Yingyong Wang

Cuprous oxide nanoparticles dispersed on reduced graphene oxide as an efficient electrocatalyst for oxygen reduction reaction

Cuprous oxide (Cu(2)O) nanoparticles dispersed on reduced graphene oxide (RGO) were prepared by reducing copper acetate supported on graphite oxide using diethylene glycol as both solvent and reducing agent. The Cu(2)O/RGO composite exhibits excellent catalytic activity and remarkable tolerance to methanol and CO in the oxygen reduction reaction.

Visible-light-driven Photocatalytic N-arylation of Imidazole Derivatives and Arylboronic Acids on Cu/graphene catalyst

N-aryl imidazoles play an important role as structural and functional units in many natural products and biologically active compounds. Herein, we report a photocatalytic route for the C-N cross-coupling reactions over a Cu/graphene catalyst, which can effectively catalyze N-arylation of imidazole and phenylboronic acid, and achieve a turnover frequency of 25.4 h−1 at 25 oC and the irradiation of visible light. The enhanced catalytic activity of the Cu/graphene under the light irradiation results from the localized surface plasmon resonance of copper nanoparticles. The Cu/graphene photocatalyst has a general applicability for photocatalytic C-N, C-O and C-S cross-coupling of arylboronic acids with imidazoles, phenols and thiophenols. This study provides a green photocatalytic route for the production of N-aryl imidazoles.

Carbonylative Suzuki coupling reactions of aryl iodides with arylboronic acids over Pd/SiC

Abstract High surface area SiC has been used to prepare a Pd/SiC catalyst using the liquid reduction method, and the resulting catalyst was used for the carbonylative Suzuki coupling reaction of aryl iodides with arylboronic acids. The catalyst was also characterized by X-ray diffraction, inductively coupled plasma-mass spectroscopy and high-resolution transmission electron microscopy. The results of these analyses showed that homogeneous Pd nanoparticles with a mean diameter of 2.8 nm were uniformly dispersed on the SiC surface. Optimization of the reaction conditions for the carbonylative Suzuki coupling reaction, including the solvent, base, pressure, temperature and reaction time, revealed that the model reaction of iodobenzene (1.0 mmol) with phenylboronic acid (1.5 mmol) could reach 90% conversion with a selectivity of 99% towards the diphenyl ketone using 3 wt% Pd/SiC under 1.0 MPa of CO pressure at 100 °C for 8 h with K2CO3 (3.0 mmol) as the base and anisole as the solvent. The Pd/SiC catalyst exhibited broad substrate scope towards the carbonylative Suzuki coupling reaction of aryl iodides with arylboronic acids bearing a variety of different substituents. Furthermore, the Pd/SiC catalyst exhibited good recyclability properties and could be recovered and reused up to five times with the conversion of iodobenzene decreasing only slightly from 90% to 76%. The decrease in the catalytic activity after five rounds was attributed to the loss of active Pd during the organic reaction.

Structural Changes in Carbon Produced by a sulfur-aided Catalytic Chemical Vapor Deposition

Branched carbon structures were formed by a chemical vapor deposition of toluene using ferrocene as a catalyst precursor and thiophene as a promoter. The effects of sulfur on the carbon products were investigated by SEM, XRD, and EDX. Results show that the product microstructure changes from tree-like to worm-like when the thiophene volume fraction in the toluene increases from 0.01 to 1%. The carbon trees consist of long, straight, and well-developed branches, while the worm carbons are composed of short and curled fibers. There is no obvious difference in d002, La and Lc for the two products.

Three-dimensional finite element analysis of stresses and energy density distributions around gamma ' before coarsening loaded in the 110 direction in Ni-based superalloy

A three-dimensional (3D) anisotropic finite element (FE) analysis was employed to analyse the features about the elastic strain energy density, von Mises stress and hydrostatic pressure distributions in Ni-based superalloy single crystals when external loads applied along the [1 1 0]-direction. The asymmetry of the strain energy density, the von Mises stress and hydrostatic pressure could be used to predict the raft morphology for alloys exhibiting a positive or negative misfit. The reason was briefly discussed.

Large scale production of highly-qualified graphene by ultrasonic exfoliation of expanded graphite under the promotion of (NH4)2CO3 decomposition.

Highly-qualified graphene was prepared by the ultrasonic exfoliation of commercial expanded graphite (EG) under the promotion of (NH4)2CO3 decomposition. The yield of graphene from the first exfoliation is 7 wt%, and it can be increased to more than 65 wt% by repeated exfoliations. Atomic force microscopy, x-ray photoelectron spectroscopy and Raman analysis show that the as-prepared graphene only has a few defects or oxides, and more than 95% of the graphene flakes have a thickness of ~1 nm. The electrochemical performance of the as-prepared graphene is comparable to reduced graphene oxide in the determination of dopamine (DA) from the mixed solution of ascorbic acid, uric acid and DA. These results show that the decomposition of (NH4)2CO3 molecules in the EG layers under ultrasonication promotes the exfoliation of graphite and provides a low-priced route for large scale production of highly-quality graphene.

