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  • Control of interfacial acid–metal catalysis with organic monolayers
    Nat. Catal. Pub Date : 2018-01-15
    Jing Zhang, Lucas D. Ellis, Bingwen Wang, Michael J. Dzara, Carsten Sievers, Svitlana Pylypenko, Eranda Nikolla, J. Will Medlin

    Numerous important reactions consisting of combinations of steps (for example, hydrogenation and dehydration) have been found to require bifunctional catalysts with both a late-transition metal component and an acidic component. Here, we develop a method for preparing and controlling bifunctional sites by employing organic acid-functionalized monolayer films tethered to the support as an alternative to traditional ligand-on-metal strategies. This approach was used to create a reactive interface between the phosphonic acid monolayers and metal particles, where active-site properties such as acid strength were manipulated via tuning of the molecular structure of the organic ligands within the monolayer. After surface modification, the resultant catalysts exhibited markedly improved selectivity and activity towards hydrodeoxygenation of aromatic alcohols and phenolics. Moreover, by tuning the ligand of the acidic modifier, the rate of deactivation was significantly reduced.

  • Metal ion cycling of Cu foil for selective C–C coupling in electrochemical CO2 reduction
    Nat. Catal. Pub Date : 2018-01-15
    Kun Jiang, Robert B. Sandberg, Austin J. Akey, Xinyan Liu, David C. Bell, Jens K. Nørskov, Karen Chan, Haotian Wang

    Electrocatalytic CO2 reduction to higher-value hydrocarbons beyond C1 products is desirable for applications in energy storage, transportation and the chemical industry. Cu catalysts have shown the potential to catalyse C–C coupling for C2+ products, but still suffer from low selectivity in water. Here, we use density functional theory to determine the energetics of the initial C–C coupling steps on different Cu facets in CO2 reduction, and suggest that the Cu(100) and stepped (211) facets favour C2+ product formation over Cu(111). To demonstrate this, we report the tuning of facet exposure on Cu foil through the metal ion battery cycling method. Compared with the polished Cu foil, our 100-cycled Cu nanocube catalyst with exposed (100) facets presents a sixfold improvement in C2+ to C1 product ratio, with a highest C2+ Faradaic efficiency of over 60% and H2 below 20%, and a corresponding C2+ current of more than 40 mA cm–2.

  • Catalyst electro-redeposition controls morphology and oxidation state for selective carbon dioxide reduction
    Nat. Catal. Pub Date : 2018-01-15
    Phil De Luna, Rafael Quintero-Bermudez, Cao-Thang Dinh, Michael B. Ross, Oleksandr S. Bushuyev, Petar Todorović, Tom Regier, Shana O. Kelley, Peidong Yang, Edward H. Sargent

    The reduction of carbon dioxide to renewable fuels and feedstocks offers opportunities for large-scale, long-term energy storage. The synthesis of efficient CO2 reduction electrocatalysts with high C2:C1 selectivity remains a field of intense interest. Here we present electro-redeposition, the dissolution and redeposition of copper from a sol–gel, to enhance copper catalysts in terms of their morphology, oxidation state and consequent performance. We utilized in situ soft X-ray absorption spectroscopy to track the oxidation state of copper under CO2 reduction conditions with time resolution. The sol–gel material slows the electrochemical reduction of copper, enabling control over nanoscale morphology and the stabilization of Cu+ at negative potentials. CO2 reduction experiments, in situ X-ray spectroscopy and density functional theory simulations revealed the beneficial interplay between sharp morphologies and Cu+ oxidation state. The catalyst exhibits a partial ethylene current density of 160 mA cm–2 (−1.0 V versus reversible hydrogen electrode) and an ethylene/methane ratio of 200.

  • High-efficiency oxygen reduction to hydrogen peroxide catalysed by oxidized carbon materials
    Nat. Catal. Pub Date : 2018-01-15
    Zhiyi Lu, Guangxu Chen, Samira Siahrostami, Zhihua Chen, Kai Liu, Jin Xie, Lei Liao, Tong Wu, Dingchang Lin, Yayuan Liu, Thomas F. Jaramillo, Jens K. Nørskov, Yi Cui

    Hydrogen peroxide (H2O2) is a valuable chemical with a wide range of applications, but the current industrial synthesis of H2O2 involves an energy-intensive anthraquinone process. The electrochemical synthesis of H2O2 from oxygen reduction offers an alternative route for on-site applications; the efficiency of this process depends greatly on identifying cost-effective catalysts with high activity and selectivity. Here, we demonstrate a facile and general approach to catalyst development via the surface oxidation of abundant carbon materials to significantly enhance both the activity and selectivity (~90%) for H2O2 production by electrochemical oxygen reduction. We find that both the activity and selectivity are positively correlated with the oxygen content of the catalysts. The density functional theory calculations demonstrate that the carbon atoms adjacent to several oxygen functional groups (–COOH and C–O–C) are the active sites for oxygen reduction reaction via the two-electron pathway, which are further supported by a series of control experiments.

