Showing papers by "Cheng Wang published in 2019"
01 Aug 2019
TL;DR: In this article, a Zr12 cluster-based metal-organic framework was proposed to catalyse CO2 hydrogenation to ethanol with remarkable selectivity upon promotion with caesium.
Abstract: Selective conversion of CO2 to ethanol is of great interest but presents a significant challenge in forming a C–C bond while keeping a C–O bond intact throughout the process. Here, we report cooperative CuI sites on a Zr12 cluster of a metal–organic framework (MOF) for selective hydrogenation of CO2 to ethanol. With the assistance of an alkali cation, the spatially proximate Zr12-supported CuI centres activate hydrogen via bimetallic oxidative addition and promote C–C coupling to produce ethanol. The Cs+-modified MOF catalyst, in 10 hours, produces ethanol with >99% selectivity and a turnover number (based on all Cu atoms) of 4,080 in supercritical CO2, with 30 MPa of CO2 and 5 MPa of H2 at 85 °C, or a turnover number of 490 at 2 MPa of CO2/H2 (1/3) and 100 °C. Our work highlights the potential of using MOFs as a tunable platform to design earth-abundant metal catalysts for CO2 conversion. The synthesis of ethanol via CO2 hydrogenation is a challenging process, often hampered by low selectivity. This work reports a Zr12 cluster-based metal–organic framework as support for cooperative Cu(i) sites that catalyse CO2 hydrogenation to ethanol with remarkable selectivity upon promotion with caesium. Credit: Cloud background, CC0 1.0 Universal Public Domain Dedication.
218 citations
TL;DR: In this article, the authors proposed a heterogeneous catalysts based on metal-organic frameworks (MOFs) for the first time, and demonstrated that the well-defined structure of these molecular materials enables the creation of high-quality catalysts.
Abstract: Heterogeneous catalysts based on metal–organic frameworks (MOFs) have attracted significant attention in the past two decades. The well-defined structure of these molecular materials enables the ra...
203 citations
TL;DR: ZrOTf-BTC was shown to be a highly active solid Lewis acid catalyst for a broad range of important organic transformations under mild conditions, including Diels-Alder reaction, epoxide ring-opening reaction, Friedel-Crafts acylation, and alkene hydroalkoxylation reaction.
Abstract: The synthesis of highly acidic metal–organic frameworks (MOFs) has attracted significant research interest in recent years. We report here the design of a strongly Lewis acidic MOF, ZrOTf-BTC, thro...
102 citations
TL;DR: Cooperative cobalt-protoporphyrin (CoPP) and pyridinium (pyH+) catalytic sites on metal-organic layers (MOLs) for electrocatalytic CO2 reduction reaction (CO2RR) and a high CO/H2 selectivity of 11.8.
Abstract: Pyridinium has been shown to be a cocatalyst for the electrochemical reduction of CO2 on metal and semiconductor electrodes, but its exact role has been difficult to elucidate. In this work, we create cooperative cobalt-protoporphyrin (CoPP) and pyridine/pyridinium (py/pyH+) catalytic sites on metal-organic layers (MOLs) for an electrocatalytic CO2 reduction reaction (CO2RR). Constructed from [Hf6(μ3-O)4(μ3-OH)4(HCO2)6] secondary building units (SBUs) and terpyridine-based tricarboxylate ligands, the MOL was postsynthetically functionalized with CoPP via carboxylate exchange with formate capping groups. The CoPP group and the pyridinium (pyH+) moiety on the MOL coactivate CO2 by forming the [pyH+--O2C-CoPP] adduct, which enhances the CO2RR and suppresses hydrogen evolution to afford a high CO/H2 selectivity of 11.8. Cooperative stabilization of the [pyH+--O2C-CoPP] intermediate led to a catalytic current density of 1314 mA/mgCo for CO production at -0.86 VRHE, which corresponds to a turnover frequency of 0.4 s-1.
94 citations
TL;DR: Density functional theory calculations reveal key steps of HER via protonation of TiIII-OH to generate the TiIII species with a vacant coordination site followed by proton-coupled electron transfer to afford the key TiIV-H intermediate.
Abstract: Herein we report the design of two new titanium metal–organic frameworks (MOFs), Ti3-BPDC-Ir and Ti3-BPDC-Ru, by doping [Ir(ppy)2(dcbpy)]Cl or [Ru(bpy)2(dcbpy)]Cl2 (bpy = 2,2′-bipyridine, ppy = 2-p...
