共查询到20条相似文献,搜索用时 15 毫秒
1.
E. Matisová D. Hudec J. Garaj G. Kraus M. Schierhorn A. Isenberg 《Chromatographia》1985,20(10):601-608
Summary Glass capillary columns were prepared from non-deactivated and deactivated glass and coated with (2-methyl-4-[trans-4-n-propyl-cyclohexylcarbonyloxy]-benzoic acid-[4-n-heptyloxy-phenylester]) as the liqud phase, in different film thicknesses. The columns were tested using substances of different structures and polarities. It was verified that the capacity factors, retention indices and selectivity significantly depend on the thickness of the liquid crystalline stationary phase film and the quality of the tube, particularly in the case of columns with thin films. Trasition temperatures (melting and clearing point) of the liquid crystal are also dependent on these two factors.Dedicated to Professor J. F. K. Huber on the occasion of the his 60th birthday. 相似文献
2.
电厂烟气脱硝催化剂VO-WO/TiO失活机理研究 《燃料化学学报》2012,40(11):1359-1365
分别以某电厂失活和新鲜的烟气选择性催化还原(SCR)脱硝催化剂为研究对象,模拟测试催化剂的脱硝效率,并采用扫描电子显微镜-能量色散X射线光谱(SEM-EDX)、X荧光光谱(XRF)、X光电子能谱(XPS)、氮气吸脱附、傅里叶红外光谱(FT-IR)、X射线衍射(XRD)和热重分析(TG)等手段对催化剂的微观结构和表面形态进行表征,探讨了SCR催化剂的失活机制。结果表明,380℃下失活催化剂的脱硝效率(35.0%)和比表面积(1.05 m2/g)明显低于新鲜催化剂(88.2%,72.50 m2/g)。与新鲜催化剂相比,失活催化剂中V5+的比例由17.4%升高到32.2%,并且表面出现了大量的Al2(SO4)3。另外,SEM和XRD结果表明,失活催化剂出现了烧结。催化剂表面V价态的改变、高温烧结和表面Al2(SO4)3相的大量生成是催化剂失活的主要原因。 相似文献
3.
Rajesh K Somasundaram M Saiganesh R Balasubramanian KK 《The Journal of organic chemistry》2007,72(15):5867-5869
Highly deactivated aromatic compounds were smoothly monobrominated by treatment with N-bromosuccinimide (NBS) in concentrated H2SO4 medium affording the corresponding bromo derivatives in good yields. Mild reaction conditions and simple workup provides a practical and commercially viable route for the synthesis of bromo compounds of deactivated aromatics. 相似文献
4.
James F. Ponder Jr. Shawn A. Gregory Amalie Atassi Abigail A. Advincula Joshua M. Rinehart Guillaume Freychet Gregory M. Su Shannon K. Yee John R. Reynolds 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(1):e202211600
Herein, a route to produce highly electrically conductive doped hydroxymethyl functionalized poly(3,4-ethylenedioxythiophene) (PEDOT) films, termed PEDOT(OH) with metal-like charge transport properties using a fully solution processable precursor polymer is reported. This is achieved via an ester-functionalized PEDOT derivative [PEDOT(EHE)] that is soluble in a range of solvents with excellent film-forming ability. PEDOT(EHE) demonstrates moderate electrical conductivities of 20–60 S cm−1 and hopping-like (i.e., thermally activated) transport when doped with ferric tosylate (FeTos3). Upon basic hydrolysis of PEDOT(EHE) films, the electrically insulative side chains are cleaved and washed from the polymer film, leaving a densified film of PEDOT(OH). These films, when optimally doped, reach electrical conductivities of ≈1200 S cm−1 and demonstrate metal-like (i.e., thermally deactivated and band-like) transport properties and high stability at comparable doping levels. 相似文献
5.
Unsymmetric comonomers consisting of thiophene, pyrrole, and furan heterocycles were prepared using azomethine bonds. Photophysical investigation of the novel pi-donor-donor-donor segmented compounds revealed that their singlet excited state is only partially deactivated by internal conversion unlike their all-thiophene azomethine analogues. Temperature-dependent steady-state and time-resolved emission studies demonstrated that the unsymmetric compounds deactivated efficiently their singlet excited state by intersystem crossing to populate the triplet manifold. This lower energy state is rapidly deactivated by nonradiative self-quenching. The comonomers and their anodically prepared conjugated homocoupled products are both electrochemically active, resulting in new compounds that can be mutually oxidized and reduced. Meanwhile, the oxidation potentials of the coupled products are shifted by up to 400 mV to more cathodic potentials relative to their corresponding comonomers, confirming their increased degree of conjugation. 相似文献
6.
