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排序方式: 共有158条查询结果,搜索用时 348 毫秒
61.
用密度泛函理论B3LYP方法详细研究了Ag_2~-催化CO氧化反应的机理.计算结果表明,O2分子在Ag_2~-和Au_2~-上吸附能相差不大,而CO分子在Ag_2~-上吸附要比在Ag_2~-上弱得多.Ag_2~-催化CO氧化反应共有四条反应途径.最可能反应通道为CO插入Ag2O_2~-中的Ag—O键形成中间体[Ag—AgC(O—O)O]-,然后直接分解形成产物CO2和Ag2O-,或另一分子CO进攻中间体[Ag—AgC(O—O)O]-形成两分子产物CO2和Ag_2~-.在动力学上最难进行的反应通道为经历碳酸根双银中间体,需要克服约0.24eV的能垒.Ag_2~-催化CO氧化反应活性要高于Au_2~-. 相似文献
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Yi Qin Ying Zhang Guangqiang Yin Yuxuan Wang Changwei Zhang Lijun Chen Hongwei Tan Xiaopeng Li Lin Xu Haibo Yang 《中国化学》2019,37(4):323-329
Photoswitchable or photoactivatable fluorescent species have been found wide applications within supramolecular chemistry and materials science. In this study, we successfully constructed two highly emissive Pt(II) metallacycles from the diarylethene ligands via coordination‐driven self‐assembly. Different from the most known fluorescent metallacycles, the obtained metallacycles have displayed “turn‐on” fluorescence switching. They are non‐fluorescent in solution, but they emit highly yellow or orange fluorescence under ultraviolet irradiation. The metallacycles were well characterized by 1H NMR, 31P NMR and ESI‐TOF‐MS. The photochromic properties of the resultant metallacycles were investigated by 1H NMR, 31P NMR, UV/Vis spectrum and fluorescence spectrum. Notably, NMR studies revealed that these two metallacycles featured excellent cyclization efficiency (90% conversion efficiency). Moreover, the closed‐ring isomers of the metallacycles displayed relatively high quantum yield (ΦF = 0.5). DFT simulations demonstrated that the antiparallel configuration of the diarylethene ligand had an angle closed to 120°, which was more stable in energy compared to the parallel configuration, thus allowing for the facile construction of highly emissive metallacycles. We believe that such highly emissive metallacycles which are in‐situ prepared upon irradiation can be used as new fluorescence materials for sensing and bioimaging in the future. 相似文献
65.
在电力系统中,利用计算机视觉和图像处理技术对输电线路的进行检测,在保障电力系统的安全运行方面具有非常重要的作用;针对复杂背景下的输电线路,提出了一种基于切比雪夫多项式描述子输电线路提取算法,该算法首先对输入图像进行预处理,其次利用随机Hough 变换提取图像中的直线和曲线,然后利用切比雪夫多项式描述子的曲线描述优势,对所提取的对象进行特征描述,为了提高提取的精确度,通过K-means聚类分析方法来训练视觉字典,通过视觉字典的比对,最终确定图像中的输电线路;实验结果说明了所提出的算法可以精确地提取复杂背景下的输电线路。 相似文献
66.
Changwei Li Haijing Liang Zhan-xin Zhang Zhaoyan Wang Lan Yu Huanxiang Liu Fengli An Shaohua Wang Lixia Ma Weihua Xue 《Tetrahedron》2018,74(29):3963-3970
The development of efficient glycosylation methods is important for gaining better insight into biological processes of significance to medicinal chemistry. Herein, we describe an In(NTf2)3 -catalyzed Koenigs-Knorr glycosylation based on the activation of an alcoholic hydroxyl group. A catalytic amount of In(NTf2)3 enables effective glycosylation of diverse alcohols with peracylated aldosyl bromides as donors, leading to the stereoselective formation of a series of glycosides in satisfactory yields. The protocol is characterized by mild reaction conditions and good functional-group tolerance, while obviating any need for any additive. Moreover, the potential utility of this transformation is demonstrated by the convenient syntheses of key building blocks for biomolecules of medicinal relevance. 相似文献
67.
