Since there is a high amount of H2 in the stream, the oxidation must be very selective towards CO. Noble metals, particularly Pt [2, 3], Au [4] and Ru [5], and some nonprecious metals such as Co, Cr, Cu, Ni and Zn supported on ceria-zirconia [6] were used as catalysts. Nevertheless, it was also demonstrated that other catalysts such as Cu-Ce, less expensive than Pt, are very active and selective [7–9]. In the COPrOx reactor the following reactions occur in the gas phase1):