Power-to-X (PtX) processes using renewable electricity for hydrogen production plus non-fossil CO2 will be an important part of the future energy system relying also on e.g. synthetic methane. The fluctuating nature of renewable energies, however, represents a challenge since it can propagate all the way through the PtX process chain. For stationary operation with well-defined feed and process conditions, the CO2 methanation reaction is well understood. However, for tuning catalyst properties and process parameters for transient operation, deeper insights based on fundamental operando studies is of crucial importance. In this contribution, we present a unique reactor setup enabling spatially resolved operando investigations of both, gas phase composition and species adsorbed on a catalyst surface using gas chromatography and infrared spectroscopy (DRIFTS). The performance of an industrial Ni/Al2O3 methanation catalyst was investigated as a function of reaction temperature (100–450 °C) and space velocity (1–20 mlN mg−1 min−1). The spatially resolved DRIFTS (SRD) reactor was modeled, and the flow profile and concentration gradients were simulated using CFD, indicating that the gas sampling does well represent the actual concentration along the reactor coordinate, which was additionally validated by benchmarking to a catalytic plate reactor reference system. The results presented and discussed not only verify the ability of the SRD reactor setup for in-depth investigation but are also in line with the methanation mechanism discussed in literature. Further, the results suggest that the formation of carbonyls which readily react to methane can be seen as the rate-determining step for this type of catalyst.

Direct Air Capture (DAC) is needed alongside other CO2 removal methods to ensure that the total amount of CO2 required is removed from the atmosphere so that global warming can be limited to below 2 degrees. While large-scale DAC farms are a promising solution, their high CAPEX and OPEX, along with societal concerns, may hinder widespread deployment. This study presents a novel, modular DAC concept designed for integration into heating, ventilation, and air conditioning (HVAC) systems of buildings. A prototype was engineered and modeled in MATLAB to analyze key physical processes in the adsorber bed using two amine-based adsorbents. A linear driving force model was applied to simulate mass transport, and the DAC unit was coupled with an HVAC system in Simulink to evaluate COQ capture from indoor air. Solar thermal energy with thermal storage was defined as the heat source. Optimization results indicate a 40 % reduction in thermal energy demand compared to separate DAC and HVAC systems. Cold, humid air improves COQ capture, while dry air significantly lowers the energy demand - up to 50 % when reducing humidity from 90 % to 10 %. A techno-economic analysis suggests that mass-produced DAC modules for HVAC systems could achieve levelized costs of DAC as low as 280 & euro; per ton CO2, particularly when waste heat is utilized. Implementation in densely occupied buildings may yield additional savings of up to 9 %. This work highlights the potential of HVAC-integrated DAC systems as a scalable, costeffective complement to centralized DAC facilities.

By control of the nanosecond pulsation, energy input, and flow, it is possible to achieve commercial-level hydrogen peroxide (H2O2) concentrations using only water and plasma in a continuous process while minimizing thermal degradation. Time-resolved ultrafast Optical Emission Spectroscopy was employed to observe the formation of reactive species, shedding light on the underlying mechanisms. This study also found that thermal degradation has a critical role, which was effectively managed through quenching of the plasma zone. A parametric scan of pulse duration and pulse repetition frequency of the microwave power showed a significant influence on H2O2 formation, whereby the mean power also plays an important role. Additionally, the H2O2 concentration was found to be inversely proportional to the water flow rate. A maximum concentration of 0.17 wt % was achieved with 1.2 g/kWh based on the absorbed power at a flow rate of 0.2 mL/min. This plasma reactor technology shows promise for further development as a decentralized solution for the green chemical synthesis of H2O2.

