Yanhui Yang

Nanyang Technological University, Tumasik, Singapore

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Publications (160)857.17 Total impact

  • Yibo Yan · Yihu Dai · Shuchao Wang · Xinli Jia · Hao Yu · Yanhui Yang
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    ABSTRACT: Carbon nanospheres (CNSs) prepared by hydrothermal approach and post-functionalization with alkali solutions were employed as solid base catalysts in aldol condensation. The negative charge and alkalinity of CNS surfaces were controlled by the concentration of alkali solutions, leading to the high selectivity superior to aqueous NaOH as the traditional catalyst. Furthermore, CNSs with varying surface alkalinity can be adopted as proper supports for highly dispersed Pd nanoparticles with well-controlled size distribution. The optimized alkaline CNS-supported Pd catalysts demonstrated enhanced reactivities in the solvent-free selective oxidation of benzyl alcohol and the aerobic oxidation of glycerol. In-depth characterizations of their structural and electronic properties by transmission electron microscope (TEM), field emission scanning electron microscope (FESEM), Fourier transform infrared spectroscope (FTIR) and X-ray photoelectron spectroscopy (XPS) were performed to elucidate the nature of the active sites and the mechanism. The effect of electron density, size of Pd nanoparticles as well as the surface alkalinity of supports on the catalytic performance has been unveiled.
    No preview · Article · May 2016
  • Xiaomei Ning · Yuhang Li · Hao Yu · Feng Peng · Hongjuan Wang · Yanhui Yang
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    ABSTRACT: The group 15 metals, bismuth and antimony, play important roles in promoting noble-metal-catalyzed oxidation reactions toward high value-added chemicals. Herein, we report that the selective oxidation of glycerol to 1,3-dihydroxyacetone (DHA) catalyzed by Pt supported on N-doped carbon nanotubes (Pt/NCNT) can be significantly promoted in the presence of Bi or Sb in reaction solution. This catalyst system showed not only comparable even better performance to the Pt/NCNT with pre-loaded Bi, but also the greatly simplified catalyst preparation. It was found that the Bi-promoted Pt/NCNT underwent dynamic surface reconstruction through leaching and adsorption of Bi adatoms, due to the formation of glyceric acid. By characterizing the adsorption of Bi on Pt catalyst with high-resolution transmission electron microscopy, CO-stripping, horizontal attenuated total reflection infrared spectroscopy and X-ray photoelectron spectroscopy, it has been ascertained that Bi preferentially deposits on the step sites of Pt, and then blocks the terrace sites to promote the Pt catalyst mainly through a geometrical effect, which facilitates the activation and transformation of the secondary hydroxyl group of glycerol through the chelation between substrate and Pt–Bi sites.
    No preview · Article · Mar 2016
  • Hong Chen · Yihu Dai · Xinli Jia · Hao Yu · Yanhui Yang
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    ABSTRACT: Biomass-based ethanol is a potentially promising feedstock and its transformations into value-added chemicals have attracted growing attention. Herein we reported that bi-functional zeolites supported Pd nanoparticle catalysts achieved superior performance in gas-phase selective aerobic oxidation of ethanol to acetaldehyde and ethyl acetate at mild condition. The selectivity to ethyl acetate and the ethanol conversion remained 94.7 % and 98.6 %, respectively, after a long-tern reaction for 73 h over 2Pd/HY catalyst, while acetaldehyde selectivity of 89.0 % was obtained on 2PdO/HY at a low temperature as 150 oC. The reaction selectivity can be readily tuned by controlling the oxidation state of Pd species, the type of zeolite support and the reaction conditions. The cosistence of Pd0 and Pd2+ species and a moderate oxygen supply played a critical role in following the partial oxidation route to form ethyl acetate other than formnation of acetaldehyde or acetic acid. The specific interaction between metallic Pd nanoparticles and acidic zeolite surface via the reverse hydrogen spillover process was also speculated to be responsible for the improved catalytic performances.
    No preview · Article · Feb 2016 · Green Chemistry
  • Jie Fan · Yihu Dai · Xin-Ping Wu · Yu Tang · Yanhui Yang · Xue-Qing Gong
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    ABSTRACT: The irreversible carbonate deposits on CeO2 lead complete switch of catalytic selectivity into formation of benzene in gas-phase oxidation of benzyl alcohol. By integrating experimental spectra and theoretical calculations, we believe that such shift derives from further decarbonylation of benzaldehyde via easy trapping of CO fragment by surface carbonate species.
