Catalytic non-thermal milli-pulse plasma for methanation of CO2 without carbon deposition and catalyst deactivation

Abstract

Catalytic routes for upgrading CO2 through Sabatier reaction CO2+4H2→CH4+2H2O have been studied for decades. To avoid water adsorption and catalyst aging, the process must be operated at 300–400 °C, which subsequently causes carbon deposition and catalyst deactivation. Non-thermal plasma is a promising approach to overcoming the barriers associated with CO2 dissociation and conversion, and avoid the carbon deposition observed in a traditional Sabatier reaction. This study elucidated; 1) the impacts of reactor geometry and plasma condition on plasma discharge; 2) the synergism between active site (Ni and Co) and catalyst support; and 3) the impact of catalyst promoter (Ru) on CO2 conversion, methanation yield, and selectivity. The physics and chemistry of plasma were investigated in 6 different reactor geometries using 28 different catalysts. The plasma physics was discussed as a function of discharge characteristics, capacitance properties, reduced electric field, power consumption, and reactor temperature. CO2 conversion, CH4 yield, and CH4/(CO + CH4) selectivity are reported and compared with those under thermo-catalysis at 400 °C. In addition, carbon deposition on the surface of high-voltage electrodes as a result of Joule heating was investigated. In contrast to γAl2O3, CO selectivity was dominant in SiO2-supported catalysts. In terms of active sites, the following trend was observed for CO2 conversion, methanation, and yield: Ru > Ni > Co. The addition of Ru promoter played a more prominent role in enhancing CH4/(CO + CH4) selectivity, other than production yield or conversion. Except for SiO2-Ni15 and SiO2-Co15, all the catalysts showed a higher methane yield in plasma discharge at 150–170 °C than thermal conversion at 400 °C.