•Washcoated foams are attractive catalysts for the Fischer-Tropsch synthesis.•Combined experiments and 1D multi-scale model explain FT reactor performance.•Mass transfer affects performance of ...washcoated foams during FT synthesis.•Experiments and model show volcano trend for conversion vs. washcoat thickness.•The selectivity to C5+ is strongly affected by diffusion limitations.
The Fischer-Tropsch synthesis (FTS) is widely applied to convert syngas to liquid fuels, being long-chain hydrocarbons (C5+) the preferred products. Combining experiments and first-principle simulations, this work analyzes the effect of intra and extra-particle mass transfer limitations on the FTS reaction rate and product selectivity using open-cell foams catalysts. Co/Al2O3 and Co/TiO2 catalysts were deposited on open-cell foam structures and tested for the FTS. A 1-D multi-scale first principle reactor model is developed in order to correlate the product distribution and the reactor performance with the system properties. Both experiments and modeling results demonstrate that an increase in the washcoat layer thickness leads to greater selectivity towards methane and that the reaction rate has a maximum at ca. 60 μm. The developed model is used to predict the foam-based reactor performance, under realistic industrial conditions, showing that the productivity to C5+ is severely affected by washcoat layers thicker than 50 μm.
•Heat and mass transfer phenomena in a packed bed membrane reactor for DME synthesis.•Thiele modulus-efficiency correlation to account for pore diffusion effects.•Sherwood-type correlation for the ...concentration polarization of carbon membranes.•2D heterogeneous reactor model for the CO2 hydrogenation to dimethyl ether.•Membrane reactor optimization based on relevant mass transfer phenomena.
This study investigates the relevant heat and mass transfer phenomena occurring at the different scales in a packed bed (membrane) reactor for the direct conversion of CO2 to dimethyl ether (DME) via the implementation of 2D heterogeneous reactor models. Intra-particle diffusion limitations were found to be relevant for particle diameters larger than 1 mm and temperature above 220 ⁰C, such that the catalyst efficiency drops down to 50% and 5% for the Cu/ZnO/Al2O3 and the HZSM-5, respectively, in the most critical conditions (i.e., 270 ⁰C and Dp of 10 mm). A component-specific Thiele modulus-efficiency correlation was developed based on the results of the rigorous particle model to account for pore-diffusion limitations without having to solve a complex heterogeneous reactor model. This correlation shows the typical behavior reported in literature for power law kinetics and accurately predicts the reaction performance with deviation of less than 5% for values of the Thiele modulus lower than 2. In the packed bed membrane reactor (PBMR), the concentration polarization (CP) also showed to affect the reactor performance. The concentration of water at the surface of the membrane selective layer was found to be up to 64% lower than the concentration in the bulk phase, hindering the effectiveness of the membrane separation. To account for this phenomenon via a simplified approach, a Sherwood-type correlation was developed to determine a CP mass transfer coefficient, based on the results obtained via the rigorous 2D PBMR model. Such correlation showed to predict with high accuracy (i.e., errors lower than 5%) the effect of the CP on the PBMR performance. Differently from the pore diffusion and CP phenomena, the intra-particle heat transfer, the particle–fluid mass and heat transfer as well as the axial dispersion were found to have a negligible effect on the reactor behavior. Finally, given the relevant mass/heat transfer phenomena, this study proposes further reactor optimization strategies, such as the reduction of the zeolite loading in the bifunctional catalyst bed by ca. 90% with respect to what is reported in literature.
Carbon membranes are a potentially attractive candidate for the in-situ removal of water vapor in CO2 hydrogenation reactions. Their hydrophilicity and pore structure can be tuned by properly ...adjusting the synthesis procedure. Herein, we assess the effect of the carbonization temperature (450–750 °C) on the performance of supported CMSM in terms of vapor/gas separation, in correlation with changes in their surface functionality and porous structure. FTIR spectra showed that the nature of the functional groups changes with the evolution of the carbonization step, leading to a gradual loss in hydrophilicity (i.e., OH stretching disappears at Tcarb ≥ 600 °C). The extent of water adsorption displays an optimum at Tcarb of 500 °C, with the membrane carbonized at 650 °C being the least hydrophilic. We found that the pore size distribution strongly influences the water permeance. At all Tcarb, adsorption-diffusion (AD) is the dominant transport mechanisms. However, as soon as ultra-micropores appear (Tcarb: 600–700 °C) molecular sieving (MS) contributes to an increase in the water permeance, despites a loss in hydrophilicity. At Tcarb ≥ 750 °C, MS pores disappear, causing a drop in the water permeance. Finally, the permeance of different gases (N2, H2, CO, CO2) is mostly affected by the pore size distribution, with MS being the dominant mechanism over the AD, except for CO2. However, the extent and mechanism of gas permeation drastically change as a function of the water content in the feed, indicating that gas/vapor molecules need to compete to access the pores of the membranes.
