Showing papers by "Cheng Wang published in 2016"
TL;DR: This work uncovers an entirely new strategy for designing single-site solid catalysts and opens the door to a new class of two-dimensional coordination materials with molecular functionalities.
Abstract: Metal-organic layers (MOLs) represent an emerging class of tunable and functionalizable two-dimensional materials. In this work, the scalable solvothermal synthesis of self-supporting MOLs composed of [Hf6O4(OH)4(HCO2)6] secondary building units (SBUs) and benzene-1,3,5-tribenzoate (BTB) bridging ligands is reported. The MOL structures were directly imaged by TEM and AFM, and doped with 4'-(4-benzoate)-(2,2',2''-terpyridine)-5,5''-dicarboxylate (TPY) before being coordinated with iron centers to afford highly active and reusable single-site solid catalysts for the hydrosilylation of terminal olefins. MOL-based heterogeneous catalysts are free from the diffusional constraints placed on all known porous solid catalysts, including metal-organic frameworks. This work uncovers an entirely new strategy for designing single-site solid catalysts and opens the door to a new class of two-dimensional coordination materials with molecular functionalities.
267 citations
TL;DR: In this article, a Fischer-Tropsch (FT) catalyst with a unique iron oxide@iron carbide core-shell structure dispersed on carbon supports was used for FT synthesis.
Abstract: We prepared highly active catalysts for Fischer–Tropsch (FT) synthesis through the pyrolysis of iron-containing metal–organic frameworks (MOFs). The Fe-time yields of the nitrogen-doped catalyst were as high as 720 μmolCO gFe–1 s–1 under the conditions of 300 °C, 2 MPa, and H2/CO = 1, which is a value that surpasses that of most FT catalysts reported in the literature. The pyrolysis of the MOFs yielded nanoparticles with a unique iron oxide@iron carbide core–shell structure dispersed on carbon supports. Such a structure is favorable for FT synthesis and has never been reported previously. Our strategy resolved the problem that the strong metal–support interactions that are usually required to stabilize dispersed particles in calcination compromise the catalytic activity, because of the difficulty of reducing metal oxides. Moreover, we found full coverage of carbonates on the particle surfaces, which likely result from decarboxylation of the MOFs and further stabilize the particles before decomposing to CO...
128 citations
TL;DR: Metal-organic frameworks with light-harvesting building blocks designed to mimic photosynthetic chromophore arrays in green plants provide an excellent platform to study exciton transport in networks with well-defined structures and "Through space" energy-jumping beyond nearest neighbor accounts for up to 67% of the energy transfer rates.
Abstract: Metal–organic frameworks (MOFs) with light-harvesting building blocks designed to mimic photosynthetic chromophore arrays in green plants provide an excellent platform to study exciton transport in networks with well-defined structures. A step-by-step exciton random hopping model made of the elementary steps of energy transfer between only the nearest neighbors is usually used to describe the transport dynamics. Although such a nearest neighbor approximation is valid in describing the energy transfer of triplet states via the Dexter mechanism, we found it inadequate in evaluating singlet exciton migration that occurs through the Forster mechanism, which involves one-step jumping over longer distance. We measured migration rates of singlet excitons on two MOFs constructed from truxene-derived ligands and zinc nodes, by monitoring energy transfer from the MOF skeleton to a coumarin probe in the MOF cavity. The diffusivities of the excitons on the frameworks were determined to be 1.8 × 10–2 cm2/s and 2.3 × 1...
122 citations
TL;DR: The recyclable and reusable MOF catalysts significantly outperformed their homogeneous counterparts, presumably via stabilizing M-PR3 intermediates by preventing deleterious disproportionation reactions/ligand exchanges in the catalytic cycles.
Abstract: Mono(phosphine)–M (M–PR3; M = Rh and Ir) complexes selectively prepared by postsynthetic metalation of a porous triarylphosphine-based metal–organic framework (MOF) exhibited excellent activity in the hydrosilylation of ketones and alkenes, the hydrogenation of alkenes, and the C–H borylation of arenes. The recyclable and reusable MOF catalysts significantly outperformed their homogeneous counterparts, presumably via stabilizing M–PR3 intermediates by preventing deleterious disproportionation reactions/ligand exchanges in the catalytic cycles.
93 citations
TL;DR: In this paper, a metal-organic framework based on (bpy)Re(CO)3Cl-containing elongated dicarboxylate ligands and Zr6(µ3-O)4 (µ 3-OH)4 clusters was synthesized and used as an effective single-site catalyst to photochemically reduce carbon dioxide to carbon monoxide and formate.
Abstract: A metal–organic framework (MOF) based on (bpy)Re(CO)3Cl-containing elongated dicarboxylate ligands and Zr6(µ3-O)4(µ3-OH)4 clusters was synthesized and used as an effective single-site catalyst to photochemically reduce carbon dioxide to carbon monoxide and formate and to provide mechanistic insights into the photocatalytic CO2 reduction process.
70 citations
TL;DR: In this paper, the first synthesis of sulfurated porous carbon materials with well-defined morphologies and uniform N/S distributions via pyrolysis of zeolitic imidazolate frameworks loaded with sulfur-containing molecules was reported.
