OD_{1} modes associated with the ice-vapor interface. As the exposure increased further, the OD_{2} and OD_{2} bands shifted to lower wavenumbers (2310 to 2284 cm^{-1}) and became stronger, with the OD_{1} mode exhibiting a larger red shift and more pronounced intensity enhancement. No significant differences in water structure were observed on the Al_{2}O_{3}, ZrO_{2}, and CoO films at the ice-vapor interfaces, apart from an approximately fivefold reduction in intensity on CoO, which is attributed to signal scattering from the rough CoO film/Co foil surface. However, when D_{2}O exposure reached ≥30 000 L, the OD_{1} band on the TiO_{2} surfaces decreased substantially in intensity and shifted to much lower wavenumbers (2065 cm^{-1} at 30 000 L; 2030 cm^{-1} at 102 000 L) than on Al_{2}O_{3} (2283 cm^{-1} at 90 000 L), ZrO_{2} (2293 cm^{-1} at 30 000 L), and CoO (2284 cm^{-1} at 900 000 L), indicating specific hydrogen-bonding interactions on the TiO_{2} surface.},

keywords = {P08},

pubstate = {published},

tppubtype = {article}

}

@article{Pollitt_2025a,

title = {Engineering Catalytic Efficiency by Thiolate-Protected Trimetallic (Cu, Pd, Au) Nanoclusters: Single-Atom Alloy Catalysts for Water–Gas Shift},

author = {Stephan Pollitt and Thomas Haunold and Sakiat Hossain and Gereon Behrendt and Michael Stöger-Pollach and Tokuhisa Kawawaki and Noelia Barrabés and Malte Behrens and Yuichi Negishi and Günther Rupprechter},

doi = {10.1021/acscatal.5c04165},

year  = {2025},

date = {2025-08-22},

journal = {ACS Catalysis},

volume = {15},

pages = {15459–15474},

abstract = {The “crude oil exodus” and energy transition will finally hinge on the availability of hydrogen. Catalytic processes like the water–gas shift (WGS) reaction may significantly contribute to its production and become crucial for utilizing alternative feedstocks. This work demonstrates how thiolate-protected gold nanoclusters can be employed as precursors for single-atom alloy (SAA) catalysts. The clusters serve as carriers of heteroatom dopants (Cu, Pd) while precisely maintaining 25 metal atoms per cluster (<1 nm). Using the 2PET ligand during synthesis led to high yield and cluster stability, but ligand exchange was required to link clusters to a ZnO support efficiently. Introducing pMBA as a ligand enabled a homogeneous cluster distribution on the ZnO surface, creating a well-defined catalyst with dual functionality. This SAA catalyst, outperforming a Cu/ZnO/Al_{2}O_{3} benchmark in WGS, may get industrial relevance when upscaled while still serving as a well-defined model system in catalysis. Thereby, it bridges the gap between practical applications and fundamental research. Pre- and postreaction analysis by XPS proved the presence of the dopants in the catalysts in the expected stoichiometry, showed changes in the electronic structures, but also revealed sulfur migration from the clusters/ligands to the support, forming ZnS. Furthermore, XPS unveiled a pretreatment-induced SMSI decoration effect, stabilizing the small particles during catalysis. (S)TEM indicated a homogeneous cluster distribution on ZnO after synthesis and proved small particle sizes throughout the experiments. In situ DRIFTS confirmed the accessibility of the dopant atoms by the reactant CO and also detected adsorbed byproducts. The precise size and doping control of thiolate-protected SAA nanoclusters, together with their catalytic performance, demonstrate the potential for targeted future investigations in a wide range of industrial applications.},

keywords = {P08},

pubstate = {published},

tppubtype = {article}

}

@article{Sidorowicz_2025a,

title = {Influence of MXene and TiO_{2} on the Performance of Microalgae-Derived Ru-Based Catalysts for CO_{2} Hydrogenation to Methane},

author = {Agnieszka Sidorowicz and Thomas Wicht and Michael Stöger-Pollach and Roberta Licheri and Giacomo Cao and Alessandro Concas and Günther Rupprechter},

