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Abstract

The aim of this study was to develop an appropriate kinetic model for propane dehydrogenation (PDH) over an industrial Pt–Sn/γ-Al2O3 catalyst in the presence of small amounts of oxygenated compounds. Experimental data were obtained from a previous study where catalytic PDH was carried out in a laboratory scale reactor at atmospheric pressure in the temperature range of 575–620 °C in the presence of small amounts of water or methanol. The kinetics of the main dehydrogenation reaction was described and the effects of water and methanol on coke deposition and catalyst sintering were considered in a catalyst deactivation model to explain the observed optimum level in the amount of added oxygenated compounds. The model predictions were in good agreement with experimental data.

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Abstract

CdxZn1−xS and Ru3+ doped Ru(m)/Cd0.5Zn0.5S photocatalysts were prepared by a simple hydrothermal method, and characterized by X-ray diffraction, UV–Vis absorption spectroscopy and electrochemistry techniques. Their photoactivities were evaluated by hydrogen evolution from aqueous solution containing Na2S and Na2SO3 as a hole scavenger under visible light (λ ≥ 420 nm) irradiation. Ru3+ doping enhances the photocatalytic activity markedly. It was found that 0.10 mol% Ru3+ doped Cd0.5Zn0.5S photocatalyst showed the highest activity. The reason for the positive effects of Ru3+ was discussed.

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Abstract

Digital image-based calibration was applied for the determination of iron(III), Fe3+, as a catalyst in the oxidation of indigo carmine (IC) using bromate ion (BrO3 ). During the reaction, a colorless product was produced and there was an induction period (IP) before the color of the solution faded. The length of IP depended on the concentration of Fe3+. The color fading of reaction was recorded as a change of red, blue and green colors (%RBG). Kinetic profiles similar to what has been reported in a previous spectrophotometric study were obtained. Fe3+ was determined in the concentration range of 6–16 ppm at pH = 2 and 25 °C. The detection limit of Fe3+ was found to be 1.994 ppm, which is better in comparison with the previous work. Optimum concentrations of IC and BrO3 were obtained as 5.5 × 10−5 and 3 × 10−3 M, respectively, using a one-at-a-time optimization method. The optimum pH value was 2. The interference effect of various cations and anions on the determination of iron is reported. In addition, the application of the method to real samples of human serum was performed. The obtained results from real samples were in accordance with the obtained results using standard methods. The analysis of images (movies) recorded from an evolutionary chemical systems seems to open new, simple and low-cost analytical opportunities.

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Abstract

A bifunctional catalyst Pt/Hβ-n (Pt loading: 0.4 wt%) was prepared by the impregnation of an aqueous solution of chloroplatinic acid with β zeolite, wherein the β zeolite support has an unusual morphology of egg-like microspheres assembled by nanocrystallites. Other two control catalysts were also prepared using a β support with micro-sized crystals and a commercial one with varying crystal sizes. The catalysts were characterized by XRD, SEM, ICP, N2 sorption isotherms and mesopore size distribution, and evaluated in the hydroisomerization of n-heptane in an atmospheric fixed bed flow reactor. Though Pt/Hβ-n has similar acidity and Pt loading (0.4 wt%) to the two control catalysts, it exhibits remarkably higher conversion of n-heptane and selectivity to isomerization. According to the characterization data, the higher activity of Pt/Hβ-n is the result of the faster diffusion of reactants in shorter channels of nanocrystallines and the uniformly distributed mesopores within the microspheres.

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Abstract

Alumina/TiO2/Apatite interface nanostructure composite filters have been developed for air purification. It was shown that these filters can efficiently absorb and decompose organic species which are suspended in air. To prepare the filters, TiO2 nanopowder was dispersed in titanium sol in 30 and 70 g/L concentrations, and the prepared mixture was deposited on the porous alumina body by dip-coating. Then, the calcined nanostructure composite TiO2–TiO2 was soaked in a simulated physiological solution (SBF) at 37 °C. The surface morphology, surface area, crystalline structure and crystallite sizes of the films were investigated by SEM, EDS, BET, and XRD. The photocatalytic activity of the composite filters, as well as the effect of the TiO2 nanopowder concentration in the titania sol and soaking time in SBF were also evaluated through the degradation of nitrogen oxides (NOx) as one of the dominant causes of air pollution in the car exhaust gases. SEM and XRD results showed that immersion in SBF forms a layer of carbonate-containing apatite on the TiO2 layer. The results showed that increasing nanopowder TiO2 concentration increases the NOx oxidation rate. The prepared alumina/TiO2/HA filter can be used to remove CO gas with the absorption mechanism, as an interesting CO degradation performance (about 95 %) was observed in the alumina/TiO2/HA filter after soaking into SBF for 20 days. However, it could not significantly alter the concentrations of other car exhaust pollutants (SO2 and CxHy).

