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Abstract

Reliable data on heterogeneous photocatalytic processes with colloidal titanium oxide obtained under well defined laboratory conditions and with direct implication to outdoor conditions are rather rare. Here we report a useful guide on how to balance between (and how to correlate) solely exterior experiments and precisely obtained laboratory data. If produced separately, and comparisons attempted, misleading conclusions might be drawn. For the sake of simplicity all tests are carried out with commercial titania catalyst samples, and with Acid Orange 7, as the quite common model reactant in such reactions.

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Abstract

The in situ electrical properties and the catalytic activity of copper ferrite obtained by co-precipitation and thermal decomposition of polynuclear coordination compounds were studied in the propane oxidation reaction. The sample prepared by complexation had a better catalytic activity. Based on the conductivity data and the relative phase distribution in fresh and used compounds, the results are discussed in terms of the redox-type mechanism.

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Abstract

The Rh-catalyzed hydrosilylation of acetophenone in the presence of [Rh(CO)2(μ-Cl)]2 and [Rh(COD)Cl]2 complexes, as well as with an in situ addition of nitrogen-containing derivatives of mono- and bicyclic terpenes was investigated in a flow microreactor and in a batch reactor. Kinetic modeling, reaction equilibrium analysis and multi-criteria optimization of the process were applied to compare the performances of the reactors. In general, the highest catalytic activity was reached in the presence of [Rh(COD)Cl]2 and [Rh(CO)2(μ-Cl)]2 without the addition of amines. The best reaction selectivity towards 1-phenylethanol silyl ether with the [Rh(CO)2(μ-Cl)]2 complex was observed in the microreactor. The addition of (R)-(−)-cis-MyrtNH2 and (R)-(+)-BornylNH2 amines, as well as an increase of the amine-to-rhodium molar ratio significantly decreased the conversion and selectivity in both reactors. In this connection, the [Rh(COD)Cl]2 complex demonstrated a better catalytic performance in all cases. The application of the flow microreactor promoted another elementary reaction pathway due to micromixing effects.

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Abstract

The bifunctional transformation of n-hexane was carried out over Pt/MCM-22 based catalysts. MCM-22 was synthesized and submitted to ion exchange with rare earth nitrate solutions of La, Nd and Yb, followed by Pt introduction. Three different methods were used to introduce about 1 wt% of Pt in the zeolite: ion exchange, incipient wetness impregnation and mechanical mixture with Pt/Al2O3. The bifunctional catalysts were characterized by transmission electron microscopy and by the model reaction of toluene hydrogenation. These experiments showed that, in the ion exchanged sample, Pt is located both within the inner micropores and on the outer surface, whereas in the impregnated one, the metal is essentially located on the outer surface under the form of large particles. The presence of RE elements increases the hydrogenating activity of Pt/MCM-22 since the location of these species at the vicinity of metal particles causes modification on its electronic properties. Whatever the mode of Pt introduction, a fast initial decrease in conversion is observed for n-hexane transformation, followed by a plateau related to the occurrence of the catalytic transformations at the hemicages located at the outer surface of the crystals. The effect of rare earth elements on the hydrogenating function leads to a lower selectivity in dibranched isomers and increased amounts of light products.

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Abstract

Several gold catalysts supported on various inorganic supports with different point zero charge (pzc) were prepared by deposition–precipitation with urea (DPU). A thermodynamic model accounting for cluster evolution was advanced. The key element in the model is the dependence of the interfacial energy on the relative approach to pzc during DP. Experimental data were compared with the model, showing a possibility to utilize the theoretical approach to predict the cluster size.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Boris N. Kuznetsov, Svetlana A. Kuznetsova, Vladimir G. Danilov, Olga V. Yatsenkova, and Andrey V. Petrov

Abstract

A green one-step catalytic process of obtaining microcrystalline cellulose (MCC) from wood in the medium “acetic acid–hydrogen peroxide–water” in the presence 2% wt. sulfuric acid catalyst is described. The influence of wood nature and conditions of the process on the yield, composition and structure of obtained samples of MCC was investigated. For hardwood (aspen wood and birch wood) the minimal content of residual lignin (<1% wt.) was achieved under the following conditions: temperature 130 °C, the concentration of H2O2 4% wt., the concentration of CH3COOH ∼ 26% wt., liquor ratio of 10 and the process time of 3 h. At these conditions, the degree of delignification of softwood (spruce wood and larch wood) is lower than for hardwood. According to X-ray and FTIR data, the structure of MCC samples obtained from wood is close to that of MCC Avicel and MCC from cotton linter.

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Abstract

Reduction of NO by NH3 in the presence of O2 may occur on single Fe or Cu atoms or dimers incorporated into the inner walls of zeolite. One of the likely schemes of this reaction implies the formation of N2 and H2O through the reaction of gas-phase NO and adsorbed NH3. The steady-state kinetics corresponding to this scheme was recently analyzed by the author assuming that the reaction runs on single metal atoms. In this work, the author presents a model including two metal atoms. Under the practically important conditions, the kinetics predicted by the one- and two-site models are demonstrated to be similar. In particular, both models allow one to interpret the apparent reaction orders observed experimentally.

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Abstract

Ultranox626 as a diphosphite ligand showed high selectivity and good yields when used with Rh(CO)2(acac) as a catalyst precursor in the hydroformylation of allylbenzene derivatives producing aldehydes, and also in the one-pot hydroformylation–acetalization forming acetals. These reactions proceed smoothly and effectively to produce the linear aldehydes or acetals with high selectivity. The recycling of the rhodium catalyst was carried out after the careful screening and optimization of the reaction conditions in order to maximize the conversion and the selectivity of the reactions.

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Abstract

A simple method to prepare copper nanoparticles under the ambient atmosphere, in an aqueous environment, is developed utilizing solid sodium borohydride as the reducing agent and sodium citrate as a stabilizer and complexing agent. This constitutes a model system having a stability of several hours, sufficient to allow kinetic measurements. The localized surface plasmon resonance band of copper nanoparticles in the UV–Vis spectrum is used to determine the rate of formation of copper nanoparticles and assess the beginning of the oxidation process. The effect of temperature, copper sulfate and sodium borohydride concentrations on the copper nanoparticle formation rate is investigated. It is found that the kinetic data obey a first order rate law with respect to both sodium borohydride and copper sulfate. Based on the kinetic data, a novel mechanism of the reduction reaction is envisaged, involving three possible pathways. As solid sodium borohydride is an important hydrogen storage material, the results of this work are relevant to the field of portable fuel cells. The optical properties of copper nanoparticles have been simulated by using the Discrete Dipole Approximation method and the Mie theory and a good agreement was found between the theoretical and experimental characteristics of the copper plasmon band. The data obtained in this work provide valuable information on the kinetics of reactions at the nanoscale.

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Abstract

Kinetic investigations on the syntheses of higher aliphatic alcohol (C7, C9, C11) phthalates have been conducted in an isothermal, semibatch reactor. The first stage of the process, the formation of monoester, is very fast and irreversible. The second stage, the esterification of monoester towards diester, is slow and catalyst should be used. These reactions appear to be first order with respect to monoester and do not depend on the concentration of alcohol.

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