Catalyst-assisted DBD plasma for coupling of methane: Minimizing carbon-deposits by structured reactors

Non-oxidative coupling of methane has been performed in DBD plasma reactors with a catalytic layer with varying thickness loaded on the reactor wall. These structured reactors allow to study the effect of the thickness of the catalyst layer, including the blank plasma reactor, without significant modification of plasma properties, SEI and residence time. Moreover, it allows analysis of the catalytic effect of Pd/Al₂O₃. The catalyst layer decreases the methane conversion only mildly, which is attributed to hydrogenation of CH_x radicals at the outer surface of the catalyst layer. This results in typically 34 % methane conversion at 2.8 W at room temperature with 6% CH₄ in Ar, independently of the layer thickness. In contrast, the thickness of the catalyst layer strongly influences the product distribution, assigned to hydrogenation of acetylenes at external and internal surfaces in the catalyst layer. The formation of undesired deposits is suppressed by a factor of 2 with value-added hydrocarbons selectivity of 70 % and a carbon balance of 93 %. In addition, catalytic-wall reactors was compared with packed bed reactors. The synergistic effect is much more evident in the structured reactor than in the packed bed reactor, independently of the position of the catalytic bed.