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[Display omitted] • The surface of cobalt was monitored by operando IR under CO 2 -CO-H 2 mixtures. • The selectivity to methane decreased monotonously with CO surface coverage. • The state of the cobalt metallic surface remained unaffected by the CO/CO2 ratio. An operando IR study was carried out to investigate the loss of selectivity to higher hydrocarbons observed over cobalt-based Fischer-Tropsch catalysts when CO is replaced with CO 2. Our data unambiguously show that the structure and oxidation state of the surface of metallic cobalt remains the same whether CO 2 or CO are cofed with H 2. The selectivity to CH 4 appears to increase monotonously with decreasing surface coverage of adsorbed CO. The switch from Fischer-Tropsch synthesis to methanation using CO 2 -rich feeds over metallic cobalt can therefore be assigned to surface coverage effects only, assuming that most, if not all, hydrocarbons products are formed on metallic cobalt. [ABSTRACT FROM AUTHOR]

The synthesis of dimethyl carbonate (DMC) from carbon dioxide and methanol was studied over a ceria- zirconia mixed metal oxide. When using oxygen-18 labeled ceria-zirconia, no oxygen-18 labeled DMC or water was observed. On the other hand, using oxygen-18 labeled methanol led almost exclusively to the formation of double labeled DMC, CH 3 18 O (C 16 O) 18 OCH 3. These results were used to further elaborate the proposed reaction mechanisms for DMC synthesis. The rate-controlling step identified was that of a nucleophilic attack of gas phase methanol on surface monomethyl carbonate species to form DMC. [Display omitted] • Dimethyl carbonate synthesis over oxides does not follow a Mars-Van Krevelen route. • The rate controlling step is a nucleophilic attack of methanol/methoxy species. • Zirconia promotion of ceria weakens the methyl carbonate species metal‑oxygen bond. [ABSTRACT FROM AUTHOR]

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]

A static volumetric method measured the equilibrium adsorption isotherms of water vapor on commercial activated carbon, alumina and hopcalite adsorbents. A type II isotherm represents water vapor adsorption on alumina and hopcalite, whereas a type V isotherm characterizes activated carbon. A method based on the sensitivity analysis of parameters is used to evaluate the estimability of unknown parameters involved in the Toth-Aranovich–Donohue (type II) and Mahle (type V) adsorption isotherm equations. The estimable parameters are then identified using experimental water vapor measurements at three different temperatures, i.e., 293, 303 and 313 K and pressures up to the saturated concentration, simultaneously. The isotherm modeling methodology is implemented and solved within COMSOL Multiphysics®. The results of the isotherm model using the fitted parameters show excellent agreement with the experimental measurements. Thus, this is confirmed by the performance indices such as the Pearson correlation coefficient and the mean square error. In addition, the isosteric water vapor heat of adsorption is estimated using the Clausius-Clapeyron equation and the temperature-dependent models developed for each adsorbent. [ABSTRACT FROM AUTHOR]

Microporous cavities and channels of zeolites frameworks have been used for decades for the encapsulation of cations, complexes and metals. In the particular case of metals, nanoparticles are usually formed after post-synthesis modifications such as ion-exchange or wetness impregnation. Tough encapsulation can provide a strict control of the nanoparticle size as well as a limitation of aggregation at high temperature; encapsulated nanoparticles are often hardly accessible due to diffusion limitations of reactants in sub-nanometric micropores. Recent developments in zeolite synthesis have offered a new class of materials with hierarchical structures or unusual morphologies in which the mean diffusion path is considerably reduced. Those zeolites with inter-crystalline and/or intra-crystalline mesopore systems are particularly adapted for supporting nanoparticles both in microporous cavities of the framework and in mesoporous channels. More sophisticated architectures such as yolk/core–shell materials, in which nanoparticles are protected against poisoning or sintering by a thin zeolite shell, are particularly attractive. In contrast to nanometric intrinsic cavities of zeolite frameworks, a large internal void is available for chemical reactions and such catalysts can be considered as nanoreactors in which the reaction is essentially governed by the permeability of the shell. This review focuses on the most recent progress as well as perspectives in the design of zeolite-containing metal nanoparticles, which differ from traditional materials by the originality of the synthesis method or the morphology of the support. [ABSTRACT FROM AUTHOR]

