Direct Formation Of Hydrogen Peroxide Research Articles

Promotional effect of surface plasmon resonance on direct formation of hydrogen peroxide from H2 and O2 over Pd/Graphene-Au nanorod catalytic system

A promotional effect of surface plasmon resonance (SPR) on direct hydrogen peroxide (H2O2) formation from H2 and O2 over a structure-controlled Pd-Au catalytic system is reported herein. Pd NPs supported on reduced graphene oxide (rGO) layer-coated Au nanorod (NR) nanocomposite catalysts were synthesized, and the structure was confirmed by multiple characterization techniques. H2O2 production is highly enhanced under visible light irradiation in the direct H2O2 formation from H2 and O2. The H2O2 decomposition test and the H2-D2 exchange reaction reveal that the SPR of Au NRs facilitates H2 activation on the Pd NP surface, leading to efficient H2O2 production. Furthermore, the rGO layer not only functions as an electron mediator in the catalytic reaction, but also contributes to the control of Pd NP sizes in the catalyst synthesis.

Direct synthesis of hydrogen peroxide using concentrated H2 and O2 mixtures in a wall-coated microchannel – kinetic study

The kinetics for direct synthesis of hydrogen peroxide out of hydrogen and oxygen has been studied over AuPd colloidal nanoparticles, which were prepared using a two-phase synthesis protocol. Reactions of direct formation of peroxide and peroxide reduction in the presence of hydrogen were studied separately to obtain the overall kinetic model, which was suitable to predict peroxide concentration at the outlet of the wall-coated microchannel reactor. The decomposition reaction was eliminated by the addition of sulfuric acid. The kinetic model of the direct formation of hydrogen peroxide from hydrogen and oxygen suggests hydrogen adsorption, pairwise dissociation, but not spill-over of H-species over the bimetallic AuPd surface. Peroxide concentration values predicted with an overall kinetic model and values experimentally measured at the outlet of the microchannel with a catalytic layer deposited on the wall are in acceptably good agreement.

Novel Catalysts of Au/SiO2 Hybrid Nanorod Arrays for the Direct Formation of Hydrogen Peroxide

Novel Catalysts of Au/SiO₂ Hybrid Nanorod Arrays for the Direct Formation of Hydrogen Peroxide

Tuning the properties of PdAu bimetallic nanocatalysts for selective hydrogenation reactions

Bimetallic PdAu nanocatalysts have been prepared in a one-step synthesis using a colloidal approach, with a variety of techniques employed to determine their structure. The supported nanocatalysts show good performance in the selective hydrogenation of 2-chloronitrobenze to 2-chloroaniline and the direct formation of hydrogen peroxide. The reaction rate for 2-chloronitrobenzene hydrogenation increased with the decrease of Pd/Au ratio, while the selectivity was only slightly affected. The structure of the bimetallic nanoparticles had a significant impact, with a Pd-rich surface offering superior selectivity and reaction rates. In contrast, for hydrogen peroxide synthesis, it was found that there was an optimal quantity of gold required to ensure high productivity and this is ascribed to avoiding the formation of Au rich alloy phase and electronic effects hindering the necessary O2 adsorption and activation.

Physical mixing of metal acetates: a simple, scalable method to produce active chloride free bimetallic catalysts

We have prepared supported gold, palladium and gold–palladium bimetallic catalysts by the physical mixing of the acetate salts of the metals followed by a simple heat treatment. The use of the acetates as the metal precursor eliminates chloride from the catalyst preparation step. Extensive characterisation shows the formation of bimetallic alloy particles. These catalysts are extremely active for alcohol oxidations and the direct formation of hydrogen peroxide.

A wall-coated catalytic capillary microreactor for the direct formation of hydrogen peroxide

The direct formation of hydrogen peroxide from H 2 and O 2 was successfully carried out in a capillary microreactor at room temperature and atmospheric pressure. A key element in sustaining the activity of the catalyst is the incarceration of the palladium nanoparticles in a cross-linkable amphiphilic polystyrene-based polymer, prepared following the protocol of Kobayashi [R. Akiyama, S. Kobayashi, J. Am. Chem. Soc. 125 (2003) 3412–3413]. The immobilization effectively reduced the leaching of palladium under acidic conditions. Applying the catalyst as a coating on the inner walls of a capillary enabled the sustained production of 1.1% hydrogen peroxide over at least 11 days. The highest catalyst utilization in a 2 mm capillary reactor was 0.54 mol H2O2/h g Pd. When the inner diameter of the reactor capillary was reduced to 530 μm, the rate was enhanced fourfold to 2.28 mol H2O2/h g Pd corresponding to a turnover frequency of 0.067 s −1.