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•Effect of the carbonization temperature on the hydrophilicity of carbon membranes.•In situ FTIR analysis used to study the membrane interaction and affinity to water.•Significant CO2 surface adsorption, increasing with the carbonization temperature.•Adsorption diffusion is the dominant mechanism for water, methanol and CO2 permeation.•Membranes carbonized at 600–700 °C show highest permeability due to the pores in the molecular sieve region.
PPARs are lipid sensors activated by dietary lipids or their metabolites, mainly fatty acids and eicosanoids, that play critical roles in CNS biology, since brain has a very high lipid content and ...has the higher energetic metabolism in the body.
In neurodegenerative diseases in addition to metabolic impairment, also neuroinflammation is observed and PPARs are also closely linked to inflammatory processes. Several studies have revealed a complicated relationship between the innate immune response and tissue metabolism.
In the brain, during pathological conditions, an alteration in metabolic status occurs, particularly involving glucose utilization and production, a condition which is generally related to metabolic changes.
Taking into account the high expression of PPARs in the brain, this review will focus on the role of these transcription factors in CNS diseases.
The separation of H2O vapor from (hydrogen-rich) gaseous streams is a topic of increasing interest in the context of CO2 valorisation, where the in situ water removal increases product yield and ...catalyst stability. In this work, composite alumina carbon molecular sieve membranes (Al-CMSM) were prepared from phenolic resin solutions loaded with hydrophilic boehmite (γ-AlO(OH)) nanosheets (0.4–1.4 wt. % in solution) which partially transform to γ-Al2O3 nanosheets upon thermal decomposition of the resin, improving the hydrophilicity and thus the adsorption-diffusion contribution of the H2O permeation. The γ-Al2O3 nanosheets showed no influence on the pore size distribution of the membranes in the range of micropores, but they increased the membrane hydrophilicity. In addition, the use of boehmite in the resin solution causes an increase in the viscosity and thus an increase in the carbon layers thickness deposited on the porous α-Al2O3 support (from 1 to 3.3 μm). Furthermore, the alumina sheets introduce defects in the carbon matrix, increasing the tortuosity of the active layer, as concluded via phenomenological modelling and parametric fitting of the experimental results. As a consequence, the water permeability exhibits a maximum (1.3ꞏ10−6 molꞏs−1 Pa−1 m−1 at 150 °C) with boehmite/alumina content of ca. 0.8 wt. %, as the combined effects of increasing hydrophilicity (which favour H2O permeability) and increasing thickness and tortuosity (which hamper permeability) upon increasing boehmite loading. Similarly, the H2O/gas perm-selectivity is optimum at 1.2 wt. % boehmite loading. We further investigated the H2O permeation mechanism by modelling the mono- and multi-layer adsorption and capillary condensation of water in microporous media, which result as the main transport mechanisms in the explored conditions.
•Several boehmite-phenolic resin composite carbon molecular sieve membranes were developed.•The hydrophilic boehmite nanosheets were used to increase the adsorption of water.•Water permeability shows an optimum with the initial boehmite content around 0.8 wt. %.•CMSM are promising material for the water separation from gaseous mixtures at relatively high temperatures.
We consider the leader-following control problem on connected directed graphs for stochastic linear agents in the presence of communications and actuator delays. We propose to use a distributed ...protocol for detecting the distance of agents from the leader and we show that by suitably using this information it is possible to solve efficiently the leader-following control problem by means of predictors, thus recovering results for the single-agent case. The proposed predictor and controller are easy to design and the delay bound that guarantees stability can be computed from closed-form expressions without resorting to LMIs.
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•The first in-situ XAS study on Au and Pd during the direct synthesis of H2O2 at relevant conditions.•Catalytic microreactor used as safe, portable and free of transport- effects ...spectroscopic cell.•Metallic Pd is the active phase for the direct synthesis of H2O2 using both Pd and AuPd catalysts.•Unlike AuPd, monometallic Pd forms Pd-H during reaction, which may explain its lower selectivity.
For the first time, we perform in-situ X-Ray Absorption Spectroscopy on both Au L3 and Pd K edges during the direct synthesis of hydrogen peroxide in a high-pressure gas-liquid-solid microreactor using SiO2 supported Pd, Au and AuPd catalysts under relevant reaction conditions. The catalysts were coated on the walls of 320 µm ID micro capillaries, used in this work both as microreactors and as spectroscopic cells, ensuring safety of operation, ease of portability and absence of reactor effects during the measurements. XANES analysis revealed that the fresh Pd and AuPd catalysts contained a mix of Pd/PdO phases which was readily reduced in H2 atmosphere. The presence of only metallic Pd under reaction conditions for both catalysts proved that metallic Pd is the active phase for this reaction. Au was present in its metallic form in both Au and AuPd under all conditions tested. Unlike the AuPd, monometallic Pd showed an increase in the Pd-Pd distance under reaction conditions, attributed to the formation of Pd-hydride. We propose that the absence of Pd-hydride in the AuPd catalysts reduces further hydrogenation of H2O2 to water, thereby explaining the increased selectivity to H2O2 observed with AuPd catalysts.