Cu 2 O/SiC as efficient catalyst for Ullmann coupling of phenols with aryl halides

Abstract A Cu2O/SiC heterogeneous catalyst was prepared via a two-step liquid-phase method using diethylene glycol as both the solvent and the reducing agent. The catalyst was characterized using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and H2 temperature-programmed reduction. All the results indicate that Cu is present on the SiC support primarily as Cu2O. The SEM and TEM results show that cubic Cu2O nanoparticles are uniformly dispersed on the β-SiC surface. The reaction conditions, namely the temperature, reaction time, and amounts of base and catalyst used, for the Ullmann-type C–O cross-coupling reaction were optimized. A model reaction was performed using iodobenzene (14.0 mmol) and phenol (14.0 mmol) with Cu2O/SiC (5 wt% Cu) as the catalyst, Cs2CO3 (1.0 equiv.) as the base, and tetrahydrofuran as the solvent at 150 °C for 3 h; a yield of 97% was obtained and the turnover frequency (TOF) was 1136 h−1. The Cu2O/SiC catalyst has a broad substrate scope and can be used in Ullmann-type C–O cross-coupling reactions of aryl halides and phenols bearing a variety of different substituents. The catalyst also showed high activity in the Ullmann-type C–S cross-coupling of thiophenol with iodobenzene and substituted iodobenzenes; a TOF of 1186 h−1 was achieved. The recyclability of the Cu2O/SiC catalyst in the O-arylation of phenol with iodobenzene was investigated under the optimum conditions. The yield decreased from 97% to 64% after five cycles. The main reason for the decrease in the catalyst activity is loss of the active component, i.e., Cu2O.

Graphene-supported CoS2 particles: an efficient photocatalyst for selective hydrogenation of nitroaromatics in visible light

CoS2/graphene composites fabricated by a facile hydrothermal method exhibit excellent photocatalytic performance for selective hydrogenation of nitroaromatics to the corresponding aniline employing molecular hydrogen as a reducing agent under visible light irradiation (400–800 nm). The rate constant of the composite catalyst for nitrobenzene hydrogenation can achieve as high as 35.50 × 10−3 min−1 with a selectivity of 100% toward the target product under mild conditions (30 °C and 0.25 MPa pressure of H2). The catalyst also shows high recyclability, and there is no decrease in the catalytic activity after five successive cycles. There exists a synergistic effect between the graphene support and the CoS2 particles: conductive graphene as the support can rapidly extract the photoexcited electrons and effectively suppress the recombination of photogenerated charges in CoS2 particles, and then improve the photocatalytic performance. The photocatalytic reduction of nitrobenzene over the CoS2/graphene catalyst to aniline occurs through the direct pathway in the presence of H2.

Effects of Yb2O3 promotor on the performance of Ni/SiC catalysts in CO2 reforming of CH4

Abstract Ni/SiC and Ni-Yb x /SiC ( x =2%, 4%, 6%, 10%) catalysts were prepared by the impregnation method, and the performances of catalysts in the carbon dioxide reforming of methane were studied in a fixed-bed reactor. The catalysts were characterized by BET, ICP-AES, XRD, H 2 -TPR, TG-DTA, XPS and TEM techniques. The experimental results indicate that the appropriate addition amount of Yb is 4% to 6%. Ni-Yb4/SiC and Ni-Yb6/SiC catalysts exhibit excellent catalytic activity and stability at 800°C, and the conversion of CH 4 and CO 2 can be maintained over 90% during the 100 h testing. Yb 2 O 3 promotor can inhibit the growth of nickel nanoparticles and reduce the amount of carbon deposition, therefore Ni-Yb/SiC catalysts show stable activity in the continuous reforming reaction.

Probing the mechanism of benzaldehyde reduction to chiral hydrobenzoin on the CNT surface under near-UV light irradiation

Metal-free CNTs exhibit high activity (conversion rate 99.6%, 6 h) towards the synthesis of chiral hydrobenzoin from benzaldehyde under near-UV light irradiation (320–400 nm). The CNT structure before and after the reaction, the interaction between the molecule and the CNT surface, the intermediate products, the substitution effect and the influence of light on the reaction were examined using various techniques. A photo-excited conduction electron transfer (PECET) mechanism for the photocatalytic reduction using CNTs has been proposed. This finding provides a green photocatalytic route for the production of hydrobenzoin and highlights a potential photocatalytic application of CNTs.