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Reaction Kinetics, Mechanisms and Catalysis
Authors: R. Thinesh Kumar, N. Clament Sagaya Selvam, T. Adinaveen, L. John Kennedy, and J. Judith Vijaya

Abstract

Strontium added CoAl2O4 nanocatalysts with spinel structure were prepared by a modified sol–gel method using ethylene diamine followed by sintering at 900 °C. The samples were labeled as CoSA1-900, CoSA2-900, CoSA3-900, CoSA4-900, CoSA5-900, CoSA6-900, where the molar ratios of Co:Sr were 1.0:0.0, 0.9:0.1, 0.8:0.2, 0.7:0.3, 0.6:0.4 and 0.5:0.5 and the aluminum molar ratio was kept constant, 900 referring to the sintering temperature. The effect of Sr addition on the structural and morphological properties of cobalt aluminate nanocatalysts was investigated by X-ray diffraction, Fourier transform infrared spectra, high resolution scanning electron microscopy, energy dispersive X-ray analysis, nitrogen adsorption/desorption isotherms, temperature dependent conductance measurements and thermoelectric power measurements. The addition of Sr improves the performance of the nano cobalt aluminate catalyst towards the selective oxidation of alcohols and decreases the grain size. The effect of solvent, oxidant and reaction time on the Sr(II)-added cobalt aluminate nanocatalysts for the oxidation of benzyl alcohol was studied. Higher activity was obtained for the conversion of benzyl alcohol to benzaldehyde for 0.3 molar percentage Sr(II) added cobalt aluminate catalyst (CoSA4-900) which was used for the selective oxidation of other alcohols. The stability and reusability of the catalyst were also investigated.

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Levulinic acid was obtained from fructose over solid acid catalysts under mild reaction conditions in water. The reaction was carried out at different temperatures and amounts of catalysts to find the best reaction conditions. Among tested heterogeneous catalysts, Amberlyst-15 gave the highest LA yield (52%) with the lowest HMF yield (below 3%) under optimum conditions. Levulinic acid was isolated from the mixture after reaction by rotary vacuum evaporator with 47% isolated yield. The recycling experiments showed that Amberlyst-15 exhibited good activity even after 5 runs, though the LA yield gradually decreased from 52 to 30%.

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Abstract

In this article, (Ph2P)2N(cyclopentyl) ligands were prepared. The catalyst system that consists of main catalyst acetylacetone chromium (Cr(acac)3), cocatalyst triethyaluminium (TEA), ligands composited with 2,5-dimmethylpyrrole (DMP) and (Ph2P)2N(cyclopentyl) was used to trimerize ethylene to 1-hexene. The catalytic activity and selectivity of ethylene trimerization were studied under various reaction conditions (reaction temperature, ethylene pressure and cocatalysts). It was found that the Cr(acac)3/TEA/(Ph2P)2N(cyclopentyl) · (DMP) catalytic system catalyzed ethylene trimerization in situ, which gave an activity of 273.83 kg/gCr h−1, selectivity of 95.74%, and a spot of PE at 50 °C and 5 MPa ethylene pressure. TEA was an effective cocatalyst for ethylene trimerization. Compared with a single ligand such as (Ph2P)2N(cyclopentyl) or DMP, the composite ligands combined their respective advantages.

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Abstract

Various Pd amounts (5 and 20 %wt) were chemically deposited on two different carbon materials (activated carbon and carbon black). Support materials were characterized using low-temperature N2 adsorption and FTIR spectroscopy. SEM images and X-ray diffraction patterns were obtained for the samples tested. Cyclic voltammetric curves in 0.1 M H2SO4 were recorded over a variable sweep potential range for carbon materials with and without Pd. For comparison, the same electrochemical measurements were performed for powdered palladium. The hydrogen electro-oxidation potential decreased and the removal of adsorbed hydrogen by activated carbon-supported palladium was facilitated, which enables these systems to be used as anodes in hydrogen–oxygen fuel cells.

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Abstract

Titanium substituted highly ordered SBA-15 spheres with a diameter about 5 μm in a ternary P123-H2O-HCl-TEOS system were prepared by the hydrothermal method and the catalytic activity in the epoxidation of cyclohexene was studied. The synthesized materials were characterized by XRD, ICP-AES, FT-IR, BET and SEM, UV–Vis and N2 adsorption/desorption isotherms. The results show that incorporation of titanium into the framework of SBA-15 makes the surface area, pore diameter and pore volume increase and the pore walls slimmer than pure SBA-15. When the titanium content is above a critical value, TiO2 anatase forms on the material surface. The Ti-SBA-15 materials showed good catalytic activity for the oxidation of cyclohexene. The catalytic activity increases with an increase of Ti content and decreases when anatase TiO2 clusters are formed.

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Abstract

The present work focuses on the study of non-sulfided catalysts in the hydroconversion of sunflower oil to aliphatic paraffins, although sulfided and non-sulfided forms of one commercial catalyst are compared, too. Supported metal and metal oxide catalysts such as palladium on activated carbon or alumina, Ni/Al2O3 with different Ni-loadings and NiMo/Al2O3 samples were compared at 340 °C and 21 bar in a fixed-bed reactor. The reaction proceeded in consecutive steps of hydrogenolysis to carboxylic acids (CA) and propane, and hydrodeoxygenation (HDO) of the CA intermediates. Two HDO routes can be distinguished on the basis of obtained product distributions regarding the dominating alkane products (C17 and/or C18) characteristic of the different catalysts compared: (i) the hydrodecarbonylation/decarboxylation resulting chain-shortened alkanes (on supported Pd and Ni) or (ii) the reduction of full oxygen content to get alkanes and water preserving the original length of linear C-chains (on NiMo/Al2O3). Some of the standard, commercial NiMo/alumina catalysts can be applied for triglyceride transformation to green diesel without modification in sulfided or partly reduced form depending on the requirements of the refinery. Simple Ni/alumina samples without the admission of any other modifying component proved to be too active in side reactions (methanation of COx evolved and alkane hydrogenolysis).

