Non-noble Metal Oxide Catalysts for CO Oxidation in Humid and Sulfur-Containing Streams: From Activity Competition to Stability Challenges

The efficient removal of carbon monoxide from industrial and vehicular emissions has become a pressing practical challenge, driven by tightening emission standards and growing concerns over ambient air quality. Noble metal catalysts, despite their excellent low-temperature activity, face persistent barriers to large‑scale deployment, including high and volatile raw material costs, limited global reserves, and a strong tendency to deactivate through sintering and poisoning. Transition metal oxides-especially those based on Mn, Cu, Co, Ce, and Fe, present a viable path forward because they offer a wide range of accessible oxidation states, high concentrations of surface oxygen vacancies, and a cost structure that is suited to large‑volume applications. Single-metal oxides, composite systems, and supported architectures each present distinct active-site chemistries, yet their comparative performance in realistic feeds remains poorly mapped. Particular attention is devoted to the fundamental roles of physicochemical properties-crystal structure, morphology, metal valence distribution, and oxygen vacancy concentration-in dictating catalytic performance. Furthermore, the classical reaction mechanisms-Langmuir–Hinshelwood (L–H), Eley–Rideal (E–R), and Mars-van Krevelen (MvK)-as well as emerging theoretical insights such as the termolecular Eley–Rideal and water-mediated MvK pathways, are analyzed in detail. In response to the persistent deactivation challenges encountered in complex industrial atmospheres (especially moisture and SO 2 poisoning), effective optimization strategies are summarized, including heteroatom doping, facet engineering, and metal-support interface regulation. Finally, the current bottlenecks in catalyst stability and scalability are discussed.