Auto-methanation for transition-metal catalysts loaded on various oxide supports: A novel route for CO2 transformation at room-temperature and atmospheric pressure

[Display omitted] •Co-fed oxygen greatly improved CO2 methanation even at room temperature.•Ru-based catalyst gave a higher activity of about 10% than Ni-based catalyst.•High CH4 yield was obtained even under co-fed oxygen.•High thermal energy generated from hydrogen-oxygen combustion.•Minimum ignition energy is a key point for producing high CH4 yield. The CO2 methanation for transition-metal catalysts loaded on various oxide-supports was investigated under feeding with a raw material gas containing oxygen. The co-feeding of the oxygen greatly improved methanation performance for Ni- and Ru-based catalysts, because of the high thermal energy generated from hydrogen–oxygen combustion. Especially, Ni/CeO2, Ni/ZrO2, Ni/Y2O3, and Ni/Al2O3 catalysts and the prepared ruthenium catalysts demonstrated high activity and high methane-selectivity even in a region at room temperature and atmospheric pressure. The auto-methanation (AM) phenomenon, which is reported in the world for the first time, proceeded over these catalysts. Compared to that of the Ni-based catalyst, the AM activity of the Ru-based catalyst was approximately 10% higher. Although it was generally predicted that the produced methane was combusted by the co-fed oxygen, yet such methane combustion was not observed so as that the minimum ignition energy of methane–oxygen is much larger than that of hydrogen–oxygen.