The conversion of methane or natural gas into turquoise H2 and carbon represents a promising pathway towards decarbonised energy. The pyrolysis of biogas (mainly a mixture of methane and CO2) is considered to be a negative carbon-emission technology, as the carbon source comes from biomass and the carbon is captured in solid form. In addition, the presence of CO2 in the gas mixture enables the dry reforming of methane into syngas. In this study, we show that direct biogas conversion in a fluidised catalytic reactor can produce a syngas whose composition meets the requirements for methanol synthesis or for liquid hydrocarbon production via the Fischer-Tropsch process. Confirmed by thermodynamic analysis, we show that the reaction proceeds at temperatures above 900 1C to produce carbon materials, whereas at lower temperatures the carbon is converted to CO by the Boudouard reaction. At 950 1C, very high methane and CO2 conversions are achieved (490% and 99%, respectively), accompanied by high hydrogen yield (490%) and the sequestration of carbon into a turbostratic structure. We believe that the direct catalytic reforming of biogas in a fluidised bed, when combined in series with an FTS process, could allow the production of liquid fuels with no need for costly gas separation units, in particular those implemented for CO2 capture. [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]

Summary: Monoterpenes are the most prevalent compounds found in essential oils. They exhibit inhibitory actions against phytopathogenic postharvest fungi. Direct application limits their effectiveness due to their instability, high volatility, hydrophobicity and susceptibility to degradation. Encapsulation systems using metal–organic frameworks (MOFs) have been developed to maximise their use. In this study, four protocols were shown to encapsulate thymol and limonene in porous solids, such as ZIF‐8, UiO‐66‐(COOH)2 and zeolite 13X. Vapourisation and diffusion at 60 °C for 16 h was found to be the most efficient encapsulation process. A larger amount of thymol than limonene was loaded in the porous solids. Thymol released from MOFs slowed down the growth of Colletotrichum musae by up to 6 days at 25 °C. There was a sustained release of thymol even beyond the period of maximum fungal growth. This proof‐of‐concept study revealed the potential utility of MOFs as carriers of thymol against postharvest fungi. [ABSTRACT FROM AUTHOR]

Hollow zeolite single crystals represent a new class of materials that have received considerable attention over the last decade. Besides facilitating the transport of molecules in zeolite crystals, the cavity present in hollow crystals offers many possibilities for encapsulating active species and constitutes a closed space that can be used as a nanoreactor. However, despite the simplicity of the concept, the synthesis of hollow zeolites is difficult, as it necessitates to control the chemistry and the spatial distribution of elements throughout the crystals. Here, the different strategies that can be used to transform bulk zeolite crystals into hollow analogs are reported. In particular, selective dissolution as well as dissolution–recrystallization methods are discussed in detail in the case of zeolites with mobile five (MFI) framework type. More sophisticated fabrication strategies are also described for two other major zeolites, namely, zeolites Beta and Y. Additionally, methods to introduce metal nanoparticles with controlled size and composition in the cavity are also addressed. The review ends with concluding remarks, including major challenges and future outlooks in the field. Hollow zeolite single crystals have recently emerged as a new class of advanced material with high potential as hosts for the encapsulation of nanoparticles. Recent advances in the methodologies used to transform standard bulk zeolite crystals into their hollow analogs are reviewed. Techniques for the encapsulation of nanoparticles with controlled size and composition into hollow zeolite crystals are also reported. [ABSTRACT FROM AUTHOR]

• Flame Sprayed Pyrolysis (FSP) cerium-zirconium oxides show high catalytic activities. • Coprecipitated (CP) and FSP mixed oxides exhibits different surface properties. • FSP enables a surface enrichment in cerium oxide at the top layer. • Cerium enrichment gives higher concentration of adsorbed methanol at the surface. The direct synthesis of Dimethyl carbonate (DMC) from methanol and CO 2 is a green process which allows CO 2 valorization. Among efficient catalysts, ceria, zirconia and cerium-zirconium mixed oxides are often reported as the most active catalysts. In a recent report, we discovered that cerium-zirconium mixed oxides prepared by Flame Spray Pyrolysis (FSP) show greater catalytic activities than those prepared by precipitation, although both exhibit very similar surface area and bulk features. The objective of this study was to find out the origins of the superior catalytic activities obtained by flame spray pyrolysis synthesis method by a deeper analysis of bulk and surface properties. We have opted to focus on mixed ceria-zirconia of equimolar composition (Ce 0.5 Zr 0.5 O 2) as it exhibits maximum catalytic activity for both synthesis methods. Combining bulk and surface characterization as well as surface adsorption measurements using probe molecules, we propose that flame spray pyrolysis enables a surface enrichment in cerium oxide still in interaction with zirconium oxide that leads to a high concentration of adsorbed methanol at the surface, which might explain the greater activity of the catalysts prepared using this method. Beyond the application of DMC synthesis, we can anticipate that Flame Spray Pyrolysis synthesis should generate relative high surface area mixed oxides with different catalytic performances with respect to mixed oxides prepared at lower temperature owing their metastable nature. [ABSTRACT FROM AUTHOR]

