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Item type:Publication, Access status: with files , Reconstruction-free EIT for injection-pattern classification and superficial gas velocity regression as proxies for local gas holdup in bubble columns(American Chemical Society (ACS), 2026-09-10); ; ; ; Electrical impedance tomography (EIT) as a noninvasive tomographic technique is increasingly applied to multiphase reactor monitoring; however, conventional image reconstruction is ill-posed and regularization-dependent and may be redundant in applications where the primary objective is operating-state identification rather than explicit spatial conductivity field reconstruction. Here, we present a reconstruction-free, measurement-domain framework for bubble-column monitoring that maps raw complex boundary impedance data directly to two reactor-relevant inference tasks: (i) gas injection pattern classification and (ii) superficial gas velocities regression. Together, these two quantities ─ the spatial injection distribution and the total volumetric flow ─ constitute the primary process-state information from which gas holdup can subsequently be inferred and are therefore reported as proxies for local gas holdup monitoring. Experiments were conducted in an acrylic bubble column (600 mm height, 104 mm inner diameter) equipped with a 256-electrode array distributed over eight axial rings and operated at four excitation frequencies (1 kHz-1 MHz). Experiments covered gas flow rates between 1.0 and 6.5 L min–1 (Ug = 1.96 → 12.75 mm s–1), within which near-perfect gas injection pattern classification was achieved with accuracies of 93–100% for excitation frequencies between 1 and 100 kHz using the full 256-electrode configuration. For quantitative superficial gas velocity estimation, increasing calibration density along Ug reduced the mean absolute error from 0.388 to 0.105 L min–1 (MAE[Ug] = 0.76 → 0.205 mm s–1, i.e. 7.0% → 1.9% of the operating range) for localized injection and from 0.298 to 0.157 L min–1 (MAE[Ug] = 0.585 → 0.307 mm s–1, i.e. 5.4% → 2.8% of the operating range) for distributed injection conditions. These results demonstrate that direct inference from raw EIT boundary measurements enables accurate, real-time monitoring of bubble-column operation without tomographic reconstruction and provide quantitative guidance on excitation frequency selection, axial sensing placement, and calibration resolution.Publicationtype: Journal Article28 25 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Iso-potential operando coupling of XRD and a profile reactor: structural insights into ZnPd/ZnO during methanol steam reforming(American Chemical Society (ACS), 2026-07-16); ; ; The dynamic structural changes of ZnPd/ZnO make it the leading contender to improve CO2 selectivity in methanol steam reforming (MSR). The dynamics are reaction-induced and depend upon local chemical potentials, thus making spatially resolved operando investigations imperative. New iso-potential operando (IPO) techniques enable the study of catalysts under identical chemical potentials in separated but coupled cells. Here, the adaptive phase composition and structural changes of ZnPd/ZnO are investigated using iso-potential operando XRD (IPO-XRD) achieved by coupling a profile reactor and operando XRD. The results demonstrate the successful coupling and reveal the spatial variation of additional reflections assigned to ZnCO3, a phase that has not been previously reported. This highlights the potential of IPO-XRD and lays the groundwork for future investigations of other complex and structurally dynamic catalytic systems.Publicationtype: Journal Article29 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Impedance-based estimation of process parameters in electrolytic systems via circuit-embedded neural network (CENN)(American Chemical Society (ACS), 2026-07-09); ; ; ; We present a physics-aware machine learning framework for real-time estimation of electrolyte concentration and temperature from electrochemical impedance spectroscopy (EIS) measurements. Using nanoporous gold electrodes in aqueous H₂SO₄ as a model system, impedance spectra were acquired across concentrations of 1−20 mM and temperatures of 26−50 °C. The spectra were interpreted using a ZARC + transmission-line equivalent circuit and globally fitted over the full (c, T) domain, revealing two characteristic time scales associated with interfacial charge transfer and porous transport. The resulting physically consistent parameter maps were embedded into a circuit-informed neural network, enabling high-fidelity forward prediction of full impedance spectra directly from state variables (RMSE = 0.06 Ω). Inversion of this model allowed accurate estimation of electrolyte properties from measured spectra, achieving mean absolute errors of 0.10 mM in concentration and 1.0 °C in temperature. To further ccelerate sensing, Jacobian-based sensitivity analysis identified three informative frequencies that preserved essential spectral information. This reduced acquisition time by more than 95%-from minutes to under 6 s-while maintaining high accuracy (0.12mM, 1.1 °C). Although demonstrated for a specific electrochemical system, the proposed framework provides an interpretable and transferable workflow for rapid multiparameter sensing, provided that the equivalent-circuit structure and calibration domain are adapted to the target system.Publicationtype: Journal Article41 64 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Iso-potential operando microwave cavity perturbation–spatial conductivity changes of a Cu/ZnO/Al₂O₃ catalyst inside a fixed-bed reactor during reverse watergas shift reaction(American Chemical Society (ACS), 2026-06-25); ; ; This work explores the combination of Microwave Cavity Perturbation (MCP) with the concept of Iso-Potential Operando Spectroscopy (IPOS) to develop IPO-MCP for measuring conductivity changes in a catalyst within a catalytic fixed-bed reactor (FBR). As proof-of-concept, spatially resolved dielectric properties, species, and temperature profiles were recorded during the reverse water–gas shift (rWGS) reaction on a commercial copper–zinc-alumina (CZA) catalyst. These results reveal a linear electronic structure–activity relationship along the catalyst packing demonstrating that hydrogen significantly enhances the Q-value compared to carbon dioxide in line with previous investigations. This research motivates further application of IPO-MCP to other catalytic systems with distinct conductivity changes.Publicationtype: Journal Article70 49 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Simulation-driven Electrical Impedance Tomography for buoyancy-driven electrolyte mixing: A hybrid hydrodynamic–circuit modeling framework(Elsevier, 2026-02-17); ; ; ; We present a modular, end-to-end simulation benchmark for Electrical Impedance Tomography (EIT) in chemical reactor monitoring. The goal is to enable controlled and repeatable evaluation of EIT reconstruction methods in a realistic, physics-based setting. The framework integrates the full pipeline—from hydrodynamic transport and electrochemical modeling to hardware emulation and image reconstruction. For this purpose, aqueous HCl mixing is modeled using Stokes–Boussinesq flow coupled with advection–diffusion; local conductivity is computed via the Debye–Hückel–Onsager approximation and mapped to resistor networks simulated in SPICE with a 32-electrode EIT analog front-end. Boundary voltages are generated and processed using the Complete Electrode Model (CEM) in EIDORS and reconstructed with NOSER and Total Variation (TV). The modular design enables independent refinement of each module for task-specific front-ends and reconstructions. A comparison of FEM/CEM and SPICE simulations under matched hardware configurations shows close agreement in voltage measurements, validating circuit translation. For homogeneous measurements, simulated voltages were further validated against data from a self-built EIT device, confirming consistency across both simulation paths. Moreover, by modifying hardware-specific parameters in SPICE, we demonstrate how design choices influence measurement behavior, supporting targeted front-end optimization. This simulative benchmark thus provides a validated, reusable testbed for studying physics–algorithm–hardware interactions and for standardized, quantitative evaluation of EIT methods in reactor-relevant settings. It integrates electrical modeling, reconstruction algorithms, and engineering aspects into a coherent cross-domain framework that highlights how modeling and reconstruction choices shape interpretation across applications.Publicationtype: Journal Article97 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Reactors for fluid-solid reactions: Fixed bed reactorsFixed bed reactors are the most commonly used reactor type in the chemical and petrochemical industry. They are also used for mobile and stationary exhaust gas cleaning. All fixed bed reactors have in common that a solid, usually a catalyst, is spatially fixed in the reactor and is flowed through or over by the reaction mixture. This chapter provides an overview of this important reactor type, with the focus on catalytic fixed bed reactors for gas reactions. After a brief introduction, catalytic fixed bed reactors are classified