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The question of how easy the transition is between design and manufacturing by the 3D printing of periodic open cellular structures occurs from the analysis of cases in which additive manufacturing and heterogeneous catalysis merge. The synergy between these two fields suggests that one of the great advantages that the catalysis of this manufacturing methodology can take advantage of is the obtaining of advanced designs that would allow improving the processes from the geometry of the reactors. However, not all 3D-printing techniques offer the same degree of resolution, and this uncertainty grows when using more complex materials to work with, such as ceramics or metals. Therefore, the present work seeks to answer this question by finding experimentation strategies, starting with a simple case study inspired by the additive manufacturing–catalysis combination, in which a ceramic polymer resin of high thermal resistance is used to obtain POCSs that are potentially useful in thermochemical or adsorption processes. This exploration concludes on the need to define limits for what we have called an "effective work zone" that combines both design criteria and the real possibility of printing and manipulating the pieces, making sweeps in structural parameters such as cell size and the diameter of struts in the POCS. Similarly, the possibility of coating these systems with inorganic oxides is explored, using a generic oxide (Al2O3) to analyse this scenario. Finally, a cartridge-type assembly of these systems is proposed so that they can be explored in future processes by other researchers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Oxidative coupling of methane (OCM) in monolith or gauze reactors is analyzed. • Impact of methane to oxygen ratio and space time on ignition-extinction is determined. • Impact of substrate thermal conductivity on ignition-extinction is presented. • Impact of operating pressure on ignition-extinction in OCM is analyzed. • Impact of volume to surface area and heat loss on ignition-extinction is presented. We use a multi-scale multi-mode reduced order model for coupled homogeneous-catalytic reaction systems to present a comprehensive bifurcation (ignition-extinction) analysis of the oxidative coupling of methane (OCM) in monolith, gauze or wire-mesh type reactors. We determine the impact of methane to oxygen ratio in the feed, space time, channel hydraulic radius (or gas phase to catalyst volume ratio), washcoat diffusional limitations, operating pressure and substrate thermal conductivity on the ignition and extinction behavior of the system as a function of the feed temperature. The computations show that for typical operating conditions, the methane conversion and C 2 product selectivity are non-monotonic on the ignited branch and there exists an optimum point of operation away from the extinction point. The predicted methane, oxygen conversions and C 2 selectivity are compared to reported experimental results in the literature. We also present the various species and temperature profiles along the length of the reactor and examine how these profiles are impacted by the substrate conductivity, space time and heat loss. The results obtained for monolith, gauze or wire-mesh reactors are compared to those in packed-bed reactors and suggestions are provided for scale-up and optimization of these reactors for carrying out OCM as well as other catalytic partial oxidations. [ABSTRACT FROM AUTHOR]

Novel catalytic systems should be tested for the valorization of CO 2 through the Sabatier reaction, since this process is gaining great importance within strategic sectors of the chemical industry. Therefore, this work explores the feasibility of structuring a catalyst (0.5%Ru–15%Ni/MgAl 2 O 4) for CO 2 methanation using metal micromonoliths. The coating of the catalyst over the surface of the micromonoliths is carried out by means of the washcoating procedure and different characterization techniques are applied to establish possible changes in the catalyst during structuring. Regarding the performance in the Sabatier reaction, the structured systems are tested as well as the powder catalyst in order to establish the possible effects of the structuring processes. For this, variables such as catalyst loading, space velocity, inclusion of water in the feed-stream and the pressurization of the process were studied. In general, the structuring of the proposed catalyst by the reported procedure is absolutely feasible. There are no substantial changes in the main features of the catalyst and this means that its catalytic performance is not altered after the structuring process either. Furthermore, the structured system exhibits high stability in a long-term test and is comparable with other CO 2 methanation catalysts reported in research to date. Image 1 • Micromonoliths were successfully coated with 0.5 wt% Ru-15 wt% Ni/MgAl2O4 catalyst. • Structuring process slightly affects the catalyst and its catalytic performances. • Heat mass transport limitations rather than mass ones could be assumed. • Structured catalysts show a considerable water tolerance. • The structured catalyst exhibited high stability in a long-term test (100 h). [ABSTRACT FROM AUTHOR]

Structured open-cell foam reactors are promising for managing highly exothermic reactions such as CO2 methanation due to their excellent heat transport properties. Especially at low flow rates and under dynamic operation, foam-based reactors can be advantageous over classic fixed-bed reactors. To efficiently design the catalyst carriers, a thorough understanding of heat transport mechanisms is needed. So far, studies on heat transport in foams have mostly focused on the solid phase and used air at atmospheric pressure as fluid phase. With the aid of pore-scale 3d CFD simulations, we analyze the effect of the fluid properties on heat transport under conditions close to the CO2 methanation reaction for two different foam structures. The exothermicity is mimicked via volumetric uniformly distributed heat sources. We found for foams that are designed to be used as catalyst carriers that the working pressure range and the superficial velocity influence the dominant heat removal mechanism significantly. In contrast, the influence of fluid type and gravity on heat removal is small in the range relevant for heterogeneous catalysis. The findings might help to facilitate the design-process of open-cell foam reactors and to better understand heat transport mechanisms in foams. [ABSTRACT FROM AUTHOR]

