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Reaction Kinetics, Mechanisms and Catalysis
Authors: K. V. Novikova, M. O. Kompanets, O. V. Kushch, S. P. Kobzev, M. M. Khliestov, and I. O. Opeida

Abstract

A series of substituted N-hydroxyphthalimides (NHPI) with electron-withdrawing groups (4-C(O)OH, C=O) and an electron-donating group (4-C(CH3)3) were investigated as catalysts for cumene oxidation. The initial reaction rates, measured by the oxygen uptake, conversion of substrate and yield of oxidation products are discussed. The catalytic activity of oxidation rate enhancement of NHPI derivatives in acetonitrile follows the order 4-tert-BuNHPI > NHPI > 4-carb-NHPI > NDHPI > NAPI. NMPT, trityl-NPI and NHPLI are inactive.

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Abstract

A series of CoMo/γ-Al2O3 catalysts was prepared with [Co/(Co + Mo)] ratios of 0.3, 0.4 and 0.5 while maintaining a total metal content of 19 wt%. These catalysts were tested in a batch autoclave reactor after presulfiding with the objective of studying the influence of Co/(Co + Mo) ratio on the hydrodesulfurization (HDS) pathways of benzothiophene (BT) and dibenzothiophene (DBT). The results of this study have clearly demonstrated that the Co/Co + Mo ratio has a significant influence on the overall HDS of BT and DBT as well on the direct desulfurization (DDS) pathway, but showed no influence on the hydrogenation pathway. A Co/Co + Mo ratio of 0.4 was found to be optimum for both overall HDS as well as the HDS by DDS pathway.

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Abstract

The kinetics of thermal decomposition of ammonium yttrium fluoride intermediates, (NH4)3Y2F9 and NH4Y2F7 were studied by a non-isothermal thermogravimetric (TG) technique at different heating rates. Kinetic parameters were determined from the TG curves by using two model-free methods, i.e. Flynn–Wall–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS). The activation energy (E) for the decomposition of (NH4)3Y2F9 was dependent on the fraction converted, α; its value was 152 kJ/mol (for α = 0.1–0.3) and 232 kJ/mol (for α = 0.4–0.8) from both models; and the pre-exponential factor (ln(A)) was 43 (for α = 0.1–0.3) and 59 (for α = 0.4–0.8). For the decomposition of NH4Y2F7, the activation energy (E) was independent of the fraction converted, α, and its value was 123 kJ/mol; the pre-exponential factor (ln(A)) was 31. The decomposition of (NH4)3Y2F9 proceeds by one-dimensional diffusion (for α = 0.1–0.3), followed by two-dimensional diffusion (for α = 0.4–0.8). The decomposition of NH4Y2F7 occurs by random nucleation and growth.

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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 a zeolite. Although this process is of considerable intrinsic interest as an example of complex reactions running on single sites and is also important from the perspective of environmental chemistry, its mechanism is still open for debate. One of the likely schemes of the process implies the formation of N2 and H2O via the reaction of gas-phase NO and adsorbed NH3. The author presents a detailed analysis of the steady-state kinetics corresponding to this scheme. The model employed includes eleven elementary steps. The results obtained allow one to interpret the apparent reaction orders observed experimentally.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Jung-Nam Park, Jeong Kuk Shon, Mingshi Jin, Soo Sung Kong, Kiyoung Moon, Gwi Ok Park, Jin-Hyo Boo, and Ji Man Kim

Abstract

Highly ordered mesoporous ruthenium dioxide (meso-RuO2) has been successfully synthesized by controlling the surface hydrophobicity of a mesoporous silica template (KIT-6) via a nano-replication method. The meso-RuO2 material, thus obtained, exhibits a well-defined mesostructure and high surface area (131 m2 g−1). The physicochemical properties of the meso-RuO2 material are characterized by electron microscopy, X-ray diffraction, N2 adsorption–desorption, temperature programmed techniques, and X-ray photoelectron spectroscopy. Pretreatment of the meso-RuO2 catalyst under different gas environments (O2, H2 and CO) strongly affects the catalytic activity towards CO oxidation. The meso-RuO2, pretreated by O2 flowing at 200 °C, exhibited excellent catalytic activity for CO oxidation, 100% CO conversion with long-term stability at room temperature, whereas the meso-RuO2 catalysts with pretreatment under other conditions are not very active at room temperature. It is found that the surface oxygen species generated on the meso-RuO2 during O2 pretreatment at 200 °C provide CO oxidation activity at room temperature.

