Anastasia Volodymyrivna Terebilenko

This study aimed to develop new catalysts, based on MoS₂, for the hydrogenation of bromoquinolines without C-Br bond cleavage. The mechanochemical exfoliation of the bulk MoS₂ in the presence of NaCl resulted in the formation of the material (MoS₂-1), consisting of flat plates of size between ca. 40 × 100 and ca. 250 × 400 nm². Similar grinding of MoS₂ in the presence of NH₄Cl produced smaller nanoplates of size between ca. 10 × 30 and ca. 50 × 300 nm² (MoS₂-2). These materials were characterized using powder XRD, TEM, SEM, Raman spectroscopy and XPS. The specific surface area of the MoS₂-1 and MoS₂-2 samples was estimated using the analysis of N₂ adsorption isotherms. Both materials were catalytically active in the hydrogenation of quinoline; 1,2,3,4-tetrahydroquinoline (THQ) was the sole product and its yield grew proportionally to the accessible surface area of the catalyst. The hydrogenation of 5- and 8-bromoquinolines in the presence of MoS₂-1 and MoS₂-2 led to the respective bromo-THQs with almost quantitative yields, while the hydrogenation of 6-bromoquinoline resulted in the formation of the respective 6-bromo-THQ with the yield up to 30%. In the case of 7-bromoquinoline, N-methylated 7-bromo-THQ was formed almost quantitatively.

Electric conduction mechanisms in the pressed powder samples consisting of the molybdenum-disulfide-oxide (MoS _x O _y ) nanoflakes depending on their content and structure have been investigated. The MoSxOy nanoflakes were synthesized in the temperatures range of 130 to 180 ^o C by reaction of (NH ₄ ) ₆ Mo ₇ O24 with thiourea in aqueous solution followed by aerial oxidation. The chemical composition and structure of the powders have been determined by means of XPS, EDS and Raman spectroscopy. The obtained nanoflakes are 10-20 nm thick and self-assembled in the “nanoflower”-shape agglomerates forming powder particles. The agglomerates in powders synthesized at different temperatures are shown to consist of MoS2 and molybdenum oxides/sulfoxides which content ratio differs from each other in powders depending on their synthesis temperature. The current vs voltage (I-V) dependences of the pressed powder films manifest a hysteresis-like behavior with substantial dependence on this ratio. For the samples with the highest content of the Mo oxide/sulfoxide nanoflake forms (>50 %) one observes the negative differential conductivity (NDC) in the I-V characteristics and very large difference between the forward and backward I-V branches at small DC biases. Unlike, the samples with low content of these forms have slightly non-linear I-V characteristics, narrower hysteresis loop and absence of NDC. All samples manifest long-lasting (tens second) transient charge/discharge process after switching “on/off” the voltage across the sample, and ability of large charge accumulation with the specific capacitance equal achieving 12-75 F/g depending on the powder synthesis temperature. These phenomena give evidence of the important role of interface charges in the MoSxOy powder electric conduction mechanisms. To describe theoretically the observed I-V curves, polar and electric-transport properties of the pressed MoSxOy nanoflake films, the Landau-Cahn-Hilliard approach considering flexo-chemical field has been used. The revealed features of electric conduction and charge accumulation look interesting for possible applications in nanoelectronics and charge storage devices

A set of 17 composites was prepared by pyrolysis of Cu ²⁺ complexes with phenanthroline and 1,2‐diaminobenzene (DAB), deposited on SiO ₂ (Aerosil). All composites contained Cu and N‐doped carbonaceous component, while some of them additionally contained Cu ₂ O or CuCl. According to the data of powder x‐ray diffraction (PXRD), the size of Cu nanoparticles was 20–37 nm. The size of Cu nanoparticles found by transmission electron microscopy (TEM) was consistent with that one determined by PXRD. Surface area of the catalysts was determined from low‐temperature nitrogen adsorption. In addition, one Cu‐free composite was prepared from MgCl ₂ and DAB. The composites were tested as the heterogeneous catalysts in the process of cycloaddition of propargylamine to ethyl 4‐oxocyclohexanecarboxylate, leading to ethyl 5,6,7,8‐tetrahydroquinoline‐6‐carboxylate. It was found that the reaction could be catalyzed by the carbonaceous materials without Cu. An increase of the carbon content in the reaction mixture led to a decrease in the product yield, while the product yield did not correlate with the content of Cu. It was shown that Cu partially dissolved in the course of the catalytic reaction. The obtained catalysts were used for the synthesis of a series of substituted fused pyridines.

A set of 22 composites was prepared by pyrolysis of Cu2+ complexes with phenanthroline and 1,2-diaminobenzene, deposited on SiO2 (Aerosil). All composites contained Cu and carboneous components, while some of them additionally contained Cu2O or CuCl. According to the data of powder X-ray diffraction, the size of Cu nanoparticles was 20-37 nm. The presence of Cu nanoparticles was confirmed by TEM, while some aggregates were found by SEM. The composites were tested as the heterogeneous catalysts in the process of cycloaddition of propargylamine with 4-oxocyclohexanecarboxylate leading to ethyl 5,6,7,8-tetrahydroquinoline-6-carboxylate. It was found that the product yield did not correlate with Cu content in the reaction mixture or other single parameters, but reached maximal values at certain values of parameters, proportional to the surface of Cu and surface of C, exposed to the reagents. It was found that the leaching of Cu takes place upon repeated use of the composites.

A series of composites containing nanoparticles of NiO (from 1 to 10% by weight per Ni), deposited on NORIT charcoal, was prepared by the decomposition of the Ni⁰ complex Ni(cod)₂ (cod = cis,cis-1,5-cyclooctadiene). Ni content in the composites was set by loading the appropriate quantities of the Ni(cod)₂ precursor. The catalytic activity of the composites was associated with the in situ generation of active sites due to a reduction in NiO, hence the composites could be stored in air without a loss in their catalytic performance. The composites were analyzed by powder XRD, TEM, XPS, and adsorption methods. The hydrogenation of quinoline was used as a reference reaction for studies of the influence of temperature, P(H₂), catalyst loading on the product yield, and for the selection of the composite possessing the highest performance. It was found that 3% Ni loading was the most optimal. This composite was used as an efficient catalyst for the hydrogenation of compounds with ethylene and acetylene bonds, nitro- and keto- groups as well as a series of substituted quinolines and analogs. The studied composites can be proposed as air-stable and efficient catalysts for the hydrogenation of a wide range of organic compounds.