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Air purification of ammonia, a toxic industrial chemicals (TICs), by adsorption process on Metal-Organic Framework solids is attracting high scientific and commercial interests. While active carbon based adsorbents required high level of relative humidity for achieving proper performance ammonia capture, zeolite performance degrades in presence of humidity. For MOFs, the presence of humidity has been shown to be MOF dependent, either beneficial or detrimental. It appears that the role of humidity is of key importance and that different ammonia adsorption mechanisms co-exist depending on the material's physico-chemical features. Based on a screening of various microporous adsorbents including carbons, zeolites and MOFs, we show that in the presence of humidity, the ammonia uptake mostly follows the Henry law of ammonia solubilization in water. At the exception of Copper based MOF, the ammonia capture is mostly correlated with the amount of “condensed water” in the micropore. We also generally observe a systematic higher uptake than the Henry law which can be attributed to the effect of confinement i. e surface-condensed phase interaction. [ABSTRACT FROM AUTHOR]

Oversolubility effects refer to a large increase of the solubility of gases in liquids confined in nanoporous solids with respect to the value predicted by Henry's law. This review presents the state of the art of oversolubility by discussing the molecular mechanisms responsible for such effects and the conditions for their observation. Both experimental and theoretical approaches are reviewed, in a non-exhaustive fashion, with special emphasis on results that have helped to unravel the oversolubility phenomenon. Different porous materials including metal-organic frameworks (MOF), ordered porous silicas, and zeolites are considered in combination with various nanoconfined liquids and gases relevant to practical applications in energy and environmental science. Depending on the gas/liquid/solid system considered, oversolubility is shown to pertain either to adsorption (increased concentration at solid/gas and liquid/gas interfaces) or to confinement-induced solubility increase. We also critically discuss when oversolubility effects are expected to lead to improved performance in catalysis or environmental applications such as for air purification. Image 1 • We present the state of the art on oversolubility in nanoporous materials. • Molecular mechanisms are presented and discussed. • Both experimental and theoretical approaches are reviewed with special emphasis on results that have helped unravel the oversolubility phenomenon. • We provide suggestions for future investigations and application perspectives. [ABSTRACT FROM AUTHOR]

Experiment and molecular simulation are used to investigate adsorption in heterogeneous porous media consisting of hierarchical solids (combining different porosity scales) or composite solids (such as silver nanoparticles adsorbed at the external surface of zeolite). It is shown that adsorption in such heterogeneous materials can be written as a linear combination of the adsorption isotherms in its different domains (i.e. porosity scales for the hierarchical sample and constituents for the composite sample). In the case of the composite material, we also show that the linear combination can be used with weighing parameters obtained for a different adsorbate. Such a superimposition principle , which is validated using well-characterized experimental samples, is of interest for characterization purpose as well as industrial applications as they can be used to determine accurately the amount of phases in a given sample (volume corresponding to a given porosity scale or constituent). In contrast, significant departure between the experimental adsorption isotherm and the linear combination can be used to detect coupling effects between the different domains or restrained access to a given domain type. Such a characterization strategy of complex heterogeneous media is complementary to other experiments, such as those probing capillary hysteresis shapes, scanning curves and subloops, which allow determining the distribution of domains within the framework of the independent domain theory. [ABSTRACT FROM AUTHOR]

Selective Xe adsorption on regenerable porous materials such as activated carbons, MOFs and zeolites has been found to be promising and economically attractive. The beneficial effect of silver doping of zeolites on Xe adsorption and Xe/Kr separation has been studied for numerous zeolites such as Ag-ZSM-5, Ag-mordenite and Ag-chabazite. Among them, we had shown that Ag-exchanged ZSM-5 is the most effective material for atmospheric Xe capture and selective separation at very low pressure (ppm level). A linear tendency was observed with a ratio of 2 mol of Ag for 1 mol of strong adsorption sites. Based on this observed tendency, we hypothesize that increasing the number of exchangeable sites by lowering the Si/Al ratio could be an approach to improve silver loading and selective xenon adsorption. The aim of this study is to evaluate the impact of desilication of ZSM-5 zeolites on decreasing their Si/Al ratio and increasing the concentration of sodium-exchanged sites and, possibly, strong silver-based adsorption sites. We have shown here that light desilication of this parent ZSM-5 makes it possible to significantly increase xenon uptake at very low pressure. The desilication creates a larger concentration of Al in the zeolite and thus enables a larger concentration of silver to be loaded. Yet we found that for severe desilication, decreased xenon uptake is observed, likely due to the facilitated formation of silver particles in which the core atoms are not accessible for xenon uptake. It appears that a concentration of 0.5 mmol g−1 of strong adsorption sites is a maximum achievable value for the Ag-ZSM-5 system. Surprisingly, we found that the parent ZSM-5 zeolite prepared by organic templating yields Ag-ZSM-5 with a similar concentration of strong adsorption sites but at higher silver loading. We could hypothesize that silanol defects present in commercial zeolites may be responsible for the stabilization of silver clusters. [Display omitted] • Higher xenon adsorption capacity for xenon atmospheric capture (ppm level). • Light desilication of ZSM-5 increases the concentration of adsorption sites. • Silanol defects present in commercial zeolites may stabilize silver clusters. • Severe desilication decreases Xe uptake due to the formation of larger silver NPs. [ABSTRACT FROM AUTHOR]

