Combination of DBD and Catalysts for CH4 and CO2 Conversion: Basics and Applications

Abstract

AbstractThis paper describes dielectric barrier discharge and catalyst combination technology which is applied for dry methane reforming (DMR: CH4 + CO2 = 2CO + 2H2) and reverse water gas shift reaction (RWGS: CO2 + H2 = CO + H2O). The purpose of this paper is not to discuss the efficiency of plasma catalytic conversion of CH4 and CO2, catalyst synthesis method, or diagnostics of surface reactions; it focuses on the macroscopic characterization of DBD and catalyst hybrid reactions for a reactor design and appropriate parameter setting. DBD is characterized by the discharge sustain voltage and the mean discharge current which are readily obtainable from the Lissajous diagram and is further correlated with a power density (W/m3) via Manley's equation. Meantime, power density is decoupled into specific energy density (SEI) and gaseous space velocity (GHSV). SEI provides a guideline for the energy efficiency of the plasma catalytic process, and GHSV is an important measure of residence time or productivity of the process. The DBD-catalyst hybrid reaction is superior to warm discharge alone when it is generated by a high-frequency power source, which is discussed based on the lifetime of vibrationally excited CH4; not only cumulative population of a fundamental mode of vibrationally excited CH4, but also overtone vibrational states of CH4 is anticipated by multiple electron collision at high-frequency operation. The importance of overtone vibrational molecules on surface reaction is proven by molecular beam study, and distinguished from the ladder-climbing mechanism in gas phase plasma chemistry; catalytic reactions would further promote without unavoidable trade-off relationship between reactant conversion rate and energy efficiency. Finally, nonequilibrium product distribution by plasma catalysis is discussed based on the surface reaction model in connection with vibrationally excited molecules.