In situ and operando diffuse reflectance FT-IR (DRIFTS) studies are often carried out over samples that may undergo changes in optical properties due to stronger absorptivity (darkening), for instance when coking or being reduced. The variation of IR optical pathlength of two Fe and Co-based Fischer-Tropsch catalysts treated at different temperatures was investigated through the use of an internal standard CaCO 3 that was physically mixed with the catalyst. The CaCO 3 overtone band at 1795 cm-1 was used, exhibiting an integral molar absorption coefficient ε = 2.68 × 105 cm mol-1. The IR penetration depth was negligible over the iron oxide sample once reduced above 400 °C, due to the formation of a strongly absorbing material. A reduction of the cobalt sample up to 350 °C revealed large changes of optical pathlength (dropping four-fold from 66 to 16 µm), likely related to the onset of cobalt oxide deep reduction. These data indicate that changes in optical pathlength should be considered when attempting quantitative DRIFTS analyses and that mixing a small concentration of CaCO 3 , e.g. 2 wt%, is a suitable way of doing so. [Display omitted] • Optical pathlengths may vary greatly during DRIFTS analyses. • Using an internal standard such as CaCO 3 can easily solve this limitation. • Iron oxide sample becomes too dark for DRIFTS upon reduction. [ABSTRACT FROM AUTHOR]

The direct synthesis of dimethyl carbonate from methanol and CO2 is particularly attractive as it provides a green alternative to other routes while allowing CO2 conversion. Although the evaluation of catalyst formulations figures prominently in the literature, one can hardly identify which formulations are the most active. One of the reasons is that there is no standard testing protocol. Initial water content in the reactive mixture is critical as it can drag down thermodynamic equilibrium. This study aims to rank catalyst activities and to identify the most active catalysts using a systematic protocol for the measurement of the true catalytic activity. Based on an assessment of critical parameters, a protocol for the measurement of the activity in the liquid phase, taking care to the limitation induced by thermodynamic equilibrium, was developed. Special attention was paid to the quantitative assessment of critical experimental parameters. Following the protocol, a screening of various pure and mixed oxides of about 60 different solids was carried out. Finally, an optimization study was carried out on Zr–Ce mixed oxides produced by different synthesis methods, leading to the discovery of the catalyst which, to the best of our knowledge, is the most active reported so far. [ABSTRACT FROM AUTHOR]

Review: 155 refs. [ABSTRACT FROM AUTHOR]

We report herein the upscaled synthesis and shaping of UiO66-COOH for NH3 air purification. The synthesis of the zirconium-based MOF was carried out in a batch reactor in an aqueous suspension with a yield of 89% and a space-time yield of 350 kg/day/m3. Neither toxic chemicals nor organic solvents were used, allowing this MOF to be employed in individual or collective air purification devices. Freeze-granulation and extrusion shaping techniques were investigated. The NH3 air purification performances of UiO66-COOH in bead, tablet and extrudate forms were compared to those of commercial carbon based materials (type K adsorbents from3M and Norit). Testing conditions were chosen to reflect current standards for ammonia concentration (600-1200 ppm) and velocity. In addition, the breakthrough measurements were carried out at three different relative humidity levels (0%, 40%, and 70%). Pellets and extrudates of UiO66-COOH outperformed commercial benchmark adsorbents in all conditions, especially in dry conditions, for which the commercial adsorbents suffered impaired ammonia uptake and shortened service life. Extrudates of UiO66-COOH also withstood attrition after intensive shaking. [ABSTRACT FROM AUTHOR]

