Inhibiting metal phase separation of redox catalysts by balancing reduction - oxidation step in chemical looping dry reforming of methane

Abstract

The suppression of metal phase separation in multimetallic redox catalysts during the oxidation-reduction process of chemical looping for efficient hydrocarbon activation continues to pose a significant challenge. In this study, we have uncovered that the modestly oxidizing CO₂ can facilitate in-situ oxygen replenishment, concurrently occupying the oxygen vacancies generated during the reduction of lattice oxygen in the LaFeO₃ redox catalyst by strongly reducing agent CH₄. This mechanism not only gives rise to the production of syngas but also promotes the self-regeneration of the redox catalyst, effectively inhibiting the segregation of metallic phases. Thermodynamic analysis and experimental evidence suggest that the oxidized and reduced states of LaFeO₃ redox catalyst can achieve partial oxidation of CH₄ and reduction of CO₂ concurrently, with the addition of CO₂ promoting the recovery of the crystal phase structure and lattice oxygen of LaFeO₃. As a result, the developed redox catalyst demonstrates remarkable stability, undergoing 30 h of continuous operation with nearly no deactivation observed. Critically, the ¹⁸O isotope tracer reveals the migration pathway between surface lattice oxygen and gaseous oxygen. Mechanistic studies indicate that the surface lattice oxygen of the redox catalyst effectively promotes rapid partial oxidation of CH₄, generating surface oxygen vacancies that are then in situ regenerated after being filled by CO₂. This finding underscores the significance of weakly oxidative atmospheres, such as CO₂, in maintaining the stability of the chemical looping process.