The metallic substrate in the washcoating procedure and the slurry preparation affected the ruthenium particle size. Thereby, the presence of PVA and colloidal alumina, the acidic aqueous media and the thermal treatment favored the surface structural reorganization of the metal towards more active catalysts. This was confirmed when the optimal range of working temperatures in which the CO concentration in the outstream is less than 20 ppm (more than 93.3% of CO conversion) and the total consumption of H2 is under 4% (implying a CO2 conversion lower than 3.2%) was compared. Thus, it was shifted to lower temperatures when S- RuAl and M-RuAl were used. In those cases the optimal ranges of working temperatures were from 149°C to 239°C for S-RuAl and from 165°C to 232 °C for the micromonoliths, whilst it was from 217°C to 226°C for the RuAl powder. Further increase in temperature resulted in a drastic decrease of CO conversion due to the concurrence of the reverse Water Gas Shift reaction, thermodynamically and kinetically favored at higher temperatures