Despite the development of selective catalyst formulations for oxidative coupling of methane (OCM), kinetic and reactor design studies have been hampered by a lack of data for truly isothermal reaction conditions. Because of the high exothermicity, the temperature of a fixed-bed reactor filled with Mn-Na 2 WO 4 /SiO 2 catalysts will show hot-spots with a loss of selectivity. The objective of this study is to measure catalyst activity under relevant reaction conditions of pressure (3 bar), biogas composition (no dilution) and contact time, while keeping the process isothermal. To this aim, we have synthesized and shaped a trilobed Mn-Na 2 WO 4 /α-Al 2 O 3 catalyst, which may be used as is at industrial scale, and measured its performance in a single-pellet reactor. We found that the presence of CO 2 did not degrade the catalyst performance, even on the long run, which should enable the use of a CO 2 -rich stream such as biogas. Actually, higher methane conversions have been obtained in the presence of CO 2 , likely due to a possible contribution of methane dry reforming reaction. We also noticed a slow catalyst activation over the first 100 h, while selectivity was kept constant. [Display omitted] • Oxidative methane coupling in the presence of carbon dioxide was studied. • A single pellet reactor was used to avoid temperature gradients. • Carbon dioxide does not impact the catalyst performance. • Opens the pathway for biogas applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights: • Numerical models are developed for all porous solid oxide fuel cells. • Electrolyte porosity changes are investigated for the solid oxide fuel cells. • Criterion of safe operations are considered in the simulation. • Effects of operating parameters for the solid oxide fuel cells are studied. • A novel design is proposed to improve the performance of solid oxide fuel cells. Abstract Conventional solid oxide fuel cells (SOFCs) could suffer from carbon deposition when fueled with hydrocarbons. For comparison, a new type of SOFC with porous electrolyte can resist carbon deposition because it allows oxygen molecules to transport from the cathode to the anode. As the transport of O 2 to the anode lowers the fuel cell performance and causes the risk of explosion, the rate of O 2 transport must be well controlled to ensure efficient and safe operation. Following our previous model, this paper focuses on electrolyte porosity optimization under various inlet methane mole fractions, inlet oxygen mole fractions and inlet gas flow rates. Furthermore, a new design with a partial porous electrolyte is proposed and numerically evaluated. The new design significantly improves the electrochemical performance compared with all-porous one. A conversion rate >90% from methane to syngas is achieved at the 0.33 inlet CH 4 mole fraction with the new design. The results enhance the understanding of all porous solid oxide fuel cells and the mechanism underlying, inspiring novel designs of solid oxide fuel cells. [ABSTRACT FROM AUTHOR]

Hollow polycrystalline Y zeolite spheres have been obtained by combining zeolite crystallization and selective dissolution steps. Beta-Y core shell composites were first obtained by hydrothermal recrystallization of a synthesis mixture containing as-made Beta crystals in the presence of Y zeolite seeds. Under such conditions, Beta zeolite crystals served not only as cores but they also progressively dissolved and provided the necessary Si species for the formation of the shell. The proportion of Beta zeolite remaining in the composite strongly depended on the composition of the solution, in particular the amount of Al and the alkalinity. It could not be decreased below 45–50 wt. % without formation of contaminating phases, mainly zeolites with GME, GIS and LTA topologies. Successive additions of Al could significantly reduce the amount of Beta zeolite in the composite but to the detriment of faujasite crystal size. Hollow shells with less than 10 wt. % Beta have been obtained by selective removal of Beta zeolite from a composite containing 20 wt. % Beta and obtained after two successive recrystallizations in the presence of aluminum. These shells are built up from faujasite nanocrystals with a high silicon content, making them potentially interesting in diffusion-limited catalytic reactions. [ABSTRACT FROM AUTHOR]

