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991.
有序介孔Sn-SBA-15负载铂催化剂上丙烷脱氢性能的提高 总被引:1,自引:0,他引:1
丙烷脱氢制丙烯能够将低级烷烃转变成烯烃,是有效扩大丙烯来源的生产工艺.铂锡催化剂用于丙烷催化脱氢的主要缺点是稳定性差、选择性低,通过稳定锡的氧化态可以大大改善催化剂的脱氢性能及稳定性.本文采用一锅水热合成法制备了一系列高比表面积具有高度有序介孔结构的Sn掺杂的Sn-SBA-15材料,并作为载体负载铂催化剂用于丙烷脱氢反应.同时利用传统浸渍法(IM)合成了Sn/SBA-15-IM材料作为对比.结合X射线衍射(XRD)、BET比表面积和孔体积测试、红外光谱(FT-IR)、X射线光电子能谱、H2程序升温脱附(H2-TPD)、热重分析(TGA)、扫描电镜和透射电镜等多种物理化学表征手段研究了Sn-SBA-15材料和催化剂的结构性质及其丙烷脱氢反应性能.XRD和BET比表面积和孔体积测试结果表明,水热合成法原位引入助剂Sn不影响载体SBA-15的有序孔道结构,同时能够保持较大的比表面积.传统浸渍法引入Sn会堵塞载体孔道,载体比表面积及孔道有序度下降.Sn掺杂进入SBA-15骨架能够增强Sn物种与载体的相互作用,有利于Sn物种在反应过程中保持氧化态,提高催化剂丙烷脱氢反应的活性及选择性.当Sn掺杂量增至2.0 wt%时,Pt,Sn组分与载体之间的相互作用减弱,催化剂中Sn0物种所占比例增多,导致催化剂丙烷脱氢性能下降.在丙烷脱氢反应过程中,一锅法引入Sn的催化剂上反应活性和稳定性明显优于浸渍法引入Sn的催化剂.其中,Pt/0.5 Sn-SBA-15催化剂表现出最优的丙烷脱氢性能,丙烷转化率为43.8%,丙烯选择性为98.5%. 相似文献
992.
Lan Luo Ziyi Zhang Yanhua Chen Lixia Zhang Xiangfeng Bu Hanqi Zhang 《International journal of environmental analytical chemistry》2017,97(12):1178-1191
A simple and sensitive surface-enhanced Raman spectroscopy (SERS) method for the detection of safranine T (ST) and Hg2+ using silver nanoparticles (AgNPs) as substrate was developed. ST can absorb on the surface of AgNPs through electrostatic interaction, the electromagnetic effect combined with chemical adsorption effect give a notable Raman enhancement for ST. The presence of Hg2+ well decreased the absorbed ST molecules on AgNPs, leading to a significant decrease of SERS signals thus enabling to detect Hg2+. The determination conditions for SERS, including the amount of AgNPs, the concentration of NaCl, the concentration of HCl, the concentration of ST and the reaction time, were optimised. Under the optimised experimental conditions, good linear responses were obtained for ST and Hg2+ in the concentration ranges of 0.01–4.0 μmol L?1 (3.5–1403.4 ng mL?1) and 0.01–2.0 μmol L?1 (2.0–401.2 ng mL?1), the limit of detection were 3.0 nmol L?1 (1.1 ng mL?1) and 2.0 nmol L?1 (0.4 ng mL?1), respectively. The present method was subsequently applied to the determination of ST in tomato sauces and Hg2+ in environmental waters, the recoveries of ST and Hg2+ in spiked samples are 95.5–107.8% and 91.4–110.8 %, respectively. 相似文献
993.
This paper presents the use of a parameter continuation method and a test function to solve the steady, axisymmetric incompressible
Navier–Stokes equations for spherical Couette flow in a thin gap between two concentric, differentially rotating spheres.
The study focuses principally on the prediction of multiple steady flow patterns and the construction of bifurcation diagrams.
Linear stability analysis is conducted to determine whether or not the computed steady flow solutions are stable. In the case
of a rotating inner sphere and a stationary outer sphere, a new unstable solution branch with two asymmetric vortex pairs
is identified near the point of a symmetry-breaking pitchfork bifurcation which occurs at a Reynolds number equal to 789.
