A novel route for in-situ H2O2 generation from selective reduction of O2 by hydrazine using heterogeneous Pd catalyst in an aqueous medium

Hydrogen peroxide in high yields can be generated with high efficiency at mild conditions (25 degrees C and atmospheric pressure) with the formation of only environment-friendly by-products (N2 and H2O) by a reduction of O2 by hydrazine from its hydrate/salt with its complete conversion in a short reaction period (相似文献   

Preparation of Pd/C catalyst for formic acid oxidation using a novel colloid method

A novel colloid method using (WO₃)_n·xH₂O as colloidal source was developed to prepare Pd/C catalyst for formic acid oxidation. Transmission electron microscopy image shows that the Pd/C nanoparticles have an average size of 3.3 nm and a narrow size distribution. Electrochemical measurements indicate that the Pd/C catalyst exhibits significantly high electrochemical active surface area and high catalytic activity with good stability for formic acid oxidation compared with that prepared by common method. The colloid method is very simple and has great potentials for mass-producing Pd/C and others noble metal catalysts.     

Preparation and thermal treatment of Pd/Ag composite membrane on a porous alumina tube by sequential electroless plating technique for H2 separation

Pd/Ag/α-Al2O3 composite membranes were prepared by sequential electroless plating technique. The prepared membranes were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, energy dispersive spectroscopy, and inductively coupled plasma atomic emission spectroscopy techniques （ICP-AES）. Effects of annealing time, Ag content, and air treatment on the hydrogen permeation flux and morphology of the alloys were investigated. The results of the investigation showed that the prepared type of tube had a good potential as substrate for membrane preparation. In addition, a uniform defect-free alloy was prepared by annealing at 550 ℃ in H2 atmosphere. The permeation results showed an increase in H2 permeation flux by increasing the Ag content and the annealing time. In addition, the air treatment of the prepared membranes at 400 ℃ for 1 h changed the morphology of the alloy and substantially enhanced the hydrogen flux.     

Development of catalytically active silver colloid nanoparticles stabilized by dextran

Colloidal silver nanoparticles (Ag-NPs) with a mean diameter of 6.1 nm and a narrow size distribution were prepared by reduction of the correspondent metal salt with injection of NaBH(4), in the presence of dextran, and characterized by UV-vis, TEM, and DLS. The concentration of all reactants involved in the formation of the nanoparticles was optimized with the use of a new multivariate method, which revealed a significant reduction in the number of experiments when compared with the vast majority of univariate methods described in the literature. The Ag-NPs-dextran composite was able to efficiently catalyze the p-nitrophenol reduction in water by NaBH(4) with a rate constant normalized to the surface area of the nanoparticles per unit volume (k(1)) of 1.41 s(-1) m(-2) L, which is higher than values ever reported for Ag-NPs catalytic systems.     

Remarks on catalytic reduction of CO2, H+ and H2 by monovalent Ni

Prompted by catalysis of CO2 electroreduction by a tetraazamacrocyclic Ni(i)(cyclam) complex (cyclam = 1,4,8,11-tetraazacyclotetradecane), we examine theoretically the possibility of H2 reduction by this molecule. We show that the process 2 Ni(i) + H2 --> 2 [Ni(ii)(H-)] is thermodynamically facile, and that H2 could be reduced by a binuclear Ni(i) complex in two concerted 1e- processes. Our calculations also indicate that hydride complexes of Ni(iii)(cyclam) are significantly unstable thermodynamically and therefore they are unlikely to serve as intermediates in process of H2 evolution from water.     

Preparation of monodisperse SiO2 nanoparticles by membrane emulsification using ideally ordered anodic porous alumina

Monodisperse SiO2 particles of nanometer dimensions were fabricated by membrane emulsification using ideally ordered anodic porous alumina. For the preparation of monodisperse emulsion droplets, the dispersed phase was pressed through a porous alumina membrane into the continuous phase. After solidification treatment of the emulsion droplets, prepared spherical SiO2 nanoparticles with uniform sizes were obtained. From scanning electron microscope observation of the obtained particles, it was confirmed that the size distribution of SiO2 nanoparticles is relatively narrow.     

Heterogeneous reductive isomerization reaction using catalytic Pd/C and H2

[reaction: see text] A highly selective catalytic reductive isomerization reaction is described. The extremely mild and neutral reaction conditions (10% Pd/C, H2, and MeOH at 0 degrees C) tolerate a wide range of functional groups and generally result in excellent yields. Mechanistic studies suggest that this reaction does not proceed via a stepwise reduction/elimination sequence or a pi-allylpalladium intermediate.     

Preparation of gold colloid using pyrrole-2-carboxylic acid and characterization of its particle growth

Gold colloid was prepared by reduction of tetrachloroaurate using pyrrole-2-carboxylic acid in the presence of α-methoxy-ω-mercaptoethyl-poly(ethylene glycol). The shape and size of the obtained gold colloids were monitored by absorption spectroscopy and transmission electron microscopy during the reduction reaction. In the early stage of the reducing reaction, large fluffy particles with diameters >100 μm were observed. Some of these large particles had rectangular parallelepiped shapes. However, the mean particle size decreased with increasing time. Eventually, these large, non-round-shaped particles disappeared almost completely, and uniform round-shaped particles with a mean diameter of 10.5 nm became dominant.     