METHANE REFORMING WITH CARBON DIOXIDE TO PRODUCE SYNGAS?a?aCATALYST REGENERATION 总被引:1,自引:0,他引:1 下载免费PDF全文
Yongchen Shang Hengyong Xu Guolin Xu Shenglin Liu Guoxing Xiong Shishan Sheng 《天然气化学杂志》1999,8(1):61-67
The regeneration conditions of the deactivated catalyst 18wt%NiO/a-A12O3 used in methane reforming with carbon dioxide were studied by using a fix-bed flow reactor and TPR technique. When the deactivated catalyst was reduced at 1 123 K in a conventional regeneration process, the activity increased a little, but was still much lower than that of the fresh catalyst. When the deactivated catalyst was reduced, then treated in site With an activity-rejuvenating agent of 5-10 vo1% C (aqueous hydrogen peroxide solution) and reduced again at 1123K, the activity was renewed to approach that of the fresh one. 相似文献
7.
8.
Photosensitized oxidation through stearate monomolecular films 总被引:1,自引:0,他引:1
Abstract— The photosensitized oxidations of rubrene by methylene blue and of diphenylan-thracene by eosin have been studied where the sensitizer and the oxidizable substrate are separated by oxygen permeable layers of barium or cadmium stearate monomolecular films. The rate of the photosensitized oxidation reaction was followed by measurements of the hydrocarbon fluorescence, as a function of the stearate layer thickness. It has been found that the sensitized reaction is observable for thickness up to 500 Å and depends only on the deactivation process of the excited species (singlet oxygen) diffusing through the layers. It has been found also that half of the excited oxygen molecules are deactivated after a diffusion path of 115 A. The starting hydrocarbon can be regenerated by heating the sample after the photoreaction to approximately 120°C showing the transannular peroxide nature of the oxidation product. 相似文献
9.
Mayer-Helm BX Rauter W Rauchbauer G Tomastik C Bangert H 《Journal of separation science》2004,27(4):335-342
Two highly phenylated tetramethyl-p-silphenylene-diphenylsiloxane copolymers were coated on fused silica capillary columns and used as stationary phases in GC. The copolymers offered new insights into the coating process and column preparation due to their physicochemical properties. The fused silica capillary surface had to be pretreated in various ways to achieve a homogeneous film and a well deactivated surface: etching with ammonium bifluoride; leaching with sodium hydroxide and hydrochloric acid; silylation with tetraphenyldimethyldisilazane and triphenylsilylamine. Droplet formation was observed on tetraphenyldimethyldisilazane silylated surfaces leading to capillary columns with low separation efficiency. The topology of inhomogeneous films was investigated by light microscopy, scanning electron microscopy, and Auger electron spectroscopy. It became apparent that the stationary phase did not form droplets but islands, which are connected by a wetting layer according to the Stranski-Krastanov growth mode. Both copolymers are potential stationary phases for high-temperature GC with promising properties. They offer a higher overall polarity than 75% phenyl, 25% methyl-polysiloxanes in combination with increased thermal stability and reduced bleed levels. 相似文献
10.
Qingfa Wang Li Wang Yaquan Wang Fei He Zhenhua Li Zhentao Mi 《Reaction Kinetics and Catalysis Letters》2004,81(2):297-304
Deactivated palladium catalysts in the hydrogenation of anthraquinione were regenerated with ethanol, nitric acid, hydrogen
peroxide, boiling water and steam, respectively. The deactivated and regenerated catalysts were characterized by XPS, ICP,
TG, FTIR, TPD, XRD, etc., and studied in the hydrogenation of anthraquinone. The results showed that the main cause of catalyst deactivation is the
coverage of the active component by deposits. The treatments by hydrogen peroxide and boiling water can effectively regenerate
the deactivated catalysts.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
The aza-Morita-Baylis-Hillman (azaMBH) reaction has been studied for electronically and sterically deactivated Michael acceptors. It is found that electronically deactivated systems can be converted with electron-rich phosphanes and pyridines as catalysts equally well. For sterically deactivated systems clearly better catalytic turnover can be achieved with pyridine catalysts. This is in accordance with the calculated affinities of the catalysts towards different Michael-acceptors. 相似文献
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13.
Mizue Fujio Toshikazu Adachi Yoshifumi Shibuya Akihisa Murata Yuho Tsuno 《Tetrahedron letters》1984,25(40):4557-4560
Substituent effects of p-MeO and p-MeS groups deactivated by additional m-substituents in cumyl and α-phenylethyl solvolyses were studied to provide evidence for the higher resonance demand in the α-phenylethyl system. 相似文献
14.
钯催化气相氧化羰基化合成碳酸二甲酯 总被引:5,自引:0,他引:5
通过催化剂反应性能和反应前后XPS谱图对比,分析了负载型钯催化剂在甲醇气相氧化羰基化合成碳酸二甲酯过程中的失活原因,研究了HCl在维持催化剂活性及失活催化剂再生中的作用.结果表明,氯离子的流失是负载型钯碳催化剂失活的主要原因.由于氯离子的流失,对于PdCl2/AC催化剂,钯很容易从二价变为零价:对于PdCl2-CuCl2/AC催化剂,CuCl2发生变化,失去使钯保持二价氯化物状态的功能.在反应过程中补充HCl可以延长催化剂的寿命,也可以利用HCl对失活催化剂进行再生,但采用HCl不能从根本上解决催化剂失活的问题. 相似文献
15.
