Aqueous Oxidation Of Alcohols Research Articles

Nanoreactor of MOF-Derived Yolk–Shell Co@C–N: Precisely Controllable Structure and Enhanced Catalytic Activity

Hollow yolk–shell nanoreactors are of great interest in heterogeneous catalysis owing to their improved mass transfer ability and stability. Here, we report a facile and straight route to synthesize a highly efficient and recyclable yolk–shell Co@C–N nanoreactor with controllable properties by the direct thermolysis of a hollow Zn/Co-ZIF precursor. Based on systematical optimization of the pyrolysis temperature and the shell-thickness of Zn/Co-ZIFs, we could completely anchor and stabilize uniform Co nanoparticles (NPs) in the hollow yolk, accommodated by the Co-ZIF derived N-doped carbon nanosheets. This nanosheet-assembled yolk was further confined by a permeable and robust N-doped carbon (C–N) shell to protect the Co NPs against leaching and also enabled the reaction to take place in the hollow void. Consequently, the optimal yolk–shell Co@C–N nanoreactor showed a significantly enhanced catalytic activity for the aqueous oxidation of alcohols, yielding >99% conversion under atmospheric air and base-fre...

Selective aqueous oxidation of alcohols catalyzed by copper (II) phthalocyanine nanoparticles

A new catalyst based on metallophthalocyanine nanoparticles has been synthesized and characterized by scanning electron microscopy (SEM). The aqueous oxidation of alcohols to the corresponding carbonyl compounds (aldehydes and ketones) has been studied using tetra-n-butyl-ammonium-peroxo-monosulfate (n-Bu4NHSO5) as an oxidant and a catalytic system consisting of copper (II) phthalocyanine nanoparticles in water. The highly selective oxidation gave excellent yields of related aldehydes or ketones without remarkable over-oxidation of the carboxylic acids. Organic co-solvents, surfactants, and co-catalysts were not used in this catalytic strategy. This strategy was green and time effective. The oxidant's by-product (TBAHSO4) and catalyst can be efficiently recovered and reused several times without any significant change of catalytic activity.

A novel iron(iii)-based heterogeneous catalyst for aqueous oxidation of alcohols using molecular oxygen

The first example of an iron(iii)-based heterogeneous catalyst for alcohol oxidation reactions in water employing molecular oxygen has been reported. Interestingly, the immobilized catalyst shows superior activity over its homogeneous counterpart.

ChemInform Abstract: Aqueous Oxidation of Alcohols Catalyzed by Recoverable Iron Oxide Nanoparticles Supported on Aluminosilicates.

ChemInform Abstract: Aqueous Oxidation of Alcohols Catalyzed by Recoverable Iron Oxide Nanoparticles Supported on Aluminosilicates.

Aqueous oxidation of alcohols catalysed by recoverable iron oxide nanoparticles supported on aluminosilicates

Supported iron oxide nanoparticles on aluminosilicate catalysts were found to be efficient and easily recoverable materials in the aqueous selective oxidation of alcohols to their corresponding carbonyl compounds using hydrogen peroxide under both conventional and microwave heating. The protocol features an easy work-up, simplicity and the utilisation of mild reaction conditions as well as high selectivity toward aldehydes is highly advantageous compared to alternatively reported methodologies. The supported iron oxide nanoparticles could be easily recovered from the reaction mixture and reused several times without any loss in activity. ICP-MS results proved that there is no metal leaching observed, demonstrating the stability of the catalyst under the investigated conditions.

Efficient and highly selective aqueous oxidation of alcohols and sulfides catalyzed by reusable hydrophobic copper (II) phthalocyanine

Abstract A practical innovative method for highly chemoselective oxidation of alcohols to the aldehyde and ketones and sulfides to the sulfones using tetra-n-butylammonium peroxomonosulfate (n-Bu4NHSO5) catalyzed by simple water-insoluble copper (II) phthalocyanine (CuPc) in neat water has been developed. Organic co-solvents, surfactants, co-catalyst and hydrophilic auxiliaries were completely missed in this heterogeneous catalytic strategy. The CuPc catalyst and by-product of oxidant (TBAHSO4) could easily be recycled and reused without loss of activity providing readily scalability.

Noble-metal-catalysed aqueous alcohol oxidation: reaction start-up and catalyst deactivation and reactivation

The influence of the reaction start-up procedure on the oxidation of a polyol, methyl α-D-glucopyranoside, was investigated. Results were obtained from semi-batch experiments with Pt catalysts and molecular oxygen as oxidant. Three types of reaction start-up procedures were applied with respect to the pretreatment of the catalyst slurry: reductive, oxidative, and inert. The experimental results are described by a recently developed dynamic electrochemical kinetic model. The reductive start-up results in the highest initial catalyst activity, compared with the other start-up procedures. It was found that the catalyst needs pretreatment before the reaction is started, as inert start-up resulted in no catalytic activity at all. The formation of inactive platinum oxides (i.e., overoxidation) is the main cause of catalyst deactivation under oxygen-rich conditions, for a weak reducing compound, and is independent of the start-up procedure. It also appeared that the rate of overoxidation is lower in the absence of reaction, which could be modelled with the assumption that overoxidation needs free sites to take place. The mechanism of catalyst deactivation has been verified through intermediate catalyst reactivation. The model adequately describes this reactivation step.

