Xinhe Bao

Xiamen University, Amoy, Fujian, China

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Publications (463)2209.61 Total impact

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    ABSTRACT: High field quantitative 27Al single pulse (SP) MAS NMR combined with temperature programmed desorption (TPD) of ethanol is used to study the surface of γ-Al2O3 during phase transformation processes induced by calcination in the temperature range of 500–1300 °C. Following ethanol adsorption, ethylene is generated during TPD with a desorption temperature above 200 °C. The amount of ethylene decreases monotonically with increasing calcination temperature prior to TPD. Significantly, 27Al SP MAS NMR reveals that the amount of penta-coordinated Al3+ ions also decreases with increasing calcination temperature. A quantitative (within experimental error) correlation between the amount of penta-coordinated Al3+ ions and the amount of strongly adsorbed ethanol molecules (i.e., the ones that convert to ethylene during TPD) is obtained. These results provide good evidence for a proposal that the penta-coordinated aluminum sites are the catalytic active sites on alumina surfaces during ethanol dehydration reaction across the entire course of γ-to-α Al2O3 phase transformations.
    No preview · Article · Apr 2016
  • Lijun Gao · Qiang Fu · Jiamin Li · Zhenping Qu · Xinhe Bao
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    ABSTRACT: It has been empirically established that graphitic carbon deposits often result in deactivation of metal catalysts due to the physical blockage of surface active sites. Our recent surface science works however demonstrate that molecules such as CO can adsorb on Pt(111) surface covered by graphene overlayers via an intercalation process, and surface reactions e.g. CO oxidation have been enhanced by the graphene covers. In this work, supported Pt nanocatalysts were coated by ultrathin graphitic carbon layers through chemical vapor deposition process forming Pt@C core-shell nanostructures, which were confirmed by characterizations of Raman spectroscopy, temperature-programmed oxidation and transmission electron microscopy. CO oxidation over the Pt@C catalysts shows a lower apparent activation energy compared with the pure Pt catalysts, and in-situ infrared studies indicate that the reactions occur under the graphitic shells. The present results suggest that coating metal nanocatalysts with ultrathin graphitic overlayers may be used to promote metal catalyzed reactions.
    No preview · Article · Feb 2016
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    ABSTRACT: We investigated the conduction properties of pristine bulk graphene oxide (GO) with different oxidation degrees. GO with low oxidation degree shows the electron/hole conduction behavior. Interestingly, however, GO with high oxidation degree exhibits mixed conduction behaviors (electron/hole conduction and proton conduction), depending on the water content. For GO with high oxidation degree, the electron/hole conduction dominates the electrical transport in the water-lean state, while the proton conduction dominates the electrical transport in the water-rich state. We reveal that the epoxide groups, which could influence the band gap, interlayer distance and water intercalation process, play a critical role in the conduction properties of GO. In electrical transport process, epoxide groups act as conduction barriers for electron/hole conduction while serving as active sites for proton conduction. We also observed that both graphite and GOs exhibit anisotropic transport behaviors. These observations will provide insightful information for the applications of GO in fuel cells, humidity sensors and supercapacitors.
    No preview · Article · Feb 2016
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    ABSTRACT: In this work, a damped oscillating crystallization process of AlPO4-5 at the presence of small amount of water is demonstrated by in situ high temperature high pressure multinuclear MAS NMR. Crystalline AlPO4-5 is formed from an intermediate semi-crystalline phase via continuous rearrangement of the local structure of amorphous precursor gel. Activated water catalyzes the rearrangement via repeatedly hydrolysis and condensation reaction. Strong interactions between organic template and inorganic species facilitate the ordered rearrangement. During the crystallization process, excess water, phosphate, and aluminums are expelled from the precursor. The oscillating crystallization reflects mass transportation between the solid and liquid phase during the crystallization process. This crystallization process is also applicable to AlPO4-5 crystallized at the presence of relatively large amount of water.
    No preview · Article · Jan 2016 · The Journal of Physical Chemistry C
  • Xuejun Xu · Qiang Fu · Xinhe Bao
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    ABSTRACT: Pt-Mo/SiO2 catalysts were prepared using impregnation-reduction methods. Mo-promoted Pt catalysts exhibit much higher water gas shift reaction activity at low temperatures than Pt/SiO2 catalysts. Various characterization methods including inductive coupled plasma atomic emission spectrometry, X-ray diffraction, transmission electron microscopy, X-ray absorption near edge spectrum, and X-ray photoelectron spectroscopy were applied to investigate the composition, structure and chemical state of the Pt-Mo/SiO2 catalysts. Our results indicate that the added Mo species effectively improves the dispersion of Pt nanoparticles and the synergistic effect between the Pt nanoparticles and surface MoOx species enhances the catalytic performance for the water gas shift reaction. Pt nanoparticles decorated with highly dispersed MoOx patches are found to be the active architecture.
