Performance Intensification of CO 2 Methanation by Co-Feeding Oxygen Over Various Ru-Based Catalysts

Abstract

Auto-methanation (AM), which autonomously progresses at room temperature (approximately 25 °C), is an effective reaction for converting CO2 to CH4 and can thus reduce the processing costs. In this study, the AM reaction over various Ru-based catalysts with different support materials positively proceeded by selecting reaction conditions such as the O2 concentration and gas flow rate. The progression of AM was the best over the Ru/CeO2 catalyst, followed by the Ru/ZrO2 and Ru/Al2O3 catalysts. The progression of AM over the Ru/SiO2 catalyst was slow. The rapid progress of AM over the Ru/CeO2 catalyst was attributed to the presence of oxygen defects on the CeO2 support that accelerates the hydrogen–oxygen combustion as well as to the differences in the CO2 and H2O adsorption characteristics between the CeO2 support and other supports. Even when the Ru-based catalyst underwent H2 reduction at low temperature, AM could proceed over each catalyst. The Ru/CeO2 catalyst was advantageous over other catalysts because AM proceeds only when H2 gas is supplied at room temperature without external heating. X-ray photoelectron spectroscopy indicated that the Ru species on the Ru/CeO2 catalyst are in a metallic state owing to H2 reduction at room temperature, which is associated with AM progression. Moreover, AM proceeded via H2 reduction at 75 °C over the Ru/ZrO2 catalyst and at 150 °C over the Ru/Al2O3 catalyst. The progression of methanation through such low-temperature reduction can strengthen the CO2 conversion process.