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Nanoporous solids are ubiquitous in chemical, energy, and environmental processes, where controlled transport of molecules through the pores plays a crucial role. They are used as sorbents, chromatographic or membrane materials for separations, and as catalysts and catalyst supports. Defined as materials where confinement effects lead to substantial deviations from bulk diffusion, nanoporous materials include crystalline microporous zeotypes and metal–organic frameworks (MOFs), and a number of semi-crystalline and amorphous mesoporous solids, as well as hierarchically structured materials, containing both nanopores and wider meso- or macropores to facilitate transport over macroscopic distances. The ranges of pore sizes, shapes, and topologies spanned by these materials represent a considerable challenge for predicting molecular diffusivities, but fundamental understanding also provides an opportunity to guide the design of new nanoporous materials to increase the performance of transport limited processes. Remarkable progress in synthesis increasingly allows these designs to be put into practice. Molecular simulation techniques have been used in conjunction with experimental measurements to examine in detail the fundamental diffusion processes within nanoporous solids, to provide insight into the free energy landscape navigated by adsorbates, and to better understand nano-confinement effects. Pore network models, discrete particle models and synthesis-mimicking atomistic models allow to tackle diffusion in mesoporous and hierarchically structured porous materials, where multiscale approaches benefit from ever cheaper parallel computing and higher resolution imaging. Here, we discuss synergistic combinations of simulation and experiment to showcase theoretical progress and computational techniques that have been successful in predicting guest diffusion and providing insights. We also outline where new fundamental developments and experimental techniques are needed to enable more accurate predictions for complex systems. [ABSTRACT FROM AUTHOR]

The ethylene hydrogenation reaction was investigated in a kinetic turbo reactor and a one-sided single-pellet reactor. An empirical kinetic expression was fitted to experimental results taken from the turbo reactor, and the gas compositions at the catalyst centers were measured for three different pore structures by means of the single-pellet reactor. A bimodal pore model was developed and applied to the computation of the gas composition profiles inside the three pore structures. The calculated results were compared to the measurements. A distinct influence of the pore structures on the gas fluxes and concentration profiles inside the pores could be detected which demonstrates that the proper choice of the pellet pore structure is of importance for a high conversion. [ABSTRACT FROM AUTHOR]

Process intensification (PI) is a rapidly growing field of research and industrial development that has already created many innovations in chemical process industry. PI is directed toward substantially smaller, cleaner, more energy-efficient technology. Furthermore, PI aims at safer and sustainable technological developments. Its tools are reduction of the number of devices (integration of several functionalities in one apparatus), improving heat and mass transfer by advanced mixing technologies and shorter diffusion pathways, miniaturization, novel energy techniques, new separation approaches, integrated optimization and control strategies. This review discusses many of the recent developments in PI. Starting from fundamental definitions, microfluidic technology, mixing, modern distillation techniques, membrane separation, continuous chromatography, and application of gravitational, electric, and magnetic fields will be described. [ABSTRACT FROM AUTHOR]

The effect of catalyst pore structure on n-butane oxidation to maleic anhydride in a fixed-bed reactor was investigated by numerical simulations. The micro- and macro-pore model of Wakao and Smith was applied to model the diffusion–reaction inside the catalyst pellet. The studied pore structure parameters were macro-pore porosity, mean macro-pore diameter and mean micro- pore diameter. A fixed-bed reactor was simulated with a detailed two-dimensional heterogeneous model under typical industrial conditions. Simulation results have demonstrated that the reactor performance is sensitive to the chosen pore structure parameters especially macro-pore porosity and mean micro-pore diameter. A bi-modal catalyst pellet with bigger macro-pores and smaller micro-pores is favored to achieve higher yields of maleic anhydride. This work highlights the potential of improving this process by pore structure optimization. [ABSTRACT FROM AUTHOR]

Abstract: Catalysts are omnipresent in the chemical industry. Understanding of catalytic chemical reactions is crucial for a rational development of catalysts. The present paper describes approaches for simulating phenomena in heterogeneous catalysis on a molecular level. Modeling of porous structures and their fractal surfaces will be presented. Simulation of adsorption and diffusion of reactants and products inside the pores by means of various Monte Carlo and Molecular Dynamics algorithms is described, followed by quantum chemical methods for calculating reactions on the active centers. Optimization of pore structures and multiscaling procedures complete the picture. [Copyright &y& Elsevier]

