Aerobic oxidation of oct-1-ene in a nanoscale microreactor

Nanoscale microreactors containing the Pd(II)/Pd(0)–1,4-benzoquinone/hydroquinone–CoSalophen _OX/ CoSalophen triple catalytic system were constructed in the supercages of zeolite Y. This catalytic system works as a closed reactor and is capable for the highly selective palladium-catalyzed oxidation of oct-1-ene to octan-2-one with molecular oxygen at room temperature.     

On form sums of positive operators

The purpose of the present note is to provide domain, kernel and range characterizations for the form sum of two positive selfadjoint operators. In addition, we establish a criterion for the closedness of the range of the form sum and give the Moore–Penrose pseudoinverse in this case.     

Biorthogonal expansions for symmetrizable operators

We give an extension of a classical result due to Krein on biorthogonal expansions of compact operators which are symmetrizable with respect to a nondegenerate positive operator. Our approach makes essential use of the spectral expansion of an appropriate compact selfadjoint operator, the existence of which is due to Dieudonné.     

The static microreactor technique a new, simple method for determination of kinetic parameters of gas-phase heterogeneous catalytic reactions

The dehydrogenation of methanol on a silver catalyst was studied in a static microreactor at 376–457°C, with initial methanol partial pressures of 60–90 Torr. The apparent activation energy agrees well with literature data. The experimental data suggest that the static microreactor is a suitable means for the rapid acquisition of preliminary kinetic data.

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376–457°C, 60–90 . . , .

     

Cold neutron energy dependent production of ultracold neutrons in solid deuterium

A measurement of the production of ultracold neutrons from velocity-selected cold neutrons on gaseous and solid deuterium targets is reported. The expected energy dependence for two-particle collisions with well defined neutron and Maxwell-Boltzmann distributed molecular velocities is found for the gas target. The solid target data agree in shape with the phonon density-of-states curve and provide strong evidence for the phonon model including multiphonon excitations.     

The effect of substituents of immobilized Rh complexes on the asymmetric hydrogenation of acetophenone derivatives

Using a modified Augustine’s method variously substituted Rh complexes were anchored on Al₂O₃ support. The prepared catalysts were characterized by spectroscopic methods and were applied in the hydrogenation of several acetophenone derivatives (p-CF₃-acetophenone, acetophenone, p-NH₂-acetophenone). Enantioselective C=O hydrogenations were observed with reasonable activity and selectivity on all heterogenized complexes, e.e. up to 80%. At the same time the immobilized samples showed the advantages of the heterogeneous systems: easy handling and recyclability.      

Operator extensions with closed range

We characterize those positive (not necessarily densely defined) operators whose Krein–von Neumann extension, the smallest among all positive selfadjoint extensions, has closed range. In addition, we construct their Moore–Penrose pseudoinverse by employing factorization via an auxiliary Hilbert space. Other extremal extensions, in particular the Friedrichs extension, are also investigated from this point of view. As an application, new characterizations of essentially selfadjoint positive operators are presented.     

Voltammetric determination of imidacloprid insecticide in selected samples using a carbon paste electrode

The voltammetry of imidacloprid was investigated by using three kinds of carbon paste electrodes (CPEs) based on tricresyl phosphate, silicone oil, and n-tetradecane. The tricresyl phosphate-based carbon paste electrode exhibited the best analytical performance with respect to peak shape and signal intensity. The method, operated in the differential pulse voltammetric mode, was applied to the determination of imidacloprid in a river water sample and two commercial formulations and works in the concentration range from 1.7 to 30 μg mL⁻¹, with a relative standard deviation not exceeding 2.2%. This appears to be the first application of a CPE to the voltammetric determination of neonicotinoid insecticides.

     

Bismuth modified carbon-based electrodes for the determination of selected neonicotinoid insecticides

Two types of bismuth modified electrodes, a bismuth-film modified glassy carbon (BiF-GCE) and a bismuth bulk modified carbon paste, were applied for the determination of selected nitroguanidine neonicotinoid insecticides. The method based on an ex situ prepared BiF-GCE operated in the differential pulse voltammetric (DPV) mode was applied to determine clothianidin in the concentration range from 2.5 to 23 μg cm?3 with a relative standard deviation (RSD) not exceeding 1.5%. The tricresyl phosphate-based carbon paste electrodes (TCP-CPEs), bulk modified with 5 and 20 w/w% of bismuth, showed a different analytical performance in the determination of imidacloprid, regarding the peak shape, potential window, and noise level. The TCP-CPE with 5% Bi was advantageous, and the developed DPV method based on it allowed the determination in the concentration range from 1.7 to 60 μg cm?3 with an RSD of 2.4%. To get a deeper insight into the morphology of the bismuth-based sensor surfaces, scanning electron microscopic measurements were performed of both the surface film and the bulk modified electrodes.