  • General synthesis and definitive structural identification of MN4C4 single-atom catalysts with tunable electrocatalytic activities
    Nat. Catal. Pub Date : 2018-01-08
    Huilong Fei, Juncai Dong, Yexin Feng, Christopher S. Allen, Chengzhang Wan, Boris Volosskiy, Mufan Li, Zipeng Zhao, Yiliu Wang, Hongtao Sun, Pengfei An, Wenxing Chen, Zhiying Guo, Chain Lee, Dongliang Chen, Imran Shakir, Mingjie Liu, Tiandou Hu, Yadong Li, Angus I. Kirkland, Xiangfeng Duan, Yu Huang

    Single-atom catalysts (SACs) have recently attracted broad research interest as they combine the merits of both homogeneous and heterogeneous catalysts. Rational design and synthesis of SACs are of immense significance but have so far been plagued by the lack of a definitive correlation between structure and catalytic properties. Here, we report a general approach to a series of monodispersed atomic transition metals (for example, Fe, Co, Ni) embedded in nitrogen-doped graphene with a common MN4C4 moiety, identified by systematic X-ray absorption fine structure analyses and direct transmission electron microscopy imaging. The unambiguous structure determination allows density functional theoretical prediction of MN4C4 moieties as efficient oxygen evolution catalysts with activities following the trend Ni > Co > Fe, which is confirmed by electrochemical measurements. Determination of atomistic structure and its correlation with catalytic properties represents a critical step towards the rational design and synthesis of precious or nonprecious SACs with exceptional atom utilization efficiency and catalytic activities.

  • Opportunities and challenges for combining chemo- and biocatalysis
    Nat. Catal. Pub Date : 2018-01-08
    Florian Rudroff, Marko D. Mihovilovic, Harald Gröger, Radka Snajdrova, Hans Iding, Uwe T. Bornscheuer

    The past decade has seen a substantial increase in successful examples of the combination of chemo- and biocatalysis for multistep syntheses. This is driven by obvious advantages such as higher yields, decreased costs, environmental benefits and high selectivity. On the downside, efforts must be undertaken to combine the divergent reaction conditions, reagent tolerance and solvent systems of these ‘different worlds of catalysis’. Owing to progress in enzyme discovery and engineering, as well as in the development of milder and more compatible conditions for operating with various chemocatalysts, many historical limitations can already be overcome. This Review highlights the opportunities available in the chemical space of combined syntheses using prominent examples, but also discusses the current challenges and emerging solutions, keeping in mind the fast progress in transition metal-, organo-, photo-, electro-, hetero- and biocatalysis.

  • Imine hydrogenation with simple alkaline earth metal catalysts
    Nat. Catal. Pub Date : 2018-01-08
    Heiko Bauer, Mercedes Alonso, Christian Färber, Holger Elsen, Jürgen Pahl, Andrea Causero, Gerd Ballmann, Frank De Proft, Sjoerd Harder

    Hydrogenation of unsaturated bonds is dominated by transition metal catalysis. Compared with transition metals, the use of other metals is less explored, especially so for the s-block elements despite their ready availability and low cost. Here, we show that group 2 metal amides (M[N(SiMe3)2]2, M = Mg, Ca, Sr, Ba) unexpectedly catalyse the hydrogenation of aldimines with H2 at 80 °C and a remarkably low H2 pressure of 1–6 bar. Conversion rates increase with metal size: Mg < Ca < Sr < Ba (for Ba, quantitative conversion is reached within 15 min). The key to this catalysis is the unanticipated formation of metal hydride species by deprotonation of H2 (pKa ≈ 49) with a weak base M[N(SiMe3)2]2 (HN(SiMe3)2: pKa ≈ 25.8). Density functional theory calculations suggest that the most favourable pathway indeed involves metal hydride intermediates. The efficient alkaline earth metal-catalysed hydrogenation of imines with molecular hydrogen at remarkably low pressure provides an attractive alternative to transition metal catalysis.

  • Catalysing water oxidation using nature’s metal
    Nat. Catal. Pub Date : 2018-01-08
    Gary W. Brudvig

    Catalysing water oxidation using nature’s metalCatalysing water oxidation using nature’s metal, Published online: 08 January 2018; doi:10.1038/s41929-017-0013-1In nature, a manganese catalyst is used for photosynthetic water oxidation, but efforts to develop artificial manganese-based counterparts have been hampered by the lability of manganese complexes. By using a bulky and hydrophilic ligand, a water-soluble Mn12 complex is found to be a stable and efficient water oxidation electrocatalyst.

Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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