Vanadium oxide monolayer catalysts. I. Preparation,characterization, and thermal stability

Vanadium oxide catalysts of the monolayer type have been prepared by means of chemisorption of vanadate(V)-anions from aqueous solutions and by chemisorption of gaseous V₂O₃(OH)₄. Using Al₂O₃, Cr₂O₃, TiO₂, CeO₂ and ZrO₂, catalysts with an approximately complete monomolecular layer of vanadium(V) oxide on the carrier oxides can be prepared, if temperature is not too high. Divalent metal oxides like CdO and ZnO may already form threedimensional surface vanadates at moderate temperature. The thermal stability of a monolayer catalyst is related to the parameter z/a, i. e. the ratio of the carrier cation charge to the sum of ionic radii of carrier cation and oxide anion. Thus, monolayer catalysts will be thermally stable only under the condition that z/a is not too high (aggregated catalyst) nor too small (ternary compound formation).     

NMR experiments on acetals—XXXVII: NMR spectral study of cis-, and trans-6-methyl-4-r-1,3-oxaselenans

The NMR spectral parameters are reported for cis-, and trans-6-Me-4-alkyl-1,3-oxaselenans with the aid of the INDOR- technique. Low temperature studies show the conformational equilibrium in the trans series to be pronouncedly one-sided and a value for the inversion barrier has been obtained.     

Proton-neutron structure of collective excitations in 94Mo

Due to the recent development of radioactive beam production, various direct reaction studies in reversed kinematics have been made to investigate the behavior of the N = 20 shell closure in the neutron-rich region. Coulomb excitation, proton inelastic scattering, and fragmentation of unstable nuclei have been studied with γ-ray detection. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: motobaya@rikkyo.ne.jp     

Proton–neutron structure of the N=52 nucleus Zr

Following the successful identification of mixed-symmetric one- and two-phonon states in the N=52 nuclei ⁹⁴Mo and ⁹⁶Ru, we have performed a photon scattering experiment on the N=52 isotone ⁹²Zr. Experimental data and shell model calculations show that both, single particle and collective degrees of freedom are present in the low-lying levels of ⁹²Zr. The second excited quadrupole state shows the signatures of the one-phonon mixed-symmetric 2⁺ state, while calculations and data indicate an almost pure neutron configuration for the 2⁺₁ state, in contradiction with the F-spin symmetric limit. Furthermore, two strong dipole excitations, which are candidates for the two-phonon quadrupole–octupole coupled E1 excitation and for the mixed-symmetric 1⁺ two-phonon state, were observed.     

Side‐Chain‐Functionalized Polyacetylenes, 1. Liquid Crystalline and Stereomutational Properties

Stereospecific polymerizations of functionalized acetylenes were successfully performed using a Rh complex as the catalyst and triethylamine as a base yielding poly(3,4,5‐tridodecyloxyphenylacetylene) ( Poly5 ) and poly[3,4,5‐tris((S)‐3,7‐dimethyloctyloxy)phenylacetylene] ( Poly6 ). Poly5 and Poly6 are liquid crystalline with presumably a bilayer‐type architecture in which the mesogens are arranged in an antiparallel overlapping interdigitated manner. Poly6 showed unusual thermal stereomutation in solution in a very narrow temperature range.     

Synthesis and self‐assembly of a chiral alternating sexithiophene–undeca(ethyleneoxy) block copolymer

An oligothiophene/chiral oligo(ethyleneoxy) block copolymer (PolyT6) has been synthesized in which a sexithiophene block alternates with a well‐defined chiral undeca(ethyleneoxy) block. The polymer shows good solubility in chloroform, and ultraviolet–visible studies in this solvent reveal a spectrum similar to that of the chirally substituted monomeric sexithiophene (T6) analogue. The aggregation of PolyT6 occurs in dioxane; however, no helicity is present in this aggregate, in contrast to aggregated T6. This behavior illustrates that although the processability and mechanical robustness of block copolymers may be superior to those of analogous oligomers, the degree of self‐assembled order found in oligomer‐based systems may be lost in the polymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1737–1743, 2003     

Synthesis of YBa2Cu3O7−x superconducting thin films on LaAlO3 by means of PAMOCVD

High-T_c superconducting thin films have been deposited in situ by means of a plasma assisted metal-organic chemical vapour deposition (PAMOCVD) process on LaAlO₃. An EMCORE high-speed rotating disc reactor was used to deposit the films at a substrate temperature of 600°C to 800°C. The system is equipped with a (remote) 120 W microwave plasma generator. The oxidising plasma gas is N₂O and/or O₂ while Ar was used as the inert carrier gas for the different metal-organics. The influence of different process parameters (such as the temperatures of the metal-organics, substrate temperature, and plasma gas composition) on the superconductive properties and on the morphology of the films was investigated. Surface morphology and composition were studied by SEM/EDX or EPMA, and AC susceptibility measurements were used to investigate the superconductive properties (T_c and J_c). X-ray diffraction measurements indicated that single-phase YBa₂Cu₃O_7−x films were epitaxially grown with the 00l orientation perpendicular to the substrate surface. The critical temperature (T_c) of the films is about 90 K and the critical current density (J_c) is higher than 10⁶ A/cm² at 77 K and zero field.