جستجوی مقالات مرتبط با کلیدواژه « Alcohol oxidation » در نشریات گروه « شیمی »

The catalytic activity of bimetallic MOFs known as STA-12(M1, M2)(M1,2= Mn, Fe, Co) was investigated in the oxidation of benzylic alcohols to corresponding aldehydes at ambient conditions. The oxidation reaction with Na2S2O4/TBHP (tert-Butyl hydroperoxide) mixture shows total selectivity and excellent efficiency under desired reaction times. The heterogeneous catalyst displays high reusability and stability for the ten consecutive reactions without decreasing in yield and selectivity. To identify radical species responsible for the oxidation process, selective radical scavenging experiments were performed and a purposed oxidation mechanism was discussed.

Current catalysts for the alcohol oxidation in fuel cells (typically noble metals-based) are susceptible to poisoning with intermediates like CO. Hence we decided to find superseded catalysts for methanol oxidation based on incorporation of mixed oxides. In this research, a nano-size perovskite SrFeO3-δ (SrFeO3-δNPs) was synthesized by a rapid co-precipitation method assisted with ultrasonic and characterized by XRD, FT-IR, SEM and EDX techniques. A modified glassy carbon electrode with Pd nanoparticles (PdNPs) and SrFeO3-δNPs dispersed into the appropriate amount of chitosan (CH) polymer as a multifunctional catalyst was prepared and its catalytic activity toward alcohols (C1 - C3) oxidation was investigated. Based on the electrochemical studies, the PdNPs-SrFeO3-δNPs-CH nanocomposite showed considerable activity for alcohols (C1 - C3) oxidation in comparison to PdNPs-CH and SrFeO3-δNPs-CH. A direct methanol fuel cell was designed, assembled and tested with suggested PdNPs-SrFeO3-δNPs-CH nanocomposite under several different conditions. The effect of experimental parameters (temperature; methanol concentration; flow rate) as well as NaOH concentration) on the electrical performances of the fuel cell were studied and optimized.

A series of transition metal complexes with two thiosemicarbazide Schiff bases, 1-(4-dimethylaminobenzyl- idene)thiosemicarbazide (ABTSC) and 1-(2-pyridincarboxyl-idene) thiosemicarbazide (TCTS) were synthesized with Co(II), Ni(II), Zn(II), Cd(II) and Ag(I) salts (chloride and acetate). These complexes were characterized by different methods including proton nuclear magnetic resonance (1HNMR), Fourier transform infrared (FT-IR), ultra violet visible (UV-Vis), molar conductance (λm), atomic absorption spectroscopy (AAS) and elemental analysis (CHNS). All complexes were applied as a catalyst for oxidation of aromatic alcohols. The effects of reaction time, temperature, catalyst amount, oxidant and solvents were investigated in detail. The oxidation of alcohols occurs effectively and selectively with H2O2 as the oxidant. For instance, 4-Methoxybenzyl alcohol is oxidized to the corresponding aldehyde with 95% conversion and 100 % benzaldehyde selectivity under the optimum conditions.

Double Potential Step Chronoamperometry (DPSC) was used to determine the rate constants for the homogeneous reactions of alcohols with the superoxide ion (O2-) at different temperatures in two room temperature ionic liquids (RTILs). The technique was first tested by determining the pseudo first order rate constant for reduction of azobenzene to hydroazobenzene that, in turn, undergoes the benzidine rearrangement. Our results were in good agreement with values reported in the literature using DPSC and conventional kinetic methods. The activation energy for the oxidation of benzyl alcohol is 19.1 kJ/mol in [bmim][HFP]; which is in good agreement with the value reported in the literature. The corresponding values of S, H and G  for the reaction of superoxide ion with benzhydrol in [bdmim][HFP] calculated at T=45C are –0.49 kJ/mole, 22.4 kJ/mole, and 177.9 kJ/mole, respectively. The second order rate constant for the oxidation of benzyl alcohol at 10C in RTIL in [bmim][HFP] was determined to be 1.3 L mol-1 s-1. The pseudo first order rate constant for the homogeneous reaction of O2 with different primary and secondary alcohols in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][HFP]) and 1-butyl-2,3-dimethylimidazolium hexafluorophosphate [bdmim][HFP] at different temperatures was measured. The pseudo first order rate constant for the reaction of O2- with benzhydrol in [bdmim][HFP] at T= 49, 57, 65, 84 C were found to be 60, 72, 92, 148 L mol-1 s-1. The pseudo first order rate constant for the reaction of O2- with benzhydrol in [bmim][HFP] at T=27, 40 and 80 C were found to be 53,74, 201 L mol-1 s-1.The Arrhenius plot was then used to determine the activation energy and pre-exponential factor for the corresponding reactions.

Well faceted CuO nanoparticles, were synthesized by thermal-assisted dissociation method at reflux temperature in a short period of time. A possible mechanism for synthesis of such highly pure and stable nanoparticles is tentatively proposed by FT-IR study. The large surface area and rich exposed active sites are expected to endow such nanoparticles with excellent performances in catalysis as demonstrated here for the remarkable catalytic activity with respect to the oxidation of alcohol. This interesting result highlights the advantage of such a CuO nanostructure over the bulk counterpart, i.e. the high density of active sites and large surface area, which places a solid foundation for the feasible and promising application of such highly faceted nanomaterials in catalysis. It is the first report on the nanometer-sized faceted CuO acting as a catalyst for an oxidation reaction and simultaneously a good example for the combination of green chemistry and functional materials.