Measurement of the infinite dilution diffusion coefficients of small molecule solvents in silicone rubber by inverse gas chromatography 总被引:1,自引:0,他引:1
The infinite dilution diffusion coefficients of n-hexane, n-heptane and n-decane in crosslinked silicone rubber with different crosslinking agent concentrations were measured in the temperature range of 348.15 K-368.15 K by inverse gas chromatography. The crosslinked silicone rubber was obtained by dissolving PDMS prepolymer, crosslinking agent and catalyst in n-heptane solvent and characterized by FTIR spectra. The Van Deemter equation was used to determine diffusion coefficients from the variation in chromatographic peak width with carrier gas flow rate. The good linear relation indicated the Van Deemter equation used in this work was reliable. The influences of small molecule solvent, crosslinking agent concentration and temperature on the infinite dilution diffusion coefficient were investigated. The results showed that the infinite dilution diffusion coefficient decreased with an increasing number of CH2 group in the alkane series. The increase in crosslinking agent concentration resulted in decrease of the infinite dilution diffusion coefficient. The infinite dilution diffusion coefficient increased with the rising of temperature. The interdependence on the infinite dilution diffusion coefficient and temperature accorded with Arrhenius equation well. Diffusion constant and activation energy obtained from the Arrhenius equation provided straight lines with the specific critical volume and crosslinking agent concentration. 相似文献
68.
制备条件对Ni在Al_2O_3表面上的分配形态及Ni/Al_2O_3体系催化加氢性能的影响 总被引:1,自引:0,他引:1
用比表面和孔体积测定、XRD和程序升温还原(TPR)方法研究了一系列不同制备条件对Ni在Al_2O_3表面上的分配形态及其对CO加氢反应催化性能的影响.实验发现,本文所用制备条件对催化剂的比表面、孔体积及孔径分布无显著的影响.浸渍时间愈长,催化剂上能在较低温度下还原的物种愈少,催化剂上CO的加氢活性愈低;在浸渍前对载体作室温抽空处理后制得的催化剂上,Ni在Al_2O_3表面是高度分散的,这一高度分散物种易于在低温下还原,使该催化剂具有很高的CO加氢活性和生成CH_4选择性;载体的抽空温度及对载体加热均对Ni物种形态及其分配、催化剂性能有明显影响. 相似文献
69.
The ground-state potential energy surface (PES) in the gas-phase H2/CO2/Ni(3D) system is investigated at the CCSD(T)//B3LYP/6-311+G(2d,2p) levels in order to explore the possible reaction mechanism of the reverse water gas shift reaction catalyzed by Ni(3D). The calculations predict that the C-O bond cleavage of CO2 assisted by co-interacted H2 is prior to the dissociation of the H2, and the most feasible reaction path for Ni(3D) + H2 + CO2 --> Ni(3D) + H2O + CO is endothermic by 12.5 kJ mol(-1) with an energy barrier of 103.9 kJ mol(-1). The rate-determining step for the overall reaction is predicted to be the hydrogen migration with water formation. The promotion effect of H2 on the cleavage of C-O bond in CO2 is also discussed and compared with the analogous reaction of Ni(3D) + CO2 --> NiO + CO, and the difference between triplet and singlet H2/CO2/Ni systems is also discussed. 相似文献
70.
还原温度对Ni/Al2O3催化剂上H2,CO吸附的影响 总被引:2,自引:0,他引:2
采用程序升温还原与程序升温逐步活化、H2、CO室温吸附、H2程序升温脱附相结合的方法,研究了Ni/Al2O3催化剂上还原活化温度对其吸脱附性能的影响.实验发现,Ni/Al2O3催化剂上,在不同温度还原的不同Ni氧化物物种,经相应温度活化后可形成不同性质的H2、CO吸附中心.催化剂经523K及573K活化后可形成极细的与Al2O3有一定相互作用的吸附中心,在这类中心上,H2的室温吸附量极小,但有一定的高温H2吸附量,且高温吸附的H2要在较高温度下才能脱附,CO在其上则可能是按单金属中心多CO方式吸附的.催化剂经673K和723K活化后均形成较强的H2、CO吸附中心,CO在这些中心上可能是按线式和桥式两种方式吸附的.催化剂经673K活化后,形成的中心上吸附的H2可在相对较低的温度下脱附.Ni/Al2O3经773K处理会发生烧结,因而丧失室温H2、CO吸附能力. 相似文献