Temperature-driven evolution of nitrogen doping sites in CeO2: Oxygen vacancy regulation and interfacial electron transfer in methanation

This study reveals the evolution of nitrogen-doping sites in CeO₂ and establishes their key role in designing sulfur-tolerant methanation catalysts. Through controlled thermal treatments, nitrogen was introduced into interstitial (N i ) and substitutional (N s ) lattice sites and their temperature-induced interconversion was elucidated. As temperature increases, lattice nitrogen escapes as NOₓ, accompanied by a dynamic evolution of oxygen vacancies (Oᵥ) that first increases and then decreases. This site-specific N doping not only raises the electron enrichment of CeO₂ and narrows its bandgap but also strengthens interfacial electron transfer from CeO₂ to Mo species (CeO₂–MoO₃), thereby enhancing the MSI (metal–support interaction). Consequently, MoO₃ precursor particles are downsized and, after sulfidation, this size effect propagates to MoS₂, yielding shorter lateral slabs and a higher fraction of catalytically active edge sites. Performance tests show that N500–MoS₂ achieves a CO conversion of 65.8 % at 500 °C, markedly outperforming the undoped counterpart. DFT calculations corroborate that N doping significantly lowers the Oᵥ formation energy and narrows the bandgap, facilitating electronic transitions and interfacial charge transfer. These findings provide a verifiable design strategy for high-efficiency, sulfur-tolerant methanation catalysts by tuning the lattice configuration and thermal evolution of nitrogen to jointly optimize support electronic structure, interfacial interactions, and edge-site exposure.