Influence of catalytic pellets on the electrical response and CO₂ conversion in packed-bed dielectric barrier discharge reactors

Catalytic packed-bed dielectric barrier discharge (DBD) reactors are widely investigated for plasma-assisted CO₂ conversion. Yet the role of catalytic pellets in shaping both discharge behaviour and reactor performance remains only partially understood. In particular, it remains unclear whether changes in CO₂ conversion arise from catalytic effects or from geometry- and dielectric-induced modifications to the electrical discharge. This work assesses the electrical response of a packed-bed DBD reactor using different packing materials with a wide range of dielectric and physicochemical properties. We analyse and compare peak, burning, and breakdown voltages with effective-medium approximations, geometric scaling, and a previously developed dimensionless framework. The results show that bulk dielectric constants alone cannot explain the observed electrical behaviour. Although dielectric and geometric corrections partially improve trend consistency, significant deviations remain, indicating additional material-dependent effects related to plasma–surface interactions. A dimensionless scaling approach improves prediction of breakdown behaviour across empty and packed configurations, suggesting its suitability as a unified reactor-scale descriptor. Finally, CO₂ conversion analysis shows that coupled discharge–chemistry interactions govern reactor performance. Importantly, higher dielectric constants of catalytic packing materials do not necessarily translate into improved CO₂ conversion, highlighting the limitations of dielectric-based design strategies.