Kim et al. [52] prepared various Ru catalysts supported on different supports such as yttria-stabilized zirconia (YSZ), ZrO2, TiO2, SiO2 and γ-Al2O3 with a wet impregnation method. Among them, Ru/YSZ showed the highest CO conversion especially at low temperatures and it can reduce the high inlet CO concentration to be less than 10 ppm even in the presence of H2O and CO2.