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1. Asymmetric Active Sites for Boosting Oxygen Evolution Reaction

   https://doi.org/10.1002/smll.202304108  

   Han, Linkai ; Yu, Haifeng ; Xiang, Zhonghua ( June 2023 , Small)

   Transition metal‐nitrogen‐carbon materials with atomically dispersed active sites are promising catalysts for oxygen evolution reaction (OER) since they combine the strengths of both homogeneous and heterogeneous catalysts. However, the canonically symmetric active site usually exhibits poor OER intrinsic activity due to its excessively strong or weak oxygen species adsorption. Here, a catalyst with asymmetric MN₄sites based on the 3‐s‐triazine of g‐C₃N₄(termed as a‐MN₄@NC) is proposed. Compared to symmetric, the asymmetric active sites directly modulate the oxygen species adsorption via unifying planar and axial orbitals (dx²‐y², dz²), thus enabling higher OER intrinsic activity. In Silico screening suggested that cobalt has the best OER activity among familiar nonprecious transition metal. These experimental results suggest that the intrinsic activity of asymmetric active sites (179 mV overpotential at onset potential) is enhanced by 48.4% compared to symmetric under similar conditions. Remarkably, a‐CoN₄@NC showed excellent activity in alkaline water electrolyzer (AWE) device as OER catalyst, the electrolyzer only required 1.7 V and 2.1 V respectively to reach the current density of 150 mA cm⁻²and 500 mA cm⁻². This work opens an avenue for modulating the active sites to obtain high intrinsic electrocatalytic performance including, but not limited to, OER.

    

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2. Understanding Support Effects of ZnO‐Promoted Co Catalysts for Syngas Conversion to Alcohols Using Atomic Layer Deposition

   https://doi.org/10.1002/cctc.202001630  

   Nathan, Sindhu S. ; Asundi, Arun S. ; Singh, Joseph A. ; Hoffman, Adam S. ; Boubnov, Alexey ; Hong, Jiyun ; Bare, Simon R. ; Bent, Stacey F. ( December 2020 , ChemCatChem)

   Co₂C, an emerging catalyst for the conversion of syngas to oxygenates, shows support‐sensitive behavior that has not yet been fully explained. Here, we characterize Co catalysts modified with ZnO atomic layer deposition on SiO₂, carbon, CeO₂, and Al₂O₃supports. We find that under syngas conditions, ZnO‐promoted Co transforms into Co₂C on SiO₂, carbon, and CeO₂, but not on Al₂O₃. Moreover, the support affects the extent of carburization: while the SiO₂‐supported catalyst carburizes completely, carbon‐ and CeO₂‐supported catalysts show incomplete conversion of Co to Co₂C. These three catalysts also exhibit different oxygenate selectivities. In contrast, the modified Al₂O₃‐supported catalyst retains the Fischer‐Tropsch catalytic properties of metallic Co. By depositing increasing amounts of Al₂O₃by ALD on the SiO₂support, decreasing Co₂C formation and oxygenate selectivity occurs.In‐situXANES reveals that Al₂O₃prevents Co₂C formation by enabling the ZnO to restructure into ZnAl₂O₄during reduction. Thus, in addition to modifying the active catalyst phase, the promoter can also strongly interact with the support, significantly impacting catalyst performance.

    

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3. Highly Active and Stable Single Atom Rh 1 /CeO 2 Catalyst for CO Oxidation during Redox Cycling

   https://doi.org/10.1002/cctc.202201210  

   García‐Vargas, Carlos E. ; Pereira‐Hernández, Xavier Isidro ; Jiang, Dong ; Alcala, Ryan ; DeLaRiva, Andrew T. ; Datye, Abhaya ; Wang, Yong ( January 2023 , ChemCatChem)

   We report a single atom Rh₁/CeO₂catalyst prepared by the high temperature (800 °C) atom trapping (AT) method which is stable under both oxidative and reductive conditions. Infrared spectroscopic and electron microscopy characterization revealed the presence of exclusively ionic Rh species. These ionic Rh species are stable even under reducing conditions (CO at 300 °C) due to the strong interaction between Rh and CeO₂achieved by the AT method, leading to high and reproducible CO oxidation activity regardless of whether the catalyst is reduced or oxidized. In contrast, ionic Rh species in catalysts synthesized by a conventional impregnation approach (e. g., calcined at 350 °C) can be readily reduced to form Rh nanoclusters/nanoparticles, which are easily oxidized under oxidative conditions, leading to loss of catalytic performance. The single atom Rh₁/CeO₂catalysts synthesized by the AT method do not exhibit changes during redox cycling hence are promising catalysts for emission control where redox cycling is encountered, and severe oxidation (fuel cut) leads to loss of performance.

    

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4. Influence of Aryl Substituents on the Alignment of Ligands in the Dirhodium Tetrakis(1,2,2‐Triarylcyclopropane‐ carboxylate) Catalysts

   https://doi.org/10.1002/cctc.202001206  

   Ren, Zhi ; Musaev, Djamaladdin G. ; Davies, Huw M. L. ( September 2020 , ChemCatChem)

   Computational studies revealed that dirhodium tetrakis(1,2,2‐triarylcyclopropanecarboxylate) (Rh₂(TPCP)₄) catalysts adopt distinctive high symmetry orientations, which are dependent on the nature of the aryl substitution pattern. The parent catalyst, Rh₂(TPCP)₄, and those with ap‐substituent at the C1 aryl, such as Rh₂(p‐BrTPCP)₄and Rh₂(p‐PhTPCP)₄, adopt aC₂‐symmetric structure. Rh₂(3,5‐di(p‐^tBuC₆H₄)TPCP)₄, 3,5‐disubstituted at the C1 aryl, adopts aD₂‐symmetric structure, whereas catalysts with ano‐substituent at the C1 aryl, such as Rh₂(o‐Cl‐5‐BrTPCP)_4,adopt aC₄‐symmetric structure.

    

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5. Aluminum‐Ligand Cooperative O−H Bond Activation Initiates Catalytic Transfer Hydrogenation

   https://doi.org/10.1002/cctc.202101869  

   Carr, Cody R. ; Vesto, James I. ; Xing, Xiujing ; Fettinger, James C. ; Berben, Louise A. ( April 2022 , ChemCatChem)

   Molecular design ultimately furnishes improvements in performance over time, and this has been the case for Rh‐ and Ir‐based molecular catalysts currently used in transfer hydrogenation (TH) reactions for fine chemical synthesis. In this report, we describe a molecular pincer ligand Al catalyst for TH, (I₂P²⁻)Al(THF)Cl (I₂P=diiminopyridine; THF=tetrahydrofuran). The mechanism for TH is initiated by two successive Al‐ligand cooperative bond activations of the O−H bonds in two molecules of isopropanol (ⁱPrOH) to afford six‐coordinate (H₂I₂P)Al(OⁱPr)₂Cl. Stoichiometric chemical reactions and kinetic experiments suggest an ordered transition state, supported by polar solvents, for concerted hydride transfer fromⁱPrO⁻to substrate. Metal‐ligand cooperative hydrogen bonding in a cyclic transition state is a likely support for the concerted hydride transfer event. The available data does not support involvement of an intermediate Al‐hydride in the TH. Proof‐of‐principle reactions including the conversion of isopropanol and benzophenone to acetone and diphenylmethanol with 90 % conversion in 1 h are described. The analogous hydride compound, (I₂P²⁻)Al(THF)H, also cleaves the O−H bond inⁱPrOH to afford (HI₂P⁻)Al(OⁱPr)H and (HI₂P⁻)Al(OⁱPr)₂, but no activity for catalytic TH was observed.

    

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