The study of structure-performance relationship of iron catalyst during a full life cycle for CO2 hydrogenation

The establishment of structure-performance relationship of catalysts during a full life cycle is highly desirable for catalyst design and understanding of nature of active sites. As a case study, lower olefins synthesis directly from CO 2 hydrogenation (CTO) was performed over iron catalyst and the catalyst structure evolution during its life cycle has been comprehensively studied. Particularly, operando techniques allow direct observation of the continuous phase transition during activation (Fe 2 O 3  → Fe 5 C 2 ), reaction and deactivation (Fe 5 C 2  → Fe 3 O 4 ), and regeneration (Fe 3 O 4  → Fe 5 C 2 ) process, respectively. After a combined CO 2 -CO regeneration, 91.8% of the initial activity and 97.7% of the initial C 2 –C 4 olefins selectivity were recovered. Our results indicate that the Fe 5 C 2 phase is the active phase for C 2 –C 4 olefins production. The iron carbide phases are irreversibly oxidized to Fe 3 O 4 under CTO conditions, which is the major factor responsible for the catalyst deactivation. This study not only reveals the dynamic structure evolution of iron catalyst during the full life cycle in CTO, but also endows deep insight into the underlying deactivation mechanism.