Tuning Ce:La ratios for enhanced Ni exsolution and carbon control in Ce_1-xLa_xNiO₃ perovskites for dry methane reforming

The promotional effect of La was investigated for dry reforming of methane by variation of Ce:La ratios of Ce_1-xLa_xNiO₃ perovskite (x = 0.02, 0.05, 0.08 and 0.10). Characterization and DRIFTS/Mass Spec analysis elucidate the role of La in reducing the temperature for CH₄ and CO₂ activation and for carbon formation. La enhanced Ce^4+/Ce³⁺ redox transition and oxygen vacancies in Ce_1-xLa_xNiO₃ to achieve a higher CO₂ and CH₄ conversion than the non-substituted CeNiO₃. Low La substitution (x = 0.02) formed socketed Ni nanoparticles (∼2–5 nm), initiating methane decomposition to H₂ at temperatures below 350 °C. However, the Ni nanoparticles caused disproportional CH₄ and CO₂ decomposition, deviating the H₂/CO ratio from one and tip-growing the carbon into nanotubes after 24 h reaction at 600 °C. At high La substitution (x = 0.10), Ni was observed as large nanoparticles (∼10–12 nm), which reduced CH₄ conversion to achieve a balanced CO₂ and CH₄ conversion and led to the formation of unstructured reactive carbon after 24 h of reaction.