CexFeyO catalysts for efficient char-CO2 gasification: Tuning oxygen vacancies and redox properties

This study investigates the catalytic mechanisms and performance of Ce x Fe y O catalysts in the CO 2 gasification of straw char. A series of Ce x Fe y O catalysts were synthesized via a hydrothermal method, and systematically evaluated in a fixed-bed reactor. Physicochemical characterization revealed a four-stage phase evolution (single CeO 2 , CeO 2 -dominant, CeO 2 -Fe 2 O 3 composite, and Fe 2 O 3 -dominant phases), each one with distinct electronic and structural properties directly governing gasification activity. Gasification tests demonstrated strong composition dependence, with different activity trends in the Ce-rich and Fe-rich regimes. In the Ce-rich regime, catalytic activity first increased and then declined as Fe doping rose, with Ce 0.7 Fe 0.3 catalyst showing the highest reactivity (c(CO)/c(CO 2 ) = 0.53). In contrast, in the Fe-rich range, Ce 0.2 Fe 0.8 catalyst achieved the best performance (c(CO)/c(CO 2 ) = 0.71). Further investigations showed that annealing time had little effect on catalytic activity, while NaBH 4 reduction-etching improved performance at high concentrations, with 16 mL of NaBH 4 -treated catalyst (Ce 0.8 Fe 0.2 -16 Re ) demonstrating the highest activity. Residual char analyses confirms that Ce-rich catalysts promote oxygen-vacancy redox cycles leading to pore collapse, while Fe-rich catalysts rely on Fe redox cycling to induce mesopore formation. Therefore, this study elucidates the structure-activity relationship of Ce x Fe y O catalysts and highlights defect engineering as a viable strategy for developing efficient, low-cost catalysts for solid waste gasification. • Four-stage phase evolution from CeO 2 to Fe 2 O 3 -dominant structures in Ce x Fe y O. • Catalytic activity in CO 2 gasification is highly composition-dependent. • Ce 0.2 Fe 0.8 achieves the highest performance with peak c(CO)/c(CO 2 ) of 0.71. • NaBH 4 reduction introduces oxygen vacancies, enhancing gasification activity. • Ce-rich catalysts promote pore collapse while Fe-rich catalysts induce mesopore structures.