Solvent-free oxidation of benzyl alcohol using titania-supported gold–palladium catalysts: Effect of Au–Pd ratio on catalytic performance

The oxidation of benzyl alcohol with molecular oxygen under solvent-free conditions has been investigated using a range of titania-supported Au–Pd alloy catalysts to examine the effect of the Au–Pd ratio on the conversion and selectivity. The catalysts have been compared at high reaction temperature (160 °C) as well as at 100 °C, to determine the effect on selectivity since at lower reaction temperature the range of by-products that are formed are limited. Under these conditions the 2.5 wt.% Au–2.5 wt.% Pd/TiO₂ was found to be the most active catalyst, whereas the Au/TiO₂ catalyst demonstrated the highest selectivity to benzaldehyde. Toluene, formed via either a hydrogen transfer process or an oxygen transfer process, was observed as a major by-product under these forcing conditions.     

Solvent free liquid phase oxidation of benzyl alcohol using Au supported catalysts prepared using a sol immobilization technique

Solvent free oxidation of benzyl alcohol was investigated in the absence of a base using Au catalysts prepared by sol immobilization on titania and carbon supports. Comparison between the Au supported catalysts revealed that activity and distribution of products was dependent on the nature of support and heat treatment. Specifically, heat pre-treatment of the Au catalysts has a beneficial effect in terms of activity, but is detrimental in terms of selectivity to the benzaldehyde. We conclude that sol immobilization is a suitable technique for preparing gold catalysts with small particle size and narrow particle size distributions and very high activity and selectivity for benzyl alcohol oxidation.     

Modeling nonisothermal impregnation of fibrous media with reactive polymer resin

The manufacture of polymer composites through resin transfer molding (RTM) or structural reaction injection molding (SRIM) involves the impregnation of a fibrous reinforcement in a mold cavity with a reactive polymer resin. The design of RTM and SRIM operations requires an understanding of the various parameters, such as materials properties, mold geometry, and mold filling conditions, that affect the resin impregnation process. Modeling provides a potential tool for analyzing the relationships among the important parameters. The present work provides the physical model and finite element formulations for simulating the mold filling stage. Resin flow through the fibers is modeled using two-dimensional Darcian flow. Simultaneous resin reaction and heat transfer among resin, mold walls, and fibers are considered in the model. The proposed technique emphasizes the use of the least squares finite element method to solve the convection dominated mass and energy equations for the resin. Excellent numerical stability of the proposed technique provides a powerful numerical method for the modeling of polymer processing systems characterized by convection dominated transport equations. Results from example numerical studies for SRIM of polyurethane/glass fiber composites were presented to illustrate the application of the proposed model and numerical scheme.     

Intramolecular vs intermolecular formation of bityrosine upon photoreaction of poly(l-tyrosine) in dilute aqueous solution

Summary The molecular weight dependence of the rate of the formation of bityrosine upon irradiation of poly(L-tyrosine) at 300 nm has been investigated in dilute aqueous solution, pH 12. The samples studied were the monodisperse monomer, dimer, trimer, and hexamer, as well as two polydisperse polymers with average degrees of polymerization of 10² and 10³. The reaction is predominantly intermolecular in the monodisperse oligomers, but it is predominantly intramolecular in the two polymers. The intramolecular reaction in the polymers involves phenolic rings on monomers i and i+j, with j>5. The steric restraints imposed by the backbone of the chain make it unlikely that two rings will approach one another with the appropriate geometry for reaction if j<5.     

Monitoring the cure of a composite matrix resin with microdielectrometry

This paper presents a study of the cure of glass and graphite fiber epoxy composites using dielectric monitoring techniques. Initial results reported here deal with the neat resin and the relationship between its conductivity and corresponding changes in glass transition temperature during cure.     

