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

In heterogeneous single-metal-site catalysts (HSMSCs) the active metal centres are located individually on a support and are stabilized by neighbouring surface atoms such as nitrogen, oxygen or sulfur. Modern characterization techniques allow the identification of these individual metal atoms on a given support, and the resulting materials are often referred as single-atom catalysts. Their electronic properties and catalytic activity are tuned by the interaction between the central metal and the neighbouring surface atoms, and their atomically dispersed nature allows for metal utilization of up to 100%. In this way, HSMSCs provide new opportunities for catalysis, and with respect to structure build a bridge between homogeneous and heterogeneous catalysis. Herein, selected publications from 2010 in this area are reviewed and their perspectives for the near future are highlighted. Where appropriate, comparisons between HSMSCs and homogeneous/heterogeneous counterparts are presented. Single-atom catalysts have drawn increasing attention as methods for their preparation and characterization improve. Here, Beller and co-workers discuss the latest developments in the field of single-metal-site catalysts, discussing how this catalyst class bridges heterogeneous and homogeneous catalysis, and providing a perspective on how the field might continue to develop.

Bridging homogeneous and heterogeneous catalysis by heterogeneous single-metal-site catalysts

Isolated atoms featuring unique reactivity are at the heart of enzymatic and homogeneous catalysts. In contrast, although the concept has long existed, single-atom heterogeneous catalysts (SACs) have only recently gained prominence. Host materials have similar functions to ligands in homogeneous catalysts, determining the stability, local environment, and electronic properties of isolated atoms and thus providing a platform for tailoring heterogeneous catalysts for targeted applications. Within just a decade, we have witnessed many examples of SACs both disrupting diverse fields of heterogeneous catalysis with their distinctive reactivity and substantially enriching our understanding of molecular processes on surfaces. To date, the term SAC mostly refers to late transition metal-based systems, but numerous examples exist in which isolated atoms of other elements play key catalytic roles. This review provides a compositional encyclopedia of SACs, celebrating the 10th anniversary of the introduction of this term. By defining single-atom catalysis in the broadest sense, we explore the full elemental diversity, joining different areas across the whole periodic table, and discussing historical milestones and recent developments. In particular, we examine the coordination structures and associated properties accessed through distinct single-atom-host combinations and relate them to their main applications in thermo-, electro-, and photocatalysis, revealing trends in element-specific evolution, host design, and uses. Finally, we highlight frontiers in the field, including multimetallic SACs, atom proximity control, and possible applications for multistep and cascade reactions, identifying challenges, and propose directions for future development in this flourishing field.

Single-Atom Catalysts across the Periodic Table.

Surface-supported isolated atoms in single-atom catalysts (SACs) are usually stabilized by diverse defects. The fabrication of high-metal-loading and thermally stable SACs remains a formidable challenge due to the difficulty of creating high densities of underpinning stable defects. Here we report that isolated Pt atoms can be stabilized through a strong covalent metal-support interaction (CMSI) that is not associated with support defects, yielding a high-loading and thermally stable SAC by trapping either the already deposited Pt atoms or the PtO2 units vaporized from nanoparticles during high-temperature calcination. Experimental and computational modeling studies reveal that iron oxide reducibility is crucial to anchor isolated Pt atoms. The resulting high concentrations of single atoms enable specific activities far exceeding those of conventional nanoparticle catalysts. This non defect-stabilization strategy can be extended to non-reducible supports by simply doping with iron oxide, thus paving a new way for constructing high-loading SACs for diverse industrially important catalytic reactions.

