Structure-activity relationship and deactivation behavior of iron oxide during CO2 hydrogenation.

[Display omitted] • Structure-activity relationships at various calcination temperatures were presented. • C 5+ yield of 16.4 % with a CO 2 conversion of 34.2 % was achieved. • Different deactivation mechanisms were observed with different iron particle size. • Fe particles with 2.18 μm size were pulverized during CO 2 hydrogenation. • Fe particles with 0.52 μm size maintained its integrity during CO 2 hydrogenation. Identifying the dynamic structural evolution of iron during the thermocatalytic conversion of CO 2 into liquid hydrocarbons is a promising approach for understanding the deactivation behavior and to design an efficient catalyst. Despite the understanding of the oxidation of χ-Fe 5 C 2 to high-valent iron oxides (e.g., Fe 3 O 4 , Fe 2 O 3) caused by water formed as the byproduct, the deactivation mechanism depending on the particle size during a long-term reaction remains unclear. Herein, the structural evolution and deactivation mechanism of Na-promoted Fe 2 O 3 catalysts with varying particle sizes were investigated. The catalyst activity and deactivation behavior were highly dependent on the initial morphology of the calcined catalysts. The reduced iron catalyst with an average particle size (d ave) of 0.52 μm maintained its domain integrity, whereas that with a d ave value of 2.18 μm was severely pulverized during the CO 2 hydrogenation. The pulverized particles exposed a new surface, making it highly susceptible to re-oxidation and catalyst deactivation. Conversely, maintenance of the iron integrity suppressed the re-oxidation, whereas the excess formation of graphitic carbon on the χ-Fe 5 C 2 site was the main deactivation mechanism during long-term CO 2 hydrogenation. [ABSTRACT FROM AUTHOR]