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In this work, two palladium-based catalysts with either ZSM-5 or Zeolite Y as support material are tested for their performance in selective catalytic reduction of NOx with hydrogen (H2-SCR). The ligh-toff measurements in synthetic exhaust gas mixtures typical for hydrogen combustion engines are supplemented by detailed catalyst characterization comprising N2 physisorption, X-ray powder diffraction (XRD), hydrogen temperature programmed reduction (H2-TPR) and ammonia temperature programmed desorption (NH3-TPD). Introducing 10% or 20% TiO2 into the catalyst formulations reduced the surface area and the number of acidic sites for both catalysts, however, more severely for the Zeolite Y-supported catalysts. The higher reducibility of the Pd particles that was uncovered by H2-TPR resulted in an improved catalytic performance during the light-off measurements and substantially boosted NO conversion. Upon exposition to humid exhaust gas, the ZSM-5-supported catalysts showed a significant drop in performance, whereas the Zeolite Y-supported catalyst kept the high levels of conversion while shifting the selectivity from N2O more toward NH3 and N2. The 1%Pd/20%TiO2/HY catalyst subject to this work outperforms one of the most active and selective benchmark catalyst formulations, 1%Pd/5%V2O5/20%TiO2-Al2O3, making Zeolite Y a promising support material for H2-SCR catalyst formulations that allow efficient and selective NOx-removal from exhaust gases originating from hydrogen-fueled engines. [ABSTRACT FROM AUTHOR]

The catalytic surface interacts with the gas-phase by a variety of chemical and physical processes. Hence, optimization of design and operation conditions of catalytic reactors do not only require the understanding of the catalytic reaction sequence but also its coupling with mass and heat transport and potential homogeneous reactions. The chemical, thermal, and mass-transport interactions between the catalytic surface and the gas-phase are discussed in terms of the individual and combined interactions. The state-of-the-art modelling of reactive flows and its coupling with the catalytic surface is summarized. The interactions are illustrated by a number of examples such as reforming of hydrocarbons, catalytic combustion, exhaust-gas after-treatment, each focusing on a special aspect of catalyst-gas interactions. The potentials and limitations of the numerical simulations will be discussed including experimental techniques for model validation. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The catalytic partial oxidation (CPOX) of methane is studied over staged palladium/alumina and rhodium/alumina coated monoliths by an in-situ sampling technique to resolve the axial species concentration and temperature profiles. A molar C/O ratio of unity, which is stoichiometric for the formation of synthesis gas (CO/H 2 ), and short residence times are chosen for this autothermal process. The profiles of the staged monoliths are compared with profiles of single-sliced palladium/alumina and rhodium/alumina coated monoliths. The investigations clearly show two zones inside the catalytic channel. In the staged catalyst with the Pd stage being on the upstream side as well as in the single-sliced Pd catalyst, hydrogen is not formed before oxygen is almost completely consumed, i.e. a total oxidation zone is observed in front of a steam reforming zone. In the Rh catalyst, in the first 2 mm zone, total oxidation and steam reforming occur as prevalent reactions followed by a reforming zone with steam reforming as dominating reaction. The observations are interpreted in terms of the indirect and direct route towards hydrogen formation in CPOX of methane. [ABSTRACT FROM AUTHOR]

Vanadium oxide (VOx‐Pd) nanotubes as well as VOx‐coated ZnO nanorods (ZnO@VOx‐Pd) and VOx‐coated, layered‐titania nanotubes (l‐TiO2@VOx‐Pd) are decorated with Pd nanoparticles and evaluated for selective catalytic reduction with hydrogen (H2‐SCR) for the first time. The nanostructures exhibit lengths of 300 to 700 nm, diameters of 20–100 nm and, in the case of the nanotubes, an inner tube diameter of about 10 nm. Pd nanoparticles (14±5 nm) are well‐dispersed over the respective nanorod/nanotube nanostructure. Structure and composition are characterized by SEM, TEM, EDXS with element mapping, XPS, FT‐IR, XRD, and sorption analysis. Thermal analysis indicates the nanostructures to be thermally stabile up to 350 °C (VOx), and 500 °C (ZnO@VOx, l‐TiO2@VOx). All catalysts are tested for their activity in regard of the selective catalytic reduction of NO with H2, revealing a significant impact of the catalyst support on both activity and selectivity. Specifically, l‐TiO2@VOx nanotubes show promising properties with an activity up to 70 % and a selectivity up to 80 % N2. [ABSTRACT FROM AUTHOR]

Looking at exhaust-gas after-treatment systems in its entirety leads to further improvement of emission control devices and to the accomplishment of future challenges such as lower legislative emission limits, new fuels, and more efficient engine concepts. This article provides an overview on the state-of-the art mobile exhaust-gas after-treatment devices. Current and future challenges are discussed in the light of present approaches such as hierarchical modeling reaching from DFT computations of molecular processes to CFD simulation of entire lines of exhaust-gas cleaning devices, close-to-reality emission control test benches and aging procedures, on-board diagnostics, and catalyst characterization at operating conditions and preferentially all length scales. In future, knowledge-based robot-controlled preparation and dynamic models coupled with information from real operation will significantly support research and development. [ABSTRACT FROM AUTHOR]

Abstract: A newly established stagnation flow reactor with analysis of spatially resolved concentrations profiles is presented as useful tool for the investigation of heterogeneously catalyzed gas-phase reactions. The simplicity of this laboratory-scale reactor enables detailed modeling of the diffusive and convective transport within the one-dimensional gas-phase boundary-layer coupled with elementary-step homogeneous and heterogeneous reaction mechanisms. This set-up is applied to study the kinetics of hydrogen oxidation over Rh/Al2O3. By combining experimental and modeling results for a wide range of temperature and fuel/oxygen ratios, a thermodynamically consistent set of kinetic data for a 12-step surface reaction mechanism is derived. The applicability of the mechanism is further tested by the model prediction of experimentally derived ignition temperatures in a stagnation flow reactor and oxygen conversion in H2-rich hydrogen oxidation in an annular flow reactor at varying flow rate and temperature. [Copyright &y& Elsevier]

