Vol 60, No 5 (2019)

The thermally stimulated luminescence (TSL) of poly(diphenylene phthalide) (PDP) films with terminal acid and diphenyl groups was studied using mathematical modeling methods. An adequate description (relative mean deviation, 6%) of the kinetic curves of TSL was obtained and the activation parameters of individual steps were determined by solving an inverse kinetic problem within the framework of a three-center four-step reaction scheme. The kinetics of TSL indicated the existence of two independent channels leading to the generation of an electronically excited diphenylene fragment of the polymer chain. The photoexcitation of PDP leads to the formation of a system of separated ion–radical states and, as a result, to the activation of individual polymer fragments. The subsequent recombination processes with the participation of the most active states occur through successive stages, and they are characterized by relatively low activation energies (E_a2 = 23 kJ/mol and E_a3 = 42 kJ/mol), which are traditionally interpreted in terms of the theory of mechanical relaxation as the vibrations of the smallest structural elements of the polymer (supposedly, the triarylmethyl-type side fragments of PDP). The high-temperature TSL (>370 K) is described in terms of the Randall–Wilkins model, and it is probably caused by the segmental mobility of the polymer (E_a1 = 70.5 kJ/mol). The data obtained indicate that the mid-chain units of the polymer mainly participate in the generation of electronically excited states: an analysis of activation parameters estimated from the kinetics of TSL of PDP films with different terminal units showed no significant differences in the described recombination processes.

To determine the mechanism of a heterogeneous catalytic reaction, a spectrokinetic method was used based on the comparison of simultaneously measured rates of transformation of surface complexes using in situ IR spectroscopy and the rate of formation of reaction products. Based on the of systemic studies of intermediates of heterogeneous catalytic reactions by this method, general patterns are found that shed light on the essence of the catalytic action. It is found that the main function of the catalyst is the preparation of a new reagent from the molecule in the gas phase (during adsorption). The transformation of this regent into the products on the surface occurs via a route that is fundamentally different from the route of transformation of the initial molecule in a gas-phase reaction. It was also found that, if the initial adsorption forms of the reactants in the reaction under study are the same for a certain group of catalysts, then the mechanism (as a sequence of steps) of this reaction on these catalysts is the same. The individual properties of different catalysts within such a group are manifested in the difference in the ratio of the rates of steps, i.e. in determining the limiting step.

The interaction of CO and O₂ and the subsequent oxidation of CO in the presence of cyclic thiolate and dithiolate complexes of Au(I), which represent the model fragments of thiolate-protected gold clusters, were studied using the density functional theory (PBE). On the basis of the calculated values, it was shown that O₂ and CO were weakly bound to a cyclic thiolate complex of Au(I). In the presence of a dithiolate complex, the activation of O₂ and CO and the subsequent oxidation of CO occurred with low activation energies. The results obtained demonstrate the important role of ligands in the catalytic process.

A physicochemical study of cobalt-containing (10 wt %) silica-supported Fischer–Tropsch catalysts was carried out. The catalysts were obtained under subcritical conditions (T = 200°C, P = 8 MPa) using water (T_c = 374.1°C, P_c = 22.1 MPa) and propanol-2 (T_c = 235.6°C, P_c = 5.8 MPa). The obtained samples were compared with a 10 wt % Co/SiO₂ catalyst prepared by incipient-wetness impregnation. Comparison of the properties of catalysts in the liquid-phase Fischer–Tropsch synthesis showed that the sample prepared in subcritical water was the most active and selective to aliphatic C₆–C₇ hydrocarbons. This sample is characterized by a high surface area (131.7 m²/g), a uniform distribution of particles in the active phase with an average size of 5 nm and higher accessibility of cobalt species for reagents. According to XPS data, the composition of catalyst active phase is mainly represented by two compounds: Co(OH)₂ and Co₃O₄.

