A detailed characterization study of Ni/CeO2 catalysts identifies Ni availability as the primary factor affecting CO2 methanation performance

• Ni/CeO 2 (10 wt%) catalysts for CO 2 methanation were modified by altering calcination temperature/atmospheres. • Characterisation was performed to evaluate the importance of properties such as Ni crystallite size, availability and oxygen vacancies. • Ni availability (i.e. catalytically accessible Ni), determined from crystallite size and SMSI extent, affects the number of interfacial sites. The structure of a catalyst has a strong impact on its performance. Here we investigate the physicochemical properties of Ni/CeO 2 in an attempt to draw structure–activity relationships for CO 2 methanation. A combination of characterisation methods (X-ray diffraction (XRD), 4D Scanning Transmission Electron Microscopy (4D-STEM), CO chemisorption and oxygen storage capacity study etc.) clearly demonstrates the effect of Ni crystallite size, Ni availability (i.e. catalytically accessible Ni) and oxygen vacancies at the Ni-CeO 2 interface in Ni/CeO 2 during CO 2 methanation. Among them, the role of exposed Ni active sites is highlighted, and two possible optimisation schemes i.e. changing the support calcination temperature and the final calcination atmosphere are proposed to obtain a better dispersal of Ni NPs (nanoparticles) on CeO 2 . Both modification methods do not affect the reaction route, and the activity differences of Ni/CeO 2 can be explained by the various hydrogenation rate of formate species, as confirmed by in situ diffuse-reflectance infrared Fourier-transform spectroscopy (DRIFTS) measurements.