    No preview · Article · Dec 2015 · Chemical Communications
  • Linlu Bai · Kaixin Li · Yibo Yan · Xinli Jia · Jong-Min Lee · Yanhui Yang

    No preview · Article · Dec 2015 · ACS Sustainable Chemistry & Engineering
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    ABSTRACT: Bimetallic AuAg/SBA-15 catalysts were disclosed to efficiently catalyze vapor-phase chemoselective hydrogenation of crotonaldehyde (CRAL) with improved hydrogenation rate and selectivity to crotonyl alcohol (CROL). The CRAL hydrogenation rate and product distribution were remarkably influenced by reaction parameters such as the reaction pressure and CRAL/hydrogen ratio. Ag decoration on Au/SBA-15 effectively stabilized bimetallic AuAg nano-alloy particles in small size and promoted the catalytic stability. In situ FT-IR investigation revealed that unusual C2M2 di-σ bonded CRAL surface species with reinforced symmetric δ(CH3) IR band under the “metal-surface selection rule” (MSSR) were formed on bimetallic AuAg/SBA-15. The stronger CRAL chemisorption on bimetallic AuAg/SBA-15 surfaces than on monometallic Au/SBA-15 was possibly due to the relatively strong ligating of CO bond on Ag active sites and the enhancement of the co-adsorption of the conjugated double bonds of CRAL. Synergistic interaction between Au and Ag active sites for the activation of HH, CC and CO bond may be the origin of positive effect of Ag decoration on Au/SBA-15.
    Full-text · Article · Oct 2015 · Journal of Catalysis
  • Chengxiong Dang · Hao Yu · Hongjuan Wang · Feng Peng · Yanhui Yang
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    ABSTRACT: Sorption enhanced steam reforming of glycerol (SESRG) enables the production of high-purity hydrogen from the by-product of biodiesel manufacture. To this end, highly stable catalysts and CO2 sorbents are desired to overcome the performance degradation at high temperatures. Herein, a bi-functional catalyst, Co-CaO-Ca12Al14O33, is proposed to couple CO2 sorption and catalytic reforming of glycerol on nanoscale. The catalyst was derived from a Co-Ca-Al hydrotalcite-like (HTl) material to achieve homogeneous mixing of Co, CaO and Ca12Al14O33 as a spacer to prevent CaO sintering. At Ca/Al of 2.8, the highest catalytic activity and sorption capability were reached. Over the optimized catalyst, high-purity H2 of 96.4% was produced at 525°C through SESRG during the pre-breakthrough stage. High stability of the bi-functional catalyst was demonstrated by a cyclic SESRG-calcination operation up to 50 times. The role of Ca12Al14O33 as spacer of CaO was proved by XRD and TEM-EDS analysis. In addition, it was found that Ca3Co2O6, which is formed during the calcination stage and is reduced during the SESRG to release Co catalysts, may act as a dynamic reservoir of Co catalysts to prevent Co from sintering, leading to an excellent SESRG activity and stability.
    No preview · Article · Oct 2015 · The Chemical Engineering Journal
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    ABSTRACT: Titania nanowires (NW) supported gold–copper (Au–Cu) bimetallic nanoparticles were synthesized and pretreated in hydrogen and air at 300, 500 and 700 • C, for the one-pot conversion of cellobiose to glu-conic acid. Catalyst samples were characterized by temperature-programmed desorption of NH 3 , Fourier transform infrared spectroscopy (FT-IR), Energy-dispersive X-ray spectroscopy, Field emission scanning electron microscopy (FE-SEM), X-ray powder diffraction (XRD), Transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The structure and activity of Au–Cu/TiO 2 NW were highly affected by the pretreatment conditions. Catalyst samples reduced in H 2 and at higher temperatures resulted better catalytic performance as compared with those calcinated in air at the same temperature. The influence of support, calcination temperature and atmosphere as well as gold content on the catalytic performance of Au–Cu/TiO 2 NWs are investigated. The characterization results suggested high hydrogen reduction temperature created oxygen vacant sites on the titania NW support. This is consequently associated with the stabilization of highly reactive oxygen species at the periphery of the metal–support interface. Interactions between the metals and the titania NWs support and between the promoter and the active metal enhanced the formation of gluconic acid.