Methodological advances in quantum chemistry and classical molecular simulation combined with the ever increasing speed of computers allow for approaching chemical accuracy in the prediction of thermodynamic and kinetic parameters of zeolite catalyzed hydrocarbon reactions. In this account, progress in the area of multiscale modeling is illustrated by two examples taken from the authors' recent work and needs for further developments are identified. [ABSTRACT FROM AUTHOR]

Bubble columns equipped with an vibration exciter, which pulsates with a frequency between 40 and 400 Hz, show significantly improved mass transfer rates. This results from a reduction of bubble size by cleavage, the associated increase in surface area and, additionally, an intensive movement at the bubble interface. The observed phenomena are explained based on flow simulations. The energy required for a oscillating bubble column is less than for a gassed stirred tank. [ABSTRACT FROM AUTHOR]

Abstract: The temperature-scanning plug flow reactor (TSPFR) enables the investigation of kinetics of chemical reactions over a wide temperature range in a relatively small time of operation. The experimental data obtained by this approach can be used to calculate the reaction rate of each component of the reactant mixture for a given set of conditions. The oxidative dehydrogenation of propane by a V2O5/γ-Al2O3 catalyst was used for illustration. As this reaction is highly exothermic some limitations of the approach had to be considered. [Copyright &y& Elsevier]

Abstract: The paper reviews recent developments in catalysis, surface science and catalytic materials. Applications of catalytic micro-reactors, high-throughput experimentation, combinatorial chemistry, catalytic membrane reactors, and reactors are discussed. [Copyright &y& Elsevier]

A combination of interpolation methods and local saddle-point search algorithms is probably the most efficient way of finding transition states in chemical reactions. Interpolation methods such as the growing-string method and the nudged-elastic band are able to find an approximation to the minimum-energy pathway and thereby provide a good initial guess for a transition state and imaginary mode connecting both reactant and product states. Since interpolation methods employ usually just a small number of configurations and converge slowly close to the minimum-energy pathway, local methods such as partitioned rational function optimization methods using either exact or approximate Hessians or minimum-mode-following methods such as the dimer or the Lanczos method have to be used to converge to the transition state. A modification to the original dimer method proposed by [Henkelman and Jónnson J. Chem. Phys. 111, 7010 (1999)] is presented, reducing the number of gradient calculations per cycle from six to four gradients or three gradients and one energy, and significantly improves the overall performance of the algorithm on quantum-chemical potential-energy surfaces, where forces are subject to numerical noise. A comparison is made between the dimer methods and the well-established partitioned rational function optimization methods for finding transition states after the use of interpolation methods. Results for 24 different small- to medium-sized chemical reactions covering a wide range of structural types demonstrate that the improved dimer method is an efficient alternative saddle-point search algorithm on medium-sized to large systems and is often even able to find transition states when partitioned rational function optimization methods fail to converge. [ABSTRACT FROM AUTHOR]

The influence of silicalite-1 pores on the reaction equilibria and the selectivity of the propene metathesis reaction system in the temperature range between 300 and 600 K and the pressure range from 0.5 to 7 bars has been investigated with molecular simulations. The reactive Monte Carlo (RxMC) technique was applied for bulk-phase simulations in the isobaric-isothermal ensemble and for two phase systems in the Gibbs ensemble. Additionally, Monte Carlo simulations in the grand-canonical ensemble (GCMC) have been carried out with and without using the RxMC technique. The various simulation procedures were combined with the configurational-bias Monte Carlo approach. It was found that the GCMC simulations are superior to the Gibbs ensemble simulations for reactions where the bulk-phase equilibrium can be calculated in advance and does not have to be simulated simultaneously with the molecules inside the pore. The confined environment can increase the conversion significantly. A large change in selectivity between the bulk phase and the pore phase is observed. Pressure and temperature have strong influences on both conversion and selectivity. At low pressure and temperature both conversion and selectivity have the highest values. The effect of confinement decreases as the temperature increases. [ABSTRACT FROM AUTHOR]

The article presents information on the problem of methane conversion and steam reforming reaction, which is an indirect method of converting methane to hydrocarbons. Information on a study conducted by Tobin Marks and colleagues is presented that described a different approach of the use of sulfur as a soft oxidant to avoid the over-oxidation issues associated with the use of oxygen in methane conversion reaction. The study showed that the conventional assumption that the kinetic stability of a reactive site is determined solely by the nature of the reactive site.

