다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Metal species with different size (single atoms, nanoclusters, and nanoparticles) show different catalytic behavior for various heterogeneous catalytic reactions. It has been shown in the literature that many factors including the particle size, shape, chemical composition, metal–support interaction, and metal–reactant/solvent interaction can have significant influences on the catalytic properties of metal catalysts. The recent developments of well-controlled synthesis methodologies and advanced characterization tools allow one to correlate the relationships at the molecular level. In this Review, the electronic and geometric structures of single atoms, nanoclusters, and nanoparticles will be discussed. Furthermore, we will summarize the catalytic applications of single atoms, nanoclusters, and nanoparticles for different types of reactions, including CO oxidation, selective oxidation, selective hydrogenation, organic reactions, electrocatalytic, and photocatalytic reactions. We will compare the results o...

Metal Catalysts for Heterogeneous Catalysis: From Single Atoms to Nanoclusters and Nanoparticles.

Single-atom catalysis has arguably become the most active new frontier in heterogeneous catalysis. Aided by recent advances in practical synthetic methodologies, characterization techniques and computational modelling, we now have a large number of single-atom catalysts (SACs) that exhibit distinctive performances for a wide variety of chemical reactions. This Perspective summarizes recent experimental and computational efforts aimed at understanding the bonding in SACs and how this relates to catalytic performance. The examples described here illustrate the utility of SACs in a broad scope of industrially important reactions and highlight the advantages these catalysts have over those presently used. SACs have well-defined active centres, such that unique opportunities exist for the rational design of new catalysts with high activities, selectivities and stabilities. Indeed, given a certain practical application, we can often design a suitable SAC; thus, the field has developed very rapidly and afforded promising catalyst leads. Moreover, the control we have over certain SAC structures paves the way for designing base metal catalysts with the activities of noble metal catalysts. It appears that we are entering a new era of heterogeneous catalysis in which we have control over well-dispersed single-atom active sites whose properties we can readily tune. Single-atom catalysts are heterogeneous materials featuring active metals sites atomically dispersed on a surface. This Review describes methods by which we prepare and characterize these materials, as well as how we can tune their catalytic performance in a variety of important reactions.

Heterogeneous single-atom catalysis

A review on g-C3N4-based photocatalysts

Atomically dispersed noble metal catalysts often exhibit high catalytic performances, but the metal loading density must be kept low (usually below 0.5%) to avoid the formation of metal nanoparticles through sintering. We report a photochemical strategy to fabricate a stable atomically dispersed palladium-titanium oxide catalyst (Pd1/TiO2) on ethylene glycolate (EG)-stabilized ultrathin TiO2 nanosheets containing Pd up to 1.5%. The Pd1/TiO2 catalyst exhibited high catalytic activity in hydrogenation of C=C bonds, exceeding that of surface Pd atoms on commercial Pd catalysts by a factor of 9. No decay in the activity was observed for 20 cycles. More important, the Pd1/TiO2-EG system could activate H2 in a heterolytic pathway, leading to a catalytic enhancement in hydrogenation of aldehydes by a factor of more than 55.

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Photochemical route for synthesizing atomically dispersed palladium catalysts

Surface coordination chemistry of nanomaterials deals with the chemistry on how ligands are coordinated on their surface metal atoms and influence their properties at the molecular level. This Perspective demonstrates that there is a strong link between surface coordination chemistry and the shape-controlled synthesis, and many intriguing surface properties of metal nanomaterials. While small adsorbates introduced in the synthesis can control the shapes of metal nanocrystals by minimizing their surface energy via preferential coordination on specific facets, surface ligands properly coordinated on metal nanoparticles readily promote their catalysis via steric interactions and electronic modifications. The difficulty in the research of surface coordination chemistry of nanomaterials mainly lies in the lack of effective tools to characterize their molecular surface coordination structures. Also highlighted are several model material systems that facilitate the characterizations of surface coordination struc...

Surface Coordination Chemistry of Metal Nanomaterials

Hollow mesoporous silica spheres have recently attracted increasing attention. However, effective synthesis of uniform hollow mesoporous spheres with controllable well-defined pore structures for fundamental research and practical applications has remained a significant challenge. In this work, a straightforward and effective “cationic surfactant assisted selective etching” synthetic strategy was developed for the preparation of high-quality hollow mesoporous silica spheres with either wormhole-like or oriented mesoporous shell. The as-prepared hollow mesoporous silica spheres have large surface area, high pore volume, and controllable structure parameters. Our experiments demonstrated that cationic surfactant plays critical roles in forming the hollow mesoporous structure. A formation mechanism involving the etching of solid SiO2 accelerated by cationic surfactant followed by the redeposition of dissolved silica species directed by cationic surfactant is proposed. Furthermore, the strategy can be extended as a general strategy to transform silica-coated composite materials into yolk-shell structures with either wormhole-like or oriented mesoporous shell.

A cationic surfactant assisted selective etching strategy to hollow mesoporous silica spheres

The design and synthesis of hollow/yolk-shell mesoporous structures with catalytically active ordered mesoporous shells can infuse new vitality into the applications of these attractive structures. In this study, we report that hollow/yolk-shell structures with catalytically active ordered mesoporous aluminosilica shells can be easily prepared by using silica spheres as the silica precursors. By simply treating with a hot alkaline solution in the presence of sodium aluminate (NaAlO(2)) and cetyltrimethylammonium bromide (CTAB), solid silica spheres can be directly converted into high-quality hollow mesoporous aluminosilica spheres with perpendicular pore channels. On the basis of the proposed formation mechanism of etching followed by co-assembly, the synthesis strategy developed in this work can be extended as a general strategy to prepare ordered mesoporous yolk-shell structures with diverse compositions and morphologies simply by replacing solid silica spheres with silica-coated nanocomposites. The reduction of 4-nitrophenol with yolk-shell structured Au@ordered mesoporous aluminosilica as the catalyst has clearly demonstrated that the highly permeable perpendicular pore channels of mesoporous aluminosilica can effectively prevent the catalytically active yolk from aggregating. Furthermore, with accessible acidity, the yolk-shell structured ordered mesoporous aluminosilica spheres containing Pd yolk exhibit high catalytic activity and recyclability in a one-pot two-step synthesis involving an acid catalysis and subsequent catalytic hydrogenation for desired benzimidazole derivative, which makes the proposed hollow ordered aluminosilica spheres a versatile and practicable scaffold for advanced catalytic nanoreactor systems.

Pengxin Liu

Papers

Photochemical route for synthesizing atomically dispersed palladium catalysts

Surface Coordination Chemistry of Metal Nanomaterials

A cationic surfactant assisted selective etching strategy to hollow mesoporous silica spheres

Hollow Mesoporous Aluminosilica Spheres with Perpendicular Pore Channels as Catalytic Nanoreactors

Strategies for Stabilizing Atomically Dispersed Metal Catalysts