<i>M</i> O _<i>X</i> ( <i>M</i> = Cu, Mn, Zn, Ni, and Fe)-Modified Co ₃ O ₄ –CeO ₂ Nanoplate Catalysts for CO Preferential Oxidation in H ₂ -Rich Streams

The Co3O4–CeO2 catalysts were modified with various metals (Cu, Mn, Zn, Ni, and Fe) by using a one-step hydrothermal method, simplifying production and increasing catalytic surface area. Systematic investigations were conducted to evaluate the impact of various metal species on the catalytic performance of CoCe-M catalysts, particularly focusing on the optimization ratio of the Co/Mn optimization and operational parameters such as space velocity, oxygen-to-carbon molar ratio, pretreatment conditions, H2 concentration, and CO2 tolerance during carbon monoxide preferential oxidation (CO-PROX) in H2-rich streams. Among all catalysts, the CoCe-Mn (Co/Mn = 1:1) formulation demonstrated superior catalytic activity, achieving nearly 100% CO conversion at 150–200 °C even under harsh conditions with 70 vol % H2 in the feed gas. Remarkably, this catalyst maintained exceptional stability over 100 h of time-on-stream testing at 175 °C, with no observable deactivation in CO conversion efficiency or O2 selectivity. Comprehensive physicochemical characterizations employing N2 sorption, H2-TPR, XRD, and XPS revealed that the synergistic interactions among Mn, Co, and Ce species contributed to the formation of abundant Co3+ active sites, enhanced redox properties, and significantly increased surface area, all of which are crucial factors for achieving high-performance CO-PROX catalysis. This study underscores the promising potential of rationally designed CoCe-Mn catalysts for practical applications in hydrogen purification processes.