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Inter-site interaction in densely populated single-atom catalysts has been demonstrated to have a crucial role in regulating the electronic structure of metal atoms, and consequently their catalytic performances. We herein report a general and facile strategy for the synthesis of several densely populated single-atom catalysts. Taking cobalt as an example, we further produce a series of Co single-atom catalysts with varying loadings to investigate the influence of density on regulating the electronic structure and catalytic performance in alkene epoxidation with O2. Interestingly, the turnover frequency and mass-specific activity are significantly enhanced by 10 times and 30 times with increasing Co loading from 5.4 wt% to 21.2 wt% in trans-stilbene epoxidation, respectively. Further theoretical studies reveal that the electronic structure of densely populated Co atoms is altered through charge redistribution, resulting in less Bader charger and higher d-band center, which are demonstrated to be more beneficial for the activation of O2 and trans-stilbene. The present study demonstrates a new finding about the site interaction in densely populated single-atom catalysts, shedding insight on how density affects the electronic structure and catalytic performance for alkene epoxidation. The interaction among single sites in densely populated single-atom catalysts (SACs) has received much attention. Here the authors report a general and facile strategy for the synthesis of several densely populated SACs and decipher the influence of density on regulating their electronic structure and catalytic performance in alkene epoxidation. [ABSTRACT FROM AUTHOR]

Olefin epoxidation plays an important role in chemical industry because of the significance of epoxides. Developing cost‐effective catalysts with high catalytic performance for epoxidation is of great importance. Herein, we report a promising heterogeneous catalyst based on Co3O4 nanoparticles encapsulated in the inside wall of a meso‐SiO2 shell (denoted as Co3O4@meso‐SiO2) as hollow nanoreactor. Due to the particular hollow structure as well as mesoporous shell wall, the resulting catalyst showed excellent activity and recyclability for various olefins with molecular oxygen and iso‐butyraldehyde as co‐oxidants. [ABSTRACT FROM AUTHOR]

In oxidation reactions with oxygen as oxidant, low O2 concentration on catalyst surface under ambient pressure is a major kinetic limitation for selective oxidation of olefins; while increasing O2 pressure to enhance the reaction rate suffers lower selectivity due to thermodynamic factors. In this study, we demonstrate that simultaneous enhancement of conversion and selectivity can be achieved under ambient pressure by solid/liquid/gas three‐phase interface design. We produced Au nanoparticles supported on graphene aerogel with superaerophilic surface (denoted as Au/GA) as the catalyst for demonstration. The results show that O2 gas shows "bursting" behavior on the surface of Au/GA under water, resulting in rapid adsorbing of O2 in 98 ms and therefore high O2 concentration on the surface of catalyst. Thus, solid/liquid/gas three‐phase interface is formed under this condition, leading to high conversion as well as high selectivity at ambient O2 pressure. Such strategy is expected to find wide applications in many other selective oxidation reactions that traditionally needed high pressure. [ABSTRACT FROM AUTHOR]

A series of active-carbon-supported PdPb and PdCu bimetal catalysts were prepared for the selective semihydrogenation of alkynes in the liquid phase. The Pd0.33Pb0.67/C catalyst showed the best performance for various alkynes under mild reaction conditions (room temperature and ambient H2 pressure) and achieved 100 % conversion with 98 % selectivity to alkenes. In particular, over-hydrogenation was avoided at complete alkyne conversion. [ABSTRACT FROM AUTHOR]

Encapsulation of surfactant-free Pd nanoparticles (NPs) in the metal-organic framework material ZIF-8 hollow nanospheres was achieved. Pd@ZIF-8 hollow nanospheres showed excellent size-selective catalytic properties in the liquid-phase hydrogenation of olefins. As a result of the uniform pore size of the ZIF-8 shell (apertures of 3.4 Å), the catalyst showed high activity for the hydrogenation of 1-hexene (1.9×8.2 Å) but very low activity for larger molecules such as cis-cyclooctene (5.3×5.5 Å), trans-stilbene (4.2×11.3 Å), and triphenylethylene (9.1×9.2 Å). Other surfactant-free noble-metal nanoparticles could also be employed to produce NPs@MOFs for catalysis. [ABSTRACT FROM AUTHOR]

Metal-free heteroatom-doped carbocatalysts with a high surface area are desirable for catalytic reactions. In this study, we found an efficient strategy to prepare nitrogen, phosphorus, and sulfur co-doped hollow carbon shells (denote as NPS-HCS) with a surface area of 1020 m2 g−1. Using a poly(cyclotriphosphazene- co-4,4′-sulfonyldiphenol) (PZS) shell as carbon source and N, P, S-doping source, and the ZIF-67 core as structural template as well as extra N-doping source, NPS-HCS were obtained with a high surface area and superhydrophilicity. All these features render the prepared NPS-HCS a superior metal-free carbocatalyst for the selective oxidation of aromatic alkanes in aqueous solution. This study provides a reliable and facile route to prepare doped carbocatalysts with enhanced catalytic properties. [ABSTRACT FROM AUTHOR]