doi = {10.1021/acscatal.5c04285},

year  = {2025},

date = {2025-08-19},

journal = {ACS Catalysis},

volume = {15},

pages = {15261–15278},

abstract = {Controlling the selectivity of CO_{2} hydrogenation to produce value-added fuels and chemicals is an actual challenge in catalysis research. The exact mechanisms underlying selectivity control often remain poorly understood, slowing the design of more efficient catalysts. In this study, we investigated RuO_{2} nanoparticles supported on MXene or TiO_{2} for CO_{2} hydrogenation at atmospheric pressure. Microalgal extracts were incorporated in the synthesis to explore their influence on catalyst properties, such as surface area, morphology, and elemental distribution. Although lower surface area and less uniform RuO_{2} dispersion were observed on MXenes than on TiO_{2}, after reductive pretreatment Ru/MXene exhibited superior catalytic activity, demonstrating that its unique textural properties and active site availability compensated for the lower surface area. A reducibility study revealed that MXene-supported catalysts undergo a more complex reduction process than those with TiO_{2} as the support. Additionally, bridge adsorption sites on MXene likely contributed to the enhanced CO_{2} hydrogenation activity, whereas TiO_{2} seemed to present a twin CO binding environment. Higher Ru loading on MXene increased the methane selectivity and conversion, whereas lower loading favored CO formation, highlighting the importance of optimizing catalyst loading. Operando diffuse reflectance infrared Fourier transform spectroscopy analysis revealed the critical role of methoxy intermediates in affecting the catalytic pathway, suggesting the potential for tuning synthesis conditions to improve yields. A partial encapsulation of Ru on MXene enhances the catalytic performance, while the stronger SMSI effect on TiO_{2} leads to complete encapsulation, reducing the catalytic efficiency. The findings underscore the promise of MXene as a support material for metal catalysts in CO_{2} hydrogenation toward environmentally friendly fuel production.},

keywords = {P08},

pubstate = {published},

tppubtype = {article}

}

@article{Sringam_2025a,

title = {Direct conversion of methane to value-added hydrocarbons using alkali metal-promoted cobalt catalysts},

author = {Sarannuch Sringam and Punyanut Thansiriphat and Thongthai Witoon and Waleeporn Donphai and Metta Chareonpanich and Chularat Wattanakit and Hiesang Sohn and Nevzat Yigit and Günther Rupprechter and Anusorn Seubsai},

doi = {10.1039/D5RA02408K},

year  = {2025},

date = {2025-07-07},

journal = {RSC Advances},

volume = {15},

issue = {28},

pages = {23103-23114},

abstract = {The oxidative coupling of methane (OCM) is a promising pathway for directly converting methane into higher hydrocarbons (C_{2+}). This research investigated the influence of alkali metal promoters (Li, Na, K, or Rb) on Co/Al_{2}O_{3} catalysts prepared based on incipient wetness impregnation for the OCM reaction. The catalyst investigations demonstrated that the catalysts promoted with K and Rb had superior performance, with the 4.6K–Co/Al_{2}O_{3} catalyst achieving a maximum C_{2+} yield of 8.1%, C_{2+} selectivity of 24.0%, and CH_{4} conversion of 32.1% at 640 °C. Catalyst characterization, based on XRD, HR-TEM, BET, XPS, CO_{2}-TPD, and H_{2}-TPR analyses, revealed the structural and physicochemical properties responsible for the enhanced catalytic activity. Specifically, K and Rb promoters increased surface basicity and enhanced the electron density of active sites, thereby promoting selective methane activation. In-situ DRIFTS and mechanistic studies highlighted the role of reactive oxygen species in promoting C_{2+} hydrocarbon formation. These results should position K–Co/Al_{2}O_{3} as a promising catalyst for OCM and provide valuable guidance for designing more efficient catalytic systems for methane utilization.},

keywords = {P08},

pubstate = {published},

tppubtype = {article}

}

@article{Phichairatanaphong_2025a,

title = {Calcium-Functionalized MgCeAl-Supported Nickel Catalysts for Enhancing Syngas Production via Dry Reforming},

author = {Orrakanya Phichairatanaphong and Nevzat Yigit and Thomas Wicht and Sanchai Kuboon and Thongthai Witoon and Günther Rupprechter and Metta Chareonpanich and Waleeporn Donphai},

