Xinhe Bao

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (370)1178.63 Total impact

  • Source
    Applied Catalysis B: Environmental. 01/2015; 162:141–148.
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    ABSTRACT: Ring current is a fundamental concept to understand the nuclear magnetic resonance (NMR) properties and aromaticity for conjugated systems, such as carbon nanotubes (CNTs). Employing the recently developed gauge including projector augmented wave (GIPAW), we studied the ring currents of CNTs systematically and visualized their distribution. The ring current patterns are determined by the semiconducting or metallic properties of CNTs. The discrepancy is mainly caused by the axial component of external magnetic fields, whereas the radial component induced ring currents are almost independent on the electronic structures of CNTs, where the intensities of ring currents are linearly related to the diameters of CNTs. Although the ring currents induced by the radial component are more intense than the ones by the axial component, only the later determines the overall NMR responses and aromaticity of CNTs as well. Furthermore, the semiconducting CNTs are more aromatic than the metallic counterparts due to the existence of delocalized ring currents on the semiconducting CNTs. These fundamental features are of vital importance for development of CNT-based nanoelectronics and applications in magnetic fields.
    Chemical Science 08/2014; · 8.31 Impact Factor
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    ABSTRACT: Silica supported Pt–Co and Au–Co nanoparticles (NPs) were subjected to various redox processes and characterized by X-ray diffraction, X-ray absorption near edge structure, and X-ray photoelectron spectroscopy. We found that most of the Co oxide (CoOx) species on Pt NPs can be reduced at 100 °C forming an alloy structure with Pt at elevated temperatures. Oxidation of Co in the reduced sample takes place gradually with increasing temperatures. In contrast, temperatures higher than 400 °C are needed to reduce CoOx on Au NPs and Co atoms hardly form an alloy with Au even at 600 °C. The Co species in the reduced Au–Co/SiO2 sample were quickly oxidized in an O2 atmosphere at room temperature. High CO oxidation activity was observed in the Pt–Co/SiO2 catalyst reduced below 300 °C; however this necessitated reduction at 600 °C of the Au–Co/SiO2 catalyst. The results illustrate a stronger interaction of Co (CoOx) with Pt than with Au. In both systems, the optimum treatment conditions are to produce a similar CoO-on-noble metal (NM) active structure and maximize the density of interface sites between the surface CoO structure and the NM support.
    Catal. Sci. Technol. 08/2014; 4(9).
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    ABSTRACT: Hydrogen is considered as an important clean energy carrier for the energy future and electrocatalytic splitting of water is one of the most efficient technologies for hydrogen production. As one potential alternative to Pt-based catalysts in hydrogen evolution reaction (HER), two-dimensional (2D) molybdenum sulfide (MoS2) nanomaterials have evoked enormous research interest while it remains a great challenge in the structure control for high-performance HER electrocatalysis due to the lack of efficient preparation techniques. Herein, we reported a one-pot chemical method to directly synthesize 2D MoS2 with controllable layers. Multiply-layer MoS2 (ML-MoS2), few-layer MoS2 (FL-MoS2) and single-layer MoS2 coating on carbon nanotubes (SL-MoS2-CNTs) can be efficiently prepared through the modulation of experimental conditions. The enhanced catalytic activity is demonstrated in HER with the layer number of MoS2 nanosheets reducing. Remarkably, the optimized SL-MoS2-CNTs sample showed long-term durability with an accelerated degradation experiment even more than 10,000 recycles, and high HER activity with an onset overpotential of only ~40 mV vs. RHE. This study introduces a novel, cheap and facile strategy to prepare layer-controlled 2D MoS2 nanosheets with a large quantity, and are expected to broaden the already widely energy applications for 2D MoS2 nanosheets.
    RSC Advances 07/2014; · 3.71 Impact Factor
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    ABSTRACT: Electrolyzers and fuel cells have been extensively investigated as a promising solution for renewable energy storage and conversion. Hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) are important electrocatalytic processes in electrolyzers and fuel cells. Exploring efficient non-precious metal catalysts for HER and ORR in acidic medium remains a great challenge. Herein, we report graphene-supported iron-based nanoparticles encapsulated in nitrogen-doped carbon (Fe@N-C) hybrid material act as an efficient HER and ORR catalyst. The hybrid material was synthesized by pyrolysis of graphene oxide and ammonia ferric citrate followed by acid-leaching. During the pyrolysis, nitrogen was doped into graphene lattice, and the carbon nanoshell grown on graphene effectively suppressed the stacking of graphene sheet, exposing more active sites to reactants. The hybrid material showed higher electrocatalytic activities than graphene sheet or Fe@N-C alone, which was probably attributed to the synergetic role of nitrogen-doped graphene and Fe@N-C towards the electrocatalytic reactions.