Multi-hollow silicalite-1 single crystals (MH) were prepared for the first time by an original synthesis pathway by using tetrabutylphosphonium hydroxide (TBPOH) as a mild desilicating agent. This new generation of hierarchical zeolite allowed the encapsulation of nanoparticles (NPs) featuring an enhanced confinement of the metallic guest and a thin wall thickness. The MH catalyst exhibited a better stability for methane steam reforming at 700 °C than a single-hollow counterpart (SH). Ni average particle size could be kept lower than 4 nm after 20 h on stream for the MH sample. However, a detailed analysis of kinetic data of the structure-insensitive CO methanation used as a model reaction revealed that the sample activity was adversely affected by two main factors deriving from the preparation steps. First, a siliceous over-layer derived from the decomposition of intermediate Ni phyllosilicates, which partly covered the resulting Ni nanoparticles. Second, phosphorus from the templates remained in the samples, probably forming a Ni-P compound upon reduction. The overall catalytic activities observed here were therefore a complex interplay of improved dispersion and poisonous effects. [ABSTRACT FROM AUTHOR]

Hollow capsules with dimensions below 1 μm have recently attracted much attention due to their potential applications as catalysts as well as biomedical and pharmaceutical vectors for controlled drug delivery. Among them, hollow zeolites are particularly interesting because they possess (i) a crystalline structure, which greatly improves their hydrothermal and chemical stability as compared to amorphous silica analogs and (ii) a microporous network that acts as a shape-selective membrane. Moreover, their properties can be continuously tuned by changing their composition, in particular the framework aluminum content. In this perspective review, we examine the recent progress in the development of synthetic methods for the preparation of hollow zeolite and zeotype structures, from templating routes providing large polycrystalline capsules to controlled dissolution methods leading to nanometer-sized hollow single crystals. The applications of these materials will be illustrated and discussed, namely their main potential as catalytic nanoreactors, these being materials particularly adapted for the encapsulation and the confinement of metal nanoparticles. Critical perspectives on future materials with specific properties are also addressed, particularly those with less common zeolite structures and/or compositions. [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]

This review article presents the fundamental and practical aspects of water adsorption in Metal-Organic Frameworks (MOFs). The state of the art of MOF stability in water, a crucial issue to many applications in which MOFs are promising candidates, is discussed here. Stability in both gaseous (such as humid gases) and aqueous media is considered. By considering a non-exhaustive yet representative set of MOFs, the different mechanisms of water adsorption in this class of materials are presented: reversible and continuous pore filling, irreversible and discontinuous pore filling through capillary condensation, and irreversibility arising from the flexibility and possible structural modifications of the host material. Water adsorption properties of more than 60 MOF samples are reported. The applications of MOFs as materials for heat-pumps and adsorbent-based chillers and proton conductors are also reviewed. Some directions for future work are suggested as concluding remarks. [ABSTRACT FROM AUTHOR]

The characterization of acid sites on solid catalysts is a key to understanding reaction mechanisms at the molecular level. This is generally done indirectly using a model probe molecule able to coordinate or be protonated on surface acid sites. For instance, Temperature Programmed Desorption (TPD) of the pyridine probe molecule followed by IR spectroscopy has become a standard method for the quantification and identification of Brønsted and Lewis acid sites found in zeolites. On the other hand, there is a lack of molecules able to be protonated on very weak Brønsted acid sites. In this work 2,6-ditert- butylpyridine is shown to be a suitable probe for characterizing weak Brønsted acidity. The proof of concept is performed on a series of Pt catalysts supported on a chlorinated alumina support (Pt--γ-Al2O3--Cl) generally used in the reforming process. In particular, we show that the area of the 1617 cm-1 vibration band is correlated to the concentration of Cl introduced into the catalyst. We also underline the relative insensitivity of pyridine as an IR probe molecule and the inadequacy of NH3 TPD for the characterization of acid sites of reforming catalysts, making 2,6-di-tert-butylpyridine a particularly important and specific probe molecule. [ABSTRACT FROM AUTHOR]

[Display omitted] • 3,3′-dimethyl-1-butene isomerization activity is correlated to the concentration of moderate Brønsted acid sites. • 2,6-di-tert-butylpyridine is are very sensitive IR probe for moderate Brønsted acid sites such as alumina supported catalysts. • A correlation between catalytic performance and acidity characterization is demonstrated for reforming catalysts. The characterization of surface acid sites is a major issue for the mechanistic understanding and activity prediction of a solid catalyst, especially for applications that require the use of bi-functional materials. The concentration of Brønsted acid sites is measured by two main methods: adsorption of a probe molecule, and catalytic activity in a model reaction. In a previous study, we reported that the adsorption of 2,6-di- tert -butylpyridine on the surface of alumina-supported reforming catalysts (PtSn/Al 2 O 3 –Cl) was very effective in determining the density of Brønsted acid sites. In this work, the acidity of reforming catalysts was studied through their activity in the model reaction of 3,3-dimethyl-1-butene isomerization. We have demonstrated that the activity of reforming catalysts is clearly correlated with the surface chlorine density and more extensively with the density of Brønsted acid sites as measured by the adsorption of 2,6-di- tert -butylpyridine. As a result, this study highlights the relevance of using 2,6-di- tert -butylpyridine adsorption in the characterization of the Brønsted acidity of an alumina with no metal phase interference. [ABSTRACT FROM AUTHOR]