考察了MgO/BaCO3催化剂上加压条件下甲烷氧化偶联反应的性能.结果表明,加压下甲烷转化率及C2选择性都明显下降,且当压力再恢复至常压后,其性能仍不能恢复,说明催化剂已经失活.XRD谱表明,加压失活催化剂表面有部分MgCO3生成.但是,活性相MgO部分碳酸化转变为MgCO3不是导致催化剂失活的主要原因,因为MgCO3的分解温度远低于反应温度,常压下其性能应当恢复.SEM结果表明,加压失活催化剂的颗粒增大.XPS表征结果表明,加压失活催化剂中的BaCO3向表面富积,致使催化剂表面活性相MgO的浓度和催化剂比表面积降低.根据以上结果可以认为,催化剂中的BaCO3向表面富积的过程中会部分覆盖活性相MgO,从而会使催化剂中MgO与BaCO3之间的协同作用遭到破坏,导致催化剂失活. 相似文献
16.
低温NH_3-SCR催化剂MnO_x-CeO_x/ACF的SO_2中毒机理(英文) 总被引:1,自引:0,他引:1
在二氧化硫(SO2)气氛下,对Fe、Cu和V改性的催化剂MnOx-CeOx/ACF(活性碳纤维)的氨选择性催化还原(NH3-SCR)一氧化氮的低温活性进行研究.实验结果表明:以Cu和V改性催化剂未提高MnOx-CeOx/ACF的低温抗SO2性能;Fe改性MnOx-CeOx/ACF在初始6h内提高了催化剂的抗SO2性能,但较长时间仍然失活.以N2吸附、X射线光电子能谱(XPS)、傅里叶变换红外(FT-IR)光谱以及热重分析(TGA)等手段对中毒催化剂进行分析.在SO2存在下,催化剂中毒归因于两个方面:一是覆盖于催化剂表面的铵盐类物质,二是SO2与催化剂中的金属氧化物反应生成的金属硫酸盐及亚硫酸盐.在中毒催化剂中硫元素主要以金属硫酸盐及亚硫酸盐的形式存在,其在中毒的MnOx-CeOx/ACF、Fe-MnOx-CeOx/ACF、Cu-MnOx-CeOx/ACF和V-MnOx-CeOx/ACF催化剂中所占比例分别为70.4%、68.9%、86.3%和71.4%(w).进一步揭示了MnOx-CeOx/ACF催化剂在低温SCR条件下的SO2中毒机理. 相似文献
17.
Nitrogen-containing chemicals are one of the important families of compounds relevant to the purposes of the Chemical Weapons Convention (CWC). Several applications, using various injection modes, of new deactivated columns specially designed for basic compounds are presented. These columns prove remarkably well-suited to the gas chromatographic (GC) analysis of the chemicals of interest, even to underivatized amino-alcohols, whose analysis on conventional GC columns is often difficult and hindered by poor resolution and high detection limits. Such a deactivated phase can even replace the typical GC phases used for CWC verification purposes. 相似文献
18.
研究了共沉淀法制备的系列金属负载型催化剂合成气制甲醇反应性能,重点考察了催化剂上合成甲醇反应体系的耐硫性能。结果表明,Cu/ZnO催化剂显示了较好的甲醇合成反应性能,但该反应在含硫气氛下迅速失活;Pd/CeO2催化剂体现了良好的甲醇合成反应性能和该反应体系的高耐硫性能。结合多种物理化学表征手段分析得出, Cu/ZnO催化剂在含硫气氛下因活性组分形成金属硫化物而失活;Pd/CeO2催化剂中的载体CeO2可优先与硫作用而保护金属活性组分,进而保持了Pd/CeO2反应体系的高抗硫性能。 相似文献
19.
Yu. E. Sklyar R. P. Evstigneeva N. A. Preobrazhenskii 《Chemistry of Heterocyclic Compounds》1967,2(2):152-155
With 2-acetyl- and 2-formylpyrrole, salt formation is via proton addition to the carbonyl oxygen. In salt formation with pyrrole derivatives having an acetyl or formyl group at position 2, position 5 is deactivated for electrophilic substitution. With salts of 3-acetyl- and 3-formylpyrroles, position 2 is also deactivated, while position 5 is activated. 相似文献
20.
丙烷脱氢PtSn/AlO催化剂积炭行为研究 《燃料化学学报》2017,45(9):1130-1136
通过HRTEM、XRD、FT-IR、Raman、~(13)C NM R、NH_3-TPD、DTG及元素分析等表征手段,研究了丙烷脱氢PtSn催化剂积炭性质及其对催化剂结构的影响,分析了催化剂的积炭失活过程。结果表明,积炭覆盖活性位并堵塞催化剂孔道是催化剂失活主要因素;与新鲜催化剂相比,催化剂积炭完全失活后,Pt颗粒粒径并没有明显变化;完全失活时,XRD谱图出现了无定形石墨炭的衍射峰;随着积炭量的增加,焦的石墨化程度越高,芳构化程度加深,难以消除的炭增多,再生难度加大。提出丙烷在Pt活性位深度脱氢形成积炭并向载体转移的历程,认为更为稳定的C_(24)H_(12)是积炭前驱体。 相似文献