Decoupling the effect of Ni particle size and surface oxygen deficiencies in CO2 methanation over ceria supported Ni

[Display omitted] •Ni/CeO2 showed higher TOF and lower activation energies than Ni/SiO2.•The presence of oxygen vacancy and Ni-CeO2 interaction enhanced CH4 formation.•By decoupling the effect of surface oxygen vacancies, a structure sensitivity was established over Ni/CeO2.•CO was preferentially generated on smaller Ni nanoparticles.•The reaction pathway depends on the Ni particle size. The study describes decoupling the effect of surface oxygen vacancies and Ni particle size in the CO2 methanation over CeO2 supported Ni nanoparticles. The availability of surface oxygen vacancies with the interaction between Ni and CeO2 served to appreciably enhance the catalytic capacity for activation of CO2, generating higher conversion rates, larger selectivity to CH4 and lower activation energies relative to Ni/SiO2. A structure-sensitivity in the reaction over Ni/CeO2 was established without the interference of different concentrations of surface oxygen vacancies, where the turnover frequencies of CO2 decreased with increasing the Ni nanoparticle sizes (8−21 nm). The TPSR and Operando FT-IR analysis demonstrated that formate was the critical intermediate for CH4 formation. The CO formation with smaller nickel size resulted from the carboxyl species. In addition, the long-term evaluations and TGA measurements revealed small Ni nanoparticles suffered a temporary loss of activity due to the carbon deposition.