CO and CO₂ Hydrogenation over CeO₂ and CeO₂-Based Composite Catalysts: Defect Chemistry, Interfacial Sites and...

CO and CO₂ hydrogenation provide essential routes for linking carbon resource recycling with renewable hydrogen utilization, yet the predictable design of CeO₂-based catalysts remains constrained by an incomplete understanding of how CeO₂ defect chemistry couples with interfacial reaction pathways. This review adopts a function-oriented rather than a metal-by-metal enumeration approach, covering pristine CeO₂, single-metal/CeO₂, bimetallic/CeO₂, and CeO₂-metal oxide composite catalysts. We argue that CeO₂ should not be viewed merely as an oxygen vacancy reservoir; its catalytic function arises from the coupled effects of exposed crystal facets, Ce⁴⁺/Ce³⁺ redox cycling, oxygen vacancy formation and migration, surface hydroxyl chemistry, water desorption, and dynamic metal-oxide interfaces. In methanol synthesis, methanation, the reverse water-gas shift reaction, and C₂ oxygenate formation, the same structural descriptors may promote or suppress the target pathway, depending on oxygen vacancy location, metal nuclearity, oxide basicity, and intermediate binding strength. We further discuss how Cu-Ce interfaces regulate methanol versus CO production, how Ni-, Co-, and Ru-based interfaces promote deep hydrogenation, and how Pd-, Rh-, and composite oxide systems expand oxygenate selectivity. Finally, we emphasize that future research needs to develop in situ descriptors, quantitatively distinguish different types of oxygen vacancies, and evaluate catalyst stability under realistic environments including water-rich, CO-containing, and cyclic operation conditions. Reinterpreting CeO₂ from a "reducible support" to a "programmable dynamic interface" holds promise for advancing catalyst design for selective CO_x hydrogenation to CO, methane, methanol, and higher-carbon oxygenates.