CO2 methanation reaction has attracted renewed interest since the power‐to‐gas (PtG) concept emerged as a promising alternative for CO2 emission abatement using surplus renewable electricity. Although the reaction has been reported for more than a century, improvements in the catalytic system and reactor design remain challenging. Recently, hydrotalcite (HT) materials known for their facile synthesis and high performance are extensively used as precursors for supported catalysts in a wide range of reactions, including CO2 hydrogenation to CH4. Herein, a comprehensive overview on HT‐derived catalysts applied for CO2 methanation is provided. More importantly, new reactor concepts are extensively investigated, such as honeycomb and microchannel reactors, to overcome issues related to the high exothermic nature of the reaction. The latest achievements with respect to structured reactors are also comprehensively reviewed and thoroughly discussed. [ABSTRACT FROM AUTHOR]

• PECVD was used to prepare CoO X and CoO X /TiO 2 catalysts on the structured support. • Strong effect of the preparation conditions on the activity of thin film catalysts. • Oxidation states, unlike the metallic cobalt state, are active in CO 2 methanation. • Superior conversion and selectivity of CoO in graphite-like matrix. Series of CoO X and CoO X /TiO 2 nanocatalysts for the conversion of CO 2 to methane were produced in the form of thin films supported on wire gauze using the plasma-enhanced chemical vapor deposition (PECVD) from volatile cobalt and titanium organic complexes. The results show that conditions of the plasma deposition process and the subsequent thermal treatment in air or argon atmosphere determine the structure and the catalytic performance of the resulting thin films. Investigations of the surface chemical structure of the catalytic films, performed by X-ray photoelectron spectroscopy (XPS), revealed the presence of cobalt in different oxidation states: Co+3, Co+2, Co°, the content of which depends on the processing path. Interestingly, not metallic cobalt but its oxidation states were found to be active in the CO 2 methanation. Among the different CoOx-based films, the specific structure of CoO in graphite-like matrix obtained after calcination in argon, revealed superior performance over the CoO x and CoO X /TiO 2 films calcined in air. At 400 °C, it achieved a high CO 2 conversion and selectivity to methane of 73% and 94%, respectively (GHSV = 1500 cm3 h−1 g cat −1). Moreover, there was no deactivation for the CoO in graphite-like matrix during time-on-stream at 400 °C indicating an excellent stability. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A translucent packed bed microstructure was assessed for use within photocatalytic reactors. • A light source with homogeneous light field was built using a verified ray-tracing model. • When benchmarked, the reactor was proven to perform as a scalable array of microreactors. • The reactor had the highest energy efficiency among immobilized catalyst photoreactors. Abstract Translucent photocatalytic reactor structures are investigated as a possible alternative to numbering up as a method for the scale-up of microreactors. The structure and the light source design is elaborated to introduce this concept. The light field was characterized using a ray tracing algorithm. A rectangular reactor made from glass was designed using borosilicate spheres small enough to create an array of interconnected microchannels in the reactor. It was found that ray tracing can be used as a proper tool to easily design multiple-LED light sources and predict respective irradiance patterns. The performance of the reactor was assessed using the apparent rate constant, the space-time yield and the photocatalytic space-time yield, a recently introduced performance parameter which takes into account the lamp power and the reactor productivity. The apparent rate constant of the reactor for an incoming irradiance of 191 W m−2 was found to be 0.82 min−1, which is, to our knowledge, in the range of microreactors and 1–2 orders of magnitude higher than any high throughput immobilized reactor in literature. With a photocatalytic space-time yield of 0.657 m3 day−1 m−3 reactor kW−1 our reactor was amongst the best reported performers in terms of productivity and energy efficiency. This performance is related to the high specific illuminated surface area of 4267 m2 m−3 and high catalyst load of 1.9 g L−1. [ABSTRACT FROM AUTHOR]

Ru catalysts supported on alumina coated monoliths has been prepared employing three different precursor, which are ruthenium chloride, ruthenium nitrosyl nitrate and ruthenium acetyl acetonate, by an equilibrium adsorption method. The Ru particle sizes could be controlled varying the metal precursor salt. Among the prepared catalysts, Ru catalyst prepared from nytrosyl nitrate exhibited the highest activity which is concomitant to the largest mean Ru particle size of 3.5 nm. The values of the apparent activation energy calculated from the Arrhenius equation are according to the Temkin-Phyzev model, indicating that the recombinative desorption of N ad-atoms is the rate-determining step of the reaction. However, the ratio between the kinetic orders with respect to ammonia and hydrogen (− α / β ), is not in agreement to the valued predict by Temkin formalism. This fact could be related to the different operational conditions used during the reaction, and/or catalyst nature, but not to any change on the controlling step of the reaction. [ABSTRACT FROM AUTHOR]