This solution transforms smoothly into an unstable asymmetric 1-vortex solution as the Reynolds number increases. Another
new pair of unstable 2-vortex flow modes whose solution branches are unconnected to previously known branches is calculated
by the present two-parameter continuation method. In the case of two rotating spheres, the range of existence in the (Re
1
, Re
2
) plane of the one and two vortex states, the vortex sizes as a function of both Reynolds numbers are identified. Bifurcation
theory is used to discuss the origin of the calculated flow modes. Parameter continuation indicates that the stable states
are accompanied by certain unstable states.
Received 26 November 2001 and accepted 10 May 2002 Published online 30 October 2002
Communicated by M.Y. Hussaini 相似文献
994.
In Part II a large-scale sound source in a time-developing planar free mixing layer is studied using an acoustic analogy
approach. It is shown that only the non-compact character of the source resembles well the character of the corresponding
source in a spatially developing flow. A model based on a continuous assembly of wave packets is derived and applied to direct
numerical simulation results of two supersonic time-developing mixing layers undergoing transition to turbulence. The analysis
predicts two distinctive dominant Mach wave sources in agreement with the direct analysis of Part~I. The first dominates during
the stage of the Λ-vortex structure and the second just prior to the final breakdown to a fine-scale structure. The convective
velocity of the second Mach wave source is higher than the first and thus its Mach angle of radiation is higher. The second
source has a reduced strength at the higher free-stream Mach number. Directivity and frequency spectra compare well with the
results of Part I, demonstrating that the assumptions inherent in the analogy are quite reasonable.
Received 5 August 1997 and accepted 6 April 1998 相似文献
995.
996.
本文提出了一种用于光弹性复合材料的简化应变——光学定律。按照这一简化定律。模型材料的主应变差和主应变方向只要利用光弹性实验测出的等差线与等倾线即可求得。些是一种正交异性光弹性分析的近似方法,这一方法所得结果与实验数据比较,最大误差在10%左右。由于采用简化应变——光学定律使得正交异性光弹性分析工作大为简便,因此它是一种适合于工程应用的近似方法。 相似文献
997.
Ziwen Jiang Yongsheng Zhao Zhixun Luo Aidong Peng Hao Wang Prof. Dr. Jiannian Yao 《中国化学》2010,28(11):2103-2108
Doped nanoparticles were prepared from pyrene and phenanthrene using a facile reprecipitation method. The doped nanoparticles presented unique delayed fluorescent emissions of pyrene under the unprotected condition. The ratio of the intensity of delayed fluorescence (IDF) to that of phosphorescence (IP) is about 4:1, which almost keeps unchanged with the decrease of pyrene content at room temperature. The intensity of the delayed fluorescence emissions is dependent on the relative content of pyrene, as well as the aggregation degree of nanoparticles. The delayed emissions are contributed to efficient triplet‐triplet energy transfer from phenanthrene (donor) to pyrene (acceptor). Steady fluorescence measurement have proved that the singlet‐singlet energy transfer process was also existent dominated by the radiation energy transfer mechanism. 相似文献
998.
Luo Mei Sun Jie Zhou Shi-Ming Yin Hao Hu Ke-Liang 《Research on Chemical Intermediates》2010,36(9):1049-1054
Two opposite configuration (R/S) of chiral complexes (C8H11N)2·CuCl2 were obtained from the reaction of chiral d(+)/l(−)-α-ethylphenyl amine with copper chloride (II) in dry ethanol. The crystal structures of 1a and 1b were characterized by
IR, elemental analysis and X-ray crystallography. 相似文献
999.
Hui Ming Ge Dr. Wen Hao Yang Yan Shen Dr. Nan Jiang Dr. Zhi Kai Guo Qiong Luo Qiang Xu Prof. Jing Ma Prof. Ren Xiang Tan Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(21):6338-6345
Two novel resveratrol aneuploids, hopeachinols A ( 1 ) and B ( 2 ), as well as a potent immunosuppressive polyphenol diptoindonesin G ( 3 ) were characterized from the ethanol extract of Hopea chinensis stem barks. The structure of the polyphenols was accommodated by comprehensive spectroscopic analysis with the absolute stereochemistry determined by the CD approach coupled with theoretical ECD spectra computer‐generated through the Gaussian 03 program. The distinct structure and biological profile of 3 recommended it as a starting molecule for the relevant drug discovery. 相似文献
1000.
The palladium-catalyzed semi-hydrogenation of alkynes to trans- or cis-alkenes employing HSiEt3 as the reductant is developed. The CuSO4 played a significant role for the trans/cis stereoselectivity. The labeling study revealed that the two olefinic hydrogen atoms came from HSiEt3 and H2O, respectively. 相似文献