Adsorption and conversion of ethylene glycol on the surface of Ag-containing catalyst modified with phosphate

The interaction of ethylene glycol with the surface of Ag-containing catalysts modified with phosphates was studied by IR spectroscopy. It was found that ethylene glycol was adsorbed at the surface phosphate groups; the presence of water vapor increased the stability of adsorbed ethylene glycol to a temperature of 400°C. A study of the kinetics of oxidation of ethylene glycol showed that it was consecutively converted into glycolaldehyde and glyoxal at 400°C. At 500–550°C, glyoxal was formed upon both the consecutive and direct conversion of ethylene glycol. The presence of a stage of the consecutive conversion of ethylene glycol into glycolaldehyde and glyoxal was caused by the participation of surface phosphate groups in the adsorption of alcohol molecules to be oxidized.     

Epitaxy‐like orientation of nanoscale Ag islands grown on air‐oxidized Si(110)‐(5 × 1) surfaces

Growth of Ag islands under ultra‐high vacuum condition on air‐oxidized Si(110)‐(5 × 1) surfaces has been investigated by in situ reflection high energy electron diffraction and ex situ scanning electron microscopy and cross‐sectional transmission electron microscopy. A thin oxide is formed on Si via exposure of the clean Si(110)‐(5 × 1) surface to air. The oxide layer has a short range order. Deposition of Ag at different thicknesses and at different substrate temperatures reveal that the crystalline qualities of the Ag film are almost independent of the thickness of the Ag layer and depend only on the substrate temperature. Ag deposition at room temperature leads to the growth of randomly oriented Ag islands while preferred orientation evolves when Ag is deposited at higher temperatures. For deposition at 550 °C sharp spots in the reflection high energy electron diffraction pattern corresponding to an epitaxial orientation with the underlying Si substrate are observed. The presence of a short range order on the oxidized surface apparently influences the crystallographic orientation of the Ag islands. Copyright © 2011 John Wiley & Sons, Ltd.     

碱性介质中分光光度法研究二羟基二（过碘酸）合银（III）配离子氧化一些二元醇的反应动力学及机理

The kinetics of oxidation of ethylene glycol and 1,3-butylene glycol by dihydroxydiperiodatoargentate（Ⅲ） in alkaline medium have been studied by spectrophotometry in the range of 298.2-318.2 K. It is shown that the reaction was first order with respect to each reductant and Ag（Ⅲ）, and kobs increased with an increase of [OH^-]. A plausible mechanism of reaction involving a pre-equilibrium of adduct formation between complex and reductants was proposed, which could be applied to explain all experimental phenomena, and the activation parameters of the ratedetermining step have been also calculated.     

Facile Synthesis of Carbon‐Supported Ultrasmall Ag@Pd Core‐Shell Nanocrystals with Superior Electrocatalytic Activity for Direct Formic Acid Fuel Cell Application

To design electrocatalysts with excellent performance, morphology, composition and structure is a decisive influential factor. In this work, ultrasmall Ag@Pd core‐shell nanocrystals supported on Vulcan XC72R carbon with different Ag/Pd atomic ratios are synthesized via a facile successive reduction approach with formaldehyde and ethylene glycol as reducing agents, respectively. The Ag‐core/Pd‐shell nanostructures are revealed by high‐resolution transmission electron microscopy (HRTEM). Ag@Pd core‐shell nanocrystals possess a narrow size distribution with an average size of ca. 4.3 nm. In comparison to monometallic Pd/C and commercial Pd black catalysts, such Ag@Pd core‐shell nanocrystals display excellent electrocatalytic activities for formic acid oxidation, which may be due to high Pd utilization derived from the formation of Ag@Pd core‐shell nanostructure and the strong interaction between Ag and Pd.     