Catalytic synthesis of hydrogen peroxide in microreactors

The direct synthesis of hydrogen peroxide from hydrogen and oxygen was investigated using capillary and stacked microreactors in which the silicone wall of a microchannel had been coated with Pd/C catalyst. To make the H 2O 2 production system compact, a flow-through solid polymer electrolyte (SPE) electrolyzer, which was used for the H 2- and O 2-feeds instead of gas cylinders, was connected to the microreactor. The influence of the gas and liquid flow rates and of the reaction temperature on H 2O 2 production was investigated to identify the optimal operating conditions for the stacked microreactor. In the previous study [Kusakabe, K., Kawaguchi, K., Maehara, S. and Taneda, M., 2007, Direct formation of hydrogen peroxide over palladium catalyst based on water electrolysis, J Chem Eng Jpn, 40: 523–528], direct synthesis of H 2O 2 over Pd/C catalyst was performed using a slurry batch reactor with two sheets of electrode for H 2 and O 2 evolution. The maximum H 2O 2 concentration of 3.4 × 10 −3 mol/L was attained after a 3-h reaction. In this study, a H 2O 2 concentration of 8.3 × 10 −3 mol/L was obtained at 10 °C in a 0.1 mol/L solution of HCl at the residence time of 93 s in the stacked microreactor. In addition, H 2O 2 was successfully produced when pure water was used as the reaction liquid with H 2 and O 2 in the stacked microreactor.

The role of the support in achieving high selectivity in the direct formation of hydrogen peroxide

Pd-only, Au-only and bimetallic AuPd catalysts supported on a range of supports (Al2O3, TiO2, MgO, and C) have been prepared by impregnation and tested for the hydrogenation and decomposition of hydrogen peroxide under conditions similar to those used in direct synthesis of hydrogen peroxide. Hydrogenation and decomposition are the main pathways for loss of selectivity and yield in the direct synthesis reaction, and the support is found to be a crucial parameter with respect to hydrogenation and decomposition activity. We show that by making the right choice of support for both the monometallic and bimetallic Au and Pd catalysts, it is possible to achieve very low hydrogen peroxide hydrogenation and decomposition activity, thus enhancing hydrogen peroxide productivity during synthesis. Carbon is found to be the optimal support for both monometallic Au and Pd catalysts as well as Au–Pd alloys, since carbon-supported catalysts gave the lowest hydrogenation and decomposition activities. Au-only catalysts were generally less active than Pd-only catalysts when utilizing the same support and metal loading. The addition of Au to Pd catalysts supported on TiO2 and carbon resulted in a decrease in both H2O2 hydrogenation and decomposition while the reverse effect was observed for the Al2O3 and MgO-supported catalysts. These effects are discussed in terms of the basicity of the support, and in particular the isoelectronic point of the support, which is a major factor in controlling the stability of hydrogen peroxide under reaction conditions.

Direct synthesis of hydrogen peroxide from H2/O2 using Pd/Al2O3 catalysts

Pd/Al2O3 catalysts were prepared by the impregnation method and were used for the direct formation of hydrogen peroxide from H2 and O2. The H2O2 concentration and selectivity were strongly dependent on the solubility of hydrogen in the reaction medium. The modification of the support by halogenate has a beneficial effect on the selectivity. The state of the active Pd on Pd/Al2O3 catalysts was studied using X-ray photoelectron spectroscopy, and Pd(0) was found to be active.

Nanocrystalline gold and gold–palladium as effective catalysts for selective oxidation

The recent interest in oxidation catalysis provides the focus for this article. Until recently, gold has been overlooked as a key component of both homogeneous and heterogeneous catalysts. However, the observation in the 1980s that nanocrystalline gold supported on oxides was an effective catalyst for low-temperature carbon monoxide oxidation has now captured the imagination of many researchers. At present, low-temperature carbon monoxide oxidation remains an intensely studied field, but in recent years increased emphasis has been placed on using gold catalysts for selective oxidation. For example, the oxidation of alkanes, alkenes, and alcohols have all been shown to be effective with gold-based catalysts. In addition gold–palladium bimetallic catalysts have been shown to be very effective for the direct formation of hydrogen peroxide, and this will be described in this article.

Direct Formation of Hydrogen Peroxide over a Palladium Catalyst Based on Water Electrolysis

Hydrogen peroxide was directly produced from hydrogen and oxygen in a slurry reactor containing a Pd/C catalyst at 5–20°C. Hydrogen and oxygen produced by a solid polymer electrolyte water electrolyzer were fed into the reactor. The effects of reaction temperature, slurry concentration, gas flow rate and solvent on the H2O2 production were investigated. The maximum production rate of H2O2 was obtained at a reaction temperature of 10°C and sharply increased along with the addition of methanol. The results show that H2O2 production is significantly influenced by the solubility of the gas, while excessive catalyst and hydrogen facilitate the decomposition of the accumulated H2O2. Finally, H2O2 production was performed in a catalytic slurry reactor with a pair of platinum electrodes inserted. The in situ feed of hydrogen and oxygen into the reactor improved H2O2 production. This could be due to an increase in gas solubility due to fine bubbles or the electrochemical generation of H2O2.

