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排序方式: 共有100条查询结果,搜索用时 15 毫秒
1.
Wataru Ueda Kenzo Oshihara Damien Vitry Tokio Hisano Youhei Kayashima 《Catalysis Surveys from Japan》2002,6(1-2):33-44
Mo-V-M(=Al, Ga, Bi, Sb and Te)–O mixed oxide catalysts were synthesized hydrothermally for the first time, characterized structurally, and tested for ethane and propane oxidation after activation by various ways. These catalysts were black solids of rod-shaped (fiber like) crystals, which had a layer structure in the direction of fiber axis and a high dimensional arrangement of metal octahedra in the cross-section plane. These fresh crystalline materials became active for catalytic oxidation of alkanes after heat-treatment at 600 °C and subsequent grinding in order to increase exposed plane of the cross-section. The resulting catalysts were very active for an oxidative dehydrogenation of ethane with 80% of the ethylene selectivity in the reaction temperature range of 300 to 400 °C and also showed about 50% selectivity to acrylic acid in the propane oxidation. Multi-functional character which derived from the high dimensional structure of the catalysts and mechanism of the selective alkane oxidation were discussed. 相似文献
2.
Rubén A. Machado David Rivillo Lindora D’Ornelas Reinaldo Atencio Esperanza Galarza 《Journal of organometallic chemistry》2004,689(15):2486-2493
The reaction of the labile compound [Re2(CO)8(CH3CN)2] with trans-1,2-bis(2-pyridyl)ethene (C12H10N2) at room temperature in tetrahydrofuran affords the compounds [Re2(μ:η3-C12H10N2)(CO)8] (1) and the oxidative addition product [Re2(μ-H)(μ:η3-C12H9N2)(CO)7] (2). When the reaction is carried out at temperatures of refluxing tetrahydrofuran, besides compounds 1 and 2, the oxidative addition product [Re2(μ-H)(μ:η4-C12H9N2)(CO)6] (3), the insertion product [Re2(μ:η4-C12H10N2)(CO)8] (4) and [Re2(μ:η6-C24H18N4)(CO)6] (5) are obtained. Compound 5 contains the organic ligand rtct-tetrakis(2-pyridyl)cyclobutandiyl which is derived from a [2 + 2] cycloaddition of 1,2-bis(2-pyridyl)ethene mediated by its coordination to the bimetallic framework. The molecular structures of 1, 2, 4 and 5 were confirmed by X-ray crystallographic studies. 相似文献
3.
Photochromism of two bispyrryl-substituted ethenes, 2, 3-bis-(1-p-methoxyphenyl-5-phenyl-2-methyl-3-pyrryl)-2-butene (BPE1) and 2,3-bis(1-p-bromophenyl-4-phenyl-2-methyl-3-pyrryl)-2-butene (BPE2), was studied by laser flash photolysis technique. The results indicate that photocyclization of these compounds proceeds mainly via the excited triplet state, and the cis-trans isomerization proceeds mainly via the excited singlet state. After UV laser pulse irradiation, both photocylization and cis-trans isomerization of BPEl occur, but photocydization is the main reaction. On the other hand, laser photolysis of BPE2 leads mainly to photocydization. The effects of the substituents on the photochromic mechanism are also discussed. 相似文献
4.
A new mercury(II) complex of 1,2‐bis(4‐pyridyle)ethene (bpe) with anionic acetate and thiocyanate ligands has been synthesized and characterized by elemental analysis, IR, 1H NMR and 13C NMR spectroscopy. The single crystal X‐ray analysis shows that the complex is a two‐dimensional polymer with simultaneously bridging 1,2‐bis(4‐pyridyle)ethane, acetate and thiocyanate ligands and basic repeating dimeric [Hg2(μ‐bpe)(μ‐OAc)2(μ‐SCN)2] units. The two‐dimensional system forms a three‐dimensional network by packing via π‐π stacking interactions. 相似文献
5.
Werner Unterberger Bernd Jenewein Bernhard Kl?tzer Simon Penner Wolfgang Reichl Günther Rupprechter Di Wang Di Wang Robert Schl?gl Konrad Hayek 《Reaction Kinetics and Catalysis Letters》2006,87(2):215-234
Summary The effect of hydrogen reduction on the structure and catalytic properties of “thin film”and “inverse”model systems for supported
metal catalysts is discussed. Thin film model catalysts were obtained by epitaxial growth of Pt and Rh nanoparticles on NaCl(001),
which were coated with amorphous or crystalline supports of alumina, silica, titania, ceria and vanadia. Structural and morphological
changes upon hydrogen reduction between 473 and 973 K were examined by high resolution electron microscopy. Metal-oxide interaction
sets in at a specific reduction temperature and is characterized by an initial “wetting”stage, followed by alloy formation
at increasing temperature, in the order VOx< TiOx< SiO2< CeOx< Al2O3. “Inverse”model systems were prepared by deposition of oxides on a metal substrate, e.g. VOx/Rh and VOx/Pd. Reduction of inverse systems at elevated temperature induces subsurface alloy formation. In contrast to common bimetallic
surfaces, the stable subsurface alloys of V/Rh and V/Pd have a purely noble metal-terminated surface, with V positioned in
near-surface layers. The uniform composition of the metallic surface layer excludes catalytic ensemble effects in favor of
ligand effects. Activity and selectivity, e.g. for CO and CO2methanation and for partial oxidation of ethene, are mainly controlled by the temperature of annealing or reduction. Reduction
above 573 K turned out to be beneficial for the catalytic activity of the subsurface alloys, but not for the corresponding
thin film systems which tend to deactivate viaparticle encapsulation.</o:p> 相似文献
6.