Molecular dynamics (MD) simulations with coarse-grained models are used to investigate the adsorption process of proteins onto an ion-exchange chromatographic medium. The adsorption of human serum albumin (HSA) and bovine hemoglobin (bHb) on the anion exchanger Q Sepharose FF is studied. These two proteins have similar molecule sizes with different isoelectric points. To obtain a reliable set of data, simulations with different initial conditions are carried out for each protein. Convincingly, the results of the MD simulations are qualitatively consistent with those of previous experiments. HSA reaches a stable adsorption in all simulations, while the binding sites can differ. In contrast, bHb reaches a stable adsorption only in one simulation. Due to the stronger protein–ligand interaction of HSA, it adsorbs faster, stronger, and with more binding sites onto Q Sepharose FF than bHb. The spatial movements during the adsorption process and the adsorbed states are investigated in detail. Moreover, we studied the underlying physical relevance of two parameters (characteristic charge and steric factor) of the steric mass action (SMA) model for HSA and for bHb with MD simulations and compared them with the results of experiments. The results reveal that MD simulations are useful to interpret the physical consistence of the SMA parameters. [ABSTRACT FROM AUTHOR]

Abstract: The reaction mechanism of the fast selective catalytic reduction (SCR) of NO x has been investigated by means of a microkinetic model based on DFT calculations. First, potential additional reaction mechanisms are presented that include the intermediate formation of Z−[NO x ]+ (x =1, 2) from the decomposition of N2O y (y =3, 4) on a Brønsted acid. The formed reacts with ammonia to nirosamine or nitramide. The DFT results are applied in a microkinetic model together with prior studies of Brüggemann et al. The simulated conversion of NO x is in agreement with experimental data over a wide range of temperature. The activity of the H-ZSM5 for the fast SCR is based on the reaction sequence via Z−[NO x ]+, the decomposition of nitrosamine and nitramide, and the reaction of nitrous and nitric acid with adsorbed ammonia at low temperatures. Ammonia blocks the active sites at low temperatures while thermodynamic limitations of the surface species N2O y restrict the conversion at high temperatures. Heat of formations and reaction rate constants were adjusted within the accuracy of the applied method for important elementary steps to cope with experimental data. [Copyright &y& Elsevier]

Abstract: Molecular dynamics simulations have been carried out to provide a microscopic description of the diffusion behavior of methanol in NaX zeolite. Previously calibrated existing force fields have been carefully examined and tested with respect to their ability to reproduce the experimentally observed adsorption behavior. The force field parameters, which were selected in this process, were used to examine temperature dependence of the self-diffusion coefficient of methanol over a wide range of methanol loadings. The simulation results were found to be in a qualitative agreement with the corresponding experimental data. The simulations provided new insights on the experimental concentration dependence of the self-diffusion coefficient. Collective effects of the mutual interactions of methanol molecules competing for the most preferable sites at the intercage window were found to be key factors responsible for the observed concentration dependence of the intercage self-diffusivity. [Copyright &y& Elsevier]

Knowledge about the structural elements of skin and its appendices is an essential prerequisite for understanding their complex functions and interactions. The hence necessary morphological description across several orders of scale not only requires the investigation at the light microscopic level but also ultrastructural investigation, ideally on the identical sample. For a correlative and multimodal observation one unique preparation protocol is mandatory. As a compromise between sample sizes of >500 μm in diameter on the one hand and optimal preservation of antigenicity and morphology on the other, we developed a new preparation protocol that allows (i) 3D reconstruction of the resin-embedded sample by confocal light microscopy prior to (ii) direct immunolocalization of target proteins within selected sample planes by light and fluorescence microscopy or transmission electron microscopy. Alternatively, (iii) serial cryosections of the frozen sample can be taken for characterizing the sample in toto. With this unique approach we were able to fully demonstrate the structural complexity of axillary skin samples, increasing the structural resolution from 3D reconstruction of the whole gland up to ultrastructural investigations at the subcellular level. We could demonstrate that axillary sweat glands are not separately distributed, as has been assumed to date; instead, they seem to be intricately twisted into one another. This promotes the concept of a complex axillary sweat gland organ instead of single sweat gland entities. [ABSTRACT FROM AUTHOR]

