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本文测量了NaY、HY和NH_4Y在不同抽空温度下的正电子寿命谱,得到了四个寿命组份,并对它们的归属进行了讨论。其中两个长寿命组份τ_s和τ_4归结为沸石内表面和笼内o-Ps的湮没。o-Ps容易被沸石内的质子酸氧化,而使其湮没寿命τ_3和τ_4缩短。利用正电子寿命谱可以监测NH_4Y沸石的脱氨过程。质子酸的存在对o-Ps的形成并无影响,但随着质子酸浓度增加,o-Ps在沸石内表面湮没的几率大于笼内,故I_3大于I_4。o-Ps的在沸石内表面和笼内的湮没速率与质子酸浓度成线性关系,以一级反应动力学处理得到的o-Ps在沸石内表面和笼内的氧化反应表观速率常数分别为9.67×10~7(mmol/g)_~(-1)s~(-1)和2.36×10~7(mmol/g)~(-1)s~(-1)。 相似文献
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本文测量了NaY、HY和NH_4Y在不同抽空温度下的正电子寿命谱, 得到了四个寿命组份, 并对它们的归属进行了讨论。其中两个长寿命组份τ_s和τ_4归结为沸石内表面和笼内o-Ps的湮没。o-Ps容易被沸石内的质子酸氧化, 而使其湮没寿命τ_3和τ_4缩短。利用正电子寿命谱可以监测NH_4Y沸石的脱氨过程。质子酸的存在对o-Ps的形成并无影响, 但随着质子酸浓度增加, o-Ps在沸石内表面湮没的几率大于笼内, 故I_3大于I_4。o-Ps的在沸石内表面和笼内的湮没速率与质子酸浓度成线性关系, 以一级反应动力学处理得到的o-Ps在沸石内表面和笼内的氧化反应表观速率常数分别为9.67×10~7(mmol/g)_~(-1)s~(-1)和2.36×10~7(mmol/g)~(-1)s~(-1)。 相似文献
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本文测定了不同类型沸石的正电子寿命谱。发现o-Ps的湮没寿命, 与沸石静电场之间有良好的对应关系, 静电场愈强, 湮没寿命愈短。根据正电子寿命谱结果。含不同阳离子的Y沸石的静电场强弱次序为KY相似文献
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用正电子湮没谱学研究氯化富铈稀土与NaY沸石机械混合形成的稀土NaY沸石(RE-NaY)中,氯化稀土在NaY中的分散.分别测量不同质量比的RE-NaY(1%-20%)经500℃烘烤1h,RE-NaY(5%)经过不同温度烘烤1h,以及RE-NaY(5%)经500℃烘烤不同时间后的正电子寿命谱.所有寿命谱都出现了5个寿命分量,其中第3,4,5寿命分别与β笼、超笼及沸石微粒界面空洞的大小和数量相关.实验表明了正电子湮没谱学能敏感地表征氯化稀土在NaY中的分散. 相似文献
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用正电子湮没谱学研究了机械混合CuCl2与NaY中CuCl2在NaY沸石中的扩散.分别测量了不同质量比的CuCl2-NaY(0~0.03)沸石分子筛经140℃烘烤1h;CuCl2-NaY(0~0.05)经450℃烘烤4h;CuCl2-NaY(0.01)经不同温度烘烤1h以及经300℃下烘烤烘不同时间后的正电子寿命谱.所有谱中都出现了5(或4)个寿命分量,其第3,4,5寿命分量分别与β笼、超笼及沸石微粒界面空间的大小和数量相关.实验表明,正电子湮没谱学可敏感地探测出少量CuCl2在NaY沸石中的扩散变化.而对于只含少量氯化铜(0.01)的情况,虽经高温长时间烘烤,但仍有相当数量的氯化铜存在于NaY外表面. 相似文献
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Mo-Co系加氢精制催化剂中TiO~2-Al~2O~3载体效应的PASCA研究 总被引:4,自引:0,他引:4
本文采用PASCA(化学分析正电子湮没谱)技术, 系统地研究了MoO~3/γ-Al~2O~3,CoO/γ-Al~2O~3, MoO~3/TiO~2-Al~2O~3, CoO/TiO~2-Al~2O~3等体系中活性组分的表面分散状态和化学状态及其变化规律, 揭示了用TiO~2改性Al~2O~3对Mo-Co系加氢精制催化剂所产生的载体效应的作用机理。Al~2O~3中引入TiO~2使得载体与MoO~3间的相互作用大大减弱, 导致分散态MoO~3易于还原和硫化。助剂CoO与TiO~2-Al~2O~3载体间存在极为显著的电子相互作用, 对于改善Co在活性相中的化学状态, 提高活性中心的内在活性具有重要的作用。PASCA研究的另一个重要结果是, 由于载体表面的不均匀性,使得上述负载型催化剂中氧化物活性组分的表面状态十分复杂, 存在与载体相互作用强弱程度不同的多类特征区, 这些特征区与内在活性不同的催化中心相关联. 通过TiO~2改性Al~2O~3载体, 有效地调节载体表面性质, 改变活性组分表面物种的分布及化学状态。 相似文献
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《Radiation Physics and Chemistry》2007,76(2):271-274
Positron annihilation measurements as a function of temperature and the length of bonded alkyl groups have been carried out on silica gel samples. Silica gel samples were bare and bonded with alkyl group from C1 up to C18. The diameters of pores were deduced from the lifetime of trapped ortho-positronium (o-Ps), and it was found that o-Ps lifetime provides reasonable information on the pore sizes for both bare and alkyl bonded silica gels. 相似文献
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《Radiation Physics and Chemistry》2000,58(5-6):575-579
Positron lifetime spectra and Doppler broadening of the annihilation line were measured for samples of carbon black/polyethylene and polypropylene composites with varying amount of the filler. Tensile strength, resistivity, EPR resonance were studied in addition to have the samples better characterized. The decrease in resistivity of samples, accompanied by the worsening of mechanical properties, the drop both in the intensities of Ps lifetime components in the lifetime spectra and in the line-shape parameter values, were observed with increase in the carbon black content. The presence of radicals associated with aromatic structure of the carbon sheets and others associated with the surface oxygen functional groups was established by EPR measurements for the carbon blacks being used as fillers. The carbon black of the highest specific surface area influenced the measured characteristics the most. 相似文献