    Full-text · Article · Sep 2015 · Applied Catalysis A: General
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    ABSTRACT: Heterogeneous catalysts that are prepared by immobilizing noble metal nanoparticles (NPs) on solid matrices can serve as efficient catalysts in various catalytic reactions. However, the immobilized NPs usually suffer from detachment or migration during the catalytic process owing to their weak interactions with the matrices. Here, we developed a facile approach for the synthesis of high active and stable heterogeneous catalysts by entrapping Pd and Ru NPs in 3D ordered hierarchically porous inverse opal carbon (IOC). For these catalysts, the 3D open-porous structure on multiple length scales provides the reactants easy access to the catalytically active NPs while the entrapment of NPs inside IOC ensures their high dispersion and stability during the catalysis. As a result, the as-prepared catalysts exhibited both high activity and stability for the oxidation of CO and electrocatalysis of VO2+/VO2+ redox couples. The conversion rate of CO over the IOC-PdNPs catalyst reached >98% at 200 °C, which showed no decrease after reacting for 10 h. The IOC-RuNPs-based working electrode exhibited highly reversible redox potentials at 1.25 V and 0.78 V, respectively, and no change of peak currents and peak potential separation were observed for 200 cycles of cyclic voltammetry (CV) measurements.
    Full-text · Article · Sep 2015 · Carbon
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    Jun Zhao · Chunmei Zhou · Chao He · Yihu Dai · Xinli Jia · Yanhui Yang
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    ABSTRACT: A carbon-based solid acid catalyst was prepared via hydrothermal method using glucose as carbon precursors and aqueous solution of H2SO4 as sulfonation agent. The as-synthesized solid acid catalyst was attempted in the catalytic dehydration of fructose to 5-hydroxymethylfurfural (HMF). The effects of acid site density, reaction time, solvents, catalyst amount, temperature and mole ratio of catalyst to substrate were investigated. Under the optimum reaction conditions, the HMF yield of 90% was achieved in dimethylsulfoxide (DMSO) solvent at 160 °C after 1.5 h reaction time duration. The solid acid catalyst can be separated from the reaction mixture after reaction and reused without substantial loss in catalytic activity.
    Full-text · Article · Aug 2015 · Catalysis Today
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    ABSTRACT: Biodiesels produced from renewable sources exhibit superior fuel properties and renewability and they are more environmentally friendly than petroleum-based fuels. In this paper, a three-step transesterification, catalyzed by a pyridinium-based Brønsted acidic ionic liquid (BAIL), for biodiesel production was investigated using density functional theory (DFT) calculations at the B3LYP/6-311++G(d) level. The DFT results elucidate the detailed catalytic cycle, which involves the formation of a covalent reactant–BAIL–(methanol)n (n = 1/3) intermediate and two transition states. Hydrogen bond interactions were found to exist throughout the process of the catalytic cycle, which are of special importance for stabilizing the intermediate and transition states. Thus, a mechanism involving cooperative hydrogen bonding for BAIL-catalyzed biodiesel production was established. The Gibbs free energy profile based on the above mechanism was validated by the subsequent kinetic study. The trend of activation energy from kinetic mathematical models was reasonably consistent with that obtained from the DFT calculations.
    No preview · Article · Aug 2015 · Green Chemistry
  • Yibo Yan · Xinli Jia · Yanhui Yang
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    ABSTRACT: A series of rare-earth oxide functionalized multi-walled carbon nanotubes (CNTs) were prepared through wet impregnation process. Palladium nanoparticles were deposited over surfaces of functionalized CNT through metal ion adsorption-reduction method and were examined using X-ray diffraction, transmission electron microscopy, in situ adsorbed pyridine Fourier Transform Infrared spectroscopy, and electrochemical measurements. Compared to the non-functionalized Pd/CNT catalyst, the catalytic activities of different rare-earth oxide functionalized CNT supported Pd catalysts were improved for aerobic solvent-free oxidation of benzyl alcohol due to the fine-tuned properties of catalytic active sites, e.g., Pd particle size, size distribution, valence status, metal-support interactions, electron density, surface acidity and basicity. Sm2O3 functionalization displayed the highest improvement in catalytic activity whereas the content of Sm2O3 had impact on Pd particle size, electrochemical surface area, and metal-support interactions which further influenced the benzyl alcohol conversion and selectivity toward benzyl aldehyde. The catalyst functionalized by an appropriate amount of Sm2O3 afforded a remarkably high turnover frequency of 318,760 h-1 for aerobic oxidation of benzyl alcohol based upon palladium electrochemical active surface areas.