One-pot preparation of mono-dispersed and physiologically stabilized gold colloid

We have developed a rapid and simple method for the preparation of nearly mono-dispersed gold colloids with a fairly high concentration above 10 mM using hydroxylamine as the reducing agents, in the presence of α-methoxy-ω-mercaptoethyl-poly(ethylene glycol)(MeO-PEG-SH). It was found that a hydroxylamine acted not only as a reducing agent, but also as a nucleation agent under alkaline reaction conditions. Though the colloid concentration was fairly high, the dispersion stability was remarkably improved even in a high ionic strength in the range greater than 1 M NaCl, in which conventional citrate gold colloids immediately flocculate and precipitate. The obtained colloid was successfully re-dispersed in aqueous media after lyophilization. In addition, the prepared gold colloid reduced a protein adsorption significantly on its surface. Concerning these results, the obtained colloidal dispersion may be suitable for biological applications, since a regionally concentrated colloidal dispersion with dispersion stability is required for bio-labeling and bio-imaging systems.Electronic Supplementary Material Supplementary material is available for this article at     

Preparation of selenides of copper,cadmium, cobalt and nickel by the reduction of selenites in aqueous solutions

Conclusions On the example of the reduction of the selenious salts of Cu, Cd, Co and Ni it was shown that selenides of stoichiometric composition can be obtained by the reduction of selenites with sodium hydrosulfite in alkaline medium.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 934–935, May, 1966.     

Preparation of alumina by sol-gel process,its structures and properties

Alumina monolithic gel has been prepared by ammonia method from anhydrous aluminium chloride and n-butanol using formamide as the solvent. The gel has been made by hydrochloric acid catalysis and using large quantity of water for hydrolysis (molar ratio of water to aluminium-n-butoxide, R>99). Transparent alumina xerogel of size 37.5×20×5 mm approximately has been prepared. The alumina gel has been dried and sintered at 400°C, 1000°C and 1200°C respectively and the powders formed thereby have been examined by XRD, FTIR spectroscopy, SEM and particle size analysis. These studies have confirmed the formation of -alumina at 1200°C having particle size as low as 0.2 m or less along with agglomerates. The density of the powder has increased gradually, where as its particle size has decreased, with the increase of the sintering temperature.     

The properties of Pd/Au bimetallic colloidal catalysts stabilized by chitosan and prepared by simultaneous and stepwise chemical reduction of the precursor ions

Bimetallic Pd/Au nanoparticle catalysts were prepared with chitosan as a stabilizer. The preparation procedure included mixing or stepwise adding palladium and gold ions in various molar ratios followed by simultaneous or stepwise reduction using either methanol or sodium borohydride (nb) as reducing agents. TEM and UV-Vis characterization showed that the particle size of bimetallic Chi-Pd/Au prepared by simultaneous reduction was smaller than that of the samples prepared by stepwise reduction methods. The particle size varied in the 1 to 24 nm range at all Pd/Au molar ratios of bimetallic compositions. Sodium borohydride was the most effective reducing agent for the preparation of bimetallic Chi-Pd_coreA_ushell by the stepwise reduction. The catalytic activities of Chi-Pd/Au prepared by either simultaneous or stepwise reductions were generally higher than those of the respective monometallic systems whereas the most active catalysts were prepared by the simultaneous reduction. Shielding the palladium metal colloid with gold sol led to the decrease in catalytic activity. The turnover frequencies (TOFs) for Chi-Pd/Au-me in catalytic hydrogenation of 1-octene were as high as 20.855 and 89.336 for monometallic and bimetallic catalysts respectively. TOFs for Chi-Pd/Au-nb were in the region between 2.978 and 87.429. The core-shell and alloy formation of the bimetallic Chi-Pd/Au were inferred from the particle size measurements and evaluation of catalytic activity.     

Preparation of core-shell polymer colloid particles by encapsulation

 By means of heterocoagulation anionic poly-[styrene] particles were coated with smaller electrosterically stabilised cationic particles of poly-[butyl methacrylate]. On heating the heterocoagulated units 45 °C above the glass transition temperature of poly-[butyl methacrylate], as predicted theoretically, the latter polymer spread over the surface of the poly-[styrene] particle to give a composite particle with a core-shell structure. It was found that the extent of packing of the small particles on the larger core particle was a critical feature of the coating process. Received: 12 September 1996 Accepted: 18 September 1996     

Preparation of nanodispersed titania using stabilized ammonium nitrate melts

An expedite one-step approach using simple precursors has been proposed to obtain metallic oxide compounds and exemplified by preparation of highly dispersed TiO₂. The technique consists in heating to 400-500 °C of molten ammonium nitrate stabilized with an organic nitrogen-containing compound (urea, melamine, ammonium oxalate) and containing dissolved metal salt precursor (TiOCl₂). The crystallites of the resulting TiO₂ demonstrated variable size and shape as a function of stabilizer used. Their activity in photocatalytic oxidation of formic acid also depends on the nature of the stabilizer. The catalysts as-prepared showed high photocatalytic performance, superior to that of the Degussa P25 reference. Nitrogen containing stabilizers play a double role of increasing the process safety and modifying the properties of the solid products.     

Preparation of gold colloid monolayer by immunological identification

The design and initial characterization of the self-assembled gold colloid monolayer by a sandwich structure via the immunological identification are reported. The 13 nm gold colloid nanoparticles and the silicon or quartz substrates have been modified with the mouse polyclonal antibody against hepatitis B virus surface antigen (PAb) and the mouse monoclonal antibody against hepatitis B virus surface antigen (MAb), respectively. They can be linked by a special reaction with their corresponding hepatitis B virus surface antigen (Antigen) as a sandwich structure. Thus, the density of gold nanoparticles self-assembled on the substrate can be readily controlled by the amount of the antigen added. The resulting substrates have been characterized by atomic force microscopy (AFM) and surface-enhanced Raman scattering (SERS) spectroscopy when the gold nanoparticles were modified with SERS-active probe molecules of 4-mercaptobenzoic acid (MBA) after silver enhancement. These data show that the gold nanoparticles are separately fixed onto the substrate and form a uniform monolayer, which possess a set of features that make them very attractive for both basic and applied uses, including roughness, high stability, and biocompatibility.