Glaser coupling of polymers: Side‐reaction in Huisgens “click” coupling reaction and opportunity for polymers with focal diacetylene units in combination with ATRP

Atom transfer radical polymerization (ATRP) was used in combination with Glaser type coupling, allowing the clean and efficient formation of symmetrically coupled polymers with a central diacetylene unit. The feasibility of the clean acetylene coupling was investigated with alkyne terminated poly(ethylene glycol) and poly(styrene) obtained by ATRP. The latter allowed subsequent ATRP to be carried out from the coupled products, offering opportunities for the formation of well defined functional materials with central diacetylene units. Glaser coupling was also observed as a side reaction in Huisgens‐type “click” reactions of polymeric alkynes with hindered surface azide groups. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3795–3802, 2009     

One pot synthesis of Ag nanoparticle modified ZnO microspheres in ethylene glycol medium and their enhanced photocatalytic performance

Ag nanoparticles (NPs) modified ZnO microspheres (Ag/ZnO microspheres) were prepared by a facile one pot strategy in ethylene glycol (EG) medium. The EG played two important roles in the synthesis: it could act as a reaction media for the formation of ZnO and reduce Ag⁺ to Ag⁰. A series of the characterizations indicated the successful combination of Ag NPs with ZnO microspheres. It was shown that Ag modification could greatly enhance the photocatalytic efficiency of ZnO microspheres by taking the photodegradation of Rhodamine B as a model reaction. With appropriate ratio of Ag and ZnO, Ag/ZnO microspheres showed the better photocatalytic performance than commercial Degussa P-25 TiO₂. Photoluminescence and surface photovoltage spectra demonstrated that Ag modification could effectively inhibit the recombination of the photoinduced electron and holes of ZnO. This is responsible for the higher photocatalytic activity of Ag/ZnO composites.     

Spontaneous formation of Ag nanoparticles in dimethylacetamide solution of poly(ethylene glycol)

The spontaneous formation of Ag nanoparticles in a dimethylacetamide (DMAC) solution of poly(ethylene glycol) (PEG) was studied. FTIR analysis showed the formation of carbonyl groups, revealing that PEG acted as not only a protective agent but also a reducing agent in the formation of Ag nanoparticles. Since no significant reactions were observed when poly(tetramethylene glycol) (PTMG) was used to replace PEG or acetonitrile was used to replace DMAC, it was suggested that PEG molecules might be coiled to form pseudo-crown ether cavities, in which Ag complexes were bound to the oxyethylene groups and reduced, and that the use of a solvent which might appropriately solvate the Ag salt was important for the formation of Ag nanoparticles. In addition, the mean diameters of the resultant Ag nanoparticles were 3.8-9.0 nm, increasing with increasing AgNO(3) concentration. A sufficiently high PEG concentration relative to AgNO(3) was necessary for the formation of smaller Ag nanoparticles. This work provided a simple route for the in situ synthesis of Ag nanoparticles.     

Formation of diethylene glycol as a side reaction during production of polyethylene terephthalate

Polymers of poly(ethylene terephthalate) (PET) always contain a certain amount of incorporated diethylene glycol (DEG), substituting the incorporated glycol. DEG is formed in a side reaction during the ester interchange of dimethyl terephthalate (DMT) with ethylene glycol or during direct esterification of terephthalic acid with ethylene glycol, and to a smaller extent during the polycondensation of the low-molecular material. DEG is formed via an unusual type of reaction: ester + alcohol → ether + acid. Some evidence of this type of reaction is given by the formation of dioxane in low molecular PET and of methyl Cellosolve and methyl carbitol during the ester interchange of DMT with ethylene glycol and diethylene glycol, respectively. The strongest support for this type of reaction, however, was obtained from kinetic data. Polyesters of low molecular weight with OH group contents ranging from 3 to 0.5 mole/kg were heated at 270°C in sealed tubes for 1–7 hr. The kinetic equation for the proposed reaction is: d[DEG]/dt = k[OH] [ester]. With the aid of one rate constant the formation of DEG in all esters could be described.     

Synthesis of Au, Au/Ag, Au/Pt and Au/Pd nanoparticles using the microwave-polyol method

Gold, Au/Ag, Au/Pt and Au/Pd bimetallic nanoparticles with varying mol fractions were synthesized in ethylene glycol and glycerol, using the microwave technique in the presence of a stabilizer poly(N-vinylpyrrolidone) (PVP). It was found that bimetallic colloids of Au/Ag, Au/Pd and Au/Pt form an alloy either on co-reduction of respective metal ions or on mixing individual sols.     

