The hydrogen which feeds the PEM fuel cells is generally obtained by the reforming of hydrocarbons or alcohols. In general, this step is followed by the Water Gas Shift reaction, where the H₂ content is increased and the CO concentration is reduced around 1 %. However, this CO content could poison the cell anode. The CO preferential oxidation (COPrOx) is an adequate method to reduce the CO concentration to less than 10 ppm.

Catalysts based on oxides, such as CoOx/CeO₂, CoMnCeOx, CuO-CeO₂/SBA-15 and bimetallic systems Pt-Cu/Al₂O₃ and Pt-Cu/mordenite were studied. For practical applications it is necessary to incorporate the active phases to monolithic structures. Then, monolithic ceramic structures coated with a catalytic layer were studied in the COPROX reaction.