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Phenyl‐bonded stationary phases—The influence of polar functional groups on retention and selectivity in reversed‐phase liquid chromatography
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The chromatographic properties of four phenyl‐bonded phases with different structures were studied. The columns used were packed with a stationary phase containing a phenyl ring attached to the silica surface using different types of linkage molecules. As a basic characteristic of the bonded phases, the hydrophobicity and silanol activity (polarity) were investigated. The presence of the polar amino and amide groups in the structure of the bonded ligand strongly influences the polarity of the bonded phase. Columns were compared according to methylene selectivity using a series of benzene homologues and according to their shape and size selectivity using polycyclic aromatic hydrocarbons. The measurements were done using methanol/water and acetonitrile/water mobile phases. The presented results show that the presence of polar functional groups in the ligand structure strongly influences the chromatographic properties of the bonded phase. 相似文献
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Quintiliani M Kahnt A Wölfle T Hieringer W Vázquez P Görling A Guldi DM Torres T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(12):3765-3775
A series of three novel ZnPc-C60 conjugates (Pc=phthalocyanine) 1 a-c bearing different spacers (single, double, and triple bond) between the two electroactive moieties was synthesized and compared to that of ZnPc-C60 conjugate 2, in which the two electroactive moieties are linked directly. The synthetic strategy- towards the preparation of 1 a-c- involved palladium-catalyzed cross-coupling reactions over a monoiodophthalocyanine precursor 4 to introduce the corresponding spacer, and subsequent dipolar cycloaddition reaction to C60. Detailed photophysical investigations of 1 a-c and 2 prompted an intramolecular electron transfer that evolves from the photoexcited ZnPc to the electron-accepting C60. In particular, with the help of femtosecond laser photolysis charge separation was indeed confirmed as the major deactivation channel. Complementary time-dependent density functional calculations supported the spectral assignment, namely, the spectral identity of the ZnPc(*+) radical cation and the C60 (*-) radical anion as seen in the differential absorption spectra. The lifetimes of the correspondingly formed radical ion-pair states depend markedly on the solvent polarity: they increase as polarity decreases. Similarly, although to a lesser extent, the nature of the linker impacts the lifetime of the radical ion-pair states. In general, the lifetimes of these states tend to be shortest in the system that lacks any spacer at all (2), whereas the longest lifetimes were found in the system that carries the triple-bond spacer (1 a). 相似文献
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A. M. A. El-Sayed Hamdy F. M. Mohamed Anmed A. A. Boraei 《Radiation Physics and Chemistry》2000,58(5-6):791-795
Positron annihilation lifetimes were measured for some solid charge transfer (CT) molecular complexes of quinoline compounds (2,6-dimethylquinoline, 6-methoxyquinoline, quinoline, 6-methylquinoline, 3-bromoquinoline and 2-chloro-4-methylquinoline) as electron donor and picric acid as an electron acceptor. The infrared spectra (IR) of the solid complexes clearly indicated the formation of the hydrogen-bonding CT-complexes.