Reducing the atmospheric CO2 concentration to a sustainable level requires large-scale carbon dioxide removal (CDR) through direct air capture (DAC). DAC is a heat-intensive process, and waste heat recovery to supply its heat demand has substantial potential to reduce the levelized cost of DAC (LCODAC). This study determines the techno-economic potential of recovering low-temperature waste heat (70◦C) from an off-grid alkaline water electrolyzer (AWE) plant for use in a solid-sorbent-based DAC plant requiring heat at 80◦C–120◦C for desorption. The waste heat recovery system, comprising heat pumps and a heat storage, and the DAC plant are dimensioned to minimize the LCODAC based on optimization at an hourly level, and a comparison with an electric-boiler-based heat supply is performed. It was found that the AWE plant producing 6.3 kt/a of H2 can provide thermal energy for a DAC plant capturing up to 27 kt/a of CO2 under Nordic conditions, where low ambient temperatures are beneficial for the solid DAC process, except for subzero temperatures. The LCODAC can be reduced by 24%–39% when a waste-heat-based heat supply is used instead of an electric boiler. Increasing the desorption temperature from 80◦C to 100◦C or 120◦C significantly reduces the LCODAC, even though the cost of heat supply increases due to the decreasing coefficient of performance of the heat pumps. From an electricity system perspective, the use of waste heat sources to supply thermal energy to DAC plants is highly beneficial, as the primary energy demand and the peak electrical power of the DAC process can be reduced by 60% and 55%, respectively, compared with an electric boiler.

Rhodium and lanthanum co-doped strontium titanate (Rh,La:SrTiO3) is a promising material for green hydrogen (H-2) production via heterogeneous photocatalytic (PC) water splitting. State-of-the-art Rh,La:SrTiO3 nanoparticle photocatalysts mitigate charge recombination using an undoped core/doped shell structure. However, the typically-employed synthesis methods use high temperatures >1000 degrees C in a slow dopant diffusion process, which induces inhomogeneities, causes nanoparticle sintering, and limits material performance. In this work, we demonstrate a rapid flash light annealing (FLA) technique that affords suitable nanoparticle doping in only 7.5 seconds. FLA samples show a PC performance three times greater than conventional thermal doping, which we attribute to mitigated particle sintering and dopants incorporated closer to the surface. Moreover, the H-2 evolution rate under full spectrum simulated solar illumination increased by 50% compared to the undoped precursor nanoparticles. Finally, varying the flash parameters shows the tunability of the FLA process. The developed method paves the way for extending rapid doping by FLA to other powdered materials without the need for ion implantation.

In the transient operation of decentralized power-to-gas plants, catalyst dynamics can play a crucial role. For the improved description of such dynamics, the rate affecting step (RAS) approach was developed by Langer et al. Following this approach, in this work, a kinetic model for the methanation reaction over an industrial Ni/Al2O3 methanation catalyst was derived and parametrized using data from a unique laboratory reactor. This reactor setup was specifically developed and built within the priority program SPP2080 "DynaKat" (German Research Foundation), aiming to collect spatially and temporally resolved DRIFTS absorbance data of catalyst surface intermediates. This data was used to tune the performance of the derived RAS model and to evaluate its prediction accuracy. For most scenarios investigated, also including sudden variations in feed composition such as H2 and CO2 drop out/in scenarios and variations in space velocity, the model describes the changes in surface coverage of formate and adsorbed CO reasonably well. Thus, in this work, a first-of-its-kind methodology for including operando DRIFTS data in a parameter estimation routine for a reaction kinetic model is presented. The results are promising and prove the feasibility of this approach, thereby illustrating future opportunities for its use in high-fidelity reaction kinetic modeling.

Converting renewable electricity and captured CO2 into synthetic natural gas is a key element of the energy transition. Compact micro-structured reactors with evaporative cooling are promising for this Power-to-Gas pathway, but their safe operation requires robust thermal stability. This work develops an open-source dynamic model to investigate the coupled effects of heat release from CO2 methanation, heat conduction through the reactor wall, and two-phase flow boiling in a plate-type microreactor. A parametric study reveals an exceptionally narrow operating window of only +/- 2 degrees C in coolant temperature, bounded by reaction extinction and temperature excursions. Two coolant distribution strategies are compared. The spatially redistributed configuration achieves conversions sufficient for injection into the German natural gas grid while producing superheated steam suitable for electrolyzer integration. Cooling failure simulations reveal a pronounced asymmetry: downstream failures are benign, whereas upstream failures induce irreversible steady-state shifts via hysteresis driven by positive feedback between heat release and hotspot migration. Even sub-threshold failures produce permanent hotspot migration, and a critical failure duration of approximately 5 s is identified beyond which recovery requires controlled shutdown. These findings establish temperature exceedance as an insufficient health indicator and provide a quantitative basis for model-based monitoring and control of this reactor class.