    No preview · Article · Aug 2015 · Catalysis Today
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    ABSTRACT: The aerobic oxidation of 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA) is one of the most attractive reactions to establish biomass-based sustainable chemical processes. Supported Au and Pt catalysts have mainly been reported for this reaction, but excess amounts of base additives are generally required, which makes the process less green. Here, we demonstrate that Pt nanoparticles loaded on functionalized carbon nanotubes (CNTs) can catalyze the aerobic oxidation of HMF to FDCA in water without any base additives. Kinetic studies suggest a tandem reaction mechanism via 2,5-diformylfuran and 5-formylfurancarboxylic acid intermediates. It has been clarified that the oxygen-containing functional groups, in particular carbonyl/quinone and/or phenol groups, on CNT surfaces play crucial roles in FDCA formation. These functional groups could enhance the adsorption of HMF as well as the reaction intermediates from water and might facilitate hydrogen transfer.
    No preview · Article · Jul 2015 · ChemCatChem
  • Chunmei Zhou · Zhen Guo · Yihu Dai · Xinli Jia · Hao Yu · Yanhui Yang
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    ABSTRACT: PtBi/CNT catalyst was synthesized by a one-step polyol reduction method assisted by microwave radiation, and its catalytic performance was investigated in aerobic oxidation of benzyl alcohol in the aqueous phase. Pt and BiOx species uniformly dispersed on the CNT surfaces and strong synergic interaction between them occurred, which confirmed by the comprehensive analysis of TEM, XRD, XPS and electrochemical characterizations. Further investigations revealed that the synergic effect effectively promoted the activation of both molecular oxygen and benzyl alcohol substrate; also protected Pt active sites from over-oxidization. The advantage of such synergic effect was reflected in the increased yield for the desired product benzaldehyde: PtBi/CNT catalyst exhibited about 3.5 times higher yield toward benzaldehyde compared to Pt/CNT catalyst. Furthermore, owing to the positive effect of Bi avoiding Pt from oxidizing, the deactivation of PtBi/CNT (with 2% selectivity and 9% conversion decrease) is much slower than that of Pt/CNT (with 8% selectivity and 39% conversion decrease) after six reaction cycles. PtBi/CNT catalyst was proved as a remarkably effective catalyst with high stability for the aerobic oxidation of benzyl alcohol.
    No preview · Article · Jul 2015
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    ABSTRACT: An integrated experimental and computational investigation reveals that surface lattice oxygen of copper oxide (CuO) nanoleaves activates the formyl CH bond in glucose and incorporates itself into the glucose molecule to oxidize it to gluconic acid. The reduced CuO catalyst regains its structure, morphology, and activity upon reoxidation. The activity of lattice oxygen is shown to be superior to that of the chemisorbed oxygen on the metal surface and the hydrogen abstraction ability of the catalyst is correlated with the adsorption energy. Based on the present investigation, it is suggested that surface lattice oxygen is critical for the oxidation of glucose to gluconic acid, without further breaking down the glucose molecule into smaller fragments, because of CC cleavage. Using CuO nanoleaves as catalyst, an excellent yield of gluconic acid is also obtained for the direct oxidation of cellobiose and polymeric cellulose, as biomass substrates. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Full-text · Article · Jun 2015 · Angewandte Chemie International Edition
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    ABSTRACT: Anatase interim layer-stabilized rutile@CrxOy core–shell nanorod arrays as photoanodes of photoelectrochemical water splitting cell can output a four-fold enhanced and stabilized visible-light photocurrent, as reported on p. 1352 by J. L. long, X. X. Wang, B. Liu et al.