Abstract: A simple and rapid method for the determination of metal dispersion of technical catalysts is presented, which is based on temperature-programmed desorption (TPD) of pre-adsorbed CO in a continuous-flow reactor at atmospheric conditions. A commercial Pt/Al2O3 diesel oxidation catalyst is studied as an example. In the TPD spectra, desorption of CO as well as CO2 is considered. Furthermore, a pulse adsorption technique is applied to better understand the adsorption–desorption behavior and the oxidation of CO. Metal dispersion based on the TPD methods presented agrees well with data derived from H2 and CO chemisorption measurements using commercial set-ups. [Copyright &y& Elsevier]

Abstract: Effect of surface diffusion on the performance of solid-oxide fuel cell is investigated. A methodical approach for the evaluation of surface diffusion coefficients of various adsorbed species based on bond-order conservation Morse potential (BOC-MP) method is presented. The surface diffusion fluxes are used for the evaluation of temporal changes in surface coverages. Our analysis shows that surface diffusion does not lead to the concentration losses in solid oxide fuel cells. Further analysis is carried out and results are presented to substantiate the significance of interface diffusion on the behavior of voltage at limiting current. [Copyright &y& Elsevier]

Abstract: Alternative chemical reaction pathways leading to polycyclic aromatic hydrocarbons (PAHs) in the pyrolysis of unsaturated light hydrocarbons were investigated to extend the previously proposed chemical kinetic model [K. Norinaga, O. Deutschmann, Ind. Eng. Chem. Res. 46 (2007) 3547–3557]. Although the previous model provided a reasonably good description of the pyrolysis behaviors observed in flow reactor experiments at 1073–1373K, the concentration profiles for large PAHs were underestimated significantly. In this study, pyrolysates from ethylene, acetylene, and propylene were analyzed in detail using gas chromatography/mass spectroscopy (GC/MS) to find the intermediates that are believed to be crucial for PAH formation. Based on the newly identified products, reaction schemes for aromatic growth via 1,2-diphenylethylene, 1,2-diphenylacetylene, triphenylene, and benz[f]indene were proposed and added to the previous model. The predictive capabilities improved slightly simply because of the minority of the newly found compounds. The addition of reaction schemes for self-combination of indenyl radicals to form benz[a]anthracene and chrysene had a significant effect, and were found to be necessary to account for the formation of large PAHs such as benz[a]anthracene, chrysene, and benz[a]pyrene. Results from reaction flux analysis to identify the likely chemical pathways important for PAH growth, as well as numerical simulations of the influence of acetone contamination on acetylene pyrolysis, are presented. [Copyright &y& Elsevier]

Abstract: Internally reforming anode supported solid-oxide fuel cells (SOFC) running on humidified is studied numerically. The computational framework employs detailed multi-step models for heterogeneous chemistry for Ni catalysts. The electrochemistry is implemented using a modified Butler–Volmer setting based on elementary charge transfer kinetics. Transport through the porous matrix is modeled using the dusty gas model (DGM). Parameters required for the electrochemical model are adjusted to reproduce experimentally observed data. Obtained parameters are then used to model a co-flow planar single cell under internally reforming conditions assuming the interconnect walls as adiabatic. Numerous runs with varying inlet conditions of cathode stream are carried out to deduce the behavior of temperature and current density distribution in the cell. Results show that internal reforming generally leads to a temperature drop near the inlet boundary. [Copyright &y& Elsevier]

Based on multi-step reaction and deposition models including the hydrogen inhibition model of pyrocarbon growth, transient 2D simulations of chemical vapor infiltration of methane were carried out by a finite element method (FEM) coupling the mass transfer (by convection and diffusion) and the evolutive surface area model with gas-phase and surface chemical reactions. The continuous infiltration, pyrolysis and deposition of methane and its consecutive products lead to continuously varying hydrogen concentration inside the carbon felt. The higher diffusibility of hydrogen compared to those of hydrocarbons results in complex distributions of []/[] ratios inside the carbon felt, significantly affecting the deposition rates of pyrolytic carbon from hydrocarbons. The favorable densification mode (from inside to outside) seems to depend not only on the concentration ratio of []/[] but also on the concentration ratio of [H2]/[]. The effect of various feed compositions of methane and hydrogen on densification of carbon felts was investigated at a temperature of 1368K. An acceptable agreement was found between the predicted density distribution and experimental data taken from literature. [Copyright &y& Elsevier]

Abstract: The high-temperature catalytic partial oxidation of methane (CPOM) over a platinum gauze reactor was modeled by integrating 3D numerical simulations of the flow field coupled with heat transport as well as detailed micro-kinetic models including gas-phase and surface reaction mechanisms. Model results describe well CPO experiments over Pt-gauzes in the literature. The conversions of CH4 and O2 increase with an increased contact time and were constant in the temperature range of 1000–1200K. The selectivity to CO linearly increases with temperature. H2 was only observed above 1200K, below this temperature H2O was the only hydrogen-containing product. The contribution of heterogeneous steps in the overall process is prominent, but in the later stages of the reactor, gas-phase reactions become important at certain conditions of temperature, pressure and residence time. Simulations predicted significant gas-phase production of ethane and ethylene via methane oxidative coupling upon increasing the total pressure and residence time. Consequently, homogeneous and heterogeneous processes should be simultaneously implemented in order to accomplish a solid reactor modeling. [Copyright &y& Elsevier]

