Engineering Defect-Rich Surfaces on Co₃O₄ Catalysts: A Stepwise Bulk Doping–Surface Etching Strategy for Enhancing Methane Combustion

Abstract

Catalytic methane combustion is a critical technology for emission control, with Co₃O₄ standing out as a promising non-noble metal catalyst. However, its low-temperature activity requires considerable enhancement. Herein, a sequential “bulk doping–surface etching” strategy is reported to develop defect-rich catalysts. Nanosheet-like Co₃O₄ (Co₃O₄–S), featuring a large specific surface area and excellent catalytic activity, was selected as the optimal platform and subjected to sequential Ni doping and mild acid etching. The resulting catalyst H–NiCo₂O₄–S exhibited exceptional activity with a T₉₀ (the temperature required for 90% methane conversion) of 316.4 °C, representing a reduction of ~ 78 °C in the T₉₀ value compared with pristine Co₃O₄–S, and hydrothermal stability. Systematic characterizations unveiled the synergistic effect of the sequential modification strategy. Ni doping considerably weakened Co–O bonding and induced the generation of abundant active adsorbed oxygen (O_ads). Acid etching introduced numerous surface oxygen vacancies (O_v) and enriched high-valency Ni³⁺ species. Mechanistic studies suggested that these combined modifications facilitated the participation of lattice oxygen, accompanied by a shift in the surface reaction pathway. The accumulation of stable carbonate species was suppressed, and an efficient conversion pathway mediated by highly active intermediates, such as formaldehyde, was promoted. Concurrently, the additional oxygen vacancies and active Co²⁺/Ni³⁺ redox coupling resulting from acid etching considerably accelerated the conversion kinetics of key intermediates. This work demonstrates that co-engineering the bulk-phase reaction pathway and surface active sites is a promising strategy for rationally designing high-performance catalysts.

Keywords

Methane combustion / Co₃O₄ / Morphological effect / Ni doping / Acid etching

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