    Faraday Discussions 07/2014; · 3.82 Impact Factor
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    ABSTRACT: Diffusion dynamics of guest molecules in nanopores has been studied intensively because diffusion is center to a number of research fields such as separation, drug delivery, chemical reactions and sensing. In the present work, we report an experimental investigation on the self-diffusion of water inside the carbon nanotube (CNT) channels using pulsed field gradient (PFG) NMR method. Dispersion of CNTs homogeneously in water and cooling down to temperatures below the melting point of bulk water allow us to probe the translational motion of confined water molecules. The results demonstrate that the self-diffusion coefficient of water in CNTs is highly dependent on the diffusion time and CNT diameter. Particularly, the diffusivity of water in double-walled carbon nanotubes (DWNTs) with an average inner diameter of 2.3±0.3 nm is twice of that in multi-walled carbon nanotubes (MWNTs) with an average inner diameter of 6.7±0.8 nm in the temperature range of 263 ─ 223 K. In addition, the effective self-diffusion coefficient in DWNTs is one order of magnitude higher than that reported for mesoporous silica materials with a similar pore size. The faster diffusivity of water in CNTs could be attributed to the ordered hydrogen bonding formed between water molecules within the confined channels of CNTs, and the weak interaction between water and CNT walls.
    Langmuir : the ACS journal of surfaces and colloids. 06/2014;
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    ABSTRACT: Interlayer expanded zeolites are derived from layered zeolite precursors by inserting a tetrahedrally coordinated atom (T-atom) in between the precursor layers. To achieve this expansion, a Si source like dichlorodimethylsilane or diethoxydimethylsilane is typically used. In the interlayer expansion of the layered zeolite precursor RUB-36, an Fe salt instead of a silylating agent was used to fill up the linking sites in between the layers. The obtained material showed a shift of the first XRD reflection similar to that of RUB-36 interlayer expanded with dichlorodimethylsilane, indicating an increase in interlayer distance. Diffuse reflectance UV-vis spectra and EPR characterization proved the incorporation of isolated Fe sites. Using FTIR spectroscopy with pyridine and acetonitrile as probe molecules, it was found that the incorporation of Fe results in an increase in Lewis acidity. The material was successfully used as a catalyst in the acylation of anisole with acetic anhydride and in the alkylation of toluene with benzyl chloride. The Fe incorporation proved to be remarkably stable. In spite of the HCl production during the alkylation reaction, no leaching was observed and the catalyst could be reused after regeneration.
    J. Mater. Chem. A. 06/2014; 2(25).
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    ABSTRACT: Structural changes of FeOx nanostructures supported on Pt(111) and Pt foil with response to oxidation and reduction treatments in O2 and H2 atmospheres upto 1.0 bar have been investigated by using X-ray photoelectron spectroscopy and scanning tunneling microscopy. We show that submonolayer O–Fe bilayer (FeO) structure on Pt(111) can be transformed to O–Fe–O trilayer (FeO2) upon oxidation in 5.0 × 10−6 mbar O2, while the FeO to FeO2 transformation happens over the full FeO film only with the O2 partial pressure above 1.0 × 10−3 mbar. Reduction of the submonolayer FeO2 structure back to the FeO structure occurs when exposed to 1.0 mbar H2 at room temperature (RT). In contrast, the full FeO2 structure can be kept even under 1.0 bar H2 exposure condition. The FeOx coverage and FeOx/Pt boundary play a critical role in the redox behavior of the supported FeOx nanostructures. Furthermore, we show that the FeOx nanostructures supported on Pt foil can be oxidized in a similar way as those on the Pt(111) surface. However, the Pt foil supported FeO2 nanostructures can be more deeply reduced to the state close to metallic Fe in 1.0 mbar H2 at RT. The close-packed Pt(111) surface exhibits a stronger confinement effect on the FeO overlayer than the open polycrystalline Pt surface.
