Efficient low-temperature methane conversion to syngas over highly stable nanocrystalline Ni/CeO₂ catalysts using air as an oxidant

Developing coke-resistant, cost-effective catalysts for methane-to-syngas conversion using air remains challenging. Herein, we report a one-pot colloidal solution combustion synthesis (CSC) to synthesize nanocrystalline Ni/CeO₂ featuring highly dispersed Ni, abundant oxygen-vacancies, and a well-developed Ni-Ce-O interface. Extensive characterization including XRD, HR-TEM, XPS, O₂-TPD, CH₄-TPD/TPSR, H₂-TPR, EPR and Raman elucidated the structural, redox, and defect features imparted by the CSC synthesis method. TEM confirmed uniformly distributed Ni nanoparticles embedded within the ceria matrix. CH₄-TPSR revealed early CO₂ and H₂O formation at ~210 °C, indicating low-temperature CH₄ activation by oxygen species. In-situ Raman spectroscopy revealed abundant oxygen vacancies and their active participation during methane activation, while in-situ DRIFTS identified surface formate and carbonate intermediates, confirming an oxygen-assisted reaction pathway. The optimized 5Ni/CeO₂ catalyst achieved 99% methane conversion with nearly 100% syngas selectivity at 700 °C. Raman and TGA/DTG analyses confirmed excellent coke resistance and stable performance throughout 300 h of testing.