Christoph Kubis

Gas chromatography (GC) is an important tool in analytical chemistry and large amounts of data are routinely produced. Despite the advances in the available software, the analysis of a dataset can still be a time‐consuming task, in part due to the manual or semi‐automated marking of peaks. An automation of this tedious task is proposed in this work.

The area of feasible solutions (AFS) quantifies factor ambiguity in multivariate curve resolution (MCR). Although AFS computation is well‐defined for noise‐free data, experimental datasets require constraint relaxation and parameter tuning, which influence the resulting feasible bands. This work addresses the computation of the AFS in the presence of noise. We propose a statistically motivated strategy for control parameter estimation based on Savitzky–Golay filtering, introduce a two‐stage preprocessing approach for baseline‐distorted data, and analyze the effect of noise in the dual space. The methods are demonstrated on model data and experimental FT‐IR datasets.

Low-temperature CO2 hydrogenation to methane has the potential to form the basis of power-to-gas technologies, which could help close the carbon cycle and address environmental concerns. Catalysts with supported metals that can activate hydrogen are typically used for this reaction but do not yet meet the requirements of large-scale applications. Their tailored design remains challenging due to the ambiguity about the role of support and supported metal and how they interact with each other to ensure industrially relevant performance. To contribute to closing this knowledge gap, we prepared ZrO2- and YZrOx-supported catalysts possessing 1 nm Ru or Rh nanoparticles at a low metal loading of about 0.1 wt %, which was chosen for economic reasons. The best-performing Ru/ZrO2 catalyst outperformed various previously developed Ru- or/and Rh-containing catalysts in terms of metal-related activity despite operating at around 90% equilibrium conversion. To gain a detailed understanding of the kinetics and mechanism of CO2 methanation, we performed a comprehensive study combining steady-state isotopic transient kinetic analysis (SSITKA), temporal analysis of products (TAP), and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The SSITKA method enabled us to determine the concentration and the lifetime of the surface intermediates of gas-phase CH4. The concentration was found (i) to be significantly higher than that of surface atoms of Rh or Ru and (ii) to increase with increasing reaction temperature. Thus, support plays a pivotal active role in the reaction kinetics and mechanism. Moreover, a direct correlation was found between the lifetime and the strength of CO2 adsorption as determined by TAP experiments. This finding suggests that the adsorptive catalyst property is an important activity-governing factor. This property can be controlled by the degree of support reduction; the higher the reduction degree, the longer the lifetime. The reduction degree depends on the kind of supported metal and dopant for ZrO2. In situ DRIFTS studies confirmed that CO2 methanation proceeds on the support via the formate (HCOO–) and methoxy (OCH3) intermediates, ultimately yielding gas-phase CH4. The synergistic action of oxygen vacancies and weak OH– basic centers was suggested to facilitate CO2 adsorption and its rapid conversion into active HCOO– species, thereby enabling the fast formation of reaction intermediates. The coexistence of oxygen vacancies and weak OH– groups on the surface of ZrO2-based supports may provide a faster pathway for CH4 formation. Therefrom, the presented approach and the obtained knowledge may be used for the purposeful design of catalysts not only for CO2 methanation but also for CO2 hydrogenation to higher hydrocarbons to hinder the formation of CH4.

Non-oxidative dehydrogenation of propane (PDH) is a well-established large-scale route for on-purpose propene production. Cobalt-based catalysts have attracted increasing attention due to their attractive performance as environmentally friendly and cost-efficient alternatives to commercially used catalysts containing chromium or platinum. However, their further development to reach an industrially attractive level is hindered by insufficient knowledge of the structure-activity-selectivity relationships for tailored catalyst design and preparation. In this work, magnesium (Mg) is introduced as a promoter to regulate the local structure of CoO_x species on the surface of silicalite-1. Owing to the formation of Co−O−Mg bond(s) in the presence of the promoter, the formed CoO_x species become isolated, less reducible, and less acidic. These changes are key to catalyst activity and propene selectivity. The promoter effectively decreases the amount of strong acidic sites, thereby facilitating propene desorption and accordingly suppressing undesired cracking and deep dehydrogenation reactions involving adsorbed propene. The optimized catalyst outperforms an analogue of commercial K-CrO_x/Al₂O₃ and demonstrates durability in a series of five PDH/regeneration cycles under industrially relevant conditions. The space-time yield of propene formation reached 1.2 kg_C3H6·kg_cat⁻¹·h⁻¹ at 550 °C and 68% of the equilibrium propane conversion, being higher in comparison to that of most previously reported cobalt-based catalysts under comparable conditions. In view of this result, the structural and mechanistic knowledge obtained on the promoter effect can be used to prepare highly efficient PDH catalysts with supported metal-oxide species, including those beyond CoO_x.

