Search

The possibility of using carbon black (CB) as a support of palladium catalysts for the selective hydrogenation of organic compounds is considered. The advantages of Pd/CB catalysts are demonstrated by examples of liquid-phase hydrogenation of aromatic aldehydes and nitro compounds. The combination of high catalytic parameters (activity, selectivity, and stability) achieved by these catalysts in hydrogenation reactions indicates that they are promising for use on an industrial scale, in particular in the syntheses of fine chemicals.

A cellular carbon support was first obtained by modifying the surface of a cellular carbon material with pyrolytic carbon. On this support, palladium catalysts with controlled particle size of deposited metal were synthesized for the first time. By the example of the reaction of gas-phase hydrogenation of acetylene, the possibility of using such catalysts in selective hydrogenation reactions was shown.

The methods for regulating the physicochemical and catalytic properties of Pd/C compositions by varying their synthesis conditions were reviewed. The effect of the nature of the carbon support, the composition of the palladium precursor and its reduction conditions, and the addition of a second active metal on the formation of palladium sites, their dispersion, electronic state, and catalytic properties in practically important hydrogenation reactions was demonstrated using the results obtained by the authors. These data may be useful for the development of Pd/C catalysts exhibiting high activity and selectivity in the hydrogenation reactions of polyfunctional organic compounds.

Some approaches to the synthesis of various modified carbon sorbents developed at the Laboratory of Synthesis of Functional Carbon Materials, Institute of Hydrocarbon Processing, Siberian Branch, Russian Academy of Sciences, were presented. Main results from studies of the physicochemical and biomedical properties of the modified carbon sorbents were reported.

The subject of this review is related to the development of research on the mechanism of interaction of platinum complex compounds, primarily, H2[PtCl6], with alumina supports and the role of this interaction in properties formation of the corresponding platinum catalysts. Based on the study of the composition of Pt(IV) chloride complexes adsorbed on the γ-Al2O3 surface, it was proposed that the complexes should be quantitatively discriminated as inner- and outer-sphere complexes in accordance with the nature of their binding with the support. The chloride ligands were found to be dominant in the bound outer-sphere Pt(IV) complexes, and adsorption of the complexes on the surface occurs due to the protonation of the hydroxyl groups of the support without any significant changes in the composition and geometry of the [PtCl6]2– complex anion. The binding of Pt(IV) in the outer-sphere complexes leads (after their reduction with hydrogen) to the formation of Pt particles with a relatively low dispersion containing platinum atoms mainly in a nearly Pt0 state, which are characterized by hydrogenating and dehydrogenating activity. The inner-sphere platinum(IV) complexes are the hydrolyzed forms of the chloride complexes formed by the replacement of chloride ligands by the hydroxyl groups of the support. Their reduction forms finely dispersed platinum particles containing a significant fraction of atoms in the ionic form, which increases the activity of the Pt/Al2O3 catalyst in dehydrocyclizations of n-alkanes. Several approaches were proposed that make it possible to vary the ratio between the outer- and inner-sphere platinum(IV) complexes (increasing the degree of hydrolysis of the complexes, or varying the nature of the surface OH groups of the alumina support) and hence to modify the properties of the catalyst. The possibility of selective synthesis of outer- and inner-sphere platinum(IV) complexes bound with other supports was shown for the Pt/MgAlOx system. Using the structural features of layered aluminum-magnesium hydroxides makes it possible to bind platinum(IV) in the complexes of the given type at high selectivity and to change the electronic state of Pt atoms in Pt particles and their activity in alkane dehydrogenations without changing the chemical composition of the catalyst.

A method for introducing small amounts of betulin (up to 1 wt %) into a mesoporous carbon material with a preset specific surface area of 300–310 m2/g, total specific pore volume of 0.35–0.40 cm3/g, and average pore diameter of 5.2–5.5 nm has been proposed and studied. The betulin content in the solid carbon matrix and in the used organic solvents has been determined by means of a gas chromatography–mass spectrometry technique. By means of scanning electron microscopy together with X-ray microanalysis and IR Fourier spectroscopy, the state of betulin on the outer and inner surfaces of carbon granules of different fractional composition, as well as in thin carbon layers, has been studied. It has been found that the main fraction of betulin is predominantly deposited on the outer surface of the globular particles of a porous carbon material. The properties of betulin impregnated into a carbon sorbent and the process of its dynamic desorption under the conditions simulating the biological environment of the gastrointestinal tract are studied.

