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Abstract

The kinetics of the oxidation of formaldehyde by octacyanomolybdate(V) ions has been studied in aqueous alkaline medium. A formaldehyde-dependent and -independent reaction has been observed. The HCHO-dependent reaction displays first order kinetics in [Mo(CN)8 3−], [HCHO], [OH] and alkali metal ion catalysis was observed. The rate law is consistent with: Activation parameters for both the formaldehyde-dependent and -independent reaction have been obtained. The activation parameters for the HCHO-independent reaction provide evidence for the identification of the reaction. A reaction mechanism is proposed.

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Abstract

One pot three-component imino Diels–Alder reactions of various types of aldehydes, aniline and dihydropyrane were studied in the presence of nano sized MCM-41 supported 12-tungstophosphoric acid (TPA) as solid acid catalyst. MCM-41 as solid support was synthesized in nano size and the catalysts with different loading amounts of TPA (5–30 wt%) were prepared and characterized by XRD, FT-IR and SEM techniques. The results confirm a good dispersion of the heteropoly acid on the solid supports and based on the experimental results, the catalyst with 10 wt% heteropoly acid shows the best catalytic activity using 0.5 mol% heteropoly acid relative to the aldehyde. The recovery experiments show that the catalyst is reusable after calcination without significant loss in its activity.

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Abstract

Vanadium complexes of N-salicylidene-l-histidine immobilized on Al-MCM-41 designated as VO(Sal-His)/Al-MCM-41, were prepared and characterized by X-ray powder diffraction (XRD), FT-IR, nitrogen adsorption–desorption and chemical analysis techniques. VO(Sal-His)/Al-MCM-41 was found to catalyze the epoxidation of trans-2-hexen-1-ol, cinnamyl alcohol and geraniol with tert-butyl hydroperoxide (TBHP). The successful catalytic behavior of VO(Sal-His)/Al-MCM-41 with 99% conversion and excellent selectivity toward the corresponding epoxides is described herein.

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Abstract

A series of catalysts containing 5–25 wt% 12-tungstophosphoric acid supported on hydrous zirconia were prepared and their catalytic activity evaluated for the esterification of palmitic acid with methanol. These catalysts were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, surface area (BET method), and potentiometric titration for the estimation of acidity. The catalyst with 20 wt% TPA calcined at 300 °C exhibited the highest activity. The effects of reaction variables such as catalyst loading, methanol to acid molar ratio and reaction temperature were studied. The pseudo-homogeneous (PH), Eley-Rideal (ER) and Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic models were applied to correlate the experimental kinetic data and kinetic parameters were evaluated. The LHHW model gave the best fit.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Mohammad Saleh Ghodrati, Mohammad Haghighi, Jafar Sadegh Soltan Mohamdzadeh, Behzad Pourabas, and Ehsan Pipelzadeh

Abstract

Ultrasound energy has been successfully employed to synthesize CdSe/TiO2 nanocatalysts for the photocatalytic degradation of phenol under solar light irradiation. The photocatalytic performance test was carried out using TiO2 as well as synthesized CdSe/TiO2 nanocatalysts. Nanocatalyst characterization was accomplished using XRD, SEM, FTIR, BET and UV–vis spectroscopy. It was shown that the synthesized nanocatalysts have crystal characteristics and are in nano-scale size range. The coupled nanocatalyst has shown a shift in the absorption spectrum from the UV range to the visible range. The results of photocatalytic tests showed that the CdSe/TiO2 coupled nanocatalyst could remove phenol from wastewater under solar light irradiation, while TiO2 did not have enough activity in this process. It is also shown that the CdSe nanoparticles act as photosensitizers, not only extending the spectral response of TiO2 to the visible region but also reducing the electron–hole recombination. Furthermore, the CdSe/TiO2 synthesized samples provided more photomineralization efficiency than that of TiO2 in terms of total organic carbon analysis.

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Abstract

A comparative study of the physicochemical properties of Cu/Cr2O3·3Al2O3 and Au–Cu/Cr2O3·3Al2O3 supported catalysts and their catalytic activity in methanol synthesis and water gas shift reactions were the main subject of this study. The promotion effect of gold addition to Cu/support catalysts in the methanol synthesis reaction was proved. The formation of an Au–Cu alloy was confirmed by XRD technique. Methanol selectivity increased after gold introduction onto the catalyst surface, which can be explained by the creation of nucleation centers for copper crystallization by metallic gold particles during catalyst reduction.

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Abstract

Ternary nanostructured CuO/Ti0.8Ce0.2O2 catalysts were prepared by a one-step surfactant-assisted method of nanoparticle assembly. The textural and structural properties of the CuO/Ti0.8Ce0.2O2 catalysts were characterized by XRD, TGA, BET, XPS and H2-TPR. Their catalytic performance for low-temperature CO oxidation was studied by using a catlab system. CuO supported on binary Ti0.8Ce0.2O2 support showed higher catalytic activity than CuO supported on single CeO2 or TiO2 support. The calcination temperature had a remarkable influence on the catalytic activity of the CuO/Ti0.8Ce0.2O2 catalysts. The CuO/Ti0.8Ce0.2O2 catalyst calcined at 500 °C exhibited the highest catalytic activity with T50% and T100% at 82 and 123 °C, respectively. According to the XRD, BET and H2-TPR analyses, the higher surface areas and more highly dispersed small particle size CuO should be responsible for the high catalytic activity of catalysts.

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Abstract

The kinetics of the decolorization reactions of triphenylmethane dyes (BG, MG and PRH) with the cyanide ion (nucleophile) were studied in the presence of anionic micelles of sodium dodecyl sulfate (SDS). The reactions follow pseudo-first order kinetics. The rate constant depends on surfactant concentration. SDS micelles inhibit the overall rate of the reaction between the dye carbocation with the nucleophile. Quantitative analysis of the micellar data obtained has been done by applying a positive cooperativity model of enzyme catalysis. For all the dyes under study, the value of n (index of cooperativity) has been found to be greater than one. The inhibitory effect has been explained in terms of hydrophobic and electrostatic interactions of various species present in the reaction systems.

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Abstract

Papaverine hydrochloride decomposes in solution easily to papaverinol, papaveraldine and 2,3,9,10-tetramethoxy-12-oxo-12-H-indolo[2,1-a]isoquinolinium chloride 1. The structure of the last compound has been elucidated lately. On the addition of alkali, the brown solution of 1 bleaches. A new compound i.e. 2-(2-carboxy-4,5-dimethoxyphenyl)-6,7-dimethoxyisoquinolinium inner salt 2 is formed. This paper reports the optimization of the compound 2 preparation.

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