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

Abstract

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 Ce0.9Ni0.1O2−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 Ce0.9Ni0.1O2−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.