排序方式: 共有29条查询结果,搜索用时 15 毫秒
1.
2.
3.
镨叶绿素a分子结构的确定 总被引:7,自引:0,他引:7
通过合成镨叶绿素a(Pr-Chla)研究了稀土在叶绿素中的结合方式.Pr-Chla的紫外可见光谱(UV-Vis)、红外光谱(FTIR)证实镨离子已配位到叶绿素a的卟啉环上.其磁圆二色谱(MCD)在Soret带具有双层夹心卟啉的特征结构;通过扩展X射线吸收精细结构谱(EXAFS),采用双层夹心结构模型拟合,确定了Pr周围的近邻结构.表明合成镨叶绿素a具有双层夹心结构.Pr(Ⅲ)夹于两个卟啉环之间,与上下卟啉环上共8个N原子配位,Pr-N键平均键长0.242nm. 相似文献
4.
5.
采用连续浸渍法制备了一系列非贵金属稀燃NOx阱(LNT)催化剂CuO-K2CO3/TiO2,考察了Cu负载量对催化剂结构和NOx储存还原性能的影响.发现8% (w) CuO-K2CO3/TiO2催化剂的催化性能最佳,其对NOx的储存量达到1.559 mmol·g-1,对NOx的还原效率高达99%,且在NOx还原过程中无副产物N2O产生.应用粉末X射线衍射(XRD),高分辩透射电子显微镜(HR-TEM), CO2程序升温脱附(CO2-TPD),扩展X射线吸收精细结构(EXAFS),氢气程序升温还原(H2-TPR)和原位漫反射红外光谱(in-situ DRIFTS)等技术详细表征了催化剂的结构.结果表明,不同Cu负载量的催化剂中,铜物种均主要以CuO相存在.铜的负载量直接影响铜物种、钾物种的存在状态,高分散的CuO相与表面K2CO3之间存在较强相互作用,这种相互作用不仅有利于NOx的储存,而且有利于增强催化剂的稳定性. in-situ DRIFTS结果表明, NOx储存过程中产生的两个负峰(1436和1563 cm-1)缘于碳酸盐的分解,这间接证明了碳酸盐作为储存介质参与到NOx储存反应中. EXAFS结果表明,经过15个稀燃/富燃循环测试,催化剂中的CuO相仍保持稳定.基于以上表征结果,提出了CuO和K2CO3在催化剂表面的分布模型,并探讨了NOx储存还原的可能机理. 相似文献
6.
ZHENG Li-Rong CHE Rong-Zheng LIU Jing DU Yong-Hua ZHOU Ying-Li HU Tian-Dou 《中国物理C(英文版)》2009,33(8):701-705
X-ray absorption fine structure (XAFS) spectroscopy is a powerful technique for the investigation of the local environment around selected atoms in condensed matter. XAFS under pressure is an important method for the synchrotron source. We design a cell for a high pressure XAFS experiment. Sintered boron carbide is used as the anvils of this high pressure cell in order to obtain a full XAFS spectrum free from diffraction peaks. In addition, a hydraulic pump was adopted to make in-suit pressure modulation. High quality XAFS spectra of ZrH2 under high pressure (up to 13 Gpa) were obtained by this cell. 相似文献
7.
The luminescent materials SrB4O7: Eu and BaB8O13: Eu were synthesized, and the valence states of europium in the materials were measured by means of XANES at Eu-L3 edge. It is found that the Eu3 and Eu2 ions are all present in the materials, and more Eu3 ions can be reduced in SrB4O7: Eu than in BaB8O13:Eu. The excitation and emission spectra of Eu3 in SrB4O7: Eu and BaB8O13:Eu were determined. 相似文献
8.
WANG Jia-Ou DU Yong-Hua Kurash Ibrahim HONG Cai-Hao XIE Ya-Ning HU Tian-Dou 《中国物理C(英文版)》2007,31(1):101-103
Perovskite oxides LaFe1-xCrxO3 were synthesized by solid state reaction method. X-ray powder diffraction was tested to characterize the crystalline structure of the samples. The result indicates that the samples are single orthorhombic phase. The lattice parameter decreases with the Chromium concentration. The extend X-ray absorption fine structures (EXAFS) of the Fe K-edge as a function of doping level x show that the Fe-La bonds distance decreases dramatically. This suggests that Lanthanum is very important for the stability of the whole LaFe1-xCrxO3 structure. 相似文献
9.
NOx储存催化剂Pt/BaAl2O4-Al2O3的XAFS研究 总被引:1,自引:0,他引:1
采用共沉淀-浸渍法在不同载体焙烧温度下,制备了不同Al/Ba原子比的Pt/BaAl2O4-Al2O3系列样品.用XRD, XANES, EXAFS,以及NSC (NOx storage capacity)测定等手段对样品的微观结构和NOx储存性能进行了详细的表征.样品中Ba物种是以BaAl2O4和BaCO3两种混合物相的形式存在,且伴随着载体焙烧温度和Ba含量的降低, BaAl2O4物相的分散度变高, NOx储存活性也随之提高,这表明BaAl2O4相的分散度与样品的NOx储存性能密切相关,小颗粒的BaAl2O4相是NOx的主要储存活性中心.在样品中, Pt物种以金属原子簇形式存在,分散度很高,其Pt-Pt壳层配位数较标样Pt粉有显著下降, Pt-Pt键长变短,出现了纳米收缩现象.高分散的小颗粒金属Pt原子簇为捕获和氧化NOx的主要活性中心. 相似文献
10.
Lei Chen Xue-Hai Yu Chang-Zheng Yang Qin Chao Gu Tian-Dou Hu Ya-Ning Xie 《Journal of Polymer Science.Polymer Physics》1997,35(5):799-806
In this study, a series of polyether-ester ionomers was prepared by neutralizing the carboxylic acid groups in 1 : 1 copolymers of benzenetracarboxylic dianhydride (BTDA) and poly(tetramethylene oxide) or poly(ethylene oxide) glycol. The base polymers were in a liquid state while the ionomers were in solid state and a separate ionic phase was formed. The local structure and the morphology of the ionomers were investigated by dynamic mechanical analysis, Fourier transform infrared spectroscopy, and small-angle x-ray scattering as well as extended x-ray absorption fine structure. Clearly, the geometric structure of the ionic sites varied with the nature of the metal ions and the morphology of the ionomers was determined by the microstructure of the ion aggregates. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 799–806, 1997 相似文献