Modulating lattice oxygen in metal oxides that conducts partial oxidation of methane in balancing C-H activation and syngas selectivity remains challenging. This paper describes the discovery of distorting FeO6 octahedra in La1-xCexFeO3 (x=0, 0.25 0.5, 0.75, 1) orthorhombic perovskites for the promotion of lattice oxygen activation. By combined electrical conductivity relaxation (ECR) measurements and density functional theory (DFT) calculations studies, this paper describes the enhancement of FeO6 octahedral distortion in La1-xCexFeO3 promoting their bulk oxygen mobility and surface oxygen exchange capability. Consequently, La0.5Ce0.5FeO3 with the highest FeO6 distortion achieves exceptional syngas productivity of about 3 times and 8 times higher than LaFeO3 and CeFeO3 respectively in CH4 partial oxidation step with simultaneous high CO2 conversion (92%) in the CO2-splitting step. The results exemplify the feasibility to tailor the active lattice oxygen of perovskite by modulating the distortion of BO6 in ABO3, which ultimately influences their reaction performance in chemical looping processes.