    Full-text · Article · May 2015 · ChemPhysChem
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    ABSTRACT: In order to reduce considerable emissions of N-containing pollutants from combustion of sewage sludge derived solid fuel, an integrated system of hydrothermal deamination and air stripping was developed to effectively remove and recover nitrogen from dewatered sewage sludge (DSS). Three characteristic hydrothermal regimes contributing to deamination were identified. Initial hydrolysis of inorganic-N and labile protein-N was responsible for ammonium (NH+ 4-N) released below 300 oC/9.3 MPa, whereas deamination of pyridine-N dominated when being raised to 340 oC/15.5 MPa. At 380 oC and 22.0 MPa, remarkable deamination of stable protein-N occurred, which was accompanied by formation of more heterocyclic-N compounds and resulted in 76.9% N removal from DSS and 7980 mg/L NH+ 4-N solution. As a result of catalytic hydrolysis and cracking, calcium oxide additive not only accelerated deamination of stable protein-N, pyrrole-N, and pyridine-N but also favored transformations of protein-N and quaternary-N to nitrile-N and pyridine-N, respectively, leading to 86.4% total N removal efficiency. The nitrogen transformation reactions and conversion pathways during hydrothermal deamination were proposed and elaborated in detail. Moreover, an efficient air stripping process was coupled to remove and recover ammonia from liquid fraction via ammonium sulfate. Consequently, this system achieved an overall N recovery rate of 62%.
    Full-text · Article · May 2015 · Environmental Science & Technology
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    ABSTRACT: Carbon nanotubes are promising materials for various applications. In recent years, progress in manufacturing and functionalizing carbon nanotubes has been made to achieve the control of bulk and surface properties including the wettability, acid-base properties, adsorption, electric conductivity and capacitance. In order to gain the optimal benefit of carbon nanotubes, comprehensive understanding on manufacturing and functionalizing carbon nanotubes ought to be systematically developed. This review summarizes methodologies of manufacturing carbon nanotubes via arc discharge, laser ablation and chemical vapor deposition and functionalizing carbon nanotubes through surface oxidation and activation, doping of heteroatoms, halogenation, sulfonation, grafting, polymer coating, noncovalent functionalization and nanoparticle attachment. The characterization techniques detecting the bulk nature and surface properties as well as the effects of various functionalization approaches on modifying the surface properties for specific applications in catalysis including heterogeneous catalysis, photocatalysis, photoelectrocatalysis and electrocatalysis are highlighted.
    Full-text · Article · Apr 2015 · Chemical Society Reviews
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    ABSTRACT: In the present study, hydrothermal conversion (HTC) of dewatered sewage sludge (DSS) under sub- and near-critical water has been performed to investigate effects of reaction temperature and pressure, moisture content of DSS, and calcium oxide (CaO) additive on evolution profile and characteristics of gas, solid, and liquid products. Although energy recovery rate decreased with increasing temperature and pressure, significant decarboxylation and dehydration reactions led to hydrochars with best fuel quality at 320 °C. High moisture content favored decarboxylation reaction but reduced H2 and CH4 yields. Compared to that in the absence of additive, H2 yield increased almost 6-fold at 380 °C and Ca/C molar ratio of 0.2, resulting in 58% H2 and 26% CH4 in final fuel gas. The results suggested that mineralization of heteroatomic compounds and dissolution of metals or mineral elements occurred during HTC. Under higher temperature and pressure, heavy metals or mineral elements were prone to be immobilized whereas dehalogenation became more distinct. CaO additive not only facilitated hydrolysis and deamination of organic compounds but also accelerated further fixation of inorganic elements and anions.
    Full-text · Article · Apr 2015 · International Journal of Hydrogen Energy
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    ABSTRACT: Mesoporous-metal-organic frameworks (meso-MOFs) with size-, shape-, and space-distribution-controlled mesopores are obtained by a facile encapsulation and selective etching strategy of metal nanoparticles. Hierarchical or functionalized meso-MOFs are achieved by the above strategy. Interestingly, the functional meso-MOFs display higher catalytic activity originating from the mesopores existing in the MOFs, as well as good selectivity due to protection of the micro-porous frameworks. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    No preview · Article · Mar 2015 · Advanced Materials

Publication Stats

4k Citations
857.17 Total Impact Points

Institutions

  • 2006-2016
    • Nanyang Technological University
      • School of Chemical and Biomedical Engineering
      Tumasik, Singapore
  • 2014-2015
    • Xiamen University
      • • Department of Chemistry
      • • College of Chemistry and Chemical Engineering
      Amoy, Fujian, China
  • 2004-2007
    • Yale University
      • • Department of Biomedical Engineering
      • • Department of Chemical & Environmental Engineering
      New Haven, Connecticut, United States