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In the past few decades, metal nanoparticles applied in heterogeneous catalysis have attracted extensive attention. The term nanocatalysis is broadly referred to as the unique catalytic effect of this series of materials. Although considerable progress has been made in nanocatalysis, it still remains a great challenge to fully understand the nature of active sites in the nanoscale. Many concepts and models have been put forwarded to describe the properties and performances of nano- and subnanoparticles in catalysis. In this review, we propose our perspective on the active sites of heterogeneous catalysis from the aspects of electronic structure and geometric structure of nanoclusters and consider briefly how these clusters function in catalysis. The challenge in nanocatalysis research methods is also discussed.

Dual‐atom site catalysts (DACs) have emerged as a new frontier in the heterogeneous catalysis field for electrochemical energy conversion systems. In this review, the superiority of DACs over single‐atom site catalysts is fully discussed. The origin of synergistic effects such as optimized d‐band structure, tailored spin state, and tuned charge transfer are pointed out. The merits in geometric and electronic structure render the active moiety versatile binding behavior toward adsorbed intermediate and beneficial synergistic effects to break the scaling relationships. The approaches to engineer the active moiety of DACs through modulating the central atoms, tuning the coordination environment, and engineering the metal‐support interaction are summarized. Finally, the current challenges and future research perspectives of DACs for efficient electrocatalysis are outlined. [ABSTRACT FROM AUTHOR]

Improving the stability of sensitive catalytic systems is an emerging research topic in the catalysis field. However, the current design of heterogeneous catalysts mainly improves their catalytic performance. This paper presents a single‐atom catalyst (SAC) strategy to improve the cobalt‐catalysed fluorination of acyl chlorides. A stable Co−F intermediate can be formed through the oxidative fluorination of Co1−N4@NC SAC, which can replace the unstable high‐valent cobalt catalytic system and avoid the use of phosphine ligands. In the SAC system, KF can be employed as a fluorinating reagent to replace the AgF, which can be applied to various substrates and scale‐up conversion with high turnover numbers (TON=1.58×106). This work also shows that inorganic SACs have tremendous potential for organofluorine chemistry, and it provides a good reference for follow‐up studies on the structure‐activity relationship between catalyst design and chemical reaction mechanisms. [ABSTRACT FROM AUTHOR]

In bimetallic heterostructured nanoparticles (NPs), the synergistic effect between their different metallic components leads to higher catalytic activity compared to the activity of the individual components. However, how the dynamic changes through which these NPs adopt catalytically active structures during a reaction and how the restructuring affects their activity are largely unknown. Here, using operando transmission electron microscopy, structural changes are studied in bimetallic Ni–Rh NPs, comprising of a Ni core whose surface is decorated with smaller Rh NPs, during a CO oxidation reaction. The direct atomic‐scale imaging reveals that, under O2‐rich conditions, Ni core partially transforms into NiO, forming a (Ni+NiO)–Rh hollow nanocatalyst with high catalytic activity. Under O2‐poor conditions, Rh NPs alloy with the surface of the core to form a NiRh‐alloy surface, and the NPs display significantly lower activity. The theoretical calculations indicate that NiO component that forms only under O2‐rich conditions enhances the activity by preventing the CO poisoning of the nanocatalysts. The results demonstrate that visualizing the structural changes during reactions is indispensable in identifying the origin of catalytic activity. These insights into the dynamic restructuring of NP catalysts under a reactive environment are critical for the rational design of high‐performance nanocatalysts. [ABSTRACT FROM AUTHOR]

In recent years, single-atom site catalysts (SACs) have achieved great advancements in heterogeneous and electrochemical catalysis due to the merits of maximal atom utilization, unique electronic and geometric structures, low costs, and high catalytic performances. The electronic structures of the isolated metal centers can greatly influence the adsorption energies of reactants and intermediates, thus determining the catalytic activities of SACs. Especially, the electronic structure regulation of the metal sites has been advanced to the atomic level and proven a powerful strategy to enhance their electrocatalytic performances, which provides great opportunities for the further development of SACs. Based on the reported synthesis and structural modulation methods, in this review, the experimental and computational advances in the electronic structure regulation strategies for SACs, including coordination adjustment, electronic metal-support interaction, oxidation state modulation, and strain engineering, will be summarized. Then, the effects of electronic structures on the adsorption behaviors and, thus, the electrocatalytic activities of water splitting and O2/CO2 reduction reactions will be emphatically exemplified and discussed. In the end, a brief conclusion of this paper and the existing challenges and future opportunities in this research direction will be proposed. This review aims to highlight the understanding of electronic structure in association to the electrocatalytic activity for SACs and provide guidance for their further development in electrochemical applications. [ABSTRACT FROM AUTHOR]

