CO₂ Driven Soot Oxidation via Reverse Boudouard Reaction over Reducible Catalyst: A Sustainable Pathway for Catalyst...

Here, we demonstrate how CO₂ as a mild oxidant can drive soot gasification via the reverse Boudouard reaction, simultaneously regenerating deactivated catalysts and valorizing a greenhouse gas into CO  a platform chemical of industrial significance. Central to this strategy is the ability of CeO₂ to undergo reduction and regeneration: its lattice oxygen oxidizes soot, while the oxygen vacancies formed during this process help activate CO₂ and restore the catalyst. Pristine CeO₂ and aliovalently doped Ce_0.9Ni_0.1O_2-δ were synthesized via a rapid, single-step solution combustion route and benchmarked for CO₂-assisted soot oxidation in a fixed-bed reactor. A suite of techniques establishes that Ni²⁺ incorporation into the CeO₂ fluorite lattice amplifies oxygen vacancy density, enhances lattice oxygen mobility, and markedly improves reducibility. Under inert N₂ atmosphere, where lattice oxygen acts as the sole oxidant, the superior reducibility of Ce_0.9Ni_0.1O_2-δ translates directly into a 75% higher soot conversion compared to pristine CeO₂ at 800 °C, producing CO as the dominant product. Post-reaction XPS confirms a marked drop in Ce⁴⁺ content and a surge in oxygen vacancy concentration, providing unambiguous spectroscopic evidence for lattice oxygen consumption via the Mars-van Krevelen mechanism. When CO₂ is introduced as oxidant, a remarkable inversion occurs: both catalysts now achieve complete soot oxidation with near-identical light-off profiles, as gas-phase CO₂ saturation overrides differences in surface basicity and CO₂ adsorption capacity. Crucially, post-reaction XPS under CO₂ atmosphere reveals a decrease in oxygen vacancy concentration  the fingerprint of vacancy replenishment through CO₂ dissociation and catalyst self-regeneration. This work opens a tangible pathway for deploying CeO₂-based materials as catalytic additives for CO₂-driven regeneration in fluid catalytic cracking and related refinery processes, contributing to both carbon utilization and long-term process sustainability.