Non defect-stabilized thermally stable single-atom catalyst

Metal atoms dispersed on the oxide supports constitute a large category of single-atom catalysts. In this review, oxide supported single-atom catalysts are discussed about their synthetic procedures, characterizations, and reaction mechanism in thermocatalysis, such as water-gas shift reaction, selective oxidation/hydrogenation, and coupling reactions. Some typical oxide materials, including ferric oxide, cerium oxide, titanium dioxide, aluminum oxide, and so on, are intentionally mentioned for the unique roles as supports in anchoring metal atoms and taking part in the catalytic reactions. The interactions between metal atoms and oxide supports are summarized to give a picture on how to stabilize the atomic metal centers, and rationally tune the geometric structures and electronic states of single atoms. Furthermore, several directions in fabricating single-atom catalysts with improved performance are proposed on the basis of state-of-the-art understanding in metal-oxide interactions.

Single-Atom Catalysts Based on the Metal-Oxide Interaction.

Catalytic hydrosilylation represents a straightforward and atom-efficient methodology for the creation of C–Si bonds In general, the application of homogeneous platinum complexes prevails in industry and academia Herein, we describe the first heterogeneous single atom catalysts (SACs), which are conveniently prepared by decorating alumina nanorods with platinum atoms The resulting stable material efficiently catalyzes hydrosilylation of industrially relevant olefins with high TON (≈105) A variety of substrates is selectively hydrosilylated including compounds with sensitive reducible and other functional groups (N, B, F, Cl) The single atom based catalyst shows significantly higher activity compared to related Pt nanoparticles

Synthesis of Single Atom Based Heterogeneous Platinum Catalysts: High Selectivity and Activity for Hydrosilylation Reactions

The reductive N-formylation of amines using CO2 and hydrogen is a promising means of incorporating CO2 into value-added chemicals. To date, there has been a lack of heterogeneous catalyst systems that are sufficiently active and selective for N-formylation of primary amines with CO2 and H2. For the first time, we report that a highly active palladium nanoparticle supported on an hydroxyl group-functionalized carbon material has been designed for the N-formylation of aliphatic primary amines with CO2 and H2. XPS, XRD, FT-Raman, and TEM characterizations revealed the adsorbing of Pd(NH3)xCly onto the carbon support during catalyst preparation, followed by in situ reduction to generate active nano-Pd particles. The catalytic activity of the Pd/C catalysts can be tuned efficiently by the hydroxyl group, which can modulate the hydrophilic/hydrophobic properties of the carbon surface, and promote the adsorption of CO2 and the amines near the Pd sites. The results described here may promote the design of an acti...

Hydroxyl Group-Regulated Active Nano-Pd/C Catalyst Generation via in Situ Reduction of Pd(NH3)xCly/C for N-Formylation of Amines with CO2/H2

Oxidative dehydrogenation of light alkanes with carbon dioxide

Generally, a homogeneous catalyst exhibits good activity and defined active sites but it is difficult to recycle. Meanwhile, a heterogeneous catalyst can easily be reused but its active site is difficult to reveal. It is interesting to bridge the gap between homogeneous and heterogeneous catalysis via controllable construction of a heterogeneous catalyst containing defined active sites. Here, we report that a molecularly defined, single-active site heterogeneous catalyst has been designed and prepared via the oxidative polymerization of maleimide derivatives. These polymaleimide derivatives can be active catalysts for the selective oxidation of heterocyclic compounds to quinoline and indole via the recycling of –C=O and –C–OH groups, which was confirmed by tracing the reaction with GC-MS using maleimide as the catalyst and by FT-IR analysis with polymaleimide as the catalyst. These results might promote the development of heterogeneous catalysts with molecularly defined single active sites exhibiting a comparable activity to homogeneous catalysts.

Feng Shi

Papers

Synthesis of Single Atom Based Heterogeneous Platinum Catalysts: High Selectivity and Activity for Hydrosilylation Reactions

Hydroxyl Group-Regulated Active Nano-Pd/C Catalyst Generation via in Situ Reduction of Pd(NH3)xCly/C for N-Formylation of Amines with CO2/H2

Oxidative dehydrogenation of light alkanes with carbon dioxide

Synthesis of a molecularly defined single-active site heterogeneous catalyst for selective oxidation of N -heterocycles

N-Monomethylation of amines using paraformaldehyde and H2