Abstract: We report the first synthesis of sulfurated porous carbon materials with well-defined morphologies and uniform N/S distributions via pyrolysis of zeolitic imidazolate frameworks loaded with sulfur-containing molecules. The optimized sulfurated catalyst demonstrates excellent electrocatalytic activity for the oxygen reduction reaction (ORR) in both acid and alkaline media. The sulfurization process under optimized conditions can lower the ORR over-potential by ca. 170 mV at 3 mA cm−2, giving a non-precious metal catalyst with an onset ORR potential of 0.90 V (vs. RHE, similarly hereinafter)/half-wave potential of 0.78 V in 0.1 M HClO4 and an onset ORR potential of 0.98 V/half-wave potential of 0.88 V in 0.1 M KOH. Furthermore, the S-doped porous carbon materials perform better in the long-term durability test than the non-S-doped samples and standard commercially available Pt/C. We also discuss different sulfuration methods for the ZIF system, morphologies of pyrolyzed samples, and catalytically active sites.
60 citations
TL;DR: It is found that the nearest-neighbor solute-vacancy binding energies and activation energies are roughly inversely proportional to the volume changes induced by solute atoms, and two other key factors governing solute diffusion in dilute α-Ti are clarified: the chemical bonding characteristics and vibrational features of X-Ti pairs.
Abstract: Using first-principles calculations accompanied by the transition state theory and an 8-frequency model, we present a comprehensive investigation of the diffusion coefficients of substitutional alloying elements X in dilute α-Ti alloys, where X denotes Al, V, Nb, Ta, Mo, Zr, and Sn. The alloying elements Mo and Al exhibit a maximum and a minimum diffusion rate in dilute α-Ti alloys, respectively. It is found that the nearest-neighbor solute–vacancy binding energies and activation energies are roughly inversely proportional to the volume changes induced by solute atoms. There are two exceptions to this trend: Al and Mo. Besides the physical effect (i.e., solute size), two other key factors governing solute diffusion in dilute α-Ti are clarified: the chemical bonding characteristics and vibrational features of X–Ti pairs. It verifies that the ultrafast diffusivity of Mo arises from the interactions with Ti atoms by metallic bonds and its low-frequency contributions to lattice vibration, while the more covalent bonding nature and the high-frequency contributions to the lattice vibration of Al lead to its ultraslow diffusivity. In addition, the correlation effects of diffusion coefficients are non-negligible for the large solutes Ta, Nb, and Zr, in which the direct solute–vacancy migration barriers are much smaller than the solvent–vacancy migration barriers.
37 citations
TL;DR: Two mechanisms of glass formation are proposed: (i) kinetic retardation of atom rearrangement or structural relaxation at a high cooling rate; and (ii) competition of icosahedral order against crystal order near the critical cooling rate.
Abstract: This work aims to achieve deep insight into the phenomenon of phase transformation upon rapid cooling in metal systems and reveal the physical meaning of scatter in the time taken to reach crystallization. The total number of pure metals considered in this work accounts for 14. Taking pure copper as an example, the correlation between phase selection of crystal or glass and cooling rate was investigated using molecular dynamic simulations. The obtained results demonstrate that there exists a cooling rate region of 6.3 × 1011–16.6 × 1011 K/s, in which crystalline fractions largely fluctuate along with cooling rates. Glass transformation in this cooling rate region is determined by atomic structure fluctuation, which is controlled by thermodynamic factors. According to the feature of bond-orientation order at different cooling rates, we propose two mechanisms of glass formation: (i) kinetic retardation of atom rearrangement or structural relaxation at a high cooling rate; and (ii) competition of icosahedral order against crystal order near the critical cooling rate.
23 citations
TL;DR: The distribution of absorption and emission energies within the same state indicates an ensemble of heterogeneous protein environments that are spectroscopically distinct, and the lifetimes of the dynamics are uniform across the ensemble, suggesting a homogeneous model involving sequential intermediates for the initial photodynamics of isomerization.
22 citations
TL;DR: The microstructures and phase equilibria of the equilibrated Co-V-Ta ternary alloys have been investigated in this paper, and the experimental information obtained in the present work is not only essential for the thermodynamic assessment of the Co-, V-Ta, but also important for the development of Co-base alloys.
16 citations
TL;DR: In this paper, the ternary interdiffusion coefficients in fcc Ni-Co-Al alloys at 1373 K were determined using Whittle and Green method together with electronic-probe microanalysis.
Abstract: The ternary interdiffusion coefficients in fcc Ni-Co-Al alloys at 1373 K were determined using Whittle and Green method together with electronic-probe microanalysis. With the help of DICTRA software, the experimental diffusion coefficients were critically assessed to obtain the atomic mobilities of Ni, Co and Al in fcc Ni-Co-Al alloys. Comprehensive comparisons between calculated and experimental diffusion coefficients showed that the experimental data could be well reproduced by the atomic mobilities obtained in the present work. The developed diffusion mobilities were further validated by the calculation of the concentration profiles and diffusion paths in diffusion couples.