77 citations
TL;DR: Metal-organic frameworks are used to stabilize low-coordinate Ir complexes for highly active methane borylation to afford the monoborylated product and a MOF-based catalyst design holds promise in addressing challenging catalytic reactions involving highly inert substrates.
Abstract: Catalytic borylation has recently been suggested as a potential strategy to convert abundant methane to fine chemicals. However, synthetic utility of methane borylation necessitates significant improvement of catalytic activities over original phenanthroline- and diphosphine-Ir complexes. Herein, we report the use of metal-organic frameworks (MOFs) to stabilize low-coordinate Ir complexes for highly active methane borylation to afford the monoborylated product. The mono(phosphine)-Ir based MOF, Zr-P1-Ir, significantly outperformed other Ir catalysts in methane borylation to afford CH3Bpin with a turnover number of 127 at 110 °C. Density functional theory calculations indicated a significant reduction of activation barrier for the rate limiting oxidative addition of methane to the four-coordinate (P1)IrIII(Bpin)3 catalyst to form the six-coordinate (P1)IrV(Bpin)3(CH3)(H) intermediate, thus avoiding the formation of sterically encumbered seven-coordinate IrV intermediates as found in other Ir catalysts based on chelating phenanthroline, bipyridine, and diphosphine ligands. MOF thus stabilizes the homogeneously inaccessible, low-coordinate (P1)Ir(boryl)3 catalyst to provide a unique strategy to significantly lower the activation barrier for methane borylation. This MOF-based catalyst design holds promise in addressing challenging catalytic reactions involving highly inert substrates.
55 citations
TL;DR: In this paper, the authors report that the Ti8-BDC (MIL-125) (BDC is 1,4-benzenecarboxylate) metal-organic framework supports single-site solid NiII-hydride catalyst for the hydrogenolysis of aryl ethers.
Abstract: Herein we report that the Ti8-BDC (MIL-125) (BDC is 1,4-benzenecarboxylate) metal–organic framework (MOF) supports single-site solid NiII-hydride catalyst for the hydrogenolysis of aryl ethers cont...
55 citations
TL;DR: The authors are able to synthesize and characterize stable molecular bilayer graphenes by the π−π stacking of two identical, well-defined nanographene sheets.
Abstract: Bilayer graphene consists of two stacked graphene layers bound together by van der Waals interaction. As the molecular analog of bilayer graphene, molecular bilayer graphene (MBLG) can offer useful insights into the structural and functional properties of bilayer graphene. However, synthesis of MBLG, which requires discrete assembly of two graphene fragments, has proved to be challenging. Here, we show the synthesis and characterization of two structurally well-defined MBLGs, both consisting of two π-π stacked nanographene sheets. We find they have excellent stability against variation of concentration, temperature and solvents. The MBLGs show sharp absorption and emission peaks, and further time-resolved spectroscopic studies reveal drastically different lifetimes for the bright and dark Davydov states in these MBLGs.
43 citations
TL;DR: The intrinsic heterogeneity of alumina surface presents a challenge for the development of single-site heterogeneous catalysts and hinders the characterization of catalyti... as mentioned in this paper, where the authors propose an approach to overcome this issue.
Abstract: The intrinsic heterogeneity of alumina (Al2O3) surface presents a challenge for the development of alumina-supported single-site heterogeneous catalysts and hinders the characterization of catalyti...
39 citations
TL;DR: The synthesis of a robust Ti–MOF with novel SBUs and its use as oxo ligands to chelate Co-hydrides for cascade reduction of N-heteroarenes is reported.
Abstract: We report here a novel Ti3–BPDC metal–organic framework (MOF) constructed from biphenyl-4,4′-dicarboxylate (BPDC) linkers and Ti3(OH)2 secondary building units (SBUs) with permanent porosity and large 1D channels. Ti–OH groups from neighboring SBUs point toward each other with an O–O distance of 2 A, and upon deprotonation, act as the first bidentate SBU-based ligands to support CoII-hydride species for effective cascade reduction of N-heteroarenes (such as pyridines and quinolines) via sequential dearomative hydroboration and hydrogenation, affording piperidine and 1,2,3,4-tetrahydroquinoline derivatives with excellent activity (turnover number ∼ 1980) and chemoselectivity.
