Showing papers by "Baldur Eliasson published in 2002"

Investigation of mechanistic aspects of the catalytic CO2 reforming of methane in a dielectric-barrier discharge using optical emission spectroscopy and kinetic modeling

Abstract: The CO2 reforming of methane by the combination of catalysts with a dielectric-barrier discharge is investigated as an alternative approach to the conventional pure catalytic process. It is shown that the use of nickel or calcium-promoted nickel catalysts in combination with the discharge leads to an increase in the CO yield of 20 to 40%. The identified products are CO, H2, water, ethane and ethylene, propane, n-butane and methanol. In addition to the experimental investigation, extensive kinetic modeling was performed. Besides a good description of the plasma reactions by a set of 308 reactions and 57 species, the programs used offered the possibility of identifying the main reaction routes towards the different products. To get an insight into the mechanistic aspects of the catalyst–plasma interaction, the gas phase was investigated with optical emission spectroscopy (OES) during the experiment. Special emphasis was placed on the interpretation of differences in the emission spectra from experiments with and without a catalyst in the discharge. A significant difference was observed for the CH A 2Δ–X 2Π band. Therein, the intensity of the signal was proportional to the activity of the catalysts used, in the sense that the CH signal was higher for a more active catalyst. Based on these results, a tentative reaction scheme is proposed that explains the enhancing effects of the catalysts in the CO2 reforming reaction. It starts with the adsorption of methane and methane fragments from the gas phase, followed by their gasification by oxygen and oxygen-containing species supplied by the discharge plasma.

Direct Conversion of Greenhouse Gases to Synthesis Gas and C4 Hydrocarbons over Zeolite HY Promoted by a Dielectric-Barrier Discharge

Abstract: The direct conversion of methane and carbon dioxide to produce C4 hydrocarbons (C4H8, n-C4H10, i-C4H10) and synthesis gas (H2 + CO) was investigated over quartz fleece, zeolite NaA, zeolite NaY, and zeolite HY catalysts promoted by dielectric-barrier discharges (DBDs) at relatively low temperatures and ambient pressure. Both pore size and electrostatic properties of zeolites influence the reaction under plasma conditions. Zeolite HY is the most promising catalyst in producing synthesis gas (H2 + CO) and C4 hydrocarbons (C4H8, n-C4H10, i-C4H10) with high selectivity at low temperatures and ambient pressure. The important variables affecting the activity and selectivity of a zeolite HY catalyst in a DBD reactor such as temporal stability, discharge power, mixing ratios of methane to carbon dioxide, space velocity, operating pressure, and wall temperature were studied. The conversion of methane was 55.1% and that of carbon dioxide 26.7%, and the selectivity to CO was 21.7% and that to C4 hydrocarbons reached...

Partial Oxidation of Methane to Syngas over Plasma Treated Ni-Fe/La2O3 Catalyst

Abstract: Ni-Fe/La2O3 catalyst prepared by a glow discharge plasma treatment following calcinations thermally exhibits higher activity and selectivity compared to the Ni-Fe/La2O3 prepared conventionally. At the same reaction temperature, the CH4 conversion, CO selectivity and H2 selectivity obtained from the plasma prepared Ni-Fe/La2O3 are 5–9%, 4–7% and 9–15% higher than those from the conventional Ni-Fe/La2O3 catalyst, respectively. At the same methane conversion, the reaction temperature with the plasma prepared Ni-Fe/La2O3 is at least 100 °C lower than that with the conventional Ni-Fe/La2O3.

A remarkable enhancement of formation of diamond-like carbon film from methane using dielectric-barrier discharges

Abstract: Introduction Plasma can create polymer films or diamond like carbon film from monomers (e.g. methane) that do not form polymers by conventional chemical technologies [1,2]. Such plasma-polymerized films exhibit excellent properties and have a great potential as electronic, optical and biomedical materials. There is an increasing interest at plasma polymerization of methane. DC glow, low frequency (50 or 60 Hz), radio frequency (13.56 MHz) or microwave (2.45 GHz) radiation usually induces plasma for such plasma polymerization. Mostly, a vacuum or low-pressure condition is required. Recently, we have achieved a fabrication of diamond like carbon film from methane and carbon dioxide or methane and carbon monoxide feed using dielectricbarrier discharge at atmospheric pressure. We have also observed a remarkable enhancement of production of diamond like carbon film if methane and carbon monoxide were used as co-feeds under the condition of dielectric-barrier discharges.