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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]

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]

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]

Review: 155 refs. [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]

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]