Effect of the modification of nanocrystalline MgO aerogels with vanadium and carbon on the destructive sorption of CF2Cl2 and CFCl3

The effect of the promotion of nanocrystalline MgO aerogels with small amounts of vanadium and carbon on the destructive sorption of the Freons CF₂Cl₂ and CFCl₃ was studied. It was found that the introduction of the promoters considerably shortened the induction period of the reaction. The pretreatment of samples modified with vanadium in an oxidizing or reducing atmosphere did not significantly affect the duration of the induction period. It was established that the acceleration of the reaction by fine-particle carbon did not depend on the mutual arrangement of carbon and MgO: on the surface of MgO nanoparticles, in the form of their mechanical mixture, or at separate positions in a reactor. It was concluded that the modifiers catalytically affect the interaction of MgO aerogels with Freons to accelerate the formation of active centers on the surface of their nanoparticles.     

Kinetic features of the carbon erosion of a bulk NiCr alloy during the catalytic decomposition of 1,2-dichloroethane

Kinetic features for the carbon erosion (CE) of bulk NiCr alloy (NiCrA, nichrome wire 0.1 mm in diameter) were studied at 450–750°C under conditions of the catalytic decomposition of 1,2-dichloroethane vapor in a reductive atmosphere (H₂). It was found that the CE process takes place more efficiently in the temperature range from 550 to 720°C, leading to the disintegration of the bulk alloy with the formation of a fibrous carbon product. The apparent activation energy of the process was estimated to be 16.8 ± 0.9 kJ/mol. The realization of CE is hampered outside the optimal temperature range because of chlorination (T < 500°C) or blocking of the alloy’s surface by carbonaceous deposits (T > 720°C). The kinetics of the process is characterized by the existence of an induction period, whose duration decreases with an increasing temperature (from 40 min at 550°C to 6 min at 710°C). According to scanning and transmission electron microscopy data, the submicron metallic particles (0.2–0.4 μm) catalyzing the growth of carbon fibers with disordered structure result from the disintegration of the NiCr alloy.     

Catalytic properties of massive iron-subgroup metals in dichloroethane decomposition into carbon products

The formation of nanocarbon materials on massive nickel, nichrome, and some other alloys via the carbide cycle mechanism is reported using 1,2-dichloroethane decomposition as an example. The role of the physical stage of the carbide cycle is elucidated, and massive metal surface activation methods ensuring the realization of this stage are considered. The surface layer of massive nickel or some nickel alloys is most effectively activated by the action of chlorine resulting from the catalytic decomposition of 1,2-dichloroethane. It has been demonstrated by ferromagnetic resonance (FMR) spectroscopy that the activation of the massive metal surface in 1,2-dichloroethane decomposition to nanocarbon is due to the surface undergoing crystal chemical restructuring. The microstructuring of the surface yields fine Ni particles similar in size (0.2–0.3 μm) and shape, whose FMR spectra are anisotropic and have similar magnetic resonance parameters. Both chlorine-free and chlorinated hydrocarbons decompose over these particles via the carbide cycle mechanism. It is demonstrated that it is possible to design catalytic reactors packed with massive nickel or its alloy. The nanocarbon material obtained in such a reactor will not be contaminated by components of conventional catalyst supports (Al, Mg, etc.). The stable performance temperature of the catalyst will be increased, and this will allow the equilibrium outlet methane concentration to be reduced.     

Analysis of the procedure for filling cells for a quantum frequency standard based on Rb87 vapors

The effect of various physical processes on the replicability of cells for a quantum frequency standard based on Rb⁸⁷ was investigated. A replication accuracy of 2 · 10^–11 was obtained experimentally for the frequency of the spectral line of the gas cell.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 15, No. 1, pp. 27–32, January, 1972.     

Nanocrystalline aerogel VOx/MgO as a catalyst for oxidative dehydrogenation of propane

Nanocrystalline aerogel VO_x/MgO catalysts for the oxidative dehydrogenation of propane with high surface area and uniform vanadium distribution were synthesized by co-gelation followed by supercritical drying. The catalysts were shown to have superior performance compared to nanocrystalline VO_x/MgO catalysts prepared by impregnation.     

Synthesis of Filamentary Carbon Material on a Self-Organizing Ni–Pt Catalyst in the Course of 1,2-Dichloroethane Decomposition

A series of model microdisperse Ni_1–xPt _x alloys (x =0–0.05) was synthesized by a coprecipitation method with the subsequent sintering of the precipitate in an atmosphere of H₂ at 800°C. Their chemical and phase compositions were determined (by AAS and XRD analysis, respectively), and it was found that the synthesis method proposed afforded Ni–Pt solid solutions based on the face-centered nickel lattice. The kinetic features of the carbon erosion of Ni_1–xPt _x alloys in their contact with 1,2-dichloroethane vapor in a temperature range of 550–700°C were studied. It was found that the presence of Pt in the alloy increased the rate of accumulation of carbon product by a factor of ~1.5 regardless of the concentration of Pt. The catalyst did not undergo deactivation for 5 h of reaction to ensure a high yield of carbon material (103 g/g_Cat). With the use of electron microscopy (SEM and TEM techniques), it was found that the carbon product consisted of carbon fibers with a segmented structure. An increase in the concentration of Pt in the alloy to 4.3 wt % sharply changed the disintegration of the alloy to cause the formation of carbon product with a bimodal fiber diameter distribution (d_av = 0.4 and 1.2 μm).