Single‐atom catalysts are emerging as a new frontier in heterogeneous catalysis because of their maximum atom utilization efficiency, but they usually suffer from inferior stability. Herein, we ...synthesized single‐atom Rh catalysts embedded in MFI‐type zeolites under hydrothermal conditions and subsequent ligand‐protected direct H2 reduction. Cs‐corrected scanning transmission electron microscopy and extended X‐ray absorption analyses revealed that single Rh atoms were encapsulated within 5‐membered rings and stabilized by zeolite framework oxygen atoms. The resultant catalysts exhibited excellent H2 generation rates from ammonia borane (AB) hydrolysis, up to 699 min−1 at 298 K, representing the top level among heterogeneous catalysts for AB hydrolysis. The catalysts also showed superior catalytic performance in shape‐selective tandem hydrogenation of various nitroarenes by coupling with AB hydrolysis, giving >99 % yield of corresponding amine products.
Together alone: Single Rh atoms were encapsulated within MFI zeolites under in situ hydrothermal conditions and a ligand‐protected direct H2 reduction. The catalyst gave a high turnover frequency of 699 molH2
(molRh)−1 min−1 at 298 K for ammonia borane (AB) hydrolysis and exhibited superior catalytic efficiency in shape‐selective tandem hydrogenation of nitroarenes by coupling with the hydrolysis of AB.
Conventional separation technologies to separate valuable commodities are energy intensive, consuming 15% of the worldwide energy. Mixed-matrix membranes, combining processable polymers and selective ...adsorbents, offer the potential to deploy adsorbent distinct separation properties into processable matrix. We report the rational design and construction of a highly efficient, mixed-matrix metal-organic framework membrane based on three interlocked criteria: (i) a fluorinated metal-organic framework, AlFFIVE-1-Ni, as a molecular sieve adsorbent that selectively enhances hydrogen sulfide and carbon dioxide diffusion while excluding methane; (ii) tailoring crystal morphology into nanosheets with maximally exposed (001) facets; and (iii) in-plane alignment of (001) nanosheets in polymer matrix and attainment of 001-oriented membrane. The membrane demonstrated exceptionally high hydrogen sulfide and carbon dioxide separation from natural gas under practical working conditions. This approach offers great potential to translate other key adsorbents into processable matrix.
Propane dehydrogenation (PDH) has great potential to meet the increasing global demand for propylene, but the widely used Pt‐based catalysts usually suffer from short‐term stability and ...unsatisfactory propylene selectivity. Herein, we develop a ligand‐protected direct hydrogen reduction method for encapsulating subnanometer bimetallic Pt–Zn clusters inside silicalite‐1 (S‐1) zeolite. The introduction of Zn species significantly improved the stability of the Pt clusters and gave a superhigh propylene selectivity of 99.3 % with a weight hourly space velocity (WHSV) of 3.6–54 h−1 and specific activity of propylene formation of 65.5 molC3H6
gPt−1 h−1 (WHSV=108 h−1) at 550 °C. Moreover, no obvious deactivation was observed over PtZn4@S‐1‐H catalyst even after 13000 min on stream (WHSV=3.6 h−1), affording an extremely low deactivation constant of 0.001 h−1, which is 200 times lower than that of the PtZn4/Al2O3 counterpart under the same conditions. We also show that the introduction of Cs+ ions into the zeolite can improve the regeneration stability of catalysts, and the catalytic activity kept unchanged after four continuous cycles.
A lean, mean, propylene machine: Subnanometer bimetallic Pt–Zn clusters are encapsulated inside silicalite‐1 (S‐1) zeolite via a ligand‐protected direct hydrogen reduction method. In the propane dehydrogenation (PDH) reaction, the PtZn4@S‐1‐H catalyst exhibited a very high propylene selectivity of 99.3 % and specific activity of propylene formation of 65.5 molC3H6
gPt−1 h−1 at 550 °C. Moreover, no obvious deactivation was observed over catalyst even after 13000 min on stream.
The Linear Response Theory (LRT) is a widely accepted framework to analyze the power absorption of magnetic nanoparticles for magnetic fluid hyperthermia. Its validity is restricted to low applied ...fields and/or to highly anisotropic magnetic nanoparticles. Here, we present a systematic experimental analysis and numerical calculations of the specific power absorption for highly anisotropic cobalt ferrite (CoFe
O
) magnetic nanoparticles with different average sizes and in different viscous media. The predominance of Brownian relaxation as the origin of the magnetic losses in these particles is established, and the changes of the Specific Power Absorption (SPA) with the viscosity of the carrier liquid are consistent with the LRT approximation. The impact of viscosity on SPA is relevant for the design of MNPs to heat the intracellular medium during in vitro and in vivo experiments. The combined numerical and experimental analyses presented here shed light on the underlying mechanisms that make highly anisotropic MNPs unsuitable for magnetic hyperthermia.
Ordered nanoporous materials including zeolites, zeotypes, and metal‐organic frameworks (MOFs) are widely used in the fields of heterogeneous catalysis, ion exchange and gas storage/separation. In ...addition, due to their particular structural features new applications are continuously being explored as a consequence of their well‐defined porous network, thermal stability, acidity and guest‐species confinement. All physicochemical properties are directly structure related and therefore characterization at atomic level is highly desired. In the current work, we have aimed to review the recent progress of electron microscopy science applied to the characterization of different nanoporous materials since the first work that made use of spherical aberration (Cs) corrected electron microscopy in 2010. All difficulties encountered for the application of this technique will be presented, together with the excellent degree of information that can be extracted and the scientific responses that only Cs‐corrected electron microscopy can provide in the area of nanoporous materials, zeolites, zeotypes and MOFs.
