Catalytic bed configuration on the valorization of greenhouse gases by DBD plasma-catalysis

Reactor design plays a crucial role in DBD plasma-catalysis performance, but the influence of catalyst particle size and bed configuration has remained largely unexplored. This study systematically investigates their impact across three key reactions on the valorization of greenhouse gases (CO<inf>2</inf> and CH<inf>4</inf>) into valuable products: steam methane reforming, dry methane reforming, and Sabatier reaction. Plasma-catalytic tests (20–60 W) using Ni/Al<inf>2</inf>O<inf>3</inf> as catalyst demonstrated that dense bed configurations consistently outperformed distributed ones across all reactions. In that sense, temperature profiles varied, with dense beds exhibiting higher temperatures, aligning with improved catalytic performance. While temperature contributes to plasma-catalysis activity, it is not the only determining factor. Electrical characterization revealed that distributed bed configuration along the plasma region increased system capacitance and effective dielectric response, negatively impacting micro-discharge stability and reaction efficiency. In dense bed configuration, micro-catalysts (500 μm) exhibited superior CH<inf>4</inf> conversion, whereas catalyst in powder form (50 μm) exhibited higher activity in CO<inf>2</inf> conversion. Optical emission spectroscopy (OES) revealed the presence of plasma-generated radicals and demonstrated differences between bed configurations, with dense beds favoring reforming-related species. Comparable spectra at different heights suggest that these radicals may reach the catalyst surface without significant quenching. Catalytic activity and characterization correlation indicated that CH<inf>4</inf> activation mainly occurs through interactions with plasma species in the gas phase, which are favored by the interparticle gaps present in micro-catalyst packed-bed configurations. In contrast, CO<inf>2</inf> conversion relies more on catalyst surface interactions, which are enhanced when the catalyst is more compactly arranged, as in powder beds. These findings highlight the significance of reactor design parameters and provide general guidelines for optimizing plasma-catalysis systems.