Surface modification of thermoplastic polyurethane in order to enhance reactivity and avoid cell adhesion

Recently, the definition of coating procedures which leads to strong cell repellent surfaces has been an extremely important issue. In the present study, the cell repellency of thermoplastic polyurethane material (Elastollan®1180A50) surfaces was achieved by chemical treatment. Samples of Elastollan®1180A50 processed by injection molding, were oxidized with hydrogen peroxide (H₂O₂) and then impregnated with poly(ethylene glycol). The oxidation time was evaluated as were the effects of the PEG impregnation. Of all the evaluated modifications, a surface oxidation for 2 h, followed by impregnation with poly(ethylene glycol) resulted in the best cell repellent surface.     

The role played by an iodine-containing promoter in the formation of active polycrystalline silver catalyst surface

The programmed temperature desorption method was used to study the interaction of oxygen with the surface of a polycrystalline silver catalyst promoted with iodine. Ethyl iodide almost did not interact with the unoxidized surface of silver. The adsorption of C₂H₅I on the oxidized catalyst surface resulted in the formation of two adsorbed iodine forms, silver iodide and iodine deeply dissolved in subsurface silver crystal lattice layers. The character of oxygen adsorption from the iodine-containing surface of the catalyst was determined by the amount and form of adsorbed iodine. In the presence of a iodine-containing promoter, the concentration of oxide-like oxygen sharply decreased, and the amount of strongly bound atomically adsorbed oxygen responsible for the selective transformation of ethylene glycol into glyoxal increased.     

Study on chemisorption of H<Subscript>2</Subscript>, O<Subscript>2</Subscript>, CO and C<Subscript>2</Subscript>H<Subscript>4</Subscript>on Pt-Ag/SiO<Subscript>2</Subscript>catalysts by microcalorimetry and FTIR

Adsorption microcalorimetry has been employed to study the interaction of ethylene with the reduced and oxidized Pt-Ag/SiO₂catalysts with different Ag contents to elucidate the modified effect of Ag towards the hydrocarbon processing on platinum catalysts. In addition, microcalorimetric adsorption of H₂, O₂, CO and FTIR of CO adsorption were conducted to investigate the influence of Ag on the surface structure of Pt catalyst. It is found from the microcalorimetric results of H₂and O₂adsorption that the addition of Ag to Pt/SiO₂leads to the enrichment of Ag on the catalyst surface which decreases the size of Pt surface ensembles of Pt-Ag/SiO₂catalysts. The microcalorimetry and FTIR of CO adsorption indicates that there still exist sites for linear and bridged CO adsorption on the surface of platinum catalysts simultaneously although Ag was incorporated into Pt/SiO₂. The ethylene microcalorimetric results show that the decrease of ensemble size of Pt surface sites suppresses the formation of dissociative species (ethylidyne) upon the chemisorption of C₂H₄on Pt-Ag/SiO₂. The differential heat vs. uptake plots for C₂H₄adsorption on the oxygen-preadsorbed Pt/SiO₂and Pt-Ag/SiO₂catalysts suggest that the incorporation of Ag to Pt/SiO₂could decrease the ability for the oxidation of C₂H₄.     

Temperature‐sensitive poly(N‐isopropylacrylamide)‐grafted surfaces modulate blood platelet interactions

Interactions between a temperature‐responsive poly(N‐isopropylacrylamide)‐grafted surface and blood platelets have been analyzed with computerized image analysis. Platelet behavior on this surface is dramatically dependent upon temperature in contrast to that on poly(ethylene glycol) (PEG)‐grafted surfaces or polystyrene. The poly(N‐isopropylacrylamide)‐grafted surface interacts with platelets similarly as the poly(ethylene glycol)‐rafted surface at 18°C. At 37°C, platelets readily adhere onto the poly(N‐isopropylacrylamide)‐grafted surface similarly as to that of polystyrene.     