Ten years: Huge steps beyond details. Since the first application of spherical aberration corrected electron microscopy for retrieving high‐resolution images of zeolites, huge progress has been achieved. This review aims to recapitulate the most significant progress carried out for ordered nanoporous materials, including zeolites, zeotypes and MOFs since 2010 until now.
Functional heterofibrous hybrid materials are prepared in an integrative approach from aqueous dispersions of nanofibrillated cellulose and sepiolite by applying high shear homogenization and ...ultrasound irradiation. Both types of nanofibers remain physically cross‐linked forming homogeneous and very stable high‐viscosity gels that can be shaped as films and considered as “hybrid nanopapers” as well. The presence of sepiolite modifies the surface roughness of the films resulting from the casting process, which can be rendered hydrophobic, as the hydrophilic characteristics of both components resulted modulated. In addition, these fibrous hybrid systems can benefit from the properties provided by the two components, such as mechanical behavior, surface properties, and chemical reactivity. Moreover, further assembly of these hybrid nanopapers to other particulate solids, such as carbon nanotubes, magnetite, or ZnO nanoparticles, results in multifunctional hybrid nanopapers, opening a versatile way for developing other numerous organic–inorganic materials of interest in diverse applications.
Herein, a functional hybrid nanopaper by assembling nanofibers of cellulose and sepiolite is demonstrated. The cross‐assembly between two kinds of nanofibers of organic and inorganic nature through mechanical and sonomechanical processes results in nanostructured biohybrids showing ability toward further functionalization giving rise to functional materials with tunable properties and diverse potential applications.
Zeolites are widely used in catalysis, gas separation, ion exchange, etc. due to their superior physicochemical properties, which are closely related to specific features of their framework ...structures. Although more than two hundred different framework types have been recognized, it is of great interest to explore from a crystallographic perspective, the atomic positions, surface terminations, pore connectivity and structural defects that deviate from the ideal framework structures, namely local structural modulation. In this article, we review different types of local modulations in zeolite frameworks using various techniques, especially electron microscopy (EM). The most recent advances in resolving structural information at the atomic level with aberration corrected EM are also presented, commencing a new era of gaining atomic structural information, not only for all tetrahedral atoms including point vacancies in framework but also for extra‐framework cations and surface terminations.
Local structure modulations deviating from ideal framework‐type structures are important fine‐structural features within zeolite frameworks. By using (S)TEM with diffraction and imaging approaches, point, column and planar modulations can be observed in both reciprocal and real space.
Tailoring the reaction kinetics is the central theme of designer electrocatalysts, which enables the selective conversion of abundant and inert atmospheric species into useful products. Here we show ...a supporting effect in tuning the electrocatalytic kinetics of oxygen reduction reaction (ORR) from four-electron to two-electron mechanism by docking metalloporphyrin-based metal-organic frameworks (MOFs) crystals on graphene support, leading to highly selective peroxide production with faradaic efficiency as high as 93.4%. A magic angle of 38.1° tilting for the co-facial alignment was uncovered by electron diffraction tomography, which is attributed to the maximization of
π
-
π
interaction for mitigating the lattice and symmetry mismatch between MOF and graphene. The facilitated electron migration and oxygen chemisorption could be ascribed to the supportive effect of graphene that disperses of the electron state of the active center, and ultimately regulates rate-determining step.
Zeolites are becoming more versatile in their chemical functions through rational design of their frameworks. Therefore, direct imaging of all atoms at the atomic scale, basic units (Si, Al, and O), ...heteroatoms in the framework, and extra‐framework cations, is needed. TEM provides local information at the atomic level, but the serious problem of electron‐beam damage needs to be overcome. Herein, all framework atoms, including oxygen and most of the extra‐framework Na cations, are successfully observed in one of the most electron‐beam‐sensitive and lowest framework density zeolites, Na‐LTA. Zeolite performance, for instance in catalysis, is highly dependent on the location of incorporated heteroatoms. Fe single atomic sites in the MFI framework have been imaged for the first time. The approach presented here, combining image analysis, electron diffraction, and DFT calculations, can provide essential structural keys for tuning catalytically active sites at the atomic level.
Down to the atom: Through different imaging methods, electron microscopy can provide direct observation of oxygen atoms and sodium cations, pointing the way for the analysis of the local structure around heteroatoms in zeolite frameworks. The data provide clear evidence of Fe on tetrahedral sites within the MFI zeolite structure, clearly distinguished as single atoms.
The assembly–disassembly–organization–reassembly (ADOR) process has been used to disassemble a parent zeolite with the UOV structure type and then reassemble the resulting layers into a novel ...structure, IPC‐12. The structure of the material has previously been predicted computationally and confirmed in our experiments using X‐ray diffraction and atomic resolution STEM‐HAADF electron microscopy. This is the first successful application of the ADOR process to a material with porous layers.
A germane assembly: The synthesis of a new zeolite IPC‐12 using the assembly–disassembly–organization–reassembly (ADOR) transformation of a germanosilicate zeolite with the UOV topology is reported.
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