CO₂ methanation over Ni-Ceria-Zirconia catalysts: effect of preparation and operating conditions

Ni-Ceria-Zirconia materials with various Ceria/Zirconia ratios were prepared by sol-gel and impregnation methods and were subsequently characterized by means of XRD, BET, TPR and TPO. Their catalytic activity and stability were evaluated in the CO₂ methanation reaction. The main parameters which seem to monitor catalytic performance are the capacity of Ni²⁺ cations to incorporate into the mixed oxide structure and the obtained ratio between incorporated Ni²⁺ and surface Ni⁰ species. Catalysts prepared by sol-gel thus exhibited higher methane yield and an improved resistance to deactivation when compared to those obtained by impregnation. The process viability was then investigated in potential industrial conditions. Operating under moderate pressure was beneficial to catalytic activity, whereas working under sub-stoichiometric H₂ resulted in a loss of both activity and stability. Even though metal sintering and carbon deposits are believed to cause deactivation, nickel partial reoxidation and site blocking have to be considered.