Microwave heating (MWH) transforms energy from an electromagnetic wave to heat. In contrast to conventional heating (CH) mechanisms that use slower heat transfer processes via conduction, convection or radiation, microwaves (MW) directly interact with MW susceptor materials and induce a rapid conversion of the electromagnetic energy into heat. This rapid heating provides MWH with distinct features that can be leveraged to increase conversion, selectivity and/or energy efficiency of chemical processes. Here we discuss recent significant advances reported in MWH processes involving gas-solid interactions. Special attention is devoted to key aspects such as the methodologies to accurately determine local temperatures under the influence of electromagnetic (EM). Other relevant aspects such as the consideration of the solid catalyst dielectric properties or the design of novel gas-solid contactor configurations will be discussed. Emerging aspects such as the potential of MWH to minimize secondary by-products in high temperature reactions or to efficiently perform in transient processes, e.g. adsorption-desorption cycles, are highlighted. Finally, current challenges and perspectives towards a wide application of MWH in gas solid contactors will be critically discussed. [Display omitted] • Critical overview of the current state of MW heterogeneous catalysis. • Evaluation of the types of MW reactors. • Advantages of gas-solid temperature gradients induced by MW. • Enhanced adsorption-desorption-reaction mechanisms. • Examples of enhanced selectivity induced by MW. [ABSTRACT FROM AUTHOR]

Structured open-cell foam reactors are promising for managing highly exothermic reactions such as CO2 methanation due to their excellent heat transport properties. Especially at low flow rates and under dynamic operation, foam-based reactors can be advantageous over classic fixed-bed reactors. To efficiently design the catalyst carriers, a thorough understanding of heat transport mechanisms is needed. So far, studies on heat transport in foams have mostly focused on the solid phase and used air at atmospheric pressure as fluid phase. With the aid of pore-scale 3d CFD simulations, we analyze the effect of the fluid properties on heat transport under conditions close to the CO2 methanation reaction for two different foam structures. The exothermicity is mimicked via volumetric uniformly distributed heat sources. We found for foams that are designed to be used as catalyst carriers that the working pressure range and the superficial velocity influence the dominant heat removal mechanism significantly. In contrast, the influence of fluid type and gravity on heat removal is small in the range relevant for heterogeneous catalysis. The findings might help to facilitate the design-process of open-cell foam reactors and to better understand heat transport mechanisms in foams.

Self-supported ZSM-5 zeolite monolith foams (ZMFs) with different Si/Al ratios have been successfully prepared by hydrothermal synthesis with a polyurethane foam (PUF) template followed by calcination in air at 550 °C to harden. Cu or Mn have been introduced on preformed ZMF samples to obtain monolithic catalysts that have been fully characterized by morphological (XRD and SEM), textural (BET and pore size distribution), mechanical (compressive strength) and chemical (ICP-MS) analyses, and eventually tested in the Selective Catalytic Reduction of NO with NH 3 in the temperature range 100–450 °C. The zeolite monolith foams are characterized by a well crystallized ZSM-5 structure, a BET surface area ca. 420 m 2  g −1 and remarkable mechanical resistance even without any binder. Those structured catalysts show specific catalytic activity in line with powdered counterparts, but they can guarantee improved NO conversion due to the higher amount of catalyst per unit volume of reactor and to their superior mass transfer coefficients coupled to low internal diffusion limitations. [ABSTRACT FROM AUTHOR]

The deposition of V-based catalysts for the oxidative dehydrogenation of propane to propene on cordierite honeycomb monoliths was optimised as a strategy to decrease the contact time in a structured reactor with respect to a conventional fixed bed one. 10 wt% VOx supported over SiO2 or Al2O3 were used as catalysts, deposed over the monolith using silica or alumina as primer, respectively. Both the alumina supported catalyst and the bohemite primer precursor were effectively deposed by dip-coating from stable powder suspensions, whereas insufficient adhesion was obtained when loading pre-synthesised SiO2 over the cordierite. A new method based on sol-gel production of SiO2 from tetraethylortosilicate (TEOS) over the monolith surface was set up. A correlation was derived for the prevision of the amount of silica deposed depending on the amount of TEOS. Both primer and catalyst loading were optimised as for uniformity and stability of the coating and resulted 0.5–1 wt % primer and 0.15 wt % of catalyst. Activity testing confirmed the strong improvement of propene productivity by increasing the time factor (i.e. Ncm3 of flowing reactant/min gcat), which ended in a one order of magnitude increase of productivity for the honeycomb-supported samples with respect to the fixed bed configuration.