Carbon black supported ultra-high loading silver nanoparticle catalyst for electro-oxidation and determination of hydrazine

Carbon black supported ultra-high loading silver nanoparticle catalyst (Ag/CB) was prepared by a modified ethylene glycol reduction method, using ethylene glycol as the reducing agent and sodium hydroxide as the pH adjusting agent. The X-ray diffraction, thermogravimetry and scanning electron microscopy characterizations showed that the Ag nanoparticles crystallized with a face-centered cubic structure and were densely stacked on the CB surface without aggregation, despite such a small average size (ca. 10 nm) and an ultra-high loading mass (392 wt.%). The electrochemical evaluation based on cyclic voltammetry, chronoamperometry and polarization tests revealed that the ultra-high loading Ag/CB catalyst possessed a superior electrocatalytic activity for the oxidation of hydrazine, via a diffusion-limited process and a 4-electron transfer pathway. Moreover, the chronoamperometry response on an electrode modified with this ultra-high loading Ag/CB catalyst exhibited a promising application for determination of hydrazine, due to a broad linear calibration ranging from 50 to 800 μM, a high sensitivity of 0.03795 A/ M and a low detection limit of 3.47 μM.     

Structural organization of phosphorus titanate oxides prepared by the alkoxo method and their catalytic activity in ethylene glycol oxyethylation

The relationship of the structural organization and acid-base properties of the surface of phosphorus titanate oxides prepared from tetra-n-butoxytitanium and phosphorous esters with the catalytic activity and selectivity of these materials in ethylene glycol oxyethylation was studied. Single-phase phosphorus-containing oxides synthesized from 2-diethylamido-4-methyl-1,3,2-dioxophosphorinane and diphenyl(methano)phosphocane have strong surface aprotic acid sites and exhibit high catalytic activity with respect to oxyethylation and a record-breaking selectivity in the formation of the lower homolog, diethylene glycol. The last-mentioned fact is a consequence of the sieve effect exerted by the homogeneous porous structure of supermicropores (8—10 ) of the oxides. An increase in the concentration of the strong acid sites (130 kJ mol^–1) on the oxide surface enhances the catalytic activity. On the basis of the temperature programmed desorption of ammonia and CO₂ and kinetic measurements, a concerted acid-base mechanism was proposed for the catalytic addition of ethylene oxide to ethylene glycol on the phosphorus-titanate surface.     

A wall-jet disc electrode for simultaneous and continuous on-line measurement of sodium dithionite, sulfite and indigo concentrations by means of multistep chronoamperometry

In this paper, a multistep chronoamperometric method is presented to measure continuously and simultaneously the concentrations of indigo, sodium dithionite and sulfite for application in textile dyeing processes. The method is based on the oxidation of sodium dithionite and the reduced form of indigo at a platinum disc electrode. Sodium dithionite is oxidized at a potential of 0.3 V versus Ag/AgCl and shows transport controlled steady state currents at a rotating disc electrode and a wall-jet electrode. The latter has been developed for the purpose of the application. Implementation of a wall-jet instead of a rotating disc electrode is much easier and cost-effective. Indigo is oxidized at −0.55 V versus Ag/AgCl to a virtually water insoluble product, which precipitates at the electrode surface. Indigo behaves quasi-reversibly, and is reduced at a potential of −0.9 V versus Ag/AgCl. In order to clean the electrode surface this reduction is used as a step in the multistep sequence. Finally, sulfite is oxidized at a potential of 0.8 V versus Ag/AgCl but did not give rise to well defined transport controlled limiting currents. However, determination of its concentration is still possible within error margins of 5%.     

An in situ temperature‐programmed XPS study of the surface chemical reactions of thiophene with Ag/titania

The Ag/titania sorbent for the ultradeep desulfurization of liquid fuels was characterized by electron spin resonance and was found to contain nearly the stoichiometric titania, without significant concentration of Ti³⁺ or the reactive oxygen species. The surface chemical reactions of thiophene adsorbed on the Ag/titania were studied by temperature‐programmed XPS from 25 to 525 °C upon in situ thermal annealing in high vacuum and in situ oxidation by oxygen gas. The titania support is not chemically reactive under those conditions. Silver oxide in the Ag/titania sorbent is converted to Ag₂ S without formation of the transient surface sulfates or sulfites and is further oxidized by molecular oxygen. Copyright © 2010 John Wiley & Sons, Ltd.     