Aqueous oxidation of alcohols catalyzed by artificial metalloenzymes based on the biotin–avidin technology

Based on the incorporation of biotinylated organometallic catalyst precursors within (strept)avidin, we have developed artificial metalloenzymes for the oxidation of secondary alcohols using tert-butylhydroperoxide as oxidizing agent. In the presence of avidin as host protein, the biotinylated aminosulfonamide ruthenium piano stool complex 1 (0.4 mol%) catalyzes the oxidation of sec-phenethyl alcohol at room temperature within 90 h in over 90% yield. Gel electrophoretic analysis of the reaction mixture suggests that the host protein is not oxidatively degraded during catalysis.

Platinum catalysed aqueous alcohol oxidation: model-based investigation of reaction conditions and catalyst design

A dynamic transport model is derived to describe the platinum catalysed aqueous alcohol oxidation, considering a single spherical catalyst particle surrounded by a stagnant liquid film. The transport model is based on a heterogeneous kinetic model with mass transfer and intra particle diffusion resistances. The developed model uses the kinetic model of Markusse et al. (Catal. Today 66 (2001) 191) and is validated with the experimental kinetic data of methyl α- D-glucopyranoside (MGP) oxidation obtained by Vleeming et al. (Ind. Eng. Chem. Res.). The model is used to investigate the effect of process conditions, catalyst and particle properties, and transport parameters on the performance of the catalyst for alcohol oxidation. It is found that the electron conductivity of the catalyst support affects the rate of MGP oxidation especially at low bulk liquid oxygen concentrations, while at high bulk liquid oxygen concentrations, the catalyst support conductivity does not play a role. A major cause of catalyst deactivation is over-oxidation under oxygen rich conditions. This can be reversed by applying redox-cycle operation, an alternating exposure of the catalyst to oxidative and reductive environments. The advantages of redox-cycle application are demonstrated using the developed model. For reactions of negative order, such as MGP oxidation, at high bulk oxygen concentrations (C O 2,L >0.3 mol/m 3) , concentrating the active catalytic material in a layer buried some distance from the surface (core) gives considerable better performance than the conventional “egg shell” design of shallow deposition near the surface or uniform distribution. However, at low bulk oxygen concentrations (C O 2,L ⩽0.3 mol/m 3) , the performance of the uniform or egg shell distribution catalyst is superior to the core catalyst.

Platinum catalysed aqueous methyl α- d-glucopyranoside oxidation in a multiphase redox-cycle reactor

Platinum catalyst deactivation during aqueous alcohol oxidation is discussed, using the selective oxidation of methyl α- d-glucopyranoside as an example. The most important causes of platinum deactivation are catalyst over-oxidation and catalyst poisoning. Deactivation by over-oxidation can be reversed by applying a redox-cycle, i.e. cyclic exposure to oxidative and reductive circumstances. A kinetic model for methyl α- d-glucopyranoside oxidation, platinum deactivation, and reactivation, based on electrochemistry is presented and implemented into a three-phase stirred slurry reactor model, showing the advantages of applying redox cycles.

Platinum catalysed aqueous alcohol oxidation: experimental studies and reaction model discrimination

The platinum catalysed aqueous oxidation of alcohols and carboxylic acids is studied using electrochemical methods under circumstances typical for catalytic oxidation reactions, being 40°C and pH 8. The investigated reactants are cyclohexanol (CL), methyl α- d-glucopyranoside (MGP), sodium oxalate (OA), and sodium formate (FA). Two catalytic oxidation regimes are distinguished: the intrinsic kinetic regime, and the oxygen transport limitation regime. Save OA, all reactants react on adsorbate-free, reduced platinum. On adsorbate-free, reduced platinum carbonaceous adsorbates are formed, inhibiting catalytic reactions. This situation is found when operating in the oxygen transport limitation regime. Under intrinsic kinetic conditions, platinum catalyst deactivation is caused by platinum oxide formation. Platinum oxide reduction is inhibited by the presence of adsorbed oxygen. A kinetic model for MGP oxidation, platinum deactivation, and reactivation is evaluated.

Platinum deactivation: in situ EXAFS during aqueous alcohol oxidation reaction

With a new set‐up for in situ EXAFS spectroscopy the state of a carbon‐supported platinum catalyst during aqueous alcohol oxidation has been observed. The catalyst deactivation during platinum‐catalysed cyclohexanol oxidation is caused by platinum surface oxide formation. The detected Pt–O co‐ordination at 2.10 Å during exposure to nitrogen‐saturated cyclohexanol solution is different from what is observed for the pure oxidised platinum surface (2.06 Å).