Several major refining catalytic processes show a strong dependence of overall performances upon catalyst formulations and their structure. This observation is particularly true in naphtha catalytic reforming for which the product distribution is sensitive to slight changes in active phase formulations. This review presents different issues encountered in naphtha reforming that are related to active phase formulation changes. Two research and development approaches are usually proposed. (i) Rationalise the development of new catalytic formulations in order to increase selectivity towads valuable products. (ii) Design simulators that would guide operation in order to maintain process performances. Current limitations to a faster process development come from the disjunction between kinetic modelling and catalyst optimisation. This critical review is not an extensive analysis of existing naphtha reforming kinetic modelling methodologies or advances in catalytic behaviour elucidation. Rather, it proposes an original and pragmatic process development approach aimed at merging catalyst development with kinetic modelling through the identification of "effective" and "measurable" catalytic descriptors. The specificities of the structure–property relationships of naphtha reforming catalysts are reviewed and taken into account in order to list potential catalytic descriptors for this process. A focus is made on a current bottleneck faced in the description of the active phase which lies in understanding the role of the proximity and the interaction between acid and metallic sites in the balance between different bi-functional pathways. A variety of experimental approaches that can be used to measure these naphtha reforming active phase catalytic descriptors are presented and compared. [ABSTRACT FROM AUTHOR]

The synthesis of 19 carefully selected Pt/γ‐Al2O3−Cl formulations was followed by high‐throughput catalytic testing in order to unravel the effect of an active phase formulation change on n‐heptane reforming performances. Pt/γ‐Al2O3−Cl catalysts were prepared with different Pt (0.3–1 %wt) and Cl (0.1–1.4 %wt) contents and using two γ‐Al2O3 supports so that both sites concentrations and sites locations at the crystallite surface vary among the catalyst pool. Catalytic tests were conducted in mild conditions for a comparison of catalysts in kinetic regime. Results show that Pt and Cl concentrations control the competition between hydroisomerisation, hydrogenolysis and hydrocracking pathways. Aromatisation, on the contrary, is poorly affected by formulation changes. Non‐monotonous trends linking Pt/Cl ratio to isomerisation selectivity are found for both γ‐Al2O3 supports. This study provides new insights for the description of bi‐functional transformations in catalytic naphtha reforming. [ABSTRACT FROM AUTHOR]

The molecular‐level structuration of two full photosystems into conjugated porous organic polymers is reported. The strategy of heterogenization gives rise to photosystems which are still fully active after 4 days of continuous illumination. Those materials catalyze the carbon dioxide photoreduction driven by visible light to produce up to three grams of formate per gram of catalyst. The covalent tethering of the two active sites into a single framework is shown to play a key role in the visible light activation of the catalyst. The unprecedented long‐term efficiency arises from an optimal photoinduced electron transfer from the light harvesting moiety to the catalytic site as anticipated by quantum mechanical calculations and evidenced by in situ ultrafast time‐resolved spectroscopy. [ABSTRACT FROM AUTHOR]

The molecular‐level structuration of two full photosystems into conjugated porous organic polymers is reported. The strategy of heterogenization gives rise to photosystems which are still fully active after 4 days of continuous illumination. Those materials catalyze the carbon dioxide photoreduction driven by visible light to produce up to three grams of formate per gram of catalyst. The covalent tethering of the two active sites into a single framework is shown to play a key role in the visible light activation of the catalyst. The unprecedented long‐term efficiency arises from an optimal photoinduced electron transfer from the light harvesting moiety to the catalytic site as anticipated by quantum mechanical calculations and evidenced by in situ ultrafast time‐resolved spectroscopy. [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]