according to the type of involved phases, the structure of the catalyst phase, and the temperature control. The operating principle of the different reactor types is explained using examples. In addition to fixed bed reactors in industry, fixed bed reactors in laboratory and research are also discussed, which are used for high-throughput screening, for measuring kinetic data, or for operando spectroscopy on catalysts. Subsequently, the mathematical modeling of fixed bed reactors is discussed. The classification of the different modeling approaches includes the dimension of the modeling domain, the mathematical structure of the equations, the description of transport processes, the number and type of involved phases, and the description of the reaction kinetics. In addition to the classic pseudo-homogeneous, pseudo-heterogeneous and heterogeneous reactor models modern modeling approaches such as the CFD simulation of catalytic fixed bed reactors are presented using examples. Finally, the unsteady operation and the dynamic behavior of fixed bed reactors are addressed. In this context, the parametric sensitivity, the thermal runaway, and the periodic flow reversal are examined in more detail.Publicationtype: Book Part64 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Elemental analysis of catalysts in a fixed-bed reactor by laser-induced breakdown spectroscopyIn situ and operando characterization techniques provide molecular, surface, electronic, and structural information about catalysts in reactors. Accessing changes in the “Elemental Composition” of catalysts under reaction conditions remains yet an unsolved challenge. This work takes a first step in this direction by investigating the potential and limitations of Laser-Induced Breakdown Spectroscopy (LIBS) for monitoring catalyst deactivation, specifically during Dry Reforming of Methane over Ni/γ-Al2O3 and Propane Dehydrogenation over VOX/γ-Al2O3. The study increases complexity stepwise, starting from spatially resolved ex situ LIBS analysis of catalyst particles removed from the reactor after reaction, to the development of a fiber-optic LIBS system and time-resolved intra-reactor measurements. Spectroscopic measurements are complemented by monitoring catalyst activity and temperature at each stage. For the dry reforming of methane, a correlation was found between catalyst performance, temperature, and the spatial distribution of coke, with distinct zoning along the catalyst bed. A cost-effective fiber-optic LIBS probe was developed, allowing for intra-reactor measurements under harsh conditions. The LIBS probe was used to study catalyst deactivation and regeneration during propane dehydrogenation by measuring time-resolved carbon and vanadium profiles. A Partial Least Squares regression model was developed to correlate the amount of carbon deposits with the LIBS spectra, allowing the derivation of quantitative statements. Despite its limitations, such as invasiveness and gas sensitivity, the study highlights the potential of LIBS as an in situ/operando elemental analysis technique.Publicationtype: Journal Article60 28 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Measuring adsorbate profiles in heterogeneous catalytic reactors by iso-potential operando DRIFTS applied to CO₂ methanation on Ni(American Chemical Society (ACS), 2024-06-07); ; ; The development and improvement of catalytic processes require a detailed understanding of catalyst dynamics, reaction mechanisms, and structure-activity relationships inside catalytic reactors, from the laboratory to production scale. This paper presents the methodology of iso-potential operando DRIFTS for measuring the profiles of surface adsorbates inside catalytic reactors. Iso-potential operando spectroscopy (IPOS) in general and iso-potential operando DRIFTS in particular separate the functionality “catalytic reactor” and “spectroscopic cell” from each other. The catalytic reactor is equipped with a mechanism of spatial sampling and spatial temperature measurement. A small fraction of the reaction mixture is sampled locally in the reactor and transferred continuously into a spectroscopic cell containing a very small amount of the same catalyst as in the reactor. The temperature is set to the same value as is locally measured in the reactor. In this way, the catalyst in the spectroscopic cell is exposed to the same chemical potential as that locally in the catalytic reactor. It is hypothesized that it takes on the same structure, the same surface adsorbates, and shows the same reactivity. IPO DRIFTS is applied to CO2 methanation on Ni/γ-Al2O3 catalysts. Two surface adsorbate species, adsorbed carbonyl (*COads) and