Search

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]

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 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]

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]

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]

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]

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]

Abstract: Metal–organic frameworks are appealing hybrid solids which attract continuously growing interest. Their advantageous application in sensing devices is demonstrated here. In particular, the use of a short‐pulse laser excitation of luminescent metal‐organic framework is reported for the first time to favor the ligand‐based emission. The designed MOF‐based system achieves in vitro H2S dosing by turn‐on fluorescence with unprecedented sensitivity. The Al‐MIL‐101‐based sensor detects sulfide produced by living cells and sulfide‐releasing molecules in physiological media with a constant accuracy at sub‐micromolar levels. The reported sensitivity is suitable for medical applications and opens new perspectives in the design of new point‐of‐care testing devices. The detailed relationship between photoluminescence mechanisms and chemical modification of the MOF upon sensing is also reported. [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]

Abstract: Standard chemical and physical methods to control the size of supported metallic nanoparticles are generally not compatible with the harsh conditions of applications (high temperature, presence of steam). Sintering of nanoparticles usually occurs, leading to particle growth and eventually to a degradation of physical properties. Here we describe a generic process for synthesizing nanoalloys of controlled size (2–10 nm) and composition encapsulated in zeolite nanoboxes. The originality of the synthesis design is that the nanoboxes act both as nanoreactors in which the bimetallic particles are formed and as protective ultra‐microporous shells, which prevent sintering by coalescence even under harsh conditions. Moreover, the present process allows for control over the size and composition of the NPs, which are factors that ultimately determine the catalytic properties. A series of mono‐ (Au, Pd, Pt) or bi‐ (AuAg, PdAg, PtAg and PdPt) metallic nanoparticles individually encapsulated in hollow silicalite‐1 single crystals have been prepared and characterized. The simultaneous presence of Ag and Au at the surface of Au161Ag22 NPs has been demonstrated by results of the catalytic activity for CO oxidation near room temperature. [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]

The first photosensitization of a rhodium-based catalytic system for CO2 reduction is reported, with formate as the sole carbon-containing product. Formate has wide industrial applications and is seen as valuable within fuel cell technologies as well as an interesting H2-storage compound. Heterogenization of molecular rhodium catalysts is accomplished via the synthesis, post-synthetic linker exchange, and characterization of a new metal-organic framework (MOF) Cp*Rh@UiO-67. While the catalytic activities of the homogeneous and heterogeneous systems are found to be comparable, the MOF-based system is more stable and selective. Furthermore it can be recycled without loss of activity. For formate production, an optimal catalyst loading of ~10% molar Rh incorporation is determined. Increased incorporation of rhodium catalyst favors thermal decomposition of formate into H2. There is no precedent for a MOF catalyzing the latter reaction so far. [ABSTRACT FROM AUTHOR]

Recently, the use of mixtures of organic-building-block linkers has given chemists an additional degree of freedom for engineering metal-organic frameworks (MOFs) with specific properties; however, the poor characterization of the chemical complexity of such MixMOF structures by conventional techniques hinders the verification of rational design. Herein, we describe the application of a technique known as photothermal induced resonance to individual MixMOF microcrystals to elucidate their chemical composition with nanoscale resolution. Results show that MixMOFs isoreticular to In-MIL-68, obtained either directly from solution or by postsynthetic linker exchange, are homogeneous down to approximately 100 nm. Additionally, we report a novel in situ process that enables the engineering of anisotropic domains in MOF crystals with submicron linker-concentration gradients. [ABSTRACT FROM AUTHOR]

NanoMOF: Hierarchical zeolitic imidazolate framework‐8 (ZIF‐8) nanocrystals catalyze esterification of glycerol with oleic acid at low temperature and become hierarchical (see TEM micrograph) upon local transformation of the framework. [ABSTRACT FROM AUTHOR]

The article offers information regarding conversion of carbon dioxide into bulk chemicals at lower energy cost. It discusses the activity of amine functionalized metal-organic frameworks. It presents the use of epoxide and carbon dioxide for the catalytic synthesis of cyclic carbonates. It investigates the various reaction involved which includes adsorption of carbon dioxide, acid-base-pair catalysis and the nucleophilic attack of the activated species.

of metal-organic frameworks is carried out in a novel fashion for the synthesis of single-site catalysts. Protection-deprotection methodologies open new perspectives to 'unlock' protected functionalities to obtain highly active and/or coordinating moieties on MOFs. This could facilitate the immobilization of organometallic catalysts inside MOF cavities. [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]

Review: 155 refs. [ABSTRACT FROM AUTHOR]