Aleksey A. Vedyagin

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.

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.

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

Ni-Cu and Ni-Co Alloys: Synthesis, Structure, and Catalytic Activity for the Decomposition of Chlorinated Hydrocarbons

Homogeneous NixCu1 − x and NixCo1 − x (x = 0.90–0.99) alloys have been prepared through the coprecipitation of precursors (hydroxides or carbonates) and reduction of the precipitate. The formation of single-phase NixM1 − x alloys in all of the samples has been confirmed by X-ray diffraction. We have assessed the catalytic activity of the alloys for 1,2-dichloroethane decomposition with carbon nanomaterial (CNM) formation. The highest catalytic activity (CNM yield, 26–27 g/gcat) was offered by the nickel alloys containing ∼1 at % Cu or Co. The carbon material obtained has the form of segmented submicron wires with high morphological uniformity.

Preparation of nanocrystalline VMg(OH)x and VOx · MgO from organometallic precursors

A process is proposed for the synthesis of nanocrystalline VMg(OH)x and VOx · MgO with specific surface areas of up to 1200 and 470 m2/g, respectively. The synthesized VOx · MgO oxides consist of nanocrystals (2′–5 nm), which form platelike agglomerates. As distinct from conventional impregnation of magnesium oxide, the aerogel process for VOx · MgO synthesis ensures a uniform vanadium distribution in MgO.

Effect of Alumina Phase Transformation on Stability of Low-Loaded Pd-Rh Catalysts for CO Oxidation

Bimetallic Pd-Rh catalysts with precious metal loading of 0.2 wt% was prepared by incipient wetness impregnation of the support (γ-Al2O3 or δ-Al2O3) with dual complex salt [Pd(NH3)4]3 [Rh(NO2)6]2. Monometallic Pd and Rh catalysts as well as its mechanical mixture were used as the reference samples. All samples were exposed for in situ prompt thermal aging procedure, and characterized by EPR spectroscopy, UV–Vis diffuse reflectance spectroscopy and photoluminescence spectroscopy. The nature of the support was found to have strong effect on high temperature stability of the samples. δ-Al2O3 having non-uniform phase structure due to presence of θ-Al2O3 and α-Al2O3 traces causes the concentrating of rhodium near the interphase boundary, thus changing the mechanism of Rh3+ bulk diffusion if compare with γ-Al2O3. No noticeable anchoring effects were observed for bimetallic Pd-Rh samples neither in terms of Rh bulk diffusion nor with regard to the Pd sintering. It has been found experimentally that phase transformation of γ-Al2O3 at high temperatures does not play dramatic role for the deactivation of bimetallic Pd-Rh active species anchored to the electron-donor site of the support.

Synthesis of Al2O3–SiO2–MgO ceramics with hierarchical porous structure

A series of asymmetric cordierite ceramics with hierarchical porous structure were prepared and characterized. The macroporous support was obtained from natural raw materials (bauxite, silica sand, kaolinite, talc, and alumina) via ceramic technology. The prepared ceramic discs were characterized by a narrow pore size distribution. The average pore size was about 9.5 μm, and the open porosity was estimated to be 30%. Coating the discs with micro/mesoporous cordierite layer was performed using the sol–gel approach. Three-component sols were obtained from organic or inorganic precursors. Corresponding gels were calcined at 1200 °C to form the cordierite structure. The nature of precursor was found to affect the pore volume distribution. Narrow pore volume distribution was observed when organic precursors were used. Another key factor to control the parameters of final material was the drying condition. Supercritical drying of the gels has allowed us to increase the surface area in two orders of magnitude comparing with conventional drying procedure.

Carbon nanoreactor for the synthesis of nanocrystalline high-temperature oxide materials

The use of nanocrystalline oxides as precursors for the synthesis of new nanomaterials in which the initial nanoparticle size is preserved is of considerable interest. Here, the major problem is the sintering and growth of the initial nanoparticles at high temperature. One method for solving this problem is the deposition of a coating on the surface of nanoparticles so that it would prevent the sintering of the nanoparticles without hindering their interactions with the molecules of the gas phase and the solid-state transformations inside the shell. This study demonstrates that a carbon coating deposited on the surface of nanocrystalline oxides can be permeable for gaseous reagents and is able to function as a rather firm shell for the nanoreactor, so that the nanoparticles of the oxides under the shell can undergo transformations into nanomaterials of different chemical origins or different phase compositions. The carbon coating prevents the nanoparticles of the solid-state reaction product from sintering and makes it possible to synthesize new nanomaterials, the particle sizes of which are similar to those of the initial nanooxide precursors. This approach was shown to be efficient for the synthesis of finely dispersed oxide materials based on TiO2 and Al2O3.