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41.
Here we report the formation and spectroscopic properties of cadmium sulfide (CdS) nanocrystal systems: individual nanocrystal and CdS aggregates. The optical absorption and luminescence spectra of the aggregated CdS nanocrystals and individual nanocrystal show exciton aggregate and individual exciton characteristics. Although it is not Bose-Einstein condensation, such aggregated quantum dots (QDs) seem to supply us opportunity to study the interactions and condensation of excitons in multi-QDs system, not in the separated QDs system. 相似文献
42.
Novel expanded porphyrinoids with advanced structure features have a wide range of benefits (such as multi-metal coordination and facile tunable aromaticity) not offered by their normal porphyrin analogues. Considering research efforts have been devoted to address their limited synthetic accessibility issue. This review highlights some of these recent synthetic progresses towards these novel expanded porphyrinoids. 相似文献
43.
合成了螺[异苯并呋喃-1(3H),9'-(9H)-2'-N,N-二苄胺基-6'-二乙胺基占吨]-酮-3,C_(37)H_(34)N_2O_3,单斜晶系,空间群Cc,晶体学参数为a=16.826(4),b=10.648(4),c=17.618(7),β=92.25(2)°,V=3154(2),Z=4,M_r=566.7,D_x=1.19g/cm3,F(000)=1200。结构由直接法解出,偏离因子R=0.080。分子由占吨和异苯并呋喃两部分组成Y形结构,占吨部分相连的苄基的两个苯环位于占吨部分的两侧。 相似文献
44.
A new potential tetradentate ligand, 1,4-bis(N-1-methylimidazol-2-ylmethyl)-1,4-diazacycloheptane (l), together with its CuII complex [CulCl]ClO4 (1), has been reported. The crystal structure of 1, determined by single-crystal X-ray analysis, shows that it is in chiral P212121 space group. The CuII centre is penta-coordinated in square pyramidal geometry and the diazacycloheptane (DACH) ring adopts normal boat configuration. The most striking feature of this complex is the formation of a 3D network bridged through the C-H?Cl hydrogen bonds with the perchlorate anions in the cavities, and stabilized via π-π stacking interactions along the a-direction. The solution behaviour of 1 has been further investigated by UV/Vis and ESR techniques. 相似文献
45.
46.
Xiucheng Zheng Xiaoli Zhang Shuping Wang Xiangyu Wang Shihua Wu 《天然气化学杂志》2007,16(2):179-185
In this work, we have reported the influence of the addition of base (KOH) on the physicochemical property of ceria synthesized by alcohothermal process, and the alcohothermal mechanism was also put forward. Furthermore, the prepared CeO2 was used as the support to prepare CuO/CeO2 catalysts via the wet impregnation method. The samples were characterized by N2 adsorption-desorption, X-ray powder diffraction (XRD), high resolution transmission electron microscopy (HRTEM), and temperature-programmed reduction by H2 (H2-TPR). The catalytic properties of the CuO/CeO2 catalysts for low-temperature CO oxidation were studied using a microreactor-GC system. The crystal size of CeO2-A was much smaller than that of CeO2-B, and the corresponding copper oxide catalysts exhibited higher catalytic activity than that of the CeO2-B-supported catalysts under the same reaction conditions. The alcohothermal mechanism indicated that KOH plays a key role in determining the physicochemical and catalytic properties of ceria-based materials. 相似文献
47.
La2O3对Ni/γ-Al2O3甲烷化催化剂的助催化作用 总被引:14,自引:0,他引:14
我国将稀土作为助剂引入镍基甲烷化催化剂,大大提高了催化剂的活性和热稳定性,并已投入工业应用[1-3].稀土对不同镍催化剂反应性能及其作用机理的研究已有一些报导[3-7].谢有畅等观察到镍负载在经单层La2O3改性的γ-Al2O3表面,其晶粒要比没有La2O3时小得多.Rotgerink等认为添加La后反应速率的增加不只是由于几何效应,而是La对甲烷化本身有促进作用,单位镍表面的活性是随La含量不同而改变的,活性增加的同时表观活化能也增加[5].作为助剂的La2O3在氢还原和反应过程中的变化及其作用的研究和讨论较少,目前一般认为添… 相似文献
48.
The thermal decomposition of ammonium vanadyl oxalate supported on La2O3, MgO, SiO2, Al2O3, ZrO2, TiO2, SAPO-5, and ZSM-5 oxides in a dynamic atmosphere of dry air was compared by thermal gravimetric analysis (TG) and differential thermal analysis (DTA). The calcined catalysts were characterized by X-ray diffractometry (XRD). The TG and DTA results demonstrate that the surface acid-base properties of the oxides play a significant role in the decomposition behaviour of the supported ammonium vanadyl oxalate, i.e. the basic oxides exhibit an endothermic effect and the acidic oxides show an exothermic effect. Two mechanisms are suggested for thermal decomposition of ammonium vanadyl oxalate on basic and acidic oxides, respectively. After transformation of the ammonium vanadyl oxalate to vanadia, subsequent rearrangement of the vanadia on the surface of the supports was also observed. During the thermal treatment or calcination in air, solid state reactions of vanadia with the surface of oxides such as La2O3, ZrO2 and TiO2 took place to form new phases. 相似文献
49.
Ionic-liquid-supported peptide synthesis demonstrated by the synthesis of Leu(5)-enkephalin 总被引:1,自引:0,他引:1
A new strategy for the synthesis of oligopeptides was developed using an ionic liquid as a soluble support. The efficiency of this ionic liquid-phase approach was demonstrated by the synthesis of a bioactive pentapeptide, Leu(5)-enkephalin, in good yield and reasonable purity. The structures and purities of the reaction intermediates in each step were verified easily by routine spectroscopic analysis, and no chromatographic procedures were needed during the synthesis. 相似文献
50.
Xin Sheng Li Yao Jun Zhang Qin Xin Chun Xin Ji Yan Fen Miao Li Wang 《Reaction Kinetics and Catalysis Letters》1996,57(1):177-182
Volumetric H2-uptake measurements on an Mo2N (79 m2g–1) sample reduced at 673 K have been carried out and the uptake isotherms in the temperature range of 308–623 K have been determined. Both the total and reversible hydrogen uptake increased with the uptake temperature. The irreversible hydrogen uptake increased abruptly when the uptake temperature was raised up to 423 K. The maximum of irreversible hydrogen uptake was measured at 473 K. The HIR/Mo ratio calculated from the uptakes obtained in the temperature range of 308–623 K varies in the range of 0.0010–0.0202. One possible mechanism for hydrogen adsorption is proposed to be heterolytic dissociation on Mo-N paris, in which the molybdenum atoms are in unsaturated coordination. 相似文献