A high flux solar simulator allows the lab-scale assessment of solar reactor concepts by irradiating a target with high flux thermal energy, similarly to reactors installed in concentrated solar radiation facilities such as central towers with a heliostat field. In the current study, the design and construction of a high flux solar simulator facility for near realistic solar experiments is presented. A simple, cavity-tubular thermochemical reactor is employed for the evaluation of the redox activity of structured monolithic bodies (foams and honeycombs) consisting entirely of NiFe 2 O 4 w.r.t·H 2 O splitting, CO 2 splitting and combined H 2 O-CO 2 splitting reactions. Experiments under realistic conditions, i.e. a solar reactor under irradiation, were conducted to assess the solar fuels production capability, which was examined at the structure level and the reactor level. The best performing structure was the NiFe 2 O 4 foam. Further multilevel research (structure, reactor as well as redox material), will improve product yield and reactor efficiency. [ABSTRACT FROM AUTHOR]

Structured bodies from redox materials are a key element for the implementation of thermochemical cycles on suitable reactors for the solar H 2 O splitting. In the current work different configurations of nickel ferrite were investigated with respect to their performance in H 2 O splitting: i) powder, ii) disk, iii) honeycomb flow-through monoliths. The structured bodies were prepared via pressing and extrusion techniques. The performance of the different structures was affected significantly by differences in the structural characteristics. Alternative approaches involving casting techniques for the structuring of nickel ferrite porous bodies were also investigated. This work constitutes a preliminary attempt towards tuning such characteristics to achieve enhanced and cycle-to-cycle stable production yields. [ABSTRACT FROM AUTHOR]

Aluminum monoliths were used as substrates to prepare structured catalysts. A rough alumina layer was generated on the surface of the substrates by anodizing followed by hydrothermal treatments. The dip-coating technique was used for coating the monolithic substrates. Aqueous suspensions with 0.15 and 0.30 g/g of Ni-Nb mixed oxides catalysts were prepared for that purpose. Colloidal SiO2 was added as a binder in order to obtain homogeneous and adherent coatings. The samples were characterized by SEM, TPR, XPS, XRD, and N2 adsorption and tested in the oxidative dehydrogenation (ODH) of ethane to ethylene. The silica particles produced a drop in catalytic activity without affecting ethylene selectivity. The former effect was attributed mainly to a decrease in surface nickel concentration and an increase in reduction temperature. The presence of anodized aluminum substrates in the reaction environment did not have a significant influence on catalytic activity and product distribution, as observed for the coated monoliths used in this work, thus being a useful material to prepare structured catalysts for low-temperature ethane ODH. [ABSTRACT FROM AUTHOR]

Metallic supports play an important role as structured reactor internals. Due to their specific properties including enhanced heat and mass transport, high mechanical resistivity and elimination of local hot-spots, they are commonly used in gas exhaust abatement from stationary and automotive industries. In this study, the performance of three structured supports with deposited Cu/USY (Ultrastabilised Y--zeolite) for deNOx abatement were modelled. Based on kinetic and flow resistance experimental results, the one-dimensional (1D) model of structured reactor was developed. The performance of the structured reactors was compared by the length of the reactor necessary to achieve an arbitrary 90% NOx conversion. The performed simulations showed that the sonochemically prepared copper USY and ZSM-5 zeolites deposited on metallic supports may be successfully used as catalysts for deNOx process. [ABSTRACT FROM AUTHOR]

A question arises whether the kinetic parameters derived from the Arrhenius equation presented in the literature in fact reflect intrinsic kinetics or are influenced by diffusional effects. It is commonly accepted that diffusion can not only influence (reduce) the reaction rate but also change the observed kinetic constants and reaction order. In this study the limitation of reaction rate ( n -hexane catalytic combustion) was observed even at moderate temperatures during experiments performed in a Continuous Stirred Tank Reactor (CSTR), gradientless reactor dedicated to determination of reaction kinetics. In this study a numerical method of the separation of intrinsic kinetics from mass transport effects has been proposed for an experiment executed under significant mass transfer resistance. It was tested using different carrier types (steel sheets and woven wire gauzes) and catalyst formulations for two combustion reactions: of n -hexane and methane. The intrinsic kinetic parameters derived in this way were then used for the numerical simulations of three types of structured reactors filled with: woven and knitted wire gauzes and monolith in terms of the optimization of a reactor length for combustion reactions. The performed simulations showed that the application of woven gauzes as the reactor internals can give rise to substantial decrease of the reactor length even by 10 times for both methane and n -hexane catalytic combustion reactions. [ABSTRACT FROM AUTHOR]

Ni/CeO 2 –MgO catalysts on powder form and supported on stainless steel plates were prepared, characterized and tested towards hydrogen generation via the steam reforming reaction of ethanol. The structured catalyst was prepared by the dip-coating technique. The coatings obtained over the stainless steel plates were homogeneous and retained their integrity after the reaction experiences. The samples were characterized by SEM, TEM, XRD, ICP-AES, TPR, OSC and N 2 adsorption–desorption measurements. Catalysts presented very good stability under reaction conditions for 16 h on-stream, without showing a significant variation in the activity or product distribution. The structured catalysts presented similar activities and selectivities respect to those of the powder, whereby the deposition method did not modify the catalytic properties of the particulate material. The presence of the AISI 430 stainless steel substrate also had not a significant influence on the performance of the deposited material. [ABSTRACT FROM AUTHOR]