    No preview · Article · Dec 2015 · Chinese Journal of Catalysis
  • Mingming Wei · Qiang Fu · Hao Wu · Aiyi Dong · Xinhe Bao
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    ABSTRACT: H2 atmosphere is often involved in growth and application of two-dimensional (2D) atomic crystals, and it is of great importance to understand interaction of the 2D materials with H2 molecules. Here, a full graphene layer and a full hexagonal boron nitride (h-BN) layer grown on Pt(111) were exposed to H2 atmosphere, which were investigated by in situ near ambient pressure X-ray photoelectron spectroscopy and quasi in situ ultraviolet photoelectron spectroscopy. We confirm the occurrence of hydrogen intercalation of the graphene and h-BN overlayers in ambient pressure H2. The hydrogen intercalation in 0.1 Torr H2 at room temperature and hydrogen desorption in 0.1 Torr H2 at 200 °C are fully reversible on the graphene/Pt(111) and h-BN/Pt(111) surfaces. Furthermore, hydrogen desorption on the graphene/Pt(111) and h-BN/Pt(111) surfaces was found to happen at lower temperature than that on the Pt(111) surface due to the graphene and h-BN cover effect.
    No preview · Article · Dec 2015 · Topics in Catalysis
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    ABSTRACT: Silicon carbide (SiC) was extracted using CCl4 and NH3 at 800 °C to form a SiC core with a derived nitrogen-doped carbon shell (SiC@N–C), which is explored as a supporting material for iron nanoparticles encapsulated in nitrogen-doped carbon (Fe@N–C) due to its excellent corrosion resistance. The carbon shell around SiC is essential to successfully grow Fe@N–C around SiC@N–C during pyrolysis of cyanamide and iron acetate. In sharp contrast, Fe3Si supported on SiC was obtained using pristine SiC as the supporting material. Fe@N–C/SiC@N–C showed much higher activity for oxygen reduction reaction than SiC@N–C and Fe3Si/SiC, even exceeding that of a commercial Pt/C catalyst in alkaline medium. Furthermore, Fe@N–C/SiC@N–C also demonstrated higher durability and methanol resistance than the Pt/C catalyst.
    No preview · Article · Dec 2015 · Catalysis Science & Technology
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    ABSTRACT: Coordinatively unsaturated (CUS) iron sites are highly active in catalytic oxidation reactions; however, maintaining the CUS structure of iron during heterogeneous catalytic reactions is a great challenge. Here, we report a strategy to stabilize single-atom CUS iron sites by embedding highly dispersed FeN4 centers in the graphene matrix. The atomic structure of FeN4 centers in graphene was revealed for the first time by combining high-resolution transmission electron microscopy/high-angle annular dark-field scanning transmission electron microscopy with low-temperature scanning tunneling microscopy. These confined single-atom iron sites exhibit high performance in the direct catalytic oxidation of benzene to phenol at room temperature, with a conversion of 23.4% and a yield of 18.7%, and can even proceed efficiently at 0°C with a phenol yield of 8.3% after 24 hours. Both experimental measurements and density functional theory calculations indicate that the formation of the Fe═O intermediate structure is a key step to promoting the conversion of benzene to phenol. These findings could pave the way toward highly efficient nonprecious catalysts for low-temperature oxidation reactions in heterogeneous catalysis and electrocatalysis.
    Full-text · Article · Dec 2015 · Science Advances
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    ABSTRACT: Metastable oxide phases containing coordinatively unsaturated metal sites are highly active in many catalytic reactions. The stabilization of these nanostructures during reactions remains a major challenge. Here, we show that metastable two-dimensional (2D) FeO structures can be grown on Pt(111) and Au(111), but not on the graphene surface. The well-defined 2D structure is achieved by an interface confinement effect originating from the strong interfacial bonding between Fe atoms and substrate surface atoms. The stabilization effect has been described by the interface confinement energy (Econfinement), which is the energy difference lowered by interfacing the 2D structure with a substrate and decreases in the sequence of Pt(111) > Au(111) > graphene. This interface effect is widely present in many metal-oxide composite catalysts and can be used to guide the rational design of catalytically active sites.
