Peter A. Gorry

Dry reforming of methane over a Ni/Al2O3 catalyst in a coaxial dielectric barrier discharge reactor

A coaxial double dielectric barrier discharge (DBD) reactor is developed for plasma-catalytic conversion of CH4 and CO2 into syngas and other valuable products. A supported metal catalyst (Ni/Al2O3) reduced in a methane discharge is fully packed into the discharge region. The influence of the Ni/Al2O3 catalyst packed into the gas gap on the electrical characteristics of the discharge is investigated. The introduction of the catalyst pellets leads to a transition in discharge behaviour from a typical filamentary microdischarge to a combination of spatially limited microdischarges and a predominant surface discharge on the catalyst surface. It is also found that the breakdown voltage of the CH4/CO2 discharge significantly decreases when the reduced catalyst is fully packed in the discharge area. Conductive Ni active sites dispersed on the catalyst surface contribute to the expansion of the discharge and enhancement of charge transfer. In addition, plasma-catalytic dry reforming of CH4 is carried out with the reduced Ni/Al2O3 catalyst using a mixing ratio of CH4/CO2 = 1 and a total flow rate of 50 ml min−1. An increase in H2 selectivity is observed compared with dry CH4 reforming with no catalyst, while the H2/CO molar ratio significantly increases from 0.84 to 2.53 when the catalyst is present.

Micellisation and gelation of diblock copolymers of ethylene oxide and propylene oxide in aqueous solution, the effect of P-block length

The aqueous solution properties of five diblock copolymers prepared by sequential anionic copolymerisation (i.e. E102P37, E104P52, E92P55, E104P60 and E98P73 where E denotes oxyethylene and P denotes oxypropylene) were studied across a wide range of concentration. The techniques used to study micellisation and micellar properties in dilute solution were static and dynamic light scattering, surface tension, and eluent gel-permeation chromatography. The gelation of concentrated solutions was also investigated. As expected, the critical micelle concentration (CMC) was lowered and the association number of the micelles was increased by an increase in P-block length. In contrast, the critical gel concentration was unchanged, consistent with the constant E-block length leading to micelles with essentially identical E-block fringes. Comparison of the CMCs of the diblock copolymers with those of triblock EmPnEm copolymers with the same P-block length shows the diblock copolymers to micellise more efficiently. A similar comparison of the CMCs of the diblock copolymers with those of EmBn copolymer (B denotes oxybutylene) shows the hydrophobicity of a P unit to be one-sixth that of a B unit. The possibility is explored of correlating the limiting association number of a spherical micelle with the hydrophobe block length of its constituent copolymer. Of the five copolymers, only dilute solutions of E98P73 were predominantly micellar at both room temperature and body temperature, and this copolymer must be a prime candidate in any consideration of the potential application of EmPn copolymers in the solubilisation and controlled release of drugs.

Chain folding in cyclic oligo(oxyethylene)s

Uniform cyclic oligo(oxyethylene)s with chain lengths E15 to E18 (unsubstituted 45-crown-15 to 54-crown-18) have been prepared by reaction of corresponding linear glycols with tosyl chloride under alkaline conditions, purified by preparative gel permeation chromatography (GPC), and characterised by analytical GPC, NMR spectroscopy, and other methods. Wide-angle and small-angle X-ray scattering were used to investigate crystal structure and layer spacing. Comparison was made with scattering from linear oligomers crystallised in unfolded conformation. It was found that cyclo-E18 crystallised into the poly(oxyethylene) structure (monoclinic sub-cell), while the lower oligomers crystallised into different structures. In confirmation of this result, the layer spacing of cyclo-E18 was that expected for the twice-folded conformation. Melting temperatures and enthalpies of fusion of cyclo-E18 and cyclo-E27 (from previous work), measured by differential scanning calorimetry, were compared with those of linear oligomers to obtain values of the enthalpy and entropy of fold formation in the crystallisation of uniform oligo(oxyethylene).

Reactive scattering study of etching dynamics: HCl on GaAs(100)

Pulsed supersonic molecular beam scattering has been used to study the inelastic scattering, trapping + desorption and reactive channels for the HCl + GaAs(100) thermal etching reactions. Temperature profiles of the reaction products GaCl, As2 and Ga are reported in the range 600 to 883 K. Angular and time-of-flight (TOF) distributions of inelastically scattered and trapped + desorbed HCl are also reported. Angular distribution of all reaction products are described by a cosn (θ) form with 0.95⩽n⩽1.4. The TOF distribution of GaCl reveals rapid production but with measurable time delay (50 μs–10 ms). The As2 signals are effectively demodulated and correspond to delayed production on the surface with a time constant >1 s. A kinetic model initially proposed by Bent and colleagues (C. Su, Z. Dai, W. Luo, D. Sun, M. F. Vernon and B. E. Bent, Surf. Sci., 1994, 312, 181) is extended and provides excellent fits to the temperature profiles and the surface residence times for GaCl and As2.