The aim of this study was to obtain and characterise the series of cobalt based structured catalysts prepared by non-equilibrium plasma deposition. The catalysts were obtained under oxygen-rich and oxygen-free conditions. The catalysts were characterised by using spectroscopic and microscopic methods including AFM, SEM, EDS, in situ μRaman and XPS. The catalytic activity of prepared catalysts was measured under n-nonane catalytic combustion reaction. The correlation of catalytic activity with the catalysts characterisation results showed that the active cobalt form of the catalysts in catalytic combustion is spinel structure and is not correlated with the particle size. [ABSTRACT FROM AUTHOR]

Catalytic sulphur trioxide splitting is the highest-temperature (850–900 °C), endothermic step of several sulphur-based thermochemical cycles targeted to production of hydrogen or solid sulphur. The demonstrated capability of centrifugal particle solar receivers of heating particle streams at such temperatures, can allow for "allothermal" implementation of this step via the enthalpy of such particle streams in a catalytic shell-and-tube reactor/heat exchanger decoupled from a solar receiver. In this context, SO 3 splitting catalytic systems shaped to spherical particles and flow-through honeycombs and foams were prepared and tested. Long-term (100–950 h) experiments with catalyst-coated SiC honeycombs demonstrated that oxide-supported Pt catalysts suffered from low conversion and severe deactivation at 650 °C, contrary to Fe 2 O 3 -coated ones. Fe 2 O 3 -coated SiC foams demonstrated reproducible near-equilibrium conversion at 850 °C, under a broad range of sulphuric acid flow rates, combined with minute pressure drop even under high catalyst loadings (35–45 wt %) being thus in principle suitable for eventual pressurized operation. [Display omitted] • Shell-and-tube catalytic SO 3 spitting reactor concept allothermally heated via solar-heated particles explored. • Structured systems considered as non-moving SO 3 splitting catalytic beds were long-term tested. • Pt-based catalysts showed low conversion and deactivation with prolonged on-stream exposure at 650 °C. • Particle and foam structures made entirely of iron oxide showed low conversion at 850 °C. • Fe 2 O 3 -coated SiC foams achieved close-to-equilibrium, reproducible conversion at 850 °C. • Such foams also exhibited very low pressure drop even under high catalyst loadings. [ABSTRACT FROM AUTHOR]

The current scenario where the effects of global warming are more and more evident, has motivated different initiatives for facing this, such as the creation of global policies with a clear environmental guideline. Within these policies, the control of Greenhouse Gase (GHG) emissions has been defined as mandatory, but for carrying out this, a smart strategy is proposed. This is the application of a circular economy model, which seeks to minimize the generation of waste and maximize the efficient use of resources. From this point of view, CO2 recycling is an alternative to reduce emissions to the atmosphere, and we need to look for new business models which valorization this compound which now must be considered as a renewable carbon source. This has renewed the interest in known processes for the chemical transformation of CO2 but that have not been applied at industrial level because they do not offer evident profitability. For example, the methane produced in the Sabatier reaction has a great potential for application, but this depends on the existence of a sustainable supply of hydrogen and a greater efficiency during the process that allows maximizing energy efficiency and thermal control to maximize the methane yield. Regarding energy efficiency and thermal control of the process, the use of structured reactors is an appropriate strategy. The evolution of new technologies, such as 3D printing, and the consolidation of knowledge in the structing of catalysts has enabled the use of these reactors to develop a wide range of possibilities in the field. In this sense, the present review presents a brief description of the main policies that have motivated the transition to a circular economy model and within this, to CO2 recycling. This allows understanding, why efforts are being focused on the development of different reactions for CO2 valorization. Special attention to the case of the Sabatier reaction and in the application of structured reactors for such process is paid.

Based on previous lab-scale heat transfer experiments performed in a test tube filled with metallic foams, extensive simulations of conjugated heat transfer were performed to systematically investigate the role of different coupling scenarios between the foam structure and the tube wall, using a 3D scanned foam geometry to enable the comparison of simulation results with experiments. The goal of this analysis is to gain insight into the prominent role of the wall coupling for radial heat transfer in a structured catalytic reactor packed with metal foams as catalyst supports. In the current numerical investigation the focus is on the characterization of the contact area between the foam and the reactor wall. Starting from perfect contact between the two, the contact area was decreased by selecting randomly some boundary spots of the foam and considering them as adiabatic. Moreover, the local distribution of the adiabatic struts was restricted to regions near the reactor inlet to additionally investigate the influence of the local distribution of the adiabatic struts at same overall contact areas. Eventually, all the contacts between the foam and the reactor wall were considered adiabatic as the other limiting case, wherein heat transfer at the foam/wall interface was governed solely by convection. The numerical analysis revealed that even if only a limited fraction of the struts have a direct contact with the tube wall, the heat transfer rate is significantly enhanced in comparison to the adiabatic case. In analogy with the previous experimental study, the numerical investigation was carried out for two different gases, nitrogen and helium, in order to address the influence of the thermal conductivity of the fluid phase. For further experimental verification, additional heat transfer measurements were performed for the case of a foam directly sintered to the tube in order to realize a perfect contact between foam and wall. [ABSTRACT FROM AUTHOR]