Abstract: Direct internal reforming in solid oxide fuel cell (SOFC) results in increased overall efficiency of the system. Present study focus on the chemical and electrochemical process in an internally reforming anode supported SOFC button cell running on humidified CH4 (3% H2 O). The computational approach employs a detailed multi-step model for heterogeneous chemistry in the anode, modified Butler–Volmer formalism for the electrochemistry and Dusty Gas Model (DGM) for the porous media transport. Two-dimensional elliptic model equations are solved for a button cell configuration. The electrochemical model assumes hydrogen as the only electrochemically active species. The predicted cell performances are compared with experimental reports. The results show that model predictions are in good agreement with experimental observation except the open circuit potentials. Furthermore, the steam content in the anode feed stream is found to have remarkable effect on the resulting overpotential losses and surface coverages of various species at the three-phase boundary. [Copyright &y& Elsevier]

Abstract: Product distributions in the pyrolysis of ethylene, acetylene, and propylene are studied to obtain an experimental database for a detailed kinetic modeling of gas phase reactions in chemical vapor deposition of carbon from these light hydrocarbons. Experiments were performed with a vertical flow reactor at 900°C and pressures from 2 to 15kPa. Gas phase components were analyzed by both on-line and off-line gas chromatography. More than 40 compounds from hydrogen to coronene were identified and quantitatively determined as a function of the residence time varied up to 1.6s. Product recoveries were generally more than 90%. Analysis of the kinetics of the conversion of the hydrocarbons resulted in global reaction orders of 1.2 (ethylene), 2.7 (acetylene), and 1.5 (propylene). First order dehydrogenation reactions and third order trimerization reactions leading to benzene are decisive reactions for ethylene and acetylene, respectively. Conversion of propylene should also be based on two simultaneous reactions, a first order dissociation reaction, and second order reactions such as bimolecular reaction of propylene resulting an allyl and a propyl radical. These insights should be useful to develop a reaction mechanism based on elementary reactions in forthcoming studies. [Copyright &y& Elsevier]

Abstract: This work focuses on the development and improvement of numerical tools for the simulation of catalytic monolith reactors. These simulations cover detailed descriptions of reaction mechanisms, transport in gas-phase and washcoats, fluid flow in single channels, and the entire reactor. In DETCHEMMONOLITH, the concept of building a transient model of the monolith reactor by the calculation of steady-state solutions of representative channels has been improved. Thus, simulations with inlet conditions varying in space and time become feasible. Furthermore, reactors with alternating channel properties can be considered. Another extension concerns storage catalysts that accounts for transient surface coverages of the storage medium. As example, three numerical studies are shown: a catalytic combustion device with alternating active and inactive channels, a catalytic combustion monolith with spatially varying inlet conditions, and a NO x storage catalyst with alternating inlet conditions. [Copyright &y& Elsevier]

Non‐fossil fuels are urgently needed for maritime and inland shipping applications to mitigate the sector's adverse impact on the global climate. This study investigates the performance of potassium borohydride (KBH4) as an alternative, carbon‐free energy carrier on the basis of detailed process simulations of the overall energy storage cycle in Aspen Plus®. After optimizing the individual on‐board and off‐board process steps, the feasibility of installing a KBH4‐based energy supply system on board of an inland‐waterway cargo vessel is evaluated and critical process steps are highlighted along with current research challenges. [ABSTRACT FROM AUTHOR]

• Diffusive mass transfer in the liquid film of Taylor flow is studied theoretically. • The physical system corresponds to the hydrogenation of nitrobenzene to aniline. • Determination of composition-dependent physical properties for two liquid mixtures. • Change of composition by reaction or dilution has notable effect on mass transfer. • Estimation of degree of film saturation depending on hydrodynamic parameters. Micro-structured reactors operated in Taylor flow are promising for intensifying heterogeneously catalyzed gas-liquid reactions. By reaction progress or dilution, physical properties may change with liquid composition. Here, the effect of composition on physical mass transfer in the liquid film of Taylor flow is studied with regard to the hydrogenation of nitrobenzene to aniline. For the liquid mixtures nitrobenzene-aniline and nitrobenzene-ethanol, composition-dependent physical properties are determined using information from literature. By numerical solution of the unsteady one-dimensional diffusion equation with composition-dependent physical properties, the instantaneous hydrogen concentration across the liquid film is obtained for different nitrobenzene mole fractions. The results indicate that in a wide composition range of reactant (nitrobenzene) and product (aniline), hydrogen diffuses slower in the mixture than in pure liquids. On the other hand, dilution of nitrobenzene by ethanol increases hydrogen mass transfer in the liquid film. A theoretical relation is provided which allows estimating for given capillary number the necessary bubble length to achieve a certain hydrogen saturation in the liquid film during the passage of one Taylor bubble. This non-dimensional relation can be applied to other physical systems and may be useful to guide optimal hydrodynamic operation conditions for applications with Taylor flow in chemical engineering. [ABSTRACT FROM AUTHOR]

• Budget analysis of liquid turbulence kinetic energy by DNS of bubble swarms. • A priori testing of models for closure of interfacial term by DNS data. • Application of models in Euler–Euler RANS simulations of industrial bubble column. • Bubble column computations for liquids water and cumene at elevated pressures. • Comparison with local measurements and empirical gas holdup correlations. This paper presents numerical studies on modeling of bubble induced turbulence at two significantly different scales. On the scale of a bubble swarm, direct numerical simulations are performed with a geometric volume-of-fluid method and the budget equation of liquid phase turbulence kinetic energy is analyzed. By a priori testing of models for the interfacial term in this equation, suitable closure relations are identified. On the scale of an industrial bubble column, simulations with a two-fluid model are performed with water and cumene as liquid phases under elevated pressures. Turbulence is taken into account by a mixture k – ε model, considering two closure relations for the interfacial term identified from the DNS. For both liquids, an influence of the model for the interfacial term on turbulence kinetic energy and gas holdup is found, which is, however, small at elevated pressures. Numerical results for local and overall gas holdup are in reasonable agreement with measurements reported for this industrial pilot-scale bubble column. For the overall gas holdup, an empirical correlation from literature is identified which predicts the present numerical results reasonably well. [ABSTRACT FROM AUTHOR]