7.
Erkki Aitola Kimmo Hakala Hedvig Byman‐Fagerholm Markku Leskelä Timo Repo 《Journal of polymer science. Part A, Polymer chemistry》2008,46(1):373-382
The influence of ligand structure on copolymerization properties of metallocene catalysts was elucidated with three C1‐symmetric methylalumoxane (MAO) activated zirconocene dichlorides, ethylene(1‐(7, 9)‐diphenylcyclopenta‐[a]‐acenaphthadienyl‐2‐phenyl‐2‐cyclopentadienyl)ZrCl2 ( 1 ), ethylene(1‐(7, 9)‐diphenylcyclopenta‐[a]‐acenaphthadienyl‐2‐phenyl‐2‐fluorenyl)ZrCl2 ( 2 ), and ethylene(1‐(9)‐fluorenyl‐(R)1‐phenyl‐2‐(1‐indenyl)ZrCl2 ( 3 ). Polyethenes produced with 1 /MAO had considerable, ca. 10% amount of trans‐vinylene end groups, resulting from the chain end isomerization prior to the chain termination. When ethene was copolymerized with 1‐hexene or 1‐hexadecene using 1 /MAO, molar mass of the copolymers varied from high to moderate (531–116 kg/mol) depending on the comonomer feed. At 50% comonomer feed, ethene/1‐olefin copolymers with high hexene or hexadecene content (around 10%) were achievable. In the series of catalysts, polyethenes with highest molar mass, up to 985 kg/mol, were obtained with sterically most crowded 2 /MAO, but the catalyst was only moderately active to copolymerize higher olefins. Catalyst 3 /MAO produced polyethenes with extremely small amounts of trans‐vinylene end groups and relatively low molar mass 1‐hexene copolymers (from 157 to 38 kg/mol) with similar comonomer content as 1 . These results indicate that the catalyst structure, which favors chain end isomerization, is also capable to produce high molar mass 1‐olefin copolymers with high comonomer content. In addition, an exceptionally strong synergetic effect of the comonomer on the polymerization activity was observed with catalyst 3 /MAO. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 373–382, 2008 相似文献
8.
2-Phenyl-3-thioformylindolizine and 1,2-dimethyl-3-thioformylindolizine undergo a novel desulfur coupling reaction in the presence of tributylphosphine to give (E)-1,2-bis(3-indolizinyl)ethenes in high yields. The structures of products were confirmed by IR, ^1H NMR, MS, elemental analysis and single crystal X-ray diffraction analysis. The mechanisms involved in various stages of the reaction were discussed. 相似文献
9.
Active osmium cluster catalysts (derived from Os3(CO)12, H2Os3(CO)10, H4Os4(CO)12, Os6(CO)18 and H2Os10C(CO)24 supported on silica, alumina, titania, and ceria) contain, in their infrared spectra, a band in the region 1930–1985 cm−1 that is characteristic of the cluster/support combination. The activities of these catalysts for reactions of hydrogen with
ethene, carbon monoxide, carbon dioxide, and ethane, relate to their characteristic CO stretching frequencies, giving ‘volcano’
curves. Evidence from ethene hydrogenation kinetics confirms that the characteristic CO-frequency is a monitor of strength
of adsorption at the catalytically active site.
Dedicated to Professor Pál Tétényi on the occasion of his 70th birthday 相似文献
10.
双矿化剂对合成ZSM分子筛酸性和织构特征及其甲醇转化制丙烯催化性能的影响 《燃料化学学报》2018,46(8):967-976
采用静态水热法在F--OH-体系中,以四丙基氢氧化铵为模板剂、偏铝酸钠为铝源、正硅酸乙酯为硅源,合成了纳米SiO2-ZSM-5分子筛,考察了F-/Al2O3物质的量比对所合成的ZSM-5分子筛织构性质和甲醇转化制丙烯催化性能的影响。结果发现,随着初始溶胶F-/Al2O3物质的量比的增大,产物中SiO2的含量增大,ZSM-5分子筛的相对结晶度有所降低;同时,分子筛的比表面积和孔容减小、酸强度降低、酸量减少。对于甲醇转化制丙烯,最佳F-/Al2O3物质的量比为12;此时,丙烯选择性高于45%,丙烯/乙烯(P/E)比值大于10。反应机理分析表明,过渡态择形选择性是控制烯烃选择性的重要因素。 相似文献