34 citations
TL;DR: The observations of Shubnikov-de Hass oscillations and quantum Hall states, together with the angular dependence of magnetotransport measurements, provide the evidence for the 2D nature of electronic states in InSb nanosheet.
Abstract: Low-dimensional narrow band gap III-V compound semiconductors, such as InAs and InSb, have attracted much attention as one of promising platforms for studying Majorana zero modes and non-Abelian statistics relevant for topological quantum computation. So far, most of experimental studies were performed on hybrid devices based on one-dimensional semiconductor nanowires. In order to build complex topological circuits toward scalable quantum computing, exploring high-mobility two-dimensional (2D) III-V compound electron system with strong spin-orbit coupling is highly desirable. Here, we study quantum transport in high-mobility InSb nanosheet grown by molecular-beam epitaxy. The observations of Shubnikov-de Hass oscillations and quantum Hall states, together with the angular dependence of magnetotransport measurements, provide the evidence for the 2D nature of electronic states in InSb nanosheet. The presence of strong spin-orbit coupling in the InSb nanosheet is verified by the low-field magnetotransport measurements, characterized by weak antilocalization effect. Finally, we demonstrate the realization of high-quality InSb nanosheet-superconductor junctions with transparent interface. Our results not only advance the study of 2D quantum transport but also open up opportunities for developing hybrid topological devices based on 2D semiconducting nanosheets with strong spin-orbit coupling.
TL;DR: This work presents a non-fullerene OSC device utilizing PBDB-T:i-IEICO-4F blend, fabricated by slot-die coating without post treatment in the ambient conditions, which showed an impressive PCE of 12.5%, which is one of the highest reported performance for slot- die coated OSC devices.
Abstract: The power conversion efficiencies (PCEs) of spin-coated organic solar cells (OSCs) have increased rapidly in recent years. However, spin-coating shows poor reproducibility for large-scale production. Slot-die coating, a lab-scale version of roll-to-roll fabrication, has been considered as the most suitable technique for the production of future large-area commercial devices. For this, the highly efficient slot-die-fabricated devices are required to approach the performance of spin-cast OSCs. We present here, a nonfullerene OSC device utilizing the PBDB-T/i-IEICO-4F blend, fabricated by slot-die coating without post-treatment in the ambient conditions. The device showed an impressive PCE of 12.5%, which is one of the highest reported performance for slot-die-coated OSC devices. Compared to the spin-coated and blade-coated films with optimized thermal annealing time, the films fabricated by slot-die coating (without any treatment) exhibit not only the highest degree of crystallinity and face-on orientation but also the smallest domain size and the purest phase toward enhanced and balanced carrier mobilities. An enhanced excited-state charge generation has been attributed to transient charge kinetics using ultrafast spectroscopic signatures. The optimized slot-die-coated devices exhibit excellent tolerance for the increased thickness of the photoactive layer, attributing to favorable molecular packing. We used slot-die coating as a simple fabrication technique, which is capable of yielding highly efficient OSCs.
TL;DR: Excited state energies on a two-dimensional light-harvesting metal-organic layer (MOL) are efficiently transported to Re- and Ir-based reaction centers for converting CO2 to CO or HCOOH and enhances the photocatalytic CO2 reduction activity.
TL;DR: This work used aberration-corrected scanning transmission electron microscopy combined with electrical measurements to study the GB characteristic of highly crystalline 2D Mo2C superconductor, a newly emerging member of the 2D TMC family, and found two new periodic GBs with different periodic structures and crystallographic orientations.
Abstract: The grain boundaries (GBs) of graphene and molybdenum disulfide have been extensively demonstrated to have a strong influence on electronic, thermal, optical, and mechanical properties. 2D transition-metal carbides (TMCs), known as MXenes, are a rapidly growing new family of 2D materials with many fascinating properties and promising applications. However, the GB structure of 2D TMCs and the influence of GB on their properties remain unknown. Here, we used aberration-corrected scanning transmission electron microscopy combined with electrical measurements to study the GB characteristic of highly crystalline 2D Mo2C superconductor, a newly emerging member of the 2D TMC family. The 2D Mo2C superconductor shows a unique tilt-angle-dependent GB structure and electronic transport properties. Different from the reported 2D materials, the GB of 2D Mo2C shows a peculiar dislocation configuration or sawtooth pattern depending on the tilt angle. More importantly, we found two new periodic GBs with different periodi...