Continuous tandem catalysis enables the direct coupling of chemical hydrogen peroxide (H2O2) synthesis with oxidative biocatalysis while avoiding external peroxide addition. In this study, a continuous-flow tandem system combining palladium-catalyzed H2O2 direct synthesis with yeast surface–displayed unspecific peroxygenases (YSD-UPOs) is presented. Peroxygenases were immobilized via a recently published surface-display on Komagataella phaffii cells, which were solvent-inactivated, and freeze-dried to allow application in standard chemical labs. A palladium-based catalyst was prepared on titanium dioxide as a support and evaluated for H2O2 generation under conditions compatible with enzymatic reactions. Chemical and enzymatic steps were first studied separately to identify suitable operating windows for 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) oxidation and hydroxylation of 1,2-(methylenedioxy)-4-nitrobenzene (NBD). The combined system was then operated in a continuous micro fixed-bed reactor proving the concept of continuous tandem catalysis reaching turnover numbers of 3596 for NBD and 6350 for ABTS oxidation.

Support materials are often considered as simple stabilising structures for the active phase, yet their physicochemical properties decisively modulate catalyst performance. Carbon nitride (CN) has frequently been combined with metal oxides, predominantly in photocatalysis, where typically only a single bulk-type CN material is employed. Consequently, the influence of different CN morphologies on the structure and catalytic behaviour of CN-modified oxide supports remains largely unexplored. Herein, we establish CN as a tuneable support modification for Co-catalysed CO2 methanation by systematically integrating distinct CN morphologies, namely sponge-like (spCN), bulk (bCN), highly porous (hpCN), self-assembled (saCN), and triazine-based (tbCN), onto a conventional Al2O3 support via a solution-deposition strategy. This approach yields CN@Al2O3 composites with comparable CN loadings (27-31 wt%) and distinct textural and chemical properties. Comprehensive characterisation confirms that the surface coverage of Al2O3 depends on the morphology of CN, which, in turn, dictates the distribution of Co3O4 during decoration with nanoparticles from a separate synthesis. Catalytic testing at 325 °C and 5 barg reveals a strong morphology-performance relationship. Co/spCN@Al2O3 exhibits the highest productivity with 60% CO2 conversion and 97% CH4 selectivity, outperforming composites based on bCN and hpCN or unmodified Al2O3 as the support material. In contrast, saCN and tbCN modifications resulted in poor performance. Post-run analyses indicate that CN modification may enhance interaction with cobalt and mitigate sintering, with the sponge-like morphology providing the most favourable metal-support interactions. These findings demonstrate that CN morphology represents a key design parameter for tailoring metal-support interactions and catalytic performance in thermocatalytic CO2 hydrogenation.

The design and manufacture of microstructured distillation equipment is challenging. Additive manufacturing has the potential to facilitate the creation of new, efficient equipment. Our design of modular distillation units with helical flow path demonstrates this potential. We examined the separation efficiency at total reflux with cyclohexane/heptane. Due to the design being ready for manufacturing, various variants with different geometric parameters, including channel height and number of turns, were investigated. The experiments revealed that the primary helical structure is critical to separation performance and that unit coupling can enhance separation efficiency. Additionally, the impact of the mounting angle on separation performance was studied and verified. Especially at low loads, a significant increase was observed. Cold flow experiments using transparent 3D-printed resin columns demonstrate the influence of tilting on flow and aid in understanding the effect. Characterizations throughout the entire operating range, up to the flooding point, conclude the research.

This paper presents a parameter-adjustable dynamic mass and energy balance process model fora 50 kW proton exchange membrane (PEM) electrolyzer plant. Energy and mass balances are derived for the electrolyzer stack, heat exchangers, and gas-liquid separation vessels. These balances, along with semiempirical submodels, are integrated and solved within MATLAB system blocks connected through a Simulink environment. The model is validated using experimental data obtained from a comparable industrial plant with similar pressure, power, and system design parameters. The PEM plant is capable of operating within a pressure range of 5-55 bar. The electrochemical and thermal behaviors, along with hydrogen production, are compared between the process model and the actual PEM plant to assess the accuracy of the simulations. The results demonstrate a satisfactory agreement between the model predictions and experimental data. In nominal operation, 68.5% of the total power supplied to the stack is converted into hydrogen, while the remaining power is dissipated as heat due to overvoltages. This excess heat is primarily transferred through the heat exchangers to the secondary leg.

