Plasma-assisted CO₂ hydrogenation in dielectric barrier discharge packed with structured metal foams

CO₂ hydrogenation in dielectric barrier discharge (DBD) coupled with catalytic materials based on structured metal foams is an appealing approach to promote its performance. Here, plasma-assisted CO₂ hydrogenation has been carried out in the DBD reactor packing plasma activated Ni and Cu foams, respectively. Measurements of electrical characteristics and optical emission spectra are performed to determine the influence of metal foams on the discharge characteristics. The CO₂ hydrogenation performance under different packing conditions is then evaluated at different applied voltage magnitudes. The results show that packing metal foams into DBD changes the filamentary microdischarges into the combination of surface discharge on the metal foam surface and the spatially limited and weak microdischarges in the pores of the metal foams, and the conductive metal foams promote the spread and expansion of surface discharge. The H₂/CO₂ DBD packing with metal foams exhibits higher discharge power and effective capacitance, as well as stronger capability of charge generation and transfer compared with the plasma-only process at low applied voltage magnitude levels, while the opposite phenomena are observed when the applied voltage magnitudes are 7.5 kV and 8 kV. However, the relatively higher intensities of typical reactive particles are detected when packing the metal foams (especially the Ni foam), which might be due to the catalytic activity of the metal foams. The highest conversions of CO₂ (32.5%) and H₂ (16.1%) are achieved when the Ni foam is packed in the plasma reaction region at the applied voltage magnitude of 8.0 kV. The corresponding selectivity of CO and CH₄ is 88.5% and 8.9%, respectively. Higher energy efficiencies for both converting CO₂ and H₂ and producing CO and CH₄ are obtained in the presence of the Ni foam. The highest values of these two energy efficiencies are 0.17 mmol/kJ and 0.06 mmol/kJ when the applied voltage magnitude is 7.0 kV.