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排序方式: 共有159条查询结果,搜索用时 15 毫秒
151.
Palladium chloride was grafted to amino‐functionalized MCM‐41 to prepare heterogeneous catalysts. XRD, N2 adsorption–desorption isotherms, IR, 13C and 29Si cross‐polarization magic‐angle spinning NMR spectroscopy and XPS techniques were employed to characterize the catalytic materials. The heterogeneous palladium catalyst exhibited excellent catalytic activity for the Heck vinylation of iodobenzene with methyl acrylate, giving 92% yield of methyl cinnamate in the presence of N‐methylpyrrolidone (NMP) and triethylamine (Et3N). The stability of the heterogeneous catalyst was also studied in detail. The catalytic tests showed that the palladium leaching correlated to solvent, base and palladium loading. The heterogeneous catalyst exhibited excellent stability towards loss of activity and palladium leaching was not observed during six recycles in the presence of toluene and Na2CO3. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
152.
In this paper we discuss determination of jumps for non-periodic function based on Malvar- Cofiman-Meyer (MCM) conjugate wavelets.
We prove the equality of Lukacs type. Furthermore we establish several criteria on concentration factors for functions that
satisfy weak-smoothness condition of Dini type.
This work was supported by National Natural Science Foundation of China (Grant No. 10671062) 相似文献
153.
154.
155.
Jianwen Da Tiancun Xiao Jianming Su Xingzhong Xu Malcolm. L. H. Green * . Research Institute of Qilu Petrochem. Corp. Zibo China . The Wolfson Catalysis Centre Inorganic Chemistry Laboratory University of O 《高等学校化学研究》2002,18(2):169-174
IntroductionZeolitesareveryimportantcatalyticmaterialsandwidelyusedinchemicalindustriesfortheircrys tallinealuminosilicatenetwork .However ,theirappli cationisstilllimitedbytherelativelysmallporeopen ings ,particularlybythedepletionofthelightreservesofth… 相似文献
156.
层状分子筛MCM-56的合成及表征 总被引:4,自引:1,他引:3
分子筛催化剂一般具有很好的择形性 ,但较小的孔径很难用于较大分子的催化转化 .目前寻找既具有一般分子筛的酸性和稳定性 ,又具有规则的较大孔径的催化剂是石油化工研究中的迫切需要 .因此 ,如果一种材料具有可让较大有机物分子接近的类分子筛的酸性点 ,就必然会引起广泛重视 .具有特殊晶体结构的 MCM- 2 2族分子筛 [1~ 5]则符合以上要求 ,其合成与催化研究已成为分子筛催化领域中的一个热点课题 .MCM- 5 6 [6]属于 MWW结构的分子筛 ,其晶胞参数 c为 2 .5 5 nm,并且层状结构经5 4 0℃焙烧后可基本保持原状 .MCM- 5 6具有可溶胀性 ,说… 相似文献
157.
Zhibin Ye Shiping Zhu Wen‐Jun Wang Hatem Alsyouri Y. S. Lin 《Journal of Polymer Science.Polymer Physics》2003,41(20):2433-2443
Polyethylene (PE) fibers were prepared by ethylene extrusion polymerization with an MCM‐41‐supported titanocene catalyst. The morphological and mechanical properties of these nascent PE fibers were investigated. Three levels of fibrous morphologies were identified in the fiber samples through an extensive scanning electron microscopy study. Extended‐chain PE nanofibrils with diameters of about 60 nm were the major morphological units present in the fiber structure. The nanofibrils were parallel‐packed into individual microfibers with diameters of about 1–30 μm. The microfibers were further aggregated irregularly into fiber aggregates and bundles. In comparison with commercial PE fibers and data reported in the literature, the individual microfibers produced in situ via ethylene extrusion polymerization without posttreatment exhibited a high tensile strength (0.3–1.0 GPa), a low tensile modulus (3.0–7.0 GPa), and a high elongation at break (8.5–20%) at 35 °C. The defects in the alignment of the nanofibrils were believed to be the major reason for the low modulus values. It was also found that a slight tensile drawing could increase the microfiber strength and modulus. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2433–2443, 2003 相似文献
158.
MCM‐41‐supported bidentate phosphine rhodium complex (MCM‐41‐2P‐RhCl3) was conveniently synthesized from commercially available and cheapγ‐aminopropyltriethoxysilane via immobilization on MCM‐41, followed by reacting with diphenylphosphinomethanol and rhodium chloride. It was found that the title complex is a highly efficient catalyst for the hydrosilylation of olefins with triethoxysilane and can be recovered and recycled by a simple filtration of the reaction solution and used for at least 10 consecutive trials without any decreases in activity. 相似文献
159.
Hynek Balcar Jan Sedl
ek Jií ejka Jií Vohlídal 《Macromolecular rapid communications》2002,23(1):32-37
The immobilization of [Rh(cod)OCH3]2 (cod = cycloocta‐1,5‐diene) on mesoporous molecular sieves MCM‐41 provides the first inorganic‐type hybrid catalyst, which affords heterogeneous polymerization of phenylacetylene and its ring‐substituted derivatives, – 2‐fluorophenylacetylene, 4‐fluorophenylacetylene, and 4‐pentylphenylacetylene – into readily isolable high‐molecular‐weight (M̄w from 50 000 to 180 000) substituted polyvinylenes of high cis‐transoid structure. The activity of this catalyst is compared with that of homogeneous catalyst [Rh(cod)OCH3]2. 相似文献