Metallic supports play an important role as structured reactor internals. Due to their specific properties including enhanced heat and mass transport, high mechanical resistivity and elimination of local hot-spots, they are commonly used in gas exhaust abatement from stationary and automotive industries. In this study, the performance of three structured supports with deposited Cu/USY (Ultrastabilised Y—zeolite) for deNOx abatement were modelled. Based on kinetic and flow resistance experimental results, the one-dimensional (1D) model of structured reactor was developed. The performance of the structured reactors was compared by the length of the reactor necessary to achieve an arbitrary 90% NOx conversion. The performed simulations showed that the sonochemically prepared copper USY and ZSM-5 zeolites deposited on metallic supports may be successfully used as catalysts for deNOx process.

A regenerable synthetic sorbent based on MnO x impregnated on high surface area γ-alumina and supported onto cordierite honeycomb monolith was tested for elemental mercury capture in different gas environments. Hg removal tests were performed in a lab-scale quartz reactor operated at 50–350 °C, with Hg concentration in the range 50–250 μg/m 3 , and GHSV = 3.6 · 10 5 h −1 . The sorbent was tested in air (reference case), nitrogen and air with added CO 2 , CO, NO, SO 2 and HCl. Results were analyzed in terms of the apparent initial Hg removal rate. In the absence of oxygen, the sorbent gradually deteriorated its performance. Both CO 2 and CO moderately and reversibly worsened the Hg capture performance, while NO did not show any appreciable effect. On the other hand, SO 2 adversely impacted on the sorbent performance and most importantly the Hg capture capacity was permanently deteriorated. No release of oxidized Hg was observed in tests containing the above components both during adsorption and desorption stages. In the presence of HCl (50 ppm in air) the sorbent both adsorbed elemental Hg and catalyzed its heterogeneous oxidation giving an overall outstanding performance. During desorption only oxidized mercury was released. [ABSTRACT FROM AUTHOR]

The enthalpy effects of reversible chemical reactions can be exploited for the so-called thermochemical storage of solar energy. Oxides of multivalent metals in particular, capable of being reduced and oxidized under air atmosphere with significant heat effects are perfect candidates for air-operated Concentrated Solar Power plants since in this case air can be used as both the heat transfer fluid and the reactant (O 2 ) and therefore can come to direct contact with the storage material (oxide). Based on the characteristics of the oxide redox pair Co 3 O 4 /CoO as a thermochemical heat storage medium and the advantages of porous ceramic structures like honeycombs and foams in heat exchange applications, the idea of employing such structures either coated with or entirely made of a redox material like Co 3 O 4 , as a hybrid sensible-thermochemical solar energy storage system in air-operated Concentrated Solar Power plants has been set forth and tested. At first, small-scale, redox-inert, cordierite foams and honeycombs were coated with Co 3 O 4 and tested for cyclic reduction-oxidation operation via Thermo-Gravimetric Analysis. Such Co 3 O 4 -coated supports exhibited repeatable operation within the temperature range 800-1000 o C for many cycles, employing all the redox material incorporated, even at very high redox oxide loading levels. To improve the volumetric heat storage capacity of such reactors, ceramic foams made entirely of Co 3 O 4 were manufactured. Such foams exhibited satisfactory structural integrity and were comparatively tested vs. the “plain” Co 3 O 4 powder and the Co 3 O 4 -coated, cordierite supports under the same cyclic redox conditions up to 15 consecutive cycles. The Co 3 O 4 -made porous foams were proved also capable of cyclic reduction–oxidation, exploiting the entire amount of Co 3 O 4 used in their manufacture, maintaining simultaneously their structural integrity. [ABSTRACT FROM AUTHOR]

In the perspective of thermochemical storage of solar energy via redox reactions of multivalent metal oxides, the manufacture and relevant testing of porous ceramic foams made entirely of Co 3 O 4 was attempted, in order to maximize the amount of redox powder that can be incorporated in a given thermochemical reactor volume. Small-scale Co 3 O 4 foams with satisfactory structural integrity were successfully produced. The foams were tested in cyclic reduction/oxidation conditions in a TGA apparatus in comparison to pellets made also entirely of Co 3 O 4 . Both these monolithic, porous, structures were capable of cyclic redox operation, exploiting for the thermochemical reactions the entire amount of redox material used for their manufacture. Full extent of reduction/oxidation was observed, in a fully reversible pattern. The initial density of the samples had an effect on specimen’s integrity: the much denser pellets could not retain their structural integrity, exhibiting cracks even after only two cycles. On the contrary, foams were tested for up to 15 redox cycles, maintaining simultaneously their structural integrity and stoichiometric redox performance. Dilatometry experiments under the same temperature-programmed conditions with the TGA ones revealed that during redox cycling, “chemically”-induced stresses are developed due to the expansion/contraction of the cobalt oxide lattice during oxygen release/uptake respectively. These stresses are superimposed to “thermal-only” ones due to temperature cycling and under certain circumstances can lead to structure deformation and fracture. In this respect “open” porous structures like the particular foams proposed and tested in this work have an advantage since their large void space can reversibly accommodate and “buffer” the large volume expansion much better. [ABSTRACT FROM AUTHOR]