Supported chromium catalysts find broad application due to metal's ability to assume a range of oxidation states and structures. However, the behavior of chromium species on reducible metal oxides under reactive conditions remains poorly understood, despite the potential for unique reactivity through metal-support interactions. Recent studies on CeO₂-supported Crⁿ⁺ single atoms for selective NH₃ oxidation to N₂O underscore this potential, attaining high performance through cocatalytic action with CeO₂, but also suffering from deactivation through agglomeration of isolated sites into Cr₂O₃. To address this challenge, we investigate how distinct CeO₂-supported chromium species evolve under varying reactive environments. We show that under oxidative conditions redispersion of Cr₂O₃ occurs, serving as a catalyst regeneration strategy and enabling the recovery of both structure and performance. Combining advanced microscopy, in situ Raman, UV-vis, electron paramagnetic resonance and X-ray absorption spectroscopies, we follow the transformation from crystalline Cr₂O₃ nanoparticles to isolated chromium species. The redispersion is proposed to proceed via particle amorphization and oxidation of Cr³⁺ to mobile Cr⁶⁺, which diffuse over the support and stabilize as chromate species or as Cr⁵⁺ upon reduction by oxygen vacancies. A slower redispersion rate is observed over less reducible ZrO₂ and TiO₂, with minimal changes on γ-Al₂O₃ and Nb₂O₅, highlighting support reducibility as the driver of the process and reflecting the potential for generating Cr⁶⁺ sites from nontoxic Cr₂O₃ by controlling support properties. These results demonstrate how redox-active supports facilitate reversible changes to metal nanostructure, offering a promising strategy for regenerating catalysts and tuning metal speciation through rational support design for various applications.

Herein, the development and application of a customized nonthermal plasma diffuse reflectance infrared Fourier transform spectroscopy cell based on the Harrick reaction chamber is presented, which integrates a miniaturized dielectric barrier discharge (DBD), implemented in a Bruker Invenio S Fourier transform infrared spectroscopy (FTIR) spectrometer. The one‐sided closed electrode‐tube arrangement, mounted in a PEEK cylindrical holder, is inserted through the observation window. The stable operation of AC‐driven (10.6 kHz) dielectric barrier discharges in binary gas mixtures of argon and CO₂ is monitored by electrical measurements, which also allows the determination of the discharge power. The gas outlet is connected to a mass spectrometer for online quantitative product gas analysis, enabling operando FTIR spectroscopic studies of plasma‐assisted heterogeneous catalyzed reactions. The impact of applied discharge voltage under the variation of the gas composition, gas flow, catalyst pretreatment procedure, and the distance between electrode and catalyst bed has been studied for the CO₂ splitting employing CeO₂ as a catalyst. The operando FTIR spectroscopic study of the plasma‐assisted CO₂ dissociation suggests both an active CO₂ dissociation on the ceria surface and a plasma‐induced reorganization of the catalyst surface structure. The results in terms of calculated specific energy input and CO₂ conversion correspond with the trends reported for this transformation in coaxial DBD reactors.

Knowledge about dynamic changes of the phase composition during catalytic reactions is indispensable for gaining a better understanding of catalyst structure‐reactivity relationships. For this purpose, in situ Raman spectroscopic experiments were conducted to monitor the structural changes of ferrous oxalate without and with an alkali metal promoter during CO₂ hydrogenation to C₂₊‐hydrocarbons under realistic reaction conditions (340 °C, 15 bar). The kind of promoter had no significant influence on the thermal transition of iron oxalate into the magnetite (Fe₃O₄) phase as the major phase under inert gas. In contrast, the promoters did have a substantial impact on the phase composition during CO₂ hydrogenation. The Raman spectroscopic results obtained, underpinned with X‐ray diffraction measurements, demonstrated a much stronger development of carbon‐containing species, notably iron carbides (FeC_x) and carbon deposits, when using the alkali metal‐promoted catalysts. The formation of carbon deposits may indirectly indicate the occurrence of carbidization, however, no quantitative correlation was discovered. It was also found that the presence of alkali metal promoters hampered the reoxidation of FeC_x toward Fe₃O₄ with water vapor.

We report the cyclotrimerization reactions of triynes using Mn(I) complexes derived from MnBr(CO)₅ and phosphine ligands, such as 1,1-bis(diphenylphosphino)methane (dppm). These reactions are driven by irradiation under mild conditions (30-80 °C) without the need of additional photoinitiators. Our catalytic screening revealed that counteranions and ligands significantly influence the process. This method accommodates a broad range of functionalities in the substrates, including alkyl, aryl, Bpin, SiMe₃, GeEt₃, PPh₂, pyridyl, and thienyl moieties, without notable interference in the transformation. Additionally, this method enables reactions with oligoalkynes-like (un)substituted hexaynes, producing 2-fold cyclization products in very good yields. Under stoichiometric conditions, the cyclization of diynes with phosphaalkynes results in the unique photochemical synthesis of phosphinines. Experimental and theoretical mechanistic studies indicate that the dissociation of the diphosphine ligand precedes the involvement of the Mn carbonyl species in the catalytic cycle. The ligand plays a crucial role in stabilizing the catalyst during the catalytic transformation and preventing the formation of unreactive cluster species.

The fundamentals of in situ formation of iron carbides are required for the tailored design of Fe‐based catalysts for the efficient conversion of CO₂ to higher hydrocarbons. Herein, time‐resolved in situ X‐ray absorption spectroscopy has been used to elucidate the mechanism of the formation of Fe₅C₂ from ferrous oxalate (FeC₂O₄) at 350 °C using a H₂/CO=3 reaction feed. Regardless of the kind of alkali metal promoter and reaction pressure (1 or 7.5 bar), FeC₂O₄ is first decomposed to FeO followed by the conversion of the latter to Fe₅C₂. Further insights into the above transformations were derived by kinetic analysis using a Johnson–Mehl–Avrami–Erofeev–Kolmogorov model and kinetics‐constrained neural ordinary differential equations method. Both approaches revealed that the formation of FeO at 1 bar follows a nucleation mechanism, while a diffusion mechanism has a higher contribution at 7.5 bar. The latter mechanism is valid for the conversion of FeO to Fe₅C₂ at both pressures. Alkali metal promoters were found to accelerate the rate of Fe₅C₂ formation. This rate decreases with increasing total pressure due to the stabilization of FeO.