Abstract: New force fields for nitrous oxide and oxygen, based on a Lennard–Jones plus point charge functional form are reported. The Lennard–Jones parameters of size and energy as well as the point charges were determined by fitting to single-component vapor–liquid equilibrium data. The new force fields accurately describe the vapor–liquid coexistance curves of nitrous oxide and oxygen. It is shown that properties not included in the parameterization process could also be reproduced. In addition to single component phase coexistance simulations, the phase equilibria of four binary mixtures (–, –, –, –) and one ternary mixture (––) have been simulated without further adjustment of the model parameters. Good agreement with experimental data was achieved over a wide range of conditions. [Copyright &y& Elsevier]

Abstract: A reaction mechanism for the decomposition of N2O on Fe-ZSM-5 has been proposed by Heyden et al. based on a detailed density functional theory analysis of the energetics for alternative pathways. This work suggested that isolated Fe cations bound to a single oxygen atom (viz., Z−[FeO]+) are the active sites for N2O decomposition. It was also shown that the presence of water vapor in the feed stream to the catalyst can deactivate these sites, but this process was demonstrated to be reversible at temperatures above about 690 K. In the present work, the decomposition of N2O was simulated under non-steady-state conditions using the mechanism of Heyden et al. and the rate coefficients calculated by these authors. These simulations closely reproduce the results of temperature-programmed reaction and pulsed N2O decomposition experiments. The dynamics of water desorption from deactivated Fe sites are found to be slow. Thus at 773 K, dehydration of a fully hydrated sample of Fe-ZSM-5 can take up to 10 h. The present study also shows that temperature-programmed desorption of O2 from Fe-ZSM-5 after N2O decomposition arises from the reaction Z−[FeO2]+ ⇄Z−[Fe]+ +O2, but that this process is not a part of the mechanism for N2O decomposition under steady-state conditions. [Copyright &y& Elsevier]

The adsorption isotherms of various alkenes and their mixtures in zeolites such as silicalite-1 (MFI-type), theta-1 (TON-type), and deca-dodecasil 3R (DDR-type) were calculated using the grand canonical Monte Carlo (GCMC) approach. Additionally, the adsorption of alkene-alkane mixtures was simulated. The GCMC approach was combined with the configurational-bias Monte Carlo (CBMC) method. Effective Lennard-Jones parameters for the interaction between the oxygen atoms of all-silica zeolites and the sp 2 -hybridized groups of linear alkenes were determined using a united atom force field. They were adjusted to the experimental adsorption data of silicalite-1 (MFI). The inflection behaviour of the 1-heptene isotherm was investigated in detail. It is shown that, in the inflection region, the 1-heptene molecules alter their end-to-end length depending on their location. The occurrence of a maximum in the mixture adsorption isotherms is attributed to two effects: entropic effects and non-ideality effects. From the mixture simulations some general conclusions concerning the separation of hydrocarbons with silicalite-1 can be drawn. The transferability of the Lennard-Jones parameters to other zeolites was investigated. Simulations of adsorption isotherms in the zeolites theta-1 and DD3R and their comparison with experimental data indicate the possibility of transferring the parameters to other all-silica zeolites. [ABSTRACT FROM AUTHOR]

• A continuum model is developed to simulate DRM in catalyst pellets. • The preferred pore diameter is 300 nm, and the optimal porosity is 0.51–0.64. • The bidisperse catalyst is 56–175% more active but uses 10–18% less catalyst. • Engineering pore structure is needed in the design of DRM catalyst pellets. Enhancing the utilization and activity of catalytic materials is crucial in designing catalysts for industrial use. This work achieves these performance enhancements in Rh/Al 2 O 3 catalyzed dry reforming of methane (DRM) at the catalyst pellet level, through engineering catalyst pore network structure. A continuum model, describing the coupled mass, heat transfer and reactions, is developed to optimize the monodisperse and bidisperse catalyst pellets under different temperatures, pressures, and CH 4 /CO 2 ratios. The results show that the preferred pore diameter for the monodisperse catalyst and macropore diameter for the bidisperse catalyst are all 300 nm, above which Knudsen diffusion is not important. Besides, the optimal porosities for the monodisperse and bidisperse catalysts are in the ranges of 0.51–0.59 and 0.61–0.64, which is the result of the trade-off between diffusion and reaction. The optimal bidisperse catalyst can be 56–175% more active but uses 10–18% less catalyst materials when compared to the optimal monodisperse catalyst with the same mesopore size, indicating the great advantage of introducing the optimal macroporosity into mesoporous catalyst pellets for DRM. These results should serve to guide the rational design of industrial catalyst pellets. [ABSTRACT FROM AUTHOR]

