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151.
SO42 - /ZrO2 SiO2 催化剂是90年代出现的一种新型复合超强酸催化剂[1 -3],它具有比表面积高、酸量大、制备成本低等显著的优点.热分析技术是研究硫酸促进型超强酸催化剂的重要工具.80年代以来 ,许多研究者曾采用热分析技术对SO4/ZrO2 等催化剂的结构及其形成过程进行了研究[4 -6],所得到的结果为揭开这类催化剂的结构和形成机理起到了重要的作用.本文采用TGA/DTA技术对该催化剂的结构及其酸性结构的形成过程进行了研究 ,结果揭示了催化剂的组成与结晶温度的关系、催化剂中SO42 - 基团与Z… 相似文献
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The Hofmeister ion effect is a very interesting but elusive phenomenon, the importance of which is revealed in self-assembly, ion recognition, and protein folding regulation. With an increasing number of studies suggesting that interactions between ions and solutes play a role in the Hofmeister ion effect, the nature of the Hofmeister phenomenon becomes more debatable. Yet, it is not clear whether the Hofmeister ion effect is a local effect or bulk effect that can reach beyond many hydration shells, where specific interactions between ions and solutes play key roles. In order to further explore this, we applied proton nuclear magnetic resonance (1H-NMR) spectroscopy to study the effects of specific ions on the local environment around N, N-dimethylpropionamide (NDA) and N-isopropylisobutyramide (NPA), which are the model compounds for poly(2-ethyl-2-oxazoline) and poly(N-isopropylacrylamide), respectively. These polymers are important bio-engineering materials that possess thermoresponsive properties and are also subject to specific ion effects. By correlating the changes in chemical shifts of the two methyl groups on either side of the amide bond, it was found that the Hofmeister ion effects on NPA were more anisotropic than on NDA, and that the cationic effects were more anisotropic than the anionic effects on NPA. These results indicated that the effects of specific ions were almost identical for all methyl groups of NDA. On the other hand, NPA is a larger molecule; thus, not all of its methyl groups were subjected to the specific ion effects to the same extent. The calculation of the electrostatic potential surfaces of NDA and NPA suggested that these observations on the Hofmeister ion effects might be due to steric hindrance, and that the observations on the cationic effects might be due to the interactions between cations and NPA being stronger than the interactions between anions and NPA. This would explain why the highly charged cations caused a significant anisotropicity. Additionally, we found that the chemical shift of the water protons (ΔδH2O) of conventional kosmotropic anions was larger than zero, which suggested a stronger HB and more charge transfer between water and these anions. The ΔδH2O of conventional chaotropic anions was less than zero. Despite the different solutes, the results were indifferent in both NDA and NPA solutions. Surprisingly, the ΔδH2O of Cl- at concentrations lower than 1 mol∙L-1 was zero, thus becoming the benchmark between chaotropes and kosmotropes. These results suggested a quantitative measurement of kosmotropicity/chaotropicity, where the anion would be kosmotropic if its ΔδH2O were higher than that of Cl- and chaotropic for the opposing condition. Moreover, the results showed that the effects of the cations on the water structure were minimal, which was consistent with minimal charge transfer between the cations and water. The overall results of this study suggest that the Hofmeister ion effect is a global effect, while local interactions of ions with solutes also play a key role. 相似文献
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Hak‐Suk Sim Xinhui Feng Jaesook Yun Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(8):1939-1943
Josi or Mandy? Asymmetric conjugate addition of diboron to acyclic enones catalyzed by copper affords chiral organoboronates that possess a boronate group at the β stereocenter with excellent chemical yields and enantioselectivities (see scheme). This method accommodates the structural variation of acyclic enones and provides access to highly functionalized chiral organoboronates in one step.
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<正>A novel closed-form expression for average capacity is derived for free-space optical(FSO) links over Gamma-Gamma turbulence channels by considering the effect of misalignment(pointing errors).The simulation results show that the average capacity of the FSO links can be analyzed with the effects of atmospheric turbulence condition,beam width,detector size,jitter variable,and transmitted optical power. Meanwhile,the results are further provided to verify the accuracy of our mathematical analysis.This work is useful for the FSO designer. 相似文献
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The split delivery vehicle routing problem (SDVRP) relaxes routing restrictions forcing unique deliveries to customers and
allows multiple vehicles to satisfy customer demand. Split deliveries are used to reduce total fleet cost to meet those customer
demands. We provide a detailed survey of the SDVRP literature and define a new constructive algorithm for the SDVRP based
on a novel concept called the route angle control measure. We extend this constructive approach to an iterative approach using
adaptive memory concepts, and then add a variable neighborhood descent process. These three new approaches are compared to
exact and heuristic approaches by solving the available SDVRP benchmark problem sets. Our approaches are found to compare
favorably with existing approaches and we find 16 new best solutions for a recent 21 problem benchmark set. 相似文献
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Ma Ruijie Liu Tao Luo Zhenghui Guo Qing Xiao Yiqun Chen Yuzhong Li Xiaojun Luo Siwei Lu Xinhui Zhang Maojie Li Yongfang Yan He 《中国科学:化学(英文版)》2020,63(3):325-330
Power conversion efficiency(PCE) of single-junction polymer solar cells(PSCs) has made a remarkable breakthrough recently.Plenty of work was reported to achieve PCEs higher than 16% derived from the PM6:Y6 binary system.To further increase the PCEs of binary OSCs incorporating small molecular acceptor(SMA) Y6,we substituted PM6 with PM7 due to the deeper highest occupied molecular orbital(HOMO) of PM7.Consequently,the PM7:Y6 has achieved PCEs as high as 17.0% by the hotcast method,due to the improved open-circuit voltage(V_(OC)).Compared with PM6,the lower HOMO of PM7 increases the gap between E_(LUMO-donor) and E_(HOMO-acceptor),which is proportional to V_(OC).This research provides a high PCE for single-junction binary PSCs,which is meaningful for device fabrication related to PM7 and commercialization of PSCs. 相似文献