Ignition of stoichiometric hydrocarbon : air mixtures by a nanosecond surface dielectric barrier discharge has been experimentally studied at room temperature and atmospheric and subatmospheric pressures. Observations were made for different voltage polarities and shapes of the high-voltage electrode. The ignition delay time and the velocity of the combustion wave were measured in a C 2 H 2 : air mixture versus applied voltage by processing discharge gap images. It was concluded that the mixtures are ignited easier by the discharge for a negative voltage polarity and when it develops from a gear-like electrode. A 2D simulation of the discharge was performed to calculate the temporal and spatial distributions of generated active species and gas temperature during the discharge and in its afterglow for both electrode polarities. It was shown that the voltage threshold for ignition by a negative-polarity discharge is lower than that for a positive-polarity discharge, in qualitative agreement with observations. This is due to the formation of a region with efficient active species production and fast gas heating in the immediate vicinity of the high-voltage electrode when a voltage of negative polarity is applied to it.
A von Hamos geometry based wavelength dispersive spectrometer combined with an in situ reactor cell has been developed to measure non-resonant sulfur Kα emission for the in situ speciation of low concentrations of sulfur.
The production of synthetic natural gas -SNGfrom dry biomass currently involves a costly and energy inefficient low temperature gas cleaning step, needed to remove various sulfur-containing poisons from syngas generated from wood gasification before the sulfur sensitive methanation step.Here we explore the use of Ru-based methanation catalysts in an alternative process, where the low temperature gas cleaning step is omitted and the syngas from the gasifier is directly used for methanation. In this process, methanation is carried out in the presence of organic and inorganic sulfur species and is followed by a periodic oxidative regeneration of the poisoned catalyst. In situ diffuse reflectance infra-red Fourier transform (DRIFTS) and Ru K-edge X-ray absorption (XAS) spectroscopy were employed to understand the deactivation mechanism of Ru nanoparticles on two different supports: Al2O3 and SiO2. The efficiency of the regeneration is better when Ru nanoparticles are supported on SiO2, on which only a small amount of unstable sulfate species is formed and Ru nanoparticles are shown to be somewhat more stable against sintering during the oxidative regeneration due to a "passivation" effect of adsorbed sulfur poison.
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