A TPR study of SiO2-supported Ru?Ag catalysts

A H₂ chemisorption and TPR study of Ru–Ag/SiO₂ catalysts reveals that after oxidation at 373 K this systems behaves like Ru–Cu/SiO₂. High temperature oxidation, however, does not result in the separation of the metal like in the Ru–Cu case but in the redispersion of Ag on top of the Ru particles.

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H₂ Ru–Ag/SiO₂ , 373 Ru–Cu/SiO₂. , , , Ru–Cu, Ag Ru.

     

A High-Resolution Dual-Doppler Technique for Fixed Multiantenna Airborne Radar

A new technique is presented for the analysis of data collected by pairs of aircraft (AC)-mounted fixed radar beams directed ~30deg apart, leading to two-dimensional wind field syntheses in the horizontal and vertical planes. The technique was applied to the 95-GHz Wyoming Cloud Radar (WCR) configurations aboard the University of Wyoming King Air and the National Center for Atmospheric Research C-130 research AC. The construction of the data grid allows to closely follow the AC flight attitude, and thus the beam scanned surfaces, with a resolution between 30 and 45 m. A weighted least squares method is employed to solve the velocity inverse decomposition problem for every valid grid cell. The effect on the solution of the nonmeasured (cross-plane) wind component is minimized by using an external estimate of the ambient wind. The error sources are discussed, and maximum expected values for the velocity field errors are provided with reference to the radar system, the data collection process, and specific aspects of the target under investigation. These uncertainties (1-2 m/s) are quantified for two case studies that show the potential of the technique in retrieving the kinematic field in transects of cumulus and stratus clouds. The technique produces smooth fine-scale kinematic fields although each velocity point is the result of an independent calculation, and no binding constraint is imposed among neighboring points as is done in other dual-Doppler techniques     

Microwave spectra of cyclohexyl bromide and cyclohexyl iodide

The microwave spectra of cyclohexyl bromide and cyclohexyl iodide have been investigated in the gas phase between 8 and 40 GHz. While for cyclohexyl bromide only low resolution spectra have been recorded, for cyclohexyl iodide high resolution spectra of both the equatorial and the axial isomer have been analyzed. The energy difference between the axial and the equatorial form is ΔG° = 0.8 ± 0.4 kcal/mole and ΔE_0,0 = 0.54 ± 0.15 kcal/mole in C₆H₁₁Br and C₆H₁₁I, respectively, the equatorial forms being more stable. Iodine nuclear quadrupole coupling constants for equatorial and axial C₆H₁₁I have been obtained. The present analysis contributes to the microwave investigation of the cyclohexyl halides.     

Microwave spectrum of axial cyclohexyl chloride and conformational equilibrium in cyclohexyl chloride

The high-resolution microwave spectrum of the axial conformer of cyclohexyl chloride has been assigned for both the Cl(35) and Cl(37) isotopic species, in natural abundance. Moreover, the high-resolution microwave spectrum of the equatorial conformer, previously assigned in the ground state [Chem. Phys. Lett.21, 592–594 (1973)], has been further investigated. Several low-energy vibrational satellites have been studied for the Cl(35) isotopic species of both the axial and the equatorial isomers. The ground state centrifugal distortion constants for both the isotopic species of the two rotamers, and the quadrupole coupling constants of Cl(35) and Cl(37) axial isomer and of Cl(37) equatorial isomer (not reported previously) have been determined. From line relative intensity measurements the energy difference between the two conformers has been calculated to be 0.51 ± 0.15 kcal/mol, the equatorial isomer being more stable. In the same way, the vibrational energies of the investigated vibrational satellites have been computed. A structural model for axial cyclohexyl chloride is proposed on the basis of the available experimental data.     

Microwave spectrum of ethynyl-cyclohexane

The ground state microwave rotational spectra of the axial and equatorial chair forms of ethynyl-cyclohexane are investigated in the frequency region 8–26.5 GHz. The spectrum of the first vibrationally excited state of the e-conformer is also assigned and intensity measurements locate this state at 130 ± 30 cm^?1. Using the ground state rotational constants obtained for the two isomers, a least-squares structural analysis is performed.     

An EHT re-examination of Acetylcholine

The results of EHT calculations on the most stable conformations of the neurotransmitter molecule acetylcholine (ACh) are reported. These results are compared with those obtained with other semiempirical quantum mechanical methods CNDO/2, INDO and PCILO, and with those obtained by the classical partitioning of the energy method (PEM). From this comparison it becomes evident a wide agreement between the results of PCILO, EHT and PEM, all these methods allowing accessibility to discrete regions in conformational space.This work has been carried out with financial support of the Consiglio Nazionale delle Ricerche.     

Effect of different donors on kinetics of Zn catalysts and molecular weight of the obtained polypropylene

This paper studies MgCl₂/internal donor/TiCl₄//external donor/AlEt₃ catalytic systems where ethyl benzoate (E.B.) or 2,2,6,6 tetramethylpiperidine (TMPiP) are used as internal and external donors. E.B. as external donor does not change the molecular weight of the product with TMPiP as internal donor. The molecular weight of polypropylene decreases drastically and global productivity and stereoselectivity are very low with MgCl₂/internal Donor/TiCl₄//external donor/AlEt₃ when TMPiP is the external and internal donor. In this case the insoluble fraction in n-heptane is highly stereospecific and the molecular weight is similar to commercial products. We present a new explanation of these results, based on Ystenes proposal, comparing both precatalysts.