    No preview · Article · Nov 2015 · The Journal of Physical Chemistry C
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    ABSTRACT: Water assisted phase transformation process from crystalized AlPO4-5 to AlPO4-tridymite was studied by the combination of X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and in situ multinuclear MAS NMR. It is found that water first activates the residue amorphous aluminophosphate in crystalized AlPO4-5 sample through hydrolysis and condensation reactions. Then the activated aluminophosphate species reassemble into AlPO4-tridymite crystalline. Meanwhile, AlPO4-5 transforms into orthorhombic phase during heating process. With further crystallization of AlPO4-tridymite, the amorphous phase is gradually consumed, and mass transportation between AlPO4-5 and AlPO4-tridymite is established through gradually amorphization of AlPO4-5. Finally, most of the AlPO4-5 transforms into the thermodynamically stable dense phase AlPO4-tridymite.
    No preview · Article · Nov 2015 · Microporous and Mesoporous Materials
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    ABSTRACT: The dynamic evolution of acetyl intermediates in the two different channels of H-mordenite (H-MOR) zeolite during dimethyl ether (DME) carbonylation is tracked by using in situ solid-state NMR spectroscopy under continuous-flow conditions. Thus, the reaction path via methyl acetate produced over active sites in 8 member ring (MR) channels, followed by diffusion into 12 MR channels, is proposed.
    No preview · Article · Oct 2015 · Chemical Communications
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    ABSTRACT: Heterostructures of two-dimensional (2D) atomic crystals have attracted increasing attention while fabrication of the 2D stacking structures remains as a challenge. In this work, we present a route towards formation of the 2D heterostructures via confined growth of 2D adlayer underneath the other 2D overlayer. Taking hexagonal boron nitride (h-BN) monolayer on Ni(111) as a model system, both epitaxial and non-epitaxial h-BN islands have been identified on the Ni surface. Surface science studies combined with density function theory calculations reveal that the non-epitaxial h-BN islands interact weakly with the Ni(111) surface, which create 2D nano-space underneath the h-BN islands. An additional h-BN or graphene layer can be grown in the space between the non-epitaxial h-BN islands and Ni(111) surface, forming h-BN/h-BN bilayer structures and h-BN/graphene heterostructures. These results suggest that confined growth under 2D covers may provide an effective route to obtain stacks of 2D atomic crystals.
    Full-text · Article · Oct 2015 · ACS Nano
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    ABSTRACT: Interlayer expansion using silylating agents to connect layer silicates to 3D framework structures has shown to be a versatile synthesis route to new crystalline, microporous frameworks. We demonstrate here that also Me cations can be introduced on the linker sites applying the same synthesis procedure. An acidic aqueous Fe-chloride solution was used in a hydrothermal reaction to convert the layered hydrous silicate precursor RUB-36 into an interlayer expanded zeolite, containing Fe at the linker sites, Fe-IEZ-RUB-36, Si19.14Fe0.86O38(OH)4. Structure analysis from powder X-ray data using the Rietveld technique confirmed that the porous framework is stable upon calcination and contains Fe on T-sites at the linker position. SEM-EDX analysis is in agreement with the analysis of the electron density maps showing that almost every other linker T-position is occupied by Fe-ions. The material crystallizes in the monoclinic space group Pm with a = 12.200(9) Å, b = 13.981(8) Å, c = 7.369(2) Å, and β = 106.9(1)°. Applying a similar synthesis procedure, the Sn-analog, Sn-IEZ-RUB-36, Si38.6Sn1.4O76(OH)8, has been obtained and structurally characterized. Despite its limited crystallinity, Rietveld analysis of the PXRD data set confirmed the materials framework topology and chemical composition (a = 23.856(14) Å, b = 14.103(7) Å, c = 7.412(7) Å, in SG Pnm21). We conclude, that the synthesis procedure is flexible and, meanwhile, has been extended to other metal cations such as Ti, Zn, Eu and Al leading to microporous materials with potentially active metal cations on well defined sites of the silicate framework.