The samples of 20% Cu/γ-Al₂O₃, 20% Co/γ-Al₂O₃ and 20% Ni/γ-Al₂O₃ were prepared as hydrogenation catalysts for continuous synthesis of 2-(2'-hydroxy-5'-methylphenyl)benzotriazole. The best yield (86.62%) was afforded by the 20% Cu/γ-Al₂O₃ catalyst. The characterizations results obtained for the 20% Cu/γ-Al₂O₃ sample confirmed that Cu particles are evenly distributed over the surface of γ-Al₂O₃. A reduction of acid sites in the catalyst favored the selectivity to 2-(2'-hydroxy-5'-methylphenyl)benzotriazole. Furthermore, the effect of Cu content, reaction temperature, hydrogen pressure and liquid hourly space velocity was studied. Finally, 2-(2'-hydroxy-5'-methylphenyl)benzotriazole in 86.62% yield was attained under the optimized conditions.

The present study describes the synthesis of a sulfonated styrene resin cross-linked with ethylene glycol dimethacrylate. The catalytic activity of the resin was assessed in the esterification of acetic acid with isoamyl alcohol. An activation energy of 16.36 kJ/mol was obtained, which is considerably lower than that of other catalyst systems reported in the literature. The developed catalyst achieved a conversion rate (87% in 2 h of reaction) higher than those obtained in studies with sulfonated styrene–divinylbenzene resins. This result was achieved at lower temperatures, using a more than 10 times lower catalyst concentration than that reported in the literature.

The article reports the synthesis of 5%CuO/Ce_{1– x}Zr_xO₂ catalysts based on CeO₂, ZrO₂ oxides and Ce_{1– x}Zr_xO₂ solid solutions with х = 0.2, 0.5, and 0.8. It is found that copper oxide is present in the catalysts in a highly dispersed form. In strong interaction with supports, it forms active oxygen, which participates in CO chemisorption and low-temperature oxidation of CO in the presence of hydrogen. In selective CO oxidation, the highest conversion (γ_mах = 100%) was obtained at temperatures of 120–160°С in the presence of 5%CuO/CeO₂. In the modification of CeO₂ by zirconium cations, the conversion on 5%Ce_0.5Zr_0.5O₂ decreases to 92% at 160°С because oxygen binding strengthens on copper-containing sites. On the 5%CuO/ZrO₂ sample, the maximum conversion is 67% at 180°С. The modification of ZrO₂ by cerium cations leads to an increase in the conversion to 87% at 160°С on the 5%CuO/Ce_0.2Zr_0.8O₂ sample as a result of increasing the amount of oxygen vacancies in the support. Taking into account the properties of CO complexes formed on copper-containing oxidation and adsorption sites, and the interaction of these complexes with adsorbed oxygen, their participation in the reaction of low-temperature CO oxidation by oxygen in excess of hydrogen on 5%CuO/CeO₂ and 5%CuO/ZrO₂ catalysts is considered.

The synthesis of light C₂–C₄ olefins from dimethyl ether (DME) in a three-phase system (slurry reactor) over nanosized MFI-type zeolites suspended in liquids with various chemical compositions (paraffins, hydrocarbon and silicone oils, and polyhydric alcohol esters) was studied. It was found that the target reaction can be accompanied by the catalytic decomposition of a dispersion liquid and its mechanical entrainment, which destabilizes the catalytic process. These negative factors can be minimized with the use of polydimethylsiloxane (Syltherm 800) as a dispersion liquid and MFI zeolite modified with magnesium as a catalyst. The rate of catalytic destruction of this oligomeric molecule in the presence of Mg–MFI was minimal at temperatures of 300°C or lower. The synthesis of olefins from DME at a temperature of 300°C over the Mg–MFI catalyst suspended in Syltherm 800 occurred in a stable way with high performance (70–90% conversion and 46–59% selectivity for the target products). The reaction carried out with the partial reflux of liquid reaction products after the dehydration of condensate excluded the loss of dispersion liquid in the course of the catalytic process due to its mechanical entrainment from the reactor.