doi = {10.1021/acs.iecr.5c00941},

year  = {2025},

date = {2025-06-18},

urldate = {2025-06-18},

journal = {Industrial & Engineering Chemistry Research},

volume = {64},

issue = {24},

pages = {11782–11793},

abstract = {The dry reforming reaction offers a promising pathway to transform CO_{2} and CH_{4} gases into H_{2} and CO, which serve as vital reactants and fuel gases in various industrial chemical processes. This research focused on the modification of Ni-based catalysts with alkaline earth metal for a dry reforming reaction. Nickel impregnated into mixed MgCeAl (MCA) oxide supports, tailored with calcium (Ca), was fabricated through a soft template-assisted coprecipitation technique, employing cetyltrimethylammonium chloride (CTAC) as the template. The calcium modification of MCA oxides supporting the nickel catalyst augmented the reducibility of nickel and intensified the interaction between nickel and the oxide support. In evaluating performance, Ni/0.3Ca-MCA catalyst demonstrated superior CH_{4} and CO_{2} conversions, an optimal H_{2}/CO ratio, and enhanced stability compared to other catalysts. This improvement can be attributed to the Ca addition, which likely enhances the basic sites on the catalyst, promoting CO_{2} adsorption and its simultaneous dissociation and thereby reducing coke formation.},

keywords = {P08},

pubstate = {published},

tppubtype = {article}

}

@article{Sringam_2024a,

title = {Effect of calcination temperature on the performance of K-Co/Al_{2}O_{3} catalyst for oxidative coupling of methane},

author = {Sarannuch Sringam and Thongthai Witoon and Chularat Wattanakit and Waleeporn Donphai and Metta Chareonpanich and Günther Rupprechter and Anusorn Seubsai},

url = {https://doi.org/10.1016/j.crcon.2024.100261},

doi = {10.1016/j.crcon.2024.100261},

issn = {2588-9133},

year  = {2025},

date = {2025-05-17},

urldate = {2024-05-28},

journal = {Carbon Resources Conversion},

volume = {8},

issue = {2},

pages = {100261},

abstract = {The oxidative coupling of methane (OCM) involves directly converting methane to C_{2+} hydrocarbons (such as ethylene and ethane) via a reaction with oxygen. This study elucidated the effect of the calcination temperature on the structure and catalytic performance of potassium-doped-cobalt oxide supported on an alumina (K-Co/Al_{2}O_{3}) catalyst for the OCM reaction. The catalyst was highly active at relatively low reactor temperatures (500–640 °C). Four calcination temperatures (400, 500, 600, and 700 °C) were investigated, with the results showing that the calcination temperature strongly affected catalytic properties, such as the crystalline phases, elemental distribution, physical properties, and catalytic basicity, leading to a wide range in catalytic performances. The catalyst calcined at 400 °C was superior among the catalysts, with 8.3 % C_{2+} yield, 24.8 % C_{2+} selectivity, and 33.6 % CH_{4} conversion at 640 °C. Furthermore, the catalyst was robust over 24 h of testing.},

keywords = {P08},

pubstate = {published},

tppubtype = {article}

}

@article{Tangpakonsab_2025a,

title = {Mechanistic Insights into CO and H_{2} Oxidation on Cu/CeO_{2} Single Atom Catalysts: A Computational Investigation},

author = {Parinya Tangpakonsab and Alexander Genest and Gareth S. Parkinson and Günther Rupprechter},

url = {https://doi.org/10.1007/s11244-025-02102-2},

doi = {10.1007/s11244-025-02102-2},

year  = {2025},

date = {2025-05-15},

urldate = {2025-05-15},

journal = {Topics in Catalysis},

abstract = {Single atom catalysts (SACs) have attracted significant interest due to their unique properties and potential for enhancing catalytic performance in various chemical reactions. In this study, we atomistically explore adsorption properties and catalytic performance of single Cu atoms anchored at low-index CeO_{2} surfaces, focusing on the oxidation of CO and H_{2}. Utilizing density functional theory (DFT) calculations, we report that Cu adatoms bind favorably on different CeO_{2} surfaces, following a stability order of (100) > (110) > (111). The charge transfer from a single adsorbed Cu atom to Ce leads to the reduction of Ce^{4+} to Ce^{3+} and the oxidation of Cu^{0} to Cu^{+}. This strengthens molecular bonds at Cu sites, particularly for CO, while H_{2} shows a by ~ 1 eV weaker adsorption. CO oxidation is energetically more favorable than H_{2} oxidation on the Cu/CeO_{2}(111) surface. The rate-controlling steps for the Mars–van Krevelen mechanism involve the formation of a bent CO_{2} intermediate for CO and H_{2}O for H_{2}. The lattice oxygen atom at the interface plays a key role for both oxidation processes. Our findings highlight the potential of single atom catalyst, Cu/CeO_{2}, for selective CO adsorption and its subsequent oxidation in heterogeneous catalysis.},

