Imaging Oxygen Distribution in Marine Sediments. The Importance of Bioturbation and Sediment Heterogeneity

The influence of sediment oxygen heterogeneity, due to bioturbation, on diffusive oxygen flux was investigated. Laboratory experiments were carried out with 3 macrobenthic species presenting different bioturbation behaviour patterns:the polychaetes Nereis diversicolor and Nereis virens, both constructing ventilated galleries in the sediment column, and the gastropod Cyclope neritea, a burrowing species which does not build any structure. Oxygen two-dimensional distribution in sediments was quantified by means of the optical planar optode technique. Diffusive oxygen fluxes (mean and integrated) and a variability index were calculated on the captured oxygen images. All species increased sediment oxygen heterogeneity compared to the controls without animals. This was particularly noticeable with the polychaetes because of the construction of more or less complex burrows. Integrated diffusive oxygen flux increased with oxygen heterogeneity due to the production of interface available for solute exchanges between overlying water and sediments. This work shows that sediment heterogeneity is an important feature of the control of oxygen exchanges at the sediment–water interface

Effect of Particle Size and Support Type on Pd Catalysts for 1,3-Butadiene Hydrogenation

Pd nanoparticles supported on SiO 2 , Si 3 N 4 and Al 2 O 3 were studied to examine the effect of particle size and support type on the hydrogenation of 1,3-butadiene. Pd nanoparticles were produced using a reverse micelle method resulting in particles with a remarkably small particle size distribution (σ < < 1 nm). The support type and particle size were observed to affect both catalytic activity and product selectivity. All catalysts showed a decrease of their activity with time on stream, paired with an increase in selectivity to butenes (1-butene and cis/trans-2-butene) from a product stream initially dominated by n-butane. In situ XAFS demonstrated a correlation between the formation of palladium hydride and n-butane production in the early stages (~ 1 h) of reaction. The extent of palladium hydride formation, as well as its depletion with time on stream, was dependent on both particle size and support type. Metallic Pd was identified as the species selective towards the production of butenes

Voice in Student Essays

Language Use in Past and Presen