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Natpakan Srisawad, Wasu Chaitree, Okorn Mekasuwandumrong, Artiwan Shotipruk, Bunjerd Jongsomjit, and Joongjai Panpranot

Abstract

The properties of Co/Al2O3 catalysts prepared by the solid-state reaction between gibbsite and various cobalt salts such as cobalt acetate (CoAc), cobalt acetylacetonate, cobalt chloride, and cobalt nitrate (CoNT) were investigated in the hydrogenation of carbon dioxide at 270 °C and atmospheric pressure and characterized by N2 physisorption, X-ray diffraction, X-ray photoelectron spectroscopy, and H2-temperature programmed reduction. Compared to the catalyst prepared by conventional impregnation of aqueous solution of cobalt nitrate on alumina (CoNT-Imp), the solid-state catalysts (CoNT and CoAc) exhibited much higher activity in the CO2 hydrogenation with comparable CH4 and CO selectivity. Unlike the impregnation catalysts, in which most of the Co3O4 particles/clusters were located deep inside the pores of alumina, the solid-state reaction resulted in the dispersion of cobalt oxides mostly on the external surface of alumina. As a consequence, CO2 adsorption and dissociation to adsorbed CO and O (the initial steps in CO2 hydrogenation) were not limited by the slow diffusion of CO2 so high CO2 hydrogenation activity was obtained. As revealed by the XRD and H2-TPR results, the average crystallite size of Co3O4 and the metal-support interaction depended on the cobalt precursor used during the solid-state synthesis. Nevertheless, the solid-state reaction of gibbsite and cobalt chloride at 650 °C resulted in very poor CO2 hydrogenation activity due to the formation of inactive cobalt aluminate.

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Abstract

The catalytic activity of nickel oxysalts NiCo2O4 NiFe2O4, NiTiO3, NiMoO4, Ni3(PO4)2, with different ionic character of the oxygen bond in the anionic ligand was investigated. The acid–base and redox properties of selected catalysts were studied on the basis of kinetics of isopropyl alcohol conversion. The kinetics of propene oxidation over the catalysts and the activation energy and selectivity of oxidation reactions were determined. Activities of the catalysts in the propene oxidation reaction were compared with their oxidation–reduction and acid–base properties. The influence of the amount and form of chemisorbed oxygen on the propene oxidation pathway was investigated. Over the most active catalysts, the non-destructive propene oxidation towards acrolein is the least selective. Oxysalt catalysts active in oxidation reactions exhibit strong redox properties but direct the process towards destructive oxidation products.

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Abstract

Ceria–alumina composite supports were prepared by the co-precipitation (cop), impregnation (imp) or deposition–precipitation (dp) methods. Co–Mo catalysts supported on these composite supports were prepared by the imp method and their catalytic activities for sulfur-resistant methanation of synthesis gas were investigated. The catalysts were characterized by nitrogen adsorption, X-ray diffraction (XRD), and hydrogen temperature-programmed reduction (TPR). It was found that the preparation method of ceria–alumina composite support had a marked influence on the surface area, the interaction between ceria and alumina, and the catalytic performance for sulfur-resistant methanation. Among them, the ceria–alumina composite support prepared by dp method achieves the best methanation activity due to its smaller ceria particle size, better ceria dispersion, weak interaction between ceria–alumina as suggested by XRD and TPR results.

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Abstract

Binary CeO2–MgO oxides with various Ce/Mg mol ratios were prepared by the co-precipitation method and were tested in the dehydrogenation of ethylbenzene to styrene. The obtained materials were characterized by N2 adsorption, X-ray diffraction, and X-ray photoelectron spectroscopy. The N2 adsorption showed that CeO2–MgO oxides were mesoporous materials and the BET surface area increased with increasing magnesia content. The fluorite type structure of ceria was observed in samples with low magnesia content while the mixture of the ceria phase and the magnesia phase existed simultaneously in samples with high magnesia content. The results showed that the Ce4+–Mg2+–O2− couple in CeO2/MgO catalyst could be supposed to be an active site in the dehydrogenation of ethylbenzene.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Frederico A. D. Araújo, Sonia V. Pereira, Deivson C. S. Sales, A. R. Schuler, and Cesar A. M. Abreu

Abstract

The free fatty acids of cotton seed oil were processed with methanol and ethanol into the corresponding alkyl fatty esters in the presence of diluted sulfuric acid. The products characterized as biodiesels presented higher mass fraction levels (43.0 wt%) of the alkyl linoleates, and 17.0 and 13.0 wt% of the alkyl esters C16:0 and C18:1, respectively. A model based on the mechanism of the acid esterification, and representing the evolutions of the fatty ester concentrations, was fitted to the experimental evolution results where the orders of magnitude of the kinetic parameters were quantified. The selectivities of the methyl and ethyl fatty esters in the biodiesel mixtures were compared, where the C18:2 ethyl linoleate selectivity (92.3 %) in the ethyl biodiesel was almost twice the methyl linoleate selectivity (57.3 %) in the methyl biodiesel.

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