Evaluation of multiphase microreactors for the direct formation of hydrogen peroxide

Abstract The direct production of hydrogen peroxide from H2 and O2 has been investigated in two types of microreactors: (1) a single-channel microreactor with a washcoat of catalyst and (2) a multichannel microreactor with eight parallel channels, where the catalyst was grown as a thin film. The multichannel microreactor mimics features of a monolith reactor, where the catalyst is contained in a structured honeycomb. The Taylor (slug) flow in a microchannel reactor under three phase (gas–liquid–solid) conditions enhances the mass transfer over the phase boundaries. The influence of liquid and gas flow rate, pressure drop, solvents, support materials and metal dispersion on the reaction were investigated in order to screen for optimal operation conditions. The productivity in the microchannel reactors increases approximately with the square root of the liquid flow rate, verifying the Taylor-flow model.

L-Arginine regulates neuronal nitric oxide synthase production of superoxide and hydrogen peroxide

Tetrahydrobiopterin (H 4B) in the absence of l-arginine has been shown to be an important factor in promoting the direct formation of hydrogen peroxide (H 2O 2) at the expense of superoxide (O 2 −) by neuronal nitric oxide synthase (NOS1) [Rosen GM, Tsai P, Weaver J, Porasuphatana S, Roman LJ, Starkov AA, et al. Role of tetrahydrobiopterin in the regulation of neuronal nitric-oxide synthase-generated superoxide. J Biol Chem 2002;277:40275–80]. Based on these findings, it is hypothesized that l-arginine also shifts the equilibrium between O 2 − and H 2O 2. Experiments were designed to test this theory. As the concentration of l-arginine and N ω-hydroxyl- l-arginine increases, the rate of NADPH consumption for H 4B-bound NOS1 decreased resulting in lower rates of both O 2 − and H 2O 2 generation, while increasing the rate of nitric oxide ( NO) production. At saturating concentrations of l-arginine or N ω-hydroxyl- l-arginine (50 μM), NOS1 still produced O 2 − and H 2O 2. Both l-arginine and N ω-hydroxyl- l-arginine have greater impact on the rate of generation of O 2 − than on H 2O 2.

Nanocrystalline gold and gold-palladium as effective catalysts for selective oxidation

ABSTRACTThe recent interest in oxidation catalysis provides the focus for this paper. Until recently gold has been overlooked as a key component of both homogeneous and heterogeneous catalysts. However, the observation in the 1980's that nanocrystalline gold supported on oxides was an effective catalyst for low temperature carbon monoxide oxidation has now captured the imagination of many researchers. At present low temperature carbon monoxide oxidation remains an intensely studied field, but in recent years increased emphasis has been placed on using gold catalysts for selective oxidation. For example the oxidation of alkanes, alkenes and alcohols have all been shown to be effective with gold based catalysts. In addition gold palladium catalysts have been shown to be very effective for the direct formation of hydrogen peroxide and this will be described in this paper.

Direct formation of hydrogen peroxide from H2/O2 using a gold catalyst.

Supported Au catalysts are very selective for the direct formation of hydrogen peroxide from H2/O2 mixtures at 2 degrees C; the rate of H2O2 synthesis is markedly increased if Au-Pd alloy nanoparticles are generated by the addition of Pd.

A reassessment of the product specificity of the NADPH:O 2 oxidoreductase of human neutrophils

Native ferricytochrome c , but not acetylated ferricytochrome c , stimulates the flow of electron equivalents passing through the neutrophil NADPH:O 2 oxidoreductase complex. At 28 uM it increases NADPH oxidase activity by 157 ± 15% (n=5) over that measured in its absence. Enhanced activity is predominantly seen in oxidoreductase-rich 27,000 x g membrane preparations obtained from phorbol myristate acetate activated cells. Superoxide formation is also enhanced. Although some of the stimulatory activity seen with addition of native ferricytochrome c to oxidoreductase-rich membrane suspensions might have been explained in terms of mitochondrial contamination, this was ruled out. Comparable membrane preparations from resting cells were devoid of NADPH oxidase activity. Azide, a well-known inhibitor of the electron transport chain, did not block the enhancing effect of native ferricytochrome c . These results indicate that native ferricytochrome c is not a suitable scavenger of superoxide in quantitating the product specificity of the oxidoreductase since it amplifies the apparent rate of superoxide formation with respect to measured rates of NADPH oxidation conducted in its absence. By using acetylated ferricytochrome c in place of native ferricytochrome c in quantitating the product specificity of the oxidoreductase we show that no more than 70% of the electrom equivalents donated by NADPH to the oxidoreductase are involved in superoxide formation. The remaining 30% of the electron equivalents given up by NADPH to the oxidoreductase appear to be involved in direct formation of hydrogen peroxide.