Sergey P. Zhuravkov

Properties and deactivation of the active sites of an MoZSM-5 catalyst for methane dehydroaromatization : Electron microscopic and EPR studies

The MoZSM-5 (4.0 wt % Mo) catalyst has been characterized by high-resolution transmission electron microscopy, EDXA, and EPR. Two types of molybdenum-containing particles are stabilized in the catalyst in the course of nonoxidative methane conversion at 750°C. These are 2-to 10-nm molybdenum carbide particles on the zeolite surface and clusters smaller than 1 nm in zeolite channels. According to EPR data, these clusters contain the oxidized molybdenum form Mo5+. The surface Mo2C particles are deactivated at the early stages of the reaction because of graphite condensation on their surface. Methane is mainly activated on oxidized molybdenum clusters located in the open molecular pores of the zeolite. The catalyst is deactivated after the 420-min-long operation because of coke buildup on the zeolite surface and in the zeolite pores.

Nonoxidative conversion of methane into aromatic hydrocarbons on Ni-Mo/ZSM-5 catalysts

The nonoxidative conversion of methane into aromatic hydrocarbons on high-silica zeolites ZSM-5 containing nanosized powders of molybdenum (4.0 wt %) and nickel (0.1–2.0 wt %) was studied. Data on the acid characteristics of the catalysts and the nature and amount of coke deposits formed on the surface of the catalysts were obtained using the thermal desorption of ammonia and thermal analysis. The microstructure and composition of Ni-Mo/ZSM-5 catalysts were studied by high-resolution transmission electron microscopy and energy-dispersive X-ray analysis. The formation of various chemical species in the samples was detected: oxide-like clusters of Mo within zeolite channels (∼1 nm), molybdenum carbide particles (5–30 nm) on the outer surface of the zeolite, and Ni-Mo alloy particles with different compositions (under reaction conditions, carbon filaments grew on these particles). It was found that, as the Ni content was increased from 0.1 to 2.0 wt %, the rate of deactivation of the catalytic system increased because of blocking pores in the zeolite structure by filamentous carbon up to the formation of condensed coke deposits.

Physicochemical properties and activity of nanopowder catalysts in the hydrodesulfurization of diesel fraction

New hydrofining catalysts based on molybdenum, nickel, and aluminum nitride nanopowders produced by electrical explosion are obtained. Their physicochemical properties are studied. The direct sulfurizing of molybdenum nanopowders with sulfides from straight-run diesel oil fraction is shown to be possible. The high hydrodesulfurization capability of nanopowder catalysts is established.

Methane conversion into aromatic hydrocarbons over Ag-Mo/ZSM-5 catalysts

Nonoxidative methane conversion into aromatic hydrocarbons over ZSM-5-type high-silica zeolites modified with nanosized powders of molybdenum (4.0 wt %) and silver (0.1–0.5 wt %) is reported. The acidic properties of the catalysts have been investigated by temperature-programmed ammonia desorption. The microstructure and composition of the Ag-Mo/ZSM-5 catalytic systems have been studied by high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy. The doping of the Mocontaining zeolite with silver enhances its activity and stability in nonoxidative methane conversion into aromatic hydrocarbons.

Influence of molybdenum nanopowder concentration on welded joint microstructure

The paper outlines experimental results of structure formation in welded joints by means of concentration change of molybdenum nanostructured powders in shielding gas. Molybdenum nanostructured powders are arc welded in a liquid welding pool by consumable electrode in argon. It was found out that different powder concentration forms different microstructure of deposited metal.

Influence of Conditions of Copper Wires Electric Explosion on Dispersity of Produced Nanopowders

The article presents the results of a study concerning the influence of conditions of copper wires electric explosion on a dispersity of produced nanopowders. It was shown that the energy introduced into the wire being increased, the specific surface area grows and the size of produced nanopowders decreases.

Production of Powders by the Method of Electrospark Dispersion

This article is devoted to the research of powders for the additive technologies made by EOS Company. Their analysis showed that the powders’ average diameter is about 30 microns. Powders are received by method of electrospark dispersion. The X-ray diffraction and metallographic analysis of these powders is presented.

Study of Products of Metallic Titanium Electrospark Dispersion in Aqueous Medium

The results of electrospark dispersion of the metallic titanium loading in aqueous medium are presented in the paper. Raster electronic microscopy, X-ray phase analysis and BET method were used to investigate properties of the obtained powder. Values of specific surface are given in the paper, and morphology and structure of the obtained powders are studied. It is established that chemical and phase composition of the obtained powders is identified by properties of the molten titanium to interact with the dissolved in dispersion medium gaseous products.

The Study of Properties Characterizing Aluminum Hydroxides Produced by Electric Discharge

The paper gives the experimental data on physicochemical and sorption properties of aluminum hydroxides produced by electric spark dispersion of aluminum metal in water and electric explosion of an aluminum conductor in argon and further interaction with water. By comparing the phase composition, specific surface area, porosity, and functional dependence of the exchange capacity of products on the solution pH, we proved the influence of preparation conditions on the properties of the said products.

Particle Size Distribution of Aluminum Powders Obtained by Electric Explosion of Wires

The paper describes the research into the effect of the energy supplied to the conductor at the time of explosion on the particle size distribution of aluminum powders obtained. Aluminum powders consist of at least three fractions with the average particle size of 20-100 μm, 1-5 μm, and 50-900 nm. The yield of each fraction and average particle size are determined by the level of energy supplied to the conductor.