Titania-supported rhodium, ruthenium and rhodium-ruthenium catalysts were prepared by impregnation followed by reduction at
573 K (low temperature reduced-LTR) and 773 K (high temperature reduced — HTR). Temperature programmed desorption of hydrogen
showed the existence of strong-metal-support-interaction (SMSI) in rhodium and ruthenium catalysts, but not in the bimetallic
catalyst. In either case, metal-hydrogen bond strength had undergone change in going from an LTR to HTR sample. X-ray photoelectron
spectroscopy (XPS) results did not show any electron transfer between metal and support in any of the catalysts but electron
transfer from rhodium to ruthenium was indicated in the bimetallic catalyst under HTR. 相似文献
This article reports the synthesis of a series of alkali metal complexes with diverse multi-dentate ligands. The sodium and potassium complexes show excellent activity in the ring-opening polymerization of ε-CL and δ-VL and rac-Lactide.
We show that (27)Al triple-quantum magic angle spinning (3Q-MAS) experiments alleviate the second-order quadrupolar broadening to reveal the structure-building units of nonequivalent aluminum octahedra in the most extensively studied aluminum hydroxides, namely, gibbsite, bayerite, and boehmite. Further, aided by ab initio calculations of the electric field gradient tensors, the 3Q-MAS/MAS results are shown to lead to the assignment of (27)Al isotropic resonances to the aluminum positions in their X-ray-determined structures. The present work paves the way for future studies on various structurally transformed materials derived from these basic aluminum hydroxides. 相似文献
The chair conformation of the forming ring in the transition structure, for its high stability, is usually considered for the determination of the overall stereoselectivity in a type-II ene cyclization reaction. However, present theoretical investigation reveals that the presence of a heteroatom like oxygen or nitrogen in the tether of type-II carbonyl ene cyclization stabilizes the transition structure, in which the forming ring adopts a boat conformation. Due to such stability of the boat conformer the overall stereoselectivity of some type-II reactions may differ from the expected one. 相似文献
Possible transition structures (TSs) of (3,4) and (3,5) ene cyclizations of 7-methyl-1,6-octadiene and 7-methylocta-1,6-dien-3-one were constructed and optimized by DFT method. Product proportions were calculated using the relative energies of the transition structures and these results are found to be in good agreement with the experimental one. Variation of the product proportions was explained using some model TSs of intermolecular ene reactions. The change of the dihedral angle around the forming carbon–carbon bond in the model transition structures was found to play a crucial role in determining the overall selectivities of cyclized products. 相似文献
Decomposition of 2-propanol has been studied on vanadium pentoxide with MoO3 and WO3 additives. It has been observed that a small amount of the additives increases the dehydration activity of the catalysts,
but at 5% or higher concentration, dehydration of 2-propanol decreases. The initial increase followed by a decrease in the
dehydration activity with increased amount of additives is due to the change in the rate-determining step. Addition of MoO3, WO3, and alkali metal oxides to vanadium pentoxide has similar effects on the V4+ concentration and catalytic activity. Based on the results of the kinetic and ESR spectral studies, a scheme for the reaction
has been proposed. It is concluded that the concentration of V4+ ion plays the crucial role in these catalysts.
Deceased October 1979 相似文献
The synthesis and characterization of the first unique binuclear manganese(I) salicylate complex is described. The structure
of the complex is unequivocally established with the help of an X-ray crystallographic study. The structure consists of two
[MnO6] units, containing octahedral MnI ions, linked together by a bridging salicylato (Hsal−) ligand and each MnI is chelated with a (H2sal) ligand. The complex possesses a metal oxidation state of +1 and is a rare example of a noncarbonyl or cyanide complex
of a binuclear MnI species. The effective magnetic moment per binuclear molecule (μeff. at 27 °C is 8.07 μb, that also describes the manganese (+1) oxidation state. 相似文献
This work focuses on the universal scaling laws, which relate scaled diffusivity to excess entropy in fluids and their mixtures. The derivation of the new scaling law for diffusivity proposed recently [A. Samanta, Sk. M. Ali, and S. K. Ghosh, Phys. Rev. Lett. 92, 145901 (2004)] is discussed in details highlighting the nature of approximations involved. Also the applicability of the scaling law is extended to a new class of liquids, viz., liquid metals. The results calculated based on the scaling laws are shown to be in very good agreement with the simulation results for liquid Rb and Cs metals along the liquid-vapor coexistence curve corresponding to a wide variation of temperature and density. The new universal scaling law discussed here is superior to the earlier empirically proposed scaling laws and provides a very simple route to calculate a dynamical quantity such as diffusivity from an equilibrium property such as the radial distribution function. 相似文献
Michael reaction of 3-(2′-nitrovinyl)indole with eight 3-unsubstituted indoles on TLC-grade silica gel furnished unsymmetrical bis(indolyl)nitroethanes in 7-12 min under microwave irradiation and in 8-14 h at rt. In contrast, the p-TsOH-catalysed reaction of the nitrovinylindole with the 3-unsubstituted and two 3-substituted indoles in solution under reflux furnished both unsymmetrical and symmetrical bis(indolyl)nitroethanes, the latter resulting from novel tandem Michael addition-elimination-Michael addition reactions. The synthesis of a 2′,3″-bis(indolyl)nitroethane, the precursor core structure of two bioactive marine metabolites, and the reduction of 2,2-bis(3′-indolyl)nitroethane to the corresponding ethylamine, isolated as its N-acetyl derivative, have been achieved. Significantly, attempted hydrolysis of three nitronates, derived from the corresponding bis(indolyl)nitroethanes, with buffered aqueous TiCl3 has led to the first isolation of oximes (syn/anti-mixture) as the only products. 相似文献