Demonstrated here is the correlation between atomic configuration induced electronic density of single‐atom Co active sites and oxygen reduction reaction (ORR) performance by combining density‐functional theory (DFT) calculations and electrochemical analysis. Guided by DFT calculations, a MOF‐derived Co single‐atom catalyst with the optimal Co1‐N3PS active moiety incorporated in a hollow carbon polyhedron (Co1‐N3PS/HC) was designed and synthesized. Co1‐N3PS/HC exhibits outstanding alkaline ORR activity with a half‐wave potential of 0.920 V and superior ORR kinetics with record‐level kinetic current density and an ultralow Tafel slope of 31 mV dec−1, exceeding that of Pt/C and almost all non‐precious ORR electrocatalysts. In acidic media the ORR kinetics of Co1‐N3PS/HC still surpasses that of Pt/C. This work offers atomic‐level insight into the relationship between electronic density of the active site and catalytic properties, promoting rational design of efficient catalysts. [ABSTRACT FROM AUTHOR]

Atomic regulation of metal catalysts has emerged as an intriguing yet challenging strategy to boost product selectivity. Here, we report a density functional theory‐guided atomic design strategy for the fabrication of a NiGa intermetallic catalyst with completely isolated Ni sites to optimize acetylene semi‐hydrogenation processes. Such Ni sites show not only preferential acetylene π‐adsorption, but also enhanced ethylene desorption. The characteristics of the Ni sites are confirmed by multiple characterization techniques, including aberration‐corrected high‐resolution scanning transmission electron microscopy and X‐ray absorption spectrometry measurements. The superior performance is also confirmed experimentally against a Ni5Ga3 intermetallic catalyst with partially isolated Ni sites and against a Ni catalyst with multi‐atomic ensemble Ni sites. Accordingly, the NiGa intermetallic catalyst with the completely isolated Ni sites shows significantly enhanced selectivity to ethylene and suppressed coke formation. [ABSTRACT FROM AUTHOR]

Incorporating atomically dispersed metal species into functionalized metal–organic frameworks (MOFs) can integrate their respective merits for catalysis. A cage‐controlled encapsulation and reduction strategy is used to fabricate single Ru atoms and triatomic Ru3 clusters anchored on ZIF‐8 (Ru1@ZIF‐8, Ru3@ZIF‐8). The highly efficient and selective catalysis for semi‐hydrogenation of alkyne is observed. The excellent activity derives from high atom‐efficiency of atomically dispersed Ru active sites and hydrogen enrichment by the ZIF‐8 shell. Meanwhile, ZIF‐8 shell serves as a novel molecular sieve for olefins to achieve absolute regioselectivity of catalyzing terminal alkynes but not internal alkynes. Moreover, the size‐dependent performance between Ru3@ZIF‐8 and Ru1@ZIF‐8 is detected in experiment and understood by quantum‐chemical calculations, demonstrating a new and promising approach to optimize catalysts by controlling the number of atoms. Single Ru atoms and triatomic Ru3 clusters confined in functionalized ZIF‐8 as composite catalysts combine the advantages of atomically dispersed Ru species and a microporous MOF structure. This facilitates highly efficient and selective catalysis for the partial hydrogenation of alkynes. Size‐dependent performance between Ru3@ZIF‐8 and Ru1@ZIF‐8 catalysts is revealed. [ABSTRACT FROM AUTHOR]

The search for constructing high-performance catalysts is an unfailing topic in chemical fields. Recently, we have witnessed many breakthroughs in the synthesis of single-atom catalysts (SACs) and their applications in catalytic systems. They have shown excellent activity, selectivity, stability, efficient atom utilization and can serve as an efficient bridge between homogeneous and heterogenous catalysis. Currently, most SACs are synthesized via a bottom-up strategy; however, drawbacks such as the difficulty in accessing high mass activity and controlling homogeneous coordination environments are inevitably encountered, restricting their potential use in the industrial area. In this regard, a novel top-down strategy has been recently developed to fabricate SACs to address these practical issues. The metal loading can be increased to 5% and the coordination environments can also be precisely controlled. This review highlights approaches to the chemical synthesis of SACs towards diverse chemical reactions, especially the recent advances in improving the mass activity and well-defined local structures of SACs. Also, challenges and opportunities for the SACs will be discussed in the later part. [ABSTRACT FROM AUTHOR]