•Systematic analysis of the mass transfer limitation in wash-coated open-cell foams.•CFD simulations on Kelvin’s cell by DNS.•Mass transfer correlation for low Reynolds number.•Practical criteria in ...terms of dimensionless numbers for rate limiting regimes.
In this work, the analysis of the mass transfer phenomena in catalytic open-cell foams is carried out through the combination of computational fluid dynamics (CFD) simulations and experiments, using the CO oxidation on Pt(1%)/γ-Al2O3/foam as a model reaction. The influence of the local hydrodynamic effects on the diffusion-reaction phenomena occurring at the gas-solid interface of the open-cell solid foams are investigated by Direct Numerical Simulations assuming an infinitely fast reaction. A correlation for the Sherwood number as function of Reynolds -for low Re- is proposed. To validate this experimentally, aluminum foams coated with Pt(1%)/γ-Al2O3 are tested at different reaction conditions for the CO oxidation. The obtained reaction rates and apparent activation energy show the presence of external mass transfer limitations. An analysis of the diffusion-reaction phenomena taking place in the wash-coated layer is presented in terms of dimensionless numbers. A practical criterion is developed in terms of the Thiele modulus (ϕw) and the Biot number (Bim) for the identification of the reaction regimes: kinetic control (ϕw2/Bim<0.1), internal and/or external mass transfer limitations (0.1<ϕw2/Bim<10), and full mass transfer control (ϕw2/Bim>10).
Notable advances in gene sequencing methods in recent years have permitted enormous progress in the phenotypic and genotypic characterization of autoinflammatory syndromes. Interferonopathies are a ...recent group of inherited autoinflammatory diseases, characterized by a dysregulation of the interferon pathway, leading to constitutive upregulation of its activation mechanisms or downregulation of negative regulatory systems. They are clinically heterogeneous, but some peculiar clinical features may lead to suspicion: a familial "idiopathic" juvenile arthritis resistant to conventional treatments, an early necrotizing vasculitis, a non-infectious interstitial lung disease, and a panniculitis associated or not with a lipodystrophy may represent the "interferon alarm bells." The awareness of this group of diseases represents a challenge for pediatricians because, despite being rare, a differential diagnosis with the most common childhood rheumatological and immunological disorders is mandatory. Furthermore, the characterization of interferonopathy molecular pathogenetic mechanisms is allowing important steps forward in other immune dysregulation diseases, such as systemic lupus erythematosus and inflammatory myositis, implementing the opportunity of a more effective target therapy.
Aqueous phase reforming of sorbitol for hydrogen production was conducted in a Pt–Ru-washcoated microchannel reactor with continuous hydrogen stripping. This study is an extension of our earlier ...investigation using the same reactor configuration with a monometallic Pt catalyst. The excellent mass transfer of hydrogen in the microchannel reactor operated under the Taylor flow regime by co-feeding nitrogen gas as stripping agent is highly beneficial for the selectivity to hydrogen. Nevertheless, the overall reaction rate is kinetically limited. Thus, more reactive conditions are needed to increase the productivity of hydrogen. The Pt–Ru bimetallic catalyst increases the catalytic activity by a factor of 2–3. However, in a reference case (with no hydrogen stripping), the Pt–Ru bimetallic catalyst resulted in a decrease of the hydrogen selectivity by a factor of 3 with respect to the reference monometallic Pt, leading to a nearly neutral effect in the productivity of hydrogen. By operating the Pt–Ru-washcoated microchannel reactor under the Taylor flow regime with simultaneous hydrogen production and hydrogen stripping we were able to maintain the benefits in catalyst activity while the selectivity to hydrogen was greatly increased with respect to the reference case with no stripping. The combined effect of a more active catalyst with the benefits of this reactor configuration in terms of selectivity led to an overall increase of the hydrogen production rate from 0.2 to 6.6 min−1. Increasing the reaction temperature from 220 to 240 °C in this reactor configuration resulted in a further increase in the conversion of sorbitol and a mild increase in the selectivity to hydrogen (from 30 to 70% and from 35 to 39% respectively). The use of hydrogen stripping was essential to combine high activities and high selectivities. Increasing the nitrogen flow ratio with constant liquid flow rate was beneficial for the sorbitol conversion and the selectivity to hydrogen. The increase in sorbitol conversion reaches a saturation point at a gas to liquid ratio of ca. 1 mN23/mliq3, while the selectivity to hydrogen continuously increases in the range of 0–2 mN23/mliq3. This reactor configuration allows operating under more reactive conditions (i.e. more reactive catalyst and higher reaction temperatures) without significant loss in hydrogen selectivity.
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•Addition of Ru to Pt increases the activity, but reduces the selectivity to H2.•APR in a microreactor with H2 stripping benefits the hydrogen selectivity.•Fast and selective production of H2 can be done in a Pt–Ru washcoated microreactor.•The microreactor can operate under reactive conditions with high H2 selectivity.
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