The aim of the present work is to synthesize a zeolite‐based catalyst with a hollow morphology and highly dispersed metal nanoparticles (NPs) encapsulated inside the zeolite micropores. For this purpose, we have studied a treatment using tetraalkylammonium (TAA) bromides for the selective removal of a large Pt particle from the outer surface of a hollow Beta zeolite. TEM analysis reveals that we succeeded in the synthesis of a hollow beta zeolite single crystal with encapsulated particles, with a high dispersion of 50–60 %. The molecular‐sieve‐type mechanism of the obtained catalysts was evaluated in the model reaction of toluene and mesitylene catalytic hydrogenation. Thanks to the high dispersion. a 10‐fold activity enhancement has been obtained with respect to hollow beta zeolites with encapsulated NPs recently described in the literature. The design of an "ideal" Pt‐supported zeolite catalyst is presented with the following features: 1) a high metal loading without NPs at the outer surface, 2) a high metal dispersion and 3) a short critical length (wall thickness <150–200 nm). Thanks to the high dispersion, a 10‐fold activity enhancement has been obtained with respect to hollow Beta zeolites with encapsulated NPs recently described in the literature. [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]

Pt/NaY zeolites with bulk and hollow morphologies have been used as model catalysts in the hydrogenation of cyclohexene as model reaction. In contrast to most hierarchical zeolites, the presence of a single internal cavity modifies only the mean diffusion length, without changing the external surface area and the crystal size. Differences in catalytic activities have been attributed to a shorter diffusion length in hollow crystals. The volume fraction of zeolite used in bulk crystals (ca. 0.63–0.70) matches well with the shell thickness in hollow crystals, leading to an efficiency factor value for the latter close to 1. No core needed! Why keep unused parts of catalysts? Removing the poorly accessible core of NaY crystals supporting Pt enabled the increase in the effectiveness factor of cyclohexene hydrogenation from 0.63 to 0.97, thus limiting the need of rare and expensive noble metals. [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]

Abstract: Herein, we report the synthesis of two bipyridine‐based porous polymers and their use as platforms for the heterogenization of pentamethylcyclopentadienylrhodium catalytic species. These highly stable heterogeneous catalysts demonstrate their efficiency in the transfer hydrogenation of α‐aryl ketones. Moreover, we show that their catalytic activity is similar to that of homogeneous analogues, highlighting the absence of diffusion limitations in the solids. We rationalize the differences in the measured activities by using the Hammett parameter as a descriptor of the electronic environment of the catalytic site in both homogeneous and heterogeneous systems. [ABSTRACT FROM AUTHOR]

Highly crystalline hollow Y zeolite has been obtained by post-synthesis modification of conventional NaY crystals. The top-down transformation involves substantial dealumination of the zeolite framework by silicon tetrachloride followed by acid leaching and finally selective dissolution of the crystal core in the presence of protective aluminium species. The formation of internal cavities depends on the extent of dealumination of the zeolite as well as on the efficiency to remove extraframework Al species prior to realumination. Hollow Y zeolite crystals possess more or less regular internal cavities of ca. 0.8 μm diameter with external size and shape similar to those of the original NaY crystals. They differ from those recently reported in the literature by much higher Si/Al ratios, higher crystallinities and pure microporous shells of ca. 0.12 μm thickness. As a result of these differences, the family of hollow faujasites is significantly enlarged towards more siliceous and less defective materials. Their formation is most likely based on the presence of an Al-rich surface generated by NaAlO2 species during the last stage of the process, which protects the outer parts of the crystals from desilication. [ABSTRACT FROM AUTHOR]

Porous metal–organic frameworks (MOFs) are attracting great attention from industry, thanks to their myriad potential applications in areas such as catalysis and gas storage. Zr-MOFs (also known as UiO-type MOFs) are especially promising, owing to their large surface areas, high chemical versatility and remarkable hydrothermal, chemical and thermal stabilities. However, among the challenges currently precluding the industrial exploitation of MOFs is the lack of green methods for their synthesis. Herein we describe a continuous-flow spray-drying method for the simultaneous synthesis and shaping of spherical MOF microbeads in a mixture of water and acetic acid. We used this approach to build two archetypical Zr-MOFs: UiO-66-NH2 and Zr-fumarate. By tuning the concentration of acetic acid in water, we were able to produce, by a scalable process, UiO-66-NH2 and Zr-fumarate beads with SBET and water-sorption values comparable to the literature values obtained with other methods. [ABSTRACT FROM AUTHOR]

We present a Pt@Beta catalyst with a unique, well-controlled location of metal nanoparticles that allows more efficient use of this rare, expensive metal in catalysis. The zeolite crystal has an inner cavity, leaving a thin zeolite shell where the metal nanoparticles are encapsulated, thereby ensuring a relatively small diffusional path length and high selectivity. Hollow Beta is obtained by a controlled dissolution–recrystallization method. The location of the particles not only was revealed by electron tomography 3D reconstruction but was further confirmed by a model hydrogenation reaction of aromatics. [ABSTRACT FROM AUTHOR]