CO2 capture using an l-arginine solution as the sorbent, combined with its regeneration via bipolar membrane electrodialysis (BPMED), is adapted to direct air capture (DAC). Results show that DAC using this approach is possible with a specific energy demand of around 2000 kWh tCO2 -1 for regeneration. Using a measuring method based on electrical conductivity developed within this work, we found the maximum loading of the l-arginine solution from ambient air to be 0.35 molCO2 molArg -1 (0.95 molCO2 molArg -1 with pure CO2). For absorption, different 3D-printed gyroid structures were manufactured and tested. These structures enhanced the gas-liquid contact, resulting in an increase of CO2 capture as compared to a reference pall ring packing, achieving competitive mass transfer coefficients (k l a) of up to 0.69 s-1. Technoeconomic analysis revealed an achievable capture cost of less than 350 tCO2 -1 with water loss, energy cost, and BPMED capex being the most relevant cost drivers.

In the industrial synthesis of ammonia, a combination of high temperature and pressure is required to achieve a reasonable educt conversion. Efforts have been undertaken to lower these requirements by utilizing ruthenium-based catalysts promoted with alkali metals, which have the potential to lower the energy barrier associated with the dissociative adsorption of nitrogen. In this work, the structure of Ru and Cs species is probed in impregnated RuCs/MgO and Ru/MgO catalysts by operando X-ray absorption spectroscopy during reduction and ammonia synthesis at pressures up to 19 bar(a) in pure gas feed as well as the deactivation behavior with unpure feed containing 25 ppm oxygen. Interconversion of three types of Ru species, including RuO2, highly dispersed RuOx, and metallic Ru, occurs for both studied catalysts. Promotion by Cs leads to higher content of metallic Ru at the expense of dispersed RuOx and results in higher NH3 concentration at the reactor outlet. Exposure of the catalysts to traces of oxygen enables a gradual transformation of bare Cs+ cations to hydrated species [Cs(H2O)x]+. The irreversible deactivation of the catalyst is traced back to the leaching of cesium species, which has a disproportionate effect on the catalytic activity.

Power-to-gas technologies, such as CO2 methanation, enable to mitigate man-made climate change. For this process to be viable, it is essential to use an active, selective and stable catalyst. This study addresses these requirements by creating a novel Ni-MnyOx/Al2O3 (0 <= y <= 1) catalyst that uses Mn not as a dopant but creates a joined Ni-Mn mixed metal oxide (MMO) phase on a Al2O3 support. To identify the ideal composition, we compare different Mn contents y from 0 to 1 and determine an Mn/Ni ratio of 0.375 as the minimum for the formation of the supported Ni-Mn MMO phase. Compared to the self-synthesized, literature-based state-of-the-art type NiOx/Al2O3 based CO2 methanation catalysts the Ni-Mn MMO based catalysts achieve about 30 % higher Ni specific methane formation rates. We carefully characterize the catalysts phase composition, surface area, active metal surface area, reducibility, surface basicity and elemental analysis. Additionally, we present a detailed in situ X-ray absorption spectroscopy (XAS) study and phase characterization on the reduction process for catalytic activation of the calcined catalysts to draw conclusions on the final activated state. It was shown that the Ni-Mn mixed metal oxide phase changes upon activation into metallic Ni supported on a Ni-depleted Ni-Mn MMO phase. Additionally, the behavior of both catalysts under reaction conditions was investigated using operando XAS, phase analysis and Diffuse Reflectance Infrared Fourier Transform Spectroscopy. Based on this, a tentative reaction mechanism was proposed which includes the possibility of additional CO2 activation pathways on the Ni-Mn MMO phase.