    No preview · Article · Oct 2015 · Microporous and Mesoporous Materials
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    Xiaoqi Chen · Dehui Deng · Xiulian Pan · Xinhe Bao
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    ABSTRACT: Fe-based catalyst is an outstanding candidate for the Fischer-Tropsch reaction to get light olefins from syngas directly. However, exposed Fe species are susceptible to sintering and coking, which lead to deactivation. Here, we demonstrate that Fe nanoparticles encapsulated in pod-like carbon nanotubes (Pod-Fe) can be used as an efficient Fischer-Tropsch catalyst to produce light olefins. It gave a higher selectivity of light olefins (45%) and high stability over 120 h reaction (P = 0.5 MPa, T = 320 ℃, CO:H2 = 1:2, gas hourly space velocity = 3500 h-1). A catalyst with exposed Fe particles on the outside of the Pod-Fe (FeOx/Pod-Fe) catalyst showed a selectivity of light olefins of 42%, but had a significantly lower stability due to the agglomeration of Fe nanoparticles and carbon deposition. These results indicated that the graphene shell of Pod-Fe played an important role in protecting the Fe particles and provided a rational way to enhance the activity and stability of Fe-based catalysts in high temperature reactions. © 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
    Full-text · Article · Sep 2015 · Chinese Journal of Catalysis
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    ABSTRACT: Zeolites synthesized without any organic structure-directing agent (OSDA) have several advantages over conventional zeolites synthesized with OSDAs. Their Al-rich compositions, however, are sometimes not suitable for applications as catalysts. In the present study, post-synthetic modification was performed using an Al-rich Beta zeolite synthesized without any OSDAs (designated as “Beta(OF)”) to obtain high-silica Beta zeolites. We have successfully developed a facile post-synthetic method for tuning the Al content of Beta(OF) with the *BEA-type structure retained by calcination at >750 °C followed by acid treatment. Solid-state 29Si and 27Al MAS NMR analyses revealed that during calcination, framework Al atoms were isomorphously substituted with Si atoms to form high-silica frameworks and concomitant extra-framework Al species. The stability of the obtained frameworks against acid treatment was evaluated in terms of the framework Al content, finding that the framework with the Si/Al ratio higher than 12 is well stabilized enough for acid treatment. Thus, dealuminated Beta(OF) zeolites with high-silica compositions were found to be effective catalysts for the methanol-to-olefin (MTO) reaction; particularly, the Beta zeolite with the Si/Al ratio of 112 maintained the conversion of methanol over 90% with selectivity to C2–C4 olefins over 70% even at 40 hours on stream at WHSV = 3.2 h−1.
    No preview · Article · Sep 2015 · Catalysis Science & Technology
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    ABSTRACT: SiO2 supported Pt-Ni bimetallic catalysts with different nickel loadings were prepared and their structural changes after redox treatments were studied by XRD, NMR, and EPR. It is found that the paramagnetic Ni species are mainly located on the surface of silica lattice. The relaxation of detected 29Si nuclei in our samples is mainly governed by a spin-diffusion mechanism. The paramagnetic effects are reflected in the spin-lattice relaxation of Q4 species, with the oxidized samples presenting faster relaxation rates than the corresponding reduced ones. Meanwhile the Q3 species, which are in close contact with the paramagnetic nickel centers, are "spectrally invisible". In reducing atmosphere Ni gradually diffuses into Pt NPs to form PtNi alloys. While under oxidization treatment, the alloyed Ni atoms migrate outward from the core of Pt NPs and are oxidized. The main EPR spectrum results from reduced nickel species, and the reduced samples show stronger EPR signal than the corresponding oxidized ones. However, in the reduced samples, the superparamagnetic or ferromagnetic metallic Ni particles were inside the PtNi NPs, making their influence on the 29Si relaxation in the SiO2 support weaker than the oxidized samples.
    No preview · Article · Sep 2015 · The Journal of Physical Chemistry C
  • Yanhong Zhang · Mingming Wei · Qiang Fu · Xinhe Bao
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    ABSTRACT: The interface between a two-dimensional (2D) atomic crystal and a metal surface can be regarded as a nanoreactor, in which molecule adsorption and catalytic reactions may occur. In this work, we demonstrate that oxygen intercalation and desorption occur at the interface between hexagonal boron nitride (h-BN) overlayer and Pt(111) surface by using near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), photoemission electron microscopy, and low-energy electron microscopy. Furthermore, CO oxidation under the h-BN cover was also observed by NAP-XPS. The present results indicate that the nanospace under the 2D cover can be used for surface reactions, in which novel surface chemistry may be induced by the nanoconfinement effect. © 2015, Science China Press and Springer-Verlag Berlin Heidelberg.
