Plasma-assisted CO2 decomposition catalyzed by CeO2 of various morphologies

Abstract

Plasma-assisted catalytic decomposition of CO2 over CeO2 nanocatalysts was investigated in this study. CeO2 nanocatalysts with different morphologies (i.e., cube, rod, and hexagon were prepared by hydrothermal method) were evaluated in a dielectric barrier discharge reaction at room temperature and atmospheric pressure. Among the above catalysts, commercial CeO2 and quartz sands, CeO2 nanorods (CeO2-R) exhibited the highest CO2 conversion under an applied voltage of 8 kV. When the discharge voltage was increased to 9 and 11 kV, all CeO2 catalysts showed increased CO2 conversion with little difference, but when the applied voltage was larger than 11 kV, the difference in catalytic performance became negligible. The better performance of CO2 activation over CeO2-R was attributed to the abundant oxygen vacancies on its exposed (110) crystal plane, which was further confirmed by XPS characterization. Oxygen vacancies on CeO2-R led to twice CO2 adsorption amount compared with the other CeO2 catalysts, and presented a more significant synergistic effect of oxygen vacancies and plasma on CO2 decomposition. The CO2 molecules adsorbed on oxygen vacancies over CeO2-R were partly activated and more easily decomposed in the plasma, resulting in higher CO2 conversion. Meanwhile, the minimum discharge voltage for CO2 decomposition over CeO2-R was 5.0 kV, which was 8.3 kV for commercial CeO2 due to its lowest oxygen vacancy density. However, due to the higher electron density and increased probability for free CO2 splitting under high discharge voltage, most CO2 molecules were activated by the plasma alone, thus less catalyst effect was observed.