Dry reforming of methane over Ru catalysts supported on CeO₂ promoted with alkaline earth metals

Dry reforming of methane (DRM) was investigated over Ru catalysts supported on CeO₂ promoted with alkaline earth metals (M = Mg, Ca, Sr, Ba), denoted RuCeM_x, where x represents the molar ratio M/(Ce + M). The catalysts were characterized by BET, H₂-chemisorption, XRD, TEM/SAED, SEM/EDX, XPS, H₂-TPR, CO₂-TPD, and post-reaction TPO. Optimization with Sr-promoted catalysts identified x = 0.2 as the optimal support composition, which was subsequently used to evaluate the influence of promoter identity on physicochemical and catalytic properties. Promotion with alkaline earth metals resulted in partial incorporation of M into the CeO₂ lattice, formation of oxygen vacancies, and enhancement of the number and strength of basic surface sites. Catalytic tests in the 550–800 °C range demonstrated that all promoted catalysts exhibited higher CH₄ and CO₂ conversions than unpromoted RuCe, with activity generally increasing down Group 2 of the periodic table. Long-term stability tests at 750 °C (40 h) confirmed the superior DRM activity of all RuCeM_0.2 catalysts relative to RuCe. However, the Ba-, Sr- and Ca-promoted catalysts exhibited gradual deactivation attributed to the formation of thermally stable carbonates (MCO₃). Conversely, RuCeMg_0.2 displayed the highest CH₄ and CO₂ conversions and H₂/CO ratio, and excellent stability, owing to the low thermal stability of MgCO₃ and the formation of minimal, readily gasifiable carbon deposits. These findings demonstrate that Mg-promotion of CeO₂ improves the redox and structural properties of Ru-based catalysts, leading to enhanced activity and long-term stability in DRM, thereby providing a promising route for efficient biogas valorization.