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Abstract

Pitfalls of peroxynitrite (ONOO) formation in diabetic rat aorta on luminol-induced chemiluminescence (LCL) are investigated based on a detailed reaction mechanism in a case where 1.0 × 10−7 M s−1 superoxide formation rate and nitric oxide (NO) formation were measured by electron paramagnetic resonance, while ONOO formation by LCL. Modeling ONOO formation at equimolar reactant ratio at pH 7.4 and 37 °C predicts 2.0 nM ONOO and 2.1 × 10−6 M steady-state NO concentrations, which are both biologically relevant. Comparison of steady-state concentrations to those obtained by modeling the LCL intensity at pH 10 shows that ONOO concentration increases with 10% while peroxynitrous acid (ONOOH) concentration decreases complying with the pH shift. Evaluation of steady-state reaction rates reveals that the contribution of CO3 •− radicals to the formation of luminol radicals is 76%, that of NO2 is 24%, considerable, but that of OH radicals negligible. The contribution of additional superoxide formation by autoxidation of luminol is 13%, not negligible, but that of ONOOH homolysis is negligible. The NO2 is predominantly formed from the decomposition of the ONOO–carbon dioxide adduct and only 0.5% directly from NO oxidized by molecular oxygen. But the contribution of the latter pathway depends strongly on the NO and superoxide formation rate ratio, at a ratio of 2:1, it would increase to 14%. The measured time interval of the initial increase of LCL intensity complies with the time needed luminol aorta outside and inside concentrations in the sample to be equalized by diffusion, the 7 × 10−3 s−1 rate constant obtained by modeling enabled to estimate 5 × 10−7 cm2 s−1 as the diffusion coefficient of luminol in the diabetic rat aorta.

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Abstract

Manganese and mixed vanadium oxides were prepared by the hydrolysis of acetylacetonates. They were characterized by different techniques, such as X-ray diffraction, XPS, temperature-programmed surface reaction (TPSR), and conversion and selectivity measurements. TPSR studies showed that H2O, CO2, and O2 are present in manganese oxide samples and that the ones containing vanadium desorb CO2, H2O, methanol, formaldehyde, O2. The vanadium-free catalysts and the ones with a lower vanadium content also exhibit high methanol conversion and selectivity to CO2 at higher temperatures. The selectivity to dimethyl ether is important in the catalyst without V at lower temperature. The greatest conversion at lower temperatures and the highest selectivities to CO2 are achieved with the catalysts having the highest vanadium content.

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Abstract

The highly efficient and visible light (λ ≥ 420 nm) responsive composite photocatalyst WO3/Bi3O4Cl was prepared by the simple incipient wetness method. The heterojunction structure WO3/Bi3O4Cl demonstrated notably higher photocatalytic activity than the individual components WO3 or Bi3O4Cl for the complete mineralization of gaseous 2-propanol, aqueous 1,4-dichlorobenzene and several other organic compounds in aqueous phase under visible-light irradiation. The photocatalytic efficiency of the composite was optimized at 7 mol% WO3/Bi3O4Cl and annealed at 700 °C for 1 h. In comparison with Degussa P25, the photocatalytic activity with optimized composition was 5.9 times in evolving CO2 and 8.8 times in decomposing IP in gas phase. While in aqueous phase, its photocatalytic efficiency was 19–22 times and 9–10 times, respectively, compared to that of Degussa P25 and Bi2O3. Remarkably, its efficiency was estimated to be 1.6 times that of typical N-doped TiO2 in the evolution of CO2. The obviously enhanced photocatalytic performance of WO3/Bi3O4Cl composite has been discussed on the basis of the relative energy band positions of the Bi3O4Cl and WO3 semiconductors.

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Abstract

This study utilized Fenton, Fenton-like, photo-Fenton, photo-Fenton-like, sono-Fenton, and sono-Fenton-like systems for the decolorization of Reactive Red 2 (RR2) dye. Fe2+ and Fe3+ were used to catalyze the actions of oxidants H2O2 and Na2S2O8. Pseudo-first order rate constants (k) were obtained by fitting the decolorization kinetics of RR2. With added oxidant at 0.3 mM and iron ion at 0.03 mM, the k values of H2O2/Fe2+, H2O2/Fe3+, Na2S2O8/Fe2+, and Na2S2O8/Fe3+ were 13, 0.67, 6.2, and 0.080 r−1, in order. Higher oxidant and iron concentrations resulted in faster decolorization in Fenton and Fenton-like systems. Additionally, decolorization was accelerated by ultraviolet (UV) and ultrasound (US) irradiation. When ethanol was used as a scavenger for the generated hydroxyl and sulfate radicals, it significantly inhibited the decolorization process in photo-Fenton and photo-Fenton-like systems. The k values obtained for the UV/H2O2/Fe2+, UV/Na2S2O8/Fe2+, UV/H2O2/Fe2+/C2H5OH, and UV/Na2S2O8/Fe2+/C2H5OH systems were 23, 14, 0.36, and 0.69 h−1, in order.

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