    Topics in Catalysis 06/2014; 57(10-13). · 2.61 Impact Factor
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    ABSTRACT: In heterogeneous catalysis, graphitic carbon formed on metal often poisons metal-catalyzed reactions through physical blockage of surface active sites. In materials science, recent works show that graphene overlayers can passivate metal surfaces acting as gas-impermeable protection coatings. However, here we show using in situ surface electron microscopy and photoemission spectroscopy that CO can be readily trapped inside the two-dimensional space between the graphene overlayer and Ru(0001) surface under near-ambient conditions. The intercalated CO molecules effectively decouple the graphene overlayer from the Ru substrate. Meanwhile, the graphene cover exerts a strong confinement effect on the surface chemistry of CO on Ru(0001), showing that a high-coverage CO adlayer can be kept at the graphene/Ru interface at room temperature which desorbs intensively and completely around 390 K. This finding challenges the traditional concept of graphene films as passivation layers, indicating that the surface graphitic carbon can be used to modify the surface chemistry of metals.
    The Journal of Physical Chemistry C. 05/2014; 118(23):12391–12398.
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    ABSTRACT: The efficient use of natural gas will require catalysts that can activate the first C-H bond of methane while suppressing complete dehydrogenation and avoiding overoxidation. We report that single iron sites embedded in a silica matrix enable direct, nonoxidative conversion of methane, exclusively to ethylene and aromatics. The reaction is initiated by catalytic generation of methyl radicals, followed by a series of gas-phase reactions. The absence of adjacent iron sites prevents catalytic C-C coupling, further oligomerization, and hence, coke deposition. At 1363 kelvin, methane conversion reached a maximum at 48.1% and ethylene selectivity peaked at 48.4%, whereas the total hydrocarbon selectivity exceeded 99%, representing an atom-economical transformation process of methane. The lattice-confined single iron sites delivered stable performance, with no deactivation observed during a 60-hour test.
    Science 05/2014; 344(6184):616-9. · 31.20 Impact Factor
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    ABSTRACT: Podlike nitrogen-doped carbon nanotubes encapsulating FeNi alloy nanoparticles (Pod(N)-FeNi) were prepared by the direct pyrolysis of organometallic precursors. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization measurements revealed their excellent electrocatalytic activities in the I−/I3− redox reaction of dye-sensitized solar cells (DSSCs). This is suggested to arise from the modification of the surface electronic properties of the carbon by the encapsulated metal alloy nanoparticles (NPs). Sequential scanning with EIS and CV further showed the high electrochemical stability of the Pod(N)-FeNi composite. DSSCs with Pod(N)-FeNi as the counter electrode (CE) presented a power conversion efficiency of 8.82 %, which is superior to that of the control device with sputtered Pt as the CE. The Pod(N)-FeNi composite thus shows promise as an environmentally friendly, low-cost, and highly efficient CE material for DSSCs.
    Angewandte Chemie International Edition 05/2014; · 11.34 Impact Factor
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    ABSTRACT: Podlike nitrogen-doped carbon nanotubes encapsulating FeNi alloy nanoparticles (Pod(N)-FeNi) were prepared by the direct pyrolysis of organometallic precursors. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Tafel polarization measurements revealed their excellent electrocatalytic activities in the I−/I3− redox reaction of dye-sensitized solar cells (DSSCs). This is suggested to arise from the modification of the surface electronic properties of the carbon by the encapsulated metal alloy nanoparticles (NPs). Sequential scanning with EIS and CV further showed the high electrochemical stability of the Pod(N)-FeNi composite. DSSCs with Pod(N)-FeNi as the counter electrode (CE) presented a power conversion efficiency of 8.82 %, which is superior to that of the control device with sputtered Pt as the CE. The Pod(N)-FeNi composite thus shows promise as an environmentally friendly, low-cost, and highly efficient CE material for DSSCs.
    Angewandte Chemie 05/2014;
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    ABSTRACT: Employing a low-cost and highly efficient electrocatalyst to replace Pt-based catalysts for hydrogen evolution reaction (HER) has attracted increasing interest in renewable energy research. Earth-abundant transition metals such as Fe, Co and Ni have been investigated as promising alternatives in alkaline electrolytes. However, these non-precious-metal catalysts are not stable in acids, excluding their application in the acidic solid polymer electrolyte (SPE). Herein, we report a strategy to encapsulate 3d transition metals Fe, Co and the FeCo alloy into nitrogen-doped carbon nanotubes (CNTs) and investigated their HER activity in acidic electrolyte. The optimized catalysts exhibited long-term durability and high activity with only a textasciitilde70 mV onset overpotential vs. RHE which is quite close to that of commercial 40% Pt/C catalyst, demonstrating the potential for the replacement of Pt-based catalysts. Density function theory (DFT) calculations indicated that the introduction of metal and nitrogen dopants can synergistically optimize the electronic structure of the CNTs and the adsorption free energy of H atom on CNTs, and therefore promote the HER with a Volmer-Heyrovsky mechanism.