adsorbed formate (*HCOOads), are detected. The band intensity of *HCOOads decreases along the catalyst bed with the CO2 concentration in the gas phase, identifying surface formate as a kinetically relevant intermediate. This finding is in line with an associative mechanism where CO2 adsorbs on γ-Al2O3 forming carbonate or bicarbonate, being rapidly hydrogenated to formate. Formate reduction is the rate-determining step, with all subsequent hydrogenation steps to CH4 being fast. The band intensity of *COads does not change, irrespective of position in the catalyst bed. This invariance of *COads can be interpreted in two ways. *COads could be a spectator species that is present at the catalyst surface but not involved in any kinetically relevant reaction channel. Alternatively, *COads could be formed by rapid dissociative adsorption of CO2 at the surface of the Ni nanoparticles with a high adsorption equilibrium constant, leading to an almost constant *COads coverage within the investigated CO2 conversion range. If the rate-determining step in the reaction sequence to CH4 would then occur after the formation of *COads, e.g., *COads → *Cads + *Oads or *COads + *Hads → *HCOads, an almost constant *COads signal would result as well.Publicationtype: Journal Article172 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Spatially resolved reaction profiles of CO2 hydrogenation to methanol using in-based catalysts in a compact profile reactor(American Chemical Society (ACS), 2024-06-07); ; ; ; The compact profile reactor (CPR) design allows for the simultaneous acquisition of species, temperature, and spatially resolved reaction profiles during high-pressure CO2 hydrogenation to methanol. Indium-based catalysts for CO2 hydrogenation have attracted significant scientific interest since they are more selective, efficient, and resistant to deactivation compared to the state-of-the-art copper-based catalyst. In this study, the reaction profile of In2O3/ZrO2 catalysts is compared to that of the state-of-the-art Cu/ZnO/Al2O3 (CZA) catalyst in a high-pressure CPR. It is demonstrated that the addition of nickel as a promoter significantly enhanced the catalytic activity of pure In2O3/ZrO2. The characterization by H2 TPR and CO2 TPD revealed an increased capacity for both hydrogen and CO2. A detailed comparison and optimization of reaction conditions using Ni–In2O3/ZrO2 as a catalyst are presented. In an optimized experiment, Ni–In2O3/ZrO2 produces 4.90 gMeOH gIn+Ni–1 h–1 at 275 °C, 50 bar, and 63,000 h–1with a methanol selectivity of 73%. Furthermore, no catalyst deactivation caused by metal leaching or sintering could be observed over 90 h time on stream.Publicationtype: Journal Article212 126 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Quantitative chemical mapping of Pt/Rh gauze catalysts for ammonia oxidation using resonant X-ray tomography(American Chemical Society (ACS), 2024-03-18); ; The loss of platinum group metals during the industrial Ostwald process for catalytic ammonia oxidation is a century-old concern. Understanding catalyst degradation requires knowledge of physicochemical changes occurring on stream, particularly on technical Pt/Rh gauze catalysts. However, such catalysts are mainly studied with surface-sensitive methods or as model systems since their composition of noble metals (e.g., 95/5 wt % Pt/Rh) makes it challenging to characterize the bulk catalyst. Here, we exploit the high-resolution and elemental sensitivity of synchrotron-based hard X-ray resonant tomography to quantify the 3D distribution of Rh and Pt in technical gauze catalysts. Resonant tomography performed above and below the Rh K-edge (23.300 and 23.208 keV, respectively) allowed computation of elemental distribution. Absorption contrast tomography was successful despite beam transmission of <0.1%. This was achieved using a single-photon counting detector. Rh segregation, Pt loss, and bulk material degradation leading to redistribution of elements were visualized and quantified within intact ∼76 μm diameter wires, with 2 μm resolution, and up to 50 days on stream. The estimated local Pt and Rh wt % changes showed significant material loss from the wire exterior and characteristic protrusions. However, the wire core was unaffected by the reaction conditions even after 50 days on stream. No volume diffusion from the wire center to the exterior was observed to mitigate material loss from the latter. This flexible and high-throughput quantitative imaging approach is uniquely possible with synchrotron hard X-ray tomography, opening further routes of study for compositionally challenging industrial catalysts.Publicationtype: Journal Article49 128