The pore structure, thermal behavior, and elasticity of aerogel-type polyvinyl alcohol/carbon black composite materials prepared by cryogenic treatment of a suspension of carbon black in an aqueous solution of polyvinyl alcohol with foamed air were studied. The macropore size in the composite materials is influenced by the size of the primary carbon black particles. The heat resistance of these materials is enhanced on introducing g aqueous suspensions of a heat-resistant fluoroplastic into their structure. An increase in the dispersity of carbon black and in the concentration of functional groups on its surface leads to an increase in the elastic modulus of the aerogel-type composite materials.

Описаны направления синтеза модифицированных углеродных сорбентов, разработанных в лаборатории синтеза функциональных углеродных материалов в ИППУ СО РАН. Представлены результаты исследований физико-химических и медико-биологических свойств модифицированных углеродных сорбентов.

The MgAl layered double hydroxides (LDHs) were prepared by two-stage synthesis, which included mechanochemical activation at the first stage and the interaction of the resulting sample with distilled water at the second stage. The influence of the material of grinding bodies (steel and ceramics), the conditions of activation (activation time and the centripetal acceleration of balls), and the nature of initial compounds on the phase composition of the resulting products was investigated. It was established that the formation of a single-phase MgAl LDH was observed upon mechanochemical activation with the use of steel grinding bodies at an acceleration of 1000 m/s2 for 30 min. The samples prepared by a traditional coprecipitation method and a method that included a stage of mechanochemical activation possessed identical structural parameters. However, the mixed oxides formed upon the calcination of LDHs synthesized by mechanochemical activation were characterized by a more uniform pore space with a pore diameter of 4–5 nm with a developed specific surface.

Modification of the composition of polyvinyl alcohol/carbon black aerogel composite materials was performed to make them hydrophobic. The physicochemical properties of the matrices obtained, including their thermal conductivity and resistance to aggressive media and water, were studied. Materials with the moisture capacity decreased by up to 96%, exhibiting resistance to aggressive organic media and high heat insulation properties, were obtained.

Adsorption properties of carbon sorbents modified with glycolic and lactic acid oligomers and copolymers of these toward organic dyes of varied nature: Methylene Blue and Metanil Yellow were studied. Differences in the adsorption of the dyes by the modified sorbents, due to the nature of their surface, were found.

The structure and electrochemical properties (specific capacitance and electrical resistance) of various grades of carbon black before and after high-temperature gas-chemical treatment were studied. The textural and structural parameters were determined by the methods of low-temperature nitrogen adsorption, dibutyl phthalate absorption, X-ray diffraction analysis, and Raman spectroscopy. The results are compared to the characteristics of Printex XE2-B extra-conductive carbon black.

The Pt/MgAlO x catalysts, in which a mixed aluminum–magnesium oxide obtained by the heat treatment of corresponding layered double hydroxides was used as a support, were studied. The effects of the nature of active-component precursors ([PtCl6]2–, [PtCl4]2–, and [Pt3(CO)6] 6 2- ), and the Mg/Al ratio in the support on the anchoring of complexes, the disperse state of platinum, and the properties of the obtained catalysts in the reactions of propane and n-decane dehydrogenation were found.

A method of lactic-acid (LA) polycondensation on a carbon sorbent, including sorbent impregnation and multistep thermal treatment with no catalysts or toxic solvents, is developed. This modification technique makes it possible to obtain materials with adjustable properties (molecular weight of the synthesized oligomer, amount of applied modifier, degree of screening of carbon-sorbent pores, etc.). The resulting sorbent samples were investigated using various physicochemical methods: 13С and 1Н NMR spectroscopy, low-temperature nitrogen adsorption, differential thermal analysis, etc. It is established that the modifier concentration has an impact on the physicochemical characteristics of the studied carbon-sorbent samples. Of greatest interest is the carbon-sorbent sample impregnated with a 50% lactic-acid solution with subsequent thermal treatment. Its composition includes a high content of the modifier (biologically active substance with biospecific properties) and exhibits durable action.

New copolymers containing reactive vinyltriazole units and polyvinylene blocks with conjugation system promising as materials with special electrical, physical, catalytic, and sorption properties have been prepared by the reaction of poly(vinyl chloride) with sodium salts of 1,2,4-triazole and 1,2,3-benzotriazole in a dimethylformamide medium.

