Operando Elucidation of Filamentous Carbon Gasification Kinetics and Mechanisms on a Spent Ni/CeO2 Catalyst

Coking is the leading cause of catalyst deactivation in many important hydrocarbon conversion technologies. Understanding regeneration mechanisms is critical for developing effective carbon removal strategies that improve catalyst longevity and reduce operational costs. Here, we present a spatially resolved operando investigation of the regeneration of a spent Ni/CeO₂ catalyst under industrially relevant air-like conditions, using in-situ environmental transmission electron microscopy (ETEM) combined with semantic segmentation. By deconvoluting competing gasification events for filamentous carbon removal, we found three distinct gasification modes─while fast catalytic gasification was expected, less steady noncatalytic combustion and cooperative gasification were also present and even more prevalent. Microstructure-informed kinetics directly linked the maximum gasification rates to axial filament consumption through either Ni/carbon contact or filament breakage, emphasizing the pivotal role of edge-plane carbon sites across all gasification pathways. Moreover, our operando characterization uncovered a Ni(−C_x)-limited carbon diffusion mechanism, which challenges the conventional carbon bulk diffusion model typically assumed for catalytic gasification. Furthermore, adverse processes such as Ni/carbon contact disruption and gasification-induced catalyst sintering were also identified. Collectively, these findings provide mechanistic insights into carbon gasification processes, highlighting critical pathways and potential pitfalls that can guide the optimization of catalyst regeneration strategies.