Tuning the selectivity of metal catalysts is of paramount importance yet a great challenge. A new strategy to effectively control the selectivity of metal catalysts, by tuning the lattice strain, is reported. A certain amount of Co atoms is introduced into Ru catalysts to compress the Ru lattice, as confirmed by aberration-corrected high-resolution transmission electron microscopy (HRTEM) and X-ray absorption fine structure (XAFS) measurements. We discover that the lattice strain of Ru catalysts can greatly affect their selectivity, and Ru with 3 % lattice compression exhibits extremely high catalytic selectivity for hydrogenation of 4-nitrostyrene to 4-aminostyrene compared to pristine Ru (99 % vs. 66 %). Theoretical studies confirm that the optimized lateral compressive strain facilitates hydrogenation of the nitro group but impedes the hydrogenation of the vinyl group. This study provides a new guideline for designing metal catalysts with high selectivity. [ABSTRACT FROM AUTHOR]

We have prepared nanocomposites of well-defined spherical AgI nanostructures wrapped in reduced graphene oxide nanosheets (AgI@RGO). The as-obtained AgI@RGO nanocomposites exhibit an enhanced photocatalytic activity and stability in the degradation of organic pollutants, namely, Rhodamine B (RhB), in comparison with bare AgI nanospheres. The hybridization of AgI nanospheres with RGO nanosheets affords a good adsorptive capacity for RhB molecules, facilitated charge transfer, and suppressed recombination of electron-hole pairs. These figures of merit lead to an enhanced photocatalytic performance over AgI@RGO. This work opens new possibilities for the development of highly efficient and stable visible-light-driven composite photocatalysts for environmental purification. [ABSTRACT FROM AUTHOR]

Integration of different active sites into metallic catalysts, which may impart new properties and functionalities, is desirable yet challenging. Herein, a novel dealloying strategy is demonstrated to decorate nickel-aluminum layered double hydroxide (NiAl-LDH) onto a Pt-Ni alloy surface. The incorporation of chemical etching of Pt-Ni alloy and in situ precipitation of LDH are studied by joint experimental and theoretical efforts. The initial Ni-rich Pt-Ni octahedra transform by interior erosion into Pt3Ni nanoframes with enlarged surface areas. Furthermore, owing to the basic active sites of the decorated LDH together with the metallic sites of Pt3Ni, the resulting Pt-Ni nanoframe/NiAl-LDH composites exhibit excellent catalytic activity and selectivity in the dehydrogenation of benzylamine and hydrogenation of furfural. [ABSTRACT FROM AUTHOR]

We have developed two strategies to optimize Pd catalysts. On one hand, Ag was introduced into Pd and then they were applied to the selective hydrogenation of citral under mild conditions. The addition of metallic Ag could tune the selectivity of Pd and made it suitable for the selective hydrogenation of the conjugated double bond. The selectivity of citronellal increased from 0 (for Pd/C and Pd0.7Ag0.3/C) to 96 % (for Pd0.4Ag0.6/C) as the Ag content increased. On the other hand, the addition of SnO2 made the Pd catalysts more inclined to activate the C=O bond and gave better performance for the hydrogenation of the conjugated double bond compared with the corresponding Pd-Ag catalysts. The selectivity of citronellal increased from 0 (for Pd0.7Ag0.3/C) to 76 % (for Pd0.7Ag0.3-SnO2/C was used) after the addition of SnO2. On the basis of these results, we developed a catalyst (Pd0.6Ag0.4-SnO2/C) with the best catalytic performance for the selective hydrogenation of citral (the conversion of citral reached 99 %, and the selectivity was up to 96 %). [ABSTRACT FROM AUTHOR]

Palladium and silver salts were combined with Cu2O octadecahedra in concave heterostructures. The formation of concave faces involved selective oxidative etching of Cu2O on the {100} faces and in situ growth of Pd/Ag on different sites. The structures showed superior catalytic activities to both single domains and their mixtures in a model Sonogashira‐type organic reaction. [ABSTRACT FROM AUTHOR]

Supported atomic clusters with uniform metal sites and definite low-nuclearity are intermediate states between single-atom catalysts (SACs) and nanoparticles in size. Benefiting from the presence of metal–metal bonds, supported atomic clusters can trigger synergistic effects among every metal atom, which contributes to achieving unique catalytic properties different from SACs and nanoparticles. However, the scalable and precise synthesis and atomic-level insights into the structure–properties relationship of supported atomic clusters is a great challenge. This perspective presents the latest progress of the synthesis of supported atomic clusters, highlights how the structure affects catalytic properties, and discusses the limitations as well as prospects. Supported atomic clusters with precise nuclearity are intermediate states between single-atom catalysts and nanoparticles in size. Here the authors summarize and discuss synthetic strategies of supported atomic clusters with unique catalytic properties for heterogeneous reactions. [ABSTRACT FROM AUTHOR]

