Authors:Joanna Wiśniewska, Grzegorz Wrzeszcz, Stanisław Koter and Tomasz Ligor
The kinetics of the oxidation of imipramine and opipramol using peroxydisulfate salts in the presence of a large excess of dibenzoazepine derivative (TCA) in acidic sulfate media was studied using UV–vis spectroscopy. The reaction between imipramine and S2O82− proceeds via the formation of two intermediates: a free organic radical and a dimeric dication. Further reaction of the intermediate dimeric dication leads to a positively charged radical dimer as one final product. Simultaneously, two other substituent cleavage degradation processes occur, leading to two dimeric derivatives. The first product, the positively charged radical dimer, and the next main product, a radical dimer without one alkyl substituent, were identified by EPR measurements. The measured kinetic trace is not first order and revealed a sigmoid shape with a characteristic induction time. The rate constants were determined by numerical analysis based on ordinary differential equations (ODEs). The reaction between opipramol and S2O82− proceeds by a two consecutive reaction scheme. The kinetics of the first degradation step were studied independently of the slower degradation reactions. Linear dependences, with zero intercept, of the pseudo-first-order rate constants (kobs) on [TCA] were determined for the first degradation process of opipramol.
Authors:Magdalena Janus, Ewelina Kusiak-Nejman and Antoni Waldemar Morawski
In this study, it was shown that a possible explanation of increasing photocatalytic activity with temperature may be the fact that with increasing water temperature, the amount of hydroxyl radicals in water also increases, because the ionic product of water increases with an increase in temperature. For measurements of the amount of hydroxyl radicals, the fluorescence technique was used. Terephthalic acid was used as a hydroxyl radical scavenger. After inducing of TiO2, positive holes in the valance band may react with OH ions and produce •OH radicals, a strong oxidizing agent.
Authors:M. Hofman, A. Świątkowski, M. Pakuła and S. Biniak
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.
Ti-SBA-15, one of the latest titanium silicalite catalysts, has been prepared according to the literature by the direct hydrothermal synthesis using Pluronic 123 as structure-directing agent. The characterization of the catalyst was performed by means of the following methods: XRD, IR, UV–Vis, X-ray microanalysis and SEM. The catalytic properties of the Ti-SBA-15 catalyst have been tested in the epoxidation of allyl alcohol, methallyl alcohol, crotyl alcohol and 1-butene-3-ol with hydrogen peroxide. The process has been described by the following main functions: the selectivity to epoxide compound in relation to allylic compound consumed and the conversion of allylic compound.
A study of the interaction between some simple molecules (dihydrogen, acetylene, and ethylene) and Pd–Pb catalysts has been performed using the B3LYP hybrid density functional. The reaction paths for the H2 molecule reacting with the PdPb dimer are reported for the singlet and triplet spin states. The C2H2 and C2H4 molecules were adsorbed in a few characteristic sites on the Pd(100) surface doped with Pb. This surface was modeled using Pd13Pb clusters. The results of the calculations indicate that the Pd–Pb catalysts interact with the H2, C2H2, and C2H4 molecules more weakly than the corresponding monometallic Pd catalysts do, and thus the bimetallic catalysts exhibit the reduced activity toward these simple molecules.
Authors:Maria Kulawska, Henryk Moroz and Aleksandra Kasprzyk
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.
Authors:Natasza Krawczyk, Stanisław Karski and Izabela Witońska
The influence of support porosity on the selectivity of home-made 5%Pd–2%In/support (support = SiO2, Al2O3, TiO2) catalysts in nitrate reduction was studied. The main final products of the reaction were N2 and NH4+. Together with the decrease in pore diameter, an increase in ammonia concentration in the reaction mixture was observed. It is probably caused by slow diffusion of OH− ions from narrow pores to the solution.
Authors:Rachid Sahki, Ouarda Benlounes, Ouiza Chérifi, René Thouvenot, Mohammed M. Bettahar and Smain Hocine
The influence of working pressure on the mechanisms of the CO2/H2 reaction on a co-precipitated CuO/ZnO/Al2O3 catalyst have been studied at 230 °C and in the pressure range of 1–75 bar. In the CO2 hydrogenation using CuO/ZnO/Al2O3, the products were found to be CO, methanol and water almost exclusively. Only a trace of methane formation was observed. Methanol and carbon monoxide are competitively formed. The former is produced directly from CO2 whatever the pressure whereas carbon monoxide stems either from CO2 directly at high pressure or both methanol decomposition and CO2 directly at low pressure.
Authors:Anna Fajdek, Agnieszka Wróblewska and Eugeniusz Milchert
The results of the epoxidation of allyl alcohol with 30% hydrogen peroxide over the Ti-MWW catalyst have been presented. The studies were carried out under atmospheric pressure and in the presence of methanol as a solvent. The influence of the following technological parameters on the course of epoxidation was examined: temperature (20–60 °C), the molar ratio of AA/H2O2 (1:1–5:1), methanol concentration (5–90 wt%), catalyst content (0–5.0 wt%), reaction time (5–300 min) and intensity of stirring (0–500 rpm).
The adsorption and dissociation of the H2 molecule on the PdAg, PdAu, PtAg, and PtAu heteronuclear dimers, both isolated and deposited on carbon, were investigated by means of density functional theory. It was found that the Pd and Pt ends of the isolated dimers adsorb H2 more exoenergetically than the Ag and Au ends. The dimers were also deposited on a carbon support and it turned out that they prefer to adsorb on the support by their Pd and Pt ends rather than by the Ag and Au ends. The adsorption of H2 on the carbon-supported dimers is somewhat less exoenergetic than that on the isolated dimers but, after the dissociation of H2, the binding of the H atoms to the dimers remains stronger in the presence of the support.
The catalytic effect of buffers (phosphate, acetate, borate, carbonate) on the degradation of doripenem in aqueous solutions was studied at 313 K in the pH range 0.82–11.56 (μ = 0.50 mol L−1) by an HPLC-UV method developed for kinetic studies of doripenem. It was observed that general acid–base catalysis occurred in all buffers and so catalytic rate constants were calculated. Specific acid–base catalysis of doripenem involved degradation of protonated molecules and zwitter ions of doripenem catalyzed by hydrogen ions, spontaneous degradation of zwitter ions under the influence of water and degradation of zwitter ions and monoanions catalyzed by hydroxide ions.
The chiral vanadyl salen complex was immobilized into mesoporous silica by a covalent grafting method using 3-aminopropyltriethoxysilane
as a reactive surface modifier. The formation and integrity of the complex have been confirmed by FT-IR, UV–vis and BET measurements
and the complex was tested in the asymmetric oxidation of sulfide to sulfoxide using H2O2 as oxidant. The immobilized complex showed better catalytic activity than the neat complex, while the neat complex has deactivated
in the reaction. The combination of the heterogenized catalyst, H2O2 and CH2Cl2 as solvent offers a selective catalytic system for oxidation of sulfide to sulfoxide with a low but significant enantioselectivity
in the range of 8–10% ee. In addition, the heterogenized catalyst could be easily separated from the products and reused.
To utilize visible light more efficiently in photocatalytic reactions, Bi2O3/CaO photocatalysts were prepared by a mechanical mixing method and characterized by X-ray diffraction (XRD) and UV–vis spectroscopy.
UV–vis spectroscopy results showed that the photocatalysts have a wide absorption band in the range of visible light. The
photocatalytic activities of obtained Bi2O3, CaO, and Bi2O3/CaO samples were evaluated by methylene blue degradation under visible light irradiation. It was found that the Bi2O3/CaO sample exhibited the highest photocatalytic activity.