Intrinsic size effects govern catalyst stability in FeAlO_x-mediated CO₂ hydrogenation

Elucidating the dynamic structural evolution of iron during thermocatalytic CO₂ hydrogenation is essential for diagnosing catalyst deactivation and enabling the rational design of durable CO₂-to-liquids catalysts. Although active Hägg carbide (χ-Fe₅C₂) progressively oxidizes to Fe₃O₄/Fe₂O₃ in the presence of in-situ formed water, the impact of iron particle size on long-term phase stability remains unclear. Here, Na-promoted FeAlO_x catalysts with controlled Fe domain sizes are systematically investigated under industrially relevant conditions to establish a structure–stability–performance relationship. Catalytic behavior is dictated by precursor morphology, which determines the extent of reconstruction during H₂ activation and subsequent redox–carburization cycling. Fe domains with an average size of 0.17 μm maintain structural integrity, suppress stress accumulation and limit formation of oxidation-prone fresh surfaces, thereby sustains high C₅₊ productivity for up to 2000 h on stream. These findings identify iron domain integrity rather than phase identity alone as a decisive descriptor for durability.