Microkinetic modeling is a widely used tool in the domain of heterogeneous catalysis to gain valuable insights about the fundamental surface kinetics, crucial to designing improved catalysts. The development of a microkinetic model is a multi‐step process that demands expertise, a wide variety of experimental techniques, substantial computational resources, and extensive time and effort. In light of these challenges, automation within catalysis research is becoming increasingly important to allow exploration of a broader range of catalytic systems in a shorter timeframe. To this extent, a variety of digital tools and software have been developed to accelerate the development of microkinetic models. This work aims to highlight a selection of these tools that address the various challenges confronting the researchers in this field. These tools address diverse aspects, from the efficient storage of research data that allows easy retrieval and reuse, to the establishment of automated workflows that harness state‐of‐the‐art numerical solvers and algorithms that reduce manual effort. Through the use of automation, these aim to expedite and streamline the development and validation of models for catalytic systems, thereby reducing errors and increasing efficiency. [ABSTRACT FROM AUTHOR]

Abstract: No abstract. [ABSTRACT FROM AUTHOR]

A high temperature gradient within a solid oxide fuel cell (SOFC) stack is considered a major challenge in SOFC operations. This study investigates the effects of the key parameters on SOFC system efficiency and temperature gradient within a SOFC stack. A 40-cell SOFC stack integrated with a bio-oil sorption-enhanced steam reformer is simulated using MATLAB and DETCHEM. When the air-to-fuel ratio and steam-to-fuel ratio increase, the stack average temperature and temperature gradient decrease. However, a decrease in the stack temperature steadily reduces the system efficiency owing to the tradeoff between the stack performance and thermal balance between heat recovered and consumed by the system. With an increase in the bio-oil flow rate, the system efficiency decreases because of the lower resident time for the electrochemical reaction. This is not, however, beneficial to the maximum temperature gradient. To minimize the temperature gradient of the SOFC stack, a decrease in the bio-oil flow rate is the most effective way. The maximum temperature gradient can be reduced to 14.6 K cm−1 with the stack and system efficiency of 76.58 and 65.18%, respectively, when the SOFC system is operated at an air-to-fuel ratio of 8, steam-to-fuel ratio of 6, and bio-oil flow rate of 0.0041 mol s−1. • Performance of the SOFC system with bio-oil reforming is investiagated. • The temperature gradient within SOFC stack is considered. • A decrease in bio-oil flow can improve the temperature gradient of SOFC stack. • Optimial operating conditions for the SOFC system are identified. [ABSTRACT FROM AUTHOR]

In this study, density functional theory calculations were performed to investigate the influence of oxygen preoccupation on the nitrogen oxide decomposition on rhodium. Besides gauging the coverage dependence of the adsorption energy of NO on the (111) rhodium facet, the influence of the initial oxygen coverage on the kinetics and thermodynamics of the nitrogen oxide decomposition reaction was also studied. The results are discussed with respect to a novel NOx decomposition catalyst. Furthermore, the influence of spin effects on the adsorption geometry as well as the adsorption energy is examined. It will be addressed why spin effects only have a minor influence on the behavior of NO on a rhodium surface. [ABSTRACT FROM AUTHOR]

A systematic study of oxygen adsorption, decomposition and diffusion on Rh(111) and its dependence on coadsorbed oxygen molecules has been performed using density functional theory calculations. First, the bonding strength between metal surface and adsorbed oxygen molecules has been studied as a function of initial oxygen coverage. The bonding strength decreases with increasing oxygen coverage, which points towards a self-inhibition of the adsorption process. The potential energy hypersurface (PES) for the dissociation of oxygen molecules adsorbed on a threefold fcc position perpendicular to the surface was calculated using a combined linear/quadratic synchronous transit method with conjugate gradient refinements. The results indicate that a minor amount of oxygen on the surface enhances the decomposition of further oxygen molecules, while this process is inhibited at higher coverage. Moreover, PES calculations of a single site jump of atomic oxygen on rhodium (111) indicate that the activation energy increases as well with increasing oxygen coverage. All results are discussed with respect to a rhodium based catalytic NOx reduction/decomposition system proposed by Nakatsuji, which decomposes nitrogen oxides in oxygen excess. © 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Die Studie stellt eine ab initio basierte Methode für die automatische Konstruktion von detaillierten Mikrokinetiken vor, welche korrelierte Unsicherheiten in allen energetischen Parametern und Schätzroutinen berücksichtigt. Hierfür wurden innerhalb des Unsicherheitsraums des BEEF‐vdW Funktionals 2000 Mikrokinetiken für die Oxidationsreaktionen repräsentativer Abgasemissionen von stöchiometrischen Verbrennungsmotoren auf Pt(111) generiert und durch Multiskalenmodellierung mit Experimenten verglichen. Das Ensemble der Simulationsergebnisse unterstreicht die Bedeutung der Berücksichtigung von Unsicherheiten. Innerhalb dieses Ensembles ist es möglich, eine Mikrokinetik zu identifizieren, welche mit den experimentellen Daten übereinstimmt. Diese Mikrokinetik lässt sich auf ein einziges Austausch‐Korrelations‐Funktional zurückführen und legt nahe, dass Pt(111) das aktive Zentrum für die Oxidation leichter Kohlenwasserstoffe sein könnte. Die Studie bietet einen universellen Rahmen für die automatisierte Konstruktion von Reaktionsmechanismen unter Berücksichtigung korrelierter Unsicherheiten und ermöglicht eine DFT‐basierte Optimierung der Mikrokinetik auch für andere heterogen katalysierte Systeme. [ABSTRACT FROM AUTHOR]

