Dry reforming of methane over a Ni/Al2O3 catalyst in a coaxial dielectric barrier discharge reactor. AbstractA coaxial double dielectric barrier discharge (DBD) reactor has been developed for plasmacatalytic conversion of CH 4 and CO 2 into syngas and other valuable products. A supported metal catalyst (Ni/Al 2 O 3 ) reduced in a methane discharge is fully packed into the discharge region. The influence of the Ni/Al 2 O 3 catalyst packed into the gas gap on the electrical characteristics of the discharge has been 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 CH 4 /CO 2 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 CH 4 has been carried out with the reduced Ni/Al 2 O 3 catalyst using a mixing ratio of CH 4 /CO 2 = 1 and a total flow rate of 50 ml min -1 . An increase in H 2 selectivity is observed compared to dry CH 4 reforming with no catalyst, while the H 2 /CO molar ratio greatly increases from 0.84 to 2.53 when the catalyst is present.

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The chain folding behavior of oxyethylene/oxybutylene (E/B) diblock copolymers, with one crystallizable E block and one noncrystallizable B block, has been studied by simultaneous SAXS and WAXS, low-frequency Raman spectroscopy, and differential scanning calorimetry. Two models, normal density (ND) and crystal/liquid-crystal (CLC) models were used to explore the results, consideration being given to the difference in the cross-sectional area of the two chains and the need to fill space at approximately normal density. It was found that both models can describe the data for the longer copolymers, but the CLC model is better for the shorter copolymers.

Five block copolymers with three linear architectures were prepared by sequential anionic copolymerization, i.e., E102P37, E103P34, E52P34E52, E57P46E57, and P19E113P19 (where E denotes oxyethylene and P denotes oxypropylene), and the properties of their aqueous solutions were studied across a wide range of concentration. The techniques used to study micellization and micellar properties in dilute solution were static and dynamic light scattering, surface tension, and elution gel-permeation chromatography. The results showed, for example, that critical micelle temperatures for solutions of given composition fell in the order E mPn < EmPnEm < PnEmPn, in agreement with the prediction of theory. The gelation of concentrated solutions was also investigated.

The vibrational distributions of the methyl fragment resulting from the photodissociation of CHzI at 248 nm are obtained by TOF photofragment spectroscopy. Only excitation of the v 2 (umbrella) mode is observed and the distribution peaks strongly at v = 2 for the electronically adiabatic pathway (I zP1/2) but extends up to v = 8 for the minor (~ 30 per cent) non-adiabatic pathway (12P3/~). Angular measurements show that both pathways result from an initial parallel ('~Q0 +-N) transition followed by a curve crossing to produce the ground state I fragment. The coupling of the curves is vibronic in nature and probably involves the v~ methyl rocking mode. The lifetime of the photodissociation is found to be ~ 1 x 10 -13 s.

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Translational photofragment spectroscopy has been used to study the photodissociation dynamics of n-C3HTI and i-C3HTI at 248 nm. The measured anisotropies of the photofragments show that the initial absorption is the (parallel polarized) 3Qo*--N transition with a dissociation lifetimes of 3.7 + 2 x 10 13s and 2.5 + 2 x 10-13s respectively. The time of flight measurements yield the energy disposal for channels leading to I(2P3/2) and I*(2P1/2) for both molecules, although with greater uncertainty for i-C3H7I. The average energy disposed into translation is 43 per cent (I) and 52 per cent (I*) for n-C3H7I , and 39 per cent (I) and 57 per cent (I*) for i-C3H7I.The energy disposal for a variety of alkyl iodides are found to be well described by an impulsive model of the dissociation dynamics with the niodoalkanes showing a near constant width for the translational energy distribution regardless of its absolute value. A simple Landau-Zener curve crossing description is used to highlight the substantial change in curve crossing probability caused by substitution at the fl carbon or change to a secondary structure for the radical. Finally a model which combines the soft-radical impulse model for energy disposal with the Landau-Zener curve crossing probability is found to provide an excellent description of the I* quantum yields for the n-iodoalkanes.

Translational photofragment spectroscopy has been used to study the photodissociation dynamics of C2HsI and CF3CH2I at 248nm. The measured anisotropies of the photofragments show that the initial absorption is the (parallel polarized) 3Q0 ,--N transition with a dissociation lifetime of 4 + 2 x 10-13s in both cases. The time of flight measurements yield the energy disposal for channels leading to I (2P3/2) and I* (2p1/2) for both molecules. The average energy disposed into translation is 62 per cent (I) and 72 per cent (I*) for C2HsI, and 36 per cent (I) and 39 per cent (I*) for CFaCH2I. The quantum yield for I* production is 0-67 + 0"03 for C2HsI and 0"82 + 0-07 for CFaCH2I. The results, combined with those of other workers, are compared to an impulsive description of the dissociation dynamics for a variety of substituted alkyl iodides. Finally a simple LandauZener curve crossing model is used to highlight the substantial change in curve crossing probability caused by introduction of fluorine atoms at the fl position.