keywords = {P04, P08},

pubstate = {published},

tppubtype = {article}

}

@article{Wu_2025a,

title = {Green Syngas from Photothermal Catalytic Cellulose Steam Reforming on Ni/SiO_{2} Nanocatalysts: Synergy of La^{3+} Promotion and Ni–O Photoactivation},

author = {Jichun Wu and Chongyang Zhou and Mengqi Zhong and Qing Du and Cong Ji and Qianqian Hu and Lei Ji and Xia Li and Günther Rupprechter and Yuanzhi Li},

doi = {10.1002/smll.202411977},

year  = {2025},

date = {2025-03-03},

journal = {Small},

volume = {21},

issue = {14},

pages = {2411977},

abstract = {Replacing fossil fuels by renewable biomass enables green syngas production in an effort to achieve carbon neutrality and sustainable circular processes. Here, an inexpensive catalyst of Ni nanoparticles supported on SiO_{2} modified by La^{3+} (Ni/La_{0.10}–S) is presented, exhibiting exceptional H_{2} and CO production rates (4051.4 and 2467.8 mmol g_{catalyst}^{−1}h^{−1}, respectively) with 7.7% light-to-fuel efficiency in cellulose steam reforming (SR), merely under focused illumination. Excellent performance is mainly attributed to photothermal catalysis resulting from the strong solar absorption and high photothermal conversion by the Ni nanoparticles. The mitigation of tar and char formation significantly benefits from the H_{2}O involvement in the reaction, which is substantially improved by La^{3+} addition enhancing H_{2}O sorption. Remarkably, the illumination exerts mere photoactivation during reaction, which is primarily attributed to the pronounced activation of Ni─O bonds at the catalyst surface. Particularly, the photoactivation of the Ni–O–La moieties, in combination with O species replenishment by H_{2}O, makes Ni/La_{0.10}–S superior to Ni/SiO_{2}. The synergy of La^{3+} promotion and Ni–O photoactivation poses a promising strategy for efficient photothermal catalytic cellulose SR to green syngas.},

keywords = {P08},

pubstate = {published},

tppubtype = {article}

}

@article{Maqbool_2025a,

title = {Upcycling hazardous waste into high-performance Ni/η-Al_{2}O_{3} catalysts for CO_{2} methanation},

author = {Qaisar Maqbool and Hamilton Uchenna Aharanwa and Michael Stöger-Pollach and Günther Rupprechter},

doi = {10.1039/D4GC05217J},

year  = {2025},

date = {2025-02-07},

urldate = {2025-02-07},

journal = {Green Chemistry},

volume = {27},

issue = {10},

pages = {2706-2722},

abstract = {Transforming hazardous and difficult-to-process waste materials, like spent Ni-MH batteries and aluminium foil, into nanocatalysts (NCts) provides a sustainable solution for resource management and reducing environmental impact. This study demonstrates a novel approach by extracting nickel sulfate (NiSO_{4}·\textit{x}H_{2}O) from battery waste and subsequently converting it into Ni(OH)_{2} hydrogel precursors using L-glutamic acid. Waste aluminium foil was processed into alumina (Al_{2}O_{3}), and combined with Ni(OH)_{2} to synthesize Ni/η-Al_{2}O_{3} NCts with 4% and 8% Ni loading. Characterization through XRD/SAED, STEM/EFTEM, and EELS revealed a disordered cubic structure of η-Al_{2}O_{3}, with well-dispersed Ni particles, making it effective for CO_{2} hydrogenation. The 8-Ni/η-Al_{2}O_{3} exhibited the best catalytic performance, with CH_{4} selectivity of 99.8% and space time yield (STY) of 80.3 mmol_{CH_{4}} g_{cat}^{−1} h^{−1} at 400 °C. The CO_{2} methanation mechanism over Ni/η-Al_{2}O_{3} NCts was further explored using operando DRIFTS aligned with GC + MS. The operando investigation suggested a preferential associative CO_{2} methanation pathway, involving sequential adsorption and hydrogenation of CO_{2} to hydrogen carbonates on Ni/η-Al_{2}O_{3}, and their transformation into formate and methoxy intermediates leading to methane. Finally, to complete the upcycling/recycling loop, the spent Ni/η-Al_{2}O_{3} NCts were recycled into Ni and Al precursors. These findings underscore the potential of upcycling waste materials for synthesizing sustainable, high-performance NCts, and offer insights into the CO_{2} methanation mechanism.},

keywords = {P08},

pubstate = {published},

tppubtype = {article}

}

@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}

}