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81.
Studies on Thoria Catalysts. II. On the Influences of Surfacechemical Properties Tho2-Catalysts on the Selective Dehydration of 2-Butanol Acid and basic properties as well as the interaction of 2-butanol with the surfaces of some ThO2catalysts were studied. Sites of low acidity and basic sites of medium strength were found on the catalysts. After CO2 adsorption we have shown by i.r. spectroscopy the formation of monodentate and bidentate carbonate as well as hydrocarbonate. There were indications of Lewis-type acid sites. Bands of alcoxide and carboxylate structure were observed in the i.r. spectra by interaction with 2-butanol and thoria. A mechanism is proposed for dehydration of 2-butanol. 相似文献
82.
Studies on Nickel Oxide Mixed Catalysts. I. Structural Properties of NiO/SiO2 Catalysts Structural properties of NiO/SiO2 catalysts prepared by precipitation-deposition and impregnation have been investigated. A nickel-layer-silicate like structure is formed only in the precipitated catalysts showed infrared spectroscopic measurements. After thermal treatment at 723 K by means of magnetic measurements and reflectance spectroscopy besides Ni2+ ions in octahedral environment tetrahedral coordinated Ni2+ions were found. The part of tetrahedral coordinated Ni2+ ions is independent of the NiO-content up to 40 mole % NiO. Nickel oxide is formed above a content of 40 mole %. In the case of the impregnated catalysts nickel oxide cluster are formed on the surface after annealing at 723 K. 相似文献
83.
A reinvestigation was undertaken in order to obtain reliable data of the relative intensities of the L spectra for the elements
24 ≤ Z ≤ 33. A TAP crystal with a periodicity of 25.757 ? was used as the dispersing element. With this crystal one is able
to resolve the lines/bands Ll = L3M1, Lη = L2M1, Lα1,2 = L3M4,5, Lβ1 = L2M4, and Lβ3,4 = L1M2,3. Among the investigated elements 33As is the only one for which the energy of the lines Lα1,2 and Lβ1 is below the L3 absorption edge. For all the other elements the lines Ll, Lη, and Lα1,2 are below the L3 edge, whereas Lβ1 and Lβ3,4 are above this edge. This difference leads to effects of differential absorption, where the absorption is stronger for decreasing
line energy. For the net peak height ratio β1/α we obtained results which are of the same order of magnitude as those given by White and Johnson (W&J) in their popular
tables. But for l/α and β3,4/β1 our results show an atomic number dependence which is completely different from those given by W&J. 相似文献
84.
超细均分散稀土化合物胶体粒子制备 总被引:2,自引:0,他引:2
利用尿素分解法制得轻、中、重稀土化合物的超细均分散胶体粒子,详细探讨了浓度、pH值、陈化温度、陈化时间及共存阴离子等因素对制备过程的影响,获得了各种粒子的最佳制备条件. 相似文献
85.
Scheidt KA Bannister TD Tasaka A Wendt MD Savall BM Fegley GJ Roush WR 《Journal of the American Chemical Society》2002,124(24):6981-6990
A highly stereoselective total synthesis of (-)-bafilomycin A(1), the naturally occurring enantiomer of this potent vacuolar ATPase inhibitor, is described. The synthesis features the highly stereoselective aldol reaction of methyl ketone 8b and aldehyde 60c and a Suzuki cross-coupling reaction of the highly functionalized advanced intermediates 12 and 39. Vinyl iodide 12 was synthesized by a 14-step sequence starting from the readily available beta-alkoxy aldehyde 14, while the vinylboronic acid component 39 was synthesized by a nine-step sequence from beta-hydroxy-alpha-methyl butyrate 44 via a sequence involving the alpha-methoxypropargylation of chiral aldehyde 49 with the alpha-methoxypropargylstannane reagent 54. Syntheses of fragments 12 and 39 also feature diastereoselective double asymmetric crotylboration reactions to set several of the critical stereocenters. The Suzuki cross-coupling of 12 and 39 provided seco ester 40, which following conversion to the seco acid underwent smooth macrolactonization to give 41. The success of the macrocyclization required that C(7)-OH be unprotected. The Mukaiyama aldol reaction between aldehyde 60c and the TMS enol ether generated from 8b provided aldol 65 with high diastereoselectivity. Finally, all silicon protecting groups were removed by treatment of the penultimate intermediate 65 with TAS-F (tris(dimethylamino)sulfonium difluorotrimethylsilicate), thereby completing the total synthesis of (-)-bafilomycin A(1). 相似文献
86.
1,4-Dimethyl-1,4-diphenylbutadiene was shown to be able to execute regiospecific HT-1 photoisomerization around a methyl group when irradiated in a low-temperature organic glass, albeit at reduced efficiency. 2,3-Dimethyl-1,4-diphenylbutadiene exhibited a different type of steric effect, causing the E,E-isomer to undergo regiospecific HT-1 photoisomerization. 相似文献
87.
88.
89.
Wendt C Abrams G Amidei D Baden AR Barklow T Boyarski AM Boyer J Burchat PR Burke DL Butler F Dorfan JM Feldman GJ Gidal G Gladney L Gold MS Goldhaber G Golding L Haggerty J Hanson G Hayes K Herrup D Hollebeek RJ Innes WR Jaros JA Juricic I Kadyk JA Karlen D Klein SR Lankford AJ Larsen RR LeClaire BW Levi M Lockyer NS Lüth V Matteuzzi C Nelson ME Ong RA Perl ML Richter B Riles K Rowson PC Schaad T Schellman H Schmidke WB Sheldon PD Trilling GH de la Vaissiere C Wood DR Yelton JM 《Physical review letters》1987,58(18):1810-1813
90.