    Energy & Environmental Science 04/2014; · 11.65 Impact Factor
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    ABSTRACT: An asymmetrically doped bilayer graphene is grown by modulation-doped chemical vapor deposition, which consists of one intrinsic layer and one nitrogen-doped layer according to AB stacking. The asymmetrically doped bilayer crystalline profile is found to extend the identical registry as adjacent pristine bilayer region, thus forming single-crystalline bilayer graphene p-n junctions. Efficient photocurrent with responsivity as high as 0.2 mA/W is generated at the bilayer p-n junctions via a hot carrier-assisted mechanism.
    Small 03/2014; · 7.82 Impact Factor
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    ABSTRACT: COE-4 zeolites possess a unique two-dimensional ten-ring pore structure with the Si(OH)2 hydroxyl groups attached to the linker position between the ferrierite-type layers, which has been demonstrated through the interlayer-expansion approach in our previous work (H. Gies et al. Chem. Mater.­ 2012, 24, 1536). Herein, density functional theory is used to study the framework stability and Brønsted acidity of the zeolite T-COE-4, in which the tetravalent Si is isomorphously substituted by a trivalent Fe, B, Ga, or Al heteroatom at the linker position. The influences of substitution energy and equilibrium geometry parameters on the stability of T-COE-4 are investigated in detail. The relative acid strength of the linker position is revealed by the proton affinity, charge analysis, and NH3 adsorption. It is found that the range of the 〈T-O-Si〉 angles is widened to maintain the stability of isomorphously substituted T-COE-4 zeolites. The smaller the 〈O1-T-O2〉 bond angle is, the more difficult is to form the regular tetrahedral unit. Thus, the substitution energies at the linker positions increase in the following sequence: Al-COE-4 < Ga-COE-4 < Fe-COE-4 < B-COE-4. The adsorption of NH3 as a probe molecule indicates that the acidity can affect the hydrogen-bonding interaction between (NH⋅⋅⋅O2) and (N⋅⋅⋅HO2). The relative Brønsted-acid strength of the interlayer-expanded T-COE-4 zeolite decreases in the order of Al-COE-4 > Ga-COE-4 > Fe-COE-4 > B-COE-4. These findings may be helpful for the structural design and functional modification of interlayer-expanded zeolites.
    ChemPhysChem 03/2014; · 3.35 Impact Factor
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    ABSTRACT: Hydroxyl-attached Sn species are highly dispersed on the surface of mesoporous silica (SBA-15) by the grafting of dimethyldichlorostannane followed by calcination to transform the methyl groups into hydroxyl groups (S–Sn–OH). S–Sn–OH has both Lewis and Brønsted acidic sites, resulting in superior catalytic activities in the acetalisation of glycerol.
    J. Mater. Chem. A. 02/2014; 2(11).
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    ABSTRACT: Ammonium ferric citrate (AFC) was used as a single-source molecular precursor to prepare Fe/Fe3C nanoparticles encapsulated in nitrogen-doped carbon by pyrolysis in Ar atmosphere followed by acid-leaching. Comparative studies, using citric acid and ferric citrate as the precursors, indicated that the ammonia and ferric ion in AFC and the pyrolysis temperature affected the composition of iron species and the properties of carbon in AFC-derived materials. Above the pyrolysis temperature of 600 °C, the iron species were Fe/Fe3C, and the carbon had a hollow graphitic nanoshell structure in AFC-derived materials. The specific surface area and content of nitrogen element decreased with increasing pyrolysis temperature. The AFC-derived material pyrolyzed at 600 °C had the optimal graphitization degree, specific surface area (489 m2 g−1) and content of nitrogen (1.8 wt.%), thus resulted in the greatest activity for oxygen reduction reaction among the AFC-derived materials pyrolyzed at different temperatures. The AFC-derived material pyrolyzed at 600 °C exhibited improved methanol-resistance ability compared with Pt/C catalyst.
    Carbon. 01/2014; 75:381–389.
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    ABSTRACT: Acetylene hydrochlorination is an important coal-based technology for the industrial production of vinyl chloride, however it is plagued by the toxicity of the mercury chloride catalyst. Therefore extensive efforts have been made to explore alternative catalysts with various metals. Here we report that a nanocomposite of nitrogen-doped carbon derived from silicon carbide activates acetylene directly for hydrochlorination in the absence of additional metal species. The catalyst delivers stable performance during a 150 hour test with acetylene conversion reaching 80% and vinyl chloride selectivity over 98% at 200 °C. Experimental studies and theoretical simulations reveal that the carbon atoms bonded with pyrrolic nitrogen atoms are the active sites. This proof-of-concept study demonstrates that such a nanocomposite is a potential substitute for mercury while further work is still necessary to bring this to the industrial stage. Furthermore, the finding also provides guidance for design of carbon-based catalysts for activation of other alkynes.