• The up-to-date reports with respect to the chemical synthesis of SAA are overviewed. • The significance of SAA for representative electrochemical and heterogeneous catalytic reactions is analyzed. • The major challenges and opportunities pertaining to this cutting-edge field are suggested. The development of low-cost, high-performance catalysts at the atomic level has become a challenging issue for large-scale applications of renewable clean energy technologies. Atomic sites catalysts, such as single atoms catalysts (SAC), single clusters catalysts (SCC), single-atom alloys (SAA), have proved their performance in various catalytic reactions due to their extremely high atom utilization efficiency, unique structure, and exceptional catalytic selectivity. A deep understanding and design of the active center of the catalyst at the atomic level has become a top priority for current research. Compared with SAC and SCC, SAA has its own uniqueness. In this review, we focused on the recent progress on the preparation methods of SAA and discussed the key factors controlling the structure of SAA. In addition, several important catalytic reactions performed over well-defined SAA are analyzed. Finally, the challenges and the perspectives of this cutting-edge field are suggested. We believe that this critical review provides a guidance for the rational design of SAA for catalytic applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Core-shell catalysts (mSiO 2 @MCM-NH 2 -OH) prove the confirmed to have –OH, –NH 2 /Br-. • Double HBD groups and Lewis base synergize to promote CO 2 cycloaddition reaction. • After 10 cycles of mSiO 2 @MCM-NH 2 -OH, the yield remained at 93%. • A synergistic catalysis mechanism was confirmed by theoretical calculations. In CO 2 cycloaddition reactions, hydrogen bond donor (HBD) groups are considered environmentally friendly substitutes for metals to promote epoxide ring-opening through interactions with nucleophilic anions. A core-shell structured ILs-based catalyst (mSiO 2 @MCM-NH 2 -OH) with dual hydrogen bond donors (–OH and –NH 2) was synthesized by copolymerization strategy. Through in-depth characterization, it has been demonstrated that the catalyst (mSiO 2 @MCM-NH 2 -OH) possesses multiple catalytic active sites including –OH, –NH 2 , Br- groups, and the synergistic effect of double HBD groups (–OH and –NH 2) and Lewis base (Br-) significantly improved the catalytic activity. Meanwhile, the core-shell structure of the catalyst effectively prevents the loss of active components, which makes the yield remain at about 94 % after 10 cycles. Based on Density Functional Theory (DFT) calculations, a synergistic catalytic mechanism, which involves dual hydrogen-bond donors (–OH and –NH 2) and Lewis bases (Br-) was proposed. The cooperative interaction between –OH/–NH 2 and Br- reduced the ring-opening barrier of epoxide from 58.6 to 32.0 kcal mol−1 significantly, and thereby facilitated the CO 2 cycloaddition reaction. [ABSTRACT FROM AUTHOR]

Review: 74 refs. [ABSTRACT FROM AUTHOR]

We have developed two strategies to optimize Pd catalysts. On one hand, Ag was introduced into Pd and then they were applied to the selective hydrogenation of citral under mild conditions. The addition of metallic Ag could tune the selectivity of Pd and made it suitable for the selective hydrogenation of the conjugated double bond. The selectivity of citronellal increased from 0 (for Pd/C and Pd0.7Ag0.3/C) to 96 % (for Pd0.4Ag0.6/C) as the Ag content increased. On the other hand, the addition of SnO2 made the Pd catalysts more inclined to activate the C=O bond and gave better performance for the hydrogenation of the conjugated double bond compared with the corresponding Pd-Ag catalysts. The selectivity of citronellal increased from 0 (for Pd0.7Ag0.3/C) to 76 % (for Pd0.7Ag0.3-SnO2/C was used) after the addition of SnO2. On the basis of these results, we developed a catalyst (Pd0.6Ag0.4-SnO2/C) with the best catalytic performance for the selective hydrogenation of citral (the conversion of citral reached 99 %, and the selectivity was up to 96 %). [ABSTRACT FROM AUTHOR]

Review: 90 refs. [ABSTRACT FROM AUTHOR]

Review: 50 refs. [ABSTRACT FROM AUTHOR]

Review: 150 refs. [ABSTRACT FROM AUTHOR]

The article presents chemical equations related to the article "Ligand-Free Hydroboration of Alkynes Catalyzed by Heterogeneous Copper Powder with High Efficiency" by J. Zhao and others published in the periodical "Chemical Communications" in 2014.

Octahedral Au-Ag nanoframes are prepared by reaction of AgNO3 with CuCl in octadecylamine solution at 115 °C, followed by dropwise addition of HAuCl4 solution (115 °C, 20 min). [ABSTRACT FROM AUTHOR]