Fossil fuel depletion, global warming, climate change, and steep hikes in the price of fuel are driving scientists to investigate commercial and environmentally friendly energy carriers like hydrogen. Steam methane reforming (SMR), a current commercial route for H 2 production, has been considered the best remedy to fulfill the requirements. Despite the remarkable quantity of H 2 produced by the SMR, this technology still faces major challenges such as catalyst deactivation due to the sintering of metal nanoparticles, coking, and generation of a large quantity of CO 2. Firstly, the effects of catalyst types, kinetic models, and operating conditions on high-yield H 2 production, the evolution path from gray to blue, via the conventional SMR are comprehensively reviewed. Secondly, exploiting intensified techniques such as membrane technology, sorption, fluidization, and chemical looping for SMR to blue H 2 are discussed in detail. Further, a novel and sustainable path for the SMR process, hybridizing the use of novel materials and emerging technologies to produce turquoise H 2 , is proposed. Finally, the critical points for steam reforming process technology that can help leverage environmental, social, and governance (ESG) profiling have been discussed. [Display omitted] • Evolution path from gray to turquoise H 2 via catalytic SMR is discussed. • Recent advances in catalysis, kinetic models, and operating conditions are reviewed. • The importance of SMR process intensification for blue H 2 production is highlighted. • A novel and sustainable path for the SMR process to efficiently produce turquoise H 2 is proposed. • Key points for SMR technology that can help leverage ESG profiling are listed. [ABSTRACT FROM AUTHOR]

Four metal-organic frameworks with similar topology but different chemical environment inside the pore structure, namely, IFP-1, IFP-3, IFP-5, and IFP-7, have been investigated with respect to the separation potential for olefin-paraffin mixtures as well as the influence of the different linkers on adsorption properties using experiments and Monte Carlo simulations. All IFP structures show a higher adsorption of ethane compared to ethene with the exception of IFP-7 which shows no selectivity in breakthrough experiments. For propane/propane separation, all adsorbents show a higher adsorption for the olefin. The experimental results agree quite well with the simulated values except for the IFP-7, which is presumably due to the flexibility of the structure. Moreover, the experimental and simulated isotherms were confirmed with breakthrough experiments that render IFP-1, IFP-3, and IFP-5 as suitable for the purification of ethene from ethane. [ABSTRACT FROM AUTHOR]

Two zeolitic imidazolate frameworks, ZIF-9 and ZIF-71, are evaluated by adsorption experiments and molecular simulations with respect to their potential towards olefin/paraffin separation. Pure component adsorption isotherms are measured and compared to grand-canonical Monte-Carlo (GCMC) simulations. The experiments show that the adsorption of the paraffin is favorable over the olefin in both structures. Whereas the isotherms are predicted well by simulations for ZIF-71, in case of ZIF-9 only the saturation loading could be computed accurately because the latter material seems to undergo a so-called gate-opening effect upon adsorption of guest molecules; ZIF-71 does not show this effect. Both structures show promising results with respect to olefin/paraffin separation. [ABSTRACT FROM AUTHOR]

Diffusion in nanoporous host–guest systems is often considered to be too complicated to comply with such “simple” relationships as Fick's first and second law of diffusion. However, it is shown herein that the microscopic techniques of diffusion measurement, notably the pulsed field gradient (PFG) technique of NMR spectroscopy and microimaging by interference microscopy (IFM) and IR microscopy (IRM), provide direct experimental evidence of the applicability of Fick's laws to such systems. This remains true in many situations, even when the detailed mechanism is complex. The limitations of the diffusion model are also discussed with reference to the extensive literature on this subject. [ABSTRACT FROM AUTHOR]