    Nature Communications 01/2014; 5:3688. · 10.02 Impact Factor
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    ABSTRACT: X-ray photoelectron spectroscopic and scanning tunneling microscopic results demonstrate that annealing of Fe/carbon-rich 6H-SiC(0001) surface between 650 and 750 °C leads to Fe intercalation under the surface carbon layer. Accompanied with the metal intercalation, the carbon nanomesh surface was transformed into a graphene surface. Moreover, the formed graphene layers always float out to the topmost surface even after deposition of more than 10 monolayer Fe, acting as a surfactant. Using graphene as the surfactant may not only promote the 2D growth but also can improve the film performance considering that graphene is stable and robust.
    Applied Physics Letters 01/2014; 104(18):181604-181604-4. · 3.79 Impact Factor
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    ABSTRACT: Monodispersed bimetallic PdAg nanoparticles can be fabricated through the emulsion-assisted ethylene glycol (EG) ternary system. Different compositions of bimetallic PdAg nanoparticles, Pd80Ag20, Pd65Ag35 and Pd46Ag54 can be obtained via adjusting the reaction parameters. For the formation process of the bimetallic PdAg nanoparticles, there have two-stage growth processes: firstly, nucleation and growth of the primary nanoclusters; secondly, formation of the secondary nanoparticles with the size-selection and relax process via the coalescence or aggregation of the primary nanoclusters. The as-prepared PdAg can be supported on the carbon black without any post-treatment, which exhibited high electro-oxidation activity towards methanol oxidation under alkaline media. More importantly, carbon-supported Pd80Ag20 nanoparticles reveal distinctly superior activities for the methanol oxidation, even if compared with commercial Pt/C electro-catalyst. It is concluded that the enhanced activity is dependant on the unique twinning structure with heterogeneous phase due to the dominating coalescence growth in EG ternary system.
    Scientific Reports 01/2014; 4:4288. · 5.08 Impact Factor

Publication Stats

2k Citations
1,178.63 Total Impact Points

Institutions

  • 1998–2014
    • Chinese Academy of Sciences
      • • State Key Laboratory of Catalysis
      • • Dalian Institute of Chemical Physics
      Peping, Beijing, China
    • Dalian Institute of Chemical Physics
      Lü-ta-shih, Liaoning, China
  • 2011–2013
    • Peking University
      • College of Chemistry and Molecular Engineering
      Peping, Beijing, China
    • State Key Laboratory of Medical Genetics of China
      Ch’ang-sha-shih, Hunan, China
  • 1999–2013
    • Northeast Institute of Geography and Agroecology
      • State Key Laboratory of Catalysis
      Beijing, Beijing Shi, China
    • Tianjin University
      T’ien-ching-shih, Tianjin Shi, China
  • 2010
    • Shandong University
      • Institute of Theoretical Chemistry
      Jinan, Shandong Sheng, China
    • Northeast Normal University
      Hsin-ching, Jilin Sheng, China
  • 1993–2010
    • Max Planck Society
      München, Bavaria, Germany
  • 2009
    • CUNY Graduate Center
      New York City, New York, United States
  • 2007
    • Northeast Forestry University
      • Key Laboratory of Plant Ecology, Ministry of Education
      Charbin, Heilongjiang Sheng, China
  • 1993–2007
    • Fritz Haber Institute of the Max Planck Society
      • Department of Inorganic Chemistry
      Berlin, Land Berlin, Germany
  • 2006
    • Tsinghua University
      Peping, Beijing, China
  • 2002–2006
    • University of Science and Technology of China
      • Department of Chemical Physics
      Hefei, Anhui Sheng, China
  • 2005
    • Universität Stuttgart
      Stuttgart, Baden-Württemberg, Germany
  • 1999–2005
    • Dalian University of Technology
      • • School of Chemical Engineering
      • • State Key Laboratory of Fine Chemicals
      Dalian, Liaoning, China
  • 2004
    • Liaoning Normal University
      Lü-ta-shih, Liaoning, China
  • 2001
    • National Academy of Sciences of Ukraine
      • Institute of Physics
      Kievo, Kyiv City, Ukraine
  • 1994
    • Fudan University
      • Department of Chemistry
      Shanghai, Shanghai Shi, China