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Hong G.,Zhejiang University | Tian X.,Zhejiang University | Jiang B.,Zhejiang University | Liao Z.,Zhejiang University | And 4 more authors.
RSC Advances | Year: 2016

In order to overcome problems of Au-Cu bimetallic catalysts for acetylene hydrochlorination reaction such as instability, Au-Cu-SH/AC catalysts were prepared through the introduction of thiol and tested to examine their activity and stability. It was found that performances of Au-Cu-SH/AC catalysts were quite excellent, with significantly higher catalytic activity and better stability than performances of Au/AC and Au-Cu/AC catalysts. The contents of Cu and thiol additives were also optimized and the optimum molar ratio of Au/Cu/SH was 1:1:10. Catalyst samples were characterized by scanning electron microscopy (SEM), nitrogen adsorption/desorption (BET), X-ray diffraction (XRD), transmission electronic microscopy (TEM), H2 temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). It was demonstrated that the Au-Cu-SH/AC catalysts were Au0-based catalysts, due to thiol reducing Au3+ to Au0 species during the preparation process. Au0 species exhibited better catalytic activity than Au3+ species for acetylene hydrochlorination, according to the comparison with the composition of active species in different samples through XPS. Furthermore, the sulfhydryl of thiol could bond to the surface of gold nanoparticles (Au NPs). It helped in mitigating the oxidation of Au0 by HCl, protecting Au NPs from structure damage, stabilizing Au NPs in a nearly constant particle size and keeping a more active structure in the reaction environment. Thus, improved dispersity of active species and protection of the active structure of the Au NPs resulted in the better catalytic activity and stability of Au-Cu-SH/AC. © 2016 The Royal Society of Chemistry.

Zi C.,Zhejiang University | Lungu M.,Zhejiang University | Huang Z.,Zhejiang University | Wang J.,Zhejiang University | And 4 more authors.
Powder Technology | Year: 2016

The unstable solids circulation behavior in a circulating fluidized bed (CFB) with sweeping bend return is investigated by monitoring pressure fluctuations in a bench-scale model. The pressure fluctuations at the top and bottom of the riser and downer are processed using the Fast Fourier Transform (FFT) technique to extract the dominant frequency and its amplitude in order to quantify the effects of riser inlet gas velocity, valve opening and bed inventory on the operation of the unit. The differential pressure drop fluctuations between riser and downer are processed in a similar manner. The study reveals that the unstable solids circulation behavior is cyclical vis-a-vis gas-solids flow pattern and solids exchange between riser and downer, named as solids oscillation circulation behavior. A dominant frequency of 0.25 Hz is observed for all pressure fluctuation signals corresponding to the cyclical change of bed inventory and gas flow rate in riser and downer induced by the oscillation circulation behavior. An additional dominant frequency for the pressure fluctuation signals at the riser and downer bottom is also observed related to the gas-solid flow pattern. The solids exchange frequency is strongly related to the dominant frequency of the differential pressure drop. The work also demonstrates that the oscillation behavior is activated by a critical inlet gas velocity or valve opening and that the oscillation frequency increases with the decrease of inlet gas velocity, while it does not change with the valve opening. The solids exchange amount decreases with the decrease of gas flow and small percentage valve opening. The oscillation behavior changes from sine model to rectangular with the increase of bed inventory and thus slugging solids circulation is established. © 2016 Elsevier B.V.

Ye J.,Zhejiang University | Jiang B.,Zhejiang University | Qin Y.,Zhejiang University | Zhang W.,Zhejiang University | And 4 more authors.
RSC Advances | Year: 2015

In order to reduce the simultaneous production of insoluble polymers during the bis(imino)pyridine (BIP) iron-catalyzed ethylene oligomerization, a series of phenolic compounds were introduced as modifiers. It was found that the polymer share in the total products would be largely reduced with the increasing dosage of the phenols and the enlargement of para-substituent size from methyl to tert-butyl. Further 1H NMR studies showed that the phenols could provide methylaluminoxane (MAO) profound structural modifications, giving rise to larger MAO aggregates and decoration of phenoxy groups on its surface. This would thus facilitate the active ion pair separation, leading the phenols to become effective polymer-retarding modifiers. Starting from the reaction between 4-tert-butylphenol, AlMe3 and water, a novel phenoxy-aluminoxane could be prepared. Its combination with AlMe3 enabled the catalyst activation, and gave us a further verification about the important role of phenoxy groups on the MAO surface. Furthermore, the introduction of electron-withdrawing groups would improve the reactivity of the -OH group, promoting the interaction between the phenols and MAO. A series of para-halogen substituted phenols were thus developed. With the relatively large size of the bromo group and the highest reactivity of the -OH group, 4-bromophenol was proved to be the most efficient polymer-retarding modifier among the studied phenols in this work. An almost polymer-free ethylene oligomerization could be achieved by this strategy without altering the mono ortho-methyl substituted BIP ligand. © The Royal Society of Chemistry.

Shen A.,Shanghai Key Laboratory of Catalysis Technology for Polyolefins | Shen A.,Shanghai Research Institute of Chemical Industry | Ni C.,Shanghai Research Institute of Chemical Industry | Cao Y.-C.,Shanghai Key Laboratory of Catalysis Technology for Polyolefins | And 6 more authors.
Tetrahedron Letters | Year: 2014

Novel monoligated imine-Pd-NHC pre-catalysts with extremely high activity for the coupling of aryl chlorides and aryl boronic acids have been well explored. Three diffident catalysts could be obtained through one reaction. Changes in imine ligands would lead to remarkable variation on catalytic activity. Under mild reaction conditions, high reaction yields were achieved. A wide range of biphenyls could be efficiently obtained at ultra low catalyst loadings of 0.005 mol %. © 2014 Elsevier Ltd. All rights reserved.

Yang B.-X.,Shanghai Research Institute of Chemical Industry | Yang B.-X.,Shanghai Key Laboratory of Catalysis Technology for Polyolefins | Yang B.-X.,East China University of Science and Technology | Ye L.-P.,Shanghai Research Institute of Chemical Industry | And 8 more authors.
Journal of Molecular Modeling | Year: 2015

The surface structures, CO adsorption, and oxidation-reaction properties of CuO1-x(111) with different reduction degree have been investigated by using density functional theory including on-site Coulomb corrections (DFT + U). Results indicate that the reduction of Cu has a great influence on the adsorption of CO. Electron localization caused by the reduction turns Cu2+ to Cu+, which interacts much stronger with CO, and the adsorption strength of CO is related to the electronic interaction with the substrate as well as the structural relaxation. In particular, the electronic interaction is proved to be the decisive factor. The surfaces of CuO1-x(111) with different reduction degree all have good adsorption to CO. With the expansion of the surface reduction degree, the amount of CO that is stably adsorbed on the surface increases, while the number of surface active lattice O decreases. In general, the activity of CO oxidation first rises and then declines. © 2015, Springer-Verlag Berlin Heidelberg.

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