Preferential oxidation of CO under excess H2 conditions over Ru catalysts

The preferential oxidation of CO in the presence of excess H2 (PROX reaction) has been examined over SiO2- and Al2O3-supported Ru catalysts. The effects of various parameters (pretreatment conditions, nature of support and precursor) on catalyst structure and performance were investigated through the use of O2 chemisorption, HRTEM, FTIR, and kinetic measurements. The combination of a direct hydrogen treatment and use of a nitrate precursor results in the synthesis of finely dispersed Ru catalysts capable of completely eliminating CO in the temperature range of 120-150 °C for Ru/SiO2 and 160-180 °C for Ru/Al2O3 at a space velocity of 120 000 mL/g h. Addition of 10% H2O essentially has no effect on the CO oxidation over Ru/SiO2, while a relatively small effect (negative below 180 °C and positive above 200 °C) is observed with Ru/Al2O3. In contrast, the addition of 15% CO2 suppresses the CO oxidation over both catalysts at the high temperature end, with the effect being more pronounced over the SiO2-supported sample. Both effects can be attributed to the onset of the forward and reverse water gas shift reactions. Overall, in the presence of both H2O and CO2 the H2O effect dominates, due to the high value of the water gas shift equilibrium constant at these temperatures.