Aerobic Oxidation Of Ethanol Research Articles

Synergistic effect of mesoporous metal oxides and PtO2 nanoparticles in aerobic oxidation of ethanol and ionic liquid induced acetaldehyde selectivity

We report on the catalytic performance of mesoporous metal oxides (MMOs) as catalysts and as potential supports for platinum (Pt) nanoparticles in aerobic oxidation of ethanol. Synthesis of MMOs was achieved through the hard-template method and the resulting MMOs resembled the 3-D structure of the templating KIT-6. The Pt nanoparticles were templated and stabilized using poly(amidoamide), PAMAM, dendrimer to achieve dendrimer-encapsulated Pt nanoparticles (Pt-DENs) with an average size of 3.5 ± 0.4 nm. All the components of the catalysts (Pt-DENs and MMOs) were first characterized separately and thereafter, followed the preparation of MMO-immobilized Pt nanoparticles. Upon characterization of the MMO-immobilized Pt nanoparticles, the Pt nanoparticle size increased as determined from hydrogen-chemisorption and organothiol-adsorption technique. Furthermore, X-ray photoelectron spectroscopy (XPS) revealed that Pt has an oxidation state of 4+ after removal of the dendrimer at 550 °C signifying an oxide state (PtO2). The hydrogen temperature-programmed reduction (H2-TPR) revealed a change in electronic structure of MMOs as reduction peaks shifted to lower temperatures upon immobilization of PtO2 nanoparticles. This change in electronic structure of the mesoporous metal oxides upon immobilization of PtO2 nanoparticles is found to be one of the reasons for enhanced catalytic activity. Improved selectivity towards acetaldehyde was induced by introduction of an ionic liquid layer in a solid catalyst with ionic liquid layer, SCILL concept. Furthermore, the amount of ionic liquid coating plays a pivotal role in impacting selectivity and has an impact in the reaction turnover frequency.

Kinetics of aerobic and anaerobic oxidations of ethanol by Fenton's reagent

AbstractFor the first time, the time dependence of [H2O2] and [Fe2+] was followed during the aerobic oxidation of ethanol by Fenton's reagent. It was found that part of the ethanol was oxidized by dissolved O2 via the transient formation of H2O2. A model was set up based on FeO2+ as the key intermediate. Both one‐ and two‐equivalent oxidations of ethanol occur, the former producing radical species derived from ethanol. No free radicals derived from H2O2 play part in the system. The relevant rate constants or their ratios were determined. The mechanism accounted successfully also for the anaerobic oxidation of ethanol. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 541–553, 2008

Gold Nano-size Effect in Au/SiO2 for Selective Ethanol Oxidation in Aqueous Solution

Narrowly sized colloidal Au particles of varying average sizes (3–30 nm) were immobilized on an inert support (SiO2) to study the Au size effect on the aerobic oxidation of ethanol in aqueous solution. Au particles with an average diameter of 5 nm showed an areal activity that was about three times that of the smaller (3 nm), and 15 times that of larger (10–30 nm) Au particles. Investigation on the dependence of product yields on ethanol conversion over these differently sized Au particles clearly uncovered that the yield of acetic acid increased always with the ethanol conversion, while that of acetaldehyde passed a maximum at an ethanol conversion of 20–30%, therefore well demonstrating that acetaldehyde is the intermediate product in the oxidation of ethanol to acetic acid.

Aerobic oxidation of aqueous ethanol using heterogeneous gold catalysts: Efficient routes to acetic acid and ethyl acetate

The aerobic oxidation of aqueous ethanol to produce acetic acid and ethyl acetate was studied using heterogeneous gold catalysts. Comparing the performance of Au/MgAl2O4 and Au/TiO2 showed that these two catalysts exhibited similar performance in the reaction. By proper selection of the reaction conditions, yields of 90–95% of acetic acid could be achieved at moderate temperatures and pressures. Based on our findings, a reaction pathway for the catalytic oxidation of ethanol via acetaldehyde to acetic acid is proposed, and the rate-determining step (RDS) in the mechanism is found to be the (possibly oxygen-assisted) dehydrogenation of ethanol to produce acetaldehyde. It also is concluded that most of the CO2 formed as a byproduct in the reaction results from the absorbed intermediate in the dehydrogenation of ethanol to produce acetaldehyde. By varying the amount of water in the reaction mixture, the possibilities for producing ethyl acetate by the aerobic oxidation of ethanol is also studied. At low ethanol concentrations, the main product is acetic acid; at concentrations >60 wt%, it is ethyl acetate.

Alcohol dehydrogenase activity and electron transport in living yeast.

1. The excretion of H(+) ions, with practically equivalent uptake of K(+) ions (from 0.1m-potassium chloride), occurs during the aerobic oxidation of ethanol. 2. Acetaldehyde and acetic acid formed at the same time are quantitatively equal to the amount of ethanol oxidized. 3. A slow uptake of K(+) ions occurs during the oxidation of acetaldehyde and a more rapid uptake during the oxidation of d-glyceraldehyde 3-phosphate. 4. The anaerobic reduction of methylene blue is studied, and the inhibitory effect of K(+) and other inorganic cations on the system demonstrated. 5. The cation requirement for equal inhibitory effect is parallel with the reciprocals of the transport affinities for the ;physiological K-carrier' (as taken from Conway & Duggan, 1958). 6. The cation inhibition of methylene blue reduction is reversed by treatment of the yeast with Teepol or by freezing-and-thawing. 7. Azide is shown to inhibit the reduction of methylene blue with intact cells. The inhibition is partially reversed by Teepol treatment and completely by freezing-and-thawing.