Interaction of Silver/Palladium Electrodes with Lead-and Bismuth-Based Electroceramics

In this study the phase relations between Pd or 70Ag/30Pd electrode systems with commercially important Bi-or Pb-based oxides were determined to establish the conditions under which detrimental interfacial chemical reactions may occur. For the reaction of Pd with Bi compounds, PdBi₂O₄ formation was observed if the reaction proceeded at temperatures less than 835°C. At higher temperatures a Pd (Bi) alloy formed containing the maximum solubility of the Bi, i.e., 16 at.%. For the reaction of Pd with Pb compounds, a Pd (Pb) alloy formed which in all instances exhibited the maximum solubility of the Pb, i.e., 14 at.%. These reactions had an adverse effect on the local stoichiometry and composition of the dielectric, causing depletion of Bi or Pb. Studies on commercial capacitor dielectrics from DuPont (X7R and Z5U formulations) and Pb (Mg_1/3Nb_2/3)O₃ showed that the use of Pd electrodes decreased the dielectric constant substantially, which was due to the formation of a low permittivity phase in series connectivity with the unaltered dielectric.     

The effect of sulfur on the dissociative adsorption of methane on nickel

The dissociative adsorption of methane was carried out on a Ni(100) surface covered with various amounts of sulfur under the high incident flux conditions of 1 Torr methane. Auger electron spectroscopy was used to measure the rate of carbon buildup and thus to determine the initial methane decomposition rates on the surface. It was shown that the sulfur atoms poison this reaction by a simple site-blocking process. These results are consistent with the activated dissociative adsorption of methane on Ni(100) occurring via a direct adsorption process.     

Direct synthesis of hydrogen peroxide from H2 and O2 using zeolite-supported Au catalysts

The direct synthesis of hydrogen peroxide from H₂ and O₂ using zeolite-supported Au catalysts is described and their activity is contrasted with silica- and alumina-supported Au catalysts. Two zeolites were investigated, ZSM-5 and zeolite Y. The effect of calcination of these catalysts is studied and it is found that for uncalcined catalysts high rates of hydrogen peroxide formation are observed, but these catalysts are unstable and lose Au during use. Consequently, reuse of these catalysts leads to lower rates of hydrogen peroxide formation. However, catalysts calcined at 400 °C are more stable and can be reused without loss of gold. The use of zeolites as a support for Au gives comparable rates of hydrogen peroxide formation to alumina-supported Au catalysts and higher rates when compared with silica-supported catalysts. prepared using a similar method. Zeolite Y-supported catalysts are more active than ZSM-5-supported catalysts for the stable calcined materials. It is considered that the overall activity of these supported catalysts may be related to the aluminium content as the activity increases with increasing aluminium content.     

Ventilation of a dead-end duct having a porous barrier

Analytic expressions for the flow and pressure in a dead-end duct which has loss of fluid through a porous wall are developed. The presence of an obstruction or auxiliary fan at the end of the duct is included. In either case there is a maximum permissible length of duct. As the duct length approaches this maximum, the main supply fan power and flow increase dramatically. There is no recirculation within the duct when there is an obstruction at the end of the duct. If an auxiliary fan is used, there is always recirculation. However the use of an auxiliary fan can yield major savings in total power requirements.     

Direct conversion of methane to higher hydrocarbons via an oxygen free,low-temperature route

The direct conversion of methane to higher hydrocarbons over a silica-supported Ru catalyst has been investigated via an oxygen free, two-step route. The reaction consists of decomposition of methane over a 3% silica-supp orted Ru catalyst at temperatures between 400 and 800 K to produce surface carbonaceous species followed by rehydrogenation of these species to higher hydrocarbons at of 368 K. It was found that the Ru/SiO₂ catalyst exhibits a trend similar to that for single-crystal Ru catalysts. However, the temperature at which a maximum in ethane selectivity occurs shifts toward a higher temperature. It was also found that the ethane yield can be optimized by changing the surface carbon coverage. Under optimum conditions a net ethane yield of about 13–15% has been realized. For this two-step reaction sequence, only a few reaction cycles could be operated without intermediate high temperature rehydrogenation and without significant loss in ethane yield. This is attributed to large amounts of inactive carbon that could not be hydrogenated at 368 K. Higher methane partial pressures were found to be desirable for this reaction. The activity of the catalyst could also be maintained at total pressures up to 10 atm.