Review: 105 refs. [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]

We use density functional theory, newly parameterized molecular dynamics simulations, and last generation 15N dynamic nuclear polarization surface enhanced solid-state NMR spectroscopy (DNP SENS) to understand graft-host interactions and effects imposed by the metal-organic framework (MOF) host on peptide conformations in a peptide-functionalized MOF. Focusing on two grafts typified by MIL-68-proline ( -Pro) and MIL-68-glycine-proline ( -Gly-Pro), we identified the most likely peptide conformations adopted in the functionalized hybrid frameworks. We found that hydrogen bond interactions between the graft and the surface hydroxyl groups of the MOF are essential in determining the peptides conformation(s). DNP SENS methodology shows unprecedented signal enhancements when applied to these peptide-functionalized MOFs. The calculated chemical shifts of selected MIL-68-NH- Pro and MIL-68-NH- Gly-Pro conformations are in a good agreement with the experimentally obtained 15N NMR signals. The study shows that the conformations of peptides when grafted in a MOF host are unlikely to be freely distributed, and conformational selection is directed by strong host-guest interactions. [ABSTRACT FROM AUTHOR]

Rare gas capture and purification is a major challenge for energy, environment, and health applications. Of utmost importance for the nuclear industry, novel separation processes for Xe are urgently needed for spent nuclear fuel reprocessing and nuclear activity monitoring. The recovered, non-radioactive Xe is also of high economic value for lighting, surgical anesthetic, etc. Here, using adsorption and breakthrough experiments and statistical mechanics molecular simulation, we show the outstanding performance of zeolite-supported silver nanoparticles to capture/separate Xe at low concentrations (0.087-100 ppm). We also establish the efficiency of temperature swing adsorption based on such adsorbents for Xe separation from Kr/Xe mixtures and air streams corresponding to off-gases generated by nuclear reprocessing. This study paves the way for the development of novel, cost-efficient technologies relying on the large selectivity/capacity of adsorbent-supported silver nanoparticles which surpass all materials ever tested. [ABSTRACT FROM AUTHOR]

Pt nanoparticles supported on ZSM-5 nanoshells have been prepared by a mild desilication method. The zeolite support is a ZSM-5 crystal with extremely thin walls (ca. 15 nm) that contain meso/microporous defects. The 2–3 nm diameter Pt nanoparticles are entrapped and highly dispersed in these ZSM-5 nanoshells. The particles are stable up to 750 °C in H 2 owing to this immobilization. Catalytic activities for toluene hydrogenation were compared with those of reference Pt-based catalysts. The reaction rates obtained on the novel Pt-ZSM-5 nanoshells catalyst were about 100 times higher than those measured over conventional Pt-ZSM-5 catalysts. The highly defective zeolite nanoshell allowed even bulky molecules such as mesitylene to access all the Pt particles. This was in contrast to Pt nanoparticles encapsulated in ZSM-5 hollow single crystals, which were totally inactive due to molecular sieving. This novel Pt-ZSM-5 nanoshell catalyst shows outstanding sintering-resistance and mass transfer properties owing to its hierarchical design. [ABSTRACT FROM AUTHOR]

We present herein the first example of metal-organic frameworks postfunctionalized with peptides. Our microwave-assisted postsynthetic modification method yields enantiopure peptides anchored inside MOF cavities. Al-MIL-101-NH2, In-MIL-68-NH2, and Zr-UiO-66-NH2 were chosen as starting platforms. A single amino acid and various oligopeptides are grafted with yields up to 60% after a 30 min microwave-assisted coupling-deprotection sequence. This allows efficient preparation of a library of functional hybrid solids for molecular recognition applications such as sensing, separation, or asymmetric catalysis, as demonstrated here for the chiral aldol reaction. [ABSTRACT FROM AUTHOR]

We report the supercell crystal structure of a ZIF-8 analog substituted imidazolate metal-organic framework (SIM-1) obtained by combining solid-state nuclear magnetic resonance and powder X-ray diffraction experiments with density functional theory calculations. [ABSTRACT FROM AUTHOR]

We report the supercell crystal structure of a ZIF-8 analog substituted imidazolate metal-organic framework (SIM-1) obtained by combining solid-state nuclear magnetic resonance and powder X-ray diffraction experiments with density functional theory calculations. [ABSTRACT FROM AUTHOR]