The quest for transition to clean energy sources and intensified chemical processes has led to growing interest in microwave-heated reactors. Microwave generated from renewable electricity is a clean energy source and can intensify chemical processes with its unique heating characteristics, especially selective heating. Selective microwave heating creates a temperature differential between phases in a multiphase reactor, allowing a new paradigm in process intensification. Numerous studies have demonstrated the potential of microwaves to achieve process intensification. Nevertheless, detailed explanations for the observations are lacking primarily due to the unavailability of accurate temperature measurements. This perspective article discusses the significant challenges hindering the development and deployment of microwave multiphase reactors and the opportunities for further research. Structured reactors, such as monoliths, are emphasized as a canonical setup for experiments and modeling. [Display omitted] • Status of microwave-assisted process intensification is presented. • Recent advancements in microwave multiphase reactors are presented. • Major challenges hindering the development of microwave reactors are discussed. • Crucial research needs for rapid deployment of microwave reactors are analyzed. • Role of microwave heated monoliths as a canonical setup is explored. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hydrogenation of squalene was investigated using a highly active Pd/CNT catalyst. • Continuous flow transposition was achieved with millimeter scale coated solid foams. • Seamless scale up was demonstrated with a commercially available intensified reactor. A process intensification study for the full hydrogenation of bio-derived platform molecule squalene (SQE) into squalane (SQA), using commercial heterogeneous Pd catalysts and Pd supported on carbon nanotubes (CNT) is reported. Pd/CNT shows a substantial improvement of the catalytic activity for the total hydrogenation of SQE into SQA thanks to cooperativities between Pd nanoparticles and single atoms simultaneously present on the CNT. However, the stirred reactor's productivity, scalability, and operability are limited by the exothermicity of the reaction (Δ r H = − 765 kJ.mol−1). The implementation of the Pd/CNT catalyst in flow was then studied after coating this catalyst on metallic open cell foams. Using the foam-based milli-reactor's characteristics, including high mass and heat transfer rates and safety, fully reduced SQA (>99 %) was obtained at 180 °C and 30 bar of H 2 for a contact time of 1.45 min with a space–time yield of 68 mol SQA.mol Pd −1.min−1. Finally, a scale-up strategy (7 fold) was successfully attempted in a commercially available pilot-scale reactor that meets further seamless scale-up requirements. A production capacity of 2 kg per day using a commercial intensified reactor with a reacting volume of 43.2 mL was obtained under mild conditions (120 °C and 30 bar of H 2). [ABSTRACT FROM AUTHOR]

Production of CH 4 by methanation of biogas provides a promising route towards sustainable energy production for the future. Utilization of biogas from biomass as CO 2 source combines the advantage of reduction of greenhouse gas emissions producing a fuel with high energy density. In this study we apply a dip-spin coating method for washcoating Ni(7.5 wt%)Rh(0.5 wt%)/CeO 2 catalyst on alumina open cell foams with different cell densities (20, 30 and 40 PPI). The catalytic activity of the structured samples was assessed using a gas mixture that simulates a typical biogas composition (CH 4 = 60%vol; CO 2 = 40%vol). The effects of the reaction temperature (300–600 °C) and H 2 /CO 2 molar ratio in the feed (3–5) on the CO 2 conversion and CH 4 selectivity were evaluated under a gas hourly space velocity (GHSV) of 5100 h−1. All samples showed appreciable CO 2 conversion ranging between 62.5 and 66.7% at reaction temperature of 500–600 °C, and a CH 4 productivity of 3.4 mol CH4 ·g Me −1·h−1 was obtained with the catalyst supported on open cell foam with 30 and 20 PPI under a reaction temperature of 400 °C. • Ni(7.5 wt%)Rh(0.5 wt%)/CeO 2 catalyst was prepared by solution combustion synthesis. • Alumina open cell foams were washcoated by dip-spin coating. • Structured catalysts were tested under methanation reaction of simulated biogas. • CO 2 conversion ranged between 62.5 and 66.7% at a reaction temperature of 500–600 °C. [ABSTRACT FROM AUTHOR]