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Abstract

A new CrIII–Schiff base complex of N,N′-ethylene-bis-salicylamide (Salm), supported on acidic alumina, was characterized by chemical and spectral (UV–Vis-DRS and FT-IR) analyses. The comparative catalytic activity of the neat and supported metal complex was evaluated using H2O2 decomposition as the model reaction at varying H2O2 concentration and amount of catalyst which showed a higher activity for the supported metal complex. A preliminary study showed that the supported CrIII(Salm) was also active for the oxidation of phenol using H2O2 as oxidant leading to catechol (selectivity ∼62%) and hydroquinone (selectivity ∼32%) as the major products.

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Abstract

Polymer-modified TiO2 was found to be a new, efficient photocatalyst for the photodegradation of organic pollutants. Another novel sensitizer-poly(fluorene-co-bithiophene) (PFB) was presented in this study. Varying the bithiophene content of PFB from 10, 20, 33, 40 to 50% in molar ratio, a series of copolymers (PFB10, PFB20, PFB33, PFB40 and PFB50) were prepared and used as the sensitizers for TiO2. The photodegradation rates of phenol catalyzed by these polymer-modified titanium dioxide composites under the irradiation of the GaN LED clusters were investigated. It was found that PFB33-modified TiO2 was the most efficient photocatalyst although the absorption spectrum of PFB50 was broader than that of PFB33.

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Abstract

A series of CuO–V2O5/Al2O3 catalysts were prepared and characterized by various techniques such as XRF, BET, XPS and XRD. These catalysts were used for liquid-phase amination of toluene to toluidines. It was found that adding copper species to V2O5/Al2O3 catalyst showed a peculiar behavior, maintaining a high activity toward toluene amination. An optimum CuO content appeared at 1.6 wt% with a CuO/V2O5 molar ratio of 0.25. More than 60% total yield of toluidines was obtained over 1.6%CuO–15%V2O5/Al2O3 catalyst under optimized conditions. Catalyst characterizations revealed that the addition of copper improved the formation of V5+ species, thus enhancing the activity of the catalyst.

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Abstract

The aim of the study was to characterize the regime of operation of a newly constructed POLITEF flat-plate gas-phase continuous flow photocatalytic reactor in view of improving its construction and selecting the optimum set of operational conditions. The nanosized photocatalytic powder material (TiO2 Degussa P25, consisting of 75% anatase and 25% rutile with average anatase particle size 25 nm) was deposited as a thin film coating on a TLC aluminum sheet, pre-coated with silica gel (Merck, 0.2 μm SiO2 film), achieving loadings of 0.6 –2.0 mg TiO2/cm2. The reactor is operated either with UV light or visible light, penetrating through a quartz glass flat-plate illumination window (56 cm2 illuminated surface area). The time interval needed to reach steady-state operation conditions was established to be 5 min, applying the criterion of Wald–Wolfowitz. The model air pollutant was ethylene with a feed concentration of 1000 ppm. All the experimental runs were carried out at an optimal relative humidity of 30%, which was established in a previous work. Varying the operational parameters—ethylene contact time, ethylene/oxygen feed ratio, the kind of light and intensity of illumination—the optimum operating conditions were established, under which maximum ethylene conversion was observed. Corrigan's criterion for the presence or absence of diffusion limitations was applied, proving that the reactor was operating in the kinetic region at low TiO2 loadings, but at high loadings, a diffusion retardation effect was observed. It was established that the flow through the reactor is laminar based on the values of the Reynolds number.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Cleanio L. Lima, Hélvio S. A. de Sousa, Santiago J. S. Vasconcelos, Josué M. Filho, Alcemira C. Oliveira, Francisco F. de Sousa, and Alcineia C. Oliveira

Abstract

Sulfated molecular sieves were synthesized and characterized by XRD, FTIR, chemical analyses, acidity measurements and N2 adsorption–desorption isotherms. Sulfatation led to structural changes in the solid framework by increasing the acidity and accessibility of the acid sites. Br⊘nsted and Lewis acid sites of mild to high strength improved the conversion of alcohols, but the selectivity was modest over sulfated FAU type Y, ZSM-5 and γ-Al2O3 solids at temperatures lower than 200 °C. The characteristics of the sulfated AlSBA-15 molecular sieve in terms of acidity, textural properties and accessibility possibly make this solid useful for catalytic reactions involving bulky organic compounds.

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