The paper presents a technique for the synthesis of molybdenum carbide using mechanical activation of carbon black, which was impregnated with a 20% aqueous solution of ammonium heptamolybdate (AHM) using the incipient wetness technique, in an inert medium at a 100 g acceleration of milling bodies for 30 min. The mechanically activated carbide-containing composites were calcined in an inert medium at 800 °C. The composites were examined by a range of physical methods. It was shown that the mechanically activated composite consists of molybdenum carbide, iron oxide and iron carbide (about 4–8% according to AES-ICP). The phase addition method was used to determine the quantitative content of Мо 2 С, which was equal to 7.2 wt% in the calcined sample. Catalytic testing of mechanically activated molybdenum carbide in the partial oxidation of methane showed that the carbide-containing catalyst provides a 48–60% conversion of methane and an 83–85% selectivity for the target product (CO).

The applicability of porous carbon materials obtained by the dehydrochlorination of poly(vinyl chloride) as supports for palladium hydrogenation catalysts was demonstrated. The efficiency of the catalysts was evaluated in the liquid-phase hydrogenations of styrene, nitrobenzene, chlorobenzene, and acetophenone. The complete conversion of the substrates with selective formation of target products was achieved under mild reaction conditions and at low Pd content in the catalysts (1.5 wt%).The applicability of porous carbon materials obtained by the dehydrochlorination of poly(vinyl chloride) as supports for palladium hydrogenation catalysts was demonstrated. The efficiency of the catalysts was evaluated in the liquid-phase hydrogenations of styrene, nitrobenzene, chlorobenzene, and acetophenone. The complete conversion of the substrates with selective formation of target products was achieved under mild reaction conditions and at low Pd content in the catalysts (1.5 wt%).

A method for carbon materials synthesis based on polyvinyl chloride has been proposed. Method includes polymer dehydrochlorination by alkali with carbon-rich conjugated structures (polyvinylenes) formation and its subsequent carbonization at relatively low temperatures. Raman and 13C NMR spectroscopy and transmission electron microscopy show that thermal treatment of the resulting polyvinylenes up to 400 °C leads to the formation of amorphous carbon material with chlorine contain less than 0.5 wt.%. These results can be used to develop dioxin-free technology of utilization of polyvinyl chloride and its wastes.

This work shows the possibility in principle of forming hydrocarbon structures in polyvinyl chloride films free of admixtures and polyvinyl chloride films modified with 5-mass % ferrocene via a radiation chemical transformation in the atmosphere with the use of an electron accelerator with a plasma cathode operating in the pulsed-periodic mode maximal electron energy no higher than 160 keV, pulse length of 40 μs, and current density of 5 mA/cm2. According to the results of semiquantitative X-ray microanalysis, an irradiated polyvinyl chloride film free of admixtures contains 92 of carbon, 6 of oxygen, and 2 mass % of chlorine; the irradiated polyvinyl chloride is an amorphous carbon material. A possible mechanism of the phenomenon is discussed.

The effect of the cationic composition of MgAl(Ga) layered double hydroxides on the structure, texture, and acid–base properties of related oxide supports for platinum catalysts has been investigated. As gallium is progressively substituted for aluminum in the mixed oxide, the properties of the support change only slightly, while the activity of the Ga–Pt catalysts in propane conversion increases, the propylene selectivity remains high (99%), and C–C bond hydrogenolysis is hampered.

A method of modification of carbon sorbents by copolymers of glycolic and lactic acids is developed. Control over the polycondensation process and adjustment of the synthesis conditions and parameters are done using the methods of NMR spectroscopy and thermogravimetric analysis. Optimal conditions for the modification of a carbon material are selected, allowing one to obtain predominantly the oligomers of glycolic and lactic acids. The surface shape and morphology, porous structure, elemental composition and composition of the functional groups, and mechanical strength of the carbon sorbent samples are investigated using a set of physicochemical methods. It is established that the adjusted conditions of polycondensation allow one to affix the modifying agent on the carbon sorbent.

The applicability of a porous carbon material obtained as a result of the “chemical” dehydrochlorination of chlorinated polyvinyl chloride as a support for palladium hydrogenation catalysts was demonstrated. The efficiency of the catalyst was evaluated in the liquid-phase reactions of nitrobenzene hydrogenation and chlorobenzene hydrodechlorination. Although the specific activity of the catalyst was lower by a factor of 3–4 than that of the samples based on Sibunit and carbon nanotubes, the complete conversion of the initial compounds with the selective formation of end products under mild conditions was achieved at a relatively low palladium content (1.5%).