The all porous solid oxide fuel cell concept is proposed to solve the carbon deposition problem of solid oxide fuel cells. The transport of oxygen molecules from the cathode to the fuel side through the porous electrolyte can resist carbon deposition but could reduce the fuel cell performance. In this paper, a two-dimensional model for all porous solid oxide button cells is developed for the first time. After model validation with experimental data, the model is then extended for a tubular cell for parametric simulations. The effects of operating conditions and the electrolyte microstructure properties on carbon resistance and electrochemical performance of all porous solid oxide fuel cells are examined. The good carbon resistance of all porous solid oxide fuel cell is numerically demonstrated. It is found that the electrochemical performance and anode surface O/C ratio is significantly affected by anode inlet gas composition and flowrate. In addition, the anode supported all porous solid oxide fuel cell shows a great potential in terms of both power generation and coking resistance. The results of this study form a solid foundation to understand the mechanism and promising future of all porous solid oxide fuel cells. [ABSTRACT FROM AUTHOR]

For the first time, a systematic, consistent domain exploration has been conducted on mono- and bi-cationic exchanged X and Y faujasites for xylene separation using a combinatorial approach. In total, a large, diverse library of 68 faujasites exchanged with alkali cations (Na + , K + , Cs + ) and alkali earth cations (Ca 2+ , Ba 2+ ) was prepared and tested in the presence of three distinct mixture conditions of relevance to the separation process. From the measurements of the 68 × 3 breakthrough curves, we calculated separation performances for the three xylene isomers (p-, m-, o-X), EB, and PDEB. The set of performance properties generated for each adsorbent was analyzed by statistical methods enabling sorting into different classes of selective adsorbents. A rational mapping of exchanged faujasites for xylene separation was performed. [ABSTRACT FROM AUTHOR]

Two cobalt imidazolate metal-organic frameworks were evaluated as a bactericidal material against the growth of the Gram-negative bacteria Pseudomonas putida and Escherichia coli. Under the most unfavourable conditions, within the exponential growth phase and in the culture media for both microorganisms, the growth inhibition reached over 50% for concentrations of biocidal material in the 5-10mgL−1 range. The release of metal gives excellent durability with the antibacterial effect persisting after 3months. Both cobalt-based materials can be prepared with simple, cheap and easily accessible commercial ligands, leading to a more affordable possible future application as antimicrobial materials. [ABSTRACT FROM AUTHOR]

Nano-zeolites and hierarchical zeolites have shown enhanced transport properties that are generally attributed to a shorter diffusion path length (L). However, the concomitant increase in the external surface of these types of zeolites may also affect overall transport as the interfaces may act as diffusion barriers. Recently, hollow zeolite crystals have been presented as an alternative zeolite morphology. They possess a large inner cavity and an overall size and shape similar to those of plain microporous zeolite. In contrast to classic hierarchical zeolite materials, the inner cavity of the hollow zeolite induces a shortened diffusion path length with no effect on external surface area. In this work, we have studied the impact of diffusion path length on transport properties by comparing the characteristic time of transport of hydrocarbons in plain zeolite crystals and their hollow counterparts, using zero-length column (ZLC) measurements. Our results show that hollow morphology doubles or quadruples the transport speed for Silicalite-1 and Beta zeolites, respectively. Compared to other reports focusing on nanosized or hierarchical zeolites, this study is free of any bias due to major modifications in external surface area, because hollow and plain zeolites have very similar crystal dimensions. 3 Main results• Hollow zeolites allow faster transport than plain zeolites• The faster transport is directly linked to the shortening of diffusion path length.• While keeping hollow and plain zeolite crystals with the same crystal size, we can investigate the impact of a different diffusion path length, without bias from different external surface area. Image 1 • Hollow zeolites allow faster transport than plain zeolites. • The faster transport is directly linked to the shortening of diffusion path length. • The impact of diffusion on hollow and plain zeolithe is investigated without bias of different external surface. [ABSTRACT FROM AUTHOR]