The study presents an ab‐initio based framework for the automated construction of microkinetic mechanisms considering correlated uncertainties in all energetic parameters and estimation routines. 2000 unique microkinetic models were generated within the uncertainty space of the BEEF‐vdW functional for the oxidation reactions of representative exhaust gas emissions from stoichiometric combustion engines over Pt(111) and compared to experiments through multiscale modeling. The ensemble of simulations stresses the importance of considering uncertainties. Within this set of first‐principles‐based models, it is possible to identify a microkinetic mechanism that agrees with experimental data. This mechanism can be traced back to a single exchange‐correlation functional, and it suggests that Pt(111) could be the active site for the oxidation of light hydrocarbons. The study provides a universal framework for the automated construction of reaction mechanisms with correlated uncertainty quantification, enabling a DFT‐constrained microkinetic model optimization for other heterogeneously catalyzed systems. [ABSTRACT FROM AUTHOR]

The presence of water vapor during the oxidation of the strong greenhouse gas methane over PdO‐based catalysts is known to result in severe inhibition and catalyst deactivation. In this context, our current study elucidates the role of the support material for different water concentrations in the reaction gas mixture. Compared to a reference PdO/Al2O3 catalyst, the catalytic activity can be significantly enhanced when using SnO2 and ZrO2 as support materials and remains stable during 24 h of operation at 823 K in the presence of 12 % H2O, whereas under identical conditions CH4 conversion drops by 68 % over PdO/Al2O3. The interplay between Pd species and catalyst support was systematically characterized by thermogravimetric analysis, temperature‐programmed reduction experiments and TEM measurements. Finally, a kinetic scheme was derived based on the experimental data. [ABSTRACT FROM AUTHOR]

The impact of radiation heat transfer and radial heat losses in small-scale monoliths, as often used for testing catalysts or qualifying process conditions, are an important consideration to design and predict performance of commercial size reactors. The paper presents the 3D modeling of a honeycomb CPOX (Catalytic Partial Oxidation) reformer, including detailed surface chemistry for the conversion of methane on rhodium. The calculation domain comprises the flow region and two monoliths (one of them coated) which are positioned in a glass tube. For the simulations the software tool DUO (coupling between OpenFOAM and DETCHEM™) was used. The objective was to model the system without any boundary conditions for the temperature (aside from the inlet). As the temperature level is above 900 K solid body radiation has to be included. The comparison of the results with detailed experimental data shows that it is possible to reproduce the species concentrations and the temperature fields of the flow and solid structures well. The effect of radiation, leading to a heat transfer between the two monoliths, can clearly be indicated. However, this effect plays only a minor role with respect to the chemical conversion. The simulations capture the measured effect of radial heat removal on the conversion process in different channels inside the catalyst. [ABSTRACT FROM AUTHOR]

The oxidative dehydrogenation of a C4 raffinate-2 consisting of n-butane, 1-butene, and 2-butene was conducted in a two-zone fluidized bed reactor using a Mo-V-MgO catalyst. This study reports the influence of the operating conditions temperature, hydrocarbon inlet height, and oxygen/hydrocarbon molar ratio on the product distribution, in particular on the formation of 1,3-butadiene. Axial concentration profiles were measured to elucidate the reaction sequence in the fluidized bed. [ABSTRACT FROM AUTHOR]

Water and NO reversibly inhibit catalytic methane oxidation to CO2 over Pd/Al2O3 and Pd−Pt/Al2O3 at temperatures near 50 % conversion. Modulation‐excitation X‐ray absorption spectroscopy (ME‐XAS) was used to characterize the interaction of the inhibitors with the Pd and Pt components. Simulated X‐ray absorption near‐edge structure (XANES) spectra of Pd and Pt with various surface species were used to verify the findings of ME‐XAS measurements. Diffuse‐reflectance infrared Fourier‐transform spectroscopy (DRIFTS) allowed to correlate methane oxidation with surface formate species. An interaction of water with active Pd sites and water coverage of the Al2O3 support caused a drastic drop in formate production, correlated with the observed inhibition. In a similar manner, nitrite groups formed from gas‐phase NO inhibited the production of formates. At higher temperatures, the inhibition was reversed into a promoting effect by surface nitrates formed from NO that oxidized gas‐phase methane. This approach is not only interesting for emission control but in general for catalysts where dynamic structural changes occur. [ABSTRACT FROM AUTHOR]

Traceability between samples, devices and data is of great importance to the catalysis community. Adacta is a new research data management (RDM) system designed to create a traceable digital twin of a testing environment, not only storing data, but also creating a readily retrievable time‐accurate record of the critical components used to measure catalyst performance. Future developments include extending Adacta to interact with electronic laboratory notebooks and to spawn simulations directly using data and measurements stored in the database. [ABSTRACT FROM AUTHOR]

This manuscript reports a CO2 hydrogenation process in a catalytic laboratory‐scale packed‐bed reactor using an Fe/BZY15 (BaZr0.85Y0.15O3‐δ) catalyst to form hydrocarbons (e. g., CH4, C2+) at elevated pressure of 30 bar and temperatures in the range 270≤T≤375 °C. The effects of temperature, feed composition (i. e., CO2/H2 ratio, and residence time (i. e., Weight Hourly Space Velocity (WHSV) are studied to understand the relationship between CO2 conversion and carbon selectivity. Catalyst characterization elucidates the relationships between the catalyst structure, surface adsorbates, and reaction pathways. Thermodynamic analyses guide the experimental conditions and assist in interpreting results. While the feed composition and temperature influence the product distribution, the results suggest that the higher‐carbon (C2+) selectivity and yield depend strongly on residence time. The results suggest that the CO2 hydrogenation reaction pathway is similar to Fischer–Tropsch (FT) synthesis. The reaction begins with CO2 activation to form CO, followed by chain‐growth reactions similar to the FT process. The CO2 activation depends on the redox activity of the catalyst. However, the carbon chain growth depends primarily on the residence time. as is the case for the FT synthesis, high residence time (on the orders of hours) is required to achieve high C2+ yield. [ABSTRACT FROM AUTHOR]