Novel synthesis of biodegradable poly(lactide-co-ethylene glycol) block copolymers

Biodegradable and amphiphilic diblock copolymers [polylactide-block-poly(ethylene glycol)] and triblock copolymers [polylactide-block-poly(ethylene glycol)-block-polylactide] were synthesized by the anionic ring-opening polymerization of lactides in the presence of poly(ethylene glycol) methyl ether or poly(ethylene glycol) and potassium hexamethyldisilazide as a catalyst. The polymerization in toluene at room temperature was very fast, yielding copolymers of controlled molecular weights and tailored molecular architectures. The chemical structure of the copolymers was investigated with ¹H and ¹³C NMR. The formation of block copolymers was confirmed by ¹³C NMR and differential scanning calorimetry investigations. The monomodal profile of the molecular weight distribution by gel permeation chromatography provided further evidence of block copolymer formation as well as the absence of cyclic species. Additional confirmation of the block copolymers was obtained by the substitution of 2-butanol for poly(ethylene glycol); butyl groups were clearly identified by ¹H NMR as polymer chain end groups. The effects of the copolymer composition and lactide stereochemistry on the copolymer properties were examined. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2235–2245, 2007     

Au–Ag Nanoflower Catalysts with Clean Surfaces for Alcohol Oxidation

Shape‐controlled metal nanocrystals, such as nanowires and nanoflowers, are attractive owing to their potentially novel catalytic properties and bimetallic nanocrystals composed of two distinct metals are expected to act as highly active catalysts. However, their catalytic activities are limited because of the capping agents adsorbed on the metal surfaces, which are necessary for the preparation and dispersion of these nanocrystals in solvents. Therefore, the preparation of bimetallic shape‐controlled noble metal nanocrystals with clean surfaces, devoid of almost all capping agents, are expected to have high catalytic activity. Herein, we report the preparation of bimetallic Au–Ag nanoflowers using melamine as the capping agent. The bimetallic Au–Ag nanoflowers with a clean surface were subsequently obtained by a support and extraction method. The bimetallic nanoflowers with a clean surface were then used for the aerobic oxidation of 1‐phenylethyl alcohol and they exhibited high rates for the formation of acetophenone compared to Au nanoflowers and spherical nanoparticles with almost the same size and Au/Ag ratio. We also show that Au–Ag nanoflowers containing only 1 % Ag (Au₉₉–Ag₁NFs) exhibit the highest rate of acetophenone formation among Au–Ag nanoflowers with different Au/Ag ratios owing to an increase in the electron density of the Au atoms that act as active sites for the oxidation of 1‐phenylethyl alcohol.     

High-pressure STM of the interaction of oxygen with Ag(111)

To identify surface phases that could play a role for the epoxidation of ethylene on Ag catalysts we have studied the interaction of Ag(111) with O(2) at elevated pressures. Experiments were performed using high-pressure scanning tunneling microscopy (STM) at temperatures between 450 and 480 K and O(2) pressures in the mbar range. Below p(O(2)) approximately 1 mbar the surface largely showed the structure of bare Ag(111). At p(O(2)) above approximately 1 mbar the (4 x 4)O structure and the closely related (4 x 5 radical 3)rect structure were observed. The findings confirm theoretical predictions that the (4 x 4)O structure is thermodynamically stable at the oxygen partial pressure of the industrial ethylene oxide synthesis. However, in other experiments only a rough, disordered structure was observed. The difference is caused by the chemical state of the STM cell that depends on the pretreatment and on previous experiments. The surface was further analyzed by X-ray photoelectron spectroscopy (XPS). Although these measurements were performed after sample transfer to ultra-high vacuum (UHV), so that the surface composition was modified, the two surface states could still be identified by the presence of carbonate or a carbonaceous species, and by the absence or presence of a high-binding energy oxygen species, respectively. It turns out that the (4 x 4)O structure only forms under extremely clean conditions, indicating that the (4 x 4)O phase and similar oxygen-induced reconstructions of the Ag(111) surface are chemically unstable. Chemical reactions at the inner surfaces of the STM cell also complicate the detection of the catalytic formation of ethylene oxide.