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Umsa Jameel,Mingqiao Zhu,Xin-Zhi Chen,Hengquan Chen,Nousheen Iqbal,Zhangfa Tong,Satmon John Timayo 대한화학회 2017 Bulletin of the Korean Chemical Society Vol.38 No.6
Selective oxidation of olefins using molecular oxygen is a great challenge. This study reports two types of novel eco-friendly heterogeneous hybrid catalysts. One comprises of a lacunary Keggin-type polyoxometalate (POM) GaW11 linked to nano-sized silica using (3-aminopropyl) triethoxysilane (APTES) to form GaW11-APTES@SiO2 . Another catalyst is Au/GaW11-APTES@SiO2 prepared by wet deposition of nano-gold on the former one. The catalysts were characterized and used for the solvent-free oxidation of cyclohexene with molecular oxygen under mild reaction conditions. Both the catalysts showed good conversion and significant selectivity towards oxidized products for cyclohexene. GaW11-APTES@SiO2 showed a high conversion of up to 62.02% with a selectivity of 59.13% towards epoxide at a mild temperature of 50°C. Au/GaW11-APTES@SiO2 showed a conversion of 69.32% with 57.34% selectivity to 2-cyclohexene-1-ol at a temperature of 80°C. The heterogeneous catalysts were reused several times with no significant loss in conversion or selectivity towards the oxidized products.
Ahn, Jong-Hyun,Zhu, Zhengtao,Park, Sang-Il,Xiao, Jianliang,Huang, Yonggang,Rogers, John A. WILEY-VCH Verlag 2008 Advanced functional materials Vol.18 No.17
<P>This paper describes experimental and theoretical studies of the mechanics of free-standing nanoribbons and membranes of single-crystalline silicon transfer printed onto patterned dielectric layers. The results show that analytical descriptions of the mechanics agree well with experimental data, and they explicitly reveal how the geometry of dielectric layers (i.e., the width and depth of the features of relief) and the silicon (i.e., the thickness and widths of the ribbons) affect mechanical bowing (i.e., “sagging”) in the suspended regions of the silicon. This system is of practical importance in the use of semiconductor nanomaterials for electronic devices, because incomplete sagging near defects in gate dielectrics provides a level of robustness against electrical shorting in those regions which exceeds that associated with conventional deposition techniques for thin films. Field effect transistors formed using silicon nanoribbons transferred onto a range of ultrathin gate dielectrics, including patterned epoxy, organic self-assembled monolayers, and HfO<SUB>2</SUB>, demonstrate these concepts.</P> <B>Graphic Abstract</B> <P>Experimental and theoretical studies of the mechanics of nanoribbons and membranes of single-crystalline silicon on patterned dielectric layers reveal key aspects of this system. As a practical matter, these type of mechanics have the advantage that they reduce greatly the sensitivity of such devices to roughness and other structural imperfections in the substrate or the supported layers. <img src='wiley_img/1616301X-2008-18-17-ADFM200800176-content.gif' alt='wiley_img/1616301X-2008-18-17-ADFM200800176-content'> </P>
Influence of pulsing-air injection distance on pressure drop in a coke dust bagfilter
서정민,Young-Il Lim,John Zhu 한국화학공학회 2011 Korean Journal of Chemical Engineering Vol.28 No.2
The effect of the pulsing-air injection distance between the nozzle and venturi on total pressure drop was investigated in a pilot-scale pulse-jet bagfilter for coke dust of a steel mill factory. Theoretical and empirical models were used to predict the pressure drop. The empirical model contains two parameters--dust cake resistance and exponent of areal mass density--to be estimated by experiment. The optimum injection distance for minimizing the total pressure drop was evaluated by 64 experimental data at a fixed filtration velocity and pulse pressure in the practical ranges of dust concentration and pulse interval time. The dust cake resistance shows a minimum value at the optimum injection distance. The empirical model is in good agreement with the experimental data, showing a correlation coefficient of 0.952.
Crandell, Douglas W.,Zhu, Haiyang,Yang, Xiaofan,Hochmuth, John,Baik, Mu-Hyun The Royal Society of Chemistry 2017 Dalton Transactions Vol.46 No.2
<▼1><P>The copper-exchanged aluminosilicate zeolite SSZ-13 is a leading catalyst for the selective catalytic reduction of NO.</P></▼1><▼2><P>The copper-exchanged aluminosilicate zeolite SSZ-13 is a leading catalyst for the selective catalytic reduction of NO. Density functional theory calculations are used to construct a complete catalytic cycle of this process paying special attention to the coordination geometries and redox states of copper. N2 can be produced in the reduction half-cycle <I>via</I> a nitrosamine intermediate generated from the reaction of the additive reductant NH3 with a NO<SUP>+</SUP> intermediate stabilized by the zeolite lattice. The decomposition of this nitrosamine species can be assisted by incipient Brønsted acid sites generated during catalysis. Our calculations also suggest that the reoxidation of Cu(i) to Cu(ii) requires the addition of both NO and O2. The production of a second equivalent of N2 during the oxidation half-cycle proceeds through a peroxynitrite intermediate to form a Cu–nitrite intermediate, which may react with an acid, either HNO2 or NH4<SUP>+</SUP> to close the catalytic cycle. Models of copper neutralized by an external hydroxide ligand are also examined. These calculations form a key basis for understanding the mechanism of NO reduction in Cu-SSZ-13 in order to develop strategies for rationally optimizing the performance in future experiments.</P></▼2>
ALMA Reveals Sequential High-mass Star Formation in the G9.62+0.19 Complex
Liu, Tie,Lacy, John,Li, Pak Shing,Wang, Ke,Qin, Sheng-Li,Zhang, Qizhou,Kim, Kee-Tae,Garay, Guido,Wu, Yuefang,Mardones, Diego,Zhu, Qingfeng,Tatematsu, Ken’ichi,Hirota, Tomoya,Ren, Zhiyuan,Liu, Sheng-Yu American Astronomical Society 2017 The Astrophysical journal Vol.849 No.1
<P>Stellar feedback from high-mass stars (e.g., H II regions) can strongly influence the surrounding interstellar medium and regulate star formation. Our new ALMA observations reveal sequential high-mass star formation taking place within one subvirial filamentary clump (the G9.62 clump) in the G9.62+0.19 complex. The 12 dense cores (MM1-MM12) detected by ALMA are at very different evolutionary stages, from the starless core phase to the UC H II region phase. Three dense cores (MM6, MM7/G, MM8/F) are associated with outflows. The mass-velocity diagrams of the outflows associated with MM7/G and MM8/F can be well-fit by broken power laws. The mass-velocity diagram of the SiO outflow associated with MM8/F breaks much earlier than other outflow tracers (e.g., CO, SO, CS, HCN), suggesting that SiO traces newly shocked gas, while the other molecular lines (e.g., CO, SO, CS, HCN) mainly trace the ambient gas continuously entrained by outflow jets. Five cores (MM1, MM3, MM5, MM9, MM10) are massive starless core candidates whose masses are estimated to be larger than 25 M-circle dot, assuming a dust temperature of <= 20 K. The shocks from the expanding H II regions ('B' and 'C') to the west may have a great impact on the G9.62 clump by compressing it into a filament and inducing core collapse successively, leading to sequential star formation. Our findings suggest that stellar feedback from H II regions may enhance the star formation efficiency and suppress low-mass star formation in adjacent pre-existing massive clumps.</P>