This study deals with the question which direct air capture technologies currently have the biggest potential for reaching a gigaton scale of capture capacity. Technologies that were examined are alkaline gas washing, temperature-vacuum swing adsorption, electro-swing adsorption, and accelerated weathering carbon capture. A multi-criteria decision-making model (PROMETHEE II) and cost predictions based on learning by doing were used to determine which technology has the highest potential. The results show that electro-swing adsorption has the highest potential but comes with a lot of uncertainties that need to be cleared in the future, such as costs and supply for adsorbents. In addition, it was not tested under ambient conditions, and therefore, it is unclear how this technology will perform at atmospheric CO2 levels. Next best would be accelerated weathering carbon capture, which needs no fresh water and has lower energy demand compared to temperature-vacuum swing adsorption. A major disadvantage might be the land requirements and the high temperatures to regenerate the carbonates. Temperature-vacuum swing adsorption follows shortly after, mainly profiting from a great cost reduction potential from learning by doing and a comparably small land footprint. Alkaline gas washing showed the lowest potential, but through improving the process, it will also have the possibility to be applied at gigaton scale.

Excellent energy efficiency and system stability are critical factors guiding the practical application of carbon dioxide reduction reaction (CO2RR) systems. This work promotes reduction reaction kinetics in a modified zerogap electrolyzer by regulating the operation temperature and pressure. The energy efficiency of the CO2RR system is enhanced, such as 52.6 % at a current of 1.2 A under alkaline conditions and 49.4 % under neutral conditions, with the characteristics of low voltage and high Faradaic efficiency. In addition, the optimization of the reaction microenvironment effectively alleviates the precipitation issue, enabling the system to operate stably for more than 100 h, with a Faradaic efficiency of more than 90 % for CO generation. Engineering-integrated electrochemistry inspires the future development of CO2RR technology.

Electrochemical CO2 reduction represents a promising approach for mitigating carbon emissions while generating value-added fuels and chemicals. While catalyst design mainly dictates activity and product selectivity, system-level performance is strongly influenced by the interplay between electrolyzer configuration and operating parameters. In this study, a zero-gap membrane electrode assembly electrolyzer incorporating a cation exchange membrane is systematically investigated under practical considerations. The applicable operating window is successfully extended to elevated temperatures and pressures, demonstrating robust practicality and efficient conversion. Comprehensive evaluation of cell voltage, Faradaic efficiency, and energy efficiency reveals that a balanced combination of catalyst loading, electrolyte concentration, and flow rate enables high CO selectivity (>90%) and energy efficiency exceeding 40% at moderate current density (100 mA/cm2). By integrating multiple operational parameters, this work advances the application of cation exchange membrane based CO2 electrolysis and offers practical insights for bridging laboratory research and scalable implementation.

For the sake of environmental reasons, additive manufacturing of catalytic converters has been an attractive topic in both computational research and product development fields within the last few years. With respect to structured catalysts, monolithic designs manage convenient characteristics by providing a large surface area for catalytic reactions within a defined volume. Because of manufacturing limitations, conventional metallic monolithic geometries were limited to sinusoidal channels. Accumulation of the catalyst and washcoat in the corners of sinusoidal channels have negative influences on the washcoat geometry and mass-transfer. These reasons together with high manufacturing costs had limiting effects on expanding applications of metallic monoliths. With the emergence of rapid prototyping technologies, complex unity structures of metallic monoliths can be printed at once. Although flexibility in design and ease in fabrication both are satisfied with additive manufacturing, still operational conditions and reaction requirements must be met for approval of any prototypes. This research uses a multidisciplinary approach to study monolithic designs suitable for a specific reactor size. Besides, these designs must be 3D-printable and suitable for washcoating. Considering design challenges and innovations in additive manufacturing of metals, relationships between mathematics, structural integrity, coating and material aspects are considered for analyzing the multi-channel monoliths. (c) 2024 The Authors. Published by Elsevier B.V.

The integration of offshore wind energy into Power-to-X (PtX) process chains offers opportunities for the efficient use of renewable energy. This article analyzes different PtX process chain configurations and their adaptation to the offshore environment. However, direct coupling of PtX platforms with fluctuating electrical energy poses major challenges. Dynamic process simulation is presented for analysis of different plant configurations and operating strategies. The article emphasizes the need for interdisciplinary research to consider technological as well as economic and environmental aspects. When coupling offshore wind turbines with Power-to-X platforms on the high seas, the plants must be able to follow the wind and energy fluctuations without a grid connection. Dynamic process simulations can help to adapt the process chains to the offshore plant environment and to investigate transient operation. image