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

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, H-2, 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 (2)Delta-X (2)Pi 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.