Ilya V. Mishakov

Oxidative dehydrogenation of butane over nanocrystalline MgO, Al2O3, and VOx/MgO catalysts in the presence of small amounts of iodine

Abstract High surface area nanocrystalline MgO, Al 2 O 3 , MgO·Al 2 O 3 , commercial MgO, and a series of 10% V/MgO samples were used as catalysts in one-step selective oxidative dehydrogenation of butane to butadiene in the presence of oxygen and iodine. Molecular iodine shifts the equilibrium of the dehydrogenation reactions to the right and makes it possible to achieve high butane conversion with high selectivity to butadiene. When excess oxygen is present in the feed, iodine is successfully regenerated and can be recycled. Butadiene selectivity as high as 64% has been achieved in the presence of small amounts of iodine (0.25 vol%) over a vanadia–magnesia catalyst at 82% butane conversion. The best performance was observed over a catalyst containing the magnesium orthovanadate phase.

Nanocrystalline ultra high surface area magnesium oxide as a selective base catalyst

Nanocyrstals of MgO having 4 nm average crystallite sizes with 450–550 m2/g surface area were prepared by the Aero-gel preparation method (AP-MgO). Dehydrohalogenation of 1-chlorobutane was performed using AP-MgO as a catalyst; And 1-butene is the selective product formed even after several cycles of 1-chlorobutane injections. AP-MgO was allowed to react with Cl2, which resulted in the formation of a highly reactive adduct which has a capability to selectively chlorinate propane.

Decomposition of Chlorinated Hydrocarbons on Iron-Group Metals

The decomposition of 1,2-dichloroethane and chlorobenzene on nickel–alumina, cobalt–alumina, and iron–alumina catalysts at 400–600°C was studied. Thermodynamic calculations demonstrated that the susceptibility of metals to chlorination under exposure to HCl increases in the order Ni < Co < Fe. The addition of hydrogen to the reaction mixture was found to dramatically decrease the rate of carbon deposition in the decomposition of 1,2-dichloroethane because of the intense hydrogenation of intermediates that are graphite precursors. Two fundamentally different reaction paths were found in the degradation of 1,2-dichloroethane: decomposition via a carbide-cycle mechanism with the formation of carbon as the main product (under conditions of a deficiency of hydrogen) and 1,2-dichloroethane hydrodechlorination accompanied by methanation of the formed carbon (under conditions of an excess of hydrogen). The degradation of chlorobenzene diluted with hydrogen in a molar ratio of 1 : 50 was not accompanied by carbon formation on the catalyst. A comparison between the selectivity for reaction products on nickel–alumina and cobalt–alumina catalysts indicated that the former catalyst is more active in the rupture of C–C bonds and in the methanation reaction of deposited carbon, whereas the latter is more favorable for hydrodechlorination. The optimum conditions and thermal regime for efficient and stable operation of the catalysts were found.

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.

Catalytic Synthesis of Nanosized Feathery Carbon Structures via the Carbide Cycle Mechanism

The morphology of carbon nanostructures obtained by 1,2-dichloroethane decomposition on the 90% Ni/Al2O3 catalyst under different reaction conditions was studied by high-resolution transmission electron microscopy. A new carbon product was discovered, which received the name of feathery carbon. The product has an extremely loose disordered structure consisting of separate fragments of a graphite-like phase. The structural disordering is assumed to be caused by the variation of chlorohydrocarbon decomposition conditions on the frontal face of the metal particle. This changes the character of carbon atom diffusion from the frontal face to the backside face of the nickel particles and finally results in a feathery morphology of the carbon phase. The specific surface area of feathery carbon is 300–400 m2/g.

Processing of organochlorine waste components on bulk metal catalysts

A method for destroying chloroorganic waste components on catalysts, particularly bulk metal nickel (99.99%), nichrome (80% Ni and 20% Cr), and chromel (90% Ni and 10% Cr) is proposed. The process is accompanied by the formation of carbon nanofibers (CNFs) with feathery morphology. Catalytic destruction of 1,2-dichloroethane on bulk nickel catalysts is characterized by a long induction period (∼3 h) with spontaneous activation of the alloy’s surface. Preactivation of the catalyst with acids or by alternative treatment in oxidizing and reducing environments shortens the induction period by one order of magnitude. The state of the surface before and after activation is studied by SEM, TEM, and EDX. The activity of catalysts is determined for the decomposition of 1,2-dichloroethane at temperatures of 500 to 700°C. Nichrome exhibited the greatest activity (yield of CNFs, 400 g/g of catalyst); the yield of CNFs on catalysts prepared by coprecipitation and mechanical activation was considerably lower. The proposed approach combines organochlorine waste disposal with the production of a useful product (CNFs). The use of bulk metal catalysts is promising since it simplifies the technology for their preparation, and the absence of carriers makes it easy to cleanse CNFs of impurities of catalyst fragments.

Morphology and structure of carbon resulting from decomposition of chlorohydrocarbons on nickel and cobalt containing catalysts

Morphology of carbons deposited from chlorohydrocarbons on Ni(Co)/Al2O3 has been investigated. It has been established that carbon filaments consist of imperfect graphite layers and possess high adsorption capacity towards hydrogen.

CO Oxidation over Pd/ZrO2 Catalysts: Role of Support′s Donor Sites

A series of supported Pd/ZrO2 catalysts with Pd loading from 0.2 to 2 wt % was synthesized. The ZrO2 material prepared by a similar technique was used as a reference sample. The samples have been characterized by means of transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), testing reaction of ethane hydrogenolysis (HGE), N2 adsorption, and electron paramagnetic resonance (EPR) spectroscopy. 1,3,5-trinitrobenzene was used as a probe molecule for the EPR spin probe method. The catalytic performance of samples was tested in the model reaction of CO oxidation. It was shown that the concentration of donor sites of support measured by EPR spin probe correlates with catalytic behavior during light-off tests. Low concentration of donor sites on a support’s surface was found to be caused by the presence of the specific surface defects that are related to existence of coordinately unsaturated structures.

Nanostructuring of the carbon macrofiber surface

The method of synthesis of CNF/MF carbon-carbon composites by growing carbon nanofibers (CNFs) on a surface of carbon macrofibres (CMFs) is described. The method is based on catalytic gas-phase deposition of carbon (using C1, C2 hydrocarbons and the mix of C2-C4). Depending on the conditions of modification (composition of catalytic particles, type of hydrocarbon, and temperature), it is possible to obtain CNFs with different morphologies (feathery, fishbone, or platelet fibers). It is found that the modification of MFs by CNFs (0.2–0.3 g/gMF) allows increasing the specific surface area of the initial material in an order of magnitude (up to 25 m2/g). The method is proven to be applicable for the modification of various materials made of CMFs (chopped fibers, tows, and carbon fabric).

Carbon erosion of hardware made of iron subgroup metals and their alloys

A paper published in 1952 described a previously unknown phenomenon of the formation of carbon tubes ~0.03–0.50 µm in diameter in carbon monoxide decomposition on dispersed iron particles at 873 K [1]. At that time, this paper almost completely eluded the attention of scientists. The interest in this phe� nomenon abruptly increased only in 1970–1980s. These studies became particularly important in the last decade in the context of the development of nanotech� nology and synthesis of nanomaterials. The nanosized carbon products obtained by the present day have a variety of morphological features and are a class of