Die Diffusion in nanoporösen Wirt ‐ Gast ‐ Systemen wird oft als viel zu kompliziert angesehen, als dass sie mit so “einfachen” Beziehungen wie dem ersten und zweiten Fickschen Gesetz vereinbar sein könnte. Wir zeigen nun, dass die mikroskopischen Diffusionsmesstechniken, vor allem die NMR ‐ Spektroskopie mit gepulsten Feldgradienten (PFG) und die Mikrobildgebung mittels Interferenzmikroskopie (IFM) und IR ‐ Mikroskopie (IRM), den direkten experimentellen Nachweis für die Anwendbarkeit der Fickschen Gesetze auf solche Systeme liefern. Dies gilt oft auch dann noch, wenn die zugrundeliegenden Transportmechanismen komplex sind. Die Grenzen des Diffusionsmodells werden unter Bezugnahme auf die umfangreiche Literatur diskutiert. Selbst in kompliziert strukturierten nanoporösen Systemen ist der Diffusionskoeffizient eine wohldefinierte Größe, weshalb seine weitere Spezifizierung als „effektiver”︁ oder „scheinbarer”︁ Diffusionskoeffizient unnötig und möglicherweise sogar missverständlich ist. Dies belegt die hier untersuchte Diffusion in einem nanoporösen Glas und in MOF ‐ 5. [ABSTRACT FROM AUTHOR]

The influence of isotypic crystal structures on adsorption and diffusion of methane in all-silica LTA, SAS and ITE zeolites is studied. Results obtained with the experimental structures are compared with structure predictions and approximations that are commonly employed. The results indicate that diffusion coefficients are much more affected than Henry coefficients. In fact, orders of magnitude deviations in the diffusivity can be observed and a systematic parameter study finally gives rise to the correlation between structure sensitivity and diffusion-window size. [ABSTRACT FROM PUBLISHER]

Abstract: The decomposition of N2O on dinuclear oxygen-bridged iron sites in Fe-ZSM-5 was simulated under steady-state conditions considering the reaction mechanism and the rate parameters proposed by Hansen et al. [J. Phys. Chem. C 111 (2007) 2092] on the basis of DFT calculations. The presence of low concentrations of water vapor in the feed stream (ppb to ppm levels) affects the calculated values for the apparent activation energy and the pre-exponential factor and thus can explain the wide variation in experimental values for these quantities, as well as the appearance of an apparent compensation effect. The activity of the dinuclear oxygen-bridged site was compared with that of the mononuclear iron site proposed earlier by Heyden et al. [J. Phys. Chem. B 109 (2005) 1857]; the latter was found to be slightly more active. Microkinetic models for both mononuclear and dinuclear iron sites were used to reproduce temperature-programmed reaction experiments reported for Fe-ZSM-5 samples with low and high iron content. This analysis leads to the conclusion that at very low Fe/Al ratios, mononuclear iron sites prevail, whereas at higher Fe/Al ratios, both mononuclear and dinuclear iron sites are likely to be present simultaneously. [Copyright &y& Elsevier]

A detailed analysis of the method for fast acquisition of kinetic data by means of a polythermal-temperature-ramping reactor (PTR) as suggested by Wojciechowski in 1995 was performed. The ammonia synthesis reaction over a commercial Fe catalyst (BASF) was taken as an example. Kinetic data evaluation was based on a kinetic model as reported by Sehested et al. in 1999. As a result of data analysis, the experimental molar rate of change of ammonia could be described adequately over a wide range of N2 and H2 partial pressures as well as temperature. The pre-exponential factors, activation energies and adsorption enthalpies are in reasonable agreement with data for promoted iron catalysts reported in literature. Accordingly, the PTR method was evaluated as a efficient tool for kinetic data analysis. The number of experiments including different initial conditions can be significantly diminished since PTR experiments have not to follow the strict sequence of varying one experimental parameter after the other by keeping all others constant. The collected exit concentrations, exit temperature and contact time are correlated by spline-functions which allow the extraction of functional relationships required for derivation of rate expressions. If the steady-state of the catalyst is rapidly attained, temperature ramping allows fast continuous data acquisition. Thus, the PTR method has the potential of significantly reducing the time needed for determining reliable kinetics over a wide range of operating conditions. [Copyright &y& Elsevier]