Transition-metal nanoparticles (Co,Ni, and Cu) encapsulated inhollow zeolite single crystals were prepared by recrystallizationof impregnated bulk MFI crystals in the presence of tetrapropylammonium(TPAOH) solutions. The size and number of particles in hollow MFIdepended mainly on the aluminum content. The encapsulation of thenanoparticles prevented them from growing, thus enabling the controlof particle size even after high temperature treatments. For low metalloadings (<3 wt %), the mean particle sizes for Co, Ni, and Cuin hollow silicalite-1 were 3.5 ± 0.3, 3.1 ± 0.5, and 1.5± 0.2 nm, respectively. In the case of hollow ZSM-5, higher loadings(∼8 wt %) could be obtained with mean particle sizes of 17± 2 nm, 13 ± 2 nm, and 15 ± 2 nm for Co, Ni, and Cusystems. The mechanism of transition metal nanoparticle formationwas markedly different from that of noble metals. At high pH values,transition-metal cations first reacted with dissolved silica speciesyielding fibrous metal phyllosilicates that were located inside thecrystal cavities. The metal phyllosilicates were then converted intonanoparticles upon reduction under H2at high temperature(500–750 °C). Silicalite-1 encapsulated Ni particles wereused in the catalytic hydrogenation of substituted benzenes and showedan outstanding size-selectivity effect. Ni particles were accessibleto toluene but not to mesitylene, confirming that the activity isdirectly related to the diffusion properties of molecules throughthe zeolite membrane. [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]

A set of 15 metal–organic frameworks (MIL-53, MIL-68, MIL-125, UiO-66, ZIF) exhibiting different pore size, morphology, and surface chemistry is used to unravel the numerous behaviors of water adsorption at room temperature in this class of materials. Outstanding “S”-shaped (type V) adsorption isotherms are observed for MIL-68 type solids. We show that the underlying mechanism of water adsorption can be rationalized using a simple set of three parameters: the Henry constant (i.e. the slope of the adsorption pressure in the low pressure range), the pressure at which pore filling occurs, and the maximum water adsorption capacity. While the Henry constant and pore filling pressure mostly depend on the affinity of water for the surface chemistry and on pore size, respectively, these two parameters are correlated as they both reflect different aspects of the hydrophobicity–hydrophilicity of the material. For a given type of porous structure, the functionalization of the material by hydrophilic moieties such as hydrogen bonding groups (amine or aldehyde) systematically leads to an increase in the Henry constant concomitantly with a decrease in the pore filling pressure. As for the adsorption mechanism, we show that, for a given temperature, there is a critical diameter (Dc∼ 20 Å for water at room temperature) above which pore filling occurs through irreversible capillary condensation accompanied by capillary hysteresis loops. Below this critical diameter, pore filling is continuous and reversible unless the material exhibits some adsorption-induced flexibility. [ABSTRACT FROM AUTHOR]

The substituted imidazolate-based MOF (SIM-1) easily forms a homogeneous layer at the surface of millimetric platinum-loaded alumina beads. This new core–shell SIM-1@Pt/Al2O3 catalyst shows the fine molecular sieving effect for the Pt-catalyzed hydrogenation of carbon–carbon double bonds. [ABSTRACT FROM AUTHOR]

A simple kinetic model based on the zeolite acid strength, the number of Brønsted acid sites, and the catalyst efficiency was developed for the cracking of n-hexane. A series of HY zeolites with a mesopore volume from 0.04 to 0.32 cm3/g was synthesized and characterized by various physical-chemical methods and tested for n-hexane cracking. The generation of mesoporosity influenced several other important parameters, such as acidity and extra-framework aluminum. Zero-length column diffusion measurements for mesitylene showed a large decrease in the characteristic diffusion time upon the introduction of mesoporosity, which changed only slightly with a further increase in mesoporosity. Similar n-hexane physisorption enthalpies were measured for all samples. The highest initial activity for n-hexane cracking per catalyst volume was observed for the sample with an intermediate mesopore volume of 0.15 cm3/g. The three mesoporous H-USY zeolites showed the same value of the intrinsic rate constant and the same activation energy. The difference in initial activity of the mesoporous zeolites was caused by the difference in the number of Brønsted acid sites. The increase in initial activity for the mesoporous zeolites compared to a microporous zeolite was caused by an increase in the acid strength. [ABSTRACT FROM AUTHOR]