Catalysts monoliths with circular and square ducts are theoretically analyzed in detail as reactor configurations for the adiabatic CH4 partial oxidation on Rh for short-contact-times hydrogen production. By the means of CFD coupled with a detailed microkinetic description of the surface reactivity, it was found that the different transport properties of the investigated configurations primarily affect the thermal behavior of the reactor. O2 consumption is fully external mass transfer limited, and thus, local variations in mass transport properties are responsible of the differences in surface temperature. [ABSTRACT FROM AUTHOR]

Highlights: [•] CuOx/CeO2 washcoated on AISI 304 and FeCrAl stainless steel monoliths were studied on PROX. [•] Oxidized and enameled stainless steels were used as monolithic substrates. [•] Both activity and selectivity depend on the nature of the alloy and of the metal-catalyst interphase. [•] Diffusion of Na, Ca and Si from enamel, and Cr and Fe from the substrate is detected. [•] The metallic substrates of stainless steels monoliths are not spectators. [ABSTRACT FROM AUTHOR]

The design of tailor-made innovative catalyst support structures enables improved reactor performance by freely tunable fluid flow and mass transport characteristics. Numerical geometry generation, fluid flow simulation and particle tracking for mass transport investigation allow for the required understanding of the structure-transport relationship. Particle tracking, as simulation of the movement of many tracer particles, is costly. This article presents simulation methods including numeric and algorithmic challenges. [ABSTRACT FROM AUTHOR]

Highlights: [•] Heat transfer data were collected for metal foams with He and N2 flow. [•] The enhancement of the fluid conductivity has a strong impact on the wall heat transfer coefficient. [•] The wall heat transfer coefficient exhibits a weak dependence on flow velocity. [•] A correlation for the wall heat transfer coefficient in metal foams is proposed. [ABSTRACT FROM AUTHOR]

Highlights: [•] Coupled AFM/Raman microscopy grasps heterogeneity of multicomponent catalysts. [•] Precalcined kanthal steel (catalyst carrier) composed of α-Al2O3 and α-Fe2O3. [•] Washcoated precalcined steel composed of non-uniform layer of CeO2. [•] Depositing of cobalt the washcoated carrier gave uniform layer of Co3O4. [•] High activity of palladium doped Co3O4 catalyst correlated with the presence of PdO. [ABSTRACT FROM AUTHOR]

A coupled AFM-Raman system was used to study the surface heterogeneity of catalytic materials at various stages of their preparation. The catalysts chosen for the analyses were cobalt oxide with and without palladium dopant deposited on surface of pre-calcined steel carriers. Steel carriers are surveyed here in terms of their application as fillers for structured reactors for the catalytic combustion of volatile organic compounds. Upon steel precalcination stage the interfaced AFM-Raman and in situ Raman analyses revealed the evolution of alumina and iron oxide phases on the surface with their final stable forms found as being α-AlO and α-FeO. Upon catalyst layering stage AFM-Raman mapping evidenced uniform coverage of precalcined steel carrier with cobalt spinel oxide CoO. For the doped catalyst except CoO palladium(II) oxide grains were also found on the surface. The differences in the composition of cobalt catalysts were correlated with the differences in their catalytic activity. [ABSTRACT FROM AUTHOR]

The main objective of this study is to develop highly active catalyst and its preparation method that would meet the requirements of steel carriers for short-channel structured converters for NO abatement from stationary biogas engines. The in situ synthesis was applied to deposit a series of Cu-exchanged MFI zeolite (ZSM-5) on kanthal sheets. The samples differ in preparation conditions: organic template assisted and template-free synthesis, Si/Al ratio and catalyst carrier pretreatment (calcined vs. non-calcined). Dip-coating method was used as a reference to compare loading efficiency. In order to evaluate preparation quality and purity of resulting structure the samples were examined by XRD and SEM/EDS at various stages of preparation. For the assessment of mechanical endurance of the deposited catalyst layers the ultrasonication method was used. The results demonstrated high depositing efficiency of the in situ synthesis as well as high activity and selectivity of the Cu-exchanged MFI samples prepared without costly organic template. [ABSTRACT FROM AUTHOR]

Abstract: Metal wire gauzes as catalyst supports and structured reactor internals offer a number of advantages over monolithic reactors. Structured catalytic reactors based on wire gauzes are explored in this study for the control of NO x emissions from a stationary engine fuelled with gas generated from a biomass gasification process. Simulations are performed on reactors filled with (a) wire gauzes, (b) multi-channel monoliths, and (c) a packed bed with 2mm beads, for the NH3-SCR process using the kinetic data obtained for copper-exchanged ultra-stabilized zeolite Y catalyst (Cu-USY). The purpose of this procedure is to select the most efficient reactor internals and to assess the necessary reactor length allowing maximum conversion of NO x . These simulations show that optimum performance is obtained when the wire gauze support is employed. The results also show that when the Cu-USY catalyst (very active in SCR) is used in combination with a wire gauze structure, the combined effects of higher rates of reaction with higher rates of heat and mass transfer may significantly increase the NO x conversion. [Copyright &y& Elsevier]