Climate change, global warming, fossil fuel depletion and rising fuel prices have created great incentives to seek alternative fuel production technologies. CO 2 transformation to value-added products using renewable H 2 has proven to be an emerging solution to enable this goal. In this regard, three different promising processes, namely methane, methanol and hydrocarbon synthesis via CO 2 hydrogenation are thoroughly discussed. In addition, the influential factors affecting process efficiencies such as catalyst design and mechanistic insight, operating conditions as well as reactor types are investigated, with key pathways that dictate catalyst activity and selectivity of the most promising materials described. Furthermore, a brief overview of the reactor configuration and its crucial role in the improving process viability is analyzed. Accordingly, fixed-bed, fluidized-bed, annular and spherical reactors along with H 2 O/H 2 perm-selective membrane reactors are disscussed for hydrocarbon production. In addition, different reactor configurations are compared to assess the best one that is adjustable depending on the reaction mechanism. Consequently, a corrugated-wall dual-type membrane reactor is proposed as an emerging alternative for CO 2 hydrogenation to value-added products. [Display omitted] [ABSTRACT FROM AUTHOR]

• Modeling of CO 2 hydrogenation to hydrocarbons in CR, AFSR and RFSR are accomplished. • Kinetic parameters are estimated via heuristic DA optimization algorithm. • Performance of the theoretical CR is compared with available experimental data. • Effect of reactor configuration is investigated in terms of conversion and selectivity. Climate change and global warming, as well as growing global demand for hydrocarbons in industrial sectors, make great incentives to investigate the utilization of CO 2 for hydrocarbons production. Therefore, finding an in-depth understanding of the CO 2 hydrogenation reactors along with simulating reactor responses to different operating conditions are of paramount importance. However, the reaction mechanisms for CO 2 hydrogenation and their corresponding kinetic parameters have been disputable yet. In this regard, considering the previously proposed Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism, which considered CO 2 hydrogenation as a combination of reverse water gas shift (RWGS) and Fischer-Tropsch (FT) reactions, and using a one-dimensional pseudo-homogeneous non-isothermal model, kinetic parameters of the rate expressions are estimated via fitting experimental and modelling data through a novel swarm intelligence optimization technique called dragonfly algorithm (DA). The predicted reactants conversion using DA algorithm are closer to the experimental data (with about 4% error) comparing to those obtained by the artificial bee colony (ABC) algorithm, and are in significant agreement with available literature data. The proposed model is used to assess the effect of reactor configuration on the performance and temperature fluctuations. Results show that axial flow spherical reactor (AFSR) and radial flow spherical reactor (RFSR) exhibiting the same surface area with that of the cylindrical reactor (CR), i.e., AFSR-2 and RFSR-2-i are the most efficient exhibiting hydrocarbons selectivity of 40.330% and 40.286% at CO 2 conversion of 53.763% and 53.891%. In addition, it is revealed that the location of the jacket has an essential role in controlling the reactor temperature. [ABSTRACT FROM AUTHOR]

• We propose a pore network model able to aid the design of Claus catalysts. • The deactivation and regeneration of Claus catalyst particles are probed. • Multiple steady states are found where capillary condensation of sulfur occurs. • Catalyst particle structures strongly affect the performance of Claus catalysts. • A bimodal catalyst particle shows higher activity and uses less catalytic material. A pore network model is proposed to study the deactivation of Claus catalysts caused by sulfur condensation, as well as the corresponding regeneration. This model allows to describe the coupled reaction, diffusion, and sulfur condensation from a single pore to a catalyst particle. The results show that the deactivation branch of apparent activities is well above the regeneration branch in the temperature and pressure ranges where capillary condensation of sulfur occurs. This phenomenon of multiple steady states can be attributed to the inconsistent contents of liquid sulfur in the catalyst particle when changing temperature and pressure in different directions. The catalyst particle shape and pore network structure directly influence diffusion resistance, internal surface area for reaction, and sulfur condensation, and subsequently pass these influences on to the apparent activity. This work should provide a proper model and some useful guidelines for the design of catalyst particles for the Claus reaction. [ABSTRACT FROM AUTHOR]