Bifunctional basic‐metallic catalysts proved to be efficient for the selective hydrogenation of CO2 to methanol. The activity of these catalysts depends on the cooperative interaction between the amine groups and metallic sites, which is a function of amine group density, Pd particle perimeter length and the geometric properties of support pores. The pore width has the highest effect on the activity, increasing the methanol yield by about half an order of magnitude. Confining the space leads to a three‐dimensional utilization of the available metal surface sites compared to a two‐dimensional distribution of the bifunctional sites in larger pores, where the metal particle diameter is the decisive factor for the catalytic properties. [ABSTRACT FROM AUTHOR]

ABSTRACT An 48-step sur face reaction mechanism with thermodynamic consistent kinetic data is presented for the catalytic conversion of the gaseous chemical system H2/O2/H2O/CO/CO2/CH4 over Rh/Al2O3 catalysts. Total and partial oxidation as well as steam reforming and dry reforming of methane over Rh catalysts is studied experimentally and numerically at varying temperature and composition. The results are used to extend the kinetic schemes we developed for H2 oxidation, CO oxidation kinetics, and the water-gas-shift reactions in former studies. Aside from the experiments in a stagnation-flow reactor presented here, we modeled a number of experiments from the literature to test the newly established kinetic scheme. [ABSTRACT FROM AUTHOR]

A synthetic exhaust gas bench was dynamically operated to investigate the impact of temperature, amplitude, split cycle, mean lambda, gas hourly space velocity, and oxygen storage capacity on average pollutant conversion and product selectivity of three-way catalysts in periodic operation. As temperature and amplitude increase and oxygen storage capacity decreases, the optimal frequency for maximum pollutant conversion increases. This is consistent with faster desorption of CO and O 2 from the catalyst, yielding free surface sites. Regarding the formation of secondary products, the optimal frequency for maximum pollutant conversion does not always correspond to minimal N 2 O and NH 3 emissions. The split cycle variation reveals the enhancement of C 3 H 8 and NO conversion after both lean-rich and rich-lean switches and C 3 H 6 and CO conversion after rich-lean switches at the optimal frequency. As periodic operation does not affect existing engine settings or operating conditions, it is a cost-effective control strategy for meeting future emission limits. [Display omitted] • Periodic operation enhances C 3 H 8 and NO conversion by 80%, and N 2 selectivity by 30% at 250 ∘C • Asymmetric periodic operation reveals conversion enhancement at optimal lean and rich half cycle • Optimal frequency increases with increasing temperature, amplitude and decreasing oxygen storage capacity • Observed optimal frequency decreases with increasing mixing upstream of the catalyst [ABSTRACT FROM AUTHOR]

Solid oxide fuel cells (SOFCs) have witnessed significant advancements in recent years, emerging as potential alternatives to low-temperature fuel cells for mobile applications owing to their wide fuel flexibility and high efficiency. This paper offers a comprehensive assessment of the progress achieved thus far and the challenges faced in transitioning from stationary to mobility sectors. Three pivotal aspects are highlighted across different levels: enhancing fuel tolerance and flexibility at the anode level, achieving rapid start-up at the cell level, and realizing compact integration at the stack level. This review can lay a theoretical foundation for the development of SOFC systems tailored to unique requirements, such as high power density and rapid start-up, crucial for mobile applications. This review will facilitate commercial breakthroughs and advances in the mobility of SOFCs, which holds substantial strategic importance. [ABSTRACT FROM AUTHOR]

In order to understand deposit formation during urea selective catalytic reduction (SCR) resulting from isocyanic acid (HNCO) formation, the present study investigates the potential of HNCO hydrolysis by spatially resolved gas phase concentration profiles along a single catalyst channel of commercial Cu‐zeolite and V‐based SCR catalysts. The spatially resolved profiles, obtained in a special hot gas test rig via capillary technique, provide information on reaction rates of HNCO hydrolysis, NH3 adsorption and NO conversion, hereby revealing a better performance of the standard V‐based catalyst regarding the HNCO hydrolysis, which is attributed to the TiO2 support. [ABSTRACT FROM AUTHOR]

[Display omitted] • 3D modeling of an 86-particle fixed bed with CPOX and DRM chemistry. • ISAT and CA methods used to accelerate the calculation of reaction source terms. • CA method is simpler than other implementations of this acceleration technique. • ISAT and CA methods were added to DUO, which couples OpenFOAM and DETCHEM. • Speedup factors were 7x for CPOX and 35x for DRM, with acceptable calculation errors. Simulation of fixed-bed catalytic reactors is important for engineering industrial technologies. The large number of catalytically active surface faces makes the application of microkinetic models too time consuming for large 3D simulations that include fully resolved particle structures (e.g., ≫ 10′s of particles). Such simulations, though, are often required for small tube-to-particle diameter ratio configurations, where local flow effects are difficult to capture with 1D or 2D simulations. A common solution for speeding up reactive computational fluid dynamics (CFD) involves the use of chemistry acceleration methods, including In-Situ Adaptive Tabulation (ISAT) and Cell Agglomeration (CA). In the present contribution, DUO (DETCHEMTM + OpenFOAM coupling) CFD software has been extended to include ISAT and CA methods for surface reactions, in particular, using a CA method that is simpler than other implementations of this acceleration technique. Speedup factors and errors were tabulated for an 86 spherical particle 3D resolved fixed-bed reactor, considering the exothermic methane catalytic partial oxidation (CPOX) and the endothermic dry reforming of methane (DRM) chemistries. For CPOX, a speedup factor of ∼ 7x was achieved, while for DRM, a speedup of ∼ 35x was obtained, with both cases achieving an acceptable error in the solution. Although a tighter error tolerance with ISAT and CA is shown to reduce the overall calculation error, for some engineering situations this tradeoff in speedup and accuracy will be acceptable. Achieving usable results in around 0.5 – 2 h instead of around 20-hours (for these chemistries on this particular grid, run on a 400-core cluster) can vastly improve the feasibility of computational fluid dynamics for the analysis of fixed-bed catalytic reactors including microkinetics mechanisms. [ABSTRACT FROM AUTHOR]