    No preview · Article · Sep 2015
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    ABSTRACT: Replacing platinum for catalyzing hydrogen evolution reaction (HER) in acidic medium remains great challenges. Herein, we prepared few-layered MoS2 by ball milling as an efficient catalyst for HER in acidic medium. The activity of as-prepared MoS2 had a strong dependence on the ball milling time. Furthermore, Ketjen Black EC 300J was added into the ball-milled MoS2 followed by a second ball milling, and the resultant MoS2/carbon black hybrid material showed a much higher HER activity than MoS2 and carbon black alone. The enhanced activity of the MoS2/carbon black hybrid material was attributed to the increased abundance of catalytic edge sites of MoS2 and excellent electrical coupling to the underlying carbon network.
    No preview · Article · Aug 2015 · Journal of Energy Chemistry
  • Jinjing Li · Xiulian Pan · Xinhe Bao
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    ABSTRACT: Direct conversion of syngas into hydrocarbons with high selectivity remains a challenge. Herein, we report the synthesis of a core–shell-structured catalyst constituting Cr-Zn oxide as the core and SAPO-34 as the shell for the conversion of syngas into hydrocarbons with high selectivity. A SiO2 layer was sandwiched between the core and the shell to prevent damage to the core during shell synthesis. Furthermore, the intermediate SiO2 layer acted as a Si source for the formation of the shell. The prepared catalyst displayed considerably higher selectivity toward the production of C2–C4 hydrocarbons (66.9%) than that of methanol and methane. The findings show the potential of the prepared core–shell-structured catalyst in the one-step production of hydrocarbons, such as liquefied petroleum gas, from syngas. However, further optimization of the catalyst is necessary to achieve higher performance.
    No preview · Article · Jul 2015 · Chinese Journal of Catalysis
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    ABSTRACT: Density functional theory (DFT) has been performed to characterize the structural stability and Lewis acidic properties of the T-COE-4 zeolites, in which the linked site between the layers is isomorphously substituted by the tetravalent Ti-, Sn-, or Zr- heteroatom. The effects of substitution energy and equilibrium geometry parameters on the stability of T-COE-4 are investigated. The computed Fukui function values and the adsorption of ammonia, pyridine, water and trimethylphosphine oxide molecules have been employed to predict the Lewis acid strength of the T-COE-4 zeolites. It is found that the smaller the O1-T-O2 bond angle is, the more difficult is to form the regular tetrahedral unit. The substitution energies at the linker position increase in the following sequence: Ti-COE-4 < Sn-COE-4 < Zr-COE-4. The incorporation of Ti-, Sn-, or Zr-heteroatom enhances the Lewis acidity of COE-4 zeolite. It is predicted that the Lewis acid strength increases in the order of Ti-COE-4 < Zr-COE-4 ≤ Sn-COE-4 by the adsorption of different base molecules. Six O-T-O bond angles are divided into different extent to form the analogous trigonal bipyramid structures in the optimized ligand adsorbed complexes. These findings could be beneficial for the structural design and catalytic function modification of the interlayer-expanded zeolites.
    No preview · Article · Jul 2015 · Microporous and Mesoporous Materials

Publication Stats

12k Citations
2,209.61 Total Impact Points

Institutions

  • 2015
    • Xiamen University
      Amoy, Fujian, China
  • 1998-2015
    • Dalian Institute of Chemical Physics
      Lü-ta-shih, Liaoning, China
  • 2013
    • Peking University
      • College of Chemistry and Molecular Engineering
      Peping, Beijing, China
  • 1998-2013
    • Chinese Academy of Sciences
      • • State Key Laboratory of Catalysis
      • • Dalian Institute of Chemical Physics
      Peping, Beijing, China
  • 2008-2011
    • State Key Laboratory of Medical Genetics of China
      Ch’ang-sha-shih, Hunan, China
  • 2010
    • Northeast Normal University
      Hsin-ching, Jilin Sheng, China
  • 1999-2005
    • Dalian University of Technology
      • • School of Chemical Engineering
      • • State Key Laboratory of Fine Chemicals
      Lü-ta-shih, Liaoning, China
  • 2001-2002
    • University of Science and Technology of China
      • Department of Chemical Physics
      Luchow, Anhui Sheng, China
  • 1992-1997
    • Fritz Haber Institute of the Max Planck Society
      • Department of Inorganic Chemistry
      Berlín, Berlin, Germany
  • 1993-1996
    • Max Planck Society
      München, Bavaria, Germany