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In this paper, room-temperature chemiresistive gas sensors for NO2 detection based on CVD-grown carbon nanofibers (CNFs) were investigated. Transmission electron microscopy, low-temperature nitrogen adsorption, and X-ray diffraction were used to investigate the carbon nanomaterials. CNFs were synthesized in a wide range of pressure (1–5 bar) by COx-free decomposition of methane over the Ni/Al2O3 catalyst. It was found that the increase in pressure during the synthesis of CNFs induced the later deactivation of the catalyst, and the yield of CNFs decreased when increasing pressure. Sensing properties were determined in a dynamic flow-through installation at NO2 concentrations ranging from 1 to 400 ppm. Ammonia detection was tested for comparison in a range of 100–500 ppm. The obtained sensors based on CNFs synthesized at 1 bar showed high responses of 1.7%, 5.0%, and 10.0% to 1 ppm, 5 ppm, and 10 ppm NO2 at 25 ± 2 °C, respectively. It was shown that the obtained non-modified carbon nanomaterials can be used successfully used for room temperature detection of nitrogen dioxide. It was found that the increase in relative humidity (RH) of air induced growth of response, and this effect was facilitated after reaching RH ~35% for CNFs synthesized at elevated pressures. [ABSTRACT FROM AUTHOR]

Two new isomeric complexes [CuBr2(R-bian)] (R = 4-Me-Ph (1), 2-Me-Ph (2)) were obtained by reacting copper(II) bromide with 1,2-bis[(2-methylphenyl)imino]acenaphthene ligands and characterized. The crystal structure of 2 was determined by X-ray diffraction analysis. The copper atom has a distorted square-planar environment; the ω angle between the CuN2 and CuBr2 planes is 37.004°. The calculated ω parameters for optimized structures 1 and 2 were 76.002° and 43.949°, indicating significant deviations from the ideal tetrahedral and square-plane geometries, respectively. Molecules 2 form dimers due to non-covalent Cu···Br contacts, which were analyzed by DFT calculations. The complexes were also characterized by cyclic voltammetry and UV-Vis spectroscopy. A quasi-reversible Cu(II)/Cu(I) redox event with E1/2 potentials of 0.81 and 0.66 V (vs. SHE) was found for 1 and 2, respectively. The electronic absorption spectra showed the presence of Cu(I) species as a result of the partial reduction of the complexes in the acetonitrile solution. Both complexes were tested as homogenous catalysts for the oxidation of isopropylbenzene (IPB) in acetonitrile at low temperatures. Differences in the mechanism of the catalytic reaction and the composition of the reaction products depending on the oxidizing ability of the catalyst were revealed. [ABSTRACT FROM AUTHOR]

Among the known synthesis procedures and reagents for unsupported Ni–Mo–W catalysts, there is no consensus about optimal preparation conditions of their precursors. In the present work, Ni–Mo–W precursors were prepared via three preparation techniques—hydrothermal synthesis, precipitation method and spray drying—after the synthesis of complex compounds in solution. Ni–Mo–W precursors were studied by the XRD analysis, SEM methods, Raman and UV-vis spectroscopies and XPS measurements and used for the hydrotreatment of straight-run gasoil. Precursors prepared by hydrothermal synthesis contain particles with stacked plate shapes, while other methods provide spherical particles. The formation of different amounts of individual molybdates, tungstates or mixed phases such as W1−xMoxO3 possibly doped by Ni was detected. The precipitation technique results in the formation of spheres, with W located at the center and is unavailable for catalysis. The catalytic activity increased when all active metals are available for the feedstock, and a more mixed phase containing Ni, Mo and W is formed. This mixed phase is realized when the synthesis of the Ni–Mo–W precursors is carried out in solution followed by spray drying. The resulting catalyst has 1.2–4 times higher activity than catalysts prepared by other methods. [ABSTRACT FROM AUTHOR]