A series of mono- and bimetallic cobalt–cerium catalysts based on ZSM-5 zeolite with different silicate moduli (SiO₂/Al₂O₃ = 30, 55, and 80) was synthesized by incipient wetness impregnation. The atomic ratio of metals (Co + Ce)/Al in bimetallic samples ranged from 0.5 to 1.5. A synergistic catalytic effect of cobalt and cerium in the prepared composites manifested itself in the reactions of total and preferential oxidation of CO (CO-PROX) in an excess of hydrogen. The catalysts in which an atomic ratio between Co and Ce was close to 3 were the most active. In these cases, the conversion of CO in the CO-PROX reaction reached 95% at 190–200°C. With the use of TEM, SEM, and DRIFT spectroscopy of adsorbed CO, including in situ studies of reduction processes under the action of CO, it was found that cobalt oxo cations and mixed cobalt and cerium oxo cations located in exchange positions of the zeolite play a key role in the oxidation reactions. The use of zeolite with SiO₂/Al₂O₃ = 55 provided an optimal balance between the high activity of Co/Ce catalysts in CO oxidation and the selectivity of CO₂ formation in the presence of hydrogen.

The treatment of Co–ZSM-5 with anhydrous AlCl₃changes the cobalt coordination state and the adsorption properties, due to the formation of Co–Cl–Al structures on the zeolite surface.