Factors determining synergism in plasma catalysis of biogas at reduced pressure

This paper presents the clear evidence of nonthermal plasma-induced synergism of biogas reforming studied at 5 kPa. Reactant conversion and product yield were increased by superposing dielectric barrier discharge (DBD) to the Ni-based supported catalyst at a fixed temperature. Reforming performance was further promoted by increasing the operating frequency from 12 to 100 kHz, while maintaining the catalyst temperature (600 °C) as well as specific energy input (SEI  =  1.37 eV/molecule). Kinetic analysis revealed the key rate-determining step, i.e. dissociative CH₄ activation is clearly promoted by plasma catalysis. However, excessive CH₄ activation accelerated coke formation when CH₄/CO₂  >  1. Reforming characteristics were correlated with the electrical properties of packed-bed DBD, showing the increase in discharge current is critically important to strengthen plasma-induced synergism, while an increase in mean electron energy seems to have a minor effect. Moreover, discharge properties were correlated with electron collision kinetics; the vibrationally excited CH₄ and CO₂ play a key role in plasma catalysis of biogas reforming. (paper)