The annihilation spectra were analyzed into two lifetime components using PATFIT program. The values of the average and bulk lifetimes divide the complexes into two groups according to the non-bonding ionization potential of the donor (electron donating power) and the molecular weight of the complexes. Also, it is found that the ionization potential of the donors and molecular weight of the complexes have a conspicuous effect on the average and bulk lifetime values. The bulk lifetime values of the complexes are consistent with the formation of stable hydrogen-bonding CT-complexes as inferred from the IR-spectral data. 相似文献
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Anand D. Kasbekar Phillip L. Jones Andrew Crowson 《Journal of polymer science. Part A, Polymer chemistry》1989,27(4):1373-1382
Positron annihilation lifetime spectroscopy (PALS) was used to investigate the thermal cycling characteristics of two different molecular weight atactic polystyrene resins. Annealed compression molded samples were thermally cycled over the temperature range 253 K to 393 K with PAL spectra taken in 10 K increments upon both cooling and heating. The longest lived component lifetime and intensity, indicative of orthopositronium pick-off, exhibit thermal dependencies that can be interpreted in a manner consistent with anticipated free volume changes associated with structural transitions. 相似文献
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Zs. Kajcsos G. Dupltre L. Liszkay I. Billard A. Bonnenfant E. Azenha K. Lzr G. Pl-Borbly P. Caullet J. Patarin L. Lohonyai 《Radiation Physics and Chemistry》2000,58(5-6):709-714
Conditions that facilitate high Ps formation and interactions that modify the o-Ps lifetime were investigated by positron annihilation techniques in silicalite-1 and various Y-zeolites. Long lifetimes, up to 135 ns, and o-Ps fractions as high as 40% were found. The influence of heat treatment (in the range of 90–520 K), capillary condensation of N2 (0.085 MPa) and correlation with water removal was examined in Y-zeolites and in silicalite-1, respectively. The latter matrix was also studied in the presence of liquids. In various samples unexpected features were found (peculiar changes in the 2γ/3γ ratio, inversion in the trend of lifetime variations, disappearance of specific components, etc.), denoting the complexity of the processes governing the fate of e+ and Ps. 相似文献
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Chenze Qi Dong Ma Youha Hu Fengyuan Yan Hui Gao Zhi Yang Xiaoxian Zhou Tainmin Wang 《Journal of Polymer Science.Polymer Physics》2001,39(3):332-336
Positron annihilation lifetime spectra were measured on pure polystyrene (PS) and PS samples whose film surfaces were coated with gold, graphite (GR‐PS), or MoS2. The results showed the longest lifetime remained constant with measured time in all experimental samples, whereas the corresponding intensity decreased with time at different rates. The experimental phenomena were associated with the buildup of an electric field inside the polymer during extended positron annihilation lifetime spectroscopy (PALS) measurement. The decrease in the rate was attributed to the presence of conductive film causing the neutrality between positive charges and negative charges, thereby reducing the buildup of the electric field. Additionally, we also performed PALS measurement on GR‐PS under different experimental conditions, such as the conductive film being grounded or not grounded or the presence of an external electric field. These results further indicated that the buildup of the electric field was responsible for the decrease in the intensity with time. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 332–336, 2001 相似文献