On the way towards a decarbonized mobility, hydrogen combustion engines can particularly contribute to applications for heavy‐duty and long‐haul routes. Using clean hydrogen as fuel results in formation of nitrogen oxides as quasi‐exclusive pollutant emissions, which can be minimized by combining motor‐related measures with an emission control system in the exhaust tailpipe. This review provides an overview on the impact of various engine operation conditions on the emissions of a hydrogen combustion engine and summarizes state‐of‐the‐art and future concepts for an efficient exhaust gas after‐treatment. [ABSTRACT FROM AUTHOR]

Experiments and simulations are presented for the interaction of single bubbles rising in a viscous liquid against a horizontal cylinder (Ø = 4 mm) of varying wettability. The slide‐off of small and the cutting of larger bubbles into two daughter bubbles observed in the experiment are reproduced by phase‐field simulations. It is shown that in the entire process bubble and cylinder are separated by a liquid film, which eliminates any influence of cylinder wettability. Before the mother bubble splits, a thinning gas thread develops below the cylinder. The rupture of this gas thread can lead to a different number of satellite bubbles depending on the conditions. [ABSTRACT FROM AUTHOR]

Abstract: In this analysis, we report an in-house model to describe the complex fundamental and functional interactions between various internal physico-chemical phenomena of a SOEC. Electrochemistry at the three-phase boundary is modeled using a modified Butler–Volmer approach that considers H2 as the electrochemically active species. Also, a multi-step elementary heterogeneous reaction mechanism for the thermo-catalytic H2 electrode chemistry, dusty-gas model to account for multi-component diffusion through porous media, and plug flow model for flow through the channels are used. Results pertaining to detailed chemical processes within the cathode, electrochemical behavior and irreversible losses during SOEC operation are demonstrated. Furthermore, efficiency analysis is performed and limiting current behavior of the SOEC system is investigated. [Copyright &y& Elsevier]

The catalytic reduction of NO inside an optically accessible channel reactor has been investigated using in situ and non-invasive planar laser-induced fluorescence (PLIF). The construction of the experimental reactor as well as an effective implementation of PLIF is presented. Two-dimensional maps of the NO fluorescence above a catalytic surface are obtained under both reactive and non-reactive conditions. NO reduction in a Diesel oxidation catalyst consisting of a Pt/Al2O3 coated monolith is studied exemplarily. [ABSTRACT FROM AUTHOR]

[Display omitted] • CH 4 pyrolysis in a packed bed reactor yields over 98 % H 2 and captures carbon. • Coupling of models for carbon deposition, soot formation, and gas-phase microkinetics. • Model captures H 2 inhibition effect and formation of by-products. • Numerical simulations of lab-scale reactor behavior align with experimental data. • Models and computational codes can support process development and scale-up. Pyrolysis of hydrocarbon feeds such as methane (CH 4) and natural gas emerges as a pivotal carbon dioxide-free large-scale hydrogen (H 2) production process combined with capturing the carbon as solid material. For fundamental understanding and upscaling, the complex kinetics and dynamics of this process in technically relevant reactors such as packed and moving beds still need to be explored, particularly concerning carbon formation and its impact on reactor performance. This study integrates kinetic modeling, numerical simulations, and experimental findings to comprehensively understand CH 4 pyrolysis under industrially relevant conditions and its implications for efficient H 2 production and carbon capture. The investigation covers temperatures from 1273 K to 1873 K, H 2 addition with H 2 :CH 4 ratios of 0 to 4, and hot zone residence time of 1 to 7 s. Two distinct pathways lead to carbon formation: soot formation and carbon deposition. Each pathway originates from different gas-phase precursors. An elementary-step-based gas-phase reaction mechanism is coupled with a soot formation model from polycyclic aromatic hydrocarbon and a newly developed deposition model from light hydrocarbons. Numerical simulations are performed in a packed bed reactor model, incorporating a method of moments for soot formation and a model for carbon deposition. The model is evaluated against experiments and predicts the effects of operating conditions on gas-phase product distribution and carbon formation. It also estimates the change in bed-voidage over operational time. The study reveals that at the temperature 1673 K, CH 4 conversion exceeds 94 %, while both H 2 and solid carbon yields surpass 96 %. The sophisticated modeling and simulation framework presented herein thus provides an enhanced understanding of the CH 4 pyrolysis process and presents a valuable tool for optimizing this process. [ABSTRACT FROM AUTHOR]

This article, titled "Cover Feature: Interconnected Digital Solutions to Accelerate Modeling of the Reaction Kinetics in Catalysis," discusses the importance of microkinetic modeling in heterogeneous catalysis. The authors highlight the challenges involved in developing these models, including the need for expertise, experimental techniques, computational resources, and time. To address these challenges, automation is crucial in catalysis research. The article showcases various tools and software that expedite the creation of microkinetic models, aiming to accelerate model development, reduce errors, and enhance efficiency in exploring different catalytic systems. The authors emphasize the significance of automation in catalysis research for improved catalyst design. [Extracted from the article]

• CH 4 coupled to C 2 species at significant rates over Pt catalysts at high temperature. • Novel thermodynamic consistent, microkinetic reaction mechanism developed. • Interactions of chemical kinetics and transport explain experimental findings. • Reactor behavior understood by detailed numerical simulation. The oxidative coupling of methane (OCM) at high temperature over monolithic Pt-based catalysts operated at short contact times is investigated as an attractive method for methane upgrading to higher value products like ethylene and acetylene. An experimental measurement campaign aiming at elucidating the effect of operation parameters on the catalyst performance revealed that lower N 2 dilution, lower CH 4 /O 2 ratio, and higher space velocities promote high C 2 yields. A maximum C 2 yield of 10 % with 94 % CH 4 conversion was obtained at a CH 4 /O 2 ratio of 1.1, 50 % N 2 dilution, and a space velocity of 4.5 × 105 h−1. Since both heterogenous and homogenous gas-phase chemistry together are required for determining C 2 formation pathways, a detailed OCM surface reaction mechanism over Pt is presented consisting of 26 species and 86 reactions that are consistent from the view of thermodynamics and micro-kinetic reversibility. The combination of this OCM surface mechanism with a detailed gas-phase mechanism allows a numerical micro-kinetic description of the experimental measurements. The simulations presented in this study suggest that C 2 formation takes place in the gas-phase at temperature above 1200 K with both oxidative and pyrolytic pathways for methane dehydrogenation to form CH 3 radicals, whose coupling results in C 2 H 6 , C 2 H 4 and C 2 H 2 formation. Furthermore, the simultaneous presence of sufficient oxygen content and heat are vital for high C 2 species yields. [ABSTRACT FROM AUTHOR]

Fuel consumption for NO trap regeneration depends on the regeneration frequency, which is a function of NO trap performance parameters. Hence, the impact of thermal aging must be considered in the operation strategy. For this purpose, the effect of thermal aging on the physical and chemical properties of a commercial NO storage/reduction catalyst containing Pt/Pd/Rh has been investigated. After thermal treatment under various conditions, the samples were characterized using CO chemisorption measurements, X-ray diffraction (XRD), N physisorption, and electron microscopy. It is shown that the major impact of lean hydrothermal treatment on the catalyst activity is the continuous decrease of the specific surface area with aging temperature due to collapse of smaller pores. The noble metal nanoparticles remained highly dispersed, even after lean aging at 800 °C. In contrast, noble metal sintering represents the main aging effect of lean/rich cycling at elevated temperatures. Furthermore, XRD and selected area electron diffraction revealed a significant loss of crystallinity for the barium component in consequence of lean/rich aging treatment. However, independent from the aging treatment, no formation of mixed oxides could be observed. [ABSTRACT FROM AUTHOR]

Abstract: The catalytic partial oxidation (CPOX) of ethanol-blended fuels is studied over rhodium/alumina coated monoliths with ethanol/iso-octane mixtures as model systems. Blends containing 5–85vol.% ethanol are investigated, as well as the pure substances. All mixtures show a hydrogen yield of over 80% in millisecond contact times, with the highest yield for a blend with 10vol.% ethanol. For a high ethanol concentration in the blend, generally a high by-product formation is observed already at fuel lean conditions. The product yields cannot be linearly interpolated from the yields of the pure substances. In addition, the commercial fuels 95 RON gasoline and E85 are studied, revealing similar product yields in CPOX of the commercial fuels and the corresponding ethanol/iso-octane blends. Thus, two-component mixtures can be proposed as model system for the complex compositions of commercial fuel. [Copyright &y& Elsevier]

Catalytic partial oxidation (CPOX) is a promising technologyforreforming of liquid hydrocarbon fuels to hydrogen or synthesis gasfor use in fuel cells. The addition of a certain amount of the tailgas of the fuel cell stack to the reformer inlet feed can increaseoverall efficiency and lead to higher H2and CO selectivitiesand reduce coke formation. The effect of carbon dioxide or steam addition(1, 5, 10, 20, and 30 vol% of the total flow) on the performance ofa CPOX reformer operated with isooctane as fuel surrogate is systematicallystudied over a wide range of C/O feed ratios (0.72–1.79) usinga Rh/alumina honeycomb catalyst. The specific impact of the coreactantsH2O and CO2on reformer behavior can be interpretedby the water gas shift (WGS) chemistry. Production of H2and CO2increases with H2O addition at theexpense of CO and H2O. Opposite trends are observed incase of CO2addition. Tail gas recycling reduces formationof soot precursors up to 50% compared to the corresponding fuel feedwithout coreactants. However, tail-gas recycling shifts the formationof soot precursors toward lower C/O ratios. [ABSTRACT FROM AUTHOR]

Abstract: A combination of experiment and modeling is used to investigate catalytic reforming of methane with carbon dioxide (dry reforming) in a stagnation-flow reactor. The catalyst surface is a porous washcoat of rhodium supported on strontium-substituted hexaaluminate. The stagnation-flow configuration enables microprobe sampling of the compositional boundary layer adjacent to the catalyst surface. This configuration also enables efficient modeling the heterogeneous chemistry, coupled with convective and diffusive transport within the gas-phase boundary layer. The measurements provide new data that assist the fundamental understanding of methane dry reforming. The modeling incorporates an elementary reaction mechanism that was developed initially to represent catalytic partial oxidation and steam reforming. Representing the new dry-reforming measurements required modification of reaction rates for CO2 and CH4 interactions on the catalyst surface. [Copyright &y& Elsevier]