TL;DR: Electrochemical acceptorless dehydrogenation of N-heterocycles to obtain quinoline or indole derivatives using metal-organic layer (MOL) catalyst to overcome the conductivity constraint for MOFs in electrocatalysis.
Abstract: The catalytic acceptorless dehydrogenation (CAD) is an attractive synthetic route to unsaturated compounds because of its high atomic efficiency. Here we report electrochemical acceptorless dehydrogenation of N-heterocycles to obtain quinoline or indole derivatives using metal-organic layer (MOL) catalyst. MOL is the two-dimensional version of metal-organic frameworks (MOF), and it can be constructed on conductive multi-walled carbon nanotubes via facile solvothermal synthesis to overcome the conductivity constraint for MOFs in electrocatalysis. TEMPO-OPO32- was incorporated into the system through a ligand exchange with capping formate on the MOL surface to serve as the active catalytic centers. The hybrid catalyst is efficient in the organic conversion and can be readily recycled and reused.
TL;DR: In this article, a mono-alkyl pyrocarbonate-bipyridinium salt intermediate was used to activate CO2 for synthesizing ethyl formate as a value-added product via tandem esterification and hydrogenation.
22 Mar 2019
TL;DR: In this paper, the magnetic field dependence of activation energy barrier exhibits an enhancement at low fields, indicating a dimensional crossover from 2D to 1D vortex states in Mo2C crystals.
Abstract: Understanding of superconducting phase and vortex states in two-dimensional (2D) superconductors is fundamentally and technologically important. Here we report on low-temperature transport measurements on high-quality ultrathin superconducting Mo2C crystals containing well-defined line-shaped domain boundaries. We observe pronounced two-stage resistive transition accompanied by an appearance of kink structure well below the superconducting transition temperature, which is related to the development of one dimensional (1D) superconducting phase within the domain boundaries. The resistive transition under the magnetic fields is found to be well described by the thermally assisted collective flux creep model. The magnetic field dependence of activation energy barrier exhibits an enhancement at low fields, indicating a dimensional crossover from 2D to 1D vortex states in Mo2C crystals. We obtain the entire magnetic field-temperature phase diagram of ultrathin Mo2C crystals, revealing the existence of additional 1D vortex state induced by the domain boundaries. Our results demonstrate that the domain structures play an important role in determining the superconducting phase and vortex dynamics of 2D superconductors.
TL;DR: In this paper, the isothermal sections of the Al-Sn-Co ternary system at 800°C and 1000°C were constructed by twentynine key samples and two solid-liquid diffusion couples using electron probe microanalysis and x-ray diffraction analysis.
Abstract: The isothermal sections of the Al-Sn-Co ternary system at 800 °C and 1000 °C were constructed by twenty-nine key samples and two solid–liquid diffusion couples using electron probe microanalysis and x-ray diffraction analysis. The results show that: (1) No ternary intermetallic compound was found in this ternary system at 800 °C and 1000 °C. (2) The solid solubility of Sn in the Al-Co binary compounds is very small. (3) As-cast Al47Sn47Co6, Al46Sn46Co8 and Al45Sn45Co10 (at.%) alloys exhibit the separated macroscopic morphologies. The reason is that the addition of Co can significantly promote the metastable liquid-phase separation in Al-Sn binary system. The newly determined phase equilibria may contribute to thermodynamic assessment and development of Al-based alloys.
TL;DR: In this article, the interdiffusion coefficients were calculated to critically assess the atomic mobilities by means of DICTRA software package, and the results showed that the calculated and experimental diffusion coefficients could well reproduce the experimental data.
Abstract: Ternary fcc Ni-Mo-Ta diffusion couples annealed at 1473 and 1573 K have been studied by using electron probe microanalysis. Based on the measured concentration-distance profiles and Whittle–Green method, the interdiffusion coefficients were calculated to critically assess the atomic mobilities by means of DICTRA software package. Comprehensive comparisons between calculated and experimental diffusion coefficients show that the atomic mobilities obtained in this work could well reproduce the experimental data. Reasonable agreements between model-predicted diffusion properties and the experimental data indicated that present mobility database can be used to study